Boiler producing steam from flue gases with high electrical efficiency and improved slag quality

Abstract

This invention relates to a boiler ( 1 ) drying, igniting and combusting refuse and producing steam ( 2, 2 a ) by heat exchange with flue gases ( 3 ). Said boiler ( 1 ) comprises a reactor ( 16 ) with firing a secondary fuel ( 18 ) for generating a less-corrosive gas flow ( 6 ) and an end superheater ( 8 ) located in the flow ( 6 ) of said less-corrosive gas. Said reactor ( 16 ) could be a sintering reactor, a rotary kiln, a fluidised bed or a spouted bed. This provides for an increased lifetime of the end superheater and makes the boiler provide a high and efficient electrical power output.

1 . A boiler drying, igniting and combusting refuse and producing steam by heat exchange with flue gases, said boiler comprising a reactor with firing a secondary fuel for generating a less-corrosive gas flow and an end superheater located in the flow of said less-corrosive gas, the reactor is a sintering reactor, a rotary kiln, a fluidized bed or a spouted bed. 
   
   
       2 . The boiler according to  claim 1 , wherein said firing with the secondary fuel takes place by means of a burner and/or in the reactor itself. 
   
   
       3 . The boiler according to  claim 1  further comprising a separator element for maintaining separation of said flue gases into streams of said less-corrosive gas flow and a corrosive gas flow, respectively. 
   
   
       4 . The boiler according to  claim 3 , wherein said separator element comprises a plate or a wall. 
   
   
       5 . The boiler according to  claim 1 , wherein a number of said separator elements forms a channel. 
   
   
       6 . The boiler according to  claim 1 , wherein said separator element or channel is adapted to be suspendable on or from the walls of the boiler. 
   
   
       7 . The boiler according to  claim 1 , wherein said less-corrosive gas and corrosive gas are cooled by means of an evaporation wall in the radiation zone and one or more superheaters, which produce steam at between 300 and 450 Celsius. 
   
   
       8 . The boiler according to  claim 1 , wherein said steam is heated in the end superheater. 
   
   
       9 . The boiler according to  claim 1 , wherein said end superheater heats said steam to become steam of an increased temperature, resulting in a temperature increase of between 25 and 200 degrees Celsius as compared to the temperature of said steam. 
   
   
       10 . The boiler according to  claim 1 , wherein the less-corrosive gas is essentially free from Cl, K, Na, Zn, Pb. 
   
   
       11 . The boiler according to  claim 1 , wherein the corrosive gas comprises one or more of Cl, K, Na, Zn and Pb. 
   
   
       12 . The boiler according to  claim 1 , wherein said flue gases are the results of incineration of refuse. 
   
   
       13 . The boiler according to  claim 1  further comprising a blow unit adapted to, by blowing secondary air, effectively mix said less-corrosive gas with said corrosive gas, whereby said mix can be effectively burnt out before it reaches the top zone of the boiler. 
   
   
       14 . The boiler according to  claim 1 , wherein the steam is utilized to produce electricity when said steam is fed into a steam turbine driving a generator. 
   
   
       15 . The boiler according to  claim 1 , wherein the reactor produces final ash and/or slag with low content of leachable trace and heavy metal species, such as a low content of leachable Pb, As, Cd, Cu, Zn, Ni and Zn. 
   
   
       16 . The boiler according to  claim 1 , wherein the secondary fuel is any combination of oil, gas, coal, biomass, air and a selected waste or refuse fraction. 
   
   
       17 . The boiler according to  claim 1 , wherein the secondary fuel is selected to develop flue gases, which are less corrosive than the flue gases from said refuse or waste.