GB1118885A - System for heat transfer at equalized pressure - Google Patents

Abstract

1,118,885. Gas cooling installations; plate heat exchangers. J. H. ANDERSON. 18 July, 1966 [22 July, 1965], No. 32106/66. Heading F4S. Heat transfer through a heat conducting wall between a first fluid stream at superatmospheric pressure and a second fluid stream initially at a lower pressure, is facilitated by pressurizing the second fluid by means of a pump and before it enters the heat exchanger, to a pressure about equal to that of the first fluid, thus enabling the heat conducting wall to be relatively thin. In the heat transfer system shown, natural gas at about 600 p.s.i.a. and at 50‹ F., from a storage vessel 12, is cooled in the heat exchanger 10 to about 0‹ F., by liquidpropane which is pressurized by a pump 20 before it enters the heat exchanger through a line 22. The propane is conducted from the heat exchanger through a line 24 to a turbine 26 where its pressure energy is utilized to drive the turbine. The pump 20 is driven both by the turbine and by an electric motor 29 through gearing 27-30. On leaving the turbine, the propane now partly vaporized is conveyed to an evaporative cooler 32 which operates. in conjunction with a compressor 48 and condenser 50 to liquefy the propane, thereafter conducted through a line 34 back to the pressurizing pump 20. The propane pressure at the pump outlet is maintained by a pressure sensitive device 56 which controls a diaphragm valve 58 in the line leading to the turbine 26. The device 56 is set to maintain a fixed pressure differential between the propane and natural gas at: the propane-inlet end of the heat exchanger; and a further device 68 (which may be either pressure or temperature sensitive) adjusts the pressure differential in the event of changes in the rate of propane flow. The valve 58 may alternatively be controlled by the pressure differential at the propane-outlet end of the heat exchanger (Fig. 2). In a further modification (Fig. 4), the speed of the pump (20b) is controlled by the pressure differential between the propane inlet and natural gas outlet of the heat exchanger; or a constantspeed pump may be used and the control effected by the throttle valve 58 or by a nozzle control on the turbine inlet. Damage to the heat exchanger 10 in the event of a pressure differential developing therein is prevented by equalizing valves 78 and 80 which then operate to bleed fluid from one side of the partition wall to the other. In a further modification (Fig. 7) the natural gas is cooled in one heat exchanger by a circulating intermediate fluid (e.g. butane), the intermediate fluid circuit including a pressurizing pump, turbine &c. as for the propane circulation above, and also another heat exchanger (152) in which the intermediate fluid is cooled after leaving the turbine, by a refrigerating system comprising a compressor (164) and a condenser (158), the second heat exchanger (152) acting as the refrigerant evaporator. Figs. 5 and 6 show one form of heat exchanger in which the cooled gas is also condensed. 114 are the walls separating the two fluids and the spacer strips 118 in the cooledgas path are slotted, Fig. 6. 128 is the gas inlet and 130 the condensate outet. Condensate collects and overflows a wier 132 to the outlet 130. The cooling fluid makes two passes from an inlet 122 to an outlet 124.