Research on liquefaction process of FLNG unit with propane precooling device and double nitrogen expander
Chen Xingyi1, Yuan Zhongming1, Xie Ying1 and Wang Shuhua2
COMPUTER MODELLING & NEW TECHNOLOGIES 2014 18(12A) 431-438
1Oil and gas engineering Institute of Southwest Petroleum University, Cheng du, 610500-China
2Schulich School of Engineering, University of Calgary, Calgary, T2N 1N4-Canada
Along with the further development of global natural gas exploration and development, more and more deepwater gas fields, marginal gas fields and associated gas fields have been found. As a new development technology of offshore deepwater gas fields, a floating LNG unit which integrates production, storage and offloading into one (FLNG), with its advantages of lower investment, shorter construction period and reusability, is warmly welcomed today. By investigating the latest liquefaction technology of natural gas both at home and abroad, and combining with the FLNG production project under construction, the study reported in this paper concluded that the nitrogen expansion liquefaction technology with precooling device is the first choice for liquefaction technology of natural gas for FLNG equipment. And based on that, this paper conducted optimized analysis of the FLNG equipment liquefaction process, and established a HYSYS simulation. The result indicated that three-stage propane refrigeration technology adopted in the precooling period is able to reduce the temperature to 273.16 K, 258.16 K and 238.16K respectively, and thus the compression power during the precooling period is reduced, while the precooling effect of natural gas is improved. In addition, double nitrogen expansion refrigeration technology is employed during the super-cooling period, the division temperature of two-stage refrigeration is chosen to be 178.16 K, the total compression function drops to the lowest value, the refrigeration effect is improved and the liquefaction ratio during the whole process reaches 95%. Therefore, the three-stage liquefaction technology with propane precooling device and double nitrogen expander is better adapted to offshore gas fields, and is suitable for FLNG equipment.