Waste Heat Recovery with a Gas Turbine
Figure 3200-15 shows how a hot pressurized water system, utilizing the unfired exhaust from a combustion gas turbine, can be used economically to recover wasteheat and to transfer the heat to various users. Most hot water systems (treated water) operate at 230°F to 280°F, which requires a minimum system pressure of 60 PSIG. Water can be used at higher temperatures, up to 400°F, but higher pressures are required to prevent boiling. The water is heated by the hot exhaust gases while flowing through the tubes. The water temperature is controlled by diverting a portion of the turbine exhaust. High water temperature or low water flow causes the entire exhaust to be diverted. An expansion tank is included in the water system to allow for the thermal expansion of the water. The pressure in the expansion tank is maintained with nitrogen gas to prevent the formation of steam. The process load shown can be a single user or a combination of many users. A system for using heating oil is similar.