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Show hazardous waste regulations. Dangerous wastes generated in Washington State must be transported to and disposed of in a RCRA-permitted facility. The Tacoma Steam Plant #2 must operate within this regulatory framework. Characteristics of Tacoma Steam Plant #2 and Related Facilities The Tacoma Steam Plant #2 is shown, schematically, in Figure 1. The general characteristics of the plant are summarized in Table 2. The plant has two atmospheric fluidized bed combustors supplied by Energy Products of Idaho, each providing gaseous combustion products to two separate waste heat boilers. Each waste heat boiler, in tum, supplies superheated steam to a 25,000 kW generator. The two generators, combined, have a gross capacity of 50 MWe, or a net capacity of 43 MWe (Colville and McCarty, 1988). The boilers, turbine-generators, and much of the balance-of-plant has existed at the Tacoma Steam Plant #2 since 1931. The repowering project added the fuel-handling and feeding systems, the fluidized bed combustors, and the air pollution control system (APCS) consisting of the cyclone and baghouse. Each fluidized bed will accept, on average, about 13,200 lb/h of RDF, 34,200 lb/h of wood waste (hog fuel), and 20,600 lb/h of low sulfur western bituminous coal. These fuels deliver 831 x 1<1 Btu/hr to the facility. The combustion occurs in a bubbling fluidized bed system with in-bed heat removal. Fuel is introduced into the reactor by overbed stoker feeding. Limestone is also introduced into the system to maintain a calcium/sulfur + chlorine molar ratio of 3.0. Bed temperatures are on the order of 1,089 - 1,144"1( (1,500 - 1,600°F), while temperatures in the freeboard space and in the cyclone are on the order of 1,256°K (1, 800°F). The overall stoichiometric ratio for the fluidized beds is specified at 35 percent, with bed stoichiometry slightly greater than 1.0. Secondary air is introduced into the freeboard space to ensure complete combustion, and in order to achieve some modified staged combustion for NOx control. Bed temperatures are carefully monitored with the in-bed tubes responsible for bed-temperature control. Over 95 percent of the solids materials removed from the system exit the process as flyash. A typical heat and mass balance for a single fluidized bed boiler at the steam plant is shown in Table 3. The fuel mixture and combustion process are somewhat limited by the Prevent Significant Deterioration (PSD) permit. That permit states that the facility can use RDF at feed rates not exceeding 50 percent of the input to the boiler, and that the facility must use coal with less than 0.8 percent sulfur. Existing facility constraints also limit the combustion process. As a practical matter, the facility can only obtain 80 percent of its heat input from hog fuel due to flue gas flow limitations in the existing boilers (Colville and McCarty, 1988). Finally, the project is somewhat influenced by the RDF-production system operated by the Refuse Division of the City of Tacoma. That process is shown schematically in Figure 2. Note that the Tacoma RDF plant utilizes an air classifier as its primary separation process. The "light" or fuel fraction generated by the air classifier is further refined by screening. The screens produce a "middlings" or "grits" fraction which is currently mixed with the "heavies" or air classifier rejects and discarded. The -3- |