Two-dimensional cascade heat recovery system and operation method thereof

Abstract

The invention discloses a two-dimensional cascade heat recovery system and an operation method thereof. The system comprises large-space environment air with non-uniform temperature distribution, an N + X stage heat recovery system and heating fluid. Ambient air is branched into N + X stages of heat recovery air flow paths to realize cascade heat recovery of a first dimension; the first N stages of active heat recovery systems adopt M stages of stepped suction and exhaust circulating heat pumps to achieve second-dimension stepped heat recovery, and the rear X stages of passive heat recovery systems are all heat recovery heat exchangers. The heating fluid realizes cascade heating through condensation heat of the first N stages of heat recovery systems, and then exchanges heat with the later X stages of heat recovery air. The system can carry out variable load operation according to actual temperature span conditions, and different operation modes are adopted under the large temperature span condition, the medium temperature span condition and the small temperature span condition so that the optimal heat recovery effect can be achieved. Through two-dimensional cascade heat recovery, the energy utilization efficiency is remarkably improved, waste heat in the industrial process can be effectively recovered, and the requirements of different technological processes for high-quality heat energy are met.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial energy conservation and carbon reduction, and particularly relates to a two-dimensional cascade heat recovery system and an operation method thereof. Background Art

[0002] A large number of industrial parts are usually processed through an assembly line. Workpieces will go through many technological processes on the assembly line, and high-temperature processes are often essential. After the workpieces go through high-temperature processes, they carry a large amount of heat capacity, and usually use the workshop environment for natural cooling. However, this process will bring some adverse effects. Specifically, during the cooling process, a large amount of waste heat carried by the workpieces directly enters the workshop environment, not only causing waste of thermal energy, but also increasing the workshop temperature, deteriorating the working environment, and affecting the thermal comfort and work efficiency of workers. In addition, due to the high temperature of the workpieces and the long cooling distance, the temperature distribution of the workshop environment air is uneven in a large space, thus forming a large temperature difference condition, and there is an urgent need to adopt an energy-saving and efficient heat recovery technology to reduce energy waste.

[0003] At present, the commonly used heat recovery system in the industrial field is a vapor compression heat pump. The heat pump does work through a compressor, absorbs heat from a low-temperature heat source and releases heat to a high-temperature heat source, thereby realizing the recovery of thermal energy and the improvement of energy quality. However, a single heat pump system has obvious limitations in the industrial heat recovery scenario with a large temperature difference condition. On the one hand, the large temperature difference condition leads to an increase in the compression ratio of the heat pump and a decrease in the system energy efficiency; on the other hand, the heat recovery of a single heat pump is limited, and the problem of energy waste is still prominent. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art and propose a two-dimensional cascade heat recovery system and an operation method thereof to achieve a more comprehensive and efficient heat recovery effect.

[0005] The applicant believes in the conception process that the ambient air under the conditions of a large space and a large temperature difference creates a heat recovery condition in one dimension, and for each stage of heat recovery, a multi-stage cascade suction and exhaust heat pump cycle can be adopted, which creates a heat recovery condition in another dimension. The two-dimensional cascade refers to the classification of the spatial temperature gradient (N + X levels) in the first dimension and the heat pump energy level gradient (M levels) in the second dimension, where N is an integer ≥ 1, X is an integer ≥ 0, and M is an integer ≥ 1. Through the two-dimensional cascade heat recovery, the heat recovery efficiency of the system can be greatly improved.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] On the one hand, the present invention provides a two-dimensional cascade heat recovery system, including ambient air with non-uniform spatial temperature distribution, an N + X-stage heat recovery system, and a heating fluid.

[0008] The ambient air with non-uniform temperature distribution in a large space has a gradually decreasing temperature along a certain direction, forming a large temperature difference condition as a whole. N+X levels of heat recovery air flow paths are branched out from this ambient air to achieve cascaded heat recovery in the first dimension.

[0009] The N+X level heat recovery system corresponds one-to-one with the N+X level heat recovery air flow paths, where the first N levels are active heat recovery systems and the last X levels are passive heat recovery systems. In the active heat recovery system described, each level of the heat recovery system can adopt an M-level cascaded suction and exhaust heat pump, that is, composed of M heat pump cycles, to achieve cascaded heat recovery in the second dimension. In the passive heat recovery system described, each level of the heat recovery system is a heat recovery heat exchanger.

[0010] The heating fluid described, according to the heating medium requirements, is generally water or air and includes N+1 heating fluid flow paths. Among them, the first N heating fluid flow paths correspond one-to-one with the first N levels of the heat recovery system, and the first N flow paths are mixed to form the (N+1)th flow path. The (N+1)th flow path flows through X heat recovery heat exchangers in sequence to exchange heat with the last X levels of the heat recovery air flow paths, thereby realizing passive heat recovery.

[0011] Furthermore, in the active heat recovery system described, each level of the heat recovery system includes 1 to M heat pump sub-cycles, and each heat pump sub-cycle consists of a compressor, a condenser, an expansion valve, and an evaporator to form a closed loop.

[0012] Furthermore, in the active heat recovery system described, 1 to M evaporators of each level of the heat recovery system are arranged on the heat recovery air flow path corresponding to this level. 1 to M condensers of each level of the heat recovery system are arranged on the heating fluid flow path corresponding to this level. In the passive heat recovery system described, the heat recovery heat exchanger of each level of the heat recovery system is arranged on the heat recovery air flow path corresponding to this level.

[0013] On the other hand, the present invention also provides an operation method for the two-dimensional cascaded heat recovery system as described above, and this system can operate with variable loads according to the actual temperature difference conditions in a large space. Specifically as follows:

[0014] When ambient air with large temperature difference conditions (air temperature difference > 40 °C) is generated in a large space, all systems operate. At this time, N+X levels of heat recovery air flow paths are branched out from the ambient air with large temperature difference conditions. The first N levels of heat recovery air all flow through 1 to M evaporators of the heat recovery system at this level in sequence, and the last X levels of heat recovery air flow through the heat recovery heat exchanger, thereby realizing two-dimensional cascaded heat recovery.

[0015] When the ambient air with medium temperature difference conditions (air temperature difference of 20 - 40 °C) is generated in a large space, the system operates flexibly according to the specific situation. For example, when the X-level heat recovery air flow path is closed, the system only realizes active heat recovery. Or for the first N-level active heat recovery system, each level of the system reduces the number of operating heat pump sub-cycles according to the situation, so as to achieve two-dimensional cascade heat recovery with load reduction.

[0016] When the ambient air with small temperature difference conditions (air temperature difference < 20 °C) is generated in a large space, the system can operate according to only one-dimensional heat recovery. For example, heat recovery is only carried out in the first dimension. At this time, N-level heat recovery air flow paths are branched out from the ambient air with small temperature difference conditions, which correspond to the N-level heat recovery system, and only the first heat pump sub-cycle of each level of the heat recovery system operates. For example, heat recovery is only carried out in the second dimension. At this time, only the N-level heat recovery air flow path is branched out from the ambient air with small temperature difference conditions, which corresponds to the N-level heat recovery system, and only 1 - M heat pump sub-cycles of this level of the heat recovery system operate.

[0017] The present invention discloses a two-dimensional cascade heat recovery system and its operation method. Compared with the traditional one-dimensional cascade heat recovery system, the two-dimensional system can effectively improve the workshop environment and generate ambient air with a relatively uniform temperature distribution. Compared with the prior art, the present invention has the following advantages:

[0018] 1. Comprehensive and efficient heat recovery effect. Through two-dimensional cascade heat recovery, the system can achieve comprehensive heat recovery under multi-temperature difference conditions. The heat recovery in the first dimension classifies and processes different temperature segments of the ambient air in the large space, and the heat recovery in the second dimension further improves the heat recovery effect of each level by using a multi-level cascade suction and exhaust system, thus greatly improving the overall heat recovery efficiency.

[0019] 2. Flexible operation mode. The system can operate with variable load according to the actual temperature difference conditions. Under large temperature difference, medium temperature difference and small temperature difference conditions, the system can automatically adjust the operation mode to ensure the optimal heat recovery effect under different working conditions, improving the adaptability and flexibility of the system.

[0020] 3. Significant energy-saving benefits. By effectively recovering and utilizing the waste heat generated in the industrial process, energy waste is reduced and the workshop working environment is improved. At the same time, the condensation heat of the heat recovery system can generate high-temperature hot air or hot water according to actual needs, meeting the demand for high-quality heat energy in different process procedures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the two-dimensional cascade heat recovery system of the present invention.

[0022] Figure 2Schematic diagram of the two-dimensional cascade heat recovery system according to Embodiment 1 of the present invention operating under large temperature difference conditions.

[0023] Figure 3 Schematic diagram of the two-dimensional cascade heat recovery system according to Embodiment 1 of the present invention operating under medium temperature difference conditions.

[0024] Figure 4 and Figure 5 Schematic diagrams of two operating states of the two-dimensional cascade heat recovery system according to Embodiment 1 of the present invention under small temperature difference conditions.

[0025] Figure 6 Schematic diagram of the two-dimensional cascade heat recovery system according to Embodiment 2 of the present invention operating under large temperature difference conditions.

[0026] In the figure:

[0027] 0, ambient air with non-uniform large space temperature distribution,

[0028] 1, …, N, N + 1, …, N + X, heat recovery air flow paths,

[0029] 1, 2, …, M - 1, M, heat pump sub-cycles (including A, compressor; B, condenser; C, expansion valve; D, evaporator),

[0030] 1 - 1, …, 1 - M, first-stage heat recovery systems,

[0031] 2 - 1, …, 2 - M, second-stage heat recovery systems,

[0032] ……,

[0033] (N - 1) - 1, …, (N - 1) - M, (N - 1)th-stage heat recovery systems,

[0034] N - 1, …, N - M, Nth-stage heat recovery systems,

[0035] E, heat recovery heat exchanger,

[0036] 1’, 2’, …, N’, N + 1’, heating fluid flow paths. Detailed implementation manners

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments described in the present invention fall within the protection scope of the present invention.

[0038] Embodiment 1

[0039] This embodiment provides a two-dimensional stepped heat recovery system, where N = 3, M = i (i = 1:N), and X = 1. As Figure 2 shown, the system mainly includes ambient air 0 with non-uniform temperature distribution in a large space, the 1st to 4th stage heat recovery systems, and the 1st to 4th heating fluid flow paths.

[0040] The ambient air 0 with non-uniform temperature distribution in the large space branches out the 1st to 4th stage heat recovery air flow paths, achieving four-stage heat recovery in the first dimension.

[0041] The 1st to 4th heat recovery systems respectively correspond to the 1st to 4th stage heat recovery air flow paths. Among them, the 1st stage heat recovery system 1 is a single-stage heat pump, the 2nd stage heat recovery system 2 is a two-stage stepped suction and exhaust heat pump, the 3rd stage heat recovery system 3 is a three-stage stepped suction and exhaust heat pump, and the 4th stage heat recovery system 4 is a heat recovery heat exchanger E. In the first three active heat recovery systems, stepped suction and exhaust heat pumps with different numbers of stages are adopted according to different heat recovery amounts, achieving differentiated multi-stage heat recovery in the second dimension.

[0042] The 1st to 3rd heating flow paths respectively correspond to the 1st to 3rd stage heat recovery systems. The first 3 heating flow paths converge to form the 4th heating flow path 4', and the 4th heating flow path 4' forms a heat exchange relationship with the 4th stage heat recovery air flow path through the heat recovery heat exchanger E.

[0043] The 1st stage heat recovery system 1 includes its 1st stage heat pump 1-1. The 1st stage heat pump 1-1 includes a compressor A, a condenser B, an expansion valve C, and an evaporator D connected in sequence. Among them, the evaporator D is a finned tube heat exchanger, arranged on the 1st stage heat recovery air flow path 1. The condenser B is arranged on the 1st heating fluid flow path 1'.

[0044] The 2nd stage heat recovery system 2 includes the same 1st stage heat pump 2-1 and 2nd stage heat pump 2-2. The 1st stage heat pump 2-1 and the 2nd stage heat pump 2-2 respectively include a compressor A, a condenser B, an expansion valve C, and an evaporator D connected in sequence. Among them, both evaporators D are finned tube heat exchangers, arranged in sequence on the 2nd stage heat recovery air flow path 2. The two condensers B are heat exchangers of the same type, arranged in sequence on the 2nd heating fluid flow path 2'.

[0045] The 3rd stage heat recovery system 3 includes the same 1st stage heat pump 3-1, 2nd stage heat pump 3-2, and 3rd stage heat pump 3-3. The 1st stage heat pump 3-1, the 2nd stage heat pump 3-2, and the 3rd stage heat pump 3-3 respectively include a compressor A, a condenser B, an expansion valve C, and an evaporator D connected in sequence. Among them, all three evaporators D are finned tube heat exchangers, arranged in sequence on the 3rd stage heat recovery air flow path 3. The three condensers B are heat exchangers of the same type, arranged in sequence on the 3rd heating fluid flow path 3'.

[0046] The working process of this embodiment is as follows:

[0047] Large temperature difference condition (for example, the ambient air temperature changes from 75 °C to 30 °C, such as Figure 2 ) When the large temperature difference condition is formed due to uneven spatial temperature distribution, first, the ambient air 0 with non-uniform large-space temperature distribution is divided into four levels in the first dimension for heat recovery. The air with the highest temperature passes through the 4th-level heat recovery air flow path 4 and flows through the heat recovery heat exchanger E; the air with a relatively high temperature passes through the 3rd-level heat recovery air flow path 3 and successively flows through the evaporators D of the 1st, 2nd, and 3rd heat pumps of the 3rd-level heat recovery system; the air with a relatively low temperature passes through the 2nd-level heat recovery air flow path 2 and successively flows through the evaporators D of the 1st and 2nd heat pumps of the 2nd-level heat recovery system; the air with the lowest temperature passes through the 1st-level heat recovery air flow path 1 and flows through the evaporator D of the 1st heat pump of the 1st-level heat recovery system. Finally, the outlet air temperatures of the 1st to 3rd heat recovery air flow paths are approximately the same, thus realizing multi-stage heat recovery with differentiation in the second dimension. Secondly, the heating fluid enters the 1st to 3rd heating fluid flow paths respectively, and successively flows through the condensers B of the 1st to 3rd heat recovery systems, realizing cascade heating of different flow paths, and converging to form the 4th heating flow path 4'. The 4th heating flow path 4' flows through the heat recovery heat exchanger E to exchange heat with the 4th-level heat recovery air, further improving the temperature grade of the heating fluid, and at the same time completing passive heat recovery. The obtained high-temperature heating fluid can be used for the high-temperature process of workpiece production and processing according to requirements.

[0048] Medium temperature difference condition (for example, the ambient air temperature changes from 60 °C to 30 °C, such as Figure 3 ) When the medium temperature difference condition is formed due to uneven spatial temperature distribution, the heat recovered at this time is reduced compared with the large temperature difference condition, so the 4th-level passive heat recovery is not required. At this time, the ambient air 0 with non-uniform large-space temperature distribution is divided into three levels in the first dimension for active heat recovery. The working process of the system is the same as that of the large temperature difference condition.

[0049] Small temperature difference condition (for example, the ambient air temperature changes from 45 °C to 30 °C): When the small temperature difference condition is formed due to uneven spatial temperature distribution, the heat recovered at this time will be further reduced, and cascade heat recovery can be carried out only in the first dimension (such as Figure 4 ). It can also be carried out only in the second dimension (such as Figure 5 ).

[0050] When only heat recovery is carried out in the first dimension, the ambient air with non-uniform temperature distribution in the large space does not branch out the 1st to 3rd stage heat recovery air flow paths, and correspondingly only the 1st stage heat pump of the 1st to 3rd stage heat recovery systems is turned on. On each heat recovery air flow path, the air flows through 1 evaporator D of this stage of the heat recovery system respectively. On each heating fluid flow path, the heating fluid flows through 1 condenser B of this stage of the heat recovery system respectively, and then converges to provide hot fluid for the high-temperature process.

[0051] When only heat recovery is carried out in the second dimension, the ambient air with non-uniform temperature distribution in the large space only branches out the 3rd stage heat recovery air flow path 3, and correspondingly only the 1st to 3rd stage heat pumps of the 3rd stage heat recovery system are turned on. On the 3rd stage heat recovery air flow path 3, the air flows through 3 evaporators D of this stage of the heat recovery system respectively. On the 3rd heating fluid flow path 3', the heating fluid flows through 3 condensers B of this stage of the heat recovery system respectively, and provides hot fluid for the high-temperature process through three-stage cascade heating.

[0052] Embodiment 2

[0053] This embodiment provides a two-dimensional cascade heat recovery system, where N = 3, M = 2, and X = 1. As Figure 6 shown, the system mainly includes ambient air 0 with non-uniform temperature distribution in the large space, the 1st to 4th stage heat recovery systems, and the 1st to 4th heating fluid flow paths.

[0054] Different from Embodiment 1, this system adopts two-stage heat recovery that is uniform and consistent in the second dimension. The advantage of this is that each stage of the heat recovery system is exactly the same, which is conducive to unified production and manufacturing.

[0055] This embodiment can also operate flexibly under large, medium, and small temperature difference conditions, and the specific working process is similar to that of Embodiment 1.

[0056] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the present invention. Those skilled in the art can obviously make various modifications to these embodiments easily, and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A two-dimensional stepped heat recovery system, characterized in that, include: Ambient air with non-uniform temperature distribution in large spaces, N+X level heat recovery system and heating fluid. The temperature of the ambient air in the large space with non-uniform temperature distribution gradually decreases along a certain direction and branches to form N+X stages of heat recovery air flow paths (1, ..., N, N+1, ..., N+X). The N+X level heat recovery system corresponds one-to-one to the N+X level heat recovery air flow paths, wherein: The first N stages are active heat recovery systems, each consisting of 1 to M heat pump sub-cycles; The last X stages are passive heat recovery systems, with each stage being a heat recovery heat exchanger (E). The heating fluid includes N+1 heating fluid flow paths (1', 2', ..., N', N+1'): the first N heating fluid flow paths correspond one-to-one to the first N stages of heat recovery systems and are merged into the N+1th flow path (N+1'), and the N+1th flow path sequentially exchanges heat with the next X stages of heat recovery air flow paths through X heat recovery heat exchangers (E). The two-dimensional steps refer to the spatial temperature gradient (N+X steps) in the first dimension and the heat pump energy level gradient (M steps) in the second dimension. The above-mentioned N is an integer ≥1, X is an integer ≥0, and M is an integer ≥1.

2. The two-dimensional cascade heat recovery system according to claim 1, characterized in that: The heat pump sub-cycle includes a closed loop consisting of a compressor (A), a condenser (B), an expansion valve (C) and an evaporator (D) connected in sequence.

3. The two-dimensional cascade heat recovery system according to claim 2, characterized in that: The 1 to M evaporators (D) of each stage of the active heat recovery system (1 to M heat pump sub-cycles) are arranged in sequence on the heat recovery air flow path corresponding to the stage, and the 1 to M condensers (B) are arranged in sequence on the heating fluid flow path corresponding to the stage.

4. The two-dimensional stepped heat recovery system according to claims 1-3, characterized in that, The heat recovery heat exchanger (E) of each stage of the passive heat recovery system is arranged on the heat recovery air flow path corresponding to the stage. The heat recovery heat exchanger (E) is configured such that the N+1th heating fluid flow path (N+1') exchanges heat with the corresponding subsequent X-stage heat recovery air flow paths (N+1 to N+X) in a countercurrent or approximately countercurrent manner.

5. The two-dimensional stepped heat recovery system according to claim 1, wherein The number M of heat pump sub-cycles may be the same or different in different levels of active heat recovery systems.

6. The two-dimensional stepped heat recovery system according to claim 1, wherein The heating fluid can be selected as air or water according to actual heating needs, and the high-temperature hot air or high-temperature hot water required for the process can be generated by step heating through heat recovery.

7. A method for operating a two-dimensional stepped heat recovery system according to any one of claims 1-6, characterized in that, The system performs variable load operation according to the actual temperature span conditions, including: Under the condition of a large temperature span with an ambient air temperature difference of >40°C, all N+X-level heat recovery systems are turned on to achieve two-dimensional cascade heat recovery; Under the medium temperature span condition of 20℃~40℃ ambient air temperature difference, according to the distribution difference of ambient air inlet temperature and target heating fluid temperature at each level, selectively shut down part of the heat recovery system or reduce the number of sub-cycles of the first N heat pumps; Under the condition of small temperature span with ambient air temperature difference <20℃, single-dimensional heat recovery is selected in the first dimension or the second dimension only.

8. The operating method according to claim 7, characterized in that, The heat recovery is performed only in the first dimension. When only the first N stages of active heat recovery systems are selected to operate, N stages of heat recovery air flow paths (1 to N) are formed by branches, and each stage of the heat recovery system only operates the first heat pump sub-cycle. When heat recovery is performed only in the second dimension and only the K-th active heat recovery system and its corresponding heat recovery air flow path (K) are operated, 1 to M heat pump sub-cycles of this stage are operated, where K is an integer from 1 to N.

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