Method and apparatus for gasifying solid biomass fuel

Abstract

A downdraft gasifier has a gas producer. The gas producer includes an introducing portion provided in an upper portion for introducing solid biomass fuel 4, an air inlet 17 provided in a central portion, a fire grate 14 provided in a lower portion, and a product gas delivery portion provided below the fire grate. In this gasifier, there are provided fire-proofball laid layers in which a plurality of metal balls 15 are disposed in layers on the fire grate substantially uniform, and a preheating unit (such as a burner) for preheating the fire-proof balls. The metal balls 15 are preheated in advance to a predetermined temperature ranging from 500° C. to 800° C. before the solid biomass fuel is introduced into the producer. After that, the solid biomass fuel 4 is introduced into the producer, and gas produced in the producer is delivered from a portion below the fire grate.

What is claimed is:  
     
         1 . A downdraft gasifier for gasifying solid biomass fuel, comprising: 
 a gas producer including a solid biomass fuel introducing portion provided in an upper portion,    an air inlet provided in a central portion,    a fire grate provided in a lower portion,    a delivery portion provided below said fire grate for delivering product gas,    fire-proof ball laid layers in which a plurality of fire-proof balls such as metal balls or ceramics balls are disposed in layers on said fire grate substantially uniform, and    a preheating unit for preheating said fire-proof balls.    
     
     
         2 . The gasifier for gasifying solid biomass fuel according to  claim 1 , wherein 
 said preheating unit is a detachable burner for preheating said fire-proof balls by combustion heat.    
     
     
         3 . The gasifier for gasifying solid biomass fuel according to  claim 1 , further comprising: 
 a cleaner/cooler for cleaning and cooling said product gas.    
     
     
         4 . A downdraft gasifying method for gasifying solid biomass fuel, comprising the steps of: 
 introducing solid biomass fuel from an upper portion of a producer;    introducing combustion air from a central portion of said producer;    delivering product gas from a portion below a fire grate, said fire grate being provided in a lower portion of said producer;    preheating a plurality of fire-proof balls such as metal balls or ceramics balls to a predetermined temperature in advance before said solid biomass fuel is introduced, said fire-proof balls being disposed in layers on said fire grate substantially uniform; and    subsequently delivering gas from a portion below said fire grate, said gas being produced in said producer after said solid biomass fuel is introduced into said producer.    
     
     
         5 . The method for gasifying solid biomass fuel according to  claim 4 , wherein 
 said preheating temperature of said fire-proof balls ranges from 500° C. to 800° C.    
     
     
         6 . The method for gasifying solid biomass fuel according to  claim 4 , wherein 
 after solid biomass fuel is introduced through a fuel feed gate from a solid biomass fuel feed hopper provided in an upper portion of said producer, said fuel feed gate is closed to stop fuel feed, and when a fuel level in said producer reaches a predetermined level due to fuel consumption in said producer, said fuel feed gate is opened to resume fuel feed.