Comprehensive evaluation on a combined refrigeration system of producing dry ice storage cold using fluctuating liquefied natural gas cold energy
摘要
In view of the fluctuations in the LNG regasification rate caused by the use of NG, in order to effectively utilize the unstable LNG cold energy, a combined refrigeration system utilizing the unstable LNG cold energy for producing dry ice storage cold is designed. Set the refrigeration capacity of the cooling room to 30 MW, the impact of fluctuations in the LNG mass flow rate on the performance of the combined system, and the refrigeration and supplement cold load of the combined system at different times of a typical day are analyzed. The exergy distribution, annual performance, annual carbon emission, and annual economy of the combined system are analyzed. It is found that with the increase of LNG mass flow rate, the COP of the combined system decreases while the exergy efficiency increases. The refrigeration capacities of the freezing rooms are 2 MW, 12 MW, 22 MW, and 32 MW, respectively, and the mass flow rates of LNG are 300–600 t/h, 350–600 t/h, 450–600 t/h, and 550–600 t/h, respectively. The COP and exergy efficiency of the combined system tend to stabilize at 3.74 and 79.04%, respectively. On a typical day, under the condition of fluctuations in the LNG regasification rate, when the refrigeration demand of the freezing room is 2 MW, the combined system does not require supplement cold from the NH3/CO2 cascade refrigeration cycle, and there is an excess of 174 MW of dry ice storage cold. When the refrigeration demand of the freezing room is 42 MW, the combined system needs the NH3/CO2 cascade refrigeration cycle to supplement the cold at all times. In addition, compared with the system supplied with coldness by the NH3/CO2 cascade refrigeration cycle alone, the annual COP of the combined system is significantly improved, and the annual power consumption and carbon emission are reduced, with the payback period reduced by 0.87~1.68 years.