Control of blowdown in steam boilers

Abstract

Blowdown of a pressurised steam boiler heated by a burner 1 and including a blowdown flow control valve 17 is controlled by opening the control valve in response to receiving a control signal from a control unit 20 to allow water to leave the boiler. The control unit receives one or more signals indicative of the steam production rate of the boiler and adjusts the amount of blowdown in dependence upon the aggregate steam production.

1 . A method of controlling blowdown of a steam boiler heated by a burner, the boiler comprising a blowdown flow control valve configured to open in response to receiving a control signal from a control unit to allow water to leave the boiler; wherein the control unit receives one or more signals indicative of the steam production rate of the boiler and adjusts the amount of blowdown in dependence upon aggregate steam production of the boiler. 
     
     
         2 . A method according to  claim 1 , wherein the control unit opens and closes the control valve a multiplicity of times over a time period, causing a multiplicity of blowdown operations, and, in order to adjust the amount of blowdown, the control unit adjusts the amount of water blown down from the boiler in each blowdown operation. 
     
     
         3 . A method according to  claim 2 , wherein the control unit adjusts the amount of water blown down from the boiler in each blowdown operation by adjusting the time for which the control valve is open during each blowdown operation. 
     
     
         4 . A method according to  claim 3 , wherein time for which the control valve is open during each blowdown operation is adjusted downwardly approximately in proportion to a reduction in the aggregate steam production. 
     
     
         5 . A method according to  claim 1 , further including an initial step of setting a blowdown amount for a given steam production rate of the boiler, the control unit thereafter adjusting the amount of blowdown according to a comparison of an actual steam production amount of the boiler with a steam production amount that would apply for a given steam production rate. 
     
     
         6 . A method according to  claim 5 , wherein the given steam production rate of the boiler is a maximum continuous rate steam production of the boiler. 
     
     
         7 . A method according to  claim 5 , wherein the initial setting step is carried out during commissioning of the boiler. 
     
     
         8 . A steam boiler comprising:
 a boiler housing for containing water in the boiler;   a burner for heating water in the boiler and converting the water into steam,   a blowdown control valve that is openable to allow water to leave the boiler in a blowdown operation, and   a control unit for controlling opening of the blowdown control valve, the control unit being connected to receive one or more signals indicative of a steam production rate of the boiler and to adjust the amount of blowdown in dependence upon aggregate steam production of the boiler.   
     
     
         9 . A boiler according to  claim 8 , wherein the control unit is arranged to open and close the control valve a multiplicity of times over a time period, causing a multiplicity of blowdown operations, and, in order to adjust the amount of blowdown, the control unit is arranged to adjust the amount of water blown down from the boiler in each blowdown operation. 
     
     
         10 . A boiler according to  claim 9 , wherein the control unit is arranged to adjust the amount of water blown down from the boiler in each blowdown operation by adjusting time for which the control valve is open during each blowdown operation. 
     
     
         11 . A boiler according to  claim 8 , wherein the control unit further includes a store arranged to store pairs of values of air and fuel valve settings at various firing rates of the burner and the control device is arranged, when a firing rate of the burner is to be changed, to control the air and fuel valve settings in dependence upon stored air and fuel valve settings.