New Waste Heat Recovery System– challenges and solutions

Heimdal New Power Generator Project
New Waste Heat Recovery System– challenges and solutions
Petroleumstilsynet
Seminar – exhaust stacks and waste heat recovery
2007-02-07
Prepared by:
Hydro:
Unn Orstein, Project manager
Knuth Jahr, Mechanical Disipline Lead
Reinertsen:
Morten Kongelf, Mechanical Discipline Lead
Introduction
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New cantilevered module to be installed on Heimdal summer 2008
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Gas turbine from GE: LM 1600 gas generator with PGT 16 power turbine
and ABB generator
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Reinertsen AS is engineering and fabrication contractor
Iso rating 14 MW, Design case 10 MW
Exhaust data:
- 40 kg/sec
492 oC (10 MW)
- 33.7 kg/sec 523 oC ( 7 MW) – normal operating)
- Max temp: 597 oC (3-4 MW)
11 MW hot oil waste heat recovery package (including silencer) - Letter of
Intent to Kanfa-Tec mid January
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Procurement direct to Kanfa–Tec and not via GE as planned
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The system has been improved - ref Åsgard B fire in the exhaust stack
2005, and other experiences
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The hot oil heat exchanger is located ”in the bypass” to avoid:
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Hot oil leakage into the turbine
Fire water inside the stack
WHRU - hot oil systems - challenges
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Leakage from tube bundle in traditional vertical exhaust stack
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Accumulates in bellows – textile a special problem
Tube rupture can result in > 3 M3 drainage to the turbine collector
Fire - due to oxygen in the exhaust, air during rundown of turbine and the
chimney effect
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Detect the hydrocarbon in the exhaust before the fire starts
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Drainage of hot oil
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Fire fighting system
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Damage to turbine and turbine casing due to fire and water
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Leakage from flanges in the hot oil piping hitting warm surfaces
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Alternative configurations evaluated
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Traditional configuration
with WHRU above the
turbine exhaust outlet
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WHRU in the bypass stream
Silencer not shown
Silencer shown partly
Drawings & photo from Kanfa-Tec
Exhaust
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Exhaust
Main issues in case of hot oil leakage
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Sump to collect hot oil leakage
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Detect liquid in sump
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Separate tank not shown on figure, 3 m3
Drain test valve
Level indication
Bellows should avoid:
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small hot oil leakage into the exhaust
stream to collect in the textile and ignite
In case of leakage:
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Close the louver (shut off air flow)
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Nitrogen to inert the volume?
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Drain the bundle to recovery tank
Fire water monitor on the LQ roof
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Ideas:
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Detection of hydrocarbon in exhaust?
Separate the 2 exhaust stream to avoid bellows?
Material selection
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Ducting:
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AISI 321
Max operating temperature is 597 0C at 25 oC ambient
WHRU Supplier recommend design temperature of 593 oC
- Ambient temperature is normally well below the 25 oC
- Max operating temperature is a transient case and not a normal operating case
- Due to cooling of the outside of the duct
- Duct downstream the bundle is exposed to lower exhaust temperature
AISI 321 is the standard material for GE Energy LM1600 Exhaust Collector.
Heatexchanger tube bundle/fins: ASTM A 106 GrB
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Duct leakages
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Design changes to reduce vibrations
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avoid fatigue
- Rounded corners
- Minimum temperature gradients
- Avoid lifting ears or other additional
structures
reduced swirls
- LM 1600 has trippel diffusers in the
Exhaust Collector
Improved bolt design
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Thermobolt has been specified
Bolt does not loose pre-tension during
turbine start cycle
Lover loads on bolts
Controlled compression loads on gasket
Reduce potential for hot oil leakage from
WHRU heat exchanger
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Improved bundle support
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Avoid U-clamps interfering with the tubes
Possible tube contacts with screw, bolts etc is avoided
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Inspection of support of tube bundle during assembly
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The deck structure to be designed to reduce WHRU casing deflection
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Leakage from hot oil piping
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The following has been specified:
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The hot oil/supply and return lines shall be welded to the WHRU
Flanges are minimized and located away from hot surfaces
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Valve comparison
Flap (new type used on Grane)
Louver – selected
Pro
Pro
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Improved sealing to avoid
oveheating the oil/cracking
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Leakage rate 0.02 %
Grane experience is positive
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Con
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Hydraulic control is required due to
high torque required
More expensive
Higher weight
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Improved temperature control
Improved flow distribution
Lower torque and material stresses
Pneumatic control system
Con
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Smoother regulation in almost
closed position
Leakage rate is 0.04 %
Pressure loss is higher – not critcal
More moving parts
2 separate exhaust outlets - idea
Pro
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Avoid potential small hot oil leakage
into the exhaust to collect in the
textile in the bellow
Reduce maintenance
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Remove 2 bellows
Simplify removal of silencer and bundle
Reduce weight
Con
l The reduced velocity in case of part
load will have effect on dispersion
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Note:
Turbine has excess power and
a restriction in the outlet to increase
flow is possible
Early detection of hydrocarbon leakage - idea
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Install suction probe downstream
hot oil heatexchanger
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Dual oven gas chromatographs to
detect the hot oil
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Large differance between exhaust and
hot oil fractions
Plan to be issued for inquiry Februar
2007
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