Method for purifying compressed air with adjustable recovery of compression residual heat and regeneration gas

Abstract

The present application relates to compressed air purification technology, and aims to provide a compressed air purification method capable of recycling compressed waste heat and adjusting regenerated gas. The method comprises the following steps: the hot compressed air at the outlet of the oil-free air compressor exchanges heat with the regenerated gas in a waste heat recycling heat exchanger, and is sent to a purifier after being cooled by a cooler and a pre-cooling machine; the purifier keeps the double-tower inlet gas adsorption and regeneration desorption alternately running; the regenerated gas to be heated is introduced into the waste heat recycling heat exchanger for preheating, and is further heated by a proportional regulating valve into an electric heater, and the high-temperature regenerated gas is used for regeneration desorption; in the process, the flow of the regenerated gas is adjusted by the proportional regulating valve, and the CO2 concentration monitor is used to ensure that the predetermined control target is met. The present application fundamentally solves the key problems in the traditional technology, such as poor regeneration gas regulation, high consumption of regenerated gas, and insufficient utilization of the compressed heat of the oil-free air compressor, and fundamentally greatly expands the practicability and universality of the purification process in different industries.

Description

Technical Field

[0001] This invention relates to compressed air purification technology, and in particular to a method for purifying compressed air that can recover waste heat from compression and allow for adjustable regeneration gas. Background Technology

[0002] In industrial production, air purification technology is frequently used to obtain compressed air with low impurity content. For example, in the air separation industry, to obtain high-purity nitrogen or oxygen, the raw material compressed air needs to be pre-purified. Therefore, compressed air purification equipment has become a basic configuration of conventional air separation units. The basic process flow in the compressed air purification stage is: Air → Inlet Filter → Raw Material Air Compressor → Air Precooler → Purifier → Dust Filter → Point of Use.

[0003] Because a dual-tower system is used as the purifier, the continuity of the purification process can be ensured. Therefore, switching between two adsorption towers is a common approach in current purification equipment. To meet the stringent requirements of subsequent processes, a double-layer adsorption bed structure is typically constructed in the adsorption tower using alumina and molecular sieves in a specific ratio to achieve stable adsorption of impurities such as water vapor, carbon dioxide, and acetylene. During operation, a switching mode is adopted, with one tower for adsorption and the other for regeneration. The gas used for regeneration can be the finished product gas or the waste nitrogen generated on-site by the air separation unit.

[0004] During the operation of the purifier, the carbon dioxide concentration is highly sensitive to the moisture content of the compressed air used as the feed gas. In traditional air separation systems, the pressure dew point requirement for the finished compressed air is very high to ensure that the carbon dioxide concentration meets the standard. The air precooler ensures that the temperature of the compressed air entering the adsorption tower is below 10°C (meeting the saturated moisture content standard); and it is equipped with a gas-liquid separator to operate in conjunction with it, so as to fully realize the separation of gas and water in the compressed air, ensure the stable operation of the double-layer adsorption bed, and ensure that the concentration of impurities such as carbon dioxide and acetylene in the finished gas remains consistently within the standard.

[0005] Given that the concentration of carbon dioxide in the air is typically around 400 ppm, while the air separation industry requires purified compressed air with a carbon dioxide concentration below 3 ppm, it is usually maintained below 1 ppm during actual operation. At optimized adsorption temperatures, alumina in the double-layer adsorption bed efficiently separates moisture, and, in conjunction with molecular sieves, achieves the adsorption and separation of impurities such as carbon dioxide. After the adsorption process, the adsorption bed needs regeneration. To ensure the adsorption characteristics of the bed, the purification process employs a regeneration mechanism combining pressure and temperature swing. The regeneration gas can be the finished compressed air produced by the purifier, or the waste nitrogen (i.e., non-high-purity nitrogen) produced by the subsequent air separation unit. The regeneration process includes depressurization, heating, cooling, pressurization, and switching, with the two towers working together to switch between continuous operation and regeneration.

[0006] Due to the adsorption characteristics of molecular sieves and alumina, and considering the concentration of carbon dioxide in the atmosphere, the main operating energy consumption of the purification process in existing technologies includes: precooling unit energy consumption, gas-liquid separator energy consumption, adsorption regeneration heating energy consumption, and adsorption regeneration cooling gas consumption (corresponding to compressed air or nitrogen energy consumption). Among these, precooling unit energy consumption is related to production load intensity and environmental conditions; gas-liquid separator energy consumption mainly depends on the separation principle and processing flow rate (velocity); adsorption regeneration heating energy consumption mainly depends on the processing gas volume, the required regeneration gas volume, heating temperature (molecular sieve characteristics), and heating time; the main energy consumption of the cooling process is the energy consumption corresponding to the released regeneration gas volume (cooling time). Currently, for purification systems using finished compressed air for regeneration, the industry generally considers the proportion of regeneration released gas (including release during the heating and cooling stages) to be 20% to ensure sufficient regeneration of carbon dioxide adsorption and system stability. Correspondingly, the target release ratio for systems using nitrogen (or waste nitrogen) for regeneration is also the thoroughness of the heating to cooling process.

[0007] For typical air separation systems, operating conditions are relatively stable, resulting in relatively stable overall energy consumption across the aforementioned stages. However, the application of compressed air purification processes is not limited to air separation; a typical example is cathode material manufacturing. Due to production process requirements, these industries also have relatively strict requirements for the carbon dioxide concentration in the finished compressed air (below 20 ppm or even lower). The production processes of these companies exhibit significant randomness in compressed air usage, a characteristic that differs markedly from the stable operation of air separation systems. This necessitates a high degree of controllability in the compressed air purification process.

[0008] Therefore, compressed air purification processes need to consider the actual application characteristics of different users and possess universal characteristics such as good controllability, low energy consumption, and high efficiency. However, current traditional purification processes have significant room for improvement in these aspects. The main problems are as follows:

[0009] (1) Problem of poor controllability in the regeneration process

[0010] For a given purification process, current control methods for the regeneration process are very limited, mainly relying on adjusting heating and cooling times (operation cycles) to address changes in operating conditions. Once the equipment selection is given, the energy consumption that can be adjusted mainly consists of the precooler and heating stages. The precooler's frequency conversion and heating can be adjusted through grouping or SCR methods. However, a significant drawback is the inability to adjust the amount of regeneration gas consumed during the continuous exchange process between the two towers, and the inability to influence the regeneration effect of the adsorbent by controlling the regeneration process, thereby affecting the dew point and carbon dioxide concentration of the finished compressed air. Therefore, the overall controllability of the purification characteristics is limited.

[0011] (2) High regeneration gas consumption

[0012] Due to the aforementioned issues, once the proportion of regeneration gas is determined, it cannot be adjusted according to changes in the actual process's requirements for carbon dioxide concentration and processing flow rate. This results in persistently high regeneration gas consumption, becoming the core problem of high energy consumption in the purification process.

[0013] (3) The heat of compression was not fully utilized.

[0014] Given that the carbon dioxide concentration in the raw air is as high as 400 ppm, the regeneration process, whether using waste nitrogen or finished compressed air, requires heating from a relatively low temperature (around 15°C) to above 170°C to ensure sufficient regeneration. If the regeneration temperature is lower than this value, the carbon dioxide adsorption effect will deteriorate. The heat required during the heating process and the energy consumption resulting from prolonged heating are also significant components of the purification process's energy consumption.

[0015] Given that traditional control methods such as frequency conversion (valve) regulation of precoolers, temperature control (SCR regulation), and cycle adjustment cannot effectively solve the above three key problems, this invention innovatively proposes an optimized solution to overcome the limitations of traditional purification processes. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for purifying compressed air that can recover waste heat from compression and allow for adjustable regeneration gas.

[0017] To solve the technical problem, the solution of the present invention is:

[0018] A method for purifying compressed air with adjustable heat recovery and regeneration gas is provided. This method is based on a device for purifying compressed air with adjustable heat recovery and regeneration gas. The device includes an air filter, an oil-free air compressor, a waste heat recovery heat exchanger, a cooler, a precooler, and a purifier connected in sequence by pipelines.

[0019] The purifier has a parallel dual-tower structure (A and B), with adsorbent packed in each tower. The inlet of each tower is connected to the compressed air inlet pipe and the regenerated gas inlet pipe, and the outlet of each tower is connected to the finished compressed air outlet pipe and the regenerated gas vent pipe. A connecting branch pipe is provided between the inlet and outlet pipes of each tower, and a valve is provided on the connecting branch pipe to switch the connection relationship between each tower and the pipeline. CO2 concentration monitors are respectively installed on the finished compressed air outlet pipe and the regenerated gas vent pipe.

[0020] The waste heat recovery heat exchanger is provided with a compressed air inlet, a compressed air outlet, a regenerated gas inlet, and a regenerated gas outlet; the gas supply pipeline for the regenerated gas to be heated is connected to the regenerated gas inlet, and the regenerated gas outlet is connected in sequence to a proportional regulating valve, an electric heater, and a purifier through a pipeline to provide heated regenerated gas.

[0021] The compressed air purification method specifically includes the following steps:

[0022] (1) By switching valves, the purifier is operated in the state of A tower inlet adsorption and B tower pressure holding standby;

[0023] (2) Use an induced draft fan to input atmospheric pressure air into the air filter, and after being compressed by an oil-free air compressor, its pressure and temperature are increased; the hot air exchanges heat with the regenerated gas in the waste heat recovery heat exchanger, and then is sent to the cooler to cool down, and then passes through the pre-cooler to obtain compressed air to be purified with a temperature below 10°C, which is used as the raw material gas for the purifier.

[0024] (3) The compressed air to be purified is sent into tower A. When passing through the adsorption bed, the gaseous CO2 and residual moisture are absorbed by the adsorbent. According to the measured value of the CO2 concentration monitor on the finished compressed air outlet pipe and the requirements of the finished product control index, the valve on the connecting branch pipe is switched in time to put tower B into operation.

[0025] (4) While adsorbing the gas at the inlet of tower B, regenerate and desorb tower A according to the following operation method:

[0026] The regenerated gas to be heated is introduced into the regenerated gas inlet of the waste heat recovery heat exchanger to exchange heat with hot air from the oil-free air compressor; the preheated regenerated gas enters the electric heater through the proportional control valve and is further heated to above 170°C; the high-temperature regenerated gas is sent to tower A to regenerate and desorb the adsorbent, and the released regenerated gas is directly discharged into the atmosphere; during this process, the flow rate of the regenerated gas is adjusted using the proportional control valve so that the measured value of the CO2 concentration monitor on the regenerated gas vent pipe meets the predetermined control target;

[0027] When the measured value of the CO2 concentration monitor reaches the regeneration and desorption requirements, stop the operation of the electric heater; switch the valve on the bypass branch of the waste heat recovery heat exchanger to allow the unheated regeneration gas to enter Tower A for cooling, and the released regeneration gas is directly discharged into the atmosphere; after the temperature of Tower A stabilizes, close the valve on the regeneration gas vent pipe to pressurize, and close the proportional regulating valve to stop the gas supply when the operating pressure is reached; close the valves on the inlet and outlet pipes of Tower A and maintain pressure for standby.

[0028] (5) Repeat steps (1) to (4) to keep the purifier running in a dual-tower alternating state and continuously and stably output the finished compressed air.

[0029] As a preferred embodiment of the present invention, the regenerated gas to be heated is the finished compressed air directly drawn from the purifier outlet, and the amount drawn out does not exceed 20% of the total finished compressed air; or, the regenerated gas to be heated is introduced from a nitrogen supply device outside the purification device, and a booster pump is provided on the nitrogen pipeline to meet the pressure charging and holding requirements.

[0030] As a preferred embodiment of the present invention, a bypass branch pipe and a valve for switching are provided between the regenerated gas inlet and the regenerated gas outlet of the waste heat recovery heat exchanger. One end of the bypass branch pipe is located on the pipeline between the regenerated gas outlet and the proportional regulating valve.

[0031] As a preferred embodiment of the present invention, the oil-free air compressor is a centrifugal air compressor or a screw air compressor.

[0032] As a preferred embodiment of the present invention, the precooling machine is equipped with a gas-water separator.

[0033] As a preferred embodiment of the present invention, the end of the regenerated gas vent pipe is an vent outlet for direct discharge into the atmosphere.

[0034] As a preferred embodiment of the present invention, the proportional regulating valve is an electrically controlled valve and is connected to the PLC controller via a signal line; the PLC controller and the CO2 concentration monitor are respectively connected to the host computer via signal lines.

[0035] As a preferred embodiment of the present invention, the layout of the dual towers and inlet / outlet pipelines of the purifier specifically includes: the two towers A and B are arranged in parallel, and a double-layer adsorption bed structure is built inside each tower with adsorbent.

[0036] The two parallel pipelines are connected to the air inlets at the bottom of the two adsorption towers respectively. One pipeline is equipped with two air inlet valves and the other pipeline is equipped with two air outlet valves. The midpoint of the two air inlet valves is connected to the outlet of the precooler through a pipeline, and a valve is installed on this pipeline. The midpoint of the two air outlet valves is connected to the regeneration gas vent pipe through a pipeline, and a CO2 concentration monitor is installed on this pipeline.

[0037] The two parallel pipelines are connected to the outlets at the top of the two adsorption towers respectively. One pipeline is equipped with two outlet valves, and the other pipeline is equipped with two regeneration valves. The midpoint of the two outlet valves is connected to the finished compressed air outlet pipeline, which is equipped with a CO2 concentration monitor and an outlet main valve. The midpoint of the two regeneration valves is connected to the outlet of the electric heater, which is equipped with a valve.

[0038] As a preferred embodiment of the present invention, the valves on each pipeline at the inlet and outlet of the purifier are electrically controlled valves, which are connected to the PLC controller via signal lines, and the PLC controller is connected to the host computer via signal lines.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. This invention introduces a proportional control valve, whose control objective is the flow rate of the regeneration gas (finished compressed air or nitrogen) used in the regeneration process. By interfering with the regeneration effect of the adsorbent in the tower, it further influences the carbon dioxide concentration of the finished compressed air produced by the tower during operation.

[0041] The design goal of the regeneration gas proportioning valve is to improve the controllability of the purification process. The technical approach employed is to optimize the regeneration gas venting ratio, with the ultimate aim of influencing the carbon dioxide concentration of the finished product gas. This innovative design fundamentally overcomes the limitations of traditional purification processes, which lack proactive control capabilities, and establishes a new adaptive control mechanism for air utilization in the purification process. Firstly, combined with the use of a CO2 concentration monitor, adjusting the regeneration gas flow rate ensures that the CO2 concentration at the regeneration gas outlet changes within a controlled range, thus controlling the regeneration effect of the adsorbent. This effect further influences the carbon dioxide concentration of the finished product gas after the tower is put into production. Secondly, the introduction of the regeneration gas proportioning valve effectively supports the universality of the same process across different industries. The control target value can be selectively determined to address the differences in outlet carbon dioxide concentration requirements across different industries. Thirdly, the regeneration gas proportioning valve can be adaptively adjusted to meet varying production load intensities and environmental conditions, ensuring efficient and stable operation of the purification process while minimizing the proportion of regeneration gas and reducing venting energy consumption. Finally, the regulation of the regeneration gas proportioning valve can be combined with traditional control methods to optimize overall operating energy consumption. In this step, due to the adjustment of the regenerated finished gas ratio, the purification process can be further optimized by combining it with traditional cycle adjustment methods. The application of the regeneration gas proportioning valve expands the adjustment range of traditional cycle adjustment methods. Considering the need to avoid tunneling effects in the purifier tower, based on a 20% regeneration gas ratio in air separation, the regeneration gas proportioning valve can optimize the regeneration gas ratio to 15%-17%, resulting in 15%-25% less gas consumption compared to traditional purification processes. Therefore, from the perspective of gas consumption, this innovative approach can optimize the amount of regeneration gas released, significantly saving the purifier's regeneration energy consumption.

[0042] 2. This invention adds a waste heat recovery heat exchanger at the outlet of the oil-free air compressor to recover the compressor's exhaust heat. Before entering the electric heater, the finished compressed air or nitrogen exchanges heat with the hot air from the oil-free air compressor in the waste heat recovery heat exchanger, achieving sufficient preheating of the regenerated gas. By fully recovering the compression heat, the energy consumption for heating the regenerated gas can be effectively reduced. Existing waste heat recovery heat exchangers are relatively mature, with increased resistance losses all below 5 kPa, which is even lower than the resistance of traditional water-cooled systems. In practical use, the waste heat of the oil-free air compressor can be directly utilized, significantly improving the heat exchange stability and thermal quality of the regenerated gas, and maximizing the savings in heating power consumption.

[0043] From a temperature difference perspective, regenerating the compression heat of an oil-free air compressor can reduce energy consumption in the heating and regeneration process by more than 50%. After recovering and utilizing the compression heat, the electric heater only needs to heat the regeneration gas from 95℃ to above 170℃, which can significantly save energy. Even without considering the reduction in regeneration gas consumption and the improvement in compressed air utilization brought about by the regeneration gas proportional control valve, at least 50% of energy consumption can be saved in the heating process of the electric heater alone.

[0044] 3. When the present invention uses a proportional regulating valve to regulate the flow rate of nitrogen as regeneration gas, compared with the traditional nitrogen regeneration purification process, the heating energy saving is more than 50%; the nitrogen emission is only 75%-85% of the traditional nitrogen purification process, which can significantly reduce nitrogen emissions and help to balance and efficiently utilize nitrogen.

[0045] 4. For this invention, the utilization of waste heat from oil-free screw compressors, especially variable frequency oil-free screw compressors, is also an important direction. At the same time, for industries with large fluctuations in air consumption, centrifuges and variable frequency oil-free screw compressors, combined with the above-mentioned purification process structure, can maximize the efficient and smooth operation of the corresponding compressed air system.

[0046] 5. The two innovative aspects of this invention fundamentally solve the three key problems in the purification process: poor controllability of regenerated gas, high consumption of regenerated gas, and failure to fully utilize the compression heat of the oil-free air compressor. This provides strong support for its high efficiency and low consumption, and fundamentally expands the practicality and versatility of the purification process in different industries. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of a compressed air purification process that regenerates from finished compressed air.

[0048] Figure 2 This is a schematic diagram of a compressed air purification process based on nitrogen regeneration.

[0049] Figure 3 The layout of the dual towers and inlet / outlet piping of a purifier is shown as an example.

[0050] The attached diagram is labeled as follows: 1 Air filter; 2 Oil-free air compressor; 3 Waste heat recovery heat exchanger; 4 Cooler; 5 Precooler; 6 Purifier; 7 CO2 concentration monitor; 8 Electric heater; 9 CO2 concentration monitor; 10 Proportional regulating valve; 11 Nitrogen pipeline. Detailed Implementation

[0051] The implementation of the present invention will now be described in detail with reference to the accompanying drawings.

[0052] The compressed air purification method described in this invention, which can recover waste heat from compression and allow for adjustable regeneration gas, is based on... Figure 1 , 2 This is achieved through a device that recovers waste heat from compression and provides adjustable compressed air purification.

[0053] The device includes an air filter 1, an oil-free air compressor 2, a waste heat recovery heat exchanger 3, a cooler 4, a precooler 5, and a purifier 6, which are connected in sequence via pipelines. The oil-free air compressor 2 can be either a centrifugal air compressor or a screw air compressor. The precooler 5 can be equipped with a built-in air-water separator, or a separate air-water separator can be configured between the precooler 5 and the purifier 6.

[0054] The purifier 6 has a parallel dual-tower structure (A and B), with adsorbent packed in each tower. The inlet of each tower is connected to the inlet pipe of the compressed air to be purified and the inlet pipe of the regenerated gas, while the outlet of each tower is connected to the outlet pipe of the finished compressed air and the vent pipe of the regenerated gas. A connecting branch pipe is provided between the inlet and outlet pipes of each tower, and a valve is installed on the connecting branch pipe to switch the connection relationship between each tower and the pipeline. A CO2 concentration monitor 7 and a CO2 concentration monitor 9 are respectively installed on the finished compressed air outlet pipe and the regenerated gas vent pipe. The end of the regenerated gas vent pipe is a direct vent outlet to the atmosphere.

[0055] The waste heat recovery heat exchanger 3 is equipped with a compressed air inlet and a compressed air outlet, as well as a regenerated gas inlet and a regenerated gas outlet. The gas supply pipeline for the regenerated gas to be heated is connected to the regenerated gas inlet, and the regenerated gas outlet is connected in sequence to a proportional regulating valve 10, an electric heater 8, and a purifier 6 via a pipeline to provide heated regenerated gas. For ease of control, the proportional regulating valve is preferably an electrically controlled valve and is connected to a PLC controller via a signal line. The PLC controller and the CO2 concentration monitor are respectively connected to a host computer via signal lines.

[0056] This invention can use finished compressed air or nitrogen as the regeneration gas. Therefore, as Figure 1 As shown, a pipeline connects to the finished compressed air outlet of the purifier and the regeneration gas inlet of the waste heat recovery heat exchanger, and a portion of the finished compressed air is drawn from the purifier outlet as regeneration gas. Alternatively, as... Figure 2As shown, the regeneration gas inlet of the external nitrogen supply equipment and the waste heat recovery heat exchanger is connected by a pipeline, and nitrogen is introduced from outside the device as regeneration gas. When the purification device of the present invention is used in an air separation system, the waste nitrogen (i.e., non-high-purity nitrogen) of the air separation unit can be directly introduced as regeneration gas.

[0057] To enable the regenerated gas to be used for cooling after desorption, a bypass branch pipe and a switching valve are installed between the regenerated gas inlet and outlet of the waste heat recovery heat exchanger. One end of this bypass branch pipe is located on the pipeline between the regenerated gas outlet and the proportional regulating valve. For ease of reading, Figure 1 , 2 The valves at the regenerated gas inlet and outlet are omitted.

[0058] As an example, the present invention provides such Figure 3 The layout of the purifier's dual towers and inlet / outlet piping is shown.

[0059] Specifically, the system includes: two towers, A and B, arranged in parallel, with a double-layer adsorption bed structure built inside each tower using adsorbent; two parallel pipelines are connected to the inlets at the bottom of the two adsorption towers, with two inlet valves on one pipeline and two exhaust valves on the other; the midpoint of the two inlet valves is connected to the outlet of the precooler via a pipeline, with a valve installed on this pipeline; the midpoint of the two exhaust valves is connected to the regeneration gas vent pipe via a pipeline, with a CO2 concentration monitor installed on this pipeline; two parallel pipelines are connected to the outlets at the top of the two adsorption towers, with two outlet valves on one pipeline and two regeneration valves on the other; the midpoint of the two outlet valves is connected to the finished compressed air outlet pipe, with a CO2 concentration monitor and an outlet main valve installed on this pipeline; the midpoint of the two regeneration valves is connected to the outlet of the electric heater via a pipeline, with a valve installed on this pipeline. Preferably, the valves on the inlet and outlet pipelines of the purifier are electrically controlled valves, connected to a PLC controller via signal lines, which in turn is connected to a host computer via signal lines.

[0060] The carbon molecular sieve in the adsorption tower can optionally be packed using a blizzard method and compacted from the top to prevent pulverization caused by high-pressure airflow, ensuring long-term operation. By employing unequal pressure equalization, the continuity of the compressed air purity distribution from low to high in the adsorption tower bed can be improved, facilitating the rapid production of compressed air with qualified purity, thereby improving purification efficiency and ensuring the performance indicators of the molecular sieve. These are all standard operating procedures for adsorption towers and are not required by this invention.

[0061] Based on the above-described apparatus, the compressed air purification method of the present invention specifically includes the following steps:

[0062] (1) By switching valves, the purifier 6 is operated in the state of A tower inlet adsorption and B tower pressure holding standby;

[0063] (2) Normal pressure air is input into air filter 1 by induced draft fan (not shown in the figure), and its pressure and temperature are increased after being compressed by oil-free air compressor 2. The hot air exchanges heat with regenerated gas in waste heat recovery heat exchanger 3, and then is sent to cooler 4 for cooling. After passing through precooler 5 (with built-in gas-water separator) for cooling and dehydration treatment, compressed air to be purified with a temperature below 10°C is obtained and used as raw material gas for purifier 6.

[0064] (3) The compressed air to be purified is sent into tower A. When passing through the adsorption bed, the gaseous CO2 and residual moisture are absorbed by the adsorbent. According to the measured value of CO2 concentration monitor 9 on the finished compressed air outlet pipe and the requirements of the finished product control index, the valve on the connecting branch pipe is switched in time to put tower B into operation.

[0065] (4) While adsorbing the gas at the inlet of tower B, regenerate and desorb tower A according to the following operation method:

[0066] The regenerated gas to be heated is introduced into the regenerated gas inlet of the waste heat recovery heat exchanger 3 to exchange heat with the hot air from the oil-free air compressor 2; the preheated regenerated gas enters the electric heater 8 through the proportional regulating valve 10 and is further heated to above 170°C; the high-temperature regenerated gas is sent to tower A to regenerate and desorb the adsorbent, and the released regenerated gas is directly discharged into the atmosphere; during this process, the flow rate of the regenerated gas is adjusted by the proportional regulating valve 10 so that the measured value of the CO2 concentration monitor on the regenerated gas vent pipe meets the predetermined control target;

[0067] When the measured value of CO2 concentration monitor 9 reaches the regeneration and desorption requirements, stop the operation of electric heater 8; switch the valve on the bypass branch pipe of waste heat recovery heat exchanger 3 to allow unheated regeneration gas to enter tower A for cooling, and release the regeneration gas directly into the atmosphere; after the temperature of tower A stabilizes, close the valve on the regeneration gas vent pipe to pressurize, and close the proportional regulating valve 10 to stop the gas supply when the operating pressure is reached; close the valves on the inlet and outlet pipes of tower A and maintain pressure for standby.

[0068] When using finished compressed air as regeneration gas, the output should be controlled to not exceed 20% of the total finished compressed air volume; when using nitrogen introduced from an external nitrogen supply device as regeneration gas, the booster pump (not shown in the figure) installed on the nitrogen pipeline should be started according to the pressure conditions to meet the pressure charging and holding requirements.

[0069] (5) Repeat steps (1) to (4) to keep the purifier 6 running in a dual-tower alternating state and continuously and stably output the finished compressed air.

[0070] Figure 1The finished compressed air is drawn directly from the outlet of purifier 6 (after the CO2 concentration monitor) and used as the regeneration gas to be heated, with its output controlled to not exceed 20% of the total finished compressed air. Since the compressed air is directly produced by purifier 6, it can meet the pressure holding requirements after regeneration and desorption, and no additional booster pump is required.

[0071] Figure 2 Nitrogen is introduced from an external nitrogen supply device (such as an air separation system) as regeneration gas. Depending on the nitrogen supply pressure, a booster pump can be optionally installed on the nitrogen pipeline to meet the pressure holding requirements after regeneration and desorption.

[0072] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for purifying compressed air with adjustable heat recovery from compression and regeneration gas, characterized in that, This method is based on a device for recovering waste heat from compression and for purifying controllable compressed air; the device includes an air filter, an oil-free air compressor, a waste heat recovery heat exchanger, a cooler, a precooler, and a purifier connected in sequence by pipelines. The purifier has a parallel dual-tower structure (A and B), with adsorbent packed in each tower. The inlet of each tower is connected to the compressed air inlet pipe and the regenerated gas inlet pipe, and the outlet of each tower is connected to the finished compressed air outlet pipe and the regenerated gas vent pipe. A connecting branch pipe is provided between the inlet and outlet pipes of each tower, and a valve is provided on the connecting branch pipe to switch the connection relationship between each tower and the pipeline. CO2 concentration monitors are respectively installed on the finished compressed air outlet pipe and the regenerated gas vent pipe. The waste heat recovery heat exchanger is provided with a compressed air inlet, a compressed air outlet, a regenerated gas inlet, and a regenerated gas outlet; the gas supply pipeline for the regenerated gas to be heated is connected to the regenerated gas inlet, and the regenerated gas outlet is connected in sequence to a proportional regulating valve, an electric heater, and a purifier through a pipeline to provide heated regenerated gas. The compressed air purification method specifically includes the following steps: (1) By switching valves, the purifier is operated in the state of A tower inlet adsorption and B tower pressure holding standby; (2) Use an induced draft fan to input atmospheric pressure air into the air filter, and after being compressed by an oil-free air compressor, its pressure and temperature are increased; the hot air exchanges heat with the regenerated gas in the waste heat recovery heat exchanger, and then is sent to the cooler to cool down, and then passes through the pre-cooler to obtain compressed air to be purified with a temperature below 10°C, which is used as the raw material gas for the purifier. (3) The compressed air to be purified is sent into tower A. When passing through the adsorption bed, the gaseous CO2 and residual moisture are absorbed by the adsorbent. According to the measured value of the CO2 concentration monitor on the finished compressed air outlet pipe and the requirements of the finished product control index, the valve on the connecting branch pipe is switched in time to put tower B into operation. (4) While adsorbing the gas at the inlet of tower B, regenerate and desorb tower A according to the following operation method: The regenerated gas to be heated is introduced into the regenerated gas inlet of the waste heat recovery heat exchanger to exchange heat with hot air from the oil-free air compressor; the preheated regenerated gas enters the electric heater through the proportional control valve and is further heated to above 170°C; the high-temperature regenerated gas is sent to tower A to regenerate and desorb the adsorbent, and the released regenerated gas is directly discharged into the atmosphere; during this process, the flow rate of the regenerated gas is adjusted using the proportional control valve so that the measured value of the CO2 concentration monitor on the regenerated gas vent pipe meets the predetermined control target; When the measured value of the CO2 concentration monitor reaches the regeneration and desorption requirements, stop the operation of the electric heater; switch the valve on the bypass branch of the waste heat recovery heat exchanger to allow the unheated regeneration gas to enter Tower A for cooling, and the released regeneration gas is directly discharged into the atmosphere; after the temperature of Tower A stabilizes, close the valve on the regeneration gas vent pipe to pressurize, and close the proportional regulating valve to stop the gas supply when the operating pressure is reached; close the valves on the inlet and outlet pipes of Tower A and maintain pressure for standby. (5) Repeat steps (1) to (4) to keep the purifier running in a dual-tower alternating state and continuously and stably output the finished compressed air.

2. The method according to claim 1, characterized in that, The regenerated gas to be heated is the finished compressed air directly drawn from the purifier outlet, and the amount drawn out does not exceed 20% of the total finished compressed air; or, the regenerated gas to be heated is introduced from a nitrogen supply device outside the purification device, and a booster pump is provided on the nitrogen pipeline to meet the pressure charging and holding requirements.

3. The method according to claim 1, characterized in that, A bypass branch pipe and a valve for switching are provided between the regenerated gas inlet and the regenerated gas outlet of the waste heat recovery heat exchanger. One end of the bypass branch pipe is located on the pipeline between the regenerated gas outlet and the proportional regulating valve.

4. The method according to claim 1, characterized in that, The oil-free air compressor is a centrifugal air compressor or a screw air compressor.

5. The method according to claim 1, characterized in that, The precooling machine is equipped with a gas-water separator.

6. The method according to claim 1, characterized in that, The end of the regenerated gas vent pipe is a vent outlet that directly discharges into the atmosphere.

7. The method according to claim 1, characterized in that, The proportional control valve is an electrically controlled valve and is connected to the PLC controller via a signal line; the PLC controller and the CO2 concentration monitor are respectively connected to the host computer via signal lines.

8. The method according to claim 1, characterized in that, The specific layout of the dual towers and inlet / outlet pipelines of the purifier includes: towers A and B are arranged in parallel, and a double-layer adsorption bed structure is built inside each tower with adsorbent. The two parallel pipelines are connected to the air inlets at the bottom of the two adsorption towers respectively. One pipeline is equipped with two air inlet valves and the other pipeline is equipped with two air outlet valves. The midpoint of the two air inlet valves is connected to the outlet of the precooler through a pipeline, and a valve is installed on this pipeline. The midpoint of the two air outlet valves is connected to the regeneration gas vent pipe through a pipeline, and a CO2 concentration monitor is installed on this pipeline. The two parallel pipelines are connected to the outlets at the top of the two adsorption towers respectively. One pipeline is equipped with two outlet valves, and the other pipeline is equipped with two regeneration valves. The midpoint of the two outlet valves is connected to the finished compressed air outlet pipeline, which is equipped with a CO2 concentration monitor and an outlet main valve. The midpoint of the two regeneration valves is connected to the outlet of the electric heater, which is equipped with a valve.

9. The method according to claim 8, characterized in that, The valves on each pipeline at the inlet and outlet of the purifier are electrically controlled valves, which are connected to the PLC controller via signal lines. The PLC controller is then connected to the host computer via signal lines.

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