Method and system of recovering the heat wasted from the steam boilers continuous blow down to preheat the boiler combustion air

Abstract

Heat from continuous blow down from a steam boiler is used to preheat boiler combustion air. Blow down from the steam boiler is fed through a flash tank and a 3-way valve to a liquid heat exchanger to heat a circulating liquid. The hot circulating liquid is fed to a preheat coil to heat combustion air for a steam boiler. A 3-way valve located between the flash tank and heat exchanger controls the flow of blow down to the heat exchanger. A temperature sensor which monitors the temperature of the circulating liquid controls the 3-way valve and a circulating pump moves the liquid around a closed loop. Motorized or variable frequency drive damper control the flow of air to the preheat coil and to the combustion air blower of the steam boiler.

1 . A system for heating combustion air before the combustion air is received by a steam boiler comprising:
 a flash tank coupled to receive blow down from the steam boiler;   a heat exchanger coupled to receive blow down from said flash tank, the said heat exchanger will recover the heat from blow down, and transfer the heat to a liquid and a circulating pump who moves the liquid between the heat exchanger and preheat coil, a preheat coil coupled to receive said circulating liquid and combustion air to transfer heat from the circulating liquid to the combustion air.   
     
     
         2 . The system of  claim 1  wherein said heat exchanger is a liquid-to-liquid heat exchanger. 
     
     
         3 . The system of  claim 2  further comprising:
 a first damper positioned to modulate the flow of combustion air from said preheat coil.   
     
     
         4 . The system of  claim 3  wherein said first damper is located downstream of the combustion air blower. 
     
     
         5 . The system of  claim 4  further comprising:
 a second damper located to modulate combustion air to the preheat coil.   
     
     
         6 . The system of  claim 5  further comprising:
 a circulating pump coupled to urge the circulating liquid to move along a closed loop.   
     
     
         7 . The system of  claim 6  further comprising:
 a control valve located between said flash tank and said heat exchanger to control the flow of blow down to said heat exchanger.   
     
     
         8 . The system of  claim 7  further comprising:
 a temperature sensor coupled to selectively operate said control valve to control the flow of blow down to the heat exchanger as the temperature of the circulating liquid changes.   
     
     
         9 . The system of  claim 8  wherein said control valve is a 3-way valve. 
     
     
         10 . The system of  claim 9  wherein said 3-way valve prevents blow down from reaching said heat exchanger when the temperature of the circulating liquid reaches a predetermined temperature. 
     
     
         11 . The method of heating combustion air before the combustion air is received by a combustion air blower of a steam boiler comprising:
 coupling a flash tank to the steam boiler to receive blow down;   coupling a heat exchanger to receive blow down from said flash tank and a circulating liquid to transfer heat from said blow down to the circulating liquid; and   feeding said circulating liquid to a preheat coil to transfer heat from the circulating liquid to combustion air going to a combustion air blower.   
     
     
         12 . The method of  claim 11  wherein said heat exchanger is a liquid-to-liquid heat exchanger. 
     
     
         13 . The method of  claim 12  further comprising:
 providing a first damper to modulate the flow of combustion air from said preheat coil.   
     
     
         14 . The method of  claim 13  wherein said first damper is located downstream of the combustion air blower. 
     
     
         15 . The method of  claim 14  further comprising:
 positioning a second damper to modulate combustion air to the preheat coil.   
     
     
         16 . The method of  claim 15  further comprising:
 using a circulating pump to move the circulating liquid along a closed loop.   
     
     
         17 . The method of  claim 16  further comprising:
 locating a control valve between said flash tank and said heat exchanger to control the flow of blow down to said heat exchanger.   
     
     
         18 . The method of  claim 17  further comprising:
 connecting a temperature sensor to selectively operate said control valve to control the flow of blow down to the heat exchanger as the temperature of the circulating fluid changes.   
     
     
         19 . The method of  claim 18  wherein said control valve is a 3-way valve. 
     
     
         20 . The method of  claim 19  wherein said 3-way valve prevents blow down from reaching said heat exchanger when the temperature of the circulating liquid reaches a predetermined temperature.