Reducing the water usage of post-combustion capture systems: The role of water condensation/evaporation in rotary regenerative gas/gas heat exchangers

Abstract

Water usage is expected to greatly increase when CO2 capture is added to thermal power plants. A major contribution is the reduction of flue gases temperatures from 100-150 ºC to 30-50 ºC. The majority of studies to date propose the use of direct contact cooling, combining a cold water loop with water cooling. This article expands on a previous study of the same authors [1] proposing dry air-cooled options with rotary regenerative gas/gas heat exchangers, relying on ambient air as the cooling fluid, to eliminate the use of process and cooling water prior to the carbon capture system. It proposes, for the first time, a new stand-alone model of a bi-sector air/gas rotary heat exchanger, which includes the contribution to heat transfer of condensation/evaporation when flue gases are cooled below the dew point. It shows that water condensation from the flue gases in one sector of the heat exchanger, enhances the total heat transfer rate, due to the diffusion of water through the non-condensable gases boundary layer. In order to maintain the cooling capacity of these rotary regenerative heat exchangers, initially designed to operate without condensation, this article shows that they should be designed with surface properties, gas velocities and heat transfer channel geometries with the aim of allowing water condensate to remain on the metal elements surface, and then evaporate into the air stream when the metal elements have rotated to the air side. The model also predicts the location of water condensation, so that enamelled elements can be incorporated to the cold-end tiers of metal elements and mitigate any possible long-term corrosion problems.

Robust Joule-heating ceramic reactors for catalytic CO oxidation

“…Accordingly, heating reactor plays an important role in achieving fast reaction rates and high energy efficiencies. Conventional reactors are based on radiative heating by electrical furnaces in laboratories or through fuel combustion in industries [1], and include heat transfer process and complicate system with large volumes, leading to large temperature gradient within reactors [2,3]. It needs to be maintained at high temperatures while reactors only occupy a small volume ratio in the system [4,5], which greatly reduces system energy efficiency.…”

Computational Analysis for Good Thermal Exchange and Low Pressure Drop in Regenerative Air Preheaters

“…Wang et al [26] developed the thermal hydraulic calculation program integrated with the multi-objective and single-objective genetic algorithms to perform design optimizations of regenerative air preheaters used in the coal-fired power plants. Herraiz et al [27] investigated the use of rotary regenerative heat exchangers for the dry cooling of flue gases in combined cycle gas turbine plants equipped with post-combustion carbon capture. Sheng and Fang [28] experimentally investigated the effect of moisture on the air cleaning performance of a desiccant wheel with the objective to guide practical operation of clear air heat pump.…”