Flare Performance Testing with PFTIR 

John Zink

Final Report

February 17

th, 2014

John Zink

Process Burner Test Facility

11920 East Apache

Tulsa, OK 74116

Prepared by

Clean Air Engineering, Inc.

Project No: 12325

 
John Zink – PFTIR Flare Performance Test Report Page 2

1.0 Introduction

John Zink conducted performance testing at the John Zink test facility in Tulsa, 

Oklahoma from November 18-22, 2013. Two ground flare burner tips were tested. The 

first burner tested was a steam-assisted tip (SKEC). The second burner tested was a 

pressure-assisted tip (LRGO). The purpose of this test was to determine the combustion 

efficiency of the LRGO and the SKEC burners under conditions representative of the 

burners’ expected normal operation when installed at a DOW Chemical facility in Texas. 

The performance tests were conducted using a Passive Fourier Transform Infrared 

(PFTIR) instrument developed by Industrial Monitor and Control Corporation (IMACC). 

This report summarizes the test results and compares them to results from previous flare 

tests.

The purpose and major benefit of an assisted flare is to significantly reduce the amount of 

smoke (visible emissions) that would otherwise be created by combustion. The burners 

tested in this program include steam-assist and pressure-assist. In a typical system, an 

assist medium such as steam or air is injected into the flare combustion zone to deliver 

educted air as well as mixing energy. Pressure assisted flares rely on increased exit 

velocity of the flare gas to educt more air into the gas. Over-assist is a generic description 

of an undesirable operating condition possible in assisted flare systems. For example, in 

an over-steaming scenario, the amount of steam and educted air introduced into the 

combustion reaction zone diminishes, rather than promotes, the efficiency of the 

combustion process if introduced in large enough quantities relative to the flare gas flow 

rate.

The operating envelope of a flare is bounded by excess smoke (too little assist) on one 

side and decreased combustion efficiency resulting in excess emissions of volatile 

organic compounds (VOCs) (too much assist) on the other. Smoke suppression is easily 

monitored by visually observing whether smoke is present. However, the ability to 

measure or even identify excess emissions caused by over-assisting is a more difficult 

task. Standard emission estimation techniques have generally assumed a 98% destruction 

efficiency or higher when calculating VOC emissions from flares regardless of assist rate.

Regulatory requirements for flares are contained in 40 CFR §60.18 and §63.11. These 

requirements were developed from a series of flare emissions tests led by the United 

States Environmental Protection Agency (US EPA) from 1983 – 1986. The requirements 

include maintaining a flare pilot, operating with a minimum net heating value of 300 

BTU/scf in the vent gas, operating at exit velocities of less than 60 ft/s (or up to 400 ft/s 

depending upon the vent gas net heating value), and operating with a limited amount of 

visible emissions. However, a flare can be operated in compliance with these 

requirements and still have low combustion efficiency due to over-assisting.

Prior to the recent refinery tests of flare performance, including the US EPA tests in the 

mid-1980s, flare tests were conducted on pilot-scale test flares at or flares operating at 

moderate to high vent gas loads. However, a flare typically operates at low vent gas loads 

(i.e. high turndown) under normal conditions until a process upset or other operating 
John Zink – PFTIR Flare Performance Test Report Page 3

condition requires the operator to flare waste gas. Thus, the flare normally operates at 

high turndown for the majority of the operating year, a condition for which there was 

little to no available performance data.

In the past, measuring the combustion products from a flare was difficult and dangerous. 

However, recent technological advances have produced remote sensing instruments 

capable of measuring combustion products such as carbon dioxide, carbon monoxide, and 

select hydrocarbons without the safety hazards introduced by physically sampling a flare 

plume. One such instrument is the PFTIR, which characterizes a plume’s chemical makeup (carbon dioxide, carbon monoxide, and total hydrocarbons) in units of concentration × 

pathlength. Using this technology, the absolute concentration cannot be determined from 

a flare plume, but the product of concentration × pathlength (e.g., ppmv × meters), can be 

used in combustion efficiency calculations. The PFTIR is a relatively new tool and was 

recently blind-validated against extractive sampling results for flare plume testing by 

TCEQ and the University of Texas in 2010. The PFTIR was first used for refinery flare 

testing at MPC Texas City in 2009. Several accuracy, precision, and bias checks were 

performed during the recent flare tests to better characterize the PFTIR measurement 

technique.

2.0 Test Conditions

Combustion efficiency was measured under several combinations of vent gas 

composition and flare operating parameters. Propylene, Tulsa natural gas (TNG), and 

nitrogen were used as vent gas components. Each of these combinations is referred to as a 

“test condition” in this report. The following test conditions were used during this 

project.

Test P1H LRGO Pressure-assist burners. 100% Propylene.

Objective: To determine the combustion efficiency of the LRGO burner using pure

propylene at the maximum operating pressure. Three replicates were conducted.

Test P1L LRGO Pressure-assist burners. 100% Propylene. 

Objective: To determine the combustion efficiency of the LRGO burner using pure 

propylene at the minimum operating pressure. Three replicates were conducted.

Test P2H LRGO Pressure-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the LRGO burner using a propylene 

/ nitrogen mix diluted to the minimum NHV required for stability when the LRGO burner 

is operating at the maximum operating pressure. Three replicates were conducted.

Test P2L LRGO Pressure-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the LRGO burner using the same 

propylene / nitrogen mix as Test P2H at the minimum operating pressure. Three 

replicates were conducted.
John Zink – PFTIR Flare Performance Test Report Page 4

Test P3H LRGO Pressure-assist burners. Propylene / TNG / nitrogen mix.

Objective: To determine the combustion efficiency of the LRGO burner using a mixture of 

50% / 50% TNG / Propylene mixture diluted to the minimum NHV required for stability 

when the LRGO burner is operating at the maximum operating pressure. Three replicates 

were conducted.

Test P3L LRGO Pressure-assist burners. Propylene / TNG / nitrogen mix.

Objective: To determine the combustion efficiency of the LRGO burner using the same 

propylene / TNG / nitrogen mix as Test P3H at the minimum operating pressure. Three 

replicates were conducted.

Test P4 LRGO Pressure-assist burners. 90% Hydrogen / 10% TNG mix.

Objective: To observe the stability of the LRGO burner flame when the fuel is 

predominantly hydrogen and when the LRGO burner is operating at the maximum 

operating pressure. Emissions measurements were not taken during this test.

Test S1 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the SKEC burner using a propylene 

/ nitrogen mixture diluted to the minimum NHV required for stability when the LRGO 

burner is operating at sonic velocity and while steam flow is set at design flow rate.

Test S2 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the LRGO burner using the same 

propylene / nitrogen mix and flow rate as Test S2 while steam flow is off.

Test S3 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the SKEC burner using a propylene 

/ nitrogen mixture with the steam flow at the minimum design rate. The nitrogen flow is 

the minimum available from the nitrogen delivery system while the propylene flow is 

adjusted to achieve a stable flame.

Test S4 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the SKEC burner using a propylene 

/ nitrogen mixture of 700 BTU/scf and steam flow at the minimum design rate. Fuel flow 

was the maximum flow rate where the SKEC flame was stable.

Test S5 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the SKEC burner using a propylene 

/ nitrogen mixture with the steam flow at a pressure of 10 psig. The nitrogen flow is the 

minimum available from the nitrogen delivery system while the propylene flow is adjusted 

to achieve a stable flame.

Test S6 SKEC Steam-assist burners. Propylene / nitrogen mix.

Objective: To determine the combustion efficiency of the SKEC burner using propylene 

fuel. The steam rate is set to the maximum design flow while the fuel is adjusted to 

achieve the incipient smoke point.
John Zink – PFTIR Flare Performance Test Report Page 5

3.0 Results

A summary of results from the LRGO tests are shown in Figure 3-1 and 3-2 below. Table 

1 contains summary data from the LRGO test runs. Test run P1L (3) was conducted 

under poor wind conditions that prevented accurate measurements. The P1L (3) data is 

excluded from the P1L results presented in Figures 3-1 and 3-2.

Figure 3-1: NHVcz vs. CE for LRGO Burners

Figure 3-2: Tip Velocity vs. NHVcz for LRGO Burners
John Zink – PFTIR Flare Performance Test Report Page 6

A summary of results from the SKEC tests are shown in Figure 3-3 and 3-4 below. Table 

1 contains summary data from the SKEC test runs.

Figure 3-3: NHVcz vs. CE for SKEC Burners

Figure 3-4: Tip Velocity vs. NHVcz for SKEC Burner
John Zink – PFTIR Flare Performance Test Report Page 7

Table 1: Data Summary

Condition Run Run	ID Flare Start	Time End	time Std	Flare	Gas	Flow Flare	Gas	Flow Flare	Tip	Velocity Flare	Gas	NHV Steam	Flow Nitrogen THC MWvg Wind	Direction Wind	Speed S/VG	(calc) NHVcz CE	(weighted)

-- -- -- Tip -- -- scf/hr lb/hr ft/s BTU/scf lb/hr mol	% mol	% lb/lbmol °	(N=0,	E=90) mph (lb/lb) BTU/scf %

P1H 1 7 LRGO 11/19/2013	15:45:00 11/19/2013	16:05:00 78,664 8,586 1011.75 2,150 0 0.0 100.0 42.1 133 7.9 -- 2150 100.0

P1H 2 8 LRGO 11/20/2013	14:09:00 11/20/2013	14:29:00 75,100 8,198 965.92 2,150 0 0.0 100.0 42.1 173 8.2 -- 2150 99.8

P1H 3 22 LRGO 11/21/2013	13:48:03 11/21/2013	14:08:53 72,590 7,923 933.63 2,150 0 0.0 100.0 42.1 33 4.2 -- 2150 99.8

P1L 1 9 LRGO 11/20/2013	14:57:10 11/20/2013	15:17:24 48,006 5,240 617.44 2,150 0 0.0 100.0 42.1 165 5.2 -- 2149 99.7

P1L 2 17 LRGO 11/21/2013	9:44:00 11/21/2013	10:04:00 49,600 5,410 637.94 2,148 0 0.0 100.0 42.0 81 5.3 -- 2139 99.9

P1L 3 27 LRGO 11/21/2013	16:32:00 11/21/2013	16:53:46 51,510 5,623 662.51 2,150 0 0.0 100.0 42.1 219 13.0 -- 2150 99.5

P2H 2 18 LRGO 11/21/2013	10:56:00 11/21/2013	11:16:00 91,547 7,919 1177.46 815 0 62.1 38.0 33.3 122 5.1 -- 815 99.8

P2H 3 26 LRGO 11/21/2013	16:02:01 11/21/2013	16:22:30 90,880 7,860 1168.88 814 0 62.1 37.9 33.3 119 5.7 -- 814 99.8

P2H 1b 11 LRGO 11/20/2013	16:37:00 11/20/2013	16:57:00 92,018 7,966 1183.51 818 0 61.9 38.1 33.4 164 5.0 -- 818 99.9

P2L 2 19 LRGO 11/21/2013	11:31:00 11/21/2013	11:51:12 57,699 4,920 742.11 742 0 65.5 34.5 32.9 112 4.0 -- 742 99.8

P2L 3 23 LRGO 11/21/2013	14:38:01 11/21/2013	14:58:10 56,631 4,824 728.37 737 0 65.7 34.3 32.8 105 6.4 -- 737 99.6

P2L 1b 13 LRGO 11/20/2013	17:39:00 11/20/2013	17:59:00 57,991 4,952 745.87 753 0 65.0 35.1 32.9 170 8.9 -- 751 99.7

P3H 1 14 LRGO 11/20/2013	19:18:03 11/20/2013	19:38:04 101,955 7,585 1311.32 723 0 52.4 47.6 28.7 177 8.7 -- 723 99.8

P3H 2 20 LRGO 11/21/2013	12:45:00 11/21/2013	13:05:50 99,954 7,394 1285.59 713 0 52.5 47.5 28.5 130 5.6 -- 713 99.8

P3H 3 25 LRGO 11/21/2013	15:34:00 11/21/2013	15:54:47 100,534 7,448 1293.05 719 0 52.3 47.7 28.6 30 6.1 -- 719 99.6

P3L 2 21 LRGO 11/21/2013	13:17:00 11/21/2013	13:38:43 59,466 4,424 764.84 692 0 53.7 46.3 28.7 85 2.5 -- 691 99.8

P3L 3 24 LRGO 11/21/2013	15:06:01 11/21/2013	15:26:38 61,803 4,601 794.90 724 0 52.4 47.6 28.7 147 6.9 -- 724 99.7

P3L 1b 16 LRGO 11/21/2013	9:06:00 11/21/2013	9:26:10 61,978 4,602 797.15 710 0 53.1 46.9 28.6 98 4.7 -- 708 99.9

S1 1 1 SKEC 11/19/2013	9:19:00 11/19/2013	9:41:52 119,810 10,753 1032.85 1,006 562 53.2 46.8 34.6 150 9.4 0.05 918 99.2

S2 1 2 SKEC 11/19/2013	9:45:00 11/19/2013	10:05:13 119,280 10,714 1028.28 1,010 0 53.0 47.0 34.6 149 10.9 -- 1010 98.9

S3 1 3 SKEC 11/19/2013	11:41:05 11/19/2013	11:53:13 19,392 1,595 167.17 564 124 73.8 26.3 31.7 147 11.6 0.08 496 98.1

S4 1 4 SKEC 11/19/2013	13:36:01 11/19/2013	13:56:02 49,152 4,171 423.72 724 130 66.2 33.8 32.7 143 11.0 0.03 686 99.1

S5 1 5 SKEC 11/19/2013	14:27:41 11/19/2013	14:38:33 21,782 1,834 187.78 686 305 68.0 32.1 32.5 145 12.2 0.17 528 96.4

S6 1 6 SKEC 11/19/2013	14:55:59 11/19/2013	15:16:02 18,064 1,972 155.73 2,150 642 0.0 100.0 42.1 144 10.5 0.33 1222 99.8

Test	Conditions Process	Data VG	Composition Weather Calculations