Combined heat recovery and emission control system

A method of recovering heat from and reducing the pollutants in a high temperature exhaust gas stream with a combined heat recovery and emission control system having a plurality of steam boilers, each having at least one bank of a plurality of steam generating tubes, a steam conduit system having a first steam header for supplying steam at a first preselected nominal pressure, an emission control unit for reducing pollutants in the exhaust gas stream by chemical conversion, a duct for conducting the exhaust gas stream through said banks of steam generating tubes and the emission control unit, the plurality of steam boilers comprising a first steam boiler having its said bank of steam generating tubes upstream of the emission control unit and a second steam boiler having its said bank of steam generating tubes downstream of the emission control unit, said first and second steam boilers being connected for supplying steam to the steam conduit system, the method comprising the step of regulating the supply of steam from said first steam boiler to the steam conduit system in accordance with the temperature of the exhaust gas stream at the emission control unit, to regulate the operating pressure of said first steam boiler, and thereby vary the temperature and heat exchange rate of said bank of steam generating tubes of said first steam boiler, to maintain the exhaust gas stream at the emission control unit at a preestablished desired nominal temperature for said chemical conversion.

A method of recovering heat from and reducing the pollutants in a high temperature exhaust gas stream with a combined heat recovery and emission control system having a plurality of steam boilers, each having at least one bank of a plurality of steam generating tubes, a steam conduit system having a first steam header for supplying steam at a first preselected nominal pressure, an emission control unit for reducing pollutants in the exhaust gas stream by chemical conversion, a duct for conducting the exhaust gas stream through said banks of steam generating tubes and the emission control unit, the plurality of steam boilers comprising a first steam boiler having its said bank of steam generating tubes upstream of the emission control unit and a second steam boiler having its said bank of steam generating tubes downstream of the emission control unit, said first and second steam boilers being connected for supplying steam to the steam conduit system, the method comprising the step of regulating the supply of steam from said first steam boiler to the steam conduit system in accordance with the temperature of the exhaust gas stream at the emission control unit, to regulate the operating pressure of said first steam boiler, and thereby regulate the temperature and heat exchange rate of said bank of steam generating tubes of said first steam boiler, to maintain the exhaust gas stream at the emission control unit at a preestablished desired nominal temperature for said chemical conversion and the step of regulating the supply of steam from said second steam boiler to the steam conduit system to maintain said first steam header at said first preselected nominal pressure.

In a cogeneration plant having a combined heat recovery and emission control system for the recovery of heat from and reduction of pollutants in a high temperature exhaust gas stream, the combined system comprising a plurality of steam boilers, each having at least one bank of a plurality of steam generating tubes, a steam conduit system, an emission control unit for reducing pollutants in the exhaust gas stream by predetermined treatment of the exhaust gas stream at a preestablished desired nominal temperature, a duct for conducting the exhaust gas stream through said banks of steam generating tubes and the emission control unit, the plurality of steam boilers comprising a first steam boiler having its said bank of steam generating tubes upstream of the emission control unit, and a second steam boiler having its said bank of steam generating tubes downstream of the emission control unit, said first and second steam boilers being connected for supplying steam to the steam conduit system, the improvement wherein said first steam boiler is an exhaust gas temperature regulating boiler having a first, temperature responsive, boiler control system for regulating the supply of steam from said first steam boiler to the steam conduit system in accordance with the temperature of the exhaust gas stream at the emission control unit, to regulate the operating pressure of said first steam boiler, and thereby regulate the temperature and heat exchange rate of said bank of steam generating tubes of said first steam boiler, to maintain the exhaust gas stream at the emission control unit at said preestablished desired nominal temperature.

A method of recovering heat from and reducing the pollutants in a high temperature exhaust gas stream having a variable inlet temperature, with a combined heat recovery and emission control system having a first steam boiler with at least one bank of a plurality of steam generating tubes, a steam conduit system, an emission control unit for reducing pollutants in the exhaust gas stream by chemical conversion at a preestablished desired nominal temperature less than said variable inlet temperature, a duct for conducting the exhaust gas stream through said bank of steam generating tubes and the emission control unit, said first steam boiler having its said bank of steam generating tubes upstream of the emission control unit and being connected for supplying steam to the steam conduit system, the method comprising regulating the supply of steam from said first steam boiler to the steam conduit system in accordance with the temperature of the exhaust gas stream at the emission control unit, to regulate the operating pressure of said first steam boiler within a pressure range having a predetermined maximum pressure no greater than the saturation pressure at said preestablished desired nominal temperature, and thereby regulate the temperature and heat exchange rate of said bank of steam generating tubes of said first steam boiler, to maintain the exhaust gas stream at the emission control unit at said preestablished desired nominal temperature.