New Cooling Application: Total Heat Removal From Base Load LNG Plants

Most new and existing liquefied natural gas (LNG) plants have used dry air cooler (DAC) technology to reject the total heat required to liquefy natural gas. Only a few others are able to overcome environmental issues such as thermal pollution and water limitations using water cooler (WC) technology. For over 50 years, the Wet Air Surface Cooler (WSAC) has been used in industries such as petrochemical, refining, mining, and power for process fluid cooling & vapor condensing. These closed-loop, evaporative systems combine elements of a heat exchanger and a cooling tower into a single structure. Water is sprayed and air is moved over the exterior tube bundle surfaces where cooling takes place through evaporative heat transfer. The chief advantage of WSAC technology as well as the WC system compared to a DAC is the lower heat sink temperature for process heat removal; the WSAC and WC cool the process fluid to a temperature that approaches the lower wet bulb temperature as opposed to the higher ambient (dry bulb) temperature with a DAC. The refrigeration compression horsepower will be reduced. Therefore, the total LNG production will increase. The impact is significant for a country such as Australia where there is high ambient air temperature but low relative humidity. This paper evaluates the use of Wet Surface Air Coolers, dry air coolers and water coolers for applications including use of sea water for cooling water makeup. Technical risks as well as environmental and economic issues are also assessed.