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Comprehensive Review of S olid W aste Collection and Disposal Options v2.1 162 10/22/12 The low-Btu gases produced by the combustion process in the first chamber are typically introduced into a secondary chamber where they are burned at temperatures ranging from 1,800 to 2,000F. Heat energy is recovered by convection in waste heat boilers in this secondary chamber, although waterwall boiler units for the primary and secondary chambers have been constructed. In recent years, several manufacturers have entered the modular plant marketplace using a batch oxidation process (BOS – Exhibit 12-3). The batch process integrates slow gasification and long exposure time at moderate temperatures followed by turbulent oxidation of gases at high temperature. After the waste is loaded into the primary chamber and sealed tight, an auxiliary burner is ignited to raise temperatures to about 200C. The interior temperature is then monitored with controls and maintained by allowing sub-stoichiometric amounts of air into the chamber during the gasification process. The combination of relatively low temperatures and only sub-stoichiometric amounts of air in the primary chamber during gasification do not disturb the gasification bed, which is said to minimize particulate emissions, heavy metals, and many combustion gasses. Depending on the waste type and system layout, the waste reduction process in the primary chamber will take approximately 10 to 15 hours. Exhibit 12 -3. Cross -Section of Batch Oxidation System, Modular Facility Source: Waste2Energy, Inc., 2009 Emissions produced during the gasification process pass through to the preheated secondary chamber also called an “afterburner” where these emissions are thermally treated. As the gasses from the primary chamber enter a preheated secondary chamber, auxiliary burners and excess oxygen create a very turbulent high temperature environment (typically between 850C and 1,200C). For most applications within the European Union (EU) 850C is the required minimum, though 1,100C is required for halogenated wastes, and in North America, 982C is usually required. Additionally, residence time in the secondary chamber is important for proper destruction of emissions from the primary chamber. In both the EU and North America, a minimum residence time of 2 seconds is required. Operation of these units is subject to stringent Primary Chambers Secondary Combustion Chamber Boiler Air Emissions Control System