Concentration method and concentration system for low-concentration gas backflow mixed stable gas

Abstract

The invention belongs to the technical field of gas separation, and particularly relates to a concentration method and a concentration system for low-concentration gas backflow mixed stable gas. According to the method, a group of parallel adsorption beds are filled with methane selective adsorbents, the temperature and pressure of a gas inlet pipeline and the adsorption beds are controlled, and low-concentration gas with fluctuating concentration is subjected to multiple circulation processes of adsorption, pressure equalization, desorption, reflux mixing and adsorption in the parallel adsorption beds. Concentration of low-concentration gas with fluctuating methane concentration is achieved through backflow mixed stable gas, and gas product gas which can be directly used and has the alkane gas concentration of 8% or above is obtained. By adopting the method and the system, the loss rate of methane in the mixed gas is low, the equipment investment is smaller, the starting and stopping are flexible, and the operation is simple and convenient; the methane concentration in the obtained gas product gas reaches 8% or above, and the gas product gas can be used for gas power generation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation, and in particular to a separation method and a device for separating low-concentration and fluctuating concentration (concentration fluctuating between 1% and 3%), and specifically to a method and a device for enriching fluctuating methane gas by reflux mixing and stabilizing gas. Background Art

[0002] Coal mine gas is the common name for coalbed methane, which is a general term for harmful gases, mainly methane (CH4), that emerge from coal and rock formations during the production process of coal mines. As a byproduct of coal mining, it is known as the "number one killer in coal mines". When not used, it will be directly extracted from underground coal mines and discharged or burned on the ground, posing a threat to the safe production of coal mines. More importantly, it will pollute the air and cause a greenhouse effect.

[0003] Compared with the well-known carbon dioxide emission reduction, most companies currently do not pay enough attention to methane emission control. Studies have shown that although methane has a relatively short life cycle, its greenhouse effect is relatively high, and its contribution to global warming is about 1 / 4. For my country, methane accounts for a relatively high proportion of total greenhouse gas emissions. Among them, the energy sector is the largest source of methane emissions, accounting for 44.7% of the total, and these mainly come from the coal mining process, accounting for 39.2%.

[0004] Coal mine gas is divided into high-concentration gas and low-concentration gas. High-concentration gas refers to gas with a concentration greater than 30%, and low-concentration gas refers to gas with a concentration less than 30%. High-concentration gas can be directly used through gas power generation and other methods, with significant economic benefits, and is currently widely used. However, the utilization of low-concentration gas varies significantly among different coal mining companies. The main reason is that on the one hand, the conditions of different coal mines are different, and the gas state underground may change at any time. It is difficult for traditional generators to "remain unchanged in the face of changes" when used for power generation. On the other hand, low-concentration gas has safety transportation problems (the concentration range of gas explosion is 5% to 16%). However, more than 60% of the gas in my country's coal mines is low-concentration gas. Because the methane concentration is low and does not meet the standards for industrial utilization, it has been directly discharged into the atmosphere for a long period of time, which not only causes a huge waste of resources, but also exacerbates the greenhouse effect.

[0005] At present, the state has explicitly prohibited the emission of low-concentration gas with a concentration higher than or equal to 8% (8% ≤ methane volume fraction < 30%). However, for concentrations lower than 8% or extraction of pure volume less than 10m 3 / min of low-concentration gas encourages enterprises to explore comprehensive utilization and avoid direct methane emissions under the premise of ensuring safety.

[0006] Theoretically, low-concentration gas can be concentrated by treatment, such as pressure swing adsorption (PSA) or membrane separation technology, to increase the methane concentration in the gas to a standard suitable for comprehensive utilization. However, due to the limitation of the level of technological development, the separation efficiency of the extracted gas with a volume concentration of 1% to 8% is greatly reduced by directly using a pressure swing adsorption (PSA) device to concentrate and enrich it, resulting in poor economic efficiency of the operation of the PSA device. In actual production, the characteristics of underground gas extraction in coal mines are that in order to ensure safety, coal mines are often equipped with gas extraction pumps with power far exceeding the set value, resulting in the methane concentration of the gas raw gas extracted from coal mines being often lower than the minimum methane concentration required for pressure swing adsorption to obtain usable product gas. In this case, even the methane product obtained by pressure swing adsorption cannot be effectively utilized, and it is not economically cost-effective. Therefore, most coal mining enterprises choose to discharge directly instead of using it. Therefore, it is of great significance to develop a method for concentrating low-concentration gas, especially extracted gas with a volume concentration of 1% to 8%. Summary of the invention

[0007] In order to solve the industry problem of low-concentration gas existing in existing coal mine production, especially the difficulty in utilizing extracted gas with a methane volume concentration of 1% to 8%, the present invention proposes a low-concentration gas reflux mixed stable gas concentration method and a corresponding concentration system.

[0008] The present invention is achieved through the following technical solutions.

[0009] A method for concentrating low-concentration gas reflux mixed stable gas, wherein a methane selective adsorbent is filled in an adsorption device, wherein the adsorption device comprises at least two parallel adsorption beds A and B; Under the condition of controlling the temperature and pressure of the air inlet pipeline and the adsorption bed to be constant, the raw gas is first introduced into the adsorption bed A. After the adsorption bed A is saturated with methane adsorption, the pressure is equalized between the adsorption bed A and the adsorption bed B. After the pressure equalization is completed, the adsorption bed A is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and the other part of the desorbed gas is returned to the system as the reflux gas and mixed evenly with the raw gas in the mixer to obtain a mixed gas. Then the mixed gas is introduced into the adsorption bed B after the pressure equalization to continue to adsorb methane. After the adsorption bed B is saturated with methane, the pressure is equalized again between the adsorption bed A and the adsorption bed B; after the pressure equalization is completed, the adsorption bed B is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and a part of the desorbed gas is returned to the system as the reflux gas and mixed evenly with the raw gas in the mixer to obtain a mixed gas; the mixed gas is passed into the adsorption bed A after the pressure equalization to continue to adsorb methane; The above process is repeated, and the desorbed gases obtained from the output adsorption system are combined to obtain a gas with a basically stable concentration and a methane volume fraction of not less than 10%.

[0010] Furthermore, the raw gas is low-concentration gas, and the volume fraction of methane in the low-concentration gas is in the range of: 1%≤methane volume fraction<3%.

[0011] Furthermore, during the adsorption process, the temperature in the adsorption bed A and the adsorption bed B was 0-35°C and the pressure was 0.1 MPa; during the vacuum analysis process, the pressure in the adsorption bed A and the adsorption bed B was -0.09 MPa.

[0012] The present invention also provides a concentration system for realizing the above-mentioned concentration method, wherein the system comprises at least one group of adsorption devices and a matching gas stabilizing device, and the devices in the system are connected by pipelines; wherein the adsorption device comprises an adsorption bed A and an adsorption bed B, wherein the adsorption bed A and the adsorption bed B are filled with a methane selective adsorbent, and an air inlet pipe, an air outlet pipe, a desorption gas pipe and a reflux pipe are arranged between the adsorption bed A and the adsorption bed B, and valves are arranged on the air inlet pipe, the air outlet pipe, the desorption gas pipe and the reflux pipe, and the methane concentration in the mixed gas input to the adsorption bed device is intelligently adjusted and coordinated by the control of the opening and closing combination mode of the valves on the pipes and the gas stabilizing device, so that the gas and the reflux gas are adsorbed, pressure-equalized, enriched and decomposed in the adsorption device, so as to obtain a basically stable gas product gas with a methane volume fraction of not less than 8%.

[0013] Furthermore, during the adsorption process, the temperature in the adsorption bed A and the adsorption bed B was 0-35°C and the pressure was 0.1 MPa; during the vacuum analysis process, the pressure in the adsorption bed A and the adsorption bed B was -0.09 MPa.

[0014] Furthermore, the valves include a plurality of inlet valves arranged on the inlet pipeline, a plurality of vacuum valves arranged on the analytical gas pipeline, a plurality of equalizing valves and a plurality of outlet valves arranged on the outlet pipeline, and a reflux valve arranged on the reflux pipeline. Preferably, the inlet valve, vacuum valve, equalizing valve, outlet valve and reflux valve are all pneumatic valves.

[0015] Furthermore, in the above-mentioned concentration system, the gas stabilizing device includes a mixer, a mixed gas buffer tank and a PLC concentration control component; one end of the mixer is connected to the raw gas inlet pipeline, and the raw gas inlet pipeline is provided with a raw gas methane concentration detector and a raw gas flow controller; the other end of the mixer is connected to the mixed gas buffer tank through the mixed gas outlet pipeline, and the mixed gas buffer tank is provided with a mixed gas methane concentration detector; the side wall of the mixer is provided with a reflux gas inlet pipeline, and the reflux gas enters the mixer through the reflux gas flow controller and mixes with the raw gas; the PLC concentration control component is used to receive the detection signals from the raw gas methane concentration detector and the mixed gas methane concentration detector, and according to the detection signal, linear modeling is performed in real time, the reflux gas flow adjustment signal is calculated, and the reflux gas flow controller is instructed to adjust the reflux gas flow, so as to obtain the raw gas with basically stable concentration that meets the minimum methane concentration design value requirements of the pressure swing adsorption concentration system. Further, in the above-mentioned concentration system, the gas stabilizing device also includes a fixed bracket, and universal wheels are installed at the four corners of the bottom of the fixed bracket.

[0016] In the above-mentioned low-concentration gas reflux mixed gas concentration system, the gas stabilization process is as follows: 1) According to the requirements of the adsorption bed device for the methane concentration in the raw gas, the minimum design value S0 of the raw gas methane concentration is input into the PLC concentration control component; 2) The gas methane concentration detector and the mixed gas concentration detector respectively collect the methane concentration in the feed gas and the methane concentration in the mixed gas in the mixed gas buffer tank, obtain the gas methane concentration measurement value C1 and the mixed gas methane concentration measurement value C2, and feed them back to the PLC concentration control component; 3) The PLC concentration control component compares the measured value of gas methane concentration C1 and the design value of the minimum concentration of raw gas methane S0: a. When C1<S0, the PLC concentration control component further compares the methane concentration C2 of the mixed gas with the design value S0 of the minimum methane concentration of the raw gas: If C2<S0, the PLC concentration control component will perform linear modeling based on the real-time data of the methane concentration measurement value C1 of the gas and the methane concentration measurement value C2 of the mixed gas, calculate and obtain the flow adjustment signal, and output an instruction to the return gas flow controller to increase the return gas flow until the PLC concentration control component receives the methane concentration measurement value C2′≥S0 of the mixed gas, and the PLC concentration control component instructs the return gas flow controller to output the return gas flow value stably; b. When C1≥S0, the gas is input into the device and directly sent to the adsorption device for concentration treatment through the mixer and the mixed gas buffer tank; c. When the measured value C1 of the methane concentration in the gas is again lower than the design value S0 of the minimum methane concentration in the raw gas, repeat the above steps 2) and 3) until the raw gas that satisfies the operation of the adsorption device is obtained.

[0017] Preferably, the mixer is an SV type static mixer, and the interior of the SV type static mixer is composed of a plurality of groups of vertical SV type static mixer units and horizontal SV type static mixer units arranged alternately.

[0018] The method for concentrating low-concentration gas reflux mixed stable gas provided by the present invention, without using externally supplied high-concentration methane gas, obtains a basically stable gas product gas with a methane volume fraction of not less than 8% by mixing the analyzed gas with the low-concentration methane in the raw gas and then performing methane adsorption concentration, thereby obtaining the gas product gas with a methane volume fraction of not less than 8%. The gas product gas can be directly applied to gas power generation lamps, solving the industry problem of low-concentration gas existing in existing coal mine production, especially the difficulty in utilizing extracted gas with a methane volume concentration of 1% to 8%.

[0019] The low-concentration gas reflux mixing and stabilizing gas concentration system provided by the present invention is designed to solve the influence of methane concentration in gas on pressure swing adsorption, and a simple-structured intelligent gas stabilizing device for low-concentration gas pressure swing adsorption concentration system is designed. The intelligent gas stabilizing device adopts a specially structured SV-type static mixer to ensure that the reflux part of the methane analysis gas after concentration is fully mixed with the gas, and monitors the methane concentration in the reflux gas and the gas raw gas by setting a PLC concentration control component, and calculates the reflux gas flow adjustment signal according to the detected methane concentration signal, and instructs the reflux gas flow controller to adjust the reflux gas flow, so as to obtain the raw gas that meets the minimum design value requirement of the methane concentration of the pressure swing adsorption concentration system, and solves the problem that when the methane concentration in the low-concentration gas is too low, the pressure swing adsorption production device cannot operate stably, resulting in low quality of methane products and ineffective utilization, and poor economic efficiency of the device operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a simplified process flow diagram of a concentration system in a specific embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of the structure of the gas stabilizing device used in the gas stabilizing system of the present invention.

[0022] Figure 3 for Figure 2 Internal structure diagram of SV type static mixer.

[0023] Figure 4 It is a schematic diagram of the gas stabilization process in the concentration system of the present invention.

[0024] Reference numerals: Figures 1 to 3In the figure: 1-SV type static mixer; 2-mixed gas methane concentration detector; 3-mixed gas buffer tank; 4-PLC concentration control component; 5-raw gas methane concentration detector; 6-raw gas flow controller; 7-return gas flow controller; a-gas inlet pipeline; b-return gas inlet pipeline; c-vertical SV type static mixer unit; d-horizontal SV type static mixer unit; e-mixed gas outlet pipeline; f-raw gas pipeline; F1-return gas valve; F2, F3-inlet valve; F4, F5-vacuum valve; F6, F7-equalizing valve; F8, F9-outlet valve. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0026] The method for enriching low-concentration gas reflux mixed stable gas of the present invention is based on the principle of enriching methane gas by pressure swing adsorption (PSA). The basic principle of the adsorption method is to separate the mixed gas by utilizing the different adsorption capacity, adsorption speed and adsorption amount of the adsorbent for different gases. In the commonly used pressure swing adsorption method, under pressurized conditions, impurity gases such as N2, CO2, H2O, etc. will be adsorbed on the surface of the adsorbent, while CH4 can pass smoothly. When the pressure is reduced, the impurity gas adsorbed on the surface of the adsorbent is released, and the adsorbent is regenerated to achieve the separation of impurity gas and CH4. The separation effect of pressure swing adsorption is mainly affected by temperature, pressure, and adsorbent. The adsorption amount decreases when the temperature increases, and increases when the temperature decreases; the adsorption amount increases when the pressure increases, and decreases when the pressure decreases; the adsorption capacity of different adsorbents is also different. It should be noted that the presence of H2S will cause permanent poisoning of the adsorbent, and the presence of H2O will also greatly reduce the adsorption effect. Therefore, before using conventional pressure swing adsorption, it is necessary to remove gases such as H2S and H2O in low-concentration gas. The process of pressure swing adsorption usually includes several steps of adsorption, venting, flushing, equalization and stamping, which are well known to those skilled in the art and will not be described in detail. In order to achieve continuous operation, several towers are usually required to be closed and opened continuously. A typical PSA unit includes 4 adsorption towers running in parallel. More adsorption towers can be added and the flow between towers can be optimized to achieve higher separation efficiency and energy efficiency, but at the same time, acceptable operational complexity and investment costs must also be considered.

[0027] Adsorbents or adsorbents play a key role in pressure swing adsorption (PAS) devices, and the quality of adsorbents determines the final effect of gas purification. Generally, different types of activated carbon and molecular sieves are used as adsorbent materials. The adsorbents suitable for gas concentration should consider both the selectivity of methane in the separated components and the regeneration performance of the adsorbent. At present, among the commonly used adsorbent materials, molecular sieves have obvious advantages in the process of separating nitrogen, and activated carbon is more suitable for being selected as an adsorbent for the decarbonization process with a large amount of gas. In the low-concentration gas to be treated by the present invention, the volume concentration of methane is between 1% and 3%. If the impurity components in the gas are directly adsorbed, it is necessary to repeat the cycle of adsorption, venting, flushing, equalization and stamping for many times, resulting in greater energy consumption and increased production costs. Therefore, the technical solution of the present invention is to directly use a methane selective adsorbent as the filling material of the adsorption bed, and after the adsorbent material adsorbs methane, the impurity gas is discharged from the adsorption system as tail gas. In the adsorption process, the methane selective adsorbent is first filled in the adsorption device.

[0028] As an exemplary illustration, the adsorption device described below includes two adsorption beds, namely, adsorption bed A and adsorption bed B, which are arranged in parallel. Of course, those skilled in the art, under the guidance of the prior art, use 3, 4 or more adsorption beds in parallel, and then obtain the sequence steps of adsorption, venting, flushing, pressure equalization and stamping in a certain manner, so as to better achieve the purpose of methane enrichment in gas.

[0029] like Figure 1 As shown, under the condition of controlling the temperature and pressure of the air inlet pipeline and the adsorption bed to be constant, the raw gas is first introduced into the adsorption bed A, and after the adsorption bed A is saturated with methane adsorption, the pressure is equalized between the adsorption bed A and the adsorption bed B; after the pressure equalization is completed, the adsorption bed A is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and the other part of the desorbed gas is returned to the system as the reflux gas and mixed evenly with the raw gas in the mixer to obtain a mixed gas; then the mixed gas is introduced into the adsorption bed B after the pressure equalization to continue to adsorb methane; After the adsorption bed B is saturated with methane, the pressure is equalized again between the adsorption bed A and the adsorption bed B; after the pressure equalization is completed, the adsorption bed B is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and a part of the desorbed gas is returned to the system as the reflux gas and mixed evenly with the raw gas in the mixer to obtain a mixed gas; the mixed gas is passed into the adsorption bed A after the pressure equalization to continue to adsorb methane; The above process is repeated, and the desorbed gases obtained from the output adsorption system are combined to obtain a basically stable gas with a methane volume fraction of not less than 8%.

[0030] In the low-concentration gas reflux mixed stable gas enrichment method of the present invention, the raw gas can be a low-concentration gas with a methane volume fraction fluctuating between 1% and 3%. Of course, if the methane volume fraction is higher, better technical effects can be achieved by using the method of the present invention. In addition, if the methane volume fraction is <1%, although theoretically, the method of the present invention can also be used to enrich the gas concentration, it is obvious that the energy consumption and cost will increase sharply when processing such raw gas. Therefore, the method of the present invention is a better solution for processing low-concentration gas with a methane volume fraction fluctuating between 1% and 3%, considering comprehensively from the perspective of gas utilization and economic efficiency.

[0031] The low-concentration gas reflux mixed gas concentration system of the present invention comprises at least one set of adsorption devices and a matching gas stabilization device, wherein the devices in the system are connected by pipelines; wherein the adsorption device comprises an adsorption bed A and an adsorption bed B, wherein the adsorption bed A and the adsorption bed B are filled with a methane selective adsorbent, wherein an air intake pipe, an air outlet pipe, a desorption gas pipe and a reflux pipe are arranged between the adsorption bed A and the adsorption bed B, wherein an air intake valve F2, F3 is arranged on the air intake pipe, a vacuum valve F4, F5 is arranged on the desorption gas pipe, a pressure equalizing valve F6, F7 and an air outlet valve F8, F9 are arranged on the air outlet pipe, and a reflux valve F1 is arranged on the reflux pipe. A preferred technical solution is that the air intake valves F2, F3, the vacuum valves F4, F5, the pressure equalizing valves F6, F7, the air outlet valves F8, F9 and the reflux valve F1 are all pneumatic valves to ensure the safety of the equipment.

[0032] By controlling the opening and closing combination of the valves on the pipeline and cooperating with the gas stabilizing device to intelligently adjust the methane concentration in the mixed gas input to the adsorption bed device, the gas and reflux gas are adsorbed, pressure-equalized, enriched, and analyzed in the adsorption device to obtain a basically stable gas product gas with a methane volume fraction of not less than 8%.

[0033] like Figure 2 As shown, the gas stabilizing device used in the low-concentration gas reflux mixed stabilizing gas concentration method and concentration system of the present invention comprises: an SV type static mixer 1, a mixed gas methane concentration detector 2, a mixed gas buffer tank 3, a PLC concentration control component 4, a raw gas methane concentration detector 5, a raw gas flow controller 6, and a reflux gas flow controller 7.

[0034] One end of the SV type static mixer 1 is connected to the gas inlet pipe, and the other end is connected to the mixed gas buffer tank 3 through the mixed gas outlet pipe e, wherein: the gas inlet pipe a is provided with a gas methane concentration detector 5 and a gas flow controller 6; the mixed gas buffer tank 3 is provided with a mixed gas methane concentration detector 2; the side wall of the SV type static mixer 1 is provided with a reflux gas inlet pipe b, which is connected to the analytical gas pipeline of the pressure swing adsorption system through the reflux gas inlet pipe b.

[0035] The gas stabilizing device of the low-concentration gas pressure swing adsorption concentration system of the present invention is provided with a special SV type static mixer, thereby ensuring that the reflux gas and the raw gas are fully mixed in the mixer.

[0036] like Figure 3 As shown, in the gas stabilizing device of the low-concentration gas pressure swing adsorption concentration system of the present invention, the SV-type static mixer is composed of a vertical SV-type static mixer unit c and a horizontal SV-type static mixer unit d arranged in a staggered manner. By staggering the SV-type static mixer units vertically and horizontally, the gas flow can be more fully divided inside the mixer, and the gas flow direction and rotation direction are continuously changed, so that the mixing is more complete. Preferably, 5-7 groups of staggered vertical and horizontal static mixer units are set.

[0037] In the gas stabilizing device of the low-concentration gas pressure swing adsorption concentration system of the present invention, the PLC concentration control component 4 is connected with the gas methane concentration detector 5, the mixed gas methane concentration detector 2, and the reflux gas flow controller 7 through wires, and they work together to control the mixed gas concentration.

[0038] In the low-concentration gas reflux mixing and stabilizing gas concentration system of the present invention, the working process of the gas stabilizing device is as follows: Figure 4 As shown: 1) Turn on the power supply, wait for the PLC concentration control component 4 to be initialized, and input the minimum methane concentration design value S0 of the raw gas of the PSA system according to the methane concentration requirement in the raw gas of the pressure swing adsorption concentration system; 2) The gas methane concentration detector 5 and the mixed gas concentration detector 2 respectively collect the methane concentration in the feed gas and the methane concentration in the mixed gas in the mixed gas buffer tank, obtain the gas methane concentration measurement value C1 and the mixed gas methane concentration measurement value C2, and feed them back to the PLC concentration control component 4; 3) PLC concentration control component 4 compares the measured value C1 of gas methane concentration and the design value S0 of the minimum methane concentration of raw gas: a. When C1<S0, it indicates that the raw gas needs to be refluxed and stabilised. The PLC concentration control component 4 further compares the methane concentration C2 of the mixed gas with the design value S0 of the minimum methane concentration of the raw gas: If C2<S0, the PLC concentration control component 4 performs data linear modeling in real time according to the measured value C1 of the methane concentration of the gas and the measured value C2 of the methane concentration of the mixed gas, calculates and obtains the flow adjustment signal, and outputs an instruction to the reflux gas flow controller 7 to adjust the reflux gas flow to H1, and the reflux gas flow controller 7 increases the reflux gas flow; this cycle continues until the PLC concentration control component 4 receives the measured value C2′≥S0 of the methane concentration of the mixed gas, and the PLC concentration control component 4 instructs the reflux gas flow controller 7 to stabilize the reflux gas flow at the reflux gas flow value H2 corresponding to C2′≥S0; b. When C1≥S0, it means that there is no need to perform reflux gas stabilization adjustment on the raw gas. At this time, after the gas is input into the device, it is mixed through the mixed gas outlet pipe e set on the SV type static mixer 1, and then directly sent from the mixed gas buffer tank 3 through the raw gas pipe f to the PSA device for concentration treatment.

[0039] c. When the measured value C1 of the gas methane concentration is again lower than the design value S0 of the minimum methane concentration of the raw gas, repeat the above steps 2) and 3) until the raw gas that meets the requirements for the operation of the PAS device is obtained.

[0040] 4) After replacing the adsorbent in the pressure swing adsorption device, according to the design value requirement of the minimum methane concentration in the raw gas for the replaced adsorbent, a new design value of the raw gas methane concentration S0′ is input into the PLC concentration control component 4, and the gas stabilization device enters a new working operation cycle according to the same gas stabilization process as steps 2) and 3) above.

[0041] The gas stabilizing device in the concentration system of the present invention utilizes the operating data received by the PLC concentration control component 4 from the gas methane concentration detector 5 and the mixed gas methane concentration detector 2 for real-time linear modeling, calculates and obtains a flow adjustment signal, and outputs an instruction to the reflux gas flow controller 7 to adjust the reflux gas flow rate, accurately controls the matching of the reflux gas and the feed gas methane concentration, and after reflux mixing treatment, the methane gas concentration in the mixed gas input to the PAS methane enrichment system meets the design value requirement of the methane adsorbent selected in the PAS device for the minimum concentration of methane in the raw gas, thereby ensuring the stability of the raw gas concentration in the pressure swing adsorption system, and solving the technical problems that when the methane concentration in the low-concentration gas is too low, the pressure swing adsorption production device cannot operate stably, resulting in low quality of methane products and ineffective utilization, as well as poor economic efficiency of the device operation.

[0042] In this process, the reflux gas is the methane analysis gas product with a methane concentration greater than 8% after being enriched by the PAS device. By controlling the reflux amount of the methane analysis gas, it is mixed with the feed gas with a concentration not exceeding 8%, so that the methane concentration in the mixed gas reaches the design value requirement of the PAS device for the minimum methane concentration in the raw gas.

[0043] In the system of the present invention, an intelligent control system is designed in the gas stabilization device, namely: PLC concentration control component 4. The methane concentration in the mixed gas is monitored and controlled by the intelligent control system, and the operating data received by the PLC concentration control component 4 from the gas methane concentration detector 5 and the mixed gas methane concentration detector 2 are used for real-time linear modeling. The minimum design value of the raw gas methane concentration of the PSA system is used as the expected concentration input value of the input main controller, and the actual concentration of the mixed gas is used as the feedback link. The difference between the two is used as the input value of the reflux gas flow controller, and the actual concentration of the mixed gas is affected by controlling the set value of the reflux gas flow rate, so as to achieve the effect of controlling the reflux gas flow rate by regulating the mixed gas concentration and then controlling the mixed gas concentration. The specific execution of this process is to achieve the follow-up control of the product gas flow rate and concentration by intelligently regulating the flow rate of the product gas, so as to achieve the control effect that the flow rate decreases when the concentration increases and the flow rate increases when the concentration decreases.

[0044] In specific applications, the temperature in adsorption bed A and adsorption bed B is 0-35°C, the pressure is 0.1 MPa, and the vacuum desorption pressure is -0.09 MPa. Better adsorption and desorption effects are achieved through pressure difference. Example

[0045] In order to better illustrate the separation effect of the method of the present invention on low-concentration gas, Figure 1 The process flow of the system of the present invention is described in detail for the enrichment of methane with a volume fraction of 2%.

[0046] (1) Open the air inlet valve F2 of adsorption bed A, and control the flow rate of methane gas with a volume fraction of 2% entering adsorption bed A through the raw gas flow controller 6. After the pressure in adsorption bed A is increased to 0.1 MPa under normal pressure, open the air outlet valve F8 of adsorption bed A to start the adsorption process. At this time, low-concentration methane is adsorbed by the methane selective adsorbent contained in the adsorption bed. When the adsorption of adsorption bed A reaches saturation, open the pressure equalizing valves F6 and F7 to equalize the pressure of adsorption bed A and adsorption bed B. The purpose of the pressure equalizing step is to allow some impurity components of adsorption bed A to enter adsorption bed B, thereby reducing the adsorption of impurity components in the raw gas by adsorption bed B and improving the enrichment effect.

[0047] (2) After the pressure equalization is completed, the pressure equalization valves F6 and F7 and the outlet valve F8 are closed, and the vacuum valve F4 is opened to vacuum desorb the adsorption bed A. The reflux valve F1 is opened, and the concentration of the mixed gas after mixing in the SV type static mixer 1 is detected by the methane concentration detector 5. The flow setting value of the reflux gas flow controller 7 is adjusted according to the concentration of the mixed gas, so that the desorbed gas partially refluxes through the reflux gas pipeline and mixes with the raw gas in the SV type static mixer 1 to achieve the effect of stabilizing the raw gas intake concentration at the set value (3.5%). After the mixed gas enters the mixed gas buffer tank 3 for buffering, it enters the adsorption bed B through the gas intake pipeline a, opens the adsorption bed B intake valve F3, and performs the same operations as the adsorption bed A in the adsorption bed B, which is carried out through the opening and closing control process of the corresponding valve. The desorbed gas other than the reflux gas enters the product gas tank through the desorbed gas pipeline, and the methane concentration in the product gas can be increased to about 10% after the enrichment operation.

[0048] (3) The PLC concentration control component 4 is used to intelligently control the gas stabilization process. The flow rate of the product gas is directly adjusted to achieve follow-up control of the flow rate and concentration of the product gas, so that the flow rate decreases when the concentration increases and increases when the concentration decreases. The concentration of the mixed gas tends to be stable after 2-3 cycles, and can quickly restore to the set concentration even if it is slightly disturbed.

[0049] (4) Adsorption beds A and B work alternately in a cycle to ensure the continuity of the process.

[0050] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for concentrating low-concentration gas by reflux mixing and stabilizing gas, characterized in that: Filling a methane selective adsorbent in an adsorption device, wherein the adsorption device comprises at least two parallel adsorption beds A and B; Under the condition of controlling the temperature and pressure of the air inlet pipeline and the adsorption bed to be constant, the raw gas is first introduced into the adsorption bed A. After the adsorption bed A is saturated with methane adsorption, the pressure is equalized between the adsorption bed A and the adsorption bed B. After the pressure equalization is completed, the adsorption bed A is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and the other part of the desorbed gas is returned to the system as the reflux gas and mixed evenly with the raw gas in the mixer to obtain a mixed gas. Then the mixed gas is introduced into the adsorption bed B after the pressure equalization to continue to adsorb methane. After the adsorption bed B is saturated with methane, the pressure is equalized again between the adsorption beds A and B; After the pressure equalization is completed, the B adsorption bed is vacuum desorbed, and a part of the desorbed gas is output to the adsorption system as the product gas, and a part of the desorbed gas is returned to the system as the reflux gas to be evenly mixed with the raw gas in the mixer to obtain a mixed gas; the mixed gas is passed into the pressure-equalized adsorption bed A to continue to adsorb methane; The above process is repeated, and the desorbed gases obtained from the output adsorption system are combined to obtain a basically stable gas with a methane volume fraction of not less than 8%.

2. The method for concentrating low-concentration gas by reflux mixing and stabilizing gas according to claim 1, characterized in that: The raw gas is low-concentration gas, and the volume fraction range of methane in the low-concentration gas is: the volume fraction of methane is not less than 2%.

3. The method for concentrating low-concentration gas by reflux mixing and stabilizing gas according to claim 1, characterized in that: During the adsorption process, the temperature in the adsorption bed A and the adsorption bed B was 0~35℃, and the pressure was 0.1MPa; during the vacuum analysis process, the pressure in the adsorption bed A and the adsorption bed B was -0.09MPa.

4. A low-concentration gas reflux mixing and stabilization gas concentration system, characterized in that: The system comprises at least one group of adsorption devices and a matching gas stabilizing device, and the devices in the system are connected by pipelines; wherein the adsorption device comprises an adsorption bed A and an adsorption bed B, wherein the adsorption bed A and the adsorption bed B are filled with a methane selective adsorbent, and an air inlet pipe, an air outlet pipe, a desorption gas pipe and a reflux pipe are arranged between the adsorption bed A and the adsorption bed B, and valves are arranged on the air inlet pipe, the air outlet pipe, the desorption gas pipe and the reflux pipe, and the methane concentration in the mixed gas input to the adsorption bed device is intelligently adjusted and coordinated by the control of the opening and closing combination mode of the valves on the pipes and the gas stabilizing device, so that the gas and the reflux gas are adsorbed, pressure-equalized, enriched and decomposed in the adsorption device, and a basically stable gas product gas with a methane volume fraction of not less than 8% is obtained.

5. The low-concentration gas reflux mixed stable gas concentration system according to claim 4, characterized in that: The valves include an air intake valve (F2, F3) arranged on an air intake pipeline, a vacuum valve (F4, F5) arranged on an analytical gas pipeline, a pressure equalizing valve (F6, F7) and an air outlet valve (F8, F9) arranged on an air outlet pipeline, and a reflux valve (F1) arranged on a reflux pipeline.

6. The low-concentration gas reflux mixed stable gas concentration system according to claim 5, characterized in that: The air inlet valves (F2, F3), vacuum valves (F4, F5), pressure equalizing valves (F6, F7), air outlet valves (F8, F9) and reflux valve (F1) are all pneumatic valves.

7. The low-concentration gas reflux mixed stable gas concentration system according to any one of claims 4 to 6, characterized in that: The gas stabilizing device comprises a mixer (1), a mixed gas buffer tank (3) and a PLC concentration control component (4); One end of the mixer (1) is connected to a raw gas inlet pipeline (a), and a raw gas methane concentration detector (5) and a raw gas flow controller (6) are provided on the raw gas inlet pipeline; The other end of the mixer (1) is connected to a mixed gas buffer tank (3) via a mixed gas outlet pipe, and a mixed gas methane concentration detector (2) is provided on the mixed gas buffer tank (3); a reflux gas inlet pipe is provided on the side wall of the mixer (1), and the reflux gas enters the mixer (1) through a reflux gas flow controller (7) and is mixed with the raw gas; The PLC concentration control component (4) is used to receive detection signals from the raw gas methane concentration detector (5) and the mixed gas methane concentration detector (2), and to perform real-time linear modeling based on the detection signals, calculate and obtain a reflux gas flow adjustment signal, and instruct the reflux gas flow controller (7) to adjust the reflux gas flow, thereby obtaining a raw gas with a basically stable concentration that meets the minimum methane concentration design value requirement of the pressure swing adsorption concentration system.

8. The low-concentration gas reflux mixed stable gas concentration system according to claim 7, characterized in that: The gas stabilizing device further comprises a fixed bracket (8), and universal wheels (9) are mounted at the four corners of the bottom of the fixed bracket (8).

9. The low-concentration gas reflux mixed stable gas concentration system according to claim 7, characterized in that: The gas stabilization process is as follows: 1) According to the requirements of the adsorption bed device for the methane concentration in the raw gas, the minimum design value S0 of the raw gas methane concentration is input into the PLC concentration control component (4); 2) The gas methane concentration detector (5) and the mixed gas concentration detector (2) respectively collect the methane concentration in the feed gas and the methane concentration in the mixed gas in the mixed gas buffer tank, obtain the gas methane concentration measurement value C1 and the mixed gas methane concentration measurement value C2, and feed them back to the PLC concentration control component (4); 3) PLC concentration control component (4) compares the measured value of gas methane concentration C1 and the design value of the minimum methane concentration of raw gas S0: a. When C1<S0, the PLC concentration control component (4) further compares the methane concentration C2 of the mixed gas with the design value S0 of the minimum methane concentration of the raw gas: If C2<S0, the PLC concentration control component 4 performs linear modeling of real-time running data based on the measured value C1 of the methane concentration of the gas and the measured value C2 of the methane concentration of the mixed gas, calculates and obtains a flow adjustment signal, and outputs an instruction to the return gas flow controller (7) to increase the return gas flow rate; this cycle is repeated until the PLC concentration control component (4) receives the measured value C2′≥S0 of the methane concentration of the mixed gas, and the PLC concentration control component (4) instructs the return gas flow controller (7) to output the return gas flow rate value stably; b. When C1 ≥ S0, the gas is fed into the device and then directly sent to the adsorption device for concentration treatment via the mixer (1) and the mixed gas buffer tank (3); c. When the measured value C1 of the methane concentration in the gas is again lower than the design value S0 of the minimum methane concentration in the raw gas, repeat the above steps (2) and (3) until the raw gas that satisfies the operation of the adsorption device is obtained.

10. The low-concentration gas back-mixing and gas stabilization concentration system according to any one of claims 7 to 9, characterized in that: The mixer (1) is an SV type static mixer, the interior of which is composed of a plurality of groups of vertical SV type static mixer units (c) and horizontal SV type static mixer units (d) arranged alternately.

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