Combustion system and method for operating same

Abstract

An oxygen combustion system includes a boiler to burn fuel using combustion gas composed of oxygen-rich gas and circulating flue gas, a dust remover disposed in a flue through which flue gas discharged from the boiler flows, a second flue leading the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted downstream of the dust remover with the oxygen-rich gas, a combustion gas heater exchanging heat between the flue gas flowing between the boiler and dust remover and the combustion gas flowing through the second flue, and a flue gas cooler disposed between the heater and the dust remover to cool the flue gas. A control unit controls at least one of a flow rate and cooling medium temperature of the flue gas cooler such that temperature of the flue gas introduced into the dust remover will be between 90° C. and 140° C.

1 . A combustion system wherein:
 a burner adapted to burn solid fuel comprises a fuel nozzle adapted to burn solid fuel supplied in accompaniment with carrier gas, a first combustion gas nozzle adapted to supply first combustion gas into the fuel nozzle, a second combustion gas nozzle placed on an outer side of the fuel nozzle and adapted to supply second combustion gas;   the combustion system is configured to be switchable between an air combustion mode in which air is used as the carrier gas, the first combustion gas and the second combustion gas, and an oxygen-based combustion mode in which mixed gas is used as the carrier gas, the first combustion gas and the second combustion gas, where the mixed gas is made by mixing oxygen-rich gas with flue gas produced when the solid fuel is burned;   respective oxygen concentrations and supplied amounts of the carrier gas, the first combustion gas, and the second combustion gas are each configured to be adjustable; and   in the oxygen-based combustion mode, the oxygen concentration in the carrier gas is adjusted to be lower than an average oxygen concentration of the carrier gas, the first combustion gas and the second combustion gas taken together, and   the oxygen concentration in the first combustion gas is adjusted to be equal to or higher than the average oxygen concentration of the carrier gas, the first combustion gas and the second combustion gas taken together.   
     
     
         2 . The combustion system according to  claim 1 , wherein:
 the fuel nozzle includes a distributor adapted to divide a flow channel in the fuel nozzle; and   an outlet of the first combustion gas nozzle is formed at a location overlapping the distributor when viewed in a direction perpendicular to a burner axis.   
     
     
         3 . The combustion system according to  claim 1 , wherein:
 the fuel nozzle includes a venturi and a concentrator located in a flow channel upstream of a position at which the first combustion gas nozzle is connected, the venturi being adapted to smoothly contract and expand a sectional area of the flow channel of the fuel nozzle from an outer peripheral side while the concentrator being adapted to smoothly expand the sectional area of the flow channel downstream of the venturi from inside; and   a flame holder is installed at a tip of a partition wall partitioning the fuel nozzle and the second combustion gas nozzle, the flame holder being adapted to block flow of the solid fuel and carrier gas ejected through the fuel nozzle and flow of the first combustion gas ejected through the first combustion gas nozzle.   
     
     
         4 . A combustion system comprising:
 an oxygen-based combustion boiler adapted to burn solid fuel by diluting oxygen-rich gas with flue gas;   a crusher adapted to crush the solid fuel;   a fuel supply device adapted to supply the crushed solid fuel to a burner of the boiler in accompaniment with carrier gas;   a dust collector adapted to collect fly ashes in flue gas discharged from the boiler; and   a carbon dioxide recovery unit adapted to separate and recover carbon dioxide from the flue gas discharged from the dust collector;   the burner in turn comprising a fuel nozzle adapted to burn the solid fuel supplied in accompaniment with the carrier gas, a first combustion gas nozzle adapted to supply first combustion gas into the fuel nozzle, and a second combustion gas nozzle placed on an outer side of the fuel nozzle and adapted to supply second combustion gas,   wherein the combustion system further comprises a carrier gas line adapted to generate the carrier gas from the flue gas branching off from a downstream side of the dust collector,   a combustion gas line adapted to generate combustion gas by adding oxygen-rich gas to the flue gas branching off from the downstream side of the dust collector, and   a controller adapted to set oxygen concentration in the carrier gas and control flow rate of the carrier gas according to a supplied amount and type of the solid fuel, control a supplied amount and oxygen concentration of the first combustion gas based on the oxygen concentration and flow rate of the carrier gas and a set amount of oxygen needed for combustion of the solid fuel, and control a supplied amount of the second combustion gas based on an amount of oxygen in the carrier gas, an amount of oxygen in the first combustion gas, and a second set amount of oxygen needed for combustion of the solid fuel.   
     
     
         5 . The combustion system according to  claim 4 , wherein an adding device adapted to add oxygen-rich gas to the flue gas based on the oxygen concentration in the carrier gas set by the controller is installed on the carrier gas line. 
     
     
         6 . The combustion system according to  claim 4 , wherein the controller sets the oxygen concentration in the carrier gas to 21% or below and controls the oxygen concentrations in the first and second combustion gases to be 25 to 35%. 
     
     
         7 . A combustion system wherein:
 a burner adapted to burn solid fuel comprises a fuel nozzle adapted to burn solid fuel supplied in accompaniment with carrier gas, a first combustion gas nozzle adapted to supply first combustion gas into the fuel nozzle, a second combustion gas nozzle placed on an outer side of the fuel nozzle and adapted to supply second combustion gas;   the combustion system is configured to be switchable between an air combustion mode in which air is used as the carrier gas, the first combustion gas, and the second combustion gas and an oxygen-based combustion mode in which the fuel gas produced by combustion of the solid fuel is used as the carrier gas while mixed gas is used as the first combustion gas, and the second combustion gas, where the mixed gas is made by mixing oxygen-rich gas with flue gas produced when the solid fuel is burned; and   in the oxygen-based combustion mode, the oxygen concentration in the carrier gas is set to be lower than an average oxygen concentration of the carrier gas, the first combustion gas, and the second combustion gas taken together and   the oxygen concentration in the first combustion gas is adjusted to be equal to or higher than the average oxygen concentration of the carrier gas, the first combustion gas, and the second combustion gas taken together.   
     
     
         8 . An operating method for a combustion system which comprises an oxygen-based combustion boiler adapted to burn solid fuel by diluting oxygen-rich gas with flue gas, a crusher adapted to crush the solid fuel, a fuel supply device adapted to supply the crushed solid fuel to a burner of the boiler in accompaniment with carrier gas, a dust collector adapted to collect fly ashes in flue gas discharged from the boiler, and a carbon dioxide recovery unit adapted to separate and recover carbon dioxide from the flue gas discharged from the dust collector,
 the burner in turn comprising a fuel nozzle adapted to burn the solid fuel supplied in accompaniment with the carrier gas, a first combustion gas nozzle adapted to supply first combustion gas into the fuel nozzle, and a second combustion gas nozzle placed on an outer side of the fuel nozzle and adapted to supply second combustion gas, the operating method comprising:   generating the carrier gas by selectively adding oxygen-rich gas to the flue gas branching off from the downstream side of the dust collector;   generating the first combustion gas and the second combustion gas by adding oxygen-rich gas to the flue gas branching off from the downstream side of the dust collector; and   setting oxygen concentration in the carrier gas and controlling flow rate of the carrier gas according to a supplied amount and type of the solid fuel, controlling a supplied amount and oxygen concentration of the first combustion gas based on the oxygen concentration and flow rate of the carrier gas and a first set amount of oxygen needed for combustion of the solid fuel, and controlling a supplied amount of the second combustion gas based on an amount of oxygen in the carrier gas, an amount of oxygen in the first combustion gas, and a second set amount of oxygen needed for combustion of the solid fuel.   
     
     
         9 . The operating method for a combustion system according to  claim 8 , wherein during a start-up operation, the carrier gas is generated by making up deficiency of the flue gas branching off from the downstream side of the dust collector, using air. 
     
     
         10 . The operating method for a combustion system according to  claim 8 , wherein the oxygen concentration in the carrier gas is set to 21% or below and the oxygen concentrations in the first and second combustion gases are controlled to be 25 to 35%. 
     
     
         11 . The operating method for a combustion system according to  claim 9 , wherein the oxygen concentration in the carrier gas is set to 21% or below and the oxygen concentrations in the first and second combustion gases are controlled to be 25 to 35%. 
     
     
         12 . The combustion system according to  claim 2 , wherein:
 the fuel nozzle includes a venturi and a concentrator located in a flow channel upstream of a position at which the first combustion gas nozzle is connected, the venturi being adapted to smoothly contract and expand a sectional area of the flow channel of the fuel nozzle from an outer peripheral side while the concentrator being adapted to smoothly expand the sectional area of the flow channel downstream of the venturi from inside; and   a flame holder is installed at a tip of a partition wall partitioning the fuel nozzle and the second combustion gas nozzle, the flame holder being adapted to block flow of the solid fuel and carrier gas ejected through the fuel nozzle and flow of the first combustion gas ejected through the first combustion gas nozzle.   
     
     
         13 . The combustion system according to  claim 5 , wherein the controller sets the oxygen concentration in the carrier gas to 21% or below and controls the oxygen concentrations in the first and second combustion gases to be 25 to 35%.