OCR Text |
Show use of generally available control technologies or management practices by such sources to reduce emissions of hazardous air pollutants." Emission standards that are more stringent than the floor must take into account economic and other impacts. New Sources- " The maximum degree of reduction in emissions that is deemed achievable for new sources in a category or subcategory shall not be less stringent than the emission control that is achieved by the best controlled similar source, as determined by the administrator." Major HAPs of Concern The Clean Air Act specifically mentions seven H A P s of Concern because of their persistence in the environment and their tendency to bioaccumulate: 2,3,7,8 tetrachlorodibenzo-p-dioxin/furan (PCDD/PCDF) - Dioxins and furans are formed in many combustion and postcombustion processes. Combustion science and research have determined several viable mechanisms for the formation of these toxic compounds. Consequently, modern combustion equipment design has been able to reduce dioxin/furan emissions through application of good combustion practices, rapid quenching in the postcombustion region to freeze formation by catalytic mechanisms and carbon injection. Stakeholders were divided in assessing the likelihood of dioxin formation when burning gaseous, liquid and wood fuels. Combustion scientists can play an important role in the rulemaking process by supporting a sound scientific analysis to eliminate frivolous claims of dioxin formation. [4,5,6,7]. Mercury (Hg) - Mercury and its compounds are highly volatile. Mercury compounds are difficult to remove from the stack. However, by maintaining air pollution control equipment below 165 °C and using carbon injection, removal efficiencies > than 9 0 % have been demonstrated. Stakeholders were divided in assessing the occurrence of mercury in various fuels [5]. Some stakeholders expressed serious concerns about the mercury content of natural gas. These concerns were addressed by other stakeholders [8]. Polycyclic Organic Matter (POMs) - Polycyclic Organic Matter consists of polycyclic aromatic hydrocarbons (PAHs) and other polycyclic compounds. There is a need for research for characterization and possible formation of the polycyclic compounds related to P A H s in the combustion process. For properly designed and operated combustion equipment, P A H s are emitted at low levels. Proper fuel/air mixing, adequate combustion temperatures and residence time [8,9] generally control these. C:\ips\icer\overviewa 6 |