API PUBL 349
Air Toxics Emission Factors for Combustion Sources Using Petroleum-Based Fuels - Graphical-User-Interface Database and User's Manual Version 2.0.1
|Publication Date:||1 October 1998|
This project was performed with the cooperation of the California Air Resources Board (CARB) to develop updated air toxics emission factors for petroleum industry combustion sources. The emission factors developed in this project will be integrated into a larger database being developed by CARB called the California Air Toxics Emission Factor (CATEF) database. They also may be used by petroleum industry environmental, health, and safety engineers to develop air toxics emissions inventories to comply with state and federal requirements. In addition, these emission factors provide an improved scientific basis for technical and policy decision-making related to the development of new environmental regulations such as federal National Emission Standards for Hazardous Air Pollutants (NESHAPs) for petroleum industry sources.
California Assembly Bill 2588 (AB2588), entitled the Air Toxics "Hot Spots" Information and Assessment Act of 1987, requires facilities to provide an inventory of their air emissions for the purpose of assessing the potential health risk to communities surrounding such facilities. Source testing to characterize air toxics emissions is required when recognized emission factors or reliable engineering estimating techniques do not exist. The results of the source testing performed to comply with AB2588 were used to develop emission factors, which relate the quantity of emissions of a substance to a process-related rate.
To develop emission factors based on the best available source test results, the petroleum industry AB2588 source test results were screened using a data validation procedure developed by CARB for the CATEF database. This procedure identifies data points and data sets with significant problems and/or reporting deficiencies in three steps including: initial screening, detailed validation, and outlier analysis. Initial screening identifies source tests which do not have sufficient documentation for emission factor development and assessment of data quality. The results of 93 of the 161 source tests were eliminated during the screening procedure. Most of the 93 source tests were eliminated because process rates needed for emission factor derivation were not provided. The detailed validation step was conducted on the remaining 68 source tests. Detailed validation includes checking to ensure the correct sampling and analysis procedures were used, qualifying Significant problems such as high field blanks, checking calculations, and evaluating the accuracy of the test results. The impact of problems identified in the detailed validation process is quantified by conducting an outlier analysis. Outliers are identified statistically using the Dixon method. Each outlier is examined to determine if a process and/or method problem occurred as documented in the results of the detailed validation. If a documented problem occurred, the outlier is eliminated.
Emission Factor Development
The validated source test data were separated into five groups: external combustion devices (boilers and process heaters), reciprocating internal combustion engines, gas turbines, asphalt blowers, and coke calciners. In general, the emissions data for each substance in each group were observed to vary over several orders of magnitude. This variability is due to a combination of measurement uncertainty and differences in the design and operation of devices tested. The variability was reduced, if possible, by identifying design and operating parameters responsible for the variation and further dividing the group into subgroups if warranted. Engineering judgment and statistical analysis were used to determine whether the design or operating parameters had a significant impact on emissions. Pooling of different system and fuel types within each of the five groups was allowed to increase the quality of the resultant emissions factors. Low sensitivity data also were eliminated from the subgroup evaluation process and emission factor calculations.
Key observations and findings from the subgroup analysis are listed below.
External Combustion Devices (Boilers and Process Heaters)
• Hazardous air pollutant (HAP) emission factors for boilers and process heaters are similar;
• HAP emission factors for external combustion sources fired by natural gas and process gas are similar;
• Polycyclic aromatic hydrocarbon (PAH) emission factors for liquid-fired sources are higher than for gas-fired sources;
• Benzene, toluene, xylene (BTX), and formaldehyde emission factors for liquid- and gas-fired sources are similar; and
• HAP emission factors for boilers and process heaters with and without NOx emission controls are similar.
Reciprocating Internal Combustion Engines
• HAP emission factors for gas- and diesel-oil-fired sources are similar, except that formaldehyde emissions from diesel sources are lower;
• HAP emission factors for 2- and 4-stroke sources are similar, except that total BTX emissions from 2-stroke sources are higher; and
• Rich burn reciprocating internal combustion engines (RICE) have higher total BTX and lower formaldehyde emissions than lean burn RICE.
Graphical User Interface
Statistics and engineering judgment were applied to identify distinct groups of devices as described above. One set of emission factors was developed for each distinct group of devices. These groups are identified in Table 1.
It should be noted that not all emission factors in the GUI are unique. One set of emission factors has been developed for each group. Many of the groups contain results from several different source tests conducted on devices with different characteristics. These devices do not have identical designs; however, the statistical and engineering analyses indicated that the differences in each device did not impact emissions significantly. Therefore, the emission factors from all of the devices within each group were averaged together for each substance. This averaging resulted in a single emission factor per substance per group. When developing the GUI, the average results were applied to each distinct design from the set of sources that were averaged together. This was done to allow users to easily find data matching their specific device. This procedure also resulted in duplicate emission factors in the GUI. These duplicate emission factors are illustrated in Table 1 as the groups which apply to more than one line. For example, each emission factor from the group identified as External Combustion, Gas is repeated nine times in the database.
The emission factors developed under this program have been compiled into the Petroleum Air Toxics Emission Factors (PATEF) database so the CARB and facility owners/operators can quickly and reliably access these newly developed factors. PATEF uses a graphical-user-inter