Pounds per cubic foot per year per cfm
Considerable data has been accumulated on the number of pounds of toxics being emitted each year in the United States. Comprehensive data has also been accumulated on the quantities of VOCs emitted from point sources and area sources. The cost of capturing these emissions is a direct function of the cubic feet of air per minute which contains these emissions. The cost of incinerators is a direct function of CFM, because the BTUs required to initiate and sustain combustion is directly a function of the quantity of air and the temperature rise needed. The size of the vessel for carbon adsorbers, catalytic incinerators and absorbers is also directly related to CFM. Auxiliary equipment, such as fans, is sized specifically on CFM. Therefore, in this study, a considerable effort has been made to relate emissions in pounds to cubic feet of air generated. The ratio is expressed in pounds of toxic emissions per year per CFM. Figure IV-1 shows a conversion of parts per million to pounds per year per CFM. Many surface coating operations incorporate control systems which experience inlet concentrations to the control equipment of 1,000 to 1,500 parts per million. A mixture of solvents can range in density from below the density of air to in excess of the density of air. Figure IV-1 shows the resultant pounds per year emitted, based on various concentrations expressed in parts per million. These assume the density of the solvents are the same as air. Also included are calculations in pounds per year per CFM for two situations in which the density of the solvents is different from air.
Large numbers of installations have been analyzed to determine these ratios. In the chemical industry following vapor recovery systems, the ratio can be very high. When highly toxic emissions are being controlled, the ratio in extreme cases is very low, but the average emissions for capturing organics is approximately 25 pounds per year per CFM.
While the average emissions of an uncontrolled organic source is 25 pounds per year per CFM, this does not mean that the average source faced with regulations under Title I and Title III will be emitting 25 pounds per year per CFM. This is because most of the large uncontrolled sources in the United States are already controlled. In fact, the Clean Air Act will be requiring reductions from poorly controlled sources rather than uncontrolled sources. Sources to be controlled under the Clean Air Act fall into the following categories:
l. Large sources with poor control.
A system with a condenser which captures product is an example of a poorly controlled source.
2. Large sources with low emission rates.
The Clean Air Act will be focusing on bakeries and other sources which emit relatively low quantities of volatile organics but which have not been controlled previously.
3. Small sources with relatively high emissions rates.
Small area sources will be controlled under the Clean Air Act. Dry cleaners, electroplaters and sterilizers are examples of small sources which will be controlled.
4. Sources which control one type of pollution, but not others.
An incinerator might presently remove the volatile organics but because the pollutants are halogenated organics, there is a substantial HCI emission. Scrubbers will be required as an add-on device to incinerators in this category. Also in this category are sources emitting toxic metals. Typically, some sort of pollution control device has already been applied to a furnace, kiln or coal-fired boiler. The existing precipitator may have an efficiency of 98 percent, however, a large percentage of the remaining emissions could be toxic metals. Cadmium mercury and other heavy metals represent only a small fraction of total emissions from coal-fired boilers. Silica, sodium calcium and other non-toxics make up the bulk of the emissions. Therefore, the ratio for heavy metals is very low comparative to organics. For purposes of this study, an average ratio of .02 pounds per year of fine toxic particulate per CFM has been utilized.