A heat exchange method for liquefied natural gas cold energy for high-temperature cold energy users

Abstract

The invention discloses a heat exchanging method of liquid natural gas (LNG) cold energy used for a high-temperature-level cold energy user. According to the method, in the process of LNG entering tube passes of the upper portions of heat exchangers from an LNG storage tank, heat exchanging is achieved among the LNG, first refrigerant and nitrogen added into shell passes of the upper portions of the heat exchangers, and the temperature rises; the LNG passes through an air vaporizer and enters a natural gas pipeline network after the temperature rises; on the upper portions of the heat exchangers, the temperature of the first refrigerant and the nitrogen coming out of a refrigerant storage tank decreases to -40 DEG C-0 DEG C after heat exchanging is performed among the first refrigerant, the nitrogen and the LNG, and the first refrigerant and the nitrogen come into a liquid phase from a gas phase and enter the lower portions of the heat exchangers; the pressure PB of the nitrogen is determined through the formula (6) shown in the specification; the cooled first refrigerant achieves heat exchanging with second refrigerant on the lower portions of the heat exchangers, the temperature of the first refrigerant rises, the first refrigerant comes into a gas phase from the liquid phase and returns to the upper portions of the heat exchangers, and therefore a cycle is completed. Through using the usage amount of the nitrogen for changing the partial pressure of the refrigerant, the sensitivity of system operation is improved while the freezing point of the first refrigerant is lowered, and safety and stability in the heat exchanging process are guaranteed.

Description

technical field [0001] The invention relates to a heat exchange method, in particular to a heat exchange method in which liquefied natural gas cold energy is used for high-temperature cold energy users, and belongs to the technical field of cold energy utilization. Background technique [0002] Liquefied natural gas (LNG, liquid natural gas) is a low-temperature liquid mixture formed by natural gas deacidification, dehydration, and freezing and liquefaction in a low-temperature process. The production process consumes a lot of energy. According to calculations, the gasification process of each ton of LNG is equivalent to releasing 830-860 megajoules of cold energy. If this part of cold energy is recovered, energy can be saved and huge economic benefits can be generated. At the same time, because the pollutant discharge during the development and utilization of LNG cold energy is zero, it is a kind of green energy. The current LNG cold energy utilization methods include low-...

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Problems solved by technology

The invention patent solves the above-mentioned problems such as high requirements for equipment, large floor space, large demand for refrigerant, and large investment in civil engineering. However, the circulation device is not sensitive to pressure and faces problems such as pressure leakage, detection and control difficulties, etc.

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