Method for refrigerating by using waste heat

Abstract

The invention discloses a method for refrigerating by using waste heat, which comprises the following steps of: connecting a plurality of heat exchangers in series to sequentially generate steam with different temperatures and pressures; the generated steam with different temperatures and pressures is respectively used as a power source of the multi-stage ejector; and the number of the ejectors is consistent with that of the heat exchangers. The method for generating steam by using flue gas waste heat is different from the prior art. According to a method in the prior art, steam with temperature and pressure is generated and serves as a power source for multi-stage jet refrigeration; according to the method, steam with multiple temperatures and pressures is generated and sequentially serves as a power source for multi-stage jet refrigeration. Under the fixed flue gas waste heat condition, the higher refrigerating capacity is achieved through the method.

Description

Technical Field

[0001] The invention relates to thermal refrigeration technology, and in particular to a method for refrigeration using waste heat. Background Art

[0002] The method of improving COP by jet cooling is mainly through increasing steam pressure or using multi-stage jet. The steam pressure can only be increased when the flue gas temperature is high enough. This method limits the reuse conditions of low-temperature flue gas. For example, when the flue gas temperature is only 150℃, the steam temperature that can be produced can only be less than 150℃, and the steam pressure can only be less than 477kPa (saturated vapor pressure at 150℃). The closer the steam temperature is to 150℃, the less steam is produced. Conventional multi-stage jet cooling, such as three-stage jet cooling, Figure 2 As shown, with flue gas as the heat source, a steam generator is used to produce steam as a power source to drive three ejectors, generate a vacuum, draw out the water vapor in the evaporator, and make the water in the evaporator evaporate and cool continuously to produce ice water. This method only produces steam of one temperature and pressure as a power source for multi-stage ejector refrigeration, which limits the reuse conditions of low-temperature flue gas. Summary of the invention

[0003] The object of the present invention is to overcome the above-mentioned deficiencies of the prior art and to provide a method for refrigeration using waste heat so as to achieve a higher refrigeration capacity under fixed waste heat conditions.

[0004] To achieve the above object, the technical solution of the present invention is:

[0005] A method for refrigeration using waste heat, comprising:

[0006] Several heat exchangers are arranged in series to sequentially generate steam of different temperatures and pressures;

[0007] The steam with different temperatures and pressures is used as the power source of the multi-stage ejector.

[0008] Optionally, there are three heat exchangers, which generate steam of three different temperatures and pressure levels in sequence, namely, high-temperature and high-pressure steam three, medium-temperature and high-pressure steam two, and low-temperature and low-pressure steam one; there are three ejectors, namely, a three-stage ejector, a two-stage ejector, and a one-stage ejector; the steam three serves as the power source of the three-stage ejector, the steam two serves as the power source of the two-stage ejector, and the steam one serves as the power source of the one-stage ejector.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] The method of using flue gas waste heat to generate steam in the present invention is different from the prior art. The prior art method generates steam of one temperature and pressure as the power source for multi-stage jet refrigeration; the method of the present invention generates steam of multiple temperatures and pressures, which are sequentially used as the power source for multi-stage jet refrigeration. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the three-stage ejection refrigeration design using the method of the present invention in Example 1;

[0012] Figure 2 It is a schematic diagram of the three-stage ejection refrigeration design using the prior art method in Example 2;

[0013] Figure 3 The calculation results of the three-stage ejection refrigeration using the method of the present invention in Example 1;

[0014] Figure 4 The calculation results of the three-stage ejection refrigeration using the prior art method in Example 2 are shown in FIG. DETAILED DESCRIPTION

[0015] Example:

[0016] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0017] Example 1: Three-stage ejection refrigeration design of the present invention

[0018] Flue gas conditions: temperature 150℃, flow rate 7065Nm 3 / h

[0019] Waste heat recovery steam: three heat exchangers are connected in series to produce steam at three different temperatures and pressures. The design and calculation results are as follows: Figure 1 and Figure 3 As shown, U is the total heat transfer coefficient of the heat exchanger, A is the area of ​​the heat exchanger, and the selection and calculation of the spray design refer to PERRY'S CHEMICAL ENGINEERS' HANDBOOK, FIG. 10-100 (Perry Chemical Engineers Handbook, Figure 10-100). When the refrigeration evaporator produces 7°C ice water, the first-stage ejector can extract 25kg / h of low-pressure steam and produce 2.97m3 / h of 7°C ice water.

[0020] Example 2: Three-stage ejection refrigeration design of the prior art

[0021] Flue gas conditions: temperature 150℃, flow rate 7065Nm 3 / h

[0022] Waste heat recovery steam: The three heat exchangers in Example 1 are combined into one heat exchanger, which can produce 113℃ steam 126.4kg / h, which is used as the power source to provide three ejectors. The design and calculation results are as follows: Figure 2 and Figure 4 As shown, the selection and calculation of the ejector still refer to PERRY'S CHEMICAL ENGINEERS' HANDBOOK, FIG. 10-100. When the refrigeration evaporator produces 7°C ice water, the first-stage ejector can extract 20.6kg / h of low-pressure steam and produce 2.45m3 / h of 7°C ice water, and the COP is equivalent to 0.16, and the refrigeration capacity is significantly less than that of the first embodiment.

[0023] It can be seen that the three-stage jet refrigeration design of the prior art must increase the temperature, pressure or steam volume of the power source to achieve the same cooling capacity as the present invention. However, when the flue gas conditions are fixed, the required steam cannot be obtained through waste heat recovery. Taking Example 2 as an example, if the cooling capacity is to be the same as that of Example 1, the steam volume of the power source at 113°C needs to be increased to 153.4kg / h. However, even if the area of ​​the heat exchanger is infinitely large, the maximum 113°C steam that can be produced is only 136.7kg / h.

[0024] In summary, it can be seen that under fixed flue gas waste heat conditions, a higher refrigeration capacity can be achieved by adopting the method of the present invention.

[0025] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for refrigeration using waste heat, characterized in that: include: Several heat exchangers are arranged in series to sequentially generate steam of different temperatures and pressures; The steam with different temperatures and pressures is used as the power source of the multi-stage ejector.

2. The method for refrigeration using waste heat according to claim 1, characterized in that: There are three heat exchangers, which generate steam of three different temperatures and pressure levels in sequence, namely, high-temperature and high-pressure steam three, medium-temperature and high-pressure steam two, and low-temperature and low-pressure steam one; there are three ejectors, namely, a three-stage ejector, a two-stage ejector, and a one-stage ejector; the steam three serves as the power source of the three-stage ejector, the steam two serves as the power source of the two-stage ejector, and the steam one serves as the power source of the one-stage ejector.

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