High performance heat exchangers

Abstract

Disclosed are means for improving the service-life of indirect tubesheet type heat exchangers used in chemical reactors, particularly those exposed to reducing, nitridizing and/or carburizing environments. Such means include the use of certain ferrules within the heat exchange tubes and/or weld types used in construction of these heat exchangers.

What is claimed is:  
     
         1 . A heat exchange apparatus for use in a reducing, carburizing and/or nitridizing environment comprising: (a) a shell having an entry tubesheet portion and an exit tubesheet portion, each tubesheet having a plurality of holes, wherein the shell has at least one inlet and one outlet for heat exchange medium; (b) a plurality of tubes disposed within the shell wherein an entry end of each tube is affixed to the entry tubesheet and an exit end of each tube is affixed to the exit tubesheet such that an axis of the tube and an axis of an entry and exit tubesheet hole are coincident; and (c) a plurality of ferrules, each ferrule having an entry end and an exit end extending through an entry tubesheet hole into a tube wherein the exit end extends below the entry tubesheet, the ferrule comprising silicon nitride.  
     
     
         2 . The apparatus of    claim 1    wherein the tubes comprise carbon steel, stainless steel, nickel alloy, nickel-chromium alloy or nickel-molybdenum alloy.  
     
     
         3 . The apparatus of    claim 2    wherein the tubes comprise carbon steel or nickel-chromium alloy.  
     
     
         4 . The apparatus of    claim 2    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         5 . The apparatus of    claim 1    wherein the ferrule has a converging/diverging design in longitudinal cross-section.  
     
     
         6 . A heat exchange apparatus comprising: (a) a shell having an entry tubesheet portion and an exit tubesheet portion, each tubesheet having a plurality of holes, wherein the shell has at least one inlet and one outlet for heat exchange medium; (b) a plurality of tubes disposed within the shell wherein an entry end of each tube is affixed to the entry tubesheet and an exit end of each tube is affixed to the exit tubesheet such that an axis of the tube and an axis of an entry and exit tubesheet hole are coincident, each tube being formed of a metal including nickel-chromium alloy; and (c) a plurality of ferrules, each ferrule having an entry end and an exit end extending through an entry tubesheet hole into a tube wherein the exit end extends below the entry tubesheet, the ferrule comprising nickel-chromium alloy.  
     
     
         7 . The apparatus of    claim 6    wherein the ferrule nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         8 . The apparatus of    claim 6    wherein the ferrule has an entry end and an exit end; the entry end having an opening tapering conically into a pipe section, the outer diameter of the entry end being greater than an inner diameter of the heat exchange tube; the pipe section having an outer diameter up to 99% of the inner diameter of the heat exchange tube; the exit end of the ferrule having an outer diameter that is substantially the same as the inner diameter of the heat exchange tube.  
     
     
         9 . A ferrule for use in a heat exchange tube wherein the ferrule has an entry end and an exit end; the entry end having an opening tapering conically into a pipe section, the outer diameter of the entry end being greater than an inner diameter of the heat exchange tube; the pipe section having an outer diameter that is not more than 99% of the inner diameter of the heat exchange tube; the pipe section having an expanded area with an outer diameter that is substantially the same as the inner diameter of the heat exchange tube.  
     
     
         10 . The ferrule of    claim 9    wherein the ferrule comprises silicon nitride or nickel-chromium alloy.  
     
     
         11 . The ferrule of    claim 10    wherein the ferrule comprises silicon nitride.  
     
     
         12 . The ferrule of    claim 10    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         13 . A ferrule for use in a heat exchange tube wherein the ferrule has an entry end and an exit end; the entry end having an opening tapering conically or trumpet-shaped into a pipe section, the outer diameter of the entry end being greater than an inner diameter of the heat exchange tube; the pipe section having an outer diameter that is substantially the same as the inner diameter of the heat exchange tube; and wherein the ferrule has a converging/diverging design in longitudinal cross-section.  
     
     
         14 . The ferrule of    claim 13    wherein the ferrule comprises ceramic, carbon steel, stainless steel, nickel alloy, nickel-molybdenum alloy, or nickel-chromium alloy.  
     
     
         15 . The ferrule of    claim 13    wherein the ferrule comprises silicon nitride, nickel-chromium alloy, carbon steel or stainless steel.  
     
     
         16 . The ferrule of    claim 14    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         17 . A heat exchange apparatus for use in a hydrogen cyanide reactor including: (a) a shell having an entry tubesheet portion and an exit tubesheet portion, each tubesheet having a plurality of holes, wherein the shell has at least one inlet and one outlet for heat exchange medium; and (b) a plurality of tubes disposed within the shell wherein an entry end of each tube is affixed to the entry tubesheet and an exit end of each tube is affixed to the exit tubesheet such that an axis of the tube and an axis of an entry and exit tubesheet hole are coincident, wherein each tube entry end is affixed to the entry tubesheet by a down-hole weld.  
     
     
         18 . The apparatus of    claim 17    wherein the tubes comprise carbon steel, stainless steel, nickel alloy, nickel-chromium alloy or nickel-molybdenum alloy.  
     
     
         19 . The apparatus of    claim 18    wherein the tubes comprise carbon steel or nickel-chromium alloy.  
     
     
         20 . The apparatus of    claim 18    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         21 . The apparatus of    claim 17    wherein the down-hole weld is heat treated.  
     
     
         22 . The apparatus of    claim 17    further comprising a plurality of ferrules, each ferrule having an entry end and an exit end extending through an entry tubesheet hole into a tube wherein the exit end extends below the entry tubesheet.  
     
     
         23 . The apparatus of    claim 22    wherein the ferrule comprises silicon nitride or nickel-chromium alloy.  
     
     
         24 . The ferrule of    claim 23    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         25 . An apparatus for preparing hydrogen cyanide by reacting hydrocarbon, ammonia and optionally oxygen-containing gas in the presence of a platinum-containing catalyst at a temperature in the range from 1000° to 1400° C., including a reaction zone, an optional refractory zone, and a heat exchange zone including: (a) a shell having an entry tubesheet portion and an exit tubesheet portion, each tubesheet having a plurality of holes, wherein the shell has at least one inlet and one outlet for heat exchange medium; (b) a plurality of tubes disposed within the shell wherein an entry end of each tube is affixed to the entry tubesheet and an exit end of each tube is affixed to the exit tubesheet such that an axis of the tube and an axis of an entry and exit tubesheet hole are coincident; and (c) a plurality of ferrules, each ferrule having an entry end and an exit end extending through an entry tubesheet hole into a tube wherein the exit end extends below the entry tubesheet, the ferrule comprising silicon nitride.  
     
     
         26 . The apparatus of    claim 25    wherein the tubes comprise carbon steel, stainless steel, nickel alloy, nickel-chromium alloy or nickel-molybdenum alloy.  
     
     
         27 . The apparatus of    claim 26    wherein the tubes comprise carbon steel or nickel-chromium alloy.  
     
     
         28 . The apparatus of    claim 27    wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.  
     
     
         29 . The apparatus of    claim 25    wherein each entry tube end is affixed to the entry tubesheet by a down-hole weld.  
     
     
         30 . A process for preparing hydrogen cyanide comprising the steps of: feeding reaction gas to a reactor, the reaction gas comprising hydrocarbon, ammonia and optionally an oxygen-containing gas; reacting the reaction gas in the presence of a catalyst to give product gas; cooling the product gas in a heat exchange apparatus comprising (a) a shell having an entry tubesheet portion and an exit tubesheet portion, each tubesheet having a plurality of holes, wherein the shell has at least one inlet and one outlet for heat exchange medium; (b) a plurality of tubes disposed within the shell wherein an entry end of each tube is affixed to the entry tubesheet and an exit end of each tube is affixed to the exit tubesheet such that an axis of the tube and an axis of an entry and exit tubesheet hole are coincident; and (c) a plurality of ferrules, each ferrule having an entry end and an exit end extending through an entry tubesheet hole into a tube wherein the exit end extends below the entry tubesheet, the ferrule comprising silicon nitride; and recovering hydrogen cyanide from the cooled product gas.