Method and system for controlling concentration of carbon dioxide in natural gas

Abstract

The invention discloses a method and system for controlling the concentration of carbon dioxide in natural gas and relates to the technical field of energy, and the method comprises the steps that when the first CO2 content is larger than a first threshold value, a first flow ratio and a second flow ratio are calculated; according to the first flow ratio, the second flow ratio and the adjustment database, obtaining a corresponding adjustment direction and an adjustment opening degree, and according to the adjustment direction and the adjustment opening degree, adjusting a slurry flow adjusting valve and a feed gas flow adjusting valve; the second CO2 content of the top of the absorption-adsorption tower is obtained again, when it is judged that the second CO2 content is larger than the first threshold value, the flow value is obtained again, the steps are repeated, and adjustment operation is stopped until the CO2 content of the top of the absorption-adsorption tower is smaller than or equal to the first threshold value. And by synchronously adjusting the opening degrees of the two valves, the CO2 concentration fluctuation is effectively reduced, so that the natural gas decarbonization device can meet the separation requirement.

Description

Technical Field

[0001] The present application generally relates to the field of energy technology, and specifically to a method and system for controlling carbon dioxide concentration in natural gas. Background Art

[0002] As a hydrocarbon gas mixture, natural gas contains more than 90% methane, as well as a small amount of carbon 2, carbon 3 and carbon 4 alkanes and acidic gases such as CO2 and H2S. The hazards of CO2 in natural gas are mainly the following three points: 1. Seriously affects the calorific value and transportation performance of natural gas. When the CO2 content is high, it will not only cause the calorific value of natural gas to decrease, consume a lot of heat during the combustion process, but also reduce the transportation performance of natural gas. 2. Cause pipeline blockage. When the CO2 content is high, it will precipitate in the solid phase. In addition, the cryogenic processing of natural gas will increase the amount of solid phase CO2 precipitated, which is easy to block the pipeline and cause the cryogenic processing equipment to run unsteadily. 3. Cause pipeline corrosion. If there is water in the natural gas, the CO2 in the natural gas will corrode the equipment and pipelines, which will not only damage the equipment and pipelines, but also cause explosions if the corrosion is serious.

[0003] In response to these hazards, the absorption-adsorption coupling method currently proposed to separate light gas mixtures for carbon dioxide capture is a new green separation process with great application prospects. However, with the long-term operation of the equipment, the CO2 concentration at the top of the absorption tower does not meet the standard, resulting in poor separation effect. Therefore, we propose a method and system for controlling the carbon dioxide concentration in natural gas to solve the above problems. Summary of the invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a method and system for controlling the carbon dioxide concentration in natural gas that can reduce CO2 concentration fluctuations and meet separation requirements.

[0005] In a first aspect, the present application provides a method for controlling the concentration of carbon dioxide in natural gas, which is applied to a natural gas decarbonization device, wherein the natural gas decarbonization device comprises: an absorption-adsorption tower, wherein the absorption-adsorption tower is connected to a slurry circulation pump and a raw gas feeding structure, wherein a slurry flow regulating valve is installed at the outlet of the slurry circulation pump, and a raw gas flow regulating valve is installed at the outlet of the raw gas feeding structure; the method comprises the following steps: Acquire a first CO2 content at the top of the absorption-adsorption tower in real time, and when the first CO2 content is greater than a first threshold, collect a first flow value of the slurry flow control valve and a second flow value of the raw gas flow control valve at the current moment, as well as a third flow value of the slurry flow control valve and a fourth flow value of the raw gas flow control valve at the previous moment; Calculating a first flow ratio according to the first flow value and the third flow value, and calculating a second flow ratio according to the second flow value and the fourth flow value; According to the first flow ratio and the second flow ratio, the adjustment direction of the slurry flow regulating valve and the raw gas flow regulating valve is determined; and the adjustment database is called, and the preset ratio ranges corresponding to the first flow ratio and the second flow ratio are searched in the adjustment database to obtain the corresponding adjustment openings, and the slurry flow regulating valve and the raw gas flow regulating valve are adjusted according to the adjustment direction and the adjustment openings; the adjustment database includes: a plurality of preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve, respectively; Repeat the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and then stop adjusting the slurry flow regulating valve and the raw gas flow regulating valve.

[0006] According to the technical solution provided in the embodiment of the present application, after determining that the second CO2 content is greater than the first threshold value, before re-acquiring the flow value of the slurry flow control valve and the flow value of the raw gas flow control valve, the following steps are also included: Acquire a second CO2 content in the raw gas supply structure in real time, and when the second CO2 content is greater than a second threshold, adjust the raw gas flow regulating valve and the slurry flow regulating valve to corresponding calibrated openings at the same time; the second threshold is greater than the first threshold; or, Obtaining a CO2 content variation curve of the raw gas supply structure within a first working duration; Identify the maximum and minimum values ​​in the CO2 content variation curve, and calculate the actual difference between the two; If the actual difference is greater than or equal to the preset difference, the raw gas flow regulating valve and the slurry flow regulating valve are adjusted to corresponding calibrated openings at the same time.

[0007] According to the technical solution provided in the embodiment of the present application, the first flow ratio is calculated according to the following formula: ; in, is the first flow ratio, is the first flow value, is the third flow value.

[0008] According to the technical solution provided in the embodiment of the present application, adjusting the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment opening specifically includes the following steps: When the first flow ratio is less than zero and the second flow ratio is equal to zero, the adjustment direction of the slurry flow regulating valve is positive, and its adjustment opening is the first opening, and the adjustment direction of the raw gas flow regulating valve is positive, and its adjustment opening is the target opening; When the first flow ratio is equal to zero and the second flow ratio is greater than zero, the adjustment direction of the slurry flow control valve is reversed, and its adjusted opening is the target opening, and the adjustment direction of the raw gas flow control valve is reversed, and its adjusted opening is the second opening.

[0009] According to the technical solution provided in the embodiment of the present application, the following steps are also included: When the feed gas flow regulating valve and the slurry flow regulating valve are both at the calibrated openings, the third CO2 content at the top of the absorption-adsorption tower is obtained in real time; When the third CO2 content is greater than the third threshold value and less than the second threshold value, calling the compensation database, searching the compensation database for the CO2 content interval in which the third CO2 content is located, and obtaining the corresponding compensation opening; the compensation database at least includes: multiple CO2 content intervals and compensation openings; Based on the current calibrated opening, the slurry flow control valve is adjusted forward to compensate for the opening, and the raw gas flow control valve is adjusted backward to compensate for the opening; the third threshold is less than the second threshold and the third threshold is greater than the first threshold.

[0010] According to the technical solution provided in the embodiment of the present application, the adjustment database is updated according to the following steps: Obtaining historical adjustment data of the slurry flow control valve and the raw gas flow control valve; the historical adjustment data includes a plurality of historical flow ratios, historical adjustment openings and corresponding historical CO2 contents; the historical adjustment openings are determined based on historical adjustment openings and historical compensation openings; The historical CO2 content greater than the first threshold value in the historical adjustment data is screened, and the endpoint value of the preset data range corresponding to the historical flow ratio is updated according to the corresponding historical adjustment opening and the historical flow ratio to obtain an updated adjustment database.

[0011] According to the technical solution provided in the embodiment of the present application, the following steps are also included: Obtaining a first pulse number of the slurry flow regulating valve and a second pulse number of the raw gas flow regulating valve; When the first pulse number or the second pulse number exceeds a preset pulse range, a non-stop maintenance operation is performed on the corresponding regulating valve; When the non-stop maintenance operation is correct, the pulse number of the corresponding control valve is obtained again. If it still exceeds the preset pulse range, a fault prompt message is generated.

[0012] In a second aspect, the present application provides a carbon dioxide concentration control system in natural gas, which is used to implement the above-mentioned carbon dioxide concentration control method in natural gas, and the system includes: a data acquisition module and a processing module that are communicatively connected to a slurry flow control valve and a raw gas flow control valve; The data acquisition module is used to obtain the first CO2 content at the top of the absorption-adsorption tower in real time; The processing module is used for collecting the first flow value of the slurry flow regulating valve and the second flow value of the raw gas flow regulating valve at the current moment, and the third flow value of the slurry flow regulating valve and the fourth flow value of the raw gas flow regulating valve at the previous moment when the first CO2 content is greater than the first threshold value, and calculating the first flow ratio according to the first flow value and the third flow value, and calculating the second flow ratio according to the second flow value and the fourth flow value; determining the adjustment direction of the slurry flow regulating valve and the raw gas flow regulating valve according to the first flow ratio and the second flow ratio; and calling the adjustment database, searching the preset ratio ranges corresponding to the first flow ratio and the second flow ratio respectively in the adjustment database, obtaining the corresponding adjustment opening, and adjusting the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment opening; the adjustment database includes: a plurality of preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve respectively; repeating the above steps until the adjustment operation of the slurry flow regulating valve and the raw gas flow regulating valve is stopped when the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value.

[0013] It can be seen from the above technical solution that the present application has at least the following beneficial effects: The present application discloses a method for controlling the concentration of carbon dioxide in natural gas, which comprises: obtaining a first CO2 content at the top of an absorption-adsorption tower in real time; when the first CO2 content is greater than a first threshold value, collecting a first flow value of a slurry flow regulating valve and a second flow value of a raw gas flow regulating valve at the current moment, as well as a third flow value of the slurry flow regulating valve and a fourth flow value of the raw gas flow regulating valve at the previous moment, and calculating a first flow ratio according to the first flow value and the third flow value, and calculating a second flow ratio according to the second flow value and the fourth flow value; determining a slurry flow regulating valve according to the first flow ratio and the second flow ratio; The adjustment direction of the throttle valve and the raw gas flow regulating valve; and calling the adjustment database, searching the preset ratio ranges corresponding to the first flow ratio and the second flow ratio in the adjustment database, obtaining the corresponding adjustment openings, and adjusting the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment openings; the adjustment database includes: a plurality of preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve, respectively; repeating the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and stopping the adjustment operation of the slurry flow regulating valve and the raw gas flow regulating valve.

[0014] The present application monitors the first CO2 content at the top of the absorption-adsorption tower in real time. When the first CO2 content exceeds the first threshold, the flow rate of the slurry flow regulating valve and the raw gas flow regulating valve is adjusted based on the adjustment database and the flow rate ratio of the slurry flow regulating valve and the raw gas flow regulating valve until the CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold. By synchronously adjusting the opening of the two valves, the CO2 concentration fluctuation is effectively reduced so that the natural gas decarbonization device can meet the separation requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings.

[0016] Figure 1 The figure is a flow chart of the method for controlling the concentration of carbon dioxide in natural gas.

[0017] Figure 2 This is a schematic diagram of the structure of the carbon dioxide concentration control system in natural gas.

[0018] Figure 3 This is a schematic diagram of the structure of a traditional natural gas decarbonization device.

[0019] Figure 4 This is a schematic diagram of the structure of a natural gas decarbonization device using a control system.

[0020] Numbers in the figure: 1. Data acquisition module; 2. Processing module. DETAILED DESCRIPTION

[0021] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] In order to make the description of the following embodiments clear and concise, a brief introduction to the related technology is first given: Figure 3 It is a schematic diagram of the structure of a traditional natural gas decarbonization device, in which T0101 is an absorption-adsorption tower; T0102 is a desorption tower; V0101 is a purified gas liquid separator tank; V0102 is a desorption gas liquid separator tank; C0101 is a raw gas compressor; E0101 is an air cooler; E0102 is a lean and rich liquid heat exchanger; E0103 is a rich liquid heater; E0104 is a lean liquid cooler; E0105 is a desorption tower top condenser; E0106 is a desorption gas rich liquid heat exchanger; P0101 is a circulating slurry pump; and P0102 is a vacuum pump.

[0024] The dimethylimidazole-water composite solvent and ZIF-8 are configured into a slurry, which can remove CO2 from the mixed gas at room temperature and pressure, and the energy consumption required for the regeneration of the absorber-adsorbent is also low. The temperature of the raw gas is 60°C, the pressure is 4 bar (G, gauge pressure, the same below), and the flow rate is 50,000 cubic meters per hour. After being compressed to 6.5 bar by the raw gas compressor and cooled to 60°C by the air cooler E0101, it is fed from the bottom of the absorption-adsorption tower T0101, and the lean liquid enters from the top of the tower. The two are in reverse contact for mass transfer and heat transfer. CO2 has a large solubility in the slurry and is enriched step by step in the slurry. Most of the CO2 is absorbed by the sieve tray and packing section at the bottom of the tower, while CH4 is enriched in the gas phase and flows out from the top of the tower into the purified gas separator tank. The purified gas at the top of the tank is sent out of the boundary area, and the rich liquid at the bottom of the tower enters the lean-rich liquid heat exchanger E0102 to exchange heat with the lean liquid flowing out of the bottom of the desorption tower, and then is reduced in pressure to 0.04 bar (G) through a throttle valve; the desorbed gas discharged from the top of the desorption tower has a temperature of 78 °C and enters the desorbed gas-rich liquid heat exchanger E0106 to exchange heat with the rich liquid. The rich liquid after heat exchange enters the rich liquid heater E0103, is heated to 80 °C with hot water, and is sent to the top of the desorption tower. After the lean liquid after desorption exchanges heat with the rich liquid, it is cooled to 35 °C with circulating cooling water and then returned to the top of the absorption-adsorption tower for recycling.

[0025] After the desorbed gas and the rich liquid have exchanged heat, in order to recover the water vapor entrained in the desorbed gas, the desorbed gas is cooled to 40 °C after passing through the condenser E0105 and enters the gas-liquid separation tank. The operating pressure in the desorber is 6.2 bar (G). The vacuum pump P0102 is connected to the top of the tank, and the desorbed gas CO2 is discharged from the top of the tank. The condensed water at the bottom of the tank is sent to the circulating slurry pump P0101 together with the supplementary slurry, and is mixed with the circulating slurry and sent to the top of the absorption-adsorption tower. During the operation of the device, the CO2 concentration in the purified gas will exceed the upper limit of 3%, resulting in poor separation effect.

[0026] The present application is about a method for controlling the concentration of carbon dioxide in natural gas, which is applied to a natural gas decarbonization device. The natural gas decarbonization device comprises: an absorption-adsorption tower, the absorption-adsorption tower is connected to a slurry circulation pump and a raw gas feeding structure, a slurry flow regulating valve is installed at the outlet of the slurry circulation pump, and a raw gas flow regulating valve is installed at the outlet of the raw gas feeding structure; Figure 4 As shown, T0101 is the absorption-adsorption tower; T0102 is the desorption tower; V0101 is the purified gas liquid separator tank; V0102 is the desorption gas liquid separator tank; C0101 is the raw gas compressor; E0101 is the air cooler; E0102 is the lean and rich liquid heat exchanger; E0103 is the rich liquid heater; E0104 is the lean liquid cooler; E0105 is the top condenser of the desorption tower; E0106 is the desorption gas rich liquid heat exchanger; P0101 is the circulating slurry pump; and P0102 is the vacuum pump.

[0027] The present application monitors the first CO2 content at the top of the absorption-adsorption tower in real time. When the first CO2 content exceeds the first threshold, the flow of the slurry flow regulating valve and the raw gas flow regulating valve is adjusted based on the adjustment database and the flow ratio of the slurry flow regulating valve and the raw gas flow regulating valve until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold. By synchronously adjusting the opening of the two valves, the CO2 concentration fluctuation is effectively reduced so that the natural gas decarbonization device can meet the separation requirements.

[0028] In order to make the method for controlling the concentration of carbon dioxide in natural gas provided in the embodiment of the present application clearer and easier to understand, the method is described below in conjunction with the accompanying drawings. Figure 1 As shown, this figure is a flow chart of a method for controlling carbon dioxide concentration in natural gas provided in an embodiment of the present application, the method comprising: S100. Acquire the first CO2 content at the top of the absorption-adsorption tower in real time, and when the first CO2 content is greater than the first threshold value, collect the first flow value of the slurry flow control valve and the second flow value of the raw gas flow control valve at the current moment, as well as the third flow value of the slurry flow control valve and the fourth flow value of the raw gas flow control valve at the previous moment.

[0029] It should be noted that the first CO2 content at the top of the absorption-adsorption tower can be collected by using a CO2 concentration infrared detector. The first threshold is, for example, 3%. If the first CO2 content is greater than the first threshold, it indicates that the CO2 content at the top of the absorption-adsorption tower has exceeded the standard; each flow value can be collected by using an ultrasonic flow meter. Here, the CO2 concentration infrared detector and the slurry flow control valve and the raw gas flow control valve are interlocked, and the two control valves are controlled in parallel, and the two control valves simultaneously control the CO2 concentration.

[0030] S200. Calculate a first flow ratio according to the first flow value and the third flow value, and calculate a second flow ratio according to the second flow value and the fourth flow value.

[0031] It should be noted that the first flow ratio is used to represent the ratio of the flow increase or decrease of the slurry flow regulating valve, and the second flow ratio is used to represent the ratio of the flow increase or decrease of the raw gas flow regulating valve.

[0032] The first flow ratio is calculated according to the following formula: ; in, is the first flow ratio, is the first flow value, is the third flow value.

[0033] Here, the calculation formula of the second flow ratio is the same as the calculation formula of the first flow ratio.

[0034] S300. Determine the adjustment direction of the slurry flow regulating valve and the raw gas flow regulating valve according to the first flow ratio and the second flow ratio; and call the adjustment database to search for the preset ratio ranges corresponding to the first flow ratio and the second flow ratio respectively in the adjustment database to obtain the corresponding adjustment direction and adjustment opening, and adjust the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment opening; the adjustment database includes: multiple preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve respectively.

[0035] Among them, when the first flow ratio is greater than zero, the adjustment direction of the slurry flow regulating valve is reverse, and when the first flow ratio is less than zero, the adjustment direction of the slurry flow regulating valve is forward; when the second flow ratio is greater than zero, the adjustment direction of the raw gas flow regulating valve is forward, and when the second flow ratio is less than zero, the adjustment direction of the raw gas flow regulating valve is reverse.

[0036] The adjustment database is shown in Table 1. The positive direction in the adjustment direction refers to the direction in which the flow rate increases after the corresponding control valve is turned, and the reverse direction refers to the direction in which the flow rate decreases after the corresponding control valve is turned.

[0037] Table 1 Adjustment database

[0038] Among them, the reason why the CO2 content at the top of the absorption-adsorption tower exceeds the standard is that the flow rate of raw gas increases when the circulation volume of slurry remains unchanged; or, the circulation volume of slurry decreases when the flow rate of raw gas remains unchanged.

[0039] Then, according to the adjustment direction and the adjustment opening, the slurry flow regulating valve and the raw gas flow regulating valve are adjusted, which specifically includes the following steps: When the first flow ratio is less than zero and the second flow ratio is equal to zero, the adjustment direction of the slurry flow regulating valve is positive, and its adjustment opening is the first opening, and the adjustment direction of the raw gas flow regulating valve is positive, and its adjustment opening is the target opening; for example, when the first flow ratio is -0.3 and the second flow ratio is 0, at this time, it can be learned in the adjustment database: the adjustment direction of the slurry flow regulating valve is positive, and its adjustment opening is 10°, and the adjustment direction of the raw gas flow regulating valve is positive, and its adjustment opening is 5°. These data are used to adjust the slurry flow regulating valve and the raw gas flow regulating valve to reduce the CO2 content at the top of the absorption-adsorption tower to below 3%.

[0040] When the first flow ratio is equal to zero and the second flow ratio is greater than zero, the adjustment direction of the slurry flow regulating valve is reversed, and its adjustment opening is the target opening, and the adjustment direction of the raw gas flow regulating valve is reversed, and its adjustment opening is the second opening. For example, the first flow ratio is 0, and the second flow ratio is 0.2. At this time, it can be learned in the adjustment database that the adjustment direction of the slurry flow regulating valve is reversed, and its adjustment opening is 5°, and the adjustment direction of the raw gas flow regulating valve is forward, and its adjustment opening is 5°, thereby reducing the CO2 content at the top of the absorption-adsorption tower to below 3%.

[0041] Further, update and adjust the database according to the following steps: Obtain historical regulation data of the slurry flow control valve and the raw gas flow control valve; the historical regulation data includes multiple historical flow ratios, historical regulation openings, and corresponding historical CO2 contents; the historical regulation openings are determined based on historical adjustment openings and historical compensation openings; The historical CO2 content greater than the first threshold value in the historical adjustment data is screened, and the endpoint value of the preset data range corresponding to the historical flow ratio is updated according to the corresponding historical adjustment opening and the historical flow ratio to obtain an updated adjustment database.

[0042] It should be noted that the CO2 content of a period of time before the moment of collecting the first CO2 content at the top of the current absorption-adsorption tower is defined as the historical CO2 content. Correspondingly, the historical flow ratio is the ratio of the flow value of the regulating valve corresponding to the corresponding historical CO2 content to the flow value of the previous moment adjacent to it. The aforementioned period of time can be set according to actual conditions and needs. According to the actual historical adjustment of the two valves, the historical adjustment opening can be the historical adjustment opening, or it can be the sum of the historical adjustment opening and the historical compensation opening.

[0043] When updating the adjustment database, the endpoint values ​​of the preset data range are changed in the adjustment database according to the historical flow ratio, the size of the preset data range is shortened, and then the adjustment opening is added to the adjustment database according to the historical adjustment opening, so that each shortened preset data range can correspond to an adjustment opening. The adjustment database formed in this way is more accurate and convenient for subsequent adjustments, so that the first CO2 content at the top of the absorption-adsorption tower can be reduced to below 3% as soon as possible.

[0044] If the historical CO2 content is greater than 3%, it indicates that the corresponding regulating valve has a flow adjustment operation. After the corresponding adjustment direction and adjustment opening are adjusted, it is determined whether the first CO2 content at the top of the absorption-adsorption tower decreases. If it does not decrease, the adjustment opening is increased to the target opening according to the aforementioned adjustment direction to obtain an updated adjustment database, so that the data in the adjustment database is more accurate and the adjustment frequency of the regulating valve is shortened.

[0045] S400, repeat the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and stop adjusting the slurry flow regulating valve and the raw gas flow regulating valve.

[0046] Among them, by calculating the corresponding flow ratio and searching the corresponding adjustment direction and adjustment opening in the adjustment database, the two valves are adjusted synchronously, which can effectively reduce the CO2 concentration fluctuation so that the natural gas decarbonization device can meet the separation requirements.

[0047] Further, after determining that the first CO2 content is continuously greater than the first threshold, the following steps are also included: Acquire the second CO2 content in the raw gas supply structure in real time, and when the second CO2 content is greater than a second threshold, adjust the raw gas flow regulating valve and the slurry flow regulating valve to corresponding calibrated openings at the same time; the second threshold is greater than the first threshold; or, Obtaining a CO2 content variation curve of the raw gas supply structure within the first working time; Identify the maximum and minimum values ​​in the CO2 content variation curve and calculate the actual difference between the two; If the actual difference is greater than or equal to the preset difference, the raw gas flow regulating valve and the slurry flow regulating valve are adjusted to the corresponding calibrated openings at the same time.

[0048] It should be noted that, under the premise that the first CO2 content is continuously greater than the first threshold value, the first CO2 content in the raw gas supply structure can also be collected in real time, and a CO2 concentration infrared detector can be used for collection here. If the second CO2 content in the raw gas supply structure is greater than the second threshold value, it indicates that the CO2 content in the raw gas supply structure is too large at this time, and simply adjusting the opening of the two valves can no longer meet the purpose of reducing the CO2 content at the top of the absorption-adsorption tower, so the two regulating valves are adjusted to the calibrated opening, which refers to the standard opening of each of the two regulating valves, which can be set according to actual conditions. Here, the second threshold value is, for example, 8%.

[0049] Alternatively, obtain a CO2 content change curve of the raw gas supply structure within the first working duration; here, the first working duration is set according to actual needs; obtain the maximum and minimum values ​​in the CO2 content change curve, and calculate the difference between the two. If the actual difference is greater than or equal to the preset difference after comparing the actual difference with the preset difference, it means that the CO2 content in the raw gas supply structure fluctuates greatly, and the raw gas flow control valve and the slurry flow control valve need to be adjusted to the corresponding calibrated openings at the same time.

[0050] Through the above two methods, when the CO2 content in the raw gas supply structure is high, the CO2 content at the top of the absorption-adsorption tower can still be reduced to below 3% by adjusting the two regulating valves.

[0051] In addition, the method further comprises the following steps: When the feed gas flow regulating valve and the slurry flow regulating valve are both at the calibrated opening, the third CO2 content at the top of the absorption-adsorption tower is obtained in real time; When the third CO2 content is greater than the third threshold value and less than the second threshold value, the compensation database is called, and the CO2 content interval in which the third CO2 content is located is searched in the compensation database to obtain the corresponding compensation opening; the compensation database at least includes: multiple CO2 content intervals and compensation openings; Based on the current calibrated opening, the slurry flow control valve is adjusted forward to compensate for the opening, and the raw gas flow control valve is adjusted backward to compensate for the opening; the third threshold is less than the second threshold and the third threshold is greater than the first threshold.

[0052] It should be noted that if the raw gas flow regulating valve and the slurry flow regulating valve are both at the calibrated opening, if the third CO2 content at the top of the corresponding absorption-adsorption tower is greater than the third threshold value and less than the second threshold value, it indicates that the current CO2 content at the top of the absorption-adsorption tower still exceeds the standard in a small range. At this time, the compensation database in Table 2 is called to obtain the CO2 content range in which the current third CO2 content is located, and the corresponding compensation opening is obtained. Based on the obtained compensation opening, the opening of the slurry flow regulating valve is positively adjusted, and the opening of the raw gas flow regulating valve is reversely adjusted to make the CO2 content at the top of the absorption-adsorption tower less than 3%. The CO2 content at the top of the absorption-adsorption tower can be quickly adjusted by fine-tuning the compensation method.

[0053] Table 2 Compensation database

[0054] Furthermore, the method further comprises the following steps: Obtaining a first pulse number of a slurry flow regulating valve and a second pulse number of a raw gas flow regulating valve; When the first pulse number or the second pulse number exceeds the preset pulse range, a non-stop maintenance operation is performed on the corresponding regulating valve; When the non-stop maintenance operation is correct, the pulse number of the corresponding control valve is obtained again. If it still exceeds the preset pulse range, a fault prompt message is generated.

[0055] It should be noted that the pulse number of the regulating valve can be collected by using a pulse counter. The preset pulse range can be set according to actual conditions.

[0056] Non-stop maintenance operations include: testing valves for leaks, checking cables and connectors for good connections, and checking pulse counters for accuracy.

[0057] If the non-stop maintenance operation is completed and there is no problem, the pulse number of the corresponding regulating valve is obtained again. If it still exceeds the preset pulse range, a fault prompt message is generated, which indicates that the corresponding regulating valve is faulty and needs to be stopped for replacement. If it does not exceed the preset pulse range, it means that the two regulating valves can work normally. When the CO2 content at the top of the absorption-adsorption tower exceeds the standard, the purpose of reducing the CO2 content can be achieved by adjusting the two valves.

[0058] like Figure 4 As shown, the natural gas decarbonization device of the present application is equipped with an infrared online monitor for CO2 concentration. The infrared online detector for CO2 concentration is interlocked with the raw gas flow control valve and the slurry circulation pump outlet flow control valve. The two controls are parallel controls, and both control the CO2 concentration at the same time. The raw gas flow control valve is the main control valve, and the slurry circulation pump outlet flow control valve is the auxiliary control valve. The effect of adding the flow control valve can be seen.

[0059] The operation data of industrial equipment shows that after adding two interlocking controls, the DCS online system shows that when the CO2 concentration is 8%, the opening of the raw gas flow control valve is first reduced, adjusted from 60% to 40%, and the flow of raw gas is adjusted from 50,000 cubic meters / h to 45,000 cubic meters / h. The CO2 concentration in the purified gas shows a downward trend in the fluctuation and stabilizes at 5.2%. Then the opening of the slurry pump outlet flow control valve gradually increases, and the slurry flow is adjusted from 830 cubic meters / h to 855 cubic meters / h. The CO2 concentration in the purified gas shows a downward trend in the fluctuation and stabilizes at 2.9%. The CO2 content in the purified gas has been below 3%, meeting the requirements, ensuring the quality and output of natural gas.

[0060] like Figure 2 As shown, the embodiment of the present application also provides a carbon dioxide concentration control system in natural gas, which is used to implement the above-mentioned carbon dioxide concentration control method in natural gas, and the system includes: a data acquisition module 1 and a processing module 2 which are communicatively connected with the slurry flow control valve and the raw gas flow control valve; Data acquisition module 1, used to obtain the first CO2 content at the top of the absorption-adsorption tower and the corresponding first flow value of the slurry flow regulating valve and the second flow value of the feed gas flow regulating valve; Processing module 2 is used to obtain the third flow value of the slurry flow regulating valve and the fourth flow value of the raw gas flow regulating valve when the first CO2 content is greater than the first threshold value, and calculate the first flow ratio according to the first flow value and the third flow value, and calculate the second flow ratio according to the second flow value and the fourth flow value; call the adjustment database, search the preset ratio ranges corresponding to the first flow ratio and the second flow ratio in the adjustment database, obtain the corresponding adjustment direction and adjustment opening, and adjust the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment opening; the adjustment database includes: multiple preset ratio ranges and adjustment directions and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve respectively; repeat the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and stop the adjustment operation of the slurry flow regulating valve and the raw gas flow regulating valve.

[0061] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A method for controlling carbon dioxide concentration in natural gas, applied to a natural gas decarbonization device, the natural gas decarbonization device comprising: An absorption-adsorption tower, wherein the absorption-adsorption tower is connected to a slurry circulation pump and a raw gas feeding structure, a slurry flow regulating valve is installed at the outlet of the slurry circulation pump, and a raw gas flow regulating valve is installed at the outlet of the raw gas feeding structure; characterized in that the method comprises the following steps: Acquire a first CO2 content at the top of the absorption-adsorption tower in real time, and when the first CO2 content is greater than a first threshold, collect a first flow value of the slurry flow control valve and a second flow value of the raw gas flow control valve at the current moment, as well as a third flow value of the slurry flow control valve and a fourth flow value of the raw gas flow control valve at the previous moment; Calculating a first flow ratio according to the first flow value and the third flow value, and calculating a second flow ratio according to the second flow value and the fourth flow value; According to the first flow ratio and the second flow ratio, the adjustment direction of the slurry flow regulating valve and the raw gas flow regulating valve is determined; and the adjustment database is called, and the preset ratio ranges corresponding to the first flow ratio and the second flow ratio are searched in the adjustment database to obtain the corresponding adjustment openings, and the slurry flow regulating valve and the raw gas flow regulating valve are adjusted according to the adjustment direction and the adjustment openings; the adjustment database includes: a plurality of preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve, respectively; Repeat the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and then stop adjusting the slurry flow regulating valve and the raw gas flow regulating valve.

2. A method for controlling carbon dioxide concentration in natural gas according to claim 1, characterized in that: The following steps are also included: Acquire a second CO2 content in the raw gas supply structure in real time, and when the second CO2 content is greater than a second threshold, adjust the raw gas flow regulating valve and the slurry flow regulating valve to corresponding calibrated openings at the same time; The second threshold is greater than the first threshold; or, Obtaining a CO2 content variation curve of the raw gas supply structure within a first working duration; Identify the maximum and minimum values ​​in the CO2 content variation curve, and calculate the actual difference between the two; If the actual difference is greater than or equal to the preset difference, the raw gas flow regulating valve and the slurry flow regulating valve are adjusted to corresponding calibrated openings at the same time.

3. A method for controlling carbon dioxide concentration in natural gas according to claim 1, characterized in that: The first flow ratio is calculated according to the following formula: ； in, is the first flow ratio, is the first flow value, is the third flow value.

4. A method for controlling carbon dioxide concentration in natural gas according to claim 1, characterized in that: According to the adjustment direction and the adjustment opening, the slurry flow regulating valve and the raw gas flow regulating valve are adjusted, which specifically includes the following steps: When the first flow ratio is less than zero and the second flow ratio is equal to zero, the adjustment direction of the slurry flow regulating valve is positive, and its adjustment opening is the first opening, and the adjustment direction of the raw gas flow regulating valve is positive, and its adjustment opening is the target opening; When the first flow ratio is equal to zero and the second flow ratio is greater than zero, the adjustment direction of the slurry flow control valve is reversed, and its adjusted opening is the target opening, and the adjustment direction of the raw gas flow control valve is reversed, and its adjusted opening is the second opening.

5. A method for controlling carbon dioxide concentration in natural gas according to claim 2, characterized in that: The following steps are also included: When the feed gas flow regulating valve and the slurry flow regulating valve are both at the calibrated openings, the third CO2 content at the top of the absorption-adsorption tower is obtained in real time; When the third CO2 content is greater than the third threshold value and less than the second threshold value, calling the compensation database, searching the compensation database for the CO2 content interval in which the third CO2 content is located, and obtaining the corresponding compensation opening; the compensation database at least includes: multiple CO2 content intervals and compensation openings; Based on the current calibrated opening, the slurry flow control valve is adjusted forward to compensate for the opening, and the raw gas flow control valve is adjusted backward to compensate for the opening; the third threshold is less than the second threshold and the third threshold is greater than the first threshold.

6. A method for controlling carbon dioxide concentration in natural gas according to claim 1, characterized in that: The adjustment database is updated according to the following steps: Obtaining historical adjustment data of the slurry flow control valve and the raw gas flow control valve; the historical adjustment data includes a plurality of historical flow ratios, historical adjustment openings and corresponding historical CO2 contents; the historical adjustment openings are determined based on historical adjustment openings and historical compensation openings; The historical CO2 content greater than the first threshold value in the historical adjustment data is screened, and the endpoint value of the preset data range corresponding to the historical flow ratio is updated according to the corresponding historical adjustment opening and the historical flow ratio to obtain an updated adjustment database.

7. A method for controlling carbon dioxide concentration in natural gas according to claim 1, characterized in that: The following steps are also included: Obtaining a first pulse number of the slurry flow regulating valve and a second pulse number of the raw gas flow regulating valve; When the first pulse number or the second pulse number exceeds a preset pulse range, a non-stop maintenance operation is performed on the corresponding regulating valve; When the non-stop maintenance operation is correct, the pulse number of the corresponding control valve is obtained again. If it still exceeds the preset pulse range, a fault prompt message is generated.

8. A carbon dioxide concentration control system in natural gas, used to implement a carbon dioxide concentration control method in natural gas according to any one of claims 1 to 7, characterized in that: The system comprises: a data acquisition module (1) and a processing module (2) which are communicatively connected to the slurry flow regulating valve and the raw gas flow regulating valve; The data acquisition module (1) is used to obtain the first CO2 content at the top of the absorption-adsorption tower in real time; The processing module (2) is used to collect the first flow value of the slurry flow regulating valve and the second flow value of the raw gas flow regulating valve at the current moment, and the third flow value of the slurry flow regulating valve and the fourth flow value of the raw gas flow regulating valve at the previous moment when the first CO2 content is greater than the first threshold value, and calculate a first flow ratio according to the first flow value and the third flow value, and calculate a second flow ratio according to the second flow value and the fourth flow value; and determine the adjustment direction of the slurry flow regulating valve and the raw gas flow regulating valve according to the first flow ratio and the second flow ratio. ; and call the adjustment database, search the preset ratio ranges corresponding to the first flow ratio and the second flow ratio in the adjustment database, obtain the corresponding adjustment opening, and adjust the slurry flow regulating valve and the raw gas flow regulating valve according to the adjustment direction and the adjustment opening; the adjustment database includes: a plurality of preset ratio ranges and adjustment openings corresponding to the slurry flow regulating valve and the raw gas flow regulating valve, respectively; repeat the above steps until the first CO2 content at the top of the absorption-adsorption tower is less than or equal to the first threshold value, and stop the adjustment operation of the slurry flow regulating valve and the raw gas flow regulating valve.

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