Burner nozzle with backflow prevention for a fluidized bed biogasifier

Abstract

A fluidized bed biogasifier is provided for gasifying biosolids. A feeder feeds biosolids into a reactor vessel at a desired feed rate during steady-state operation. A fluidized bed in the base of the reactor vessel has a cross-sectional area that is proportional to at least the fuel feed rate such that the superficial velocity of gas is in the range of 0.1 m/s to 3 m/s. The biosolids are heated inside the fluidized bed reactor to a temperature range between 900° F. and 1700° F. in an oxygen-starved environment having a sub stoichiometric oxygen level, whereby the biosolids are gasified. A burner system having a hooded nozzle below the fluidized bed in the reactor vessel provides high temperature gas to the biogasifier.

What is claimed is: 
     
         1 - 9 . (canceled) 
     
     
         10 . A method for gasifying biosolids comprising the steps of:
 feeding biosolids in a fluidized bed biogasifier, the biogasifier having:
 a reactor vessel; 
 a freeboard section of said reactor vessel; 
 a feeder for feeding biosolids into said reactor vessel, said feeder being configured to feed said biosolids into said reactor vessel at a biosolids fuel feed rate during steady-state operation of the biogasifier; and 
 a fluidized bed in a bed section of said reactor vessel; 
 wherein the freeboard section has a greater diameter than the fluidized bed; 
   providing gas to said fluidized bed; and   heating and reacting said biosolids inside said biogasifier, whereby biosolids are gasified.   
     
     
         11 . The method of  claim 10 , wherein the step of providing gas to said fluidized bed comprises providing high temperature gas below the fluidized bed. 
     
     
         12 . The method of  claim 10 , wherein the step of providing gas to said fluidized bed comprises providing high temperature gas through a nozzle, where the nozzle is below the fluidized bed. 
     
     
         13 . The method of  claim 12 , wherein the nozzle includes a hood, where the hood restricts solids from flowing into the nozzle. 
     
     
         14 . The method of  claim 12 , further comprising the step of providing additional fluidizing gas into the reactor vessel, where the additional fluidizing gas is recycled flue gas. 
     
     
         15 . The method of  claim 10 , wherein the freeboard has a diameter of at least 57 inches. 
     
     
         16 . The method of  claim 10 , where there is a temperature within the reactor vessel, wherein the method further comprises the step of adjusting the temperature within the reactor vessel by adjusting a rate at which oxidant gas is provided to the reactor vessel. 
     
     
         17 . The method of  claim 10 , wherein the bed section has a height and a media bed depth, where the height of the bed section is 1.5 times the media bed depth. 
     
     
         18 . A biogasifier comprising
 a reactor vessel having a freeboard section and a bed section, where the bed section is below the freeboard section, where the bed section has a fluidized bed;   a burner system having a nozzle, where the nozzle is below the bed section, where the burner system provides heated gas to the reactor vessel.   
     
     
         19 . The biogasifier of  claim 18 , further comprising a hood, where the hood is secured to the nozzle, and where the hood restricts solids from flowing into the nozzle. 
     
     
         20 . The biogasifier of  claim 18 , wherein the hood is welded to the nozzle. 
     
     
         21 . The biogasifier of  claim 18 , wherein the hood comprises stainless steel. 
     
     
         22 . The biogasifier of  claim 18 , wherein the nozzle is a slot in a pipe. 
     
     
         23 . A method of gasifying a biosolid comprising the steps of:
 providing biosolids into a reactor with a fluidized bed;   providing a heated gas to the reactor from below the fluidized bed;   waiting until the fluidized bed reaches a minimum threshold temperature and then providing additional fluidizing gas into the reactor;   removing flue gas from the reactor; and   passing flue gas removed from the reactor through a heat exchanger.   
     
     
         24 . The method of  claim 23 , wherein the heated gas is provided to the reactor through a nozzle. 
     
     
         25 . The method of  claim 24 , wherein the nozzle comprises a hood, where the hood restricts solids from flowing into the nozzle. 
     
     
         26 . The method of  claim 23 , wherein the minimum threshold temperature is 900° F. 
     
     
         27 . The method of  claim 23 , further comprising step of adjusting a temperature in the reactor by adjusting amount of oxidant gas entering into the reactor. 
     
     
         28 . The method of  claim 23 , wherein the additional fluidizing gas comprises flue gas previously removed from the reactor. 
     
     
         29 . The method of  claim 23 , wherein the heat exchanger transfers heat from flue gas removed from the reactor to the additional fluidizing gas before it is provided into the reactor. 
     
     
         30 . The method of  claim 23 , further comprising the step of transferring heat from the heat exchanger to sludge to form dried sludge, wherein the biosolids provided into the reactor comprise the dried sludge.