Exhaust gas processing system and method for rotary hearth type reducing furnace

Abstract

Provided are an exhaust gas processing system and method capable of effectively utilizing the sensible heat of an exhaust gas for preheating air for burner combustion in a rotary hearth type reducing furnace while preventing troubles caused by adhesion of dust such as blockage in an exhaust gas processing facility for a rotary hearth type reducing furnace and corrosive deterioration in the facility without increasing the facility costs excessively. The system comprises a radiant heat exchanger 2 for heat exchange between an exhaust gas exhausted from the rotary hearth type reducing furnace and air. The radiant heat exchanger 2 includes an inner cylinder 22 made of metal surrounding a space through which the exhaust gas flows; an outer cylinder 21 disposed on an outer side in a radial direction of the inner cylinder to define a flow channel between the inner cylinder and the outer cylinder 21 for allowing the air to flow so as to exchange heat with the exhaust gas; and a highly thermal conductive refractory 23 applied to an inner side of the inner cylinder 22 so as to cover an inner surface thereof.

1 . An exhaust gas processing system for processing an exhaust gas exhausted from a rotary hearth type reducing furnace, comprising:
 a radiant heat exchanger configured to perform a heat exchange between the exhaust gas exhausted from the rotary hearth type reducing furnace and air, wherein the radiant heat exchanger includes:   an inner cylinder made of metal surrounding a space through which the exhaust gas flows;   an outer cylinder disposed on an outer side in a radial direction of the inner cylinder to define a flow channel between the inner cylinder and the outer cylinder for allowing the air therethrough so as to exchange heat with the exhaust gas; and   a highly thermal conductive refractory applied to an inner side of the inner cylinder so as to cover an inner surface of the inner cylinder.   
     
     
         2 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 1 , wherein:
 the highly thermal conductive refractory contains any one of SiC, ZrB 2 , and BN as a main constituent.   
     
     
         3 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 2 , wherein:
 the highly thermal conductive refractory is a silicon carbide refractory containing SiC as the main constituent.   
     
     
         4 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 3 , wherein:
 an SiC content in the silicon carbide refractory is 60% or greater by mass.   
     
     
         5 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 1 , further comprising:
 heat exchanger inlet gas temperature control means for controlling a temperature of the exhaust gas at an inlet of the heat exchanger to be a target temperature of 1100° C. or above.   
     
     
         6 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 5 , wherein:
 the heat exchanger inlet gas temperature control means controls the temperature of the exhaust gas at the inlet of the heat exchanger to be a target temperature of 1200° C. or above.   
     
     
         7 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 5 , wherein:
 the heat exchanger inlet gas temperature control means controls the temperature of the exhaust gas at the inlet of the heat exchanger by introducing air into the exhaust gas from the rotary hearth type reducing furnace.   
     
     
         8 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 5 , wherein:
 the heat exchanger inlet gas temperature control means controls the temperature of the exhaust gas at the inlet of the heat exchanger by introducing a cooled exhaust combustion gas into the exhaust gas from the rotary hearth type reducing furnace.   
     
     
         9 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 1 , further comprising:
 an exhaust gas cooling tower provided at a latter stage of the heat exchanger to forcibly cool the exhaust gas exhausted from an outlet of the heat exchanger.   
     
     
         10 . The exhaust gas processing system for the rotary hearth type reducing furnace according to  claim 9 , further comprising:
 a refractory duct from the outlet of the heat exchanger to the exhaust gas cooling tower,   wherein the refractory duct includes a duct main body made of metal and a refractory applied so as to cover at least a part of an inner surface of the duct main body.   
     
     
         11 . A method of peeling dust adhering onto a heat transfer surface in the exhaust gas processing system for the rotary hearth type reducing furnace set forth in  claim 1 , comprising:
 temporarily lowering a temperature of the surface below a temperature of the surface during a reducing operation to generate cracking which promotes peeling of a dust layer adhering onto a surface of the highly thermal conductive refractory, in the dust layer.   
     
     
         12 . An exhaust gas processing method for processing an exhaust gas exhausted from a rotary hearth type reducing furnace, comprising:
 introducing the exhaust gas exhausted from the rotary hearth type reducing furnace into a heat exchanger for performing a heat exchange between the exhaust gas and air to preheat the air,   wherein the heat exchanger is a radiant heat exchanger that includes:   an inner cylinder surrounding a space through which the exhaust gas flows;   an outer cylinder disposed on an outer side in a radial direction of the inner cylinder to define a flow channel between the inner cylinder and the outer cylinder for allowing the air to flow therethrough; and   a highly thermal conductive refractory disposed so as to cover an inner surface of the inner cylinder.   
     
     
         13 . The exhaust gas processing method for the rotary hearth type reducing furnace according to  claim 12 , further comprising:
 controlling a temperature of the exhaust gas at an inlet of the heat exchanger to be a target temperature of 1100° C. or above.   
     
     
         14 . The exhaust gas processing method for the rotary hearth type reducing furnace according to  claim 13 , wherein:
 the target temperature of the temperature of the exhaust gas at the inlet of the heat exchanger is 1200° C. or above.   
     
     
         15 . The exhaust gas processing method for the rotary hearth type reducing furnace according to  claim 12 , wherein:
 the heat exchanger performs heat exchange between the exhaust gas and the air so as to lower an exhaust gas temperature at an outlet of the heat exchanger to a temperature that is 600° C. or above but lower than an exhaust gas temperature at an inlet of the heat exchanger; and   the method further comprises forcibly cooling the exhaust gas to lower the temperature thereof from 600° C. to 200° C. within 5 seconds by introducing the exhaust gas exhausted from the heat exchanger into an exhaust gas cooling tower.