Assessment of dust explosion with adipic acid and p

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Assessment of dust explosion with adipic acid and p-terephthalic acid
in powder resin process
Sheng-Yi Lin(1), Yun-Ting Tsai(1), Kuang-Hua Hsueh(2) , Tzu-Hao Lin(3), Chi-Min Shu(1)
(1)
Doctoral Program, Graduate School of Engineering Science and Technology, National Yunlin
University of Science and Technology (YunTech), Yunlin, 123, University Rd., Sec. 3, Douliou,
Yunlin 64002, Taiwan, ROC
e–mail: [email protected]
(2)
Department of Safety, Health, and Environmental Engineering, Chung Hwa University of
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Medical Technology, 89, Wen-Hwa 1st St., Jen-te, Tainan 71703, Taiwan, ROC
(3)
Department of Safety, Health, and Environmental Engineering, YunTech, 123, University
Rd., Sec. 3, Douliou, Yunlin 64002, Taiwan, ROC
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ABSTRACT:
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Dust explosions are an important issue for process safety. No matter which
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high-tech or petrochemical industries are operating, a significant relationship between
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process safety and dust explosion, exists with threats emerging from of inherent process
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hazards. In the petrochemical industry, methanol and acids are main raw materials
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which are normally dosed via hopper to batch reactor. In specific process conditions,
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high–pressure and high–temperature are yielded while the reaction undergoes
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polymerization. Adipic acid (AA) and p-terephthalic acid (PTA) were a bulk raw
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materials in this reaction. Focused on the AA and PTA to obtain various explosion
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characteristic parameters, such as particle size, minimum ignition energy (MIE),
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maximum explosion pressure (Pmax), maximum pressure raising rate ((dP/dt)max),
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lower explosion limit (LEL), limiting oxygen concentration (LOC) and deflagration
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index by particle size analyzer (PSA), minimum ignition energy analyzer, and
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20-L-Apparatus. Therefore, the evaluation of explosion could establish relevant
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parameters and precautionary measures to prevent the damage for polyester resin
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process.
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Keywords
20-L-Apparatus．Lower explosion limit．Maximum explosion
pressure．Maximum pressure raising rate．Particle size
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INTRODUCTION (draft)
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We have enjoyed better living standards through advanced technologies in various
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industrial sectors, such as smartphones, tablet computers, laptops, smart TVs, hybrids
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cars, and other high-tech equipment, which have made life much more convenient and
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comfortable. Those high-tech products can be broadly used in our daily life because the
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shining technologies developed from RD (research and design) well advance our
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standard of living.
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In Taiwan, many high-tech and petrochemical plants are currently operated to
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manufacture 3C products (computer, communication, and consumer electronics) that are
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popular and applied in the market. To produce the strong cover for electronic equipment,
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aluminum, magnesium, and zinc (powder status) are applied in manufacturing processes,
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which carry the potential risk of dust explosion. However, although the plants create
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many job opportunities, they may also jeopardize the environment, along with
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occupational accidents such as runaways, fires, explosions, chemical releases as well as
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social outcries [1]. Most powder materials in the petrochemical process possesses
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potential hazards related to dust that can result in a dust explosion. When leaked raw
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material accumulates in the workplace, accidents with dust explosion situation will
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inevitably happen.
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We can also find accidents of dust explosion happening in the USA, Europe, and Asia
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causing casualties and property damages. Thus, dust explosion is always an important
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issue in process safety. In these selected accidents (Table 1), dust explosions frequently
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happen in the petrochemical industries.
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BACKGROUND AND PROCESS
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In the petrochemical industry, methanol and acids are main raw materials which are
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normally dosed via hopper to batch reactor (Table 2). In specific process conditions,
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high–pressure and high–temperature are yielded while the reaction undergoes
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polymerization. Polyester (liquid) was transported from the bottom valve of a batch
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reactor to cooling belt, and then liquid polyester turned to solid status due to the cooling
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effect. Polyester (solid) was, in turn, smashed by crusher machine immediately, as
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shown in Figure 1. The final product is polyester at powder status, and powder polyester
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was stored in silo and backed by bagging machine when it needed to be sold.
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 pressure high temperature
Methanol(liquid)  Acid ( solid) high

 Polyester( solid)
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In practice, two critical scenarios with dust explosion must be focused. First scenario
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is that raw materials were dosed to batch reactor via hopper and some dusts
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accumulated in the workplace if it did not have an effective removal or ventilation.
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In the second scenario polyester at powder status was stored in a silo. When polyester
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is pumped to a silo, the dust may normally be dispersed in air in silo so as to create a
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flammable environment.
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Definition of Dust Explosion
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According to the possibility and period of combustible dust cloud/atmosphere, IEC
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(International Electrotechnical Commission) and BSI (British Standards Institution)
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define three kinds of zones on dust explosion: Zone 22, Zone 21, and Zone 22, as listed
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in Table 3 [4].
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Triangle Theory and Dust Explosion Pentagon
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The general analysis of combustion hazards uses the“Fire Triangle,”and the three
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factors: oxygen, fuel, and ignition source. If one of the factors is absent, fire will not
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happen [5].
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In addition to triangle theory, dust explosion has two important factors, dispersion
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and confinement, as shown in Figure 2. Suspended dust burns more rapidly, and
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confinement allows for pressure buildup. Removal of either the suspension or the
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confinement elements could properly prevent an explosion, although a fire may still
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occur [6]. A dust explosion occurs when a minimum quantity of finely divided dust is
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dispersed into the atmosphere and fits “dust explosion pentagon” conditions [6,7].
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Scenario 1 and scenario 2 in dust explosion pentagon are compared in Table 4.
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RESULTS
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Extent of Zones with Batch Reactor (Shown in Figure 3)
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
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Dusts of raw materials often existed on hopper and rotary. There were combustible
dusts. Identify this area to be Zone 21.

It is possible to observe the phenomena of dust emission near the area of hopper
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and rotary, but a lesser amount of dust emission and little chance of dust emission
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occurrence can drive the phenomenon of dust emission located in Zone 22.
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Raw materials (given in Table 2), semi-manufactured goods, and flammable gases
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are filled in the reactor, which may result in fire or explosion accidents if there is
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sufficient amount or air. Accordingly, the above phenomenon belonged to Zone 20.
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Extent of Zones in Silo (Shown in Figure 4)
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
Powder resins were stored in silo for 16 hrs per day, and the D50
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(mass-median-diameter) of powder resins was 3.9 mm, which can be defined as
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incombustible dust. However, there were a few fine powders whose diameter was
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less than 100 µm, which can be defined as combustible dust, so the above
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phenomenon belonged to Zone 21.
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
The diameter of dust accumulated in the filter was less than 1,000 µm, which
belonged to combustible dust, so the above phenomenon belonged to Zone 21.
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However, some air and dust have half-diameter of 1 m, which may be emitted from
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the filter. Therefore, the above phenomenon belonged to Zone 22.
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CONCLUSIONS
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Depending on raw materials, equipment, and process conditions, we can identify
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the extent of zones in the neighborhood before any instrument or detector. Considering
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the “dust explosion pentagon” rule, the process area will be securely safe if we can
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prevent one or more parameters.
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If you want to make sure your hypothesis is correct, the 20-L-apparatus may be the
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best solution. It can provide valuable parameters, such as vapor/gas explosion constant,
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lower explosion limit, upper explosion limit, minimum oxygen concentration,
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maximum explosion pressure, and maximum rate of explosion pressure rise [8]. These
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parameters can help prevent dust explosions and describe the extent of zones properly.
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LITERATURE CITED
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[1] C.C. Chen, T.C. Wang, L.Y. Chen, J.H. Dai, and C.M. Shu, Loss prevention in the
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petrochemical and chemical-process high-tech industries in Taiwan, J Loss Prev
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Process Ind 23 (2010), 531–538.
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[2] CSB Investigations. Available at: http://www.csb.gov/, accessed January 22, 2014.
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[3] T.J. Myers and A.F. Ibarreta, Tutorial on combustible dust, Process Saf Prog 32
(2013), 298–306.
[4] Explosive atmospheres – Part 10–2: Classification of areas – Combustible dust
atmospheres, August, 2009, UK, BSI British Standards.
[5] D.E. Kaelin Sr. and R.W. Prugh, Explosible dusts US codes and standards of safe
management practices, Process Saf Prog 25 (2006), 298–302.
[6] Investigation report–Combustible dust hazard study, November 15, 2006, US
Chemical Safety and Hazard Investigation Board.
[7] T. Skjold and K.V. Wingerden, Investigation of an explosion in a gasoline
purification plant, Process Saf Prog 32 (2013), 268–276.
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[8] Y.M. Chang, R.L. Yun, T.J. Wan, and C.M. Shu, Experimental study of
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flammability characteristics of 3-picoline/water under various under various initial
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conditions, IChemE, 85 (2007), 1020–1026.
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Table captions
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Table 1. Selected accidents related to explosion/dust explosion in USA, Europe, and
Asia since 2001 [2,3].
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Table 2.
Information for raw material with powder status.
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Table 3. Definition of dust explosion with Zones 20, 21, and 22 [4].
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Table 4. Assessment with scenario 1 and scenario 2 in dust explosion pentagon rule.
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Table 5.
Ignition types and sources in reactor and silo.
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Table 6. Assessment with extent of zones for reactor area.
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Table 7. Assessment with extent of zones for silo area.
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Table 1.
Selected accidents related to explosion/dust explosion in USA, Europe, and Asia since 2001 [2,3].
Fatalities (F)/
Date
Location
Explosion type
Material
injuries (I)
Ammonium
09/21/2001 Toulouse, France
Explosion
22 F/650 I
nitrate
01/29/2003 North Carolina, USA
Dust explosion 6 F/10 I
Powdered plastic
10/29/2003 Indiana, USA
Dust explosion 1 F/1 I
Aluminum dust
04/23/2004 Illinois, USA
Explosion
5 F/0 I
Polyvinyl chloride
05/11/2004 Scotland, Great Britain Explosion
9 F/10 I
LPG
08/19/2004 Ontario, Canada
Explosion
0 F/4 I
Ethylene oxide
05/01/2005 Tao-yuan, Taiwan
Explosion
0 F/10 I
Boiler
02/07/2008 Georgia, USA
Dust explosion 14 F/38 I
Sugar
11/02/2008 Ning-xia, China
Dust explosion 0 F/4 I
Powdered fodder
12/06/2008 Shan-tou, China
Dust explosion 10 F/11 I
Sugar
03/11/2009 Jiang-su, China
Dust explosion 11 F/20 I
Aluminum dust
02/24/2010 Qinhuangdao, China
Dust explosion 21 F/37 I
Corn starch
11/09/2010 New York,USA
Explosion
1 F/1 I
Flammable vapors
12/09/2010 West Virginia, USA
Dust explosion 3 F/0 I
Powdered titanium
Pesticide
01/20/2011 West Virginia, USA
Explosion
2 F/0 I
methomyl
01/31/2011 Tennessee, USA
Dust explosion 2 F/0 I
Powdered iron
05/20/2011 Sih-chuan, China
Dust explosion 3 F/15 I
Aluminum dust
07/28/2011 Tainan, Taiwan
Explosion
0 F/10 I
Toluene, xylene
10/09/2012 New Jersey, USA
Dust explosion 0 F/7 I
Ink
Ammonium
04/17/2013 Texas, USA
Explosion
70 F/200 I
nitrate
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Table 2.
Information for raw material with powder status.
Material
MP
FP
MIE
code
(°C) (°C)
(mJ)
A
153
191
5
B
347
100
3.7
C
165
227
4.5
D
407
260
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E
462
NA
NA
F
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184
NA
G
206
210
NA
H
NA
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NA
I
40
185
NA
J
NA
250
NA
K
110
297
NA
L
209
204
30
M
65
110
NA
Products
NA
400
3–10
Particle size D50
315 µm
83 µm
Flake
122 µm
100 µm
Flake
10 µm
<10 µm
Flake
500 mm
10 µm
10 µm
> 500mm
D50 = 3.9 mm
but some fine powder <100
µm
AIT
(°C)
405
648
400
496
NA
375
280
NA
NA
NA
410
380
NA
Risk of dust explosion
NA
Combustible dust
Combustible dust
Combustible dust
Incombustible dust
Combustible dust
Combustible dust
Incombustible dust
Combustible dust
Combustible dust
Incombustible dust
Combustible dust
Combustible dust
Combustible dust
Incombustible dust
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MP: melting point
FP: flash point
NA: not applicable
D50: median particle size
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According to the definition of combustible dust from PSA (process safety assessment), when median particle size <500 µm or <10 mass%
particle size <100 µm, are incombustible dust as given in Table 2.
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Table 3. Definition of dust explosion with Zones 20, 21, and 22 [4].
Zone
Zone 20
Zone 21
Zone 22
Specification
(a)
(b)
(c)
(d)
(a)
(b)
(c)
(a)
(b)
(c)
Continuous grade of release
Exists continuously
Expect to continue for long periods
Short periods but occur frequently
Primary grade of release
Occur periodically
Occasionally during normal operation
Secondary grade of release
The release is not anticipated to occur in normal operation
Even if it does occur, it is likely to do so only infrequently and for
short periods
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Table 4. Assessment with scenario 1 and scenario 2 in dust explosion pentagon rule.
Condition
Oxygen
Fuel
Ignition
Dispersion
Confinement
Scenario 1
N2 will fill reactor in the whole
process, and the O2 detector
installed to avoid O2 staying in
reactor
From Table 2, we cannot avoid
fuel in reactor with process
design
Identify ignition source in
process and list it in Table 5
Dosing raw material via hopper,
some dust will disperse
Volume of reactor is ca. 60 m3
Scenario 2
Oxygen exists in the silo
Product (polyester resin) with
powdered status
Identify ignition source in
process and list it in Table 5
Product (powder resin) is
disturbed and shaken dust layers
lift dust off of the floor in the
silo
Volume of silo is to 200 m3
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Table 5.
Ignition types and sources in reactor and silo.
Ignition type
Open flame
Item
Welding, etc.
Explanation
Approval is necessary before using open flame
Hot surface
Hot surface
The temperature of surface must be less than the “ MIT 
Electrical equipment
Spark from
equipment
Mechanical spark
electrical
It can ignite those dusts that have MIT > 400°C and MIE < 1 mJ
Grinding
It can ignite those dusts that have MIT > 400°C and MIE < 10 mJ
Mechanical sparks are to be considered, whenever the relative velocity of the moving parts is
>1 m/s
The maximum energy < 0.025 mJ
It occurs between conductor and insulator. It only can ignite very sensitive dust
It occurs between conductor (with charge and no grounding) and conductor (with no charge
and grounding)
a. When dust is piled in a big container, dust can accumulate static and discharge
b. The energy is related to particle size and diameter of the container. The formula is
Econe  5.22  d 3.36  M 1.462
It occurs if a double layer of charges of opposite polarity is generated across a thin sheet of a
non-conducting material
Self-heating and/or self-ignition reaction
Corona discharge
Brush discharge
Spark discharge
Exothermic reaction
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It depends on electrical equipment
Impacting
Mechanical friction
Static electricity
discharge
2
” (minimum ignition temperature)
3
Cone discharge
Propagating brush
discharge (PBD)
Runaway reaction
Econe = energy of cone discharge in mJ; d = diameter in m; M = median particle size of the powder as processed in mm
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Table 6. Assessment with extent of zones for reactor area.
Equipment name
Inner of dosing hopper
Zone
21
Ignition source
Dust of category and
existing time
Raw material,
2.3 hr/day
Description
OF HS EE MS SD
–
Raw material exists when dosing
–
–
–
V
Safety provision
CR
–
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N2 gas is in the reactor when dosing, about 5 mbar
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Reactor keeps vacuum (-0.1 bar) when dosing
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Grounding
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Use correct type of FIBC (flexible intermediate
bulk containers) with certificate
1.
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When dosing FIBC /25 Kg bag, the powder sometimes
drops on the floor. The quantity is small and will be
Whole dosing area
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Raw material
cleaned immediately
2.
After dosing, operators have to fold those FIBC bags on
electrical pallet truck
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–
V
–
V
–

Use correct type of FIBC with certificate
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The released powder from dosing hopper is a
the floor to make them small and easy to take out. Little
little, and will be cleaned after dosing (within 1
powder in FIBC may fly and rise from FIBC
Inner of rotary (between
dosing hopper and batch
reactor)
Around the rotary valve and
blind blade valve (1 m in
radius)
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22
Raw material
2.3 hr/day
Raw material
hr)
–
Raw material exists when dosing
Electrical equipment with explosion proof except
–
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V
V
–

N2 gas is in the reactor when dosing, about 5 mbar

Reactor keeps vacuum (-0.1 bar) when dosing

The velocity of rotary valve is < 1 m/sec, the
energy is too little to ignite the powder
Raw material may release (not expected to occur in normal
operation)
–
–
V
–
V
–

Grounding

Electrical equipment with explosion proof

The material of duct is conductive (105 ohm*cm),
and grounded
OF = Open flame; HS = Hot surface; EE = Electrical equipment; MS = Mechanical spark; SD = Static discharge; CR = Chemical reaction
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Table 7. Assessment with extent of zones for silo area.
Equipment name
Inner of silo
Inner of the filter within silo
Around the filter within silo
(1 m in radius)
Zone
Dust of category and
existing time
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Product
8 hr/day
21
Product
16 hr/day
22
Product
16 hr/day
Ignition source
Description
OF HS EE
Powder resin often exists. According to PSA, it is Zone 21
–
–
–
MS SD
–
V
Safety provision
CR
–

Upper of the silo is the confined space
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Grounding (not appropriate, because of the inner
coating of silo is epoxy)
–
Powder resin often exists in filter
Powder resin may release (not expected to occur in normal
–
operation)
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–
–
–
V
–
–
V
–
–

Filter bag: antistatic material (<106 ohm)

Grounding

Electrical equipment with explosion proof (only
–
solenoid valves cannot be checked)

Grounding
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Figure captions
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Figure 1. Process flowchart of polyester and two scenarios with dust explosion.
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Figure 2.
Dust explosion pentagon [5].
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Figure 3.
Extent of zones with reactor.
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Figure 4.
Extent of zones in silo.
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Figure 1. Process flowchart of polyester and two scenarios with dust explosion.
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Figure 2.
Dust explosion pentagon [5].
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Figure 3.
Extent of zones with reactor.
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Figure 4.
Extent of zones in silo.
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