Water balance control method for waste heat recovery system of centrifugal air compressor

Abstract

The invention discloses a water balance control method for a waste heat recovery system of an air compressor, which is a comprehensive method starting from the whole system and considering a heat source (available heat in operation of a centrifugal machine), a heat demand (heat using end demand), a cooling process (subtracting used heat from total heat source quantity) and a conveying process (hot water and cooling water). An efficient heat exchanger is communicated between each stage of host and each stage of cooler; the first-stage main machine sucks environment gas and compresses the environment gas to form gas with certain pressure, and the temperature of the gas rises to 120 DEG C or above; high-temperature gas compressed by the first-stage main machine firstly passes through the efficient heat exchanger, and low-temperature hot water in the environment is heated into high-temperature hot water in the efficient heat exchanger; the cooled compressed air passes through the first-stage cooler to be about 40 DEG C, then enters the second-stage main engine to be compressed and heated, passes through the efficient heat exchanger, then is cooled to about 40 DEG C through the second-stage cooler, and then enters the next-stage main engine compression and cooling device; and cooling water flows into each stage of cooler for heat exchange.

Description

Technical Field

[0001] The invention belongs to the technical field of air compressors, and in particular relates to a water balance control method for a waste heat recovery system of a centrifugal air compressor. Background Art

[0002] As a general-purpose equipment, centrifugal air compressors are widely used in industrial production, especially in the chemical, textile, electronics, shipbuilding, air separation, steel and other industries. The average power of air compressors is about 1000Kw / unit. While providing compressed air in production, they also continue to consume a large amount of energy. In addition, during the operation of air compressors, when converting electrical energy into compressed air, about 85% of the electrical energy is converted into compression heat. This wasted heat energy can be recovered and converted into hot water for use in factory production. Compression heat recovery has been achieved in some scenarios. However, the current compression heat recovery technology usually simply controls the water flow and water temperature of the recovery process, without maximizing (optimizing) the heat recovery of the centrifugal unit, and also does not take into account the control of the cooling process and the heat use process. As a result, the temperature of the recovered hot water is relatively limited, usually between 70°C and 80°C, and the overall economic benefits are insufficient, the output hot water temperature is not high, the water volume is insufficient, and there are large fluctuations with the changes in the air compressor workload, resulting in a decrease in quality and efficiency in thermal energy applications. Summary of the invention

[0003] In view of the shortcomings of the above background technology, the purpose of the present invention is to provide a water balance control method for an air compressor waste heat recovery system. Starting from the entire system, a comprehensive method taking into account the heat source (available heat during centrifuge operation), heat demand (heat end demand), cooling process (total heat source minus used heat), and transportation process (hot water and cooling water) can achieve sufficient heat recovery and reach high-temperature hot water of 90°C.

[0004] To solve the above technical problems, the purpose of the present invention is achieved as follows: A water balance control method for an air compressor waste heat recovery system includes: a primary host is connected to a plurality of primary hosts, and coolers are connected between adjacent hosts; a high-efficiency heat exchanger is connected between each primary host and each cooler; The first-stage main engine inhales ambient gas and compresses it to form gas of a certain pressure, and the temperature of the gas rises to above 120 degrees. The high-temperature gas compressed by the first-stage main engine first passes through a high-efficiency heat exchanger, and the low-temperature hot water in the environment is heated to high-temperature hot water in the high-efficiency heat exchanger. The compressed air is cooled down after passing through the first-stage cooler and becomes about 40°C. It then enters the second-stage main engine for compression and temperature increase. It first passes through the high-efficiency heat exchanger, and then is cooled to about 40°C through the second-stage cooler before entering the next-stage main engine compression and cooler. Cooling water flows into each stage of cooler for heat exchange. After the compressed air is cooled down, it is ensured to be cooled to about 40°C after entering each stage of cooler again, in preparation for the next stage of compression process. The steps include: Setp1: Collect the operating status of the centrifugal air compressor through the logic controller; Setp2: The hot water volume and hot water temperature of each usage scenario are determined by the hot end, and the maximum water supply target temperature is determined. The maximum hot water flow of the system is adjusted at the maximum water supply target temperature; Setp3: Calculate the total recovered heat energy through the hot water flow meter and the temperature difference before and after; Step 4: If the heating capacity is greater than the total demand, the flow rate at the highest water supply target temperature in Setp2 is adjusted to reduce the amount of hot water recovered and achieve a balance between supply and demand; otherwise, the heating of some equipment at the heat-using end is terminated, and some of the system (V3) is shut down according to the heating priority level to ensure the heating quality of the remaining heat-using end; Step 5: The heat demand of each heat-using end is summarized into the total heat demand, that is, the heat that needs to be recovered by the centrifugal air compressor at the moment; Step 6: Based on the total heat demand in Step 5, decompose it to the high-efficiency heat exchangers corresponding to each centrifugal air compressor in operation, and maximize heat recovery while ensuring the highest target water supply temperature; Step 7: The total cooling capacity required by the cooler of the running centrifugal air compressor is equal to the total heat generated by the running centrifugal air compressor minus the heat consumed by the hot end. The total cooling capacity is calculated and the total cooling capacity is met by adjusting the water flow control valve (V2); Step 8: Open the corresponding number of cooling towers based on the total cooling capacity and the minimum cooling water volume requirements of each cooling tower; Step 9: Changes in cooling water volume will be responded to synchronously by the variable frequency water pump to achieve water balance.

[0005] On the basis of the above scheme and as a preferred scheme of the above scheme: a temperature sensor and a water flow regulating valve are added to the water channel on the other side of the high-efficiency heat exchanger, and the opening of the regulating valve is controlled by setting the comparison between the outlet water target temperature and the actual temperature.

[0006] On the basis of the above scheme and as a preferred scheme of the above scheme: a temperature sensor and a water flow regulating valve are added to the water circuit of each stage of the cooler, and the opening of the water flow regulating valve is controlled by setting a comparison between the target temperature of the compressed gas and the actual temperature.

[0007] On the basis of the above scheme and as the preferred scheme of the above scheme: multiple units form a hot water main after waste heat recovery, and the water supply temperature, return water temperature and water flow meter are added; a pressure sensor is set at the outlet of the hot water pump and a variable frequency drive is set for the water pump.

[0008] On the basis of the above scheme and as a preferred scheme of the above scheme: a temperature sensor and a hot water flow control valve are set on the hot water supply pipe, and the opening of the hot water flow regulating valve is controlled by comparing the return water target temperature and the actual temperature at the hot end.

[0009] On the basis of the above scheme and as the preferred scheme of the above scheme: a water flow meter is added to the cooling water supply main pipe, and the number of cooling towers to be opened is decided in combination with the minimum cooling water volume requirement of each cooling tower to measure the cooling water volume; a pressure sensor is set at the outlet of the cooling water pump and a variable frequency drive is set for the water pump.

[0010] On the basis of the above scheme and as a preferred scheme of the above scheme: an outlet water temperature sensor and a water flow control valve are added to the water circuit of each cooling tower, and the opening of the water flow control valve is controlled by comparing the outlet water target temperature with the actual temperature.

[0011] On the basis of the above scheme and as a preferred scheme of the above scheme: in the system, the temperature requirements of each heat-consuming end are different, so the target temperature corresponding to the branch pipes of different heat-consuming ends in the system can be set to meet the branch pipe control requirements of different heat-consuming ends.

[0012] Compared with the prior art, the present invention has the following outstanding and beneficial technical effects: Compared with the prior art, the water balance control method of the air compressor waste heat recovery system of the present invention is 1. The original cooling system is maintained. By adding modular high-efficiency heat exchangers to each stage, the waste heat recovery technical transformation project is small, which saves the project investment cost and reduces the construction difficulty of the project; 2. By controlling the amount of hot water recovered from waste heat and the temperature of the hot water, the quality of high-temperature heating is ensured (high-temperature hot water reaches 90°C), and the goal of dynamic balance of the shared heat volume as the demand of the heat-using end changes is achieved.

[0013] 3. By controlling the cooling water volume and compressed air temperature of the cooler, overcooling is avoided and the heat recovered by the next stage high-efficiency heat exchanger is increased.

[0014] 4. Through the frequency conversion control of the system cooling water pump and the system heating hot water pump, the water supply and demand balance is achieved while saving the energy consumption of water pump operation.

[0015] 5. By adjusting the heat of water supply at the heat-using end, the heat supply can be dynamically adjusted according to demand, achieving the stability of constant temperature heating, and meeting the needs of different heating temperatures at different hot spots.

[0016] 6. Through online metering of hot water flow and temperature difference, the number of heat-using end connections (load) is reasonably adjusted to ensure the quality of high-temperature heating.

[0017] 7. By adjusting the water balance of the cooling tower, the number of cooling tower operations can be reasonably reduced, ensuring the cooling efficiency of the cooling tower, saving energy consumption and improving the stability of the cooling return water temperature, which is more conducive to the stable operation of the equipment; 8. Realize the measurement of the amount of recovered hot water. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the working process of an existing air compressor.

[0019] Figure 2 It is a structural schematic diagram of the working process of the air compressor of the present invention.

[0020] Figure 3 It is a structural schematic diagram of the working process of the air compressor of the present invention.

[0021] Figure 4 It is a schematic diagram of the water balance process of the present invention.

[0022] Reference numerals: water flow regulating valve V1, water flow regulating valve V2, hot water flow control valve V3, water quantity control valve V4. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings; Figure 1 It is the isothermal compression process of the existing centrifugal air compressor, which is usually composed of one or more stages of main engines. After sucking in the ambient atmosphere, it is compressed by the first-stage main engine to form a gas of a certain pressure. At the same time, the temperature of the gas usually rises to above 120°. After passing through the first-stage cooler and becoming about 40°C, it enters the second-stage main engine for compression and temperature increase again, and then cools to about 40°C through the second-stage cooler before entering the next stage of main engine compression and cooler (the specific number of stages is determined by the gas supply pressure requirements).

[0024] Figure 2 In order to realize the recycling of compression heat, the present invention designs a new process. On the basis of making full use of the equipment of the original process, a set of high-efficiency heat exchangers are added between the compression and cooling of each stage. The high-temperature gas coming out of the compression of each stage of the main engine first passes through the high-efficiency heat exchanger ( Figure 2In part [1]), the low-temperature hot water in the environment is heated in a high-efficiency heat exchanger to high-temperature hot water output, achieving the goal of recovering the compression heat. After the cooled compressed air enters each stage of the equipment again, it is ensured that it can be cooled to about 40°C to prepare for the next stage of compression process; The advantage of this design is that even if the heat load used at the high-efficiency heat exchanger changes with use, it can ensure that the temperature of the compressor before entering the next stage of compression is about 40°C, maintaining the isothermal compression process unchanged.

[0025] The above is only a heat recovery design method for a single air compressor unit. However, in actual factory scenarios, there are usually multiple units with different models (power sizes) and multiple cooling towers. The temperature requirements of hot water recovered through waste heat (depending on the requirements of the specific production process) are also different. There will also be multiple shared hot ends during use, forming a relatively complex system.

[0026] This is also the key point to be solved by the present invention. The present invention takes two devices in each link as an example (see Figure 3 ) to illustrate the water balance control method of the present invention.

[0027] Figure 3 The medium-thick lines represent compressed gas, the thin lines represent cooling water or recovered hot water, and the color of the lines corresponds to the temperature; the green sequence represents the key points of the present invention.

[0028] Figure 3 [①]: The temperature and flow rate (mass) of the high-temperature gas compressed by the first-stage main engine will change with the load of the machine, which is a property of the centrifugal air compressor itself and is difficult to control or adjust externally. In view of this characteristic, the present invention adds a temperature sensor T and a water flow regulating valve V1 to the water path on the other side of the high-efficiency heat exchanger added for heat recovery. The opening of the water flow regulating valve V1 is controlled by setting the comparison between the target water outlet temperature and the actual temperature (PID mode), so as to achieve the goal of hot water volume regulation to output hot water at a constant temperature. In the system, temperature sensors T and water flow regulating valves V1 are added to the water paths of the high-efficiency heat exchangers at each level, namely V1-1, V1-2, V1-3, V1-4, V1-5, V1-6, ..., so that independent adjustment can be achieved according to the change of heat load at each level and the target temperature required for hot water after recovery, and the scenario of different models of centrifuges in the same system can also be met.

[0029] Figure 3 Middle [②]: High temperature compressed air passes through Figure 3After the high-efficiency heat exchanger in the middle [①] part, the temperature will be reduced to a certain extent, that is, the heat content of the gas will be reduced. After entering the original cooler, if the original cooling water is maintained without adjustment, two unfavorable factors will be formed: first, because the heat of the gas passing through the original cooler is reduced, it does not require the original amount of cooling water to cool it to 40°C to prepare for the next stage of compression process. Continuing to maintain the original amount of cooling water will cause overcooling, resulting in a waste of cooling water; second, if it is overcooled, the temperature of the compressed air entering the next stage of the main engine will be lower than the target of 40°C, which will reduce the temperature after the next stage of compression, reduce the heat of waste heat recovery in the next stage, and reduce the economic benefits.

[0030] To this end, the present invention adds a temperature sensor T and a water flow regulating valve V2 to the water circuit of each stage of the cooler, and controls the opening of the water flow regulating valve V2 by setting the comparison between the target temperature of the compressed gas and the actual temperature (PID mode), so as to achieve the goal of regulating the cooling water volume to output compressed air at a constant temperature (about 40°C). In the system, temperature sensors T and water flow regulating valves V2 are added to the water circuits of each stage of the cooler, namely V2-1, V2-2, V2-3, V2-4, V2-5, and V2-6. In this way, independent regulation can be achieved according to the heat change of the compressed air after the waste heat recovery in front of each stage, and it can also meet the scenarios of different models of air compressors in the same system. At the same time, it can take into account the dynamic regulation of the cooling water volume after the cooling water temperature drops in low temperature climates such as winter.

[0031] Figure 3 [③]: The present invention forms a hot water main pipe after waste heat recovery for multiple units, and adds water supply temperature T, return water temperature T and hot water flow meter F, so that the heat value of waste heat recovery in the entire system can be counted in real time. This is used as the maximum heat supply of the system, and the number of heat-using end devices that can be turned on is determined based on the minimum heat load demand of each heat-using end in the scene, to avoid the situation where supply is less than demand, and ensure the stability of heat supply at the heat-using end.

[0032] because Figure 3 It is mentioned in [①] that in order to ensure the temperature of waste heat recovery hot water is stable, the amount of hot water will be adjusted through the water flow regulating valve V1 according to the operating load of the air compressor unit, thereby affecting the change of the hot water amount of the entire system. The present invention sets a pressure sensor at the outlet of the hot water pump and sets a variable frequency drive for the water pump, the purpose of which is also to achieve water balance and stability in the hot water system.

[0033] Figure 3[④]: In view of the different temperature requirements of the heat-using end, the present invention designs a temperature sensor T and a hot water flow control valve V3 on the hot water supply pipeline. By setting the comparison between the return water target temperature and the actual temperature of the heat-using end, the opening of the hot water flow control valve V3 is controlled (PID mode), so that the hot water supply volume is regulated to achieve the goal of constant temperature heating. In the system, a temperature sensor T and a hot water flow control valve V3 are added to each heat-using end, namely V3-1 and V3-2, so that independent regulation can be achieved according to the requirements of the heating temperature and heat load changes of each heat-using end, and the requirements of lower heating temperature of different hot spots can be met by reducing the heating supply, so as to meet the needs of different scenarios.

[0034] pass Figure 3 The actual heat supply measured in [③] is combined with the minimum heat load demand data of each heat-using end. If the heat demand cannot be fully met, the hot water flow control valve V3 will be used to shut down the heat supply to some heat-using ends (the priority level is set according to the heat demand and the importance of the heat demand), so as to ensure the heat stability of the heat-supplied end.

[0035] Figure 3 Middle [⑤]: front Figure 3 In the method [②], in order to ensure the economy and stability of waste heat recovery, the flow rate of cooling water at each level will be adjusted according to the change of cooling load at each level, which will also lead to the change of cooling water volume of the whole system. The present invention adds a water flow meter F to the cooling water supply main pipe to measure the cooling water volume, and combines the minimum cooling water volume requirement of each cooling tower to decide the number of cooling towers to be opened, so as to achieve the best cooling effect and realize the lowest energy consumption in the cooling process.

[0036] The delivery of cooling water is achieved through a water pump. In order to match the changes in the amount of cooling water, the present invention designs a pressure sensor at the outlet of the cooling water pump and designs a variable frequency drive for the water pump, so as to achieve the goal of automatically adjusting the water pump flow as the cooling water amount changes, thereby providing a guarantee for the water balance of the entire system.

[0037] Figure 3 [⑥]: The function of the cooling tower is to cool the cooling water and dissipate the heat. However, a suitable cooling tower should be used according to the heat dissipation load of the entire system. The present invention adds an outlet water temperature sensor T and a water volume control valve V4 to the water path of each cooling tower. By setting the comparison between the outlet water target temperature and the actual temperature, the opening of the water volume control valve V4 is controlled (PID mode), so as to achieve the goal of balancing the water volume of each cooling tower by adjusting the cooling water volume passing through the cooling tower, and balancing the water volume between multiple cooling towers according to the cooling performance of each cooling tower, which is achieved by adjusting the opening of V4-1 and V4-2 respectively.

[0038] Figure 4This is the water balance model for the entire system, taking into account the heat source (available heat during centrifuge operation), heat demand (demand at the heat end), cooling process (total heat source minus used heat), and transportation process (hot water and cooling water): Setp1: Collect the operating status of the centrifugal air compressor through the logic controller; this is the source of waste heat for the entire system; Setp2: The hot water volume and hot water temperature of each usage scenario are determined by the hot end, and the maximum water supply target temperature is determined. The maximum hot water flow of the system is adjusted at the maximum water supply target temperature; The actual adjustment process of V1 in the control system will be combined with the demand of the heat-using end, and gradual adjustment will be adopted to avoid overheating; Setp3: Calculate the total recovered heat energy through the hot water flow meter and the temperature difference before and after; Evaluate the matching relationship between heating capacity and demand at the heat-using end, and also facilitate visualization of the heat recovery benefits; Step 4: When the heating capacity is greater than the total demand, the flow rate of the highest water supply target temperature in Setp2 is adjusted to reduce the amount of hot water recovered to achieve a balance between supply and demand; otherwise, the heating of some equipment at the heat-using end is terminated, and some of the system (V3) is shut down according to the heating priority level to ensure the heating quality of the remaining heat-using end; In the system, the temperature requirements of each heat-using end are different. In this case, the target temperature of the hot water flow control valve (V3) corresponding to the branch pipes of different heat-using ends in the system can be adjusted to meet the branch pipe control requirements of different heat-using ends. The change of hot water volume will change with the change of the heat source of the centrifuge or the load of the heat-using end equipment, and this change will correspond to the number and frequency of operation of the hot water variable frequency pump; Step 5: The heat demand of each heat-using end is summarized into the total heat demand, that is, the heat that needs to be recovered by the centrifugal air compressor at the moment; It represents the balance point between heat supply and heat use; Step 6: Based on the total heat demand in Step 5, decompose it to the high-efficiency heat exchangers corresponding to each centrifugal air compressor in operation, and maximize heat recovery while ensuring the highest target water supply temperature; According to Step 5, the number of controlled air compressors is used to recover heat. Some centrifugal air compressors are working while others are not. V1 of the centrifugal air compressors that are not working is closed to avoid water mixing.

[0039] Step 7: The total cooling capacity required by the cooler of the running centrifugal air compressor is equal to the total heat generated by the running centrifugal air compressor minus the heat consumed by the hot end. The total cooling capacity is calculated and the total cooling capacity is met by adjusting the water flow control valve (V2); Step 8: Open the corresponding number of cooling towers based on the total cooling capacity and the minimum cooling water volume requirements of each cooling tower; Step 9: Changes in cooling water volume will be responded to synchronously by the variable frequency water pump to achieve water balance.

[0040] Based on the cooling water volume data and the minimum flow requirements of each cooling tower, the number of cooling towers to be invested is determined to avoid deviation from normal operating conditions due to the inability of cooling towers to effectively distribute water due to too small water flow. This saves energy consumption for cooling tower operation and ensures the efficiency of cooling towers. This is achieved through V4 in the system. In order to meet the impact of changes in working conditions and seasons on the cooling capacity of the cooling tower, a temperature sensor is installed in the system. It is based on the constant temperature regulation of the minimum water flow of the cooling tower. It ensures cooling while avoiding overcooling, and improves the waste heat recovery and efficiency of the system. The control system realizes the overall control strategy from the heat source end, heat recovery, heat transfer, heat use end and cooling end, and the above parts constitute a set of system water balance control methods.

[0041] In summary, the present invention starts from the system, controls and adjusts multiple factors in the system, and adopts a systematic approach from system hardware design to software control logic, which ensures the maximization of heat recovery while ensuring the quality of heating at a higher temperature. The core of the method of the present invention includes: 1. Established a process for waste heat recovery of centrifugal air compressors; 2. The output hot water temperature is kept constant through the water flow regulating valve; 3. Adjust the water volume of the original cooling process of the equipment to avoid overcooling and increase the recovered heat; 4. Measure the heat recovered by the system to determine the number of heat-using devices that can be started; 5. The heat-using end adjusts the hot water supply according to the heat load to achieve stable heat use and avoid turning on too many heat-using devices; 6. Measure the cooling water volume at the cooling end to confirm the maximum number of cooling towers to be opened; 7. Balance and control the cooling water volume of the cooling tower to achieve optimal cooling efficiency; 8. Dynamic regulation is used to achieve system stability for the transportation of recovered hot water and cooling water.

[0042] 9. Through the above process control, a water balance model with multi-factor relationships is formed.

[0043] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0044] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. In the present invention, unless otherwise clearly specified and limited, the terms "install", "set", "connect", "fix", "screw" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; The above embodiments are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A water balance control method for a waste heat recovery system of a centrifugal air compressor, characterized in that: It includes connecting one level of host to multiple levels of host, and coolers are connected between adjacent hosts; each level of host is connected with each level of cooler with a high-efficiency heat exchanger; The first-stage main engine inhales ambient gas and compresses it to form gas of a certain pressure, and the temperature of the gas rises to above 120 degrees. The high-temperature gas compressed by the first-stage main engine first passes through a high-efficiency heat exchanger, and the low-temperature hot water in the environment is heated to high-temperature hot water in the high-efficiency heat exchanger. The compressed air is cooled down after passing through the first-stage cooler and becomes about 40°C. It then enters the second-stage main engine for compression and temperature increase. It first passes through the high-efficiency heat exchanger, and then is cooled to about 40°C through the second-stage cooler before entering the next-stage main engine compression and cooler. Cooling water flows into each stage of cooler for heat exchange. After the compressed air is cooled down, it is ensured to be cooled to about 40°C after entering each stage of cooler again, in preparation for the next stage of compression process. The steps include: Setp1: Collect the operating status of the centrifugal air compressor through the logic controller; Setp2: The hot water volume and hot water temperature of each usage scenario are determined by the hot end, and the maximum water supply target temperature is determined. The maximum hot water flow of the system is adjusted at the maximum water supply target temperature; Setp3: Calculate the total recovered heat energy through the hot water flow meter and the temperature difference before and after; Step 4: If the heating capacity is greater than the total demand, the flow rate of the highest water supply target temperature in Setp2 is adjusted to reduce the amount of hot water recovered to achieve a balance between supply and demand; otherwise, the heating of some equipment at the heat-using end is terminated, and some parts of the system are shut down according to the heating priority level to ensure the heating quality of the remaining heat-using end; Step 5: The heat demand of each heat-using end is summarized into the total heat demand, that is, the heat that needs to be recovered by the centrifugal air compressor at the moment; Step 6: Based on the total heat demand in Step 5, decompose it to the high-efficiency heat exchangers corresponding to each centrifugal air compressor in operation, and maximize heat recovery while ensuring the highest target water supply temperature; Step 7: The total cooling capacity required by the cooler of the running centrifugal air compressor is equal to the total heat generated by the running centrifugal air compressor minus the heat consumed by the hot end. The total cooling capacity is calculated and the total cooling capacity is met by adjusting the water flow control valve (V2); Step 8: Open the corresponding number of cooling towers based on the total cooling capacity and the minimum cooling water volume requirements of each cooling tower; Step 9: Changes in cooling water volume will be responded to synchronously by the variable frequency water pump to achieve water balance.

2. The water balance control method for the waste heat recovery system of a centrifugal air compressor according to claim 1, characterized in that: A temperature sensor and a water flow regulating valve (V1) are added to the water circuit on the other side of the high-efficiency heat exchanger. The opening of the regulating valve (V1) is controlled by comparing the target water outlet temperature with the actual temperature.

3. The water balance control method for the waste heat recovery system of a centrifugal air compressor according to claim 1, characterized in that: A temperature sensor and a water flow regulating valve (V2) are added to the water circuit of each stage of the cooler, and the opening of the water flow regulating valve is controlled by setting a comparison between the target temperature of the compressed gas and the actual temperature.

4. The water balance control method for a waste heat recovery system of a centrifugal air compressor according to claim 1, characterized in that: Multiple units form a hot water main after waste heat recovery, adding water supply temperature, return water temperature and water flow meter; a pressure sensor is set at the outlet of the hot water pump and a variable frequency drive is set for the water pump.

5. The water balance control method for the waste heat recovery system of a centrifugal air compressor according to claim 4, characterized in that: A temperature sensor and a hot water flow control valve (V3) are installed on the hot water supply pipe, and the opening of the hot water flow control valve is controlled by comparing the return water target temperature at the hot end with the actual temperature.

6. The water balance control method for the waste heat recovery system of a centrifugal air compressor according to claim 3, characterized in that: A water flow meter is added to the cooling water supply main pipe, and the number of cooling towers to be opened is decided in combination with the minimum cooling water volume requirements of each cooling tower to measure the cooling water volume; a pressure sensor is installed at the outlet of the cooling water pump and a variable frequency drive is installed for the water pump.

7. The water balance control method for a waste heat recovery system of a centrifugal air compressor according to claim 2, characterized in that: An outlet water temperature sensor and a water flow control valve (V4) are added to the water circuit of each cooling tower. The opening of the water flow control valve (V4) is controlled by comparing the outlet water target temperature with the actual temperature.

8. The water balance control method for a waste heat recovery system of a centrifugal air compressor according to claim 1, characterized in that: In the system, the temperature requirements of each heat-consuming end are different. In this case, the target temperature of the hot water flow control valve (V3) corresponding to the branch pipes of different heat-consuming ends in the system can be adjusted to meet the branch pipe control requirements of different heat-consuming ends.

Images