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MEMORANDUM 

TO: Andrew Bouchard and Brenda Shine, EPA 

FROM: Donna Lazzari, Jason Renzaglia, Mae Thomas, ERG 

DATE: January 20, 2012 

SUBJECT: Design Criteria for Combustion 

1.0 INTRODUCTION 

In lieu of conducting a performance test on a control device, some National Emission 

Standards for Hazardous Air Pollutants (NESHAP) allow an owner or operator to conduct a 

design evaluation to show that the control device achieves the required emission limit during 

expected conditions. The design evaluation requires documentation of the vent stream 

composition entering each control device, including flow, regulated material concentration, 

other site-specific information for each control device, and a discussion of how these 

operating parameters affect the destruction efficiency of the device. 

For a combustion unit, 40 CFR 63, Subpart SS (GMACT) requires the design 

evaluation to consider the autoignition temperature of the stream being combusted, the flow 

rate of the stream, the combustion temperature, and the residence time at the combustion 

temperature. The GMACT also allows an owner or operator (of an enclosed combustion 

device controlling storage vessels or transfer racks) to forego all other considerations in the 

design evaluation if the combustion unit has a minimum residence time of 0.5 seconds and a 

minimum temperature of 760 degrees Celsius; the owner or operator is only required to 

document that these specific conditions exist. Traditionally, boilers and process heaters have 

been exempt from performance test requirements because of this particular residence time and 

temperature criteria provision. 

ERG conducted an investigation to determine whether the residence time and 

temperature criteria (0.5 seconds and 760 °C) for a combustion device ensures a high level of 

destruction for all types of chemicals that could be encountered in the chemical industry. This 

memorandum provides the results of this investigation. 
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This memorandum is organized as follows: 

1.0 Introduction 

2.0 Investigation Discussion 

3.0 Analysis and Recommendation 

4.0 References 

2.0 Investigation Discussion 

As a general guideline, past methods for determining the design or operating 

temperature of an incinerator suggest that temperature should be maintained several hundred 

degrees Fahrenheit above the volatile organic compound (VOC) autoignition temperature 

(Cooper, 2002). However, more precise methods have been developed using experimental 

data from combustion tests. The most straightforward method uses a relationship between the 

autoignition temperature of the VOC being combusted, the residence time, and the destruction 

efficiency required. Table 1 shows how the destruction efficiency increases as you increase 

the residence time and the temperature above the autoignition temperature (Lewandowski, 

2000). 

Table 1. VOC Destruction Efficiency vs. Temperature and Time 

VOC 

Destruction Efficiency 

(%) 

Degrees Above 

Autoignition Temperature 

(°F) 

Residence 

Time 

(Sec) 

95 300 0.5

98 400 0.5

99 475 0.75

99.9 550 1.0

99.99 650 2.0

 There is also a method for predicting destruction efficiency which develops a firstorder rate constant for hydrocarbon incineration and includes a steric factor to account for the 

fact that some molecular collisions are not effective in producing reactions because of 

molecular geometry (Cooper, 2002). Another method, developed using experimental data, 

shows that predicting a temperature that would achieve 99% or 99.9% destruction efficiency 

of a VOC is dependent on a number of properties of the VOC being combusted. These 

properties include: autoignition temperature, residence time, the ratio of hydrogen to carbon 
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atoms in the molecule, the presence of aromatic ring structures or double bonds, and presence 

of sulfur or nitrogen atoms. Both of these methods give more precise, but similar results to 

those presented in Table 1. 

3.0 Analysis and Recommendation 

Assuming a residence time of 0.5 seconds, ERG determined the specific temperatures 

that would be required to achieve the predicted destruction efficiencies for several compounds 

based on the information provided in Table 1 (see Table 2). The compounds chosen for this 

analysis have relatively high autoignition temperatures and are commonly found in the 

chemical process industry. At these conditions, there is 95-98% destruction efficiency of most 

organic compounds; however, Table 2 reveals that some organic compounds would need a 

higher temperature than the GMACT temperature criteria of 760°C (1400°F) in order to

ensure a high level of destruction. 

Table 2. Thermal Destruction Efficiency (DE) of Selected Organic Compounds 

Compound 

Autoignition 

Temperature 

(°F) 

+ 300 °F

{95% DE Prediction} 

(°F) 

+ 400 °F

{98% DE Prediction} 

 (°F) 

Acetone 1000 1300 1400

Acylonitrile 898 1198 1298

Benzene 1075 1375 1475

Chlorobenzene 1245 1545 1645

Phenol 1319 1619 1719

Toluene 1026 1326 1426

Xylene 924 1224 1324

Furthermore, the EPA Air Pollution Control Technology Fact Sheet for a thermal 

incinerator (U.S. EPA, 2003) states that the typical design conditions needed to meet 98% or 

greater control or a 20 parts per million by volume (ppmv) compound exit concentration are: 

870 °C (1600 °F) combustion temperature, 0.75 second residence time, and proper mixing. 

For halogenated VOC streams, 1100 °C (2000 °F) combustion temperature and 1.0 second 

residence time are required. 
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Based on these findings, ERG recommends that the proposed Uniform Standard 

require consideration of the autoignition temperature and residence time when developing 

rationale for a design evaluation to show that a combustion device meets the applicable 

control efficiency. The owner or operator may determine that the appropriate temperature and 

residence time are 760° C and 0.5 seconds for their equipment and process; however, under 

the proposed rule, the owner or operator should have to provide the rationale in their design 

evaluation documentation.

4.0 References 

Cooper, D., and F.C. Alley. 2002. Air pollution control: A design approach. Long Grove, IL: 

Waveland Press, Inc. 

Lewandowski, D. 2000. Design of thermal oxidation systems for volatile organic compounds. 

Boca Raton, FL: CRC Press. 

U.S. EPA. 2003. Air pollution control technology fact sheet. EPA-452/F-03-022.