Processes for controlling afterburn in a reheater and for controlling loss of entrained solid particles in combustion product flue gas

Abstract

Processes for controlling afterburn in a reheater and loss of entrained solid particles in reheater flue gas are provided. Carbonaceous biomass feedstock is pyrolyzed using a heat transfer medium forming pyrolysis products and a spent heat transfer medium comprising combustible solid particles. The spent heat transfer medium is introduced into a fluidizing dense bed. The combustible solid particles of the spent heat transfer medium are combusted forming combustion product flue gas in a dilute phase above the fluidizing dense bed. The combustion product flue gas comprises flue gas and solid particles entrained therein. The solid particles are separated from the combustion product flue gas to form separated solid particles. At least a portion of the separated solid particles are returned to the fluidizing dense bed.

1 . A process for pyrolysis of a carbonaceous biomass feedstock, the process comprising the steps of:
 pyrolyzing carbonaceous biomass feedstock using a heat transfer medium forming pyrolysis products and a spent heat transfer medium comprising combustible solid particles;   introducing the spent heat transfer medium into a fluidized dense bed and combusting the combustible solid particles of the spent heat transfer medium forming combustion product flue gas in a dilute phase above the fluidized dense bed, the combustion product flue gas comprising flue gas and solid particles entrained therein; and   separating the solid particles from the combustion product flue gas to form separated solid particles and returning at least a portion of the separated solid particles to the fluidized dense bed.   
     
     
         2 . The process of  claim 1 , wherein the step of introducing spent heat transfer medium comprises introducing spent heat transfer medium comprising combustible solid particles mixed with inert solid particles, catalytic solid particles, or both. 
     
     
         3 . The process of  claim 1 , wherein the step of introducing spent heat transfer medium comprises introducing the spent heat transfer medium into a fluidized dense bed maintained by an oxygen-containing regeneration gas stream at a superficial gas velocity above the minimum velocity to fluidize the fluidized dense bed. 
     
     
         4 . The process of  claim 1 , wherein the step of separating is performed using a flue gas-solids separator. 
     
     
         5 . The process of  claim 4 , wherein the fluidized dense bed and the flue gas-solids separator are in a reheater. 
     
     
         6 . The process of  claim 1 , wherein the step of separating is performed with a cyclone separator, a vortex separator, or a combination thereof. 
     
     
         7 . The process of  claim 6 , wherein the step of separating comprises separating with the cyclone separator having a lower end of a solids discharge dipleg immersed below a top surface of the fluidized dense bed. 
     
     
         8 . The process of  claim 1 , wherein the step of separating comprises separating combustible solid particles to form separated combustible solid particles and returning at least a portion of the separated combustible solid particles to the fluidized dense bed for combustion therein. 
     
     
         9 . The process of  claim 1 , wherein the step of separating comprises separating inert solid particles, catalytic solid particles, or both, to form separated inert solid particles, separated catalytic solid particles, or both, and returning the separated inert solid particles, separated catalytic solid particles, or both, to the fluidizing dense bed. 
     
     
         10 . A process for controlling afterburn in a reheater and loss of entrained solid particles from combustion product flue gas, the process comprising the steps of:
 introducing spent heat transfer medium comprising combustible solid particles mixed with inert solid particles, catalytic solid particles, or both, into an oxygen-containing regeneration gas upwardly passing through a fluidized dense bed of heat transfer medium in a reheater at a temperature between about 300° C. to about 900° C., producing combustion product flue gas having at least a portion of the combustible solid particles mixed with the inert solid particles, the catalytic solid particles, or both entrained therein;   passing the combustion product flue gas through a flue gas-solids separator disposed in the reheater to produce substantially solids-free flue gas and separated combustible solid particles mixed with separated inert solid particles, separated catalytic solid particles, or both; and   passing at least a portion of the separated combustible solid particles mixed with the separated inert solid particles, the separated catalytic solid particles, or both, to the fluidized dense bed.   
     
     
         11 . The process of  claim 10 , wherein the step of passing at least a portion of the separated combustible solid particles comprises passing at least a portion of the separated combustible solid particles to the fluidized dense bed and combusting the separated combustible solid particles. 
     
     
         12 . The process of  claim 10 , further comprising the step of recirculating the separated inert solid particles, the separated catalytic solid particles, or both, from the fluidized dense bed for use as the heat transfer medium in pyrolyzing carbonaceous biomass feedstock. 
     
     
         13 . The process of  claim 10 , further comprising the step of recirculating the separated catalytic solid particles from the fluidized dense bed for use as a catalyst in pyrolyzing carbonaceous biomass feedstock. 
     
     
         14 . The process of  claim 10 , wherein the step of passing the combustion product flue gas through a flue gas-solids separator comprises passing the combustion product flue gas through a cyclone separator, a vortex separator, or a combination thereof. 
     
     
         15 . The process of  claim 14 , wherein the step of passing the combustion product flue gas through a flue gas-solids separator comprises passing the combustion product flue gas through the cyclone separator having a lower end of a solids discharge dipleg immersed below a top surface of the fluidized dense bed. 
     
     
         16 . A process for controlling afterburn in a reheater and loss of entrained solid particles in combustion product flue gas, the process comprising the steps of:
 discharging the combustion product flue gas with entrained solid particles from a fluidized dense bed of a reheater into a dilute vapor phase in an upper portion of the reheater;   recovering centrifugally separated solid particles in the fluidized dense bed in a bottom portion of the reheater from a flue gas-solids separator disposed in the reheater; and   passing a substantially solids-free flue gas separated from the entrained solid particles through a flue gas transfer line in open communication with an external cyclone separator wherein residual entrained solid particles are further separated from the substantially solids-free flue gas before effecting recovery of product flue gas from the external cyclone separator.   
     
     
         17 . The process of  claim 16 , wherein the step of recovering centrifugally separated solid particles comprises recovering separated combustible solid particles and combusting at least a portion of the separated combustible solid particles in the fluidized dense bed. 
     
     
         18 . The process of  claim 16 , wherein the step of recovering centrifugally separated solid particles comprises recovering centrifugally separated inert solid particles, centrifugally separated catalytic solid particles, or both. 
     
     
         19 . The process of  claim 18 , wherein the step of recovering centrifugally separated solid particles comprises recirculating the centrifugally separated catalytic solid particles to a pyrolysis reactor. 
     
     
         20 . The process of  claim 16 , wherein the step of passing a substantially solids-free flue gas comprises recovering the further separated residual entrained solid particles.