Grate assembly

Abstract

A grate assembly for use in a bottom section ( 28 ) of a combustion chamber ( 12 ) of a fluidized bed boiler ( 10 ), comprising: a grate bottom wall ( 32 ); a protective refractory material layer ( 36 ); a plurality of nozzle devices ( 38 ) for supplying fluidizing primary air; at least one grate module ( 40 ) formed on the grate bottom wall ( 32 ). Each grate module ( 40 ) comprises a solids removal opening ( 42 ); a plurality of concentric landings ( 46 ) formed in the refractory material layer ( 36 ) and separated by frontal surfaces ( 48 ) between the landings. Each frontal surface ( 48 ) surrounds one of the landings and follows the shape of the perimeter of a rectangle or a rectangle with at least one shaped corner. The landings ( 46 ) define a stepped structure. Each landing comprises a group of the nozzle devices embedded in the refractory material layer ( 36 ) and adapted to jet the air through one of the frontal surfaces ( 48 ) along one of the landings ( 46 ) that is adjacent to the frontal surface.

1 - 15 . (canceled) 
     
     
         16 . A grate assembly for use in a bottom section of a combustion chamber of a fluidized bed boiler,
 the grate assembly comprising
 a grate bottom wall; 
 an arrangement for supplying fluidizing primary air above the grate bottom wall into the combustion chamber for maintaining combustion of fuel and fluidization of bed material; and 
 at least one grate module; 
 wherein each grate module comprises
 a solids removal opening via which solids are guided downwards through the grate bottom wall; 
 a plurality of concentric landings situated at intervals in a vertical direction and being separated by frontal surfaces between the landings,
 wherein each frontal surface surrounds one of the landings and follows the shape of the perimeter of a rectangle; and 
 wherein the landings define a stepped structure that descends towards the solids removal opening situated in the center of the landings; and 
 
 
   the grate assembly further comprising
 a plurality of cooling tubes of the grate bottom wall and attached to the grate bottom wall; and 
 a protective refractory material layer on the grate bottom wall and covering the plurality of cooling tubes, 
 wherein the at least one grate module is formed on the grate bottom wall and each one of the plurality of concentric landings is formed in the refractory material layer; 
 wherein the solids removal opening is in the refractory material layer to guide the solids on the refractory material layer downwards through the refractory material layer and the grate bottom; 
 wherein the arrangement for supplying fluidizing primary air includes a plurality of nozzle devices for supplying fluidizing primary air above the grate bottom wall and the protective refractory material layer into the combustion chamber; and 
 wherein each landing comprises a group of nozzle devices belonging to the plurality of nozzle devices and being embedded in the refractory material layer, the group of nozzle devices being adapted to jet the air through one of the frontal surfaces along one of the landings that is adjacent to the frontal surface. 
   
     
     
         17 . The grate assembly according to  claim 16 , wherein the rectangle has at least one shaped corner, and wherein the at least one shaped corner includes a chamfer, multiple chamfers, a step, multiple steps, a shape extending inwards the rectangle, and/or a shape extending outwards the rectangle. 
     
     
         18 . The grate assembly according to  claim 16 , wherein the landings extend horizontally and the nozzle devices are adapted to jet the air in horizontal directions. 
     
     
         19 . The grate assembly according to  claim 16 , wherein each frontal surface is formed by surfaces of the group of nozzle devices, or by the refractory material layer, or by both the surfaces and the refractory material layer. 
     
     
         20 . The grate assembly according to  claim 18 , wherein each frontal surface is formed by surfaces of the group of nozzle devices, or by the refractory material layer, or by both the surfaces and the refractory material layer. 
     
     
         21 . The grate assembly according to  claim 16 , wherein the grate bottom wall extends horizontally and the plurality of cooling tubes are parallel, extend horizontally, and are attached to the grate bottom wall at intervals along the grate bottom wall. 
     
     
         22 . The grate assembly according to  claim 16 , wherein each landing comprises a first, second, third and fourth row of nozzle devices aligned in a row and belonging to the group of nozzle devices and being arranged horizontally in such a way that the first and second rows are parallel and are situated on opposite sides of the landing, and that the third and fourth rows are parallel, are situated on opposite sides of the landing, and are perpendicular to the first and second rows. 
     
     
         23 . The grate assembly according to  claim 18 , wherein each landing comprises a first, second, third and fourth row of nozzle devices aligned in a row and belonging to the group of nozzle devices and being arranged horizontally in such a way that the first and second rows are parallel and are situated on opposite sides of the landing, and that the third and fourth rows are parallel, are situated on opposite sides of the landing, and are perpendicular to the first and second rows. 
     
     
         24 . The grate assembly according to  claim 22 , wherein each nozzle device in each row is adapted to jet the air in a horizontal direction perpendicular to the opposite row towards the opposite row along the landing. 
     
     
         25 . The grate assembly according to  claim 16 , wherein each frontal surface comprises four corners constituting the corners of the rectangle, each corner having at least one nozzle device belonging to the group of nozzle devices and being between two of the rows of nozzle devices that are perpendicular to each other, and the at least one nozzle device is adapted to jet the air at an angle in a horizontal direction towards the solids removal opening or the one of the four corners that is situated diagonally opposite. 
     
     
         26 . The grate assembly according to  claim 16 , wherein the grate assembly further comprises at least one air plenum chamber for receiving the air to be supplied via the plurality of nozzle devices as the fluidizing primary air, wherein the at least one air plenum chamber is situated below the grate bottom wall. 
     
     
         27 . The grate assembly according to  claim 16 , wherein the grate assembly further comprises on at least one side of at least one of the grate modules an additional landing formed in the refractory material layer, the additional landing forming an extension to the stepped structure of the grate module,
 the additional landing is separated from the uppermost landing of the grate module or another additional landing by an additional frontal surface between them;   wherein the additional landing comprises a group of additional nozzle devices being embedded in the refractory material layer, the group of additional nozzle devices being adapted to jet the air through one of the additional frontal surfaces along the uppermost landing or the other additional landing that is adjacent to the additional frontal surface.   
     
     
         28 . The grate assembly according to  claim 27 , wherein the additional landing comprises an additional row of additional nozzle devices aligned in a row and belonging to the group of additional nozzle devices and being arranged horizontally in such a way that the additional row is parallel to the first and second rows or the third and fourth rows. 
     
     
         29 . The grate assembly according to  claim 27 , wherein the additional landing extends rectilinearly along one side of at least two of the grate modules that are adjacent. 
     
     
         30 . The grate assembly according to  claim 29 , wherein the additional landing comprises an additional row of additional nozzle devices aligned in a row and belonging to the group of additional nozzle devices and being arranged horizontally in such a way that the additional row is parallel to the first and second rows or the third and fourth rows. 
     
     
         31 . The grate assembly according to  claim 28 , wherein the additional landing comprises at one or both ends of the additional row at least one additional nozzle device belonging to the group of additional nozzle devices and adapted to jet the air at an angle in a horizontal direction towards the solids removal opening. 
     
     
         32 . The grate assembly according to  claim 22 , wherein two or more nozzle devices belonging to the plurality of nozzle devices and being situated on different landings are aligned in a row along a direction perpendicular to the first and second rows or the third and fourth rows. 
     
     
         33 . A fluidized bed boiler for use in steam production and having a combustion chamber with a bottom section comprising the grate assembly according to  claim 16 .