Performance of direct-contact heat and mass exchangers with steam-gas mixtures at subatmospheric pressures

Abstract

Tests were conducted to determine the performance of direct-contact heat and mass exchangers containing structured packings in field applications. The exchangers tested serve as intercoolers-condensers between the various stages of a vacuum compression train that discharges the exhaust gases from a low-temperature power plant. The gases, which consist of low-pressure steam and a mixture of noncondensible gases, are contacted with seawater as the coolant. The structured packing is more commonly used as fill in evaporative cooling towers, which operate at atmospheric pressure. These tests were conducted at absolute pressures between 1.6 and 16 kPa, and noncondensible mass fractions between 0.1 and 0.9, significantly extending the existing data base on condensers. The new data show the effect of high noncondensible mass fractions and superheat on the heat and mass transfer process. The results indicate that these exchangers can be designed to condense the steam to within a few percent of the theoretical limits, while attaining small temperature approaches, and incurring low pressure drops. Useful approximations to estimate their performance are discussed. The data were also used to validate detailed computer models, which accurately predict the heat and mass transfer over the entire range tested. These models can now be used with confidence for engineering design of condensers in geothermal and conventional power plants.