초록 ▼

A method for removing pollutants from flue gas generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the flue gas being discharged through an outlet end of the stack. The pollutants are removed by an emission treatment system which includes a major

A method for removing pollutants from flue gas generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the flue gas being discharged through an outlet end of the stack. The pollutants are removed by an emission treatment system which includes a major component module and inlet and outlet ductwork providing fluid communications between the stack and the major component module. The major component module includes an SCR segment, a heat exchanger segment, and an ID fan, the SCR segment having at least one catalyst unit composed of materials for selectively catalyzing at least one pollutant. The method comprises the steps of drawing the flue gas from the stack and through the major component module with the ID fan, removing the pollutant from the flue gas with the SCR segment to produce a clean flue gas, and discharging the clean flue gas to the stack with the ID fan.

대표청구항 ▼

What is claimed is: 1. A method for removing pollutants from flue gas with an emission treatment system, the flue gas being generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the stack including a first ID fan disposed therein, the flue gas bein

What is claimed is: 1. A method for removing pollutants from flue gas with an emission treatment system, the flue gas being generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the stack including a first ID fan disposed therein, the flue gas being discharged through an outlet end of the stack, the emission treatment system including a major component module, inlet ductwork attached to the stack at a first position intermediate the inlet end of the stack and the first ID fan, and outlet ductwork attached to the stack at a second position intermediate the first ID fan and the outlet of the stack, the major component module having an SCR segment, a heat exchanger segment, and a second ID fan, the SCR segment having at least one catalyst unit composed of materials for selectively catalyzing at least one pollutant, the inlet and outlet ductwork providing fluid communications between the stack and the major component module, the method comprising the following steps: closing the stack at a third position intermediate the first and second positions to prevent the flow of flue gas through the first ID fan; drawing the flue gas from the stack through the inlet ductwork and through the major component module with the second ID fan; removing the pollutant from the flue gas with the SCR segment of the major component module to produce a clean flue gas; and discharging the clean flue gas through the outlet ductwork to the stack with the second ID fan. 2. The method of claim 1 further comprising the step of controlling the flow rate of the flue gas through the major component module by regulating the pressure decrease across the second ID fan with a damper controller. 3. The method of claim 2 wherein the step of controlling the flow rate of the flue gas comprises the sub-steps of: monitoring a second ID fan supply pressure with the controller; monitoring a second ID fan discharge pressure with the controller; monitoring differential pressure across the SCR segment with the controller; monitoring differential pressure across the heat exchange segment with the controller; and regulating the position of a damper upstream of the second ID fan on the basis of the second ID fan supply and discharge pressures and the differential pressures across the SCR and heat exchange segments. 4. The method of claim 3 wherein the step of controlling the flow rate of the flue gas comprises the sub-step of monitoring the temperature of the flue gas in the inlet ductwork. 5. The method of claim 1 wherein the pollutant to be removed is NOX, the emission treatment system also includes an ammonia addition subsystem in fluid communication with the inlet ductwork, and at least one catalyst unit is composed of materials for selectively catalyzing NOX, the method further comprising the step of mixing ammonia vapor with the flue gas upstream of the SCR segment. 6. The method of claim 5 wherein the step of mixing ammonia vapor includes: injecting ammonia vapor into the inlet ductwork; and mixing the ammonia vapor with the flue gas over the length of the inlet ductwork. 7. The method of claim 6 wherein the step of mixing ammonia vapor also includes creating turbulence in the flue gas by changing the direction of flue gas flow from a vertical direction in the stack to a horizontal direction in the inlet ductwork. 8. The method of claim 6 wherein the ammonia addition subsystem includes a source of ammonia vapor, an ammonia injection grid disposed in the inlet ductwork, an ammonia vapor pipe providing fluid communication between the source of ammonia vapor and the ammonia injection grid, and a throttle valve disposed in the ammonia vapor pipe, the step of mixing ammonia vapor also including controlling the rate of ammonia addition by regulating the throttle valve with an ammonia addition controller. 9. The method of claim 8 wherein the step of mixing ammonia vapor also includes biasing the ammonia vapor into the flue gas stream with the vapor pressure of the ammonia in the source of ammonia. 10. The method of claim 8 wherein the step of controlling the rate of ammonia addition includes: monitoring the flue gas flow rate with the ammonia addition controller; monitoring the level of NOX entering the emission treatment system with the ammonia addition controller; monitoring the level of NOX exiting the emission treatment system with the ammonia addition controller; and regulating the throttle valve on the basis of the flue gas flow rate and the level of NOX entering and exiting the emission treatment system. 11. The method of claim 8 wherein the step of controlling the rate of ammonia addition includes: monitoring the level of ammonia exiting the second ID fan; and regulating the throttle valve on the basis of ammonia carry-over. 12. The method of claim 8 wherein the step of controlling the rate of ammonia addition includes: monitoring the rate of fuel flow to the burners with the ammonia addition controller; monitoring the composition of the fuel with the ammonia addition controller; and regulating the throttle valve on the basis of the fuel flow rate and the composition of the fuel. 13. The method of claim 8 wherein the step of controlling the rate of ammonia addition includes monitoring the pressure, temperature and flow rate of the ammonia vapor flow in the ammonia vapor pipe. 14. The method of claim 1 wherein the plant also has a boiler and a feed pump circulating feedwater to the boiler, the step of closing the stack prevents the flow of flue gas through the feedwater heating coil, and the method further comprises the step of controlling the flow of the feedwater through the heat exchange segment by regulating the speed of the feed pump with a pump speed controller. 15. The method of claim 14 wherein the step of controlling the flow of feedwater comprises the sub-steps of: monitoring the pressure of the feedwater in the feed line with the pump speed controller; monitoring the temperature of the feedwater in the feed line with the pump speed controller; monitoring the pressure of the feedwater in the return line with the pump speed controller; monitoring the temperature of the feedwater in the return line with the pump speed controller; and regulating the feed pump on the basis of the feedwater temperature and pressure in the feed and return lines. 16. The method of claim 1 further comprising the step of monitoring the temperature of the flue gas in the SCR segment and the second ID fan. 17. A method for removing NOX from flue gas with an emission treatment system, the flue gas being generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the stack including a first ID fan disposed therein, the flue gas being discharged through an outlet end of the stack, the emission treatment system including a major component module, inlet ductwork, outlet ductwork, and an ammonia addition subsystem, the major component module having an SCR segment, a heat exchanger segment, and a second ID fan, the SCR segment having at least one catalyst unit composed of materials for selectively catalyzing NOX, the ammonia addition subsystem being in fluid communication with the inlet ductwork, the method comprising the following steps: attaching the inlet ductwork to the stack at a first position intermediate the inlet end of the stack and the first ID fan; attaching the outlet ductwork to the stack at a second position intermediate the first ID fan and the outlet of the stack; closing the stack at a third position intermediate the first and second positions to prevent the flow of flue gas through the first ID fan; drawing the flue gas from the stack through the inlet ductwork and through the major component module with the second ID fan; injecting ammonia vapor into the inlet ductwork with the ammonia addition subsystem; removing the NOX from the flue gas with the SCR segment of the major component module to produce a clean flue gas; and discharging the clean flue gas through the outlet ductwork to the stack with the second ID fan. 18. The method of claim 17, wherein the plant also has a boiler and a feed pump circulating feedwater to the boiler through a feedwater heating coil disposed in the stack, the step of closing the stack prevents the flow of flue gas through the feedwater heating coil, and the method further comprises the step of controlling the flow of the feedwater through the heat exchange segment by regulating the speed of the feed pump with a pump speed controller. 19. A method for removing NOX from flue gas with an emission treatment system, the flue gas being generated by a plant having one or more burners located at an inlet end of a vertically extending stack, the stack including a first ID fan and a feedwater heating coil disposed therein, the flue gas being discharged through an outlet end of the stack, the plant also having a boiler and a feed pump circulating feedwater to the boiler, the emission treatment system including a major component module, inlet ductwork, outlet ductwork, and an ammonia addition subsystem, the major component module having an SCR segment, a heat exchanger segment, and a second ID fan, the SCR segment having at least one catalyst unit composed of materials for selectively catalyzing NOX, the heat exchanger segment having feedwater feed and return lines, the ammonia addition subsystem having a source of ammonia vapor, an ammonia injection grid disposed in the inlet ductwork, an ammonia vapor pipe providing fluid communication between the source of ammonia vapor and the ammonia injection grid, and a throttle valve disposed in the ammonia vapor pipe, the method comprising the following steps: attaching the inlet ductwork to the stack at a first position intermediate the inlet end of the stack and the first ID fan; attaching the outlet ductwork to the stack at a second position intermediate the first ID fan and the outlet of the stack; closing the stack at a third position intermediate the first and second positions to prevent the flow of flue gas through the first ID fan and the feedwater heating coil; drawing the flue gas from the stack through the inlet ductwork and through the major component module with the second ID fan; injecting ammonia vapor into the inlet ductwork with the ammonia addition subsystem; removing the NOX from the flue gas with the SCR segment of the major component module to produce a clean flue gas; discharging the clean flue gas through the outlet ductwork to the stack with the second ID fan; controlling the flow rate of the flue gas through the major component module by regulating the pressure decrease across the second ID fan; controlling the rate of ammonia addition by regulating the throttle valve; and controlling the flow of the feedwater through the heat exchange segment by regulating the speed of the feed pump.