Patent Publication Number: US-2003234497-A1

Title: Gas seal structure for high-temperature denitration apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a gas seal structure for a high-temperature denitration apparatus.  
       [0003] 2. Description of the Related Art  
       [0004] A conventional denitration apparatus for boiler exhaust gas generally comprises, as shown in FIGS. 1 and 2, a box-shaped casing  1  with front and rear open ends for passage of exhaust gas from a boiler (not shown) and a frame body  2  in the casing  1 .  
       [0005] The frame body  2  comprises a plurality of vertical frame members  3  erected in a spaced-apart relationship widthwise and in a direction of exhaust gas flow of the casing  1  and a plurality of horizontal frame members  4  fixed to the vertical frame members  3  through welding into a latticework. Thus, spaces  5  to be filled or charged with catalysts are formed in a plurality of widthwise rows and in a plurality of vertical stages within the casing  1 , brace members  6  being welded to interconnect slantwise the frame members  3  and  4  for reinforcement against horizontal forces generated for example in an earthquake. A plurality of (two in the example shown in FIG. 2) such frame bodies  2  with the same construction are arranged and interconnected in the direction of exhaust gas flow.  
       [0006] The casing  1  is internally lined with thermal insulation material  7 , and upon operation, temperature difference is caused between the casing  1  and the frame body  2  so that a degree in thermal expansion of the latter is greater than that of the former. Such difference in thermal expansion between the casing  1  and the frame body  2  upon operation may be absorbed such that the frame body  2  is supported in the casing  1  partly by fixed supports  8  and partly by slide supports  9  so as to make the frame body  2  slidable widthwise and in the direction of exhaust gas flow of the casing  1 .  
       [0007] A catalyst port  11  with an openable lid  10  protrudes from a top of the casing  1 . With the lid  10  being opened, catalyst modules  12  each charged with catalysts are suspended for example by cranes as shown in FIG. 2 and are set in the spaces  5  within the frame bodies  2 .  
       [0008] Short pass of the exhaust gas through between an inner surface of the casing  1  and a rim of the frame body  2  would causes the short-passed exhaust gas not to pass through the catalysts, resulting in deterioration of denitration performance. To overcome this, conventionally, as shown in FIGS. 3 and 4, seal plates  30  for prevention of short pass of the exhaust gas are mounted to and extend from the rim of the frame body  2  to the inner surface of the casing  1  which receives the seal plates  30  through seal guides  31  mounted thereon such that the seal plates  30  are slidable upon thermal expansion of the frame body  2 .  
       [0009] As to the seal plate  30  mounted to a bottom of the frame body  2 , since substantially no consideration is needed for vertical displacement of the seal plate  30  upon thermal expansion of the frame body  2 , the plate  30  is trailed down from the bottom of the frame body  2  with its low end folded forward to contact the thermal insulation material  7  on a bottom of the casing  7  as shown in FIG. 5; as to the seal plate  30  mounted to an upper portion of the frame body  2 , as shown in FIG. 6, the seal guides  31  mounted below a stopper  40  on the inner surface of the casing  1  receive a tip end of the seal plate  30  extending upward from the frame body  2  such that the seal plate  30  is slidable to the seal guides  31 .  
       [0010] Recently, a gas turbine is frequently used for generation of electricity and in such a case, exhaust gas from the gas turbine must be denitrated. To this end, it has been envisaged that, as a high-temperature denitration apparatus for gas-turbine exhaust gas, the above-mentioned denitration apparatus for boiler exhaust gas is utilized, with no structural change and with material of which the members  3 ,  4  and  6  are made being changed from carbon steel to stainless steel.  
       [0011] In the case of the high-temperature denitration apparatus for gas-turbine exhaust gas, though extremely hot exhaust gas passes through the casing  1 , the casing  1  is retained substantially to ambient temperature by the thermal insulation material  7  on the inner surface of the casing  1 .  
       [0012] However, because of the seal guides  31  directly mounted on the inner surface of the casing  1  as shown in FIG. 4, thermal conduction through the seal guides  31  may disadvantageously produce hot spots with temperature of more than 200° C. on portions of the casing  1  where the seal guides  31  are mounted.  
       [0013] As to the seal guides  31  directly mounted to an upper portion of the casing  1 , as is clear from FIG. 6, they are hardly in direct contact with the exhaust gas and extend from the casing  1  in a bent form hard for thermal conduction; therefore, there is substantially no fear of a hot spot being produced on the upper portion of the casing  1  where the seal guides  31  are mounted.  
       [0014] The invention was made in view of the above and has its object to provide a gas seal structure for a high-temperature denitration apparatus which can suppress thermal conduction through seal guides to minimum and can prevent hot spots from being produced on the casing.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015] The invention is directed to a gas seal structure for a high-temperature denitration apparatus which comprises a box-shaped casing with front and rear open ends for passage of hot exhaust gas and internally lined with thermal insulation material, a frame body within said casing, seal plates mounted to and extending from a rim of said frame body to an inner surface of the casing so as to prevent short pass of the exhaust gas, and seal guides mounted via heat shield bases on the inner surface of the casing, said seal guides receiving the seal plates such that the seal plates are slidable upon thermal expansion of the frame body.  
       [0016] The gas seal structure for the high-temperature denitration apparatus thus constructed has the following effect.  
       [0017] Heat of the hot exhaust gas passing through the casing makes to propagate via the seal guides to the casing. However, because of the heat shield bases being interposed between the casing and the seal guides, such heat conduction is suppressed to minimum by the heat shield bases, whereby no hot spots are produced on portions of the casing where the seal guides are mounted.  
       [0018] Each of the heat shield bases may comprise stud bolts protruded from the inner surface of the casing and a base plate fixed to tips of the stud bolts.  
       [0019] Next, a preferred embodiment of the invention will be described in conjunction with the drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0020]FIG. 1 is a front view of a conventional denitration apparatus;  
     [0021]FIG. 2 is a view looking in the direction of arrows II in FIG. 1;  
     [0022]FIG. 3 is an enlarged fragmentary vertical sectional front elevation of a conventional gas seal structure for the denitration apparatus;  
     [0023]FIG. 4 is an enlarged fragmentary horizontal sectional view taken along lines IV-IV in FIG. 3;  
     [0024]FIG. 5 is an enlarged fragmentary sectional side elevation taken along lines V-V in FIG. 3 for showing a bottom of the conventional gas seal structure for the denitration apparatus;  
     [0025]FIG. 6 is an enlarged fragmentary sectional side elevation taken along line VI-VI in FIG. 3 for showing an upper portion of the conventional gas seal structure for the denitration apparatus;  
     [0026]FIG. 7 is an enlarged fragmentary vertical sectional front elevation of an embodiment of the invention; and  
     [0027]FIG. 8 is an enlarged fragmentary sectional side elevation taken along lines VIII-VIII in FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0028]FIGS. 7 and 8 show an embodiment of the invention in which parts similar to those in FIGS.  1  to  6  are represented by the same reference numerals and which is basically similar in structure to that in the related art shown in FIGS.  1  to  6 . The embodiment resides in that, as shown in FIGS. 7 and 8, seal plates  30  are mounted to and extend from a rim of the frame body  2  to an inner surface of the casing  1  so as to prevent short pass of the exhaust gas and that seal guides  31  are mounted via heat shield bases  50  on the inner surface of the casing  1 , said seal guides  31  receiving the seal plates  30  such that the seal plates  30  are slidable upon thermal expansion of the frame body  2 .  
     [0029] Each of the heat shield bases  50  comprises stud bolts  51  extruded from the inner surface of the casing  1  and a base plate  53  fixed to tips of the stud bolts  51  by screwing nuts  52  up. The seal guides  31  are fixed to the base plate  53 .  
     [0030] Next, the mode of operation of the embodiment will be described.  
     [0031] Heat of the hot exhaust gas passing through the casing  1  tried to propagate via the seal guides  31  to the casing  1 . However, because of the heat shield bases  50  interposing between the casing  1  and the seal guides  31 , heat conduction is suppressed to minimum by the heat shield bases  50  and no hot spots with temperature of more than 200° C. are produced on the portions of the casing  1  where the seal guides  31  are mounted. Temperature of the portions of the casing  1  where the stud bolts  51  of the heat shield bases  50  are mounted may be as low as about 50-70° C.  
     [0032] Thus, heat conduction through the seal guides  31  is suppressed to minimum and hot spots are prevented from being produced on the casing  1 .  
     [0033] It is to be understood that the present invention is not limited to the above-mentioned embodiment and that various changes and modifications may be made without deferring from the scope and spirit of the invention.  
     [0034] As is clear from the foregoing, according to a gas seal structure for a high-temperature denitration apparatus in the invention, heat conduction through the seal guides is suppressed to minimum and hot spots are prevented from being produced on the casing.