Improvement of heat transfer performance and unmatched characteristics of a water-cooled carbon dioxide gas cooler

Abstract

The problem of mismatch in temperature glides in a water-cooled carbon dioxide (CO2) gas cooler has attracted much attention. This paper quantifies the degree of mismatch in temperature glides using an unmatched coefficient and then investigates and improves the unmatched characteristics and heat transfer performance of direct heating (DH) gas coolers with a validated simulation model. The results show that for a DH gas cooler, two zones can be specified with the mass flow ratio of water to CO2. Zone I, with a low flow ratio, produces high-temperature hot water and shows good temperature-glide matching, but the CO2 exit temperature and heat transfer rate are unsatisfactory. Zone II, with a high flow ratio, achieves acceptable CO2 exit temperature and heat transfer rate, but its hot water temperature is low, and its matching characteristic is poor. A segmentation heating (SH) gas cooler is thus developed to compensate for the weaknesses of the two zones while preserving their advantages by selectively adjusting the water flow of a certain part of the gas cooler. The results indicate that an SH gas cooler can increase the heat transfer rate by 4.4% at most and reduce the CO2 exit temperature by 2.3 °C at most. The hot water temperature can be increased by 6.9 °C at most, and the unmatched coefficient can be decreased by 8.2% at most.