Method of and Arrangement for Feeding Fuel Into a Circulating Fluidized Bed Boiler

Abstract

A method of feeding at least one of light, fine, volatile and moist fuel into a furnace of a circulating fluidized bed boiler. Fuel is introduced into the furnace and is combusted in the presence of a fluidized bed material to form flue gases. The fluidized bed material is circulated both inside the furnace in an internal circulation in which bed material returns along walls of the furnace down to the bottom of the furnace, and outside the furnace in an external circulation that includes at least a solids separator arranged in flow communication with the furnace. Bed material is separated from the flue gases in the separator. The flue gases are removed from the separator for further treatment. The separated bed material is returned to the furnace. Circulating bed material from at least the internal circulation flowing down along the furnace walls to a return flow is collected, and the return flow is introduced in a consolidated form into communication with the fuel being introduced in the furnace, so that the bed material return flow and the fuel flow are mixed together and flow downwards in the furnace. This increases the residence time of the fuel in the furnace.

1 - 20 . (canceled) 
     
     
         21 . A method of feeding at least one of light, fine, volatile and moist fuel into a furnace of a circulating fluidized bed boiler, the method comprising:
 introducing a fuel flow into a furnace of a circulating fluidized bed boiler, the fuel flow being selected from at least one of light, fine, volatile and moist fuel;   combusting the fuel in the presence of a fluidized bed material in the furnace of the boiler to form flue gases;   circulating the fluidized bed material both inside the furnace in an internal circulation, in which bed material returns along walls of the furnace down to the bottom of the furnace, and outside the furnace in an external circulation that includes at least a solids separator arranged in flow communication with the furnace;   separating bed material from the flue gases in the separator;   removing the flue gases from the separator for further treatment;   returning the separated bed material to the furnace;   collecting circulating bed material from at least the internal circulation flowing down along the furnace walls to a return flow; and   introducing the return flow in consolidated form into communication with the fuel being introduced in the furnace, so that the bed material return flow and the fuel flow are mixed together and flow downwards in the furnace, in order to increase the residence time of the fuel in the furnace.   
     
     
         22 . The method as recited in  claim 21 , further comprising introducing the return flow on top of the fuel flow, while the fuel is being introduced in the furnace. 
     
     
         23 . The method as recited in  claim 22 , further comprising guiding the return flow to cover the fuel flow being introduced into the furnace. 
     
     
         24 . The method as recited in  claim 21 , further comprising directing the fuel flow being introduced into the furnace down towards the bottom of the furnace. 
     
     
         25 . The method as recited in  claim 21 , further comprising taking a portion of the solids from the external circulation outside of the furnace to be introduced into communication with the fuel about to be introduced into the furnace. 
     
     
         26 . The method as recited in  claim 21 , further comprising taking a portion of the solids from the internal circulation to be introduced into communication with the fuel about to be introduced into the furnace. 
     
     
         27 . The method as recited in  claim 21 , further comprising arranging a collector on or in the wall of the furnace to collect the return flow, and for introducing the collected return flow on top of the fuel flow. 
     
     
         28 . An arrangement for feeding at least one of light, fine, volatile and moist fuel into a furnace of a circulating fluidized bed boiler, the boiler comprising:
 a furnace delimited at least by a grid at the bottom of the boiler, side walls, and a roof;   a solids separator arranged in flow communication with an upper portion of the furnace;   at least one air feed for providing the furnace with primary and secondary air;   a return for returning the solids separated from the flue gases in the separator into the furnace;   a feed for feeding fuel into the furnace, the fuel being selected from at least one of light, fine, volatile and moist fuel; and   a conduit for introducing in consolidated form at least solids circulating inside the furnace and flowing down along the furnace walls into communication with the fuel to force the fuel flow down towards the grid in order to increase the residence time of the fuel in the furnace.   
     
     
         29 . The arrangement as recited in  claim 28 , wherein the feed for feeding fuel into the furnace comprises a fuel feed opening in the wall of the furnace, and the conduit for introducing solids into communication with the fuel are arranged substantially above the feed opening. 
     
     
         30 . The arrangement as recited in  claim 29 , wherein the conduit for introducing solids into communication with the fuel comprises a channel arranged in or on the wall of the furnace above the fuel feed opening. 
     
     
         31 . The arrangement as recited in  claim 30 , wherein the channel is arranged in flow communication with one of a fluidized bed heat exchange chamber and the solids separator. 
     
     
         32 . The arrangement as recited in  claim 30 , wherein the channel has side walls, and the side walls are inclined for collecting solids flowing down along the furnace side walls. 
     
     
         33 . The arrangement as recited in  claim 29 , wherein the conduit for introducing solids into communication with the fuel comprises inclined guide plates arranged on the wall of the furnace above the fuel feed opening for collecting solids flowing down along the wall and for introducing such on top of the fuel feed. 
     
     
         34 . The arrangement as recited in  claim 29 , wherein the conduit for introducing solids into communication with the fuel comprises an opening substantially above the fuel feed opening in the wall of the furnace. 
     
     
         35 . The arrangement as recited in  claim 29 , wherein the feed for feeding fuel into the furnace comprises, in addition to the fuel feed opening, a cover arranged above the fuel feed opening to direct the fuel entering the furnace through the opening down towards the grid of the furnace. 
     
     
         36 . The arrangement as recited in  claim 35 , wherein the conduit for introducing solids into communication with the fuel comprises at least one guide plate being arranged in connection with the cover. 
     
     
         37 . The arrangement as recited in  claim 28 , wherein the fluidized bed heat exchanger is arranged one of (i) adjacent to an upper portion of the furnace, (ii) adjacent to a converging bottom portion of the furnace, and (iii) in connection with the separator. 
     
     
         38 . The arrangement as recited in  claim 28 , wherein the conduit for introducing solids into communication with the fuel comprises an opening in the inclined walls of the furnace for taking some solids flowing down along the furnace wall out of the furnace, a conduit outside of the furnace in flow communication, at one end thereof, with the opening, and, at the opposite end thereof, with the fuel feed. 
     
     
         39 . The arrangement as recited in  claim 28 , further comprising a loop-seal type control arranged in the conduit outside of the furnace for controlling the solids flow out of the furnace.