Integral waterwall external heat exchangers

Abstract

A combustion system having a combustor that includes tubing for carrying boiler water, a cyclone to recover solids from exhaust of the combustor and an external heat exchanger to recover heat from the solids, includes: a bypass for providing boiler water from the combustor to tube bundles of the external heat exchanger and a boiler water return for providing boiler water from the tube bundles to waterwall tubing of the combustor. A method and an external heat exchanger are also provided.

1 . A combustion system including a combustor comprising tubing to carry boiler water, a cyclone to recover solids from exhaust of the combustor and an external heat exchanger to recover heat from the solids, the system comprising:
 a bypass for providing boiler water from the combustor to a tube bundle of the external heat exchanger and a boiler water return for providing boiler water from the tube bundle to waterwall tubing of the combustor.   
   
   
       2 . The system as in  claim 1 , wherein the bypass comprises at least one of waterwall tubing and an inlet header. 
   
   
       3 . The system as in  claim 1 , wherein the bypass comprises an input for receiving boiler water from a downcomer. 
   
   
       4 . The system as in  claim 1 , wherein the external heat exchanger is adapted for natural circulation. 
   
   
       5 . The system as in  claim 1 , further comprising ash flow controls for controlling heat absorption of an evaporative surface that is external to a combustor. 
   
   
       6 . The system as in  claim 1 , wherein the tube bundles of the external heat exchanger are at least one of horizontal and substantially horizontal. 
   
   
       7 . The system as in  claim 1 , wherein each tube in the tube bundle is coupled to, and in fluid communication with, a waterwall tube of a circulating fluidized bed steam generator to provide the boiler water return. 
   
   
       8 . A method for providing boiler water to a heat exchanger in a combustion system including a combustor comprising tubing for carrying boiler water, a cyclone to recover solids from exhaust of the combustor and an external heat exchanger to recover heat from the solids, the method comprising:
 directing boiler water from the combustor into a bypass; and   providing the boiler water to tube bundles of the external heat exchanger.   
   
   
       9 . The method of  claim 8 , further comprising receiving the boiler water from the tube bundles and directing the boiler water to waterwall tubing of the combustor. 
   
   
       10 . The method as in  claim 8 , wherein providing the boiler water comprises absorbing heat in the boiler water. 
   
   
       11 . The method as in  claim 8 , wherein the directing comprises controlling ash flow over an effective evaporative surface of at least one of the external heat exchanger and the combustor. 
   
   
       12 . The method as in  claim 11 , wherein controlling comprises directing combustor solids. 
   
   
       13 . The method as in  claim 8 , further comprising controlling an air supply to the combustor. 
   
   
       14 . The method as in  claim 8 , wherein the directing comprises directing the boiler water from a lower portion of the combustor. 
   
   
       15 . The method as in  claim 8 , further comprising circulating solids from the cyclone in the heat exchanger. 
   
   
       16 . An external heat exchanger comprising:
 a tube bundle wherein each tube in the tube bundle is coupled to, and in fluid communication with, a waterwall tube of a circulating fluidized bed steam generator.   
   
   
       17 . The external heat exchanger as in  claim 16 , wherein at least a portion of the tube bundles are at least one of horizontal and substantially horizontal.