CO2 냉매를 이용한 초저온 액화사이클 성능특성

Abstract

Since the introduction of the world's first cascade liquefaction process in the 1 960s, there has been continuous development of liquefaction processes. N2 exp ansion process is one of the many liquefaction processes and is suitable for s mall scale LNG plant due to its less equipment and simplicity. However, the major issue of this process is low energy efficiency. In this paper, a pre-cooli ng cycle using CO2 refrigerant is designed to improve the N2 expansion proces s and its performance is evaluated. The process configuration with only one he at exchanger for pre-cooling and liquefaction is designed for simplicity. In the pre-cooling cycle, N2 gas is separated by a gas-liquid separator and separated N2 gas flows to the seawater cooler. It is used to improve energy efficiency b y additional cooling of the compressor pressure. The some analyses(e.g., a com parison of refrigerants, effects of evaporation temperature and liquefaction rate) are adapted to the proposed process. The results are as follows. With the incre ase of evaporation temperature, the compressor work of pre-cooling decrease a nd the energy consumption increase along with the increase of liquefaction rat e. As the result of optimization, the designed process with separator shows 45 % of coefficient of performance reduction compared with the basic process. Al so, heat transfer performance in LNG heat exchanger is investigated. In heat fl ow curves, the cold stream curve and hot stream curve matches better in the optimized process than the base process.