Option 1 Option 2
Determined in trial burn
No limit 20mL/L
Source: U.S. EPA, Boilers and Industrial Furnaces, 40 CFR Part 266, Subpart H, EPA530-R-99-042, U.S. Environmental Protection Agency, Washington, DC, February 2000.
220.127.116.11.1.2 Products of Incomplete Combustion Poor combustion conditions result in the release of a high concentration of organic materials formed during the combustion process. These PICs may be present in the original waste stream or may be new compounds that form during the thermal breakdown and subsequent recombination of organic compounds. In order to control the emission of PICs, U.S. EPA places limits on carbon monoxide (CO) emissions or, if necessary, hydrocarbon (HC) emissions from the unit. The presence of carbon monoxide is an indicator of incomplete combustion. Therefore, a high level of carbon monoxide in emissions is an indicator of incomplete combustion and thus an indication of a high release of PICs. The BIF owner/operator has two options to meet this CO emission standard. They may meet a CO emission standard of 100 mL/L, with no limits on HC emissions, or they may meet an HC limit of 20 mL/L, with CO emission limits based on levels demonstrated during the unit's trial burn (Table 23.4).
The second emission U.S. EPA regulates is PM. PM consists of small dust-like particles emitted from BIFs. Although the particles themselves may cause adverse health effects (e.g., increased asthma), they also provide a point of attachment for toxic metals and organic compounds. The particulates may become caught in the lungs or be absorbed into the environment. To minimize these adverse conditions, U.S. EPA set an emission limit of 180mg/dscm. BIFs that qualify for the low-risk waste exemption mentioned above, however, are not subject to the PM standard.5
The third aspect of the emissions standards involves limits on metals. Metals regulated under the BIF standards are categorized as either noncarcinogenic (i.e., antimony, barium, lead, mercury, silver, and thallium) or carcinogenic (i.e., arsenic, cadmium, chromium, and beryllium). The owner/ operator can determine the allowable feed or emission rate for each regulated metal by selecting any one of three approaches, called tiers (Figure 23.3). Each tier differs in the amount of monitoring and, in some cases, modeling the owner/operator is required to do.21
Factors that may be considered in selecting a tier include the physical characteristics of the facility and surrounding terrain, the anticipated waste compositions and feed rates, and the level of resources available for conducting the analysis. The main distinction between the tiers is the focal
Lots of monitoring monitoring
Lots of monitoring
FIGURE 23.3 Continuum of tiers and monitoring. (Adapted from U.S. EPA, Boilers and Industrial Furnaces, 40 CFR Part 266, Subpart H, EPA530-R-99-042, U.S. Environmental Protection Agency, Washington, DC, February 2000.)
point (Figure 23.4). This is the point at which the owner/operator must ensure that the metal concentration of their waste will be below U.S. EPA's acceptable exposure levels for that constituent.
18.104.22.168.3.1 Tier I The focal point of Tier I is the waste feed. This tier limits the hourly feed rate of individual metals into the combustion device. These limits have been developed by U.S. EPA and can be found in Part 266, Appendix I.5 U.S. EPA established these feed rate limits by considering flue gas flows, stack height, terrain, and land use in the vicinity of the facility. It determined acceptable air quality levels for each type of metal as a function of terrain, stack height, and land use in the vicinity of the facility. This value is also the waste feed rate, as Tier I assumes that 100% of the metals that are fed into the unit will be released into the atmosphere.
22.214.171.124.3.2 Tier II The focal point of Tier II is the stack. This tier limits the emissions of individual metals from the stack. As with Tier I, emission limits have been predetermined by U.S. EPA by considering a number of different factors (i.e., stack height, terrain, and surrounding land use) and can be found in Part 266, Appendix I.5 Tier II differs from Tier I, however, in that owners/ operators are able to conduct emission testing to take credit for reduced metal emissions achieved either by the partitioning of pollutants to bottom ash or products or by the removal of the pollutants through the facility's APCD. By conducting tests to determine how much of the metals fed into the BIF are emitted through the stack, owners/operators using Tier II can conceivably increase the amount of metals in the waste feed by accounting for waste partitioning and pollution control activities.
126.96.36.199.3.3 Tier III The focal point of Tier III is the surrounding environment. Tier III limits must be set such that the metals will not adversely affect the ambient air quality. It allows the owner/ operator to use site-specific factors to back calculate from the ambient levels to determine the unit's waste feed. Tier III standards are implemented in the same way as Tier II, by placing emission limits on metals, but unlike Tiers I and II, there are no predetermined levels established by U.S. EPA. Instead, the facility owner/operator determines emission levels by testing emission rates for each individual metal using air dispersion modeling techniques14 24-26 to predict maximum ground-level metal concentrations that will not adversely affect human health and the environment, and by demonstrating that ambient air levels will not be exceeded.
188.8.131.52.3.4 Adjusted Tier I A BIF owner/operator may choose to adjust the feed rate limits that have been established by combining some of the aspects of Tier I and Tier III. This alternative is implemented in the same way as the Tier I standards, by regulating feed rates into the BIF, but allows for limits that are more relevant to a given facility. As with the Tier III methodology, owners/operators may back calculate maximum allowable emission rates for their facility from acceptable ambient air levels using site-specific air dispersion modeling. These emission limits then become the adjusted feed rate limits for that facility.
184.108.40.206.3.5 Alternative Implementation Owners/operators are also allowed to use a combination of the Tier II and Tier III methodologies. Under this approach, rather than monitoring metal feed rates, a BIF would monitor the emission rates contingent upon approval from the Regional waste management director.
The final emission standard under the BIF regulations limits the unit's output of HCl and chlorine gas (Clj). These compounds combine with water in the air to form acid rain. They are also a known cause of human respiratory problems. The emission controls are implemented in the same way as the metal emissions, using the tiered approach. The owner/operator has a choice of three tiers with varying focal points. The Tier I and Tier II screening levels for waste feed and stack emission limits are located in Part 266, Appendices II and III.5
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