System and method for comprehensive utilization of liquefied natural gas cold energy

Abstract

The invention relates to an LNG cold energy comprehensive utilization system which comprises a combined Rankine cycle electricity generation subsystem, an ice-making subsystem and a direct expansion electricity generation subsystem, wherein the combined Rankine cycle electricity generation subsystem comprises an LNG evaporator, a mixed working medium booster pump, a heat exchanger, a mixed working medium heater, a mixed working medium evaporator, a mixed working medium expansion machine, a single medium booster pump, a single medium evaporator and a single working medium expansion machine; the ice-making subsystem comprises a first natural gas superheater, an ice maker unit and a natural gas heater; the direct expansion electricity generation subsystem comprises a natural gas expansion machine and a second natural gas superheater. According to the LNG cold energy comprehensive utilization system and method, the cooling capacity of LNG from minus 162 DEG C to minus 10 DEG C is used, only little cooling capacity is taken away by seawater, and most comprehensive utilization of LNG cooling capacity is realized under the condition that the complexity degree of the technological process is not increased.

Description

technical field [0001] The invention belongs to the field of recovery and utilization of low-temperature heat energy, and relates to a power generation and ice-making system based on utilization of liquefied natural gas cold energy and a power generation and ice-making method based on the system, in particular to a system and method for comprehensive utilization of liquefied natural gas cold energy. Background technique [0002] Liquefied natural gas (LNG) is natural gas (NG) that exists in liquid form at low temperatures. Its storage temperature is about -160°C, which is more convenient for storage and transportation than NG. However, LNG usually needs to be re-gasified into NG to be widely used. LNG The cold energy released during vaporization is about 840kJ / kg, so the cold energy stored in LNG is very huge. Recovering this part of cold energy has considerable economic and social benefits. On the contrary, if it is not recycled, this part of cold energy is usually stored in...

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Problems solved by technology

In this way, the cooling capacity required for ice making is completely provided by the working fluid in the Rankine cycle. When the market demand for ice making decreases, the ice making cycle will stop, resulting in the Rankine cycle not working properly.

The Rankine cycle is a single cycle of mixed working fluid, which is 10-20% lower than the power generation efficiency of the mixed working medium Rankine cycle and the single working medium Rankine cycle.

The Chinese patent with publication number 104989473A provides a power generation system and a power generation method based on the system. This method only utilizes the cold energy and possible pressure energy of LNG-162~-51°C. The cold energy above -51°C is due to The limit of seawater temperature cannot be taken away by seawater. At the same time, it is mentioned in this method that the pressure and temperature of the ninth stream will change with the seawater temperature. Fluctuations, (0.5~2MPa) cannot make the expander run stably for a long time, so this method does not consider the bearing capacity of the expander under different working conditions; The temperature is 28°C (the third stream III) (the temperature of the sea water varies with the seasons), the pressure is 10MPa... through the propane working medium pump 10, it is boosted to 1.0MPa (the twelfth stream XII), and the power consumption of the booster pump is 40.32kW. Enter the seawater vaporizer 11 to exchange heat and evaporate into steam at 28°C", it is mentioned in paragraph 0037-0039 of the manual that "the NG temperature at the outlet of the seawater heat exchanger 3 is 5°C (the third stream III) (the seawater temperature varies with the seasons ), the pressure is 10MPa... pressurized to 0.49MPa by the propane working medium pump 10 (the twelfth stream Ⅻ), the booster pump consumes 21.75kW, and enters the seawater vaporizer 11 for heat exchange and evaporates into steam at 5°C." From this we can see that, The pressure difference changes greatly, and the expander cannot perform work

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