Defrosting method of high-energy-efficiency transcritical carbon dioxide two-stage compression combined cooling and heating system

Abstract

The invention discloses a defrosting method of a high-energy-efficiency transcritical carbon dioxide two-stage compression combined cooling and heating system, and belongs to the technical field of low-temperature refrigeration. When a frost layer of an evaporator reaches a certain thickness and starts to influence the heat exchange effect, a pipeline valve is adjusted, and high-temperature and high-pressure or medium-temperature and medium-pressure exhaust gas is introduced into the corresponding evaporator for defrosting; and after defrosting is finished, normal refrigeration cycle can be quickly recovered. Additional defrosting circulation can achieve simultaneous or graded defrosting, high-temperature and high-pressure exhaust and medium-temperature and medium-pressure exhaust of a high-pressure compressor and a low-pressure compressor are introduced into inlets of a medium-temperature evaporator and a low-temperature evaporator correspondingly, and a high-temperature working medium heats a frost layer on the outer side of a pipe through the pipe wall; meanwhile, cooling heat generated by the two refrigeration cycle air coolers is recycled by the system and used for heating water for heat supply, and cold and heat combined supply is achieved; economical and pollution-free CO2 is used as a cycle working medium in the main cycle and the defrosting cycle, compressed air or compressed steam in the mechanical supercooling cycle can be both used, and preferably, transcritical CO2 which is the same as that of a main system is used as the cycle working medium.

Description

technical field [0001] The invention relates to a low-temperature refrigeration system, in particular to a high-energy-efficiency transcritical carbon dioxide two-stage compression combined cooling and heating system with defrosting, which is mainly used in the fields of refrigeration and heating at various evaporation temperatures, such as supermarkets , cold storage, ice rink, district heating and other fields. Background technique [0002] With the continuous improvement of my country's national economic level, my country's energy and environmental problems are becoming more and more serious, especially in the context of carbon peak and carbon neutrality, the environmental problems are more prominent; the existing district heating coal The technical route of boiler and thermal power cogeneration has low energy efficiency of the system and CO emission 2 For the refrigeration and air-conditioning industry, there are also high power consumption during the use of existing equ...

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Problems solved by technology

[0002]With the continuous improvement of our national economy, the energy and environmental problems our country is facing are becoming increasingly severe, especially in the context of carbon peaking and carbon neutrality, The environmental problems faced are more prominent; the existing technical route of coal-fired boilers for district heating and cogeneration of thermal power has the defects of low system energy efficiency and large CO2 emissions, and its development is subject to For the refrigeration and air-conditioning industry, there is also high power consumption during the use of existing equipment, and commonly used refrigerants are likely to cause ozone layer damage and induce greenhouse effect problems; there is an urgent need to develop energy-saving, environmentally friendly, Low-carbon new refrigeration technology to achieve timely replacement of existing technologies; CO2 is a natural refrigerant that is safer than NH3, and its ODP The value (Ozone Depression Potential ozone depletion potential value) is 0, and the GWP (Global Warming Potential global warming potential value) is 1. It has good low temperature fluidity, heat transfer and high temperature heating performance, and is regarded as a refrigerant One of the most ideal alternative working fluids; compared with the traditional refrigeration system, the CO2 refrigeration cycle is safe and non-toxic, with large cooling capacity per unit volume, more compact system equipment, and low evaporation temperature The system has higher energy efficiency and other characteristics, and is suitable for industries such as supermarkets and cold storages that have low-temperature refrigeration requirements for refrigeration and freezing; when CO2 is used as the single refrigerant, transcritical CO2 The pressurized refrigeration cycle has better system performance, but the existing technical solutions all have the problem of being unable to comprehensively improve the system's use efficiency

[0003] During the operation of the low-temperature refrigeration system, when the air flows through the surface of the evaporator whose temperature is lower than 0°C, it will evaporate due to the condensation of water vapor in the air When the frost layer reaches a certain thickness, it will seriously affect the heat exchange effect of the heat exchanger and increase the energy consumption of the system; the commonly used defrosting methods are manual defrosting, electric heater defrosting, water flushing and Hot gas defrosting, etc.; the Chinese patents whose publication number is CN111174455A and publication number are CN110160292A disclose a method of using hot gas to defrost and introduce the high-temperature and high-pressure exhaust gas produced by the compressor into the evaporator to realize the rapid defrosting method. Compared with other method, hot air defrosting, because the frost layer starts to melt from the inside to the outside, and the frost layer will radiate heat to the environment after melting, so the resulting temperature fluctuation is smaller and more energy-saving; how to comprehensively increase the transcritical CO2The combination of the refrigeration cycle and the introduction of high-temperature and high-pressure exhaust gas into the evaporator to realize the rapid defrosting method, which is used in the field of refrigeration and heating under various evaporation temperatures has become a problem that needs to be solved on site

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