Gossman Consulting, Inc.
December 1991

Trial Burn POHC Selection and the Use of SF6

This month Gossman Consulting, Inc. (GCI) is pleased to introduce Tracer Technologies. Tracer Technologies is an energy and environmental consulting firm that, among its many capabilities, provides expert services for clients performing trial burn projects throughout the United States and abroad. They perform trial burns on boilers and industrial furnaces to support RCRA permitting requirements for hazardous waste incinerators. Tracer Technologies' North American offices are located in San Marcos, Los Angeles, and Santa Maria, California; Houston, Texas; and Washington, DC.

The objective of trial burn POHC selection for cement kilns is to determine which POHC or set of POHCs meet the following criteria:

All POHCs should come from class 1 (very stable) compounds on the Thermal Stability Index.1

The POHC(s) should demonstrate both thermal and oxidation failure modes in the kiln should either occur.

The POHC(s) should not be PICs.

The smaller the number of chlorinated POHCs used the better, since cement kilns are chlorine input limited and detection limits could be negatively impacted if too many chlorinated POHCs are used simultaneously.

POHC(s) should be commercially available, of limited toxicity and easily fed into the kiln with the HWF.

Established stack sampling and testing methods must be available for the POHC(s).

Cyanogen and hydrogen cyanide, ranked 1 and 2 on the index, do not meet the criteria because of toxicity and handling difficulties. Benzene, ranked 3, is a PIC from coal combustion as well as being a carcinogen and therefore unsuitable. Sulfur hexafluoride (SF6) meets all of the criteria except that it does not test the oxidation failure mode. The addition of 1,2,4-trichlorobenzene solves this problem and adds a second POHC meeting all of the above criteria.

The use of SF6 as a POHC requires supporting data demonstrating its effectiveness as a surrogate POHC. Referred are a series of research reports including some supported by the EPA which consistently demonstrate that SF6 is a conservative indicator of DE when compared to other commonly used POHCs.2,3,4,5,6,7,8

Principal Hazardous Organic Constituent Thermal Stability Index

Class 1 Rank
Cyanogen 1
Hydrogen Cyanide 2
Benzene 3
Sulfur Hexafluoride 4
Naphthalene 5
Fluoranthene 6
Benzo[j]fluoranthene 7
Benzo[b]fluoranthene 8
Benzanthracene 9
Chrysene 10
Benzo[a]pyrene 11
Dibenz[a,h]anthracene 12
Indeno(1,2,3-cd)pyrene 13
Dibenzo[a,h]pyrene 14
Dibenzo[a,i]pyrene 15
Dibenzo[a,e]pyrene 16
Cyanogen Chloride 17-18
Acetonitrile 17-18
Chlorobenzene 19
Acrylonitrile 20
1,4-Dichlorobenzene 21-22
Chloronaphthalene 21-22
Cyanogen Bromide 23-24
1,2-Dichlorobenzene 23-24
1,3 Dichlorobenzene 25
1,3,5-Trichlorobenzene 26-27
1,2,4-Trichlorobenzene 26-27
1,2,3,5-Tetrachlorobenzene 28
Chloromethane 29-30
1,2,4,5-Tetrachlorobenzene 29-30
Pentachlorobenzene 31-33
Hexachlorobenzene 31-33
Bromomethane 31-33
Tetrachlorodibenzo-p-dioxin (2,3,7,8) 34

SF6 Injection Procedures

The SF6 injection system should be designed to accurately measure and inject a desired amount of SF6 into the HWF prior to combustion. A diagram of the injection system used by Tracer Technologies is shown in Figure 1. SF6 is present as a liquid in a pressurized cylinder. At ambient conditions it has a vapor pressure of 300 PSI which is used to force the material into the WDF stream. The flow rate is controlled with a metering valve, and monitored with a mass flowmeter that has been specifically calibrated for SF6. A strip chart recorder is connected to the flowmeter and records the time history of the injection rates. Copper connections are pressurized to 80 psi prior to use to check for leaks in the system. The mass flowmeter is calibrated in the laboratory prior to being sent out in the field.

SF6 Sampling Methodology

SF6 sampling procedures are conducted in accordance to EPA method 5 methodology. A stainless steel probe is used with a conventional button hook nozzle. The sample is drawn from the stack through the probe, through a filter/impinger system to remove condensate and particulates and then is pumped to a gas chromatograph located at the base of the stack in a vehicle or trailer. Since the sampling may be performed in conjunction with stack velocity measurements (EPA methods 2,4), transects may be made across the stack to obtain SF6 samples.

SF6 is an extremely stable and inert substance. It does not adhere to, or react with most substances thereby making it relatively easy to sample without worrying about contamination or reaction with the sampling apparatus. The materials used in the system that are in direct contact with the flue gas have been proven to be inert to SF6. The probe is made of stainless steel, the impingers are made of glass, and the sampling line is made of polyethylene. Swagelok brand fittings are used to ensure leak-proof connections. All sampling lines are leak-checked prior to the field test and the sampling train is leak-checked prior to and after each test in the field to ensure sample integrity.

The sample is then pumped to a Tracer Technologies SF6 analyzer. The analyzer is a specialized gas chromatograph that has been developed over the years for detecting SF6. It is small and lightweight which allows it to be easily set up for in-field testing. The unit is capable of analyzing a sample every 5 minutes, thus allowing up to 12 data points to be recovered in one hour of testing. The analyzer is capable of measuring 5 parts per trillion of SF6. The sample is pumped directly from the sampling train into the 1 cc sample loop of the instrument. When a sample analysis is desired, the operator switches the sample valve to the analyze position and the sample is flushed with nitrogen through the molecular sieve column and through the electron-capture detector. The output of the detector is recorded on a strip-chart recorder.

Prior to testing each day, a multi-point calibration and zero check are performed on the instrument. In addition, span checks are performed every hour during testing to verify the calibration. If there is a deviation of more than 10% from the calibration, a new calibration is performed.

Tracer Technologies and Gossman Consulting, Inc. have requested that the EPA allow the use of a continuous on-line SF6 spiking and analysis system as an alternative to combustion zone temperature monitoring.


1. Guidance on Setting Permit Conditions and Reporting Trial Burn Results; Volume II of the Hazardous Waste Incineration Guidance Series (Cincinnati, Ohio, US EPA 625/6-89/019, January 1989), p.105-110.

2. Acurex Corporation, Operations and Research at the U.S. EPA Combustion Research Facility in Jefferson, Arkansas (Monthly Progress Report #8250-36, Contract # 68-03-3267, Oct. 17. 1988).

3. Pilot-Scale Testing of SF6 as a Hazardous Waste Incinerator Surrogate (For presentation at the 82nd Annual Meeting & Exhibition in Anaheim, CA, June 25-30, #89-23B.4A).

4. S. Roychoudhury, D.J. Fournier Jr. and C.L. Proctor II, Correlating the Destruction Removal Efficiency of Hazardous Waste Surrogates and Tracers, (Presented at the Winter Annual Meeting in Anaheim, CA, December 7-12, 1986).

5. D.J. Fournier Jr., C.L. Proctor II and M.L. Berger, Sulfur Hexaflouride Destruction in a Laboratory Turbulent Diffusion Flame, (Presented at the Winter Annual Meeting in Anaheim, CA, December 7-12, 1986).

6. Andrew Trenholm,Dr. C.C. Lee and Capt. Helen Jermyn, Full Scale POHC Incinerability Ranking and Surrogate Testing (Cincinnati, Ohio, US EPA).

7. Walter G. England, Lynn Teuscher and Steven Quon, The Correlation of SF6 Destruction with Principal Organic Hydrocarbon Destruction in Incineration Processes (Presented at the 80th Annual Meeting of the Air Pollution Control Association, June 21-26, 1987, No. 87-23.2).

8. Walter England, Stephen L. Kerrin, Thomas Rappolt, Robert Mourninghan and Lynn Teuscher, Measurement of Hazardous Waste Incineration Destruction and Removal Efficiencies Using Sulfur Hexaflouride as a Chemical Surrogate (Presented at the 79th Annual Meeting of the Air Pollution Control Association, June 22-27, 1986, #86-61.1)