Heat Exchanger Having Improved Drain System

Abstract

A heat recovery steam generator (HRSG) (A) has a casing ( 2 ) and several heat exchangers in the casing. Some of those heat exchangers ( 12,16 ) take the form of coils ( 18 ) having multiple lower headers ( 36 ) into which the lower ends of tubes ( 18 ) open. The tubes ( 18 ) and headers ( 36 ) hold or may hold water and need to be drained from time to time. To this end, the heat ex changer ( 12,16 ) has a drain system ( 20 ) provided with drain pipes ( 40 ) that are connected to the lower headers ( 36 ) and contain check valves ( 48 ) that permit the water to flow away from the headers ( 36 ), but not into them. The drain pipes ( 40 ) lead to and open into a drain manifold ( 46 ). The drain pipes ( 40 ), check valves ( 48 ) and drain manifold ( 46 ) are assembled in a shop along with the coil ( 18 ) and, when the HRSG (A) is assembled in the field, lie within the interior of the casing ( 2 ). The drain system ( 20 ) also includes a single common drain line ( 52 ) that extends downwardly from the drain manifold ( 46 ) and through the floor ( 8 ) of the casing ( 2 ), beyond which it is provided with a drain valve ( 56 ) that, when opened, allows water to drain from the coil ( 18 ).

1 . A heat exchanger comprising:
 tubes arranged generally vertically;   lower headers into which the lower ends of the tubes open;   drain pipes connected to the lower headers and extending downwardly from the lower headers; and   check valves in at least some of the drain pipes where they are oriented to allow flow out of the lower headers, but not substantially into the lower headers.   
     
     
         2 . A heat exchanger according to  claim 1  and further comprising a drain manifold located below the lower headers, the drain pipes being connected beyond their check valves to the drain manifold. 
     
     
         3 . A heat exchanger according to  claim 2  wherein each drain pipe has a generally upright segment that is connected to one of the lower headers and a generally horizontal segment that is connected to the drain manifold. 
     
     
         4 . A heat exchanger according to  claim 3  wherein the lower headers are generally parallel, and the horizontal segments of the drain pipes are generally parallel to the lower headers; and wherein the drain manifold extends generally transversely with respect to the lower headers. 
     
     
         5 . A heat exchanger according to  claim 4  wherein the drain pipes connect with the lower headers beyond the drain manifold, with the drain pipes for adjacent headers being on opposite sides of the drain manifold. 
     
     
         6 . A heat exchanger according to  claim 4  wherein the tubes are organized in rows, with the lower ends of the tubes for at least some of the rows opening into separate lower header. 
     
     
         7 . A heat exchanger according to  claim 6  wherein the upper ends of some of the tubes in one row that is endmost open into a supply header;
 and wherein the tubes of another row that is endmost at their upper ends open into a discharge headers. 
 
     
     
         8 . A heat exchanger according to  claim 4  and further comprising:
 a common drain line connected to the drain manifold and extending downwardly from it, and 
 a drain valve in the common drain line. 
 
     
     
         9 . A heat exchanger according to  claim 8  and further comprising water in the lower headers, the drain pipes, the drain manifold and the common drain line ahead of the drain valve. 
     
     
         10 . A heat recovery steam generator comprising:
 a casing having an inlet and an outlet and also a floor between the inlet and outlet; and   the heat exchanger of  claim 1  located in the casing with its drain pipes and check valves being located above the floor.   
     
     
         11 . A heat recovery steam generator comprising:
 a casing having an inlet and an outlet and also a floor between the inlet and outlet; and   the heat exchanger of  claim 4  located in the casing with its drain pipes and check valves and drain manifold being located above the floor;   a common drain line connected to the drain manifold and extending downwardly through the floor of the casing; and   a drain valve located in the common drain line and being outside of the casing.   
     
     
         12 . A heat recovery steam generator according to  claim 11  wherein the drain pipes connect with the lower headers beyond the drain manifold, with the drain pipes for adjacent headers being on opposite sides of the drain manifold. 
     
     
         13 . A heat exchanger comprising:
 a coil including:   tubes extending vertically and organized in rows; and   lower headers into which the tubes at their lower ends open; and   a drain system including;
 drain pipes connected to the lower headers and extending downwardly from them; 
   a drain manifold into which the drain pipes open; check valves in at least some of the drain pipes and oriented to allow flow from the headers to the drain manifold but not in the opposite direction;   a common drain line extending downwardly from the drain manifold; and   a valve in the common drain line.   
     
     
         14 . A heat exchanger according to  claim 13  wherein the tubes of the rows open into a separate lower header. 
     
     
         15 . A heat exchanger according to  claim 13  wherein each drain pipe includes an upright segment and a horizontal segment. 
     
     
         16 . A heat exchanger according to  claim 15   wherein the drain manifold extends transversely with respect to the lower headers;   wherein the drain pipes open into the drain manifold at their horizontal segments; and   wherein the drain pipes are connected to the lower headers at their upright segments on opposite sides of the drain manifold, with the upright segments of the drain pipes for adjacent lower headers being on opposite sides of the drain manifold.   
     
     
         17 . A drain system for a heat exchanger having lower headers arranged side by side, said drain system comprising:
 drain pipes extending downwardly from the lower headers and then generally horizontally;   a drain manifold into which the drain pipes open, the drain manifold extending generally transversely with respect to the drain pipes;   check valves in the drain pipes and being oriented to allow fluid to flow out of the headers into the drain manifold, but not in the opposite direction into the headers;   a drain line extending downwardly from the drain manifold; and   a drain valve in the drain line.   
     
     
         18 . A drain system according to  claim 17  wherein the drain pipes are connected to the headers near the ends of the headers, and the drain pipes for adjacent headers are at opposite ends of those headers.