Block heat exchanger assembly for dust-containing flue gases and method of operating the same

Abstract

A method of operating a heat exchanger assembly for combustion devices which operate by using condensing boiler technology and produce dust-containing flue gases, e.g. from the combustion of biomass, reduces the formation of dust deposits in flue gas channels of the heat exchanger. A heat exchanger assembly suitable for operation in the presence of dust-containing flue gases is also provided.

1 . A method of operating a block heat exchanger assembly for a combustion device operating by using condensing boiler technology and producing dust-containing flue gases, the method comprising the following steps: 
 causing flue gas and condensate to flow in countercurrent in a heat exchanger block.    
   
   
       2 . A method of operating a block heat exchanger assembly for a combustion device operating by using condensing boiler technology and producing dust-containing flue gases, the method comprising the following steps: 
 spraying condensate from a neutralization and collection vessel and/or fresh water, continuously or at intervals, into hot flue gas, at or immediately before entry into a heat exchanger block.    
   
   
       3 . A method of operating a block heat exchanger assembly for a combustion device operating by using condensing boiler technology and producing dust-containing flue gases, the method comprising the following steps: 
 causing flue gas and condensate to flow in cocurrent, and spraying condensate from a neutralization and collection vessel and/or fresh water into hot flue gas at or immediately before entry into a heat exchanger block, in an amount causing a flue gas stream to be saturated with water vapor.    
   
   
       4 . The method according to  claim 2 , wherein the heat exchanger block is made of graphite, and clarified condensate is used without neutralization for moistening the flue gases.  
   
   
       5 . The method according to  claim 3 , wherein the heat exchanger block is made of graphite, and clarified condensate is used without neutralization for moistening the flue gases.  
   
   
       6 . A block heat exchanger assembly for a combustion device operating by using condensing boiler technology and producing dust-containing flue gases, the assembly comprising: 
 a heat exchanger block having a flue gas inlet in a flue gas inlet region;    a flue gas line having an entry into said flue gas inlet region of said heat exchanger block;    a neutralization and collection vessel for condensate with overflow;    a nozzle disposed at said flue gas inlet region of said heat exchanger block or at said flue gas line immediately before said entry into said heat exchanger block;    a line connecting said neutralization and collection vessel to said nozzle; and    a pump for conveying the condensate from said neutralization and collection vessel through said line to said nozzle.    
   
   
       7 . A block heat exchanger assembly for a combustion device operating by using condensing boiler technology and producing dust-containing flue gases, the assembly comprising: 
 a heat exchanger block being made of graphite and having a flue gas inlet in a flue gas inlet region;    a flue gas line having an entry into said flue gas inlet region of said heat exchanger block;    a collection vessel for condensate having an overflow connected to a neutralization and purification vessel;    a nozzle disposed at said flue gas inlet region of said heat exchanger block or at said flue gas line immediately before said entry into said heat exchanger block;    a line connecting said collection vessel with said nozzle; and    a pump for conveying the condensate from said collection vessel through said line to said nozzle.    
   
   
       8 . The block heat exchanger assembly according to  claim 6 , wherein said heat exchanger block includes flue gas channels having walls provided with a coating reducing adhesion of dust particles and having a thickness of from 30 to 500 μm, said coating including a fluoropolymer or a dust-repellent paint or varnish.  
   
   
       9 . The block heat exchanger assembly according to  claim 7 , wherein said heat exchanger block includes flue gas channels having walls provided with a coating reducing adhesion of dust particles and having a thickness of from 30 to 500 μm, said coating including a fluoropolymer or a dust-repellent paint or varnish.  
   
   
       10 . The block heat exchanger assembly according to  claim 7 , wherein in the vicinity of said flue gas inlet, said heat exchanger block has flue gas channels formed by grooves defining ridges between said grooves being slanted in direction of said flue gas inlet, causing individual adjacent channels to open into a slit-shaped flue gas inlet opening extending over all of said flue gas channels at said flue gas inlet.  
   
   
       11 . The block heat exchanger assembly according to  claim 7 , wherein said heat exchanger block has plates facing one another, said plates have gas channels, and said plates have ridges defining a gap between at least some of said ridges, for connecting adjacent gas channels to one another through said gap.  
   
   
       12 . The block heat exchanger assembly according to  claim 7 , wherein said heat exchanger block has gas channels and ridges, and said ridges have transverse channels milled into said ridges interconnecting adjacent gas channels.  
   
   
       13 . The block heat exchanger assembly according to  claim 12 , wherein said transverse channels are milled at an angle of between 30 and 75° relative to a direction of gas flow.  
   
   
       14 . The block heat exchanger assembly according to  claim 7 , wherein said heat exchanger block has flue gas channels, and turbulence-inducing fixtures are disposed in said flue gas channels.  
   
   
       15 . The block heat exchanger assembly according to  claim 14 , wherein said turbulence-inducing fixtures are rod-shaped.  
   
   
       16 . The block heat exchanger assembly according to  claim 14 , wherein said turbulence-inducing fixtures are wire matrices each containing a plurality of wire slings deposited in said flue gas channels.  
   
   
       17 . The method according to  claim 1 , which further comprises separating condensate droplets from a flue gas stream leaving the heat exchanger block, with a demister.  
   
   
       18 . The method according to  claim 2 , which further comprises separating condensate droplets from a flue gas stream leaving the heat exchanger block, with a demister.  
   
   
       19 . The method according to  claim 3 , which further comprises separating condensate droplets from a flue gas stream leaving the heat exchanger block, with a demister.  
   
   
       20 . The block heat exchanger assembly according to  claim 6 , which further comprises a demister for separating condensate droplets from a flue gas stream leaving said heat exchanger block.  
   
   
       21 . The block heat exchanger assembly according to  claim 7 , which further comprises a demister for separating condensate droplets from a flue gas stream leaving said heat exchanger block.