AFS Emissions Benchmarking Database: An Evolving Repository of Information
The Clean Air Act, first promulgated in 1970, required federal and state governments to limit emissions related to both stationary (e.g., industries) and mobile sources (e.g., automobiles). To help identify and control emission sources, state environmental protection agencies developed rules requiring companies to obtain approvals or air permits for their equipment that emit pollutants and to meet prescribed emission limits by installing emission control equipment. By the mid-1970s, the requirement to obtain an air permit or “license” for industrial facilities to meet emission limits, became fairly commonplace.
During the 1970s and 1980s when these new regulations were promulgated, the foundry industry included many large, high volume, green sand operations. When state and federal EPA staff visited these foundries, particulate emissions were identified as the most common air pollutant of concern.
The recognition of particulate matter (PM) as the primary pollutant of concern is evidenced by review of EPA’s “holy grail” of emissions information, known as the U.S. EPA Compilation of Emission Factors or more commonly as AP-42. AP-42 was first published in 1972 and is identified on the U.S. EPA website as the “primary compilation of emissions factors and process information for more than 200 air pollution source categories.”
While there is no AP-42 section addressing nonferrous foundries, there are sections on both iron and steel foundries. Reviewing both sections confirms the idea that particulate matter was the primary air pollutant of concern at that time. In fact, the only non-particulate emission information in the iron and steel foundry sections is for cupolas and electric arc furnaces. In addition to quantifying particulate matter emissions from various foundry operations, the benefit of AP-42 for the foundry industry is the initial identification of foundry processes that would be expected to emit air pollutants.
The limited information and understanding of non-particulate emissions from foundry operations such as pouring, cooling, and shakeout—combined with the fact it is the regulated industry’s responsibility to identify and then quantify emissions—resulted in a challenging regulatory environment for the metalcasting industry. The industry was tasked with obtaining a “license” without having sufficient information to fill out the application.
This landscape of limited emissions information regarding non-particulate pollutants continued from the 1970s to the mid-1990s. This situation was further complicated by the increasing volume and complexity of air regulations and a general lack of understanding by both the regulators and the regulated community. Also, in the 1980s the growing use of chemically-bonded molds and cores resulted in more installations with limited information on emission rates for volatile organic compounds (VOCs).
Today, a foundry environmental professional is typically tasked with quantifying emissions of criteria pollutants, such as particulate matter, VOCs, carbon monoxide (CO), nitrogen dioxide, sulfur dioxide and lead, as well as any of the applicable 187 hazardous air pollutants state-level air toxins. This requirement, along with the fact that AP-42 currently doesn’t have non-particulate emissions information for foundry processes other than melting, set the stage for the inception of this project.
AP-42 has been updated very infrequently. In fact, the most recent update, the fifth edition, was completed in 1995. Interestingly, much of the particulate matter emissions information included in the fifth edition is from work that was conducted prior to 1970 and published in Modern Castings in January 1970. So much of the emissions information that is available for use today is from studies conducted over 50 years ago.
In 2002, the AFS Air Quality Committee learned that EPA was in the middle of developing a subsequent edition of AP-42. Rather than leave this task to EPA, a working group began to compile available emissions information from AFS member foundries. At that point in time, with stack testing for non-particulate matter pollutants becoming more of the norm, foundry supplier engagement and the Castings Emission Reduction Program (CERP, see sidebar) in operation, the working group objectives were ambitious. Broadly, the objectives included obtaining sufficient emissions information from both ferrous and nonferrous foundries to develop more accurate emission factors that could be adjusted to account for process variables that typically change from foundry to foundry.
Realizing the project was too large an undertaking given the lack of participation from nonferrous foundries, the limited emissions information received, lack of information on process variables during emission tests, and the winding down the of CERP program, the initial working group objectives were modified. The working group moved forward with a focus on developing an industry database that could be used by individual foundries to compare their emissions to industry benchmarks. The working group agreed to accept all emissions information from foundries while placing an emphasis on priority operations and pollutant combinations where gaps existed.
The time commitment to gather and submit test reports, confidentiality concerns by foundries, or reluctance to share emissions information slowed the working group’s efforts over the last couple of years. With the understanding that the database will be continually updated as new emissions data are received, AFS is making the existing database available as a service to AFS members.
From 2002 through 2021, the Emission Benchmark Working Group’s volunteer efforts amounted to an estimated “in-kind” contribution in excess of $120,000. To complete the work needed to validate and format the database for publication, a Request for Research Funds was submitted to AFS. The work included populating the database with any outstanding emissions information and validating all database entries, while customizing the database to allow filtering and search capabilities.
Table 1 identifies the foundry processes usually identified as discrete sources of air emissions and the pollutants associated with each process. It is beneficial for a metalcasting facility to review current air permits for each of its operations and determine if they have missed any pollutant.
Because of the importance and a general shortfall of emissions information, the working group placed additional emphasis on the following operations and/or pollutants:
- VOC emissions from pouring, cooling, and shakeout.
- CO emissions from pouring, cooling, and shakeout.
- Filterable and condensable fraction of particulate matter associated with any foundry process.
Noteworthy conclusions from the current database include:
The U.S. EPA VOC emission factor for pouring, cooling, and shakeout when viewed collectively (1.34 lbs. of VOC per ton of metal) appears to be representative of actual emissions from green sand foundries.
Carbon monoxide emissions from phenolic urethane operations show some of the largest emissions variability.
Methane is a large component of the VOCs measured from pouring, cooling, and shakeout. For foundries that are mandated to test for VOCs, methane—a definitionally exempt VOC—should be quantified during each sampling run and subtracted from the measured VOC value.
There was an initial concern that the condensable portion of particulate matter (which became regulated around 2010) would be much greater than the filterable emissions from operations such as melting, pouring, cooling, and shakeout. The database indicates that the condensable portion is likely less than anticipated but is significant and should be considered in estimates of particulate matter.
There was substantial variability in CO and NOx emissions from electric arc melting furnaces—likely the result of air infiltration and/or regulation of combustion air.
As expected, the EPA particulate matter emissions factor for pouring, cooling, and shakeout substantially overestimates the emissions. This is also corroborated by the CERP Mexico testing conducted in the later 1990s.
The database includes benchmarks for emissions for operations for which limited data are currently available. Examples include several entries for cupola NOx emissions and SO2, CO, and VOC information for thermal sand reclamation.
The Emissions Benchmarking Database includes over 240 stack tests from over 30 iron and steel foundries. It is a password-protected Microsoft Excel filterable worksheet available on the Air Quality Committee Members Only area of the AFS Website.
The database fields of particular interest are the “Categorized Process,” whether the stack test includes “commingled operations,” and if “commingled,” the commingled processes. Control device information, throughput rates, emissions information, and test method are then provided.
As the project name suggests, the database was developed to allow foundries to compare their emissions against actual measured emissions from similar operations. In addition to the ability to compare emissions, other uses of the database include:
- Framing the range of emissions from a particular operation and pollutant such as VOCs from pouring, cooling, and shakeout.
- Reviewing the condensable portion of PM that can be expected from available database information (though as acknowledged previously there is wide variability in this data).
- Doing a reality check on stack test results by confirming that measured emissions are indicative of what would be expected from a similar operation. For example, in some instances stack tests have showed non-detectable emissions for carbon monoxide or volatile organic compounds from pouring, cooling, and shakeout operations, which points to emission testing concerns.
As discussed earlier, emissions information received from foundry operations is currently limited. The plan going forward is to continue to request more emissions information from foundries and update the database. Because of project deadlines, budgetary concerns or limited knowledge, foundries and/or their consultants may be tempted to use emissions data from the AFS emission benchmarking database as emission factors in their air permit applications. However, the emissions information contained in the database must not be used for this purpose for the following main reasons:
- All of the tests in the database with the exception of the CERP test were conducted in foundries for the purpose of demonstrating compliance with permit limits. They were not conducted under controlled experimental conditions for the purpose of establishing accurate emission factors.
- Many of the emission datapoints are from stacks where exhaust gases from multiple processes were commingled for a variety of reasons. This means the results reflected emissions from more than one process.
- The hood capture efficiency was often not specified or known and therefore the actual emissions from the process could not be accurately quantified. Many variables influence emissions from foundry operations, including mold and core type, sand-to-metal ratio, casting geometry, pouring temperature, and time to shakeout. Some of these variables were addressed in AFS Transactions 02-126, An Examination of the Effects of Process Variables on Air Emission from Metal Casting (Crandel, Knight, Schifo, Rarick).
Our industry has been around for centuries, but the wide variation in process parameters from foundry to foundry make the transfer of emissions information between foundries difficult. The AFS Emission Benchmarking Working Group is planning to continue collecting additional emissions information from foundries, especially for the targeted processes and pollutants. We also will begin gathering information on foundry process greenhouse gas emissions (“direct”) to allow for better characterization of our industry’s impact on climate change and provide foundries more representative GHG emissions data to respond to customer requests.
AFS and the Emission Benchmarking Working Group appreciate the foundries that have contributed emissions information for this project. Foundries willing to share stack test data to facilitate continuous improvements of the database can contact Greg Kramer at AFS, email@example.com