Cold Energy Utilization by Stirling Engine
Liquefied natural gas (LNG) will play an important role in the World, as evidenced by the constantly growing LNG market. One of its branches is the small-scale LNG market, which includes supplies to satellite gas networks, factories, or as fuel for car and bunker, fuel for vessels. LNG is mainly redistributed by trucks and then regassify in atmospheric air vaporizes (AAV), where the gas is heated by atmospheric air and the cold is thereby lost. Effective utilization of this energy, will allow the LNG technology to be more competitive, as well as to recover some of the energy lost in the liquefaction process. The purpose of this article is to explore the possibility of utilizing the cold energy from the LNG regasification process to drive a Stirling engine. For the aim of this analysis, an analytical method were used - Schmidt analysis, which assumes an isothermal processes of gas expansion and compression inside the engine, as well as excellent regenerator performance. Helium was used as a working factor. It was assumed, that the engine was arranged in accordance with alpha geometry. Average monthly air temperatures and average hourly temperatures for the coldest and warmest day of the year were applied to the model using macros and Excel worksheets. Those temperatures are the average from many years for Warsaw. Based on the applied data, the amount of regassified LNG, power of the entire system, indicated engine power, engine and system efficiency, as well as temperature in cylinders (and thus in heat exchangers) were calculated. The results showed the reasonability of using LNG as the lower heat source, and atmospheric air as the upper heat source. The system generates sufficient power, in all conditions, to meet the system energy consumption requirements i.e. fan. It produces significant excess amount of energy, which varies on the external conditions, i.e. the air temperature. In addition, the system meets the requirements for regassify amount of LNG at the end user.