Fluidized bed furnace and waste treatment method

Abstract

A waste treatment technique includes: blowing a fluidizing gas from around a non-combustible substance discharge port toward fluidizable particles to form a first fluidization region, while blowing a fluidizing gas between the first fluidization region and a front wall at a flow velocity less than that in the first fluidization region to form a second fluid region having a relatively low degree of fluidization of fluidizable particles; returning fluidizable particles discharged from the non-combustible substance discharge port to a fluidized bed from the side of the front wall to form, in the fluidized bed, a flow of fluidizable particles directed from the front wall to the non-combustible substance discharge port; supplying waste from the front wall onto the fluidized bed to cause the waste to be accumulated on the second fluidization region while causing the accumulated waste to be moved into the first fluidization region step-by-step and gasified.

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 non-combustible substance 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 together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance 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 a side opposite to the non-combustible substance discharge port across 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 the non-combustible substance discharge port; and   a sand circulation device for returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the waste supply section to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion located on the side opposite to the non-combustible substance discharge port, to the non-combustible substance discharge port,   wherein:   the gas supply section is adapted to blow the fluidizing gas from around the non-combustible substance discharge port to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern and mixed with the waste to gasify the waste, while blowing the fluidizing gas between the first fluidization region and the waste supply section at a flow velocity less 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 lower than that in the first fluidization region; 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 second fluidization region while causing the accumulated waste to be moved into the first 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 second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step. 
     
     
         3 . The fluidized bed furnace as defined in  claim 1 , wherein the air supply section is adapted to blow the fluidizing gas in the second 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 first 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. 
     
     
         4 . 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. 
     
     
         5 . The fluidized bed furnace as defined in  claim 4 , 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. 
     
     
         6 . 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 non-combustible substance 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 together with a part of the fluidizable particles, and an upper surface of the bottom wall is inclined to become lower toward the non-combustible substance discharge port so as to cause the non-combustible substances to fall on the upper surface of the bottom wall toward the non-combustible substance 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 non-combustible substance discharge port toward the fluidizable particles to form a first fluidization region where the fluidizable particles are moved in a convection-like pattern, while blowing a fluidizing gas between the first fluidization region and a supply-side portion of the sidewall located on a side opposite to the non-combustible substance discharge port across the center position of the bottom wall, at a flow velocity less 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 lower than that in the first fluidization region;   a fluidizable-particle-flow formation step of returning the fluidizable particles discharged from the non-combustible substance discharge port, to the fluidized bed from the side of the supply-side sidewall portion to circulate the fluidizable particles, thereby forming a flow of the fluidizable particles directed from the supply-side sidewall portion to the non-combustible substance discharge port; and   a gasification step of supplying waste from the supply-side sidewall portion to a region on the fluidized bed adjacent to the supply-side sidewall portion, thereby causing the waste to be accumulated on the second fluidization region, while causing the accumulated waste to be moved into the first fluidization region step-by-step and gasified.   
     
     
         7 . The waste treatment method as defined in  claim 6 , wherein the gasification step includes pushing new waste generally horizontally from the supply-side sidewall portion toward the waste accumulated on the second fluidization region, thereby causing the waste accumulated on the second fluidization region to be moved into the first fluidization region step-by-step and gasified. 
     
     
         8 . The waste treatment method as defined in  claim 6 , wherein the fluidizing gas is blown in the second 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 first 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.