Compact, high-effectiveness, gas-to-gas compound recuperator with liquid intermediary

Abstract

A liquid-loop compound recuperator is disclosed for high-ε heat exchange between a first shell-side fluid stream and a second shell-side fluid stream of similar thermal capacity rates (W/K). The compound recuperator is comprised of at least two fluid-to-liquid (FL) recuperator modules for transfer of heat from a shell-side fluid, usually a gas, to an intermediary tube-side heat transfer liquid (HTL). Each FL module includes a plurality of thermally isolated, serially connected, adjacent exchanger cores inside a pressure vessel. The cores are rows of finned tubes for cross-flow transfer of heat, and they are arranged in series to effectively achieve counterflow exchange between the HTL and the shell-side stream. The HTL may be water, an organic liquid, a molten alloy, or a molten salt. Alumina-dispersion-strengthened-metal fins, superalloy tubes, and a lead-bismuth-tin alloy HTL may be used for high temperatures. Cumene may be used as the HTL in cryogenic applications.

1 . A method for heat exchange between a first shell-side fluid stream at mean pressure p 1  and a second shell-side fluid stream at mean pressure p 2 , said method using
 a first set of serially connected thermally isolated cross-flow exchanger cores for transfer of heat between an intermediary tube-side heat transfer fluid (HTF) and the first shell-side stream,   a second set of serially connected thermally isolated cross-flow exchanger cores for transfer of heat between the HTF and the second shell-side stream,   said HTF characterized as being substantially liquid phase throughout all cores and having critical temperature not less than 370 K,   wherein a core is characterized as comprising at least one row of finned tubes,   said finned tubes are further characterized in that the length of the tube fins per row in the shell-side flow direction is typically less than 80 mm and the fin pitch is typically less than 8 mm.   
     
     
         2 . The method of  1  further characterized as having more than 4 thermally isolated cores exchanging with each shell-side stream and having effectiveness ε greater than 60% at design operating conditions. 
     
     
         3 . The method of  1  in which said shell-side fluids are further characterized as selected from the set comprised of organic liquids having viscosity greater than 1 cP at 310 K and gases at pressure greater than 0.05 MPa. 
     
     
         4 . The method of  1  where said HTF is further characterized as having flow rate G L  kg/s, specific heat C PL  J/kg-K,
 and W L =G L C PL , 
 said first shell-side fluid has flow rate G 1 , specific heat C P1 , and W 1 =G 1 C P1 , 
 said second shell-side fluid has flow rate G 2 , specific heat C P2 , and W 2 =G 2 C P2 , 
 said geometric mean shell-side conditions defined by W S =(W 1 W 2 ) 0.5 , 
 said tube-side conditions further characterized in that W L >0.7 W S  and W L <1.4 W S . 
 
     
     
         5 . The method of  1  further characterized in that said HTF is selected from the set comprised of water, organics, molten alloys, and molten salts and is further characterized as having F D  greater than 2E5 J 2 /(s-m 4 -K 2 -cP) at the mean operating temperature, where
     F   D   =k   t   ρC   P /μ,
 
 where k t  is in W/m-K, ρC P  is in J/m 3 -K, and μ is in cP. 
 
     
     
         6 . The method of  1  further characterized in that said tube-side HTF has F D  greater than the lesser of the F D  of either of the shell-side streams by more than a factor of 10 at mean operating conditions. 
     
     
         7 . The method of  5  further characterized in that each of said shell-side streams has F D  less than 2E5 J 2 /(s-m 4 -K 2 -cP) at the operating conditions. 
     
     
         8 . The method of  1  further characterized as including a plurality of liquid pumps and liquid reservoirs for circulation of a plurality of HTFs. 
     
     
         9 . The method of  1  in which said HTF is further characterized as substantially selected from the set comprised of polyphenyl ethers, polyol esters, polyalphaolefins, phosphate esters, phthalates, silicones, fluorocarbons, polymer esters, organic liquid mixtures that include alkylated polynuclear aromatics, and engine oils. 
     
     
         10 . The method of  9  further characterized as including a liquid reservoir with overhead gas space, said gas having H 2  partial pressure greater than 0.01 MPa, O 2  partial pressure less than 1 kPa, H 2 O partial pressure less than 10 kPa, and total pressure greater than 0.15 MPa. 
     
     
         11 . The method of  1  in which said HTF is further characterized as substantially comprised of a lead-bismuth-tin alloy. 
     
     
         12 . The method of  1  further characterized in that the mean pressure in said HTF is between 50% and 200% of the mean of p 1  and p 2 . 
     
     
         13 . The method of  1  wherein one of said shell-side fluids is further characterized as an organic solvent containing a dissolved gas that effervesces when the fluid is heated, and means are included between cores for separating the effervesced gas from the liquid. 
     
     
         14 . The method of  1  wherein one of said shell-side fluids is further characterized as a gas containing a vapor that condenses when the fluid is cooled, with means for draining the condensed liquid from a core. 
     
     
         15 . The method of  1  in which said HTF is further characterized as an organic liquid, and means are included for separation of reaction products from said HTF. 
     
     
         16 . The method of  1  further characterized in that p 2  is greater than 3p 1  and the typical fin pitch in said second set of cores is less than 70% of the typical fin pitch in said first set of cores. 
     
     
         17 . The method of  1  further characterized as including transverse passages between thermally isolated cores to equilibrate shell-side pressures across the faces of said cores, wherein cores are considered thermally isolated if fewer than 30% of the fins are continuous between adjacent cores in the shell-side flow direction and the tube pattern is not interleaved between adjacent cores.