Final Report 1 - Observatory for Renewable Energy

Transcription

Final Report
Katja Kurki-Suonio
6 Feb 2006
Distribution
1 (45)
FEA-219
Checked by, Date
M. Raiko, 7.2.06
Approved by, Date
Jukka Rahkonen, 7.2.06
Replaces
SELF-SUFFICIENT ENERGY SUPPLY SYSTEM FOR BENEFICIO ATAPASCO'S
COFFEE INDUSTRY IN QUEZALTEPEQUE, LA LIBERTAD, EL SALVADOR
FEASIBILITY STUDY
1
INTRODUCTION................................................................................................................................................... 3
2
DESCRIPTION OF THE EXISTING SYSTEM ................................................................................................. 3
2.1
2.1.1
2.1.2
2.1.3
2.2
2.2.1
2.2.2
2.3
2.3.1
2.3.2
2.3.3
2.4
3
GENERAL DESCRIPTION OF THE COFFEE PRODUCTION PROCESS ........................................................................ 3
The wet process........................................................................................................................................... 4
Drying......................................................................................................................................................... 5
Hulling and sorting..................................................................................................................................... 7
ENERGY REQUIREMENTS .................................................................................................................................. 8
Electricity requirements.............................................................................................................................. 8
Heat requirements ...................................................................................................................................... 9
MASS AND ENERGY BALANCE CALCULATIONS ............................................................................................... 10
Mass balance ............................................................................................................................................ 10
Secondary flows ........................................................................................................................................ 11
Energy flows ............................................................................................................................................. 11
PHYSICAL CONDITIONS AND RESTRICTIONS RELATED..................................................................................... 14
COMPARISON OF THE TECHNICAL SOLUTIONS.................................................................................... 14
3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.2
3.2.1
3.3
3.4
3.5
3.5.1
3.5.2
3.5.3
3.6
COMBINED HEAT AND POWER PRODUCTION ................................................................................................... 15
CHP with a fluidized-bed boiler ............................................................................................................... 16
CHP with a gas boiler .............................................................................................................................. 17
Size consideration for the CHP plant ....................................................................................................... 18
Summary of the CHP alternatives............................................................................................................. 21
GAS ENGINE ................................................................................................................................................... 21
Burning bio fuel with the existing engines ................................................................................................ 22
ETHANOL PRODUCTION .................................................................................................................................. 22
SUMMARY OF ENERGY PRODUCTION AND CONSUMPTION ............................................................................... 23
AVAILABILITY OF FUEL .................................................................................................................................. 24
Possibilities of buying biomass................................................................................................................. 25
Characteristics of fuel............................................................................................................................... 25
Fuel transportation and feeding ............................................................................................................... 25
STORAGE OF END PRODUCTS .......................................................................................................................... 26
4
ASSESSMENT OF ENVIRONMENTAL IMPACT OF THE PROJECT ...................................................... 26
5
FINANCIAL CALCULATIONS ......................................................................................................................... 27
5.1
5.2
Enprima Ltd
INVESTMENT COST ESTIMATE ......................................................................................................................... 27
FIXED OPERATION AND MAINTENANCE COSTS ................................................................................................ 28
Postal Address
Visiting Address
Phone/Fax
POB 61
FI-01601 Vantaa
FINLAND
Rajatorpantie 8
Vantaa
Tel. +358 40 348 5511
Fax +358 9 3487 0810
www. enprima.com
Business ID 1800189-6
Domicile Helsinki
Final Report
Katja Kurki-Suonio
5.3
5.4
5.5
5.6
5.7
5.7.1
5.7.2
5.7.3
6 Feb 2006
2 (45)
FEA-219
VARIABLE OPERATION AND MAINTENANCE COSTS ......................................................................................... 28
TOTAL PRODUCTION COSTS ............................................................................................................................ 28
CARBON FINANCING OPPORTUNITY ................................................................................................................ 29
FINANCIAL ANALYSIS ..................................................................................................................................... 29
SENSITIVITY ANALYSIS................................................................................................................................... 31
Improving the process values ................................................................................................................... 31
Waste to energy plant ............................................................................................................................... 33
Introducing new technical solutions ......................................................................................................... 34
6
SITE AND LOCATION DATA ........................................................................................................................... 35
7
PERMITTING ...................................................................................................................................................... 36
8
LEGAL FRAMEWORK AND AUTHORITY REQUIREMENTS ................................................................. 36
9
RECOMMENDATIONS...................................................................................................................................... 37
9.1
9.2
FEASIBILITY OF THE PROJECT ......................................................................................................................... 37
IMPLEMENTATION PROJECT SCHEDULE ........................................................................................................... 38
10
SUMMARY ........................................................................................................................................................... 39
11
NEXT STEP .......................................................................................................................................................... 45
APPENDICES................................................................................................................................................................. 45
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
3 (45)
FEA-219
SELF-SUFFICIENT ENERGY SUPPLY SYSTEM FOR BENEFICIO ATAPASCO'S
COFFEE INDUSTRY IN QUEZALTEPEQUE, LA LIBERTAD, EL SALVADOR
FEASIBILITY STUDY
1
INTRODUCTION
This feasibility study is prepared as a joint effort between Enprima Ltd., CAFECO
(Beneficio Atapasco) and DIMMA S.A. de C.V. (local consultant).
The purpose of this feasibility study is to identify the suitable technical alternatives
for self-sufficient energy production at Beneficio Atapasco’s coffee industry in
Quezaltepeque, La Libertad, El Salvador, and to evaluate the financial feasibility and
the environmental impact of these alternatives. CAFECO S.A., which Beneficio
Atapasco is a part of, intends to utilize the residues of the coffee making process in
order to produce energy according to the idea of sustainable development. This report
will not include detailed engineering of the energy production alternatives. The
objective is to present the possible alternatives for the self-sufficient energy supply
system as well as the technical, financial and environmental aspects related.
The initial report concentrated on studying the coffee making process including the
residue flows and energy requirements and the existing energy production system.
The progress report presented and compared the different technical solutions for the
self-sufficient energy production system. This final report includes also the financial
analysis, recommendations etc.
2
DESCRIPTION OF THE EXISTING SYSTEM
2.1
General description of the coffee production process
To get a general idea of the circumstances, a basic understanding of the coffee
production process is essential. This description of the coffee making process is
mainly based on the description written by DIMMA, see appendix 1.
The crop season of coffee in El Salvador is from the end of October to the beginning
of March. At the plantations delivering the coffee pulp to Beneficio Atapasco, the
coffee is handpicked in three passes as only the red ripe fruits are harvested. At the
plantations, the picked coffee is spread out on plastics or fabrics on the ground at the
end of each day to pick out leaves, small branches and other impurities and to separate
unripe fruits. The amount of leaves etc. is 1 to 2 % by weight of the picked coffee and
they are returned to the soil of the plantations. At Beneficio Atapasco, the amount of
unripe fruits is comparatively low, about 1 to 4 % of the picked coffee.
The coffee is brought to Beneficio Atapasco by trucks, which are weighed on a truck
scale upon arrival. The coffee is unloaded from the trucks to cherry tanks. The unripe
fruits are weighed as well, placed in bags in the shade to ripen for 3 to 4 days, and
then processed as ripe coffee but separately as they are a lower quality product.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
4 (45)
FEA-219
Figure 1. Cherry tanks to which the trucks unload the coffee at Beneficio Atapasco
The coffee making process consists of three main stages:
– Wet process
– Drying
– Hulling and sorting
The wet process and the drying take place during the crop season. The hulling and
sorting can be done according to market conditions during the rest of the year but
normally between the end of November and May or July.
2.1.1
The wet process
In the wet process, the coffee is pumped with recycled water from the cherry tanks to
siphon and sink traps to separate good fruits by sinking from dried up ones, small
impurities, sand etc. These impurities are about 1 to 1.2 % of the coffee cherries
processed. After this classification, the coffee fruits are conveyed to drum type
depulpers where the coffee beans are separated from the skin and pulp (fruit flesh)
surrounding them. Some of the fruits, 12 to 18 %, need to pass through the secondary
and tertiary depulpers, as the fruits are not yet depulped after the primary depulpers.
About 2 to 4 % of the fruits are let out of the circuit, handled as inferiors and sent to
the patio.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
5 (45)
FEA-219
Figure 2. Depulpers
The depulped coffee beans have a sticky film, mucilage, around them. This mucilage
can be released after fermentation and attrition, which takes place in agitator tanks.
After the attrition process, the coffee is sent to tanks where it is skimmed from
floaters, the amount of which is about 0.5 %. The already softened mucilage is
separated from the coffee beans in a perforated bed screw conveyor with water
flowing in counter flow. The mucilage containing water is led to water treatment. The
washed coffee is sent to the drying section with fresh clean water. The water returning
from this transport is recycled for the wet process.
2.1.2
Drying
In the drying section, the coffee is first dewatered in an elevating screw conveyor
from where it leaves with a moisture content of 54 %. After that the coffee is blown
with air in two types of machines (deschamuscadoras and oreadoras de cascada) that
have some drying effect but the main purpose of which is to blow off water and
debris (rest of the pulp mixed with loose husks etc.) that could stick to the dryers.
After these machines, the moisture content of the coffee is about 52 %.
The coffee is dried first in pre-dryers that reduce the moisture content to about 41 %.
There are eight perforated sheet-type high tower dryers, in which both warm and cool
air is used for the drying. Dry saturated steam with a pressure of circa 5 bars is used in
the radiators to warm the air.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
6 (45)
FEA-219
Figure 3. Drying of coffee beans in pre-dryers
After the pre-dryers, the coffee passes through two sections of intermediate drying,
the Mardones and Villatas dryers. Finally, the Medisa dryers are used just to fix the
end humidity point to 12%. The coffee may be warmed or cool-ventilated or it may
just pass through these dryers and it can be returned back to the same dryer or be sent
to the next one according to need.
Figure 4. Mechanical dryers for coffee beans
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
2.1.3
6 Feb 2006
7 (45)
FEA-219
Hulling and sorting
After the pulp and mucilage have been removed from the coffee beans in the wet
process, the beans are still surrounded by their parchment husk, therefore called
parchment coffee. After drying the parchment coffee waits in small silos for quality
control. If the quality is fine, the coffee is stored in intermediate storage waiting for
hulling. Some of the coffee processed at Beneficio Atapasco, about 35 %, is bought as
dry parchment coffee. In the hulling process, the husks are removed from the beans as
they rub against each other and the walls of the hulling (threshing) machine.
Figure 5. Threshing machine for removing the husks
In Beneficio Atapasco, machines do the sorting or classifying of coffee. The machines
sort the coffee by size, form proportions, flotation in air currents and by color. The
best coffee, about 95 %, is for export. The rest, 5 %, goes to domestic consumption or
low quality export.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
8 (45)
FEA-219
Figure 6. Classifying system for coffee
2.2
Energy requirements
The coffee making process consumes both electricity and heat. As this study
concentrates on the self-sufficient energy supply system, the energy consumption is
considered as base data. The improving of the coffee making process itself and the
studying of the energy saving possibilities related are outside the scope of this study.
2.2.1
Electricity requirements
The annual electricity consumption at Beneficio Atapasco is about 0.60 GWh out of
which about 0.56 GWh per year is produced by diesel engines. There are six diesel
engines, the total power of which is 640 kW. The rest of the electricity needed, about
0.04 GWh per year, is bought from the net. The electricity bought from the net is used
mainly for lighting and the office buildings.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
9 (45)
FEA-219
Figure 7. Diesel engines
The process is vulnerable to power failures. Especially during the crop season, the
continuous electricity feed to the coffee process must be guaranteed.
2.2.2
Heat requirements
Steam is used to warm up the air for the dryers. Based on DIMMA’s calculations
about 1.5 – 1.7 kg of steam is needed per one kilogram of evaporated water. The
amount of steam required in the radiators is about 2100 - 2400 tons (or 1.4 - 1.6 GWh
in energy content) per year. The steam is produced with two boilers, a HRT
(Horizontal Return Tubular) boiler and a sectional boiler. The peak production of the
two boilers together is nearly 7800 kg/h dry saturated steam at 4.85 bars.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
10 (45)
FEA-219
Figure 8. Biomass boiler at Beneficio Atapasco
2.3
Mass and energy balance calculations
The mass balance of the coffee process at annual level is presented in the block
diagram of appendix 2. The energy flows are shown in appendix 3. The residue flows
of the coffee process represent the biomass potential for the energy production. The
energy requirements of the coffee process and the biomass potential are the base data
for finding a sustainable alternative for the energy production.
2.3.1
Mass balance
The mass balance is based on the description of the coffee making process at
Beneficio Atapasco written by DIMMA S.A. (see App. 1). The content of dry matter
is essential in the studying of the biomass potential. The amounts of circulating water
and coffee fruit humidity during the wet process are more or less best guesses. The
amount of recycled water is not essential in considering the possibilities of utilizing
the biomass; it is shown only for the sake of the mass balance.
The annual amount of evaporated water is calculated from the mass balance based on
the humidity of the parchment coffee before and after the drying section.
The factor for the conversion of berries to green coffee was calculated to be 5.8
according to the mass balance calculations, which is more than the average conversion
rate of 5.25. A conversion rate of 5 to 1 has been agreed between the planters and
processors for unclean coffee.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
2.3.2
11 (45)
6 Feb 2006
FEA-219
Secondary flows
As described above, the coffee making process consists of several phases. There are
secondary flows from different points of the process that consist of residue flows and
lower quality berries which are separated from the main flow to be processed
separately. The secondary flows at each point have been estimated by DIMMA as
percentages of the flow. The average secondary flows based on the mass flow
calculations are presented in table 1.
Table 1. Secondary flows
Process
Picking
Secondary flow
Percent of
flow, %
1-2
Leaves, branches
(very humid), to soil
plantations
Siphon and
Dried coffee cherries 1-1.2
sink traps
+ very small amounts
of impurities, sand,
etc.
Depulpers
Poor quality cherries, 2-4
to patios
Depulpers
Pulp to patios
41.7 % of
coffee fruit
After
"Floaters" to patios
1
fermentation for drying
Washing
Water and mucilage
18.2 % of
coffee fruit
Drying
Rest of pulp, loose
0.05 % of
husks
pergamino
coffee
Hulling
Husks
16.3 % of
pergamino
coffee
Classification Low quality green
5
coffee
Mass flow
(dry), t/a
30
10 - 15
25 - 45
710 - 730
10
Type of flow
Residue, not
transported
(c. 50 km)
Lower quality
coffee, very small
amount of residues
Lower quality
coffee
Residue
210 -225
Lower quality
coffee
Residue
0.3
Residue
370 - 380
Residue
80 - 95
Lower quality
coffee
Measured by dry matter, the biggest residue flows are the pulp, mucilage and husks
that are separated from the beans during the process. The other residue flows are
impurities. Low quality fruits are taken to the patios and processed later separate from
the export quality.
2.3.3
Energy flows
Energy flow diagrams based on the biomass potential are shown in appendix 3 for the
base case (existing system) and the different alternatives considered for energy
production in future. The base case represents the current situation. Now, most of the
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
12 (45)
6 Feb 2006
FEA-219
biomass available is not utilized for energy production. Heat and electricity are
produced separately. Bio fuel is utilized for steam production but electricity is
produced with diesel oil. About 1.4 GWh of diesel oil is used annually. Part of the
electricity is bought from the net, about 0.04 GWh per year.
The available biomass potential is nearly 7.7 GWh per year (Table 2). Only the husks
and wood from shadow trees in the plantations are used in the boilers for steam
generation. The energy content of the husks is about 2.1 GWh and the energy content
of the shadow trees is about 0.4 GWh per year. On annual level, the calculation shows
that some husks are left over. In reality, all husks are utilized at some point. The
mucilage is being partly used for biogas production. However, as the biogas is not
used for energy production, only about 30% of the total biomass capacity is utilized
for energy production today.
Table 2. Biomass potential
Biomass
Energy potential, GWh/a
Utilized
for
production, %
Pulp, dry
3.9
0
Impurities
0.001
0
Husks
2.1
80 - 100
Wood
0.4
100
Mucilage, dry
1.2
(c. 40)
Total
7.7
30 (- 40)
energy
The mucilage is treated in an up-flow anaerobic sludge blanket reactor (UASBreactor) which reduces the organic compounds in the wastewater to methane, carbon
dioxide and a small amount of cell material. This biogas is an excellent source of
energy. However, it is just burned to atmosphere at Beneficio Atapasco today. The use
of the UASB-reactor for wastewater treatment reduces the odor problems caused by
the mucilage but, in addition, it could be connected to the energy production system.
The energy content of the dry matter of the mucilage is estimated to be about 1.2
GWh per year. Not all of the mucilage is treated in the UASB-reactor; some of it is
led to the lagoon. About 30 % of the energy content of the entering dry mucilage is
estimated to be converted to energy of biogas in the UASB.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
13 (45)
FEA-219
Figure 9. UASB-reactor
The biggest energy flow is wasted in the pulp. The energy content of the dry matter in
the pulp is almost 4 GWh per year. The pulp is conveyed to a pulp hill where its
moisture content reduces. Then the pulp is taken by trucks back to the plantations
where it is composted and spread to the fields for fertilizing. Lixiviate squeezed from
the pulp hill is led to the water treatment. This lixiviate has a high sugar content. The
pulp and lixiviate could be utilized for energy production and the inorganic
compounds could still be returned to the soil for fertilizing in the form of ash or
sludge depending on the use. A preliminary estimate for the energy content of the
pulp lixiviates, if the pulp is squeezed, is 0.16 to 0.2 GWh/a.
There are, in addition, smaller secondary flows of biomass that could be considered
for energy production. The leaves and branches separated right after picking are
returned to the soil of plantations, which seems practical. Otherwise, they would need
to be transported separately to the mill (Beneficio Atapasco) about 50 km away. The
flow of dried berries and impurities from the siphon and sink traps contains mostly
lower quality coffee, which is separated to be produced separately, and only small
amounts of sand. The rest of pulp and husks from the drying section, instead, could be
utilized for energy production. However, the energy content of these flows only is
about 1.5 MWh per year. The dust lost in the hulling process can hardly be collected
for energy production. The poor quality fruits from the re-pass depulpers and the
floaters from the agitator tanks are not considered residue flows as they are just
separated from the main flow and processed separately later on. The coffee separated
in the classification process as not export quality is sold for domestic consumption or
lower quality export.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
2.4
6 Feb 2006
14 (45)
FEA-219
Physical conditions and restrictions related
At the moment, the UASB-reactor is too small to process all the mucilage containing
water. Part of the wastewater is led directly from sedimentation tanks to a lagoon.
There are plans for increasing the capacity of the UASB by heating it. The heat of the
diesel engines, for example, could be utilized for the purpose. Now there is no gas
motor or boiler to burn the biogas in so the energy content of it cannot be utilized for
the production of heat or electricity. Instead, the gas is burned to atmosphere.
Diesel engines are used for the production of electricity for stability reasons because
blackouts are disastrous for the process during crop season. Short blackouts of the net
are common in the area. Now, there is no equipment for producing electricity from
biomass.
The pulp is very wet coming from the process. It cannot be burned as such in the
existing boilers. It dries in the pulp hill and it is transported back to the plantations at
the end of the crop. At the plantations, the pulp is composted before being used as
fertilizer. It cannot be used raw because the microorganisms that discompose the pulp
compete with the coffee trees in nitrogen absorption at the time the trees need it the
most. There are also plans for drying the pulp on patios. According to local
calculations, the cost of drying pulp on patios may be less than the cost of disposing it
the traditional way. The pulp lixiviates have a high sugar content. They are led to the
wastewater treatment.
The length of the crop season is fairly short, from the end of October to the beginning
of March, considering the operation hours for a power plant that could convert all the
potential biomass to heat and electricity. If biomass were available from somewhere
in the neighborhood, another food processing plant or an energy forest, for example,
the operation time could be longer. The power plant could run all year round
producing electricity to be sold to the net when it is not needed at Beneficio Atapasco.
However, now, there is no other source of biomass nearby, at least not outside the
crop season.
3
COMPARISON OF THE TECHNICAL SOLUTIONS
As summarized in figure 10 of the base case, the handling of residues and production
of energy consists of separate lanes at the moment. Steam is produced with the
boilers, electricity with the diesel engines. The mucilage is treated in the UASBreactor and the pulp is used for fertilizing.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
15 (45)
FEA-219
Base case
•Unused bio fuel
• Small amount of impurities - > disposal
• Pulp -> pulp hill -> fertilizing, lixiviates to waste water treatment
•Steam production
• Husks, wood -> boiler -> steam, ash, heat loss
•Electricity
• Diesel oil -> engines -> electricity, heat loss
• Electricity from the grid (for lighting etc.)
•Bio gas (not used!)
• Mucilage -> UASB-reactor -> Bio gas, water for irrigation
-> part of mucilage to lagoon (capacity of UASB)
Figure 10. Base case: current situation
The first idea in finding the suitable alternatives for the energy production is to close
the open cycles of energy flow and utilize the biomass potential in the energy
production. There are several possible alternatives for achieving this goal. The main
alternatives compared in this report are a CHP-plant, a gas engine and ethanol
production.
3.1
Combined heat and power production
A combined heat and power plant (CHP) could consist of either a fluidized-bed boiler
or a gas boiler and a steam turbine. Figure 11 presents a schematic drawing of a CHPplant. Bio fuel is burned in the boiler and the steam produced in the boiler is used to
generate electricity in the turbo generator. The existing boilers can be operated at 9
bar (a) pressure without modification. The end pressure for the expansion of steam in
the turbine can be set according to the steam value requirements of the process. As the
steam consumption varies with time and the coffee making process does not consume
all steam, an air-cooled condenser is required. The turbine could be equipped with a
condensing part to make more electricity but in a small-scale steam turbine, the
investment cost for the condensing part would probably be relatively high. The
process and turbine condensates are pumped to a feed water tank for gas removal.
Feed water is pumped from the tank back to the boiler to complete the power plant
cycle.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
16 (45)
6 Feb 2006
FEA-219
9 bar(a), 175 °C
TURBINE
G
BOILER
STEAM
CONSUMER
FEED WATER
TANK
CONDENSER
PUMP
PUMP
Figure 11. Schematic drawing of a CHP-plant
Neither the existing boilers nor the radiators require high water/steam purity.
However, the steam turbine will probably have stricter steam purity requirements for
proper operation. The need for water treatment of the raw water from the spring, as
well as filters for the condensates, will need to be checked in the possible preengineering phase.
3.1.1
CHP with a fluidized-bed boiler
A fluidized bed boiler could burn all the biomass available (husks, wood, pulp and
other impurities) including the biogas from the UASB-reactor. The pulp would not
even have to be dried on patios; perhaps a screw conveyor would be required to
squeeze it dry enough. The boiler ash could be returned to the soil of the plantations
as fertilizer. The water from the UASB would be used for irrigation as today.
However, the existing old boilers cannot be modified to fluidized-bed boilers so they
would not be in operation anymore in this alternative. Considering that, a new boiler
is required, the steam values after the boiler can be chosen differently.
A bubbling fluidized-bed boiler (Figure 12) is the recommended type of for a small
scale CHP-plant. Fuel is fed into the bed above an air-distribution grid in the bottom
of the bed. The air flows upwards through the grid into the bed, which now becomes
the furnace where combustion of the swirling mixture takes place. The fluidized bed
looks like a boiling liquid and has the physical properties of a fluid. In fluidized-bed
combustion of biomass, the bed is usually sand. The air acts as the fluidizing medium
and is the oxidant for biomass combustion. About 30 to 40 % of the air is fed from the
air plenum below the bed. To insure complete combustion over-fire air is added to the
freeboard space above the bed. Bed temperature is governed by the desire to obtain
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
17 (45)
FEA-219
complete combustion versus the need to maintain the bed temperature below the ash
fusion temperature of the biomass ash. Fluidized-bed combustors have the advantage
of good mixing and high heat transfer, resulting in uniform bed conditions.
Combustion takes place at relatively low temperatures, giving low NOx emissions.
Combustion is very efficient, and 99-100% carbon burnout is typical. Bubbling
fluidized-bed boilers are normally designed for complete ash carryover, necessitating
the addition of cyclones and/or bag houses for particulate control. Fluidized-bed
boilers are efficient when firing fuels with low heating value and high moisture and
ash content. They are reliable and easy to operate with low maintenance requirements.
Bubbling fluidized-bed boiler
Flue gas
Air
Air
Fuel
Air
Figure 12. Bubbling fluidized-bed boiler, schematic drawing
3.1.2
CHP with a gas boiler
Another possibility of building a CHP-plant is modifying one of the existing boilers to
a gas boiler. This would require at least a burner modification after which the boiler
could burn the biogas from the UASB. In this alternative, the capacity of the UASBreactor would be increased and the mucilage and the pulp lixiviates, and possibly the
pulp itself, would be processed to biogas. The water would be used for irrigation as
today. The boiler ash could be returned to the soil of the plantations as fertilizer. The
existing boilers could be used. The burner modification would be done to one of the
boilers, which could then burn both biogas and solid biomass (husks and wood). The
other boiler would be on stand-by and burn solid biomass when in use. The possibility
of adding a superheater to the existing boiler should also be checked as part of the
boiler modification.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
3.1.3
18 (45)
6 Feb 2006
FEA-219
Size consideration for the CHP plant
The size consideration for the CHP plant generated six alternatives (Table 3):
Table 3. CHP alternatives
CHP 1
CHP-plant, fluidized bed boiler, pulp burned in the boiler
CHP 2
CHP-plant, old boiler, pulp to biogas – biogas burned in the boiler
CHP 3
CHP-plant, fluidized bed boiler, self-sufficient electricity production
w/biomass
CHP 4
CHP-plant, old boiler, pulp to biogas – biogas burned in the boiler, max
steam w/old boilers
CHP 5
CHP-plant, fluidized bed boiler, 1 MW turbine, diesel engines not needed
anymore
CHP 6
CHP-plant, fluidized bed boiler, 3 MW turbine, power plant
In the existing system, the energy content of pulp, biogas and mucilage (for the part
that exceeds the capacity of the UASB-reactor) is wasted. In all the CHP-alternatives
presented, these energy streams can be utilized. Block diagrams of the energy flows of
the alternatives are shown in appendix 3 (3.1 -3.6). The alternatives CHP 1 and CHP 2
are based on the idea of the utilizing all the biomass available from the coffee making
process at Beneficio Atapasco. CHP 3 was calculated to check the size required for
the new fluidized-bed boiler in case the steam turbine was designed for the capacity of
0.6 GWh/a, which represents the average annual electricity production with the diesel
engines today. CHP 4 was based on the idea of running both the existing boilers at
maximum capacity and checking the need for extra fuel and, on the other hand, the
size of the turbine that could be operated with the corresponding amount of steam. As
the steam turbine seemed to be quite tiny in all the previous alternatives, CHP 5 and
CHP 6 are alternatives with 1 and 3 MW steam turbines. If the steam turbine produces
1 MW of electricity, it covers the electricity needs of the coffee plant at all times, also
peak hours, and the diesel engines could be set to be stand-by equipment. As the
electricity consumption varies a lot, the excess electricity could be sold when the
consumption is lower. With a bigger 3 MW steam turbine, electricity could be sold to
the grid continuously. The power plant’s own use of electricity (about 5%) has not yet
been taken into account in the calculation of the alternatives.
3.1.3.1
Alternative CHP 1
In CHP 1, the fluidized-bed boiler would burn pulp, biogas and possible impurities
left over from the process in addition to the husks and wood utilized in the boilers
now. The capacity of the UASB-reactor would be increased to process all the
mucilage to biogas. Also, if the pulp was squeezed dry or dried some other way, the
pulp lixiviates could be fed to the UASB-reactor. We have assumed that about 30% of
the energy content of the dry matter in the mucilage can be converted to energy of
biogas (mostly methane). The annual energy of biomass to the boiler including the
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
19 (45)
FEA-219
biogas is thus 6.8 GWh as an average (see app. 3.1). With an operation time of 4
months (2880 h), the boiler would be operating with a fuel power of 2.4 MW.
Assuming 80% efficiency, the average boiler power would be about 1.9 MW. To get a
figure of the power plant as whole, preliminary process simulation calculations with
mass and energy balances were made of the process (see app. 4). With 2.4 MW fuel
power, the average shaft power of the steam turbine would be only 80 kW meaning an
alternator power of about 70 kW. With the 2880 operation hours, the annual electrical
energy produced would be about 0.2 GWh, which is about a third of the annual need
of 0.6 GWh. In other words, the amount of electricity produced with the alternative
CHP 1 would be so small that the diesel engines would still be in operation.
3.1.3.2
Alternative CHP 2
The main difference between CHP 1 and CHP 2 is that in CHP 2 the pulp would be
processed to biogas in the UASB-reactor. The capacity of the reactor would thus need
to be enlarged. The pulp may even require a reactor of its own to digest and convert it
to biogas. Anyway, the idea is that the solids (husks, wood and possible impurities)
would be burned in the existing boiler as today. In addition, a burner modification
would be done so that the biogas could be utilized as well. With the same energy
conversion rate of 30 % in the biogas reactor as in CHP 1, the total energy of biomass
including biogas would be only about 4 GWh/a as an average (see app. 3.2). With an
operation time of 4 months (2880 h), the boiler would be operating with a fuel power
of 1.4 MW. Assuming 75% efficiency (old boiler), the average boiler power would be
almost 1.1 MW. The preliminary process simulation calculations with mass and
energy balances are in app. 4. With 1.4 MW fuel power, the average alternator power
of the steam turbine would be only 40 kW. With the 2880 operation hours, the annual
electrical energy produced would be about 0.1 GWh, which is about a sixth of the
annual need of 0.6 GWh. In other words, most of the electricity would still be
produced with the diesel engines.
3.1.3.3
Alternative CHP 3
In alternative CHP 3 (see app. 3.3), the steam turbine size was chosen according to the
annual electric energy consumption 0.6 GWh. With the annual operation time of 2880
hours, this would mean an average power of 0.2 MW for the turbine. According to the
preliminary process calculations (app. 4), this would require 5.3 MW of boiler power.
A fluidized-bed boiler with 80% efficiency would thus require 6.6 MW of bio fuel
power. The existing bio fuel capacity at Beneficio Atapasco is about 2.4 MW
including the pulp, husks, wood and biogas (all mucilage converted to biogas). The
difference, 4.2 MW, would need to be bought from outside. We have understood,
however, that buying of bio fuel would not be easy. Anyhow, this alternative would
require a recheck of the biomass potential of the surrounding agricultural plants etc.
Theoretically, CHP 3 could produce the electrical energy needed at annual level. It
should be noticed, however, that the electrical load varies with time. Thus, the diesel
engines would still be in operation, as in reality, the consumption of electricity varies
depending on which sections of the coffee process are in operation. The peak load is
over 1 MW of which, in alternative CHP 3, the steam turbine could produce about
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
20 (45)
FEA-219
20%. There was no load curve available at this point, but it will be necessary for
further development of the concepts to produce one. If there are very few peak hours
during the operation season, they can be handled with the diesel engines. The size of
the CHP-plant shall be chosen so that it covers the electricity need for most of the
time.
3.1.3.4
Alternative CHP 4
Only one of the existing boilers is in operation today but actually, the capacity of the
two boilers together is close to the size of the boiler of alternative CHP 3. The idea of
CHP 4 (see app. 3.4) was to utilize both the existing boilers, the maximum steam
production of which is 7800 kg/h (2.2 kg/s). According to the preliminary process
calculations (app. 4), this would require 4.6 MW of boiler power. Assuming 75%
efficiency for the old boilers, it would require 6.2 MW of bio fuel power. The existing
bio fuel capacity at Beneficio Atapasco is about 1.4 MW including the husks, wood
and biogas (all mucilage and pulp converted to biogas). The difference, 4.8 MW,
would need to be bought from outside as in alternative CHP 3. The alternator power
for the steam turbine in CHP 4 would be nearly the average annual load of Beneficio
Atapasco 0.2 MW. However, this would still require the utilization of diesel engines
for higher loads as in CHP 3.
3.1.3.5
Alternatives CHP 5 and CHP 6
The problem with all the alternatives CHP 1-4 is the small size of the steam turbine
and thus rather small electrical power. The diesel engines will still be needed. If we
consider the existing system the base case, it is hard to see the feasibility of the
alternatives CHP 1-4. There will be investment costs in all alternatives, but as diesel
oil will still be used, there will be no or minor savings of fuel costs. In addition, the
operation time is rather short and there will not be much excess electricity to sell to
the grid. The heat the process requires can well be produced with the existing system
using “free” bio fuel.
The idea of CHP 5 and CHP 6 was to scale the concept so that the diesel engines
would not be in operation anymore (see app. 3.5 and 3.6). This would mean at least a
1 MW steam turbine. Of course, the boiler size grows too for the bigger turbine.
According to the preliminary process calculations (app. 4), a 1 MW (CHP 5) steam
turbine would require 24 MW of boiler power. A fluidized-bed boiler with 80%
efficiency would thus require 30 MW of bio fuel power. Similarly, a 3 MW (CHP 5)
steam turbine would require 70 MW of boiler power (with 80% efficiency 87 MW of
bio fuel power). The existing bio fuel capacity at Beneficio Atapasco is about 2.4 MW
including the pulp, husks, wood and biogas (all mucilage converted to biogas). In both
cases, practically all fuel would need to be bought from outside.
When the new power plant is designed to produce enough electricity to cover the
maximum load, the diesel engines can be left as auxiliary power sources. There will
be no fuel costs for oil. On the other hand, the bio fuel will cost something, when
bought from elsewhere. To cover the investment cost of a bigger CHP-plant and to be
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
21 (45)
FEA-219
profitable, the new power plant should operate all year round so biomass would need
to be available also outside the crop season.
The preliminary process calculations for CHP 5 and CHP 6 were done with the same
process values as for the smaller CHP alternatives. If these alternatives seem
interesting for further concept development, the process values could be thought over
to produce more electricity to be sold to the grid. In addition, the investment costs for
the connection to the grid to sell the excess electricity should be checked.
3.1.4
Summary of the CHP alternatives
In conclusion, the electricity production of the small CHP alternatives CHP 1-2 is too
small to cover the electricity requirement of the coffee process. In the bigger
alternatives CHP 3-6, the bio fuel produced in the coffee process is not enough and
more will be required from elsewhere. The alternatives CHP 3-4 cover the electricity
load at annual level but as there is great variation in the load, the diesel engines will
still be in operation.
The electricity production will need to exceed the peak load of the coffee plant
(1 MW) to replace the diesel engines and be self-sufficient in electricity production.
However, a power plant in the size group of CHP 5-6 or bigger seems like a
remarkable investment for a coffee producer. However, the possibility of a power
company coming to the area and making the investment would be quite interesting.
Beneficio Atapasco could perhaps own only a share of the power plant and at least
have contracts for selling all bio fuel and buying the required electricity and heat at a
reasonable price with no worries of producing the electricity by itself after all. This
idea would obviously require other similar producers from the area with same kind of
ideas and problems of insuring continuous electricity and heat supply.
3.2
Gas engine
The biogas would be an excellent fuel for a gas engine. More biogas could be
produced by increasing the capacity of the UASB and possibly converting the pulp to
biogas. The water from the UASB would be used for irrigation. Steam would be
produced with the existing boilers as today. The ash would be used for fertilizing. The
impurities from the process would be disposed of as today.
Considering the size of a gas engine, we run into similar questions as with the CHP
alternatives. Assuming that no bio fuel can be bought from elsewhere and the pulp can
be converted to biogas (with a 30% conversion rate), the gas engine could produce
electricity about 0.53 GWh per year (the annual consumption at Beneficio Atapasco is
0.6 GWh). The efficiency of the gas engine was assumed 35%. Thus, about 70 MWh
would need to be produced by the diesel engines, when looking at the production at
annual level. However, the electrical load varies and, in reality, the diesel engines
would be running more. With the 2880-hour operation time, the power of the gas
engine would be about 0.2 MW, which is only 20 % of the peak load. Once again, a
load curve showing the variation of the electrical load with time would be very useful.
The diesel engines would be running whenever the load exceeds 0.2 MW. A block
diagram of the energy flows of the gas engine alternative is shown in appendix 3.7.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
22 (45)
FEA-219
If additional bio fuel (convertible to biogas) was available from the surroundings, the
gas engine could be bigger and possible excess electricity could be sold to the grid.
With a bigger gas engine, the diesel engines would not be in operation anymore but
they could be stand-by equipment in order to guarantee the electricity supply at all
times.
3.2.1
Burning bio fuel with the existing engines
There are also other solutions worth checking, for example, with minor modifications,
the existing diesel engines could perhaps burn the biogas along with diesel oil. The
biogas would partly replace the diesel oil. This should be checked with the supplier.
Modifying one of the existing engines for biogas represents an alternative with
minimum investments and modifications. Everything else would be as today, except
the biogas would be utilized instead of burning it to atmosphere.
3.3
Ethanol production
A somewhat different alternative would be to continue the fermentation process of the
mucilage after the agitator tanks and to produce ethanol. The ethanol could be burned
in the diesel engines along with oil. There is a growing interest towards the use of
ethanol for example in vehicles. Possible excess ethanol could be another product to
be sold in addition to electricity. As ethanol is fairly easy to store, it can be produced
also outside the crop season, if suitable biomass is available.
The idea is to produce ethanol with a fermentation process using pulp and possibly
mucilage as feed. The sludge from the fermentation could be converted to biogas in
the UASB-reactor. If necessary, the mucilage could pass the fermentation and be used
only for biogas production in the UASB. In this alternative, the existing diesel engines
would be in operation and the existing boilers would operate as before using husks
and wood. Ethanol would replace at least part of the diesel oil in electricity
production. The separation of ethanol after the fermentation process requires heat,
which would raise the heat demand of the plant.
The preliminary capacity estimates were done assuming that no additional biomass
was available for the fermentation process. The energy content of the pulp and
mucilage is about 5.2 GWh/a. With a conservative estimate that about 15 % of the
energy content could be converted to energy of ethanol, the energy content of ethanol
would be about 0.7 to 0.8 GWh/a. About 0.3 GWh of electricity, in other words, 50
% of the electricity demand could be produced annually from ethanol, with a 40 %
efficiency estimated for the diesel engines. A block diagram of the energy flows of the
ethanol production alternative is shown in appendix 3.8.
The question with this alternative is if coffee pulp has been used for ethanol
production in commercial scale before. In principle, ethanol production is possible
from different kinds of biomass including wood, so utilizing coffee pulp should not be
a problem. The pulp would not need to be dried and the pulp lixiviates with a high
sugar content should convert to ethanol easily.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
23 (45)
6 Feb 2006
FEA-219
Basically, ethanol production from sugar and starch containing raw material is
commercial technology. Ethanol can be produced also from materials with
lignocelluloses (straw, wood) based on hydrolysis and fermentation of the extracted
sugars. In the hydrolysis step, the hemi-cellulose and cellulose are broken down into
fermentable sugars by a chemical treatment using, for example, sulfuric acid. Due to
its structure, the hydrolysis of wood is more complicated than the hydrolysis of starch.
However, the hydrolysis of coffee pulp can be assumed less complicated than the
hydrolysis of wood. Figure 13 shows the idea of the ethanol production process for
starch and cellulose containing material.
Ethanol from starch containing material
Amylase
Starch
Yeast
Glucose
Ethanol
Ethanol from cellulose containing material
Sulfuric acid
Cellulose
Special yeast
Fermentable
sugars
Ethanol
Figure 13. Ethanol production
The lack of an alcohol market in the area is not a problem as the amount of ethanol
produced can be consumed in the diesel engines. Besides, ethanol can easily be
transported if necessary. If there were excess biomass from the surroundings, this
alternative could be scaled bigger like the CHP-alternatives. The investment could be
more interesting to a petrol or chemical company than to a coffee producer. Beneficio
Atapasco could sell the biomass for the ethanol producer and buy the ethanol needed
to replace the diesel oil.
3.4
Summary of energy production and consumption
Table 4 draws a summary of the annual energy balances for the alternatives based on
appendix 3. In all cases, the calculations were done using 2880 hours for operation
time. The annual heat production is 1.6 GWh per year based on the process
requirements. The electricity production covers at least the production level of the
base case, 0.56 GWh/a. For the first round of comparison, the process values,
including the steam values in and out of the turbine, were kept the same for all cases.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
24 (45)
6 Feb 2006
FEA-219
Case:
BASE
CHP 1
CHP 2
CHP 3
CHP 4
CHP 5
CHP 6
Gas
engine
Ethanol
Table 4. Energy production and consumption (GWh/a)
Bio fuel to
boiler
2.1
6.8
4.0
19
18
86
252
4.01
3.32
0
0
0
12
14
80
245
0
0
Unused bio
fuel
5.5
0.9
3.6
0.9
3.6
0.9
0.9
3.6
4.4
Diesel oil
1.4
0.9
1.1
0
0.2
0
0
0.2
0.7
Heat
production
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
Electricity
production
0.56
0.56
0.56
0.6
0.6
2.9
8.6
0.6
0.6
Electricity
bought
0.04
0.04
0.04
0
0
0
0
0
0
Electricity
sold
0
0
0
0
0
2.3
8.0
0
0
Bio fuel
bought
1
2.5 GWh to boiler and 1.5 GWh/a (biogas) to gas engine
2
2.5 GWh to boiler and 0.8 GWh/a (ethanol) to diesel engine
The figures for unused bio fuel include the energy lost in the biogas reactor or
fermentation process. Only part of the energy of biomass is converted to energy of
biogas in the biogas reactor (30% estimated) or energy of ethanol in fermentation
(15% estimated) so there will always be a loss of energy. The possibility of using the
sludge of the fermentation process in the biogas reactor before using it for fertilization
or irrigation was not yet taken into account.
In alternatives CHP 3 and CHP 4 and with the gas engine, the figure in the table
represents the amount of diesel oil at annual level. However, the maximum power in
these alternatives is at the level of average consumption and diesel oil will be used to
cover the peak hours over the average. In other words, the consumption of diesel oil
will probably be higher in reality. To estimate the consumption of diesel oil more
specifically, knowledge of the hourly power consumption is required.
3.5
Availability of fuel
The amount of coffee to be processed at Beneficio Atapasco will not increase in the
next years. In other words, neither the biomass potential nor the energy consumption
is foreseen to rise. The sizing of the energy production system is based on the average
production and consumption of the last three to four crop seasons.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
3.5.1
25 (45)
6 Feb 2006
FEA-219
Possibilities of buying biomass
Now, buying of other biomass from the neighborhood does not seem possible. Some
additional biomass may be available during the crop season as the coffee and sugar
crop are collected at almost the same time. This limits the number of possible process
alternatives for energy production remarkably.
However, if, for example, the alternative CHP 5 or CHP 6 seems interesting, the
possibilities of buying biomass from a bit further away should be checked. In
addition, the price that could be paid for the biomass still keeping the investment
feasible can affect the apparent availability of biomass. The idea of establishing an
energy forest should also be checked, if the alternatives that require biomass all year
round seem interesting.
3.5.2
Characteristics of fuel
Today, husks and wood are burned in the boilers. The lower heating value of husks is
about 17.6 MJ/kg (HHV 20.1 MJ/kg) and the humidity about 11.2%. The LHV of the
wood from the shadow trees was assumed about 8.5 MJ/kg. For some type of trees,
the LHV can be higher, 11-13 MJ/kg for birch trees for example, so the assumption is
rather conservative.
The existing boilers cannot burn the pulp with an initial humidity of almost 75 – 85%.
However, with this level of humidity, the pulp could be fed to a fluidized-bed boiler.
After being squeezed in the pulp hill, the end humidity of pulp is still nearly 45%. The
pulp can be dried on patios, or a pulp press could be utilized, to lower the humidity
down to 8 – 12 %. The LHV used for pulp in the calculations is 17.6 MJ/kg and the
humidity 12%.
On the other hand, pulp has never been fed to the UASB-reactor because of its high
solids amount. It contains cellulose fiber of low decomposition. The pulp lixiviates are
high in dissolved solids like sugars which can be decomposed easily.
The diesel oil used today has a sulfur content of < 0.5 %, typically 0.05 %.
3.5.3
Fuel transportation and feeding
In the alternatives with the existing boilers, the biogas would require a new burner or
a burner modification. The first assumption would be to draw a pipeline from the
UASB-reactor to the boiler to transport the biogas. Some kind of a gas tank or
gasholder bell would even out the differences between production and consumption.
The husks and wood would be fed as today.
A new fluidized-bed boiler would have modern fuel feeding systems. In addition, the
transportation systems would need to be checked for the increasing capacity of a
bigger boiler operating perhaps all year round. In the next phase of pre-engineering,
after the energy production concept has been chosen, the fuel transportation system
can be designed based on the fuel characteristics, taking into account dust problems,
self-ignition etc.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
26 (45)
6 Feb 2006
FEA-219
A new gas engine would require a pipeline for gas transportation from the UASBreactor to the engine. The possibility of modifying one of the existing engines, after
which the biogas could be fed in with the combustion air, should be checked with the
engine supplier.
No pressure increasing equipment has been taken into account for the biogas. The
need for a compressor will have to be checked in the future phases of engineering.
3.6
Storage of end products
Today, pulp is one of the end products and it is stored during crop season in a pulp hill
from where it is later transported back to the plantations to be used as fertilizer. As the
energy of pulp is thus wasted, the idea in all the suggested alternatives is to utilize the
pulp for energy production first so that it will no longer be an end product. The
minerals of pulp can still be utilized for fertilizing purposes in the form of ash or
sludge. The ash will also take less space than the pulp when stored.
The electricity produced is used by the coffee process. For the larger scale CHP
alternatives, a connection to the grid will be made along with proper contracts to sell
the excess electricity.
Biogas can be to some extent stored in a gas tank or bell. However, it will be
consumed right away as it replaces diesel oil in the engines or other biomass (that can
be stored more easily) in the boiler.
Ethanol is easy to store and transport in containers which is the base idea of the
ethanol production alternative.
4
ASSESSMENT OF ENVIRONMENTAL IMPACT OF THE PROJECT
Considering the environmental impact of the project, using biomass instead of diesel
oil (fossil fuel) is essential. However, as stated before, the amount of excess bio fuel
from the coffee process that could be utilized for electricity production is not enough,
with any of the alternatives, to cover totally the electricity consumption of the coffee
process.
Anyway, biogas is already produced for the sake of water treatment and burning it to
atmosphere means wasting the energy of it. The CO2 from bio fuels is counted to be
consumed by the vegetation. The sulfur content of diesel oil is not very high but
replacing it with biogas, and most likely with other biomass (depending on the
analysis), reduces the SO2-emissions a bit. The level of NOx-emission depends on the
combustion temperature etc.
Now, the capacity of the UASB-reactor is not sufficient and part of the water is lead
past the reactor to the lagoon. Increasing the capacity of the reactor would thus
decrease the organic load of the lagoon and the possible odor problems related.
Replacing the existing boilers with a new fluidized-bed boiler increases the boiler
efficiency. Less fuel will be used, and thus, the emissions will be smaller for the same
energy produced.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
27 (45)
6 Feb 2006
FEA-219
Considering the traffic around the plant, if the pulp were used for energy production
and only the ash taken to the plantations for fertilizing purposes, there would be less
truck traffic between the coffee plant and the plantations.
5
FINANCIAL CALCULATIONS
The financial calculations are based on Enprima’s knowledge of similar size boilers,
steam turbines, engines etc. Many aspects are unknown at this point so the estimate is
made on a harsh level to get a figure of the differences between the alternatives and a
first look up on the feasibility of the project. Once the concept is chosen, a more
specific and accurate estimate based on budget prices of suppliers can be made for the
chosen alternative.
5.1
Investment cost estimate
The preliminary investment cost estimate is based on the knowledge that Enprima has
gathered of prices of power plant components in numerous implementation and preengineering projects. The prices are in 2005 price level without taxes. The accuracy of
the preliminary investment cost estimate is not very high at this point. Once the
concept alternative has been chosen, the estimate can be adjusted to be more accurate
in the proceeding phases of engineering. The total investment cost estimates of the
alternatives are presented in table 5.
CHP 1
CHP 2
CHP 3
CHP 4
CHP 5
CHP 6
Gas
engine
Ethanol
Table 5. Total investment costs for the alternatives (MEUR)
Machines and
instruments
2.5
2.5
3.3
2.8
9.4
22.4
2.5
3.3
Civil work
0.3
0.2
0.5
0.3
1
1.3
0.3
1
Other costs
0.6
0.6
0.7
0.6
2.8
3.8
0.8
1.1
Total
3.4
3.3
4.5
3.7
13.2
27.4
3.6
5.4
Case:
Comparing the alternatives CHP 1 and CHP 2, the burner modification in CHP 2 will
cost less than the new boiler in CHP 1. On the other hand, the capacity of the new or
enlarged biogas reactor would be bigger in CHP 2.Thus, the total cost for machines
and instruments is estimated to be about the same in both cases.
With the bigger boiler, CHP 3 compared to CHP 1, the investment cost of the boiler
and the fuel handling system is estimated to increase as the fuel power grows. The
price of the steam turbine does not increase relatively as much in this size group. In
CHP 4, the burner modification is done for only one of the boilers as in CHP 2. We
see some additional cost for the balance-of-plant, piping etc. and civil works
compared to CHP 2 due to the increased plant sized.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
28 (45)
FEA-219
In alternatives CHP 5 and CHP 6, the boiler size grows remarkably increasing the
total investment costs to a different level. The connection to the grid to sell excess
electricity and the cost of the connection will need to be checked in the next phase of
engineering.
The investment for the gas engine is estimated to be about the same as for the small
steam turbine of alternatives CHP 1 to CHP 4. If a modification for one of the existing
engines was possible, so that it could burn the biogas along with diesel oil, the
investment for the gas engine alternative would probably be the lowest. To convert the
pulp to biogas, the capacity of the biogas reactor would still need to be enlarged.
The investment for the ethanol plant is a bit uncertain. If the idea seems interesting at
all at this point, a budget price should be asked from a supplier in the next phase.
5.2
Fixed operation and maintenance costs
The cost for local labor (operators of the power plant) is estimated to be 30 kEUR per
year. In addition, the cost for services (cleaning etc.) is estimated to be 15 kEUR/a.
In addition, the maintenance costs of the boiler, turbine, UASB, fuel transfer system
and electrification and control were estimated at rough level for the fixed costs.
5.3
Variable operation and maintenance costs
Bio fuel is considered free as long as it comes from the coffee process. However, in
the alternatives where bio fuel needs to be bought, the price is assumed to be
3 EUR/MWh. The price used for diesel oil in the calculations is 157 EUR/MWh.
Electricity from the grid is assumed to be bought for the price of 241 EUR/MWh. The
price for electricity sold to the grid in alternatives CHP 5 and CHP 6 is
85 EUR/MWh.
The costs for the waters (raw water, cooling water, potable water and wastewater,
etc.) have not yet been taken into account due to lack of information. Neither have the
costs for bottom and fly ash or chemicals necessary for water treatment and the
fermentation process.
5.4
Total production costs
The production costs for the alternatives are presented in table 6. The total production
costs include the costs for fuel, operation and maintenance and the capital costs
estimated with 6% interest rate and 25-year time. For alternatives CHP 5 and CHP 6
in which excess electricity is sold to the grid, the sum from electricity sales is
subtracted from the total production cost.
As can be seen from the total production cost per electricity produced, the production
cost of electricity is higher in all the alternatives compared to the base case presenting
the existing system. The capital costs are 0 kEUR per year for the existing system, and
the smallest CHP-alternatives still use the diesel engines for power production.
However, the production cost for the bigger CHP-alternatives is reasonable compared
with the base case considering the operation time used in the calculations. Obviously,
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
29 (45)
6 Feb 2006
FEA-219
if CHP 5 or CHP 6 was chosen, the operation time should be longer and thus the sum
higher from the selling of electricity.
BASE
CHP 1
CHP 2
CHP 3
CHP 4
CHP 5
CHP 6
Gas
engine
Ethanol
Table 6. Total production costs for the alternatives
Fuel costs, total (kEUR/a)
88
56
70
36
54
239
735
10
45
Operation & maintenance
costs, total (kEUR/a)
66
85
76
76
67
76
76
57
59
Capital costs, total
(kEUR/a)
0
265
257
349
290
1 034 2 146
281
421
154
407
403
461
411
1 349 2 957
348
526
Electricity to the grid
(kEUR/a)
0
0
0
0
0
194
683
0
0
Carbon financing
(kEUR/a)
0
1
1
4
3
4
4
3
2
Total production cost 1
(kEUR/a)
154
406
402
457
408
345
524
Total production cost per
electricity produced
(EUR/
MWh)
275
723
717
756
680
575
874
Case:
Total production cost 1
(kEUR/a)
1
5.5
1 151 2 270
400
263
Electricity and heat
Carbon financing opportunity
For carbon financing, the maximum amount of carbon dioxide we are discussing is the
amount released today in burning the diesel oil. Replacing all diesel oil with bio fuel
will save about 370 tons of CO2. With an emission fee of about 5 – 20 EUR/t CO2, the
sum from the carbon financing would be 1800 – 7400 EUR per year, if all diesel oil
was replaced. For the calculation (Table 6.), the sum from carbon financing was
calculated with 10 EUR/t CO2 for diesel oil replaced.
5.6
Financial analysis
The financial key figures of the alternatives were calculated for the investment based
on the difference in the cash flow compared with the base case. The feasibility of the
investment was checked with the financial figures, namely internal rare of return,
payback time and net present value of the investment. The financial figures for the
feasibility of the project are presented in table 7.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
30 (45)
6 Feb 2006
FEA-219
Table 7. Financial figures for the investment
Key figures
CHP 1
CHP 2
CHP 3
CHP 4
CHP 5
CHP 6
Gas
engine
4%
6%
8%
IRR
%
-13.3 %
-13.3 %
-13.3 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
IRR
%
-3.2
-15.3 %
-3.2
-15.3 %
-3.2
-15.3 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
IRR
%
-3.1
-8.7 %
-3.2
-8.7 %
-3.2
-8.7 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
-3.7
-3.8
-3.9
IRR
%
-8.9 %
-8.9 %
-8.9 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
-3.1
-3.2
-3.3
IRR
%
-5.9 %
-5.9 %
-5.9 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
-9.6
-10.3
-10.8
IRR
%
-3.4 %
-3.4 %
-3.4 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
-16.5
-18.4
-19.9
IRR
%
-3.5 %
-3.5 %
-3.5 %
Pay-back time
a
>25 a
>25 a
>25 a
NPV
MEUR
-2.2
-2.4
-2.6
IRR
%
-9.3 %
-9.3 %
-9.3 %
a
>25 a
>25 a
>25 a
MEUR
-4.6
-4.7
-4.8
Ethanol
Pay-back time
production
NPV
In the calculation of the internal rate of return, the cost savings of the investment are
discounted to the calculation time (year 2008) with such an interest rate that the
difference is zero between the investment and the savings discounted. The investment
is considered feasible, if the internal rate of return is higher than the return
requirement for the investment.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
31 (45)
FEA-219
The payback time is calculated so that the net savings of the investment pay off the
investment made in the beginning of the calculation time. It states how the investment
is paying itself back as the money invested is released due to the income or savings.
In calculating the net present value, the future income and payments of the time span
are discounted to the beginning of year 2008. For the feasibility of the project, the
better the bigger the difference is between the discounted savings and the investment.
The interest rate of discount used in the calculation is 6%. The project period and thus
calculation time used is 25 years. The first operation year of the new plant was
assumed 2008.
According to the financial figures, the feasibility of the project does not seem very
good with any of the alternatives studied. The savings from diesel oil and the income
from carbon emissions etc. do not pay off the investment in the expected lifetime of
the plant. The financial figures for the biggest CHP-plant and the gas engine are less
terrible than for the other alternatives. In addition, alternative CHP 6 could produce
more electricity with higher steam values and a longer annual operation time, which
could be studied further to increase the feasibility of the alternative. Of course, the
problem will be the lack of available bio fuel. Similarly, the investment cost for the
gas engine would perhaps be lower if a modification of one of the existing engines
were possible. With a smaller investment, the project would pay itself back more
easily.
5.7
Sensitivity analysis
The sensitivity of the total production cost per electricity produced (EUR/MWh) to
the variation of investment cost, price of fuels and electricity was analyzed. The
results of the sensitivity analysis, in diagrams, are included in appendix 5. Generally,
the investment cost has the greatest effect on the production price. However, even a
20% drop in the investment costs would not draw the feasibility of the alternatives to
a desired level. In CHP 6, where most electricity could be sold to the grid, an increase
in the selling price of electricity lowers the production cost. Anyhow, even a 20 %
lower investment cost and 20 % increase in the price of electricity sold to the grid
together could not make the project financially feasible.
A typical sensitivity analysis is quite useless, as the financial figures look miserable.
How could we increase the feasibility? Improving the process values, considering a
gate fee or introducing new technologies could be the solution.
5.7.1
Improving the process values
As stated before, the process values were kept the same through calculation of the
CHP-alternatives for comparison reasons. However, the process values fit for the
small turbines of the smallest CHP-alternatives are not the best possible for the 1 MW
or especially the 3 MW turbine of the bigger alternatives. A 3 MW steam turbine
would most probably be chosen to be a condensing turbine. In addition, a new boiler
would be designed for higher steam values.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
32 (45)
6 Feb 2006
FEA-219
Figure 14 presents a simple process diagram of a CHP-plant with a condensing steam
turbine. The steam turbine makes the same power, 3 MW, with less than one fifth of
the steam mass flow compared to CHP 6 presented previously. Thus, the boiler and its
investment cost are smaller. With the bigger alternative, it is worth buying a more
expensive condensing type steam turbine because it leads to remarkable savings in
boiler costs. The boiler is smaller but it produces superheated steam. If required by
the process, the steam for the consumers can be sprayed with feed water for
temperature control. The process simulation calculations for the condensing steam
turbine are included in appendix 6. In this preliminary look upon the condensing
turbine, the process steam is produced through a reduction valve from main steam.
There could as well be an extraction in the condensing turbine so that this amount of
steam would produce electricity as it expands. However, the amount of process steam
is relatively small and an extraction adds the costs of the steam turbine.
320 °C, 23 bar(a)
3 MW
TURBINE
15 MW
4.85 bar(a), 299 °C
G
0.5 bar(a)
BOILER
STEAM
CONSUMER
FEED WATER
TANK
CONDENSER
PUMP
PUMP
Figure 14. CHP-process with a 3 MW condensing steam turbine
The fuel power of the boiler would be 19.5 MW with 80 % efficiency. Assuming the
power plant would be in operation all year round, 8000 hours, thus the annual fuel
consumption would be 156 GWh out of which nearly all, 149 GWh would be bought
from elsewhere. On the other hand, the power plant would produce 24 GWh of
electricity, about 23.4 GWh to be sold annually.
Considering that, the
smaller than in CHP
expensive condensing
about 13 MEUR as
Enprima Ltd
boiler with the improved process values is actually 10 MW
5 but higher technology and the steam turbine of the more
type, as a preliminary estimate, the total investment would be
for CHP 5. The remarkable difference compared with the
Domicile Helsinki
Final Report
Katja Kurki-Suonio
33 (45)
6 Feb 2006
FEA-219
alternatives presented before is that the income from electricity sales, nearly 2000
kEUR/a, exceeds the production costs including capital costs, O&M and fuel costs by
about 450 kEUR at annual level. Thus the preliminary financial figures look fine
(table 8).
Table 8. Financial figures for the CHP-plant with a condensing turbine and 8000 h
operation time
Key figures
CHP
w/cond.
turbine
4%
6%
8%
IRR
%
27.8 %
27.8 %
27.8 %
Pay-back time
a
3.9
4.2
4.4
NPV
MEUR
42.2
32.4
25.1
Unfortunately, the same problem of availability of biomass still exists with this
solution. The calculation was made with a bio fuel price of 3 EUR/MWh as in the
main alternatives.
5.7.2
Waste to energy plant
What if we took a different perspective and checked the effect of a negative bio fuel
price. Table 9 shows the financial key figures for CHP 5 and 6, the biggest CHPalternatives, with a negative price or actually a gate fee for bio fuel, -10 EUR/MWh.
The power plant would operate as a waste incineration plant at the same time, a wasteto-energy plant.
Table 9. Financial figures for CHP 5 and CHP 6 with a 10 EUR/MWh gate fee
Key figures
CHP 5
CHP 6
4%
6%
8%
IRR
%
8.1 %
8.1 %
8.1 %
Pay-back time
A
13.7
16.8
23.3
NPV
MEUR
6.1
2.7
0.1
IRR
%
13.6 %
13.6 %
13.6 %
Pay-back time
A
8.4
9.4
10.7
NPV
MEUR
32.1
21.6
13.7
Developing the idea a bit further, the increasing of the capacity of the plant increases
the financial feasibility of it. Thus, the size should be at least as in CHP 6 producing
3 MW of electrical power or more. The idea would be to produce electricity and to get
rid of waste in an environmentally acceptable way. A modern waste-to-energy plant
can utilize the biomass from the coffee process and in addition other agricultural or
animal waste from nearby (poultry farms, piggeries, slaughterhouses etc.) as well as
household waste. The environmental impact of the project would be greater by far,
than what is achieved by replacing the diesel oil with bio fuel. The waste to energy
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
34 (45)
FEA-219
solution would be interesting to investors. The plant would be designed for all year
operation and finally the fuel (biomass and waste fuel) capacity of the area would
determine the size of the plant. As the price of electricity is high and there is a
shortage of dependable sources of electricity there would be a condensing type steam
turbine to maximize the power production. The steam values would finally be chosen
according to the characteristics (Cl-content etc.) of the waste available. The waste to
energy plant would supply power to Beneficio Atapasco and other consumers. The
plant would be located near the power consumer who could best take advantage of the
heat production.
The waste-to-energy plants represent existing technology and there is growing interest
towards them worldwide.
5.7.3
Introducing new technical solutions
As there is a worldwide interest towards the utilization of biomass, new technologies
are being developed. However, the problem with these is that most of them are not
commercial technology yet. The adaptation of such technologies would mean building
a more or less demonstration type plant, which would obviously be interesting but
perhaps have a higher risk than with commercial solutions.
5.7.3.1
Gasification
Biomass fuels are increasingly being used with advanced conversion technologies,
such as gasification systems, which may offer better efficiencies compared with
conventional power generation. Gasification is a thermo-chemical process in which
biomass is heated with little or no oxygen present to produce a low-energy gas. The
process involves partial combustion of biomass. Partial combustion produces carbon
monoxide (CO) as well as hydrogen (H2) which are both combustible gases. There are
different types of gasifiers: fixed-bed, fluidized-bed etc. with updraft, down-draft and
cross-draft solutions. The fuel characteristics determine the gasification method. On
the other hand, the composition of the gas will depend on the nature of the gasification
process used. The gas can be burned in a boiler or used to fuel a gas turbine or a
combustion engine to generate electricity.
With fixed-bed gasifiers the solutions for gas engine use are commercially available.
(Please see, for example: http://www.condens.fi/eng/Novel_kokemaki_e.html).
Considering the coffee pulp, the fluidized-bed type gasification process would be the
recommended type. This is commercially available technology for bigger scale power
plants and direct combustion in boilers. (Please see, for example:
http://www.fwc.com/publications/heat/heat_pdf/summer99/biomas.pdf for an article
about a biomass CFB gasifier in the Kymijärvi power plant in Lahti, Finland).
However, we see it as new technology concerning gas engines. The product gas is
lean or poor as the fluidized-bed gasification takes place in hotter temperatures than
the fixed-bed gasification. The heat is developed by the partial combustion in the
gasifier so more oxygen is being fed in and a greater part of the material is already
burned in the fluidized-bed type gasifier. The hot gas will need to be cleaned before
the engine. For the scrubber, the gas needs to be cooled down, and coming from the
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
35 (45)
FEA-219
scrubber, the gas is wet and needs to be dried before the engine. In this process, part
of the energy is lost. Anyway, this may be a future solution once the technology is
developed to a level where it is commercially available. Please see also
http://www.opet-chp.net/download/wp2/small_scale_biomass_chp_technologies.pdf
for a report on small-scale biomass CHP technologies and especially figure 1 of
gasification technologies for different power plant size classes in chapter 1.2.3 of the
report.
5.7.3.2
Pyrolysis
In pyrolysis, the biomass is heated to around 500°C. A limited amount of oxygen is
allowed to enter the reactor to provide the heat to sustain the pyrolysis process. The
biomass does not burn; instead, it produces bio-fuel vapors, which condense to a darkbrown, mobile liquid that can substitute for fuel oil. The pyrolysis process takes place
at a lower temperature and the residence times are shorter than in gasification. In
addition, the partial combustion of the fuel is not involved as in gasification. Pyrolysis
has the advantage over gasification that bio-fuel has a much higher energy density.
Moreover, it can be stored for long periods and easily pumped and transported. There
is a lot of interest also towards the pyrolysis technology today.
6
SITE AND LOCATION DATA
The intended location of the project is in the town of Quezaltepeque, at a site held by
CAFECO, Beneficio Atapasco. Quezaltepeque is marked on the map of El Salvador in
figure 15. The town is located about 20 km north-west of San Salvador (capital city)
at an altitude of about 430 m above sea level.
A site layout showing the existing coffee production plant and power production
system is presented in appendix 7. The connections to the local environment,
infrastructure and existing plant, power connections for the selling of electricity, the
need for a ground survey, etc. will need to be checked locally in the proceeding
phases of engineering after the plant concept has been chosen.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
36 (45)
FEA-219
Figure 15. Map of El Salvador
7
PERMITTING
The permitting requirements will need to be clarified locally. In the feasibility study
phase, quite many process alternatives were studied for the self-sufficient energy
supply system. The need of permits may vary depending of the alternative chosen for
the next phase of engineering. Anyhow, certain local permits will be necessary,
including construction and environmental permits. Once the type and size of power
production equipment has been chosen the need of different local permits will have to
be clarified. The permitting procedure for the implementation phase can be quite long
sometimes and should be started early enough.
8
LEGAL FRAMEWORK AND AUTHORITY REQUIREMENTS
The legal framework and authority requirements for the possible implementation
phase will need to be identified locally. Once the alternative for the next phase of
engineering has been chosen, the legal aspects of the project will need to be checked
as well as the authority requirements related.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
9
RECOMMENDATIONS
9.1
Feasibility of the project
6 Feb 2006
37 (45)
FEA-219
According to the financial figures, the feasibilities of the small CHP-plants, the gas
engine and the ethanol-plant alternative do not look very appealing. The main
problem is the relatively short operation time. In addition, there is not enough
biomass, after all, from the coffee process for electricity production to cover the
consumption at all times and thus fully replace the diesel engines. In other words, in
every alternative, there are investment costs, naturally. However, there is no or not
enough income from electricity sales and not enough savings from diesel oil to pay
back the investment.
The alternatives were calculated, for comparison reasons, all with same process values
for steam - the same values as today for connection to the existing boilers. However,
with a new fluidized-bed boiler and a condensing-type steam turbine the financial
figures are remarkably better. The improvement of financial figures requires,
however, higher process values for steam and year round operation with additional
biomass available from the surroundings.
Similarly, the waste-to-energy concept is financially feasible with a negative price,
gate fee, for fuel, biomass and waste material. Considering El Salvador is densely
populated, the handling of agricultural, animal and municipal wastes, in an
environmentally friendly way, must be at least as tough a problem to solve as it is
anywhere else. A waste-to-energy plant would have a remarkably more significant
impact on the surrounding environment than just replacing the diesel oil with bio
fuels. On the other hand, the transportation and storage of waste fuels as well as the
location of a waste-to-energy plant are yet to be studied, if this concept is chosen.
Perhaps Beneficio Atapasco would only be a shareholder with a contract for
continuous power supply and the plant itself would be located on another site.
The new technologies, ethanol production, gasification, pyrolysis etc. may well offer a
feasible solution for self-sufficient power supply in the near future. For these
alternatives, the recommendation would be to wait and see. The technologies are
there, a lot of research is going on around the world. However, with a specific and
globally thinking a bit exotic fuel, it can be worthwhile to wait a while and be a bit
careful on what is really commercially available and what references the companies
offering the solutions have. On the other hand, if Beneficio Atapasco wants to take
part in the research of the new technologies, the companies offering the new
technologies will be delighted to get references. In this case, the feasibility may not be
the best possible and there may be problems at first with adjusting the process for the
residues available from the coffee process.
Thinking of minimum investment, the modification of one of the existing diesel
engines so that it could burn the biogas produced by the UASB-reactor would be
something to consider. Diesel oil would still be needed and there would not be excess
electricity to sell to the grid, so financially the investment would not be extremely
feasible. However, the wasting of the biogas by burning it to atmosphere is not
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
38 (45)
FEA-219
environmentally or financially recommendable. At least some diesel oil could be
saved by utilizing the biogas that is being produced already.
In conclusion, there are several alternatives to consider and we hope that this report
will help Beneficio Atapasco in making the right decision. The small-scale CHPplants with only biomass from the coffee process do not look financially feasible. The
bigger scale power plants, with improved process values and possible utilization of a
wider range of wastes, show better financial figures. However, these alternatives are
not realistic unless bio fuel or wastes are available and either Beneficio Atapasco or
some other investor is ready to make the investment. The new technologies offer
possibilities but also bring a risk if the process has not been tested on coffee residues
or similar.
9.2
Implementation project schedule
Considering that there are so many alternatives for the self-sufficient power
production at Beneficio Atapasco and so many questions still open, a detailed
implementation schedule shall be produced in the next phase of engineering when the
right alternative has been chosen.
For the CHP-alternatives, the delivery time of the steam turbine determines the project
schedule. Usually, the turbine suppliers start the production upon order so the delivery
time is about 12 months and considering the time for start-up and test run the total
delivery time from order to start of operation will add up to about 18 months.
The boiler can be delivered within the delivery time of the steam turbine. Most
probably, a local workshop could deliver the fluidized-bed boiler, which is quite
simple to construct. If an alternative with the old boilers and a burner modification is
chosen, the burner modification could be done outside the crop season and it would
not take much time.
The delivery times for gas engines are probably shorter than for the steam turbines.
There will be some research first, though, as the supplier will want to know the
properties of the gas to be burned to define the filtration requirements etc. Actually,
the gas properties will be necessary for a possible burner modification of the boiler
too but the requirements are stricter for the engine.
For the new technologies, perhaps not tested on coffee pulp, such as ethanol
production, gasification or pyrolysis, a reservation should be made for the start-up.
Alternatively, the process should be tested first somewhere, not necessarily at
Beneficio Atapasco. There are testing and analyzing equipment and demonstration
plants around the world where the preliminary tests could be made and the properties
of bio fuel as well as biogas analyzed. The pioneer work will of course take time and
delay the implementation project.
Considering the bigger CHP-alternatives (CHP 3 to CHP 6), the improved CHPprocess with a condensing turbine or the waste to energy concept, a throughout study
on the availability of bio fuel or other waste material should be made before the
implementation decision. The price of bio fuel or the possible gate fee will have an
effect on the economy of the project. Besides, if no additional bio fuel can be found,
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
39 (45)
FEA-219
these alternatives are not applicable. Assuming that bio and waste material can be
found in such a densely populated country, the making of the supply contracts shall be
reserved the adequate time. On the other hand, if the investor is not solely Beneficio
Atapasco but some power company, for example, the negotiation of the contracts for
the continuous power supply to the coffee process shall be reserved time.
The handling of permission applications and legal framework is often time consuming
so the process should be started right away when the best suiting alternative has been
chosen in order not to have the permitting or licensing procedure slow down the
project.
10
SUMMARY
The purpose of this feasibility study was to identify suitable technical alternatives for
self-sufficient energy production at Beneficio Atapasco’s coffee production plant and
to evaluate the financial feasibility and the environmental impact of these alternatives.
The study was prepared as a joint effort between Enprima, CAFECO (Beneficio
Atapasco) and DIMMA S.A. de C.V.
A general understanding of the coffee process was necessary for collecting the base
data on the mass and energy balances, consumption of heat and electricity and the
type and amount of residues available to be used as bio fuel. The description of the
coffee production plant and the existing energy production system was based on
information collected by DIMMA.
The series of figures from 16 to 20 presents the process of finding the suitable
alternatives for the energy production system. The coffee process requires heat.
However, the heat production is not at all the main question at Beneficio Atapasco as
the required heat can well be produced with available bio fuel in the existing boilers.
Therefore, no investment is necessary for self-sufficient heat production. Electricity,
instead, is now mainly produced with diesel oil in engines. Thus, the issue is
expanding the use of bio fuel to electricity production. Now, coffee pulp, which
represents over half of the energy flow of the potential bio fuel available, is the main
flow of biomass that has not yet been utilized for energy production. A UASB-reactor
is used for producing biogas of the coffee mucilage. The capacity of the biogas reactor
is too small and part of the mucilage is lead past the reactor directly to the lagoon.
There are some plans for heating the reactor to increase the capacity, however, the
biogas is not utilized today but burned to atmosphere.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
40 (45)
6 Feb 2006
FEA-219
Coffee process
Heat demand
•self-suffiecient heat
production with biomass
Electricity consumption
• produced with diesel oil
• biomass could be utilized
for electricity production
Biomass (residues)
• coffee pulp and part of
mucilage not utilized
•biogas burned to
atmosphere
Figure 16. The coffee process determines the base data for the study
First, we checked possibilities for producing both heat and electricity with only coffee
process residues (Figure 17.). The existing energy production system was considered
the base case. The operation time was determined by the availability of fuel, the crop
season, which lasts only four months. A combined heat and power plant (CHP), with
two different boiler alternatives for utilizing the coffee pulp, was introduced. A
fluidized-bed boiler could burn the wet pulp in addition to the other coffee residues
burned in the existing boilers today (CHP 1). Another possibility for utilizing the
energy of the pulp would be converting it to biogas. With a burner modification, also
the existing boilers could burn biogas (CHP 2). Converting the pulp to biogas would
require more capacity for the UASB-reactor. The steam values for the CHP-processes
were chosen by the existing process: the existing boilers can produce 9 bar (a) steam
and the process steam pressure c. 5 bar (a). As only part of the energy of pulp is
converted to the energy of biogas (30 % conversion rate estimated), the average fuel
power for alternative CHP 2 is lower than for CHP 1. Thus, the steam turbine is also
smaller for CHP 1. Anyway, in both cases the electricity production is too small to
cover even the average consumption of the coffee process. With the diesel engines
still in operation, the savings from diesel oil would not be significant. There would not
be electricity produced with bio fuel to sell to the grid. Thus, the financial feasibility
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
41 (45)
FEA-219
of alternatives CHP 1 and CHP 2 does not seem very good, as there are not enough
savings and no income to pay back the investment.
Considering the gas engine alternative, if the coffee pulp were converted to biogas in
addition to the mucilage as in alternative CHP 2 (the capacity of the UASB-reactor
would be increased), a gas engine could nearly cover the average electricity
consumption burning the biogas. With a 200 kW gas engine the consumption peaks
would be handled by the diesel engines. As the crop season is short and there is no
income from electricity sales, this alternative does not pay itself back either. The
feasibility would perhaps be better with the smaller investment of converting one of
the existing engines for biogas operation.
Only biomass from
coffee process
CHP 1
CHP 2
• fluidized-bed
boiler, average fuel
power 2.4 MW
• existing boiler
with burner
modification for
biogas, average fuel
power 1.4 MW
•steam turbine with
alternator power
70 kW
Gas engine
• new gas engine,
power 200 kW
alternator power
40 kW
•short operation time
•electricity production too small, diesel engines still
in operation (for gas engine during consumption
peaks)
•poor feasibility
Figure 17. Alternatives for heat and electricity production using only biomass
available from the coffee process
The next idea was to check the size of the fluidized-bed boiler, if, during crop season,
the average electricity consumption of the coffee process was covered with electricity
from the CHP-plant (Figure 18.). This would mean that most of the biofuel would
need to be bought from elsewhere. Still, the operation time is short and the feasibility
poor as the diesel engines would be operating whenever the power exceeds the
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
42 (45)
6 Feb 2006
FEA-219
average level and there would not be notable amounts of electricity to sell. Besides,
the additional biofuel is not easily available according to local information.
Average electricity demand, 200 kW
CHP 3
CHP 4
• fluidized-bed
power 6.6 MW
• existing boiler
with burner
modification for
biogas, average fuel
power 6.2 MW
•Additional bio
mass required
alternator power
200 kW
Gas engine
• new gas engine,
power 200 kW
•Additional bio
mass required
alternator power
nearly 200 kW
•diesel engines still in operation for peak loads
•poor feasibility
Figure 18. Alternatives for covering the average electricity consumption
Finally, assuming that additional biofuel were available from somewhere, the concept
was scaled to a size where the electricity production by diesel oil would be fully
replaced by production with biofuels (Figure 19.). In this case, the steam turbine
would need to produce at least 1 MW of electricity (CHP 5), which is the peak load,
or rather more (3 MW in CHP 6) to sell to the grid as the price of electricity is quite
high. The steam values and the operation time were kept the same throughout the
calculation for comparison reasons. The efficiency of the big CHP-plant is quite low
with these process values. The boiler price is dependent on the boiler size and as the
boiler size grows remarkably for these bigger alternatives, the feasibility is still not
acceptable. Large amounts of additional biofuel would need to be bought and the
selling of electricity does not bring enough income in the short operation time.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
6 Feb 2006
43 (45)
FEA-219
Self-sufficient electricity production with biomass,
1 MW required for peak loads
CHP 5
CHP 6
• fluidized-bed
power 30 MW
• fluidized-bed
power 87 MW
alternator power
1 MW
alternator power
3 MW
•additional bio mass required
•poor efficiency w/process values of existing boiler
•poor feasibility
Figure 19. Alternatives for self-sufficient electricity production with biomass so that
the diesel engines are replaced
According to financial calculations, the feasibility of the alternatives was so miserable
that a normal sensitivity analysis did not bring any hope. New alternatives needed to
be analyzed to find a feasible solution for the electricity production with biomass
(Figure 20).
Developing further the idea of the CHP concept with at least a 3 MW steam turbine,
the process values should be set higher. In this scale of size, the turbine should be
chosen to be a condensing-type steam turbine to maximize the electricity production.
Considering a new fluidized-bed boiler with a superheater and steam values of, for
example, 320 °C and 23 bar(a), the boiler size does not grow relatively as much with
the steam turbine power, in other words, the plant efficiency is much better.
Calculating with year round operation, this concept would pay itself back quickly.
Another idea to introduce was the waste-to-energy concept, where the boiler could
burn agricultural, animal and municipal waste in addition to the biomass available.
The project would be financially feasible with a negative price for fuel, a gate fee. The
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
44 (45)
6 Feb 2006
FEA-219
positive environmental impact would be remarkably more meaningful than with just
replacing the diesel oil with the use of biofuels.
The new technologies including ethanol production, gasification and pyrolysis may
well be financially feasible solutions in near future. There are, however, limitations to
each technique and the applicability to coffee residues will need to be checked
carefully. The estimation of investment costs is a bit problematic with only few
commercial references and for different kind of fuel. The reliability of a new
demonstration type plant may not be on as high a level as required so there are some
risks included to adapting the new technologies.
Improving the feasibility
Improvement of
process values
• fluidized-bed boiler,
average fuel power
19.5 MW
Waste-to-energy concept
New technologies
• gate fee for fuel
Ethanol production
• plant size determined by
availability of fuel
•condensing steam
turbine with alternator
power 3 MW
Gasification
•all year operation
Pyrolysis
• offer possibilities
•bring risk
•investment cost
estimation?
•reliability?
Figure 20. Alternatives for improving the feasibility of the project
In conclusion, the coffee process and its heat and electricity demand as well as the
availability and properties of coffee process residues and other biomass determine the
possibilities and limitations for process development of the self-sufficient energy
supply. With only the biomass from the coffee process, the use of diesel oil cannot be
fully replaced and there will not be excess electricity to sell to the grid. With
additional biomass, the operation time could be longer and the size of the energy
production system could be increased to be able to sell electricity. The income from
electricity sales would easily payback the investment for the plant.
Enprima Ltd
Domicile Helsinki
Final Report
Katja Kurki-Suonio
45 (45)
6 Feb 2006
FEA-219
Unless biomass or waste is available from the surroundings, a minimum investment
for the purpose of disposing of the residues in an environmentally friendly way is the
main question. In that case, a modification of the gas engine for biogas operation
could be the solution together with increasing the capacity of the biogas reactor. As
there would be no income to pay back the investment, this would simply be an
investment for environmental protection.
This report presents various options for the energy production system with the
technical, financial and environmental aspects related. A recheck of the biomass
potential available from the surroundings is strongly recommended as the biomass
capacity limits the choice of financially feasible alternatives. Once the recheck has
been done, a pre-engineering phase can commence during which the investment costs
will be inquired from the suppliers, the project schedule planned and the permitting
and legal framework started for a specific concept.
11
NEXT STEP
Based on discussions between Dimma and Beneficio Atapasco, an improved version
of alternative CHP 5 seems most attractive at this point. The process should be
improved as for CHP 6 in chapter 5.7.1 of this report. For all year operation, biofuel
(or municipal waste) will need to be searched for from the surroundings and the price
for fuel negotiated etc. With improved process values, the boiler size will be smaller
as discussed for improving the process values for CHP 6. The final investment costs
will depend on the process values and the type of boiler and turbine chosen. Once
down to one alternative, the pre-engineering phase can concentrate on this concept,
improving the process, specifying the equipment and estimating the investment costs
more accurately based on offers from potential suppliers.
Further, the concept could have potential for a development project to find a suitable
concept to be copied for local conditions at similar plants in the area. With possible
public funding, the concept development costs would not lie entirely on one company,
and, the same concept could be copied for other plants in the area with similar
conditions. The multiplying of the concept utilizing biofuel and possibly municipal
waste for energy production would undoubtedly have a positive impact on the
environment of the area in addition to assuring the availability of electricity.
APPENDICES
1.
2.
3.
4.
5.
6.
7.
Enprima Ltd
Description of the coffee making process (Dimma)
Mass flow diagram
Energy flow diagrams
Preliminary process simulation calculations
Sensitivity analysis
Preliminary process simulation calculation for condensing steam turbine
Site layout of the Beneficio Atapasco coffee production plant
Domicile Helsinki

Final Report 1 - Observatory for Renewable Energy

Transcription

Similar documents

Rothschild Biomass Cogeneration Plant

Selected sample questions from actual licensing - Cleaver

Three (3) Waste Heat Recovery Boilers recover 2000°F heat from

Nescafé Espresso Instant Coffee Tin Features

case study - Gas Networks Ireland

Grab Coffee Breaker

bosque nublado - Intelligentsia Coffee

ordering instructions mail order

Franchise Opportunities - World Franchise Centre

G M X ON LINE FLUID CONDEIONING