System and method for comprehensively utilizing cold energy of LNG

Abstract

The invention relates to a system for comprehensively utilizing cold energy of LNG. The system comprises a composite Rankine cycle power generation sub-system, a single-working-medium Rankine cycle power generation sub-system, an ice-making sub-system and a direct expansion power generation sub-system, wherein the composite Rankine cycle power generation sub-system comprises an LNG evaporator, a mixed-working-medium booster pump, a heat exchanger, a mixed-working-medium evaporator, a mixed-working-medium superheater, a mixed-working-medium expander, a first single-working-medium booster pump, a first single-working-medium evaporator, a first single-working-medium superheater and a first single-working-medium expander; the single-working-medium Rankine cycle power generation sub-system comprises a first NG superheater, a second single-working-medium booster pump, a second single-working-medium evaporator, a second single-working-medium superheater and a second single-working-medium expander; and the direct expansion power generation sub-system comprises a second NG superheater, a third NG superheater, a fourth NG superheater and an NG expander. The system disclosed by the invention realizes the most abundant comprehensive utilization for the cold energy of LNG by virtue of the cold energy from minus 162 DEG C to minus 10 DEG C of the LNG.

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 LNG cold energy utilization and a power generation and ice-making method based on the system, in particular to a system and method for comprehensive utilization of LNG 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 the LNG vaporizer Being taken away by...

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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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