Under the CAA, EPA is required to regulate emissions of HAPs. In the 1990 CAA, 189 HAPs were identified for potential regulation presented in Table C.2. Industrial and commercial waste incinerators, industrial boilers and process heaters, and other combustion sources are suspected of emitting large quantities of many of these HAPs. Some HAPs are components of the waste and/or fuels, and others are formed during combustion process.
National Emission Standards for Hazardous Air Pollutants
A separate category of standards for emissions from point sources have been created for HAPs. These are known as the NESHAPs that apply to those substances that do not have ambient air quality standards (AAQSs) but that may result in an increase in serious irreversible, or incapacitating, reversible illness. As of today, the NESHAPs have been promulgated by the EPA for only a few sources of pollutants, but activity in this area has increased greatly as a result of CAA Amendments of 1990. The NESHAPs are very specific as to sources and types of control methods. A brief summary is presented in Table 3.10.
Fugitive Emissions
Fugitive emissions are emissions of gases or vapors from pressurized equipment due to leaks and other unintended or irregular releases of gases, mostly from industrial activities. As well as the economic cost of lost commodities, fugitive emissions contribute to air pollution and climate change. A detailed inventory of greenhouse gas emissions from upstream oil and gas activities in Canada for the year 2000 estimated that fugitive equipment leaks had a global warming potential equivalent to the release of 17 million MT of carbon dioxide, or 12% of all greenhouse gases emitted by the sector (Clearstone Engineering 1994). Venting of natural gas, flaring, accidental releases, and storage losses accounted for an additional 38%.
Table 3.10 Summary of National Emission Standards for Hazardous Air Pollutants (NESHAPs).
Source: Adopted from 40 CFR 61 (Code of Federal Regulations).
| 1. Beryllium | The emissions from all point sources are limited to 10 g of beryllium per 24 hours. If the EPA approves, the source owner/operator may substitute the requirement to meet an ambient air quality standard of 0.01 μg/m3 averaged over a 30‐day period. Separate standards are listed for rocket motor testing using a beryllium‐containing propellant. |
| 2. Mercury | The emissions from mercury ore processing facilities and mercury cell chlor‐alkali plants shall not exceed 2300 g of mercury per 24 hours. Emissions from sludge incinerators or dryers shall not exceed 3200 g/24 hours. |
| 3. Vinyl chloride | The standards are listed for specific equipment and processes in ethylene dichloride plants, vinyl chloride plants, and PVC plants. In general, the standard is 10 ppm of vinyl chloride in any exhaust gases. |
| 4. Benzene | The standard is very specific and basically applies to plants and equipment within plants that handle benzene. The standards are designed to prevent or minimize leakage of benzene into the atmosphere. |
| 5. Asbestos | The standards apply to asbestos mills, eleven manufacturing operations using commercial asbestos, demolition and renovation of facilities containing asbestos, and other processes. Basically, the standard requires that any air exhausts must contain no visible emissions. |
Fugitive emissions present other risks and hazards. Emissions of VOCs such as benzene from oil refineries and chemical plants pose a long‐term health risk to workers and local communities. In situations where large amounts of flammable liquids and gases are contained under pressure, leaks also increase the risk of fire and explosion.
Leaks from pressurized process equipment generally occur through valves, pipe connections, mechanical seals or any other equipment that can potentially leak (e.g. pumps, flanges). Fugitive emissions also occur at evaporative sources such as wastewater treatment ponds and storage tanks. Because of the huge number of potential leak sources at large industrial facilities and the difficulties in detecting and repairing some leaks, fugitive emissions can be a significant proportion of total emissions. Though the quantities of leaked gases may be small, gases that have serious health or environmental impacts can cause a significant problem.
To minimize and control leaks at process, facilities operators carry out regular leak detection and repair activities. Routine inspections of process equipment with gas detectors can be used to identify leaks and estimate the leak rate in order to decide on appropriate corrective action. Proper routine maintenance of equipment reduces the likelihood of leaks.
An oil refinery or large petrochemical facility might have thousands of such pieces of equipment, making it impractical to measure the emissions from every source. Because of the technical difficulties and costs of detecting and quantifying actual fugitive emissions at a site or facility, and the variability and intermittent nature of emission flow rates, bottom‐up estimates based on standard emission factors are generally used for annual reporting purposes.
New technologies are under development that could revolutionize the detection and monitoring of fugitive emissions. One technology, known as differential absorption lidar (DIAL), can be used to remotely measure concentration profiles of hydrocarbons in the atmosphere up to several hundred meters from a facility. DIAL has been used for refinery surveys in Europe for over 15 years. A pilot study carried out in 2005 using DIAL found that actual emissions at a refinery were 15 times higher than those previously reported using the emission factor approach. The fugitive emissions were equivalent to 0.17% of the refinery throughput (Chambers et al. 2008).
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