Design of small scale liquefaction cycle for natural gas

Abstract

Liquefied natural gas is found to be the most economical mode of transportation for distances covering more than 3500 miles. The boiling point of natural gas is 111 .7 K at atmospheric pressure and falls under the category of cryogenics. The process has components such as compressor, heat exchanger, expansion valve, insulating material, storage tank and pipes. The liquefaction of natural gas is achieved by processing natural gas in the liquefaction cycle. There are many parameters affecting the cycle such as compressor efficiency, heat exchanger effectiveness, ambient temperature, friction losses in pipes and insulating materials. In this thesis, some of the above mentioned parameters are considered while some parameters are neglected or assumed appropriately. It is observed that out of the existing cycles such as simple Linde-Hampson cycle, Pre-cooled cycle, Claude cycle and Kapitza cycle, each cycle has its own benefits and drawbacks. The fraction of liquefaction is found maximum for simple Claude cycle while the work required also reduces due to expansion of the high pressure gas through reciprocating expansion engine. The iterative procedure to find the configuration of each cycle is explained in the thesis and can be used with minimum bare inputs. An experimental setup can be built through these configurations and better study can be performed. To obtain the results, residue in the iterations is taken to 0.1 for temperature, pressure and mass flow rate both. In the Claude cycle, for mass flow rate of 1.02 kg/sec and the pressure ratio of 40, the fraction of liquefaction is found 0.0646 while in the kapitza cycle, for mass flow rate of 1.35kg/sec and the pressure ratio of 40, the fraction of liquefaction is found as 0.040. It is found that, the pressure required to liquefy the gas is not practical in the case of Linde-Hampson cycle. Further, it is found that Claude and Kapitza cycle can be used for experimental purpose.