Heat exchanger for preheating an oxidizing gas

Abstract

A heat exchanger useful for preheating oxidizing gases in a combustion process includes a shell having an inlet and an outlet for the ingress and egress of a first heat exchange fluid, such as a flue gas or preheated air. A first tube manifold couples an inlet end-cap to the first end of the shell. The inlet end-cap has an inlet for receiving a second heat exchange fluid, such as an oxidizing gas. In one embodiment, a second manifold couples an outlet end-cap to the second end of the shell. The second manifold includes an outlet tube therein extending from the second manifold through an outlet opening in the outlet end-cap. A tube bundle is disposed within the shell for transporting the oxidizing gas through the heat exchanger and is coupled to the first and second tube manifolds. The outlet tube collects oxidizing gas flowing through the tube bundle for discharge to a combustion system. The outlet end-cap is pressurized with an inert atmosphere and houses a chemical detector to detect the presence of oxidizing gas within the outlet end-cap.

1 . A heat exchanger for preheating an oxidizing gas comprising: 
 a shell having an inlet and an outlet for respectively permitting the ingress and the egress of a first heat exchange fluid comprising a gas selected from the group consisting of flue gas and preheated air;    a first chamber having an inlet for receiving a second heat exchange fluid, the second heat exchange fluid comprising an oxidizing gas;    an inner tube;    a first manifold configured to transfer the second heat exchange fluid from the first chamber to the inner tube;    a second chamber having an outlet tube extending through an opening therein;    a second manifold configured to transfer the second heat exchange fluid from the inner tube to the outlet tube,    wherein the second chamber contains a gas different from the second heat exchange fluid; and    a chemical detector configured to detect the presence of the oxidizing gas.    
     
     
         2 . The heat exchanger of    claim 1   , wherein the inner tube comprises a multi-pass tube bundle disposed about a longitudinal axis within the shell, 
 wherein the tube bundle includes a plurality of tubes arranged about the longitudinal axis, each tube characterized by a tube diameter, and    wherein tubes positioned proximal to the longitudinal axis have a larger tube diameter than tubes positioned distal to the longitudinal axis.    
     
     
         3 . The heat exchanger of    claim 2   , wherein the tube bundle includes first, second, and third pass tubes and, wherein first and second pass tubes are positioned distal to the longitudinal axis, and wherein third pass tubes are positioned proximal to the longitudinal axis.  
     
     
         4 . The heat exchanger of    claim 3   , wherein the first manifold comprises: 
 a first transverse segment adjacent to a second transverse segment, the first transverse segment having a plurality of holes therethrough proximal to the longitudinal axis, and a plurality of passageway therein distal to the longitudinal axis,    wherein the second transverse segment includes a first plurality of holes therethrough for receiving the first pass tubes, a second plurality of holes for receiving the second pass tubes, and a third plurality of holes for receiving the third pass tubes, and    wherein the first transverse segment is aligned with the second transverse segment so as to form a fluid pathway from the first end-cap to the first pass tubes, and to form a reversing fluid pathway from the second pass tubes through the plurality of passageways and into the third pass tubes.    
     
     
         5 . The heat exchanger of    claim 3   , wherein the second manifold comprises: 
 a first transverse segment adjacent to a second transverse segment, the first transverse segment having a first plurality of holes therethrough for receiving the first pass tubes, a second plurality of holes therethrough for receiving the second pass tubes, and a third plurality of holes therethrough for receiving the third pass tubes; and    the second transverse segment having a plurality of passageways distal to the longitudinal axis and a hole therethrough proximal to the longitudinal axis for receiving the outlet tube,    wherein the first transverse segment is aligned with the second transverse segment so as to form a reversing fluid pathway from the first pass tubes to the second pass tubes and to form a fluid pathway from the third pass tubes to the outlet tube.    
     
     
         6 . The heat exchanger of    claim 1    further comprising: 
 a first flange at an inlet end of the inner tube;  
 first and second gaskets adjacent to either side of the flange; and  
 a coupling portion of the first manifold having a bore therein for receiving the first flange and the first and second gaskets.  
 
     
     
         7 . The heat exchanger of    claim 6   , wherein the first gasket resides at a location distal to the first chamber and the second gasket resides at a location proximal to the first chamber, and wherein the first gasket is comprised of alumina-silica ceramic fiber, and the second gasket is comprised of a material selected from the group consisting of a metal fiber and copper.  
     
     
         8 . The heat exchanger of    claim 6    further comprising: 
 a second flange at an outlet end of the inner tube;  
 first and second gaskets adjacent to either side of the second flange; and  
 a coupling portion of the second manifold having a bore therein for receiving the second flange and the first and second gaskets.  
 
     
     
         9 . The heat exchanger of    claim 6   , wherein the first gasket resides at a location distal to the second chamber and the second gasket resides at a location proximal to the second chamber, and wherein the first gasket is comprised of alumina-silica ceramic fiber, and the second gasket is comprised of a material selected from the group consisting of a metal fiber and copper.  
     
     
         10 . A heat exchanger for preheating an oxidizing gas comprising: 
 a shell having a first manifold at a first end and a second manifold at a second end, and having an inlet and an outlet for respectively permitting the ingress and egress of a first heat exchange fluid;    at least one tube disposed within the shell for transporting the second heat exchange fluid therethrough and engaging the first manifold and the second manifold at a first side of the first manifold and at a first side of the second manifold;    an inlet chamber adjacent to a second side of the first manifold, the inlet chamber having an opening for receiving a second heat exchange fluid, the second heat exchange fluid comprising an oxidizing gas;    an outlet chamber adjacent to a second side of the second manifold, the outlet chamber having an outlet opening therein;    an outlet tube coupled to the second side of the second manifold passing through the outlet opening in the outlet chamber and configured to receive the second heat exchange fluid,    wherein the outlet chamber contains an inert atmosphere; and    a gas analyzer in communication with the inert atmosphere and configured to detect the oxidizing gas.    
     
     
         11 . The heat exchanger of    claim 10   , wherein the at least one tube comprises a multi-pass tube bundle disposed about a longitudinal axis within the shell, 
 wherein the tube bundle includes a plurality of tubes arranged about the longitudinal axis, each tube characterized by a tube diameter, and    wherein tubes positioned proximal to the longitudinal axis have a larger tube diameter than tubes positioned distal to the longitudinal axis.    
     
     
         12 . The heat exchanger of    claim 11   , wherein first and second pass tubes are positioned distal to the longitudinal axis, and wherein third pass tubes are positioned proximal to the longitudinal axis.  
     
     
         13 . The heat exchanger of    claim 11   , wherein the gas analyzer comprises an oxygen detector.  
     
     
         14 . The heat exchanger of    claim 10    further comprising a thermocouple mounted to an instrument port on the outlet chamber and configured to measure the temperature of the outlet tube.  
     
     
         15 . The heat exchanger of    claim 10   , wherein the inert gas is selected from the group consisting of nitrogen, argon, and mixtures thereof.  
     
     
         16 . A heat exchanger for preheating an oxidizing gas comprising: 
 a shell having an inlet and an outlet for permitting the ingress and egress of a gas selected from the group consisting of flue gas and preheated air;    at least one tube longitudinally disposed within the shell and configured to receive an oxidizing gas,    an inlet manifold transversely positioned at an inlet end of the shell and configured to receive a first end portion of the at least one tube;    an outlet manifold transversely positioned at an outlet end of the shell and configured to receive a second end portion of the at least one tube;    an inlet end-cap positioned around the segmented inlet manifold and coupled to the inlet end of the shell; and    an outlet end-cap having an axial opening therein, the end-cap positioned around the segmented outlet manifold and sealed to the outlet end of the shell;    an outlet tube partially inserted into an opening in the segmented outlet manifold and passing through the axial opening of the outlet end-cap,    wherein the outlet tube is in communication with the at least one tube;    an inert atmosphere within the outlet end-cap;    means in communication with the inert atmosphere for detecting the presence of the oxidizing gas within the inert atmosphere; and    means mounted to the outlet end-cap for measuring the temperature of the outlet tube.    
     
     
         17 . The heat exchanger of    claim 16    further comprising an expansion bellows integral with the shell.  
     
     
         18 . The heat exchanger of    claim 16   , wherein a tube bundle is longitudinally disposed within the shell, and wherein the tube bundle includes a plurality of parallel spaced tubes.  
     
     
         19 . The heat exchanger of    claim 18   , wherein the plurality of parallel-spaced tubes have inner tube walls of iron nickel chromium alloy lined with a ceramic material, and wherein the oxidizing gas comprises oxygen.  
     
     
         20 . The heat exchanger of    claim 18   , wherein the plurality of parallel-spaced tubes comprise first pass tubes, second pass tubes, and third pass tubes, and wherein the first and second pass tubes are alternatingly arranged about a longitudinal axis at a first radial distance, and wherein the third pass tubes are arranged about the longitudinal axis at a second radial distance, and wherein the first radial distance is greater than the second radial distance.  
     
     
         21 . The heat exchanger of    claim 20   , wherein each of the first, second, and third pass tubes are characterized by a diameter, and wherein the diameter of the first pass tubes is less than the diameter of the second pass tubes, and wherein the diameter of the second pass tubes is less than the diameter of the third pass tubes.  
     
     
         22 . The heat exchanger of    claim 16   , wherein the means for measuring the temperature comprises a thermocouple.  
     
     
         23 . A heat exchanger for preheating an oxidizing gas comprising: 
 a shell having an inlet and an outlet for permitting the ingress and egress of a heating gas selected from the group consisting flue gas and preheated air;    a tubular oxidizing gas pathway disposed within the shell, the pathway configured to receive an oxidizer gas at an inlet and to discharge the oxidizer gas at an outlet,    wherein the tube diameter increases along the direction of oxidizing gas flow, such that the tube diameter at the inlet is smaller than the tube diameter at the outlet, and    wherein the oxidizing gas pathway is of metallic weld-free construction, such that only weld-free metallic surfaces are exposed to the oxidizing gas.    
     
     
         24 . The heat exchanger of    claim 23   , wherein the oxidizing gas pathway comprises: 
 a plurality of parallel-spaced tubes longitudinally disposed within the metallic shell between a first manifold and a second manifold, each tube having an inner tube wall of a high-temperature metallic alloy lined with ceramic material,    wherein the plurality of parallel-spaced tubes include first pass tubes and third pass tubes configured to receive an oxidizing gas at the first manifold and to discharge the oxidizing fluid at a second manifold, and second pass tubes configured to receive the oxidizing gas at the second manifold and to discharge the oxidizing gas at the first manifold.    
     
     
         25 . The heat exchanger of    claim 24   , wherein the ceramic material is selected from the group consisting of aluminum oxide, zirconium oxide, chromium oxide, silica, and rare earth oxides.  
     
     
         26 . The heat exchanger of    claim 25   , wherein the first and second manifolds comprise iron, nickel chromium alloy coated with a metallic oxide ceramic material.  
     
     
         27 . The heat exchanger of    claim 24   , wherein the first pass tubes are arranged in a first square pattern, the second pass tubes are arranged in a second square pattern, and the third pass tubes are arranged in a third square pattern, and 
 wherein the centers of the first pass tubes are located at the corners of the first square pattern, the centers of the second pass tubes are located at the corners of the second square pattern, and intersect the first square pattern at the midpoint of each side of the first square pattern, and the centers of the third pass tubes are located at the corners of the third square pattern and intersect the midpoints of each side of the second square pattern.    
     
     
         28 . The heat exchanger of    claim 24   , wherein the first pass tubes are arranged in a first square pattern, the second pass tubes are arranged in a second square pattern, and the third pass tubes are arranged in a third square pattern, and 
 wherein the first pass tubes, the second pass tubes and the third pass tubes are positioned at the corners of the first, second, and third square pattern, respectively, and the tube walls of each first pass tube are tangent to two sides of the first square pattern, the tube walls of the second pass tubes are tangent to two sides of the second square pattern, and the third pass tubes are tangent to two sides of the third square pattern.    
     
     
         29 . A heat exchanger for preheating an oxidizing gas comprising: 
 a shell having an inlet and an outlet for respectively permitting the ingress and the egress of a first heat exchange fluid;    a chamber having an inlet for receiving a second heat exchange fluid, the second heat exchange fluid comprising an oxidizer;    a U-shaped inner tube having a first end and a second end;    a manifold configured to transfer the second heat exchange fluid from the chamber to the first end of the U-shaped inner tube and to receive the second heat exchange fluid from the second end of the U-shaped tube,    wherein the end-cap contains a gas atmosphere different from the second heat exchange fluid; and    a chemical detector in communication with the gas atmosphere and configured to detect the presence of the oxidizing gas.    
     
     
         30 . The heat exchanger of    claim 29   , wherein the U-shaped tube comprises a tube bundle disposed about a longitudinal axis within the shell, 
 wherein the tube bundle includes a plurality of tubes arranged about the longitudinal axis, each tube characterized by a tube diameter, and    wherein tubes positioned proximal to the longitudinal axis have a larger tube diameter than tubes positioned distal to the longitudinal axis.    
     
     
         31 . The heat exchanger of    claim 30   , wherein the tube bundle includes first, second, and third pass tubes and, wherein first and second pass tubes are positioned distal to the longitudinal axis, and wherein third pass tubes are positioned proximal to the longitudinal axis.  
     
     
         32 . The heat exchanger of    claim 31   , where each of the first, second, and third pass tubes include a first segment, a second segment and a third segment, a first union coupling the first segment to the second segment, and a second union coupling the second segment to the third segment.  
     
     
         33 . The heat exchanger of    claim 31   , wherein an inner surface of each of the first, second , and third segments includes a lining comprising a ceramic material.  
     
     
         34 . The heat exchanger of    claim 30   , wherein the first pass tubes are arranged in a first square pattern, the second pass tubes are arranged in a second square pattern, and the third pass tubes are arranged in a third square pattern, and 
 wherein the centers of the first pass tubes are located at the corners of the first square pattern, the centers of the second pass tubes are located at the corners of the second square pattern, and intersect the first square pattern at the midpoint of each side of the first square pattern, and the centers of the third pass tubes are located at the corners of the third square pattern and intersect the midpoints of each side of the second square pattern.    
     
     
         35 . The heat exchanger of    claim 31   , wherein the first and second ends of the first pass tubes are arranged in a first rectangular pattern, wherein the first and second ends of the second pass tubes are arranged in a second rectangular pattern, wherein the first and second ends of the third pass tubes are arranged in a third rectangular pattern, wherein each of the first, second and third rectangular pattern is characterized by a height and wherein the height of the third rectangular pattern is less than the height of the second rectangular pattern, and the height of the second rectangular pattern is less than the height of the first rectangular pattern.  
     
     
         36 . The heat exchanger of    claim 31   , wherein the manifold and the first, second, and third pass tubes comprise an alloy of iron, chromium, and nickel lined with a ceramic material.  
     
     
         37 . The heat exchanger of    claim 29   , wherein the manifold comprises a first transverse segment adjacent to a second transverse segment, the first transverse segment having a plurality of holes therethrough proximal to the longitudinal axis, and a plurality of passageway therein distal to the longitudinal axis, 
 wherein the second transverse segment includes a first plurality of holes therethrough for receiving the first pass tubes, a second plurality of holes for receiving the second pass tubes, and a third plurality of holes for receiving the third pass tubes, and    wherein the first transverse segment is aligned with the second transverse segment so as to form a fluid pathway from the end-cap to the first pass tubes, and to form a reversing fluid pathway from the second pass tubes through the plurality of passageways and into the third pass tubes.