Classification of VOCs and HAPs

The HAPs described in this manual are not limited to the specific compounds listed in current laws such as the CAAAs of 1990, the Resource Conservation and Recovery Act (RCRA), or the Toxic Substances Control Act. HAPs can be classified relative to the type of compounds (i.e., organic or inorganic) and the form in which they are emitted from process point, process fugitive, or area fugitive sources (i.e., vapor or particulate).

This section discusses two examples of VOC and HAP emissions from chemical plant classes. Table 5.2.1 summarizes emissions from the inorganic chemical manufacturing industry. This industry produces basic inorganic chemicals for either direct use or use in manufacturing other chemical products. Although the potential for emissions is high, in many cases they are recovered due to economic reasons. As shown in Table 5.2.1, the chemical types of inorganic emissions depend on the source category, while the emission sources vary with the processes used to produce the inorganic chemical.

The second example is from petroleum-related industries, including the oil and gas production industry, the petroleum refining industry, and the basic petrochemicals industry. Table 5.2.2 summarizes the emission sources within these three categories. Sources of emissions from the oil and gas production industry include blowouts during drilling operations; storage tank breathing and filling losses; wastewater treatment processes; and fugitive leaks in valves, pumps, pipes, and vessels. In the petroleum refining industry, emission sources include distillation and fractionating columns, catalytic cracking units, sulfur recovery processes, storage tanks, fugitives, and combustion units (e.g., process heaters). Fugitive emissions are a major source in this industry. Emission sources in the basic petrochemicals industry are similar to those from the petroleum refining segments (U.S. EPA 1991).

Table 5.2.3 summarizes the potential HAP emissions from the petroleum refining segment of the petroleum industries. A large proportion of the emissions occur as organic vapors; for example, benzene, toluene, and xylenes are the principal organic vapor emissions. These organic vapors are due to the chemical composition of the two starting materials used in these industries: crude oil and natural gas. Crude oil is composed chiefly of hydrocarbons (paraffins, napthalenes, and aromatics) with small amounts of trace elements and organic compounds containing sulfur, nitrogen, and oxygen. Natural gas is largely saturated hydrocarbons (mainly methane). The remainder

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