Fluidized bed furnace and waste treatment method

Abstract

A waste treatment technique includes: blowing a fluidizing gas from around a mixture discharge port to form a first fluidization region having a degree of fluidization of the fluidizable particles which is set to an extent allowing waste to be accumulated on fluidizable particles, while blowing a fluidizing gas between the first fluidization region and an opposite-side wall at a higher flow velocity to form a second fluid region having a degree of fluidization of fluidizable particles greater than that in the first fluidization region, whereby the fluidizable particles are mixed with the waste to gasify the waste; and supplying waste from a supply-side sidewall portion onto the fluidized bed to cause the waste to be accumulated on the first fluidization region while causing the accumulated waste to be moved into the second fluidization region step-by-step.

1 . A fluidized bed furnace for heating waste to extract a combustible gas from the waste, comprising:
 fluidizable particles making up a fluidized bed to heat the waste;   a furnace body having a bottom wall supporting the fluidizable particles from therebelow, and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a mixture discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste and carbides produced by heating of the waste, together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the mixture discharge port so as to cause the fluidizable particles to fall on the upper surface of the bottom wall toward the mixture discharge port;   a gas supply section for blowing a fluidizing gas from the bottom wall of the furnace body toward the fluidizable particles to fluidize the fluidizable particles;   a waste supply section for supplying waste from a supply-side portion of the sidewall located on the same side as the mixture discharge port with respect to the center position of the bottom wall, to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste on the fluidized bed to be moved toward an opposite-side portion of the sidewall on a side opposite to the mixture discharge port across the center position of the bottom wall,   wherein:   the gas supply section is adapted to blow the fluidizing gas from around the mixture discharge port to form a first fluidization region having a degree of fluidization of the fluidizable particles which is set to an extent allowing waste to be accumulated on the fluidizable particles, while blowing the fluidizing gas between the first fluidization region and the opposite-side sidewall portion at a flow velocity greater than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles greater than that in the first fluidization region, whereby the fluidizable particles are moved in a convection-like pattern and mixed with the waste to gasify the waste; and   the waste supply section is adapted to supply waste from the supply-side sidewall portion to the fluidized bed to cause the waste to be accumulated on the first fluidization region while causing the accumulated waste to be moved into the second fluidization region step-by-step.   
     
     
         2 . The fluidized bed furnace as defined in  claim 1 , wherein the waste supply section is adapted to push new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the first fluidization region, thereby causing the waste accumulated on the first fluidization region to be moved into the second fluidization region step-by-step. 
     
     
         3 . The fluidized bed furnace as defined in  claim 1 , which comprises a carbide introduction device for separating the carbides from a mixture of the non-combustible substances, the carbides and the fluidizable particles discharged from the mixture discharge port, and returning the separated carbides to the fluidized bed from the side of the opposite-side sidewall portion. 
     
     
         4 . The fluidized bed furnace as defined in  claim 1 , wherein the gas supply section is adapted to blow the fluidizing gas in the first fluidization region at a flow velocity satisfying a condition that U o /U mf  ranges from 1 to less than 2, and blow the fluidizing gas in the second fluidization region at a flow velocity satisfying a condition that U o /U mf  ranges from 2 to less than 5, where U mf  is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown enough to fluidize the fluidizable particles, and U o  is a cross-sectional average flow velocity of the fluidizing gas. 
     
     
         5 . The fluidized bed furnace as defined in  claim 1 , which comprises a sand circulation device for separating the fluidizable particles from a mixture of the non-combustible substances, the carbides and the fluidizable particles, the mixture discharged from the mixture discharge port, and returning the separated fluidizable particles to the furnace body. 
     
     
         6 . The fluidized bed furnace as defined in  claim 5 , wherein the sand circulation device is adapted to return the fluidizable particles separated from the mixture onto the waste accumulated on the first fluidization region. 
     
     
         7 . The fluidized bed furnace as defined in  claim 1 , wherein the furnace body has a shape in plan view, in which a dimension in a width direction perpendicular to a pushing direction along which waste is pushed by the waste supply section is equalized in the pushing direction. 
     
     
         8 . The fluidized bed furnace as defined in  claim 7 , wherein the waste supply section comprises a pusher having a pushing surface extending in the width direction, and a drive unit for reciprocatingly moving the pusher in a direction parallel to the pushing direction to allow the pushing surface of the pusher to push waste onto the fluidized bed simultaneously by the entire widthwise region of the pushing surface. 
     
     
         9 . A waste treatment method for heating waste to extract a combustible gas from the waste, comprising:
 a preparation step of preparing a fluidized bed furnace comprising fluidizable particles making up a fluidized bed to heat the waste, a furnace body having a bottom wall supporting the fluidizable particles from therebelow and a sidewall standing upwardly from the bottom wall, wherein the bottom wall has a mixture discharge port provided at a position offset from a center position of the bottom wall in a specific direction to discharge non-combustible substances in the waste and carbides produced by heating of the waste, together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the mixture discharge port so as to cause the fluidizable particles to fall on the upper surface of the bottom wall toward the mixture discharge port;   a fluidization-region formation step of blowing a fluidizing gas from a region of the bottom wall of the furnace body around the mixture discharge port toward the fluidizable particles to form a first fluidization region having a degree of fluidization of the fluidizable particles which is set to an extent allowing waste to be accumulated on the fluidizable particles, while blowing the fluidizing gas between the first fluidization region and an opposite-side portion of the sidewall on a side opposite to the mixture discharge port across the center position of the bottom wall, at a flow velocity greater than that of the fluidizing gas to be blown in the first fluidization region, to form a second fluidization region having a degree of fluidization of the fluidizable particles greater than that in the first fluidization region; and   a gasification step of supplying waste from a supply-side portion of the sidewall located on the same side as the mixture discharge port with respect to the center position of the bottom wall, to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste to be accumulated on the first fluidization region, while causing the accumulated waste to be moved into the second fluidization region step-by-step and gasified.   
     
     
         10 . The waste treatment method as defined in  claim 9 , wherein the gasification step includes pushing new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the first fluidization region, thereby causing the waste accumulated on the first fluidization region to be moved into the second fluidization region step-by-step and gasified. 
     
     
         11 . The waste treatment method as defined in  claim 9 , which comprises a step of separating the carbides from a mixture of the non-combustible substances, the carbides and the fluidizable particles, the mixture discharged from the mixture discharge port, and returning the separated carbides to the fluidized bed from the side of the opposite-side sidewall portion. 
     
     
         12 . The waste treatment method as defined in  claim 9 , wherein the fluidizing gas is blown in the first fluidization region at a flow velocity satisfying a condition that U o /U mf  ranges from 1 to less than 2, and blown in the second fluidization region at a flow velocity satisfying a condition that U o /U mf  ranges from 2 to less than 5, where U mf  is a minimum fluidization velocity which is a minimum flow velocity of the fluidizing gas to be blown so as to fluidize the fluidizable particles, and U o  is a cross-sectional average flow velocity of the fluidizing gas.