Multi

- Point Ground Level Flare Modeling Discussion

September 12, 2014 Page 1 Multi

- Point Ground Level Flare Modeling Discussion

The flare being installed for this project is a multipoint ground flare that functions as a steam assisted flare when receiving vents from normal operations and functions as a pressure

- assisted flare during periods of upset, maintenance, startup, and shutd own (high

- pressure, high flow periods). Pressure assisted flares are also known as sonic flares because the exit velocity during periods of high

- pressure feeds is at sonic velocities. This flare is constructed differently than a normal elevated flare in that it consists of many rows of independent flare tips, and all flare tips are approximately eight feet above ground level. The flare is designed to operate in stages, with multiple burners (flare tips) in each row, and many rows comprising the flare sy stem. Stage 1 is the low pressure stage in which the flare acts as a steam

- assisted flare. Stages 2 and beyond are activated for high

- pressure/high exit velocity flows. The flare system is surrounded by a panel type fence to protect nearby workers from the radiant heat from the flare system. At various times, Dow will have emissions from the multi

- point ground level flare for the following MSS activities: perform plant start

- up and shutdown, process equipment startup and shutdown, off

- spec flaring, non

- routine clearing and commissioning of process equipment and piping, fuel purging, and flaring to maintain pressure of the net

- gas system. During MSS activities, the exit velocity from the flare is in a range between 600 feet per second (or 183 meters pe r second) and sonic velocity ( sonic velocity ranges from 700 to 1,400 feet per second for common hydrocarbon gases that will be flared)

. There is no available dispersion modeling guidance for multi

- point ground flares at this time. However, during a meet ing with TCEQ on June 11, 2012, TCEQ suggested to model this multi

- point ground flare as a point source at the center of the ground flare with the actual exit velocity for startup, shutdown, and maintenance activities. Therefore, the modeling analysis was performed using the expected lower

- end velocity of 183 m/s (600 fps) and a higher representative velocity of 300 m/s (984.25 fps).

Per existing modeling guidance for flares , the default exit temperature of 1273 Kelvin was used. There will be a fence c onstructed around the multi

- point ground flare with the height of 51 feet above grade

. The flare tip height combined with the expected flame length make s the effective flare height 45 feet above grade level. As the radiation fence is higher than the flame height, it is guaranteed that the emission would not be horizontally dispersed until it reaches to the radiation fence height. Therefore, the analysis used the effective height as the stack height (45 ft) . Dow calculated an effective flare diameter for startup and shutdown activities separately according to TCEQ guidance. The modeled emission rates and stack parameters are shown in T able 1

. Using the generic unit impact from Table 1, the predicted concentration of expected air pollutants from the flare during startup and shutdown activities were evaluated in Table 2 and 3 for the lower

- end exit velocity (183 m/s) and in Table 4 and 5 for the higher exit velocity (300 m/s). The predicted impact using lower

- end exit velocity is slightly greater than the predicted impact using the higher exit velocity. The analysis used the American Meteorological Society/Environmental Protection Agency Regulatory (AERMOD) model (Versions 14134). AERMOD was chosen because it is classified by EPA as Preferred/Recommended model and is approved by the TCEQ modeling staff. AERMOD is a steady

- state plume dispersion model for assessment of pollutant concentrations from a variety of sources. The modeled parameters follow the EPA

- recommended “regulatory default option”, which i ncludes the use of stack

- tip downwash and calms and missing data processing routines. The analysis used TCEQ pre

- processed meteorological data suitable for Brazoria County. AERSURFACE version 13016 was run to estimate which land use category best describ es the area around the Dow complex where the flare is located. AERSURFACE predicted a composite surface roughness of 0.374 meters for a circular area within a 1

- kilometer radius centered on the main plant site. Based on these results, the meteorological data set that utilized the Medium surface roughness length values for Brazoria County was used.Multi

- Point Ground Level Flare Modeling Discussion

September 12, 2014 Page 2 Table 1. Stack Parameters and Generic Unit Impact

Model ID Source Description Height (ft) Temp

(K) Exit Velocity (m/s) Effective

Diameter (m) Unit

Emission Rate (lb/hr) 1

- hour Unit

Impact ( μ g/m 3 per 1 lb/hr) Annual Unit

Impact ( μ g/m 3 per 1 lb/hr)
GF300SU Ground Flare FX

- 9552 (MSS Startup) 45.00 1273.15 300 10.33 1 0.00311 0.00009
GF183SU Ground Flare FX

- 9552 (MSS Startup) 45.00 1273.15 183 10.33 1 0.00381 0.00012
GF300SD Ground Flare FX

- 9552 (MSS Shutdown) 45.00 1273.15 300 14.47 1 0.00211 0.00007
GF183SD Ground Flare FX

- 9552 (MSS Shutdown) 45.00 1273.15 183 14.47 1 0.00285 0.00009Multi

- Point Ground Level Flare Modeling Discussion

September 12, 2014 Page 3 Table 2. Predicted Maximum Off

- Property Concentration from Multi

- Point Ground Flare During Start

- U p U sing 183 m/s of E xit V elocity
1

- Hour Analysis Annual Analysis

Compound CAS Hourly Emission Rate (lb/hr) Off

- site 1

-

Hour Unit Impact ( μ g/m 3 per 1 lb/hr) Modeled

off

- site 1

- Hr conc. (μ g/m 3 ) TCEQ 1

-

Hr ESL (μ g/m 3 ) Percent

ESL Annual Emission Rate (tpy) Off

- site

Annual Unit Impact ( μ g/m 3 per 1 lb/hr) Modeled

off

- site Annual

conc

. (μ g/m 3 ) TCEQ

Annual ESL (μ g/m 3 ) Percen

t ESL Ethylene 74

- 85

- 1 2.95 0.00381 0.01 1400 0.00% 0.11 0.00012 2.91E

- 06 34 0.00%
Butane 106

- 97

- 8 75.00 0.00381 0.29 66000 0.00% 0.70 0.00012 1.92E

- 05 7200 0.00%

Table 3. Predicted Maximum Off

- Property Concentration from Multi

- Point Ground Flare During Shutdown Using 183 m/s of Exit Velocity
1

- Hour Analysis Annual Analysis

Compound CAS Hourly Emission Rate (lb/hr) Off

- site 1

-

Hour Unit Impact ( μ g/m 3 per 1 lb/hr) Modeled

off

- site 1

- Hr conc

. (μ g/m 3 ) TCEQ 1

-

Hr ESL (μ g/m 3 ) % of

ESL Annual Emissio n Rate (tpy) Off

- site

Annual Unit Impact ( μ g/m 3 per 1 lb/hr) Modeled

off

- site Annual

conc

. ( μ g/m 3 ) TCEQ

Annual ESL (μ g/m 3 ) % of

ESL Ethylene 74

- 85

- 1 90.08 0.00285 0.26 1400 0.02% 0.19 0.00009 3.92E

- 06 34 0.00%
Butene 106

- 98

- 9 2.49 0.00285 0.01 820 0.00% 0.03 0.00009 5.70E

- 07 1600 0.00%
Butane 106

- 97

- 8 85.49 0.00285 0.24 66000 0.00% 0.95 0.00009 1.96E

- 05 7200 0.00% C5's 109

- 66

- 0 1.88 0.00285 0.01 4100 0.00% 0.02 0.00009 4.32E

- 07 7100 0.00%
Benzene 71

- 43

- 2 5.86 0.00285 0.02 170 0.01% 0.07 0.00009 1.34E

- 06 4.5 0.00% DMDS (dimethyl disulfide)

-- 20.26 0.00285 0.06 20 0.29% 0.23 0.00009 4.64E

- 06 2 0.00% Methanol 67

- 56

- 1 1.48 0.00285 0.00 3900 0.00% 0.02 0.00009 3.39E

- 07 2100 0.00% Note: Emissions of propylene and propane were not evaluated since they are simple asphyxiants

.Multi

- Point Ground Level Flare Modeling Discussion

September 12, 2014 Page 4 Table 4. Predicted Maximum Off

- Property Concentration from Multi

- Point Groun d Flare During Start

- Up Using 300 m/s of Exit Velocity
1

- Hour Analysis Annual Analysis

Compound CAS Hourly Emission Rate (lb/hr) Off

- site

1

- Hour Unit Impact (ug/m3 per 1 lb/hr) Modeled off

site 1

- Hr concentration (μ g/m 3 ) TCEQ 1

-

Hr ESL (μ g/m 3 ) Percent

ESL Annual Emission Rate (tpy) Off

- site

Annual Unit Impact (ug/m3 per 1 lb/hr) Modeled off

site Annual concentration (μ g/m 3 ) TCEQ

Annual ESL (μ g/m 3 ) Percent

ESL Ethylene 74

- 85

- 1 2.95 0.00311 0.01 1400 0.00% 0.11 0.00009 2.18E

- 06 34 0.00%
Butane 106

- 97

- 8 75.00 0.00311 0.29 66000 0.00% 0.70 0.00009 1.44E

- 05 7200 0.00%

Table 5. Predicted Maximum Off

- Property Concentration from Multi

- Point Ground Flare During Shutdown Using 300 m/s of Exit Velocity
1

- Hour Analysis Annual Analysis

Compound CAS Hourly Emission Rate (lb/hr) Off

- site 1

-

Hour Unit Impact ( μ g/m 3 per 1 lb/hr) Modeled off

site 1

- Hr concentratio

n (μ g/m 3 ) TCEQ 1

-

Hr ESL (μ g/m 3 ) % of

ESL Annual Emissio n Rate (tpy) Off

- site

Annual Unit Impact (ug/m3 per 1 lb/hr) Modeled off

site Annual concentratio n ( μ g/m 3 ) TCEQ

Annual ESL (μ g/m 3 ) % of

ESL Ethylene 74

- 85

- 1 90.08 0.00211 0.26 1400 0.02% 0.19 0.00007 3.05E

- 06 34 0.00%
Butene 106

- 98

- 9 2.49 0.00211 0.01 820 0.00% 0.03 0.00007 4.43E

- 07 1600 0.00%
Butane 106

- 97

- 8 85.49 0.00211 0.24 66000 0.00% 0.95 0.00007 1.52E

- 05 7200 0.00% C5's 109

- 66

- 0 1.88 0.00211 0.01 4100 0.00% 0.02 0.00007 3.36E

- 07 7100 0.00%
Benzene 71

- 43

- 2 5.86 0.00211 0.02 170 0.01% 0.07 0.00007 1.04E

- 06 4.5 0.00% DMDS (dimethyl disulfide)

-- 20.26 0.00211 0.06 20 0.29% 0.23 0.00007 3.61E

- 06 2 0.00% Methanol 67

- 56

- 1 1.48 0.00211 0.00 3900 0.00% 0.02 0.00007 2.64E

- 07 2100 0.00% Note: Emissions of propylene and propane were not evaluated since they are simple asphyxiants

.