Feedwater preheating system and method

Abstract

The feedwater preheating system includes a feedwater tank and a constant volume recirculation pump. The feedwater tank is adapted to store the feedwater. The feedwater tank includes feed and return lines. The feed line is adapted to feed the feedwater to the HRSG, and the return line enables returning of the feedwater into the feedwater tank. The return line precludes a control valve, and is configured to the feedwater tank to reduce component loss while feedwater recirculation. The constant volume recirculation pump is configured in the feed line to recirculate the feedwater between the HRSG and the feedwater tank. The pump is capable of recirculating the feedwater at constant speed and volume to reduce heat loss while feedwater recirculation, as against the prior art feedwater preheating systems.

What is claimed is: 
     
         1 . A feedwater preheating system for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the feedwater preheating system, comprising:
 a feedwater tank to store the feedwater, the feedwater tank having a feed line to feed the feedwater to the HRSG, and a return line to enable returning of the feedwater into the feedwater tank, wherein the return line precludes a control valve and is configured to the feedwater tank to reduce component loss while feedwater recirculation; and   a constant volume recirculation pump configured in the feed line to recirculate the feedwater between the HRSG and the feedwater tank, wherein the constant volume recirculation pump is capable of recirculating the feedwater at constant speed and volume to reduce heat loss while feedwater recirculation, thereby increasing efficiency of the HRSG.   
     
     
         2 . The feedwater preheating system as claimed in  claim 1 , wherein the feedwater is maintained at or above a minimum set temperature. 
     
     
         3 . The feedwater preheating system as claimed in  claim 2 , further comprising a pegging steam source line configured to the feedwater tank to supply pegging steam to preheat the feedwater as and when the temperature of the feedwater in the feedwater tank reaches below the minimum set temperature. 
     
     
         4 . The feedwater preheating system as claimed in  claim 3 , further comprising a control valve configured in the pegging steam source line to close and open the pegging steam source line to supply the pegging steam. 
     
     
         5 . The feedwater preheating system as claimed in  claim 4 , further comprising a temperature control circuit configured to the control valve of the pegging steam source line and to the feedwater tank, to send signals to open and close the control valve based on the temperature of the feedwater tank in order to maintain the minimum set temperature of the feedwater. 
     
     
         6 . The feedwater preheating system as claimed in  claim 1 , wherein the feedwater is maintained at a temperature, a required minimum temperature, as required by the HRSG. 
     
     
         7 . The feedwater preheating system as claimed in  claim 6  further comprising a pegging steam source line configured to the feedwater tank to supply pegging steam to preheat the feedwater as and when the temperature of the feedwater in the feedwater tank reaches below the required minimum temperature. 
     
     
         8 . The feedwater preheating system as claimed in  claim 7  further comprising a Continuous Emission Monitoring System (CEMS) circuit configured to the pegging steam source line and to the HRSG to enable calculation of the required minimum temperature, based on parameters of the HRSG, at which the feedwater is required to be kept for recirculation in the HRSG, to enable the pegging steam source line to supply the pegging steam in the feedwater tank to reheat the feedwater to the required minimum temperature calculated by the CEMS circuit. 
     
     
         9 . The feedwater preheating system as claimed in  claim 8 , further comprising a control valve configured in the pegging steam source line to close and open the pegging steam source line to supply the pegging steam. 
     
     
         10 . The feedwater preheating system as claimed in  claim 9 , further comprising a temperature control circuit configured to the control valve of the pegging steam source line and to the feedwater tank, to send signals to open and close the control valve based on the temperature of the feedwater tank in order to maintain the required minimum temperature of the feedwater. 
     
     
         11 . A feedwater preheating system for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the feedwater preheating system, comprising:
 a feedwater tank to store the feedwater, the feedwater tank having a feed line to feed the feedwater to the HRSG, and a return line to enable returning of the feedwater into the feedwater tank, wherein the return line precludes a control valve and is configured to the feedwater tank; and   a constant volume recirculation pump configured in the feed line to recirculate the feedwater between the HRSG and the feedwater tank, wherein the constant volume recirculation pump is capable of recirculating the feedwater at constant speed and volume to reduce heat loss while feedwater recirculation, and maintain a minimum set temperature of the feedwater.   
     
     
         12 . The feedwater preheating system as claimed in  claim 11 , further comprising a pegging steam source line configured to feedwater tank to supply pegging steam to preheat the feedwater as and when the temperature of the feedwater in the feedwater tank  110  reaches below the minimum set temperature. 
     
     
         13 . The feedwater preheating system as claimed in  claim 12 , further comprising a control valve configured in the pegging steam source line to close and open the pegging steam source line to supply the pegging steam. 
     
     
         14 . The feedwater preheating system as claimed in  claim 13 , further comprising a temperature control circuit configured to the control valve of the pegging steam source line and to the feedwater tank, to send signals to open and close the control valve based on the temperature of the feedwater tank in order to maintain the minimum set temperature of the feedwater. 
     
     
         15 . A feedwater preheating system for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the feedwater preheating system, comprising:
 a feedwater tank to store the feedwater, the feedwater tank having a feed line to feed the feedwater to the HRSG, and a return line to enable returning of the feedwater into the feedwater tank, wherein the return line precludes a control valve and is configured to the feedwater tank;   a constant volume recirculation pump configured in the feed line to recirculate the feedwater between the HRSG and the feedwater tank, wherein the constant volume recirculation pump is capable of recirculating the feedwater at constant speed and volume to reduce heat loss while feedwater recirculation;   a pegging steam source line configured to feedwater tank to supply pegging steam to preheat the feedwater; and   a Continuous Emission Monitoring System (CEMS) circuit configured to the pegging steam source line and to the HRSG,
 to enable calculation of a required minimum temperature at which the feedwater is required to be kept for recirculation in the HRSG, based on parameters of the HRSG, and 
 to enable the pegging steam source line to supply the pegging steam in the feedwater tank to reheat the feedwater to the required minimum temperature calculated by the CEMS circuit. 
   
     
     
         16 . The feedwater preheating system as claimed in  claim 15 , further comprising a control valve configured in the pegging steam source line to close and open the pegging steam source line to supply the pegging steam as and when the temperature of the feedwater in the feedwater tank reaches below the required minimum temperature. 
     
     
         17 . The feedwater preheating system as claimed in  claim 16 , further comprising a temperature control circuit configured to the control valve of the pegging steam source line and to the feedwater tank, to send signals to open and close the control valve based on the temperature of the feedwater tank in order to maintain the required minimum temperature of the feedwater. 
     
     
         18 . A feedwater preheating system for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the feedwater preheating system, comprising:
 a feedwater tank to store the feedwater, the feedwater tank having a feed line to feed the feedwater to the HRSG, and a return line to enable returning of the feedwater into the feedwater tank, wherein the return line precludes a control valve and is configured to the feedwater tank;   a constant volume recirculation pump configured in the feed line to recirculate the feedwater between the HRSG and the feedwater tank, wherein the constant volume recirculation pump is capable of recirculating the feedwater at constant speed and volume to reduce heat loss while feedwater recirculation; and   a pressure control means configured to a steam turbine inlet at an evaporator of the HRSG to increase an operational pressure of steam in the evaporator to shift heat to the feed line to increase heat gain in the feedwater and maintain a minimum set temperature of the feedwater, thereby increasing the efficiency of the HRSG.   
     
     
         19 . The feedwater preheating system as claimed in  claim 18 , further comprising a temperature control circuit configured to the pressure control means of the evaporator and to the feedwater tank, to send signals to increase or decrease the operational pressure of the steam in the evaporator based on the temperature of the feedwater tank in order to maintain the minimum set temperature of the feedwater. 
     
     
         20 . A method for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the method comprising:
 circulating the feedwater in a feed line and a return line of a feedwater tank at constant speed and volume to reduce heat loss while feedwater recirculation to maintain a minimum set temperature of the feedwater, wherein the return line precludes a control valve and is configured to the feedwater tank to reduce component loss while feedwater recirculation, thereby increasing the efficiency of the HRSG.   
     
     
         21 . The method as claimed in  claim 20 , further comprising supplying pegging steam to preheat the feedwater as and when the temperature of the feedwater reaches below the minimum set temperature. 
     
     
         22 . A method for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the method comprising:
 circulating the feedwater in a feed line and a return line of a feedwater tank at constant speed and volume to reduce heat loss while feedwater recirculation, wherein the return line precludes a control valve and is configured to the feedwater tank to reduce component loss while feedwater recirculation;   calculating a required set temperature of the HRSG at a last stage; and   supplying pegging steam to preheat the feedwater in the feedwater tank as and when the temperature of the feedwater reaches below the required minimum temperature.   
     
     
         23 . A method for preheating feedwater to be fed into a Heat Recovery Steam Generator (HRSG), the method comprising:
 circulating the feedwater in a feed line and a return line of a feedwater tank at constant speed and volume to reduce heat loss while feedwater recirculation, wherein the return line precludes a control valve and is configured to the feedwater tank to reduce component loss while feedwater recirculation; and   increasing an operational pressure of steam in an evaporator of the HRSG to shift heat to the feed line to increase heat gain in the feedwater and maintain a minimum set temperature of the feedwater, thereby increasing the efficiency of the HRSG.