Design and optimization of natural gas liquefaction process using brazed plate heat exchangers based on the modified single mixed refrigerant process

Abstract

The multi-stream plate-fin heat exchangers (PFHEs) are widely used as the core heat transfer equipment in small-scale natural gas liquefaction processes. However, the PFHEs have disadvantages such as the strict pre-treatment standard and the complicated engineering and transportation. The brazed plate heat exchangers (BPHEs) have been suggested to replace the PFHEs to overcome such disadvantages. In this paper, the methodology for transforming PFHE processes into BPHE processes was introduced and a novel liquefaction process using BPHEs was proposed based on the modified single mixed refrigerant process. The key parameters of the new process were optimized by using the genetic algorithm, and the optimal operating conditions were compared with the base case. The results showed that the specific energy consumption (SEC) of the optimized case was 10.3% lower than that of the base case, while it was slightly higher than the SEC of the original PFHE process. Additionally, the exergy losses of the major equipment in the process were analyzed. The exergy losses were reduced by 7.6%, 19.5%, 29.5% and 15.3% respectively for the compressors, the heat exchangers, the Joule-Thompson valves and the water coolers in the optimized case. The total exergy loss was lower by 14.7% after the optimization.