Anaerobic fermentation gas automatic metering device and method based on pressure method

Abstract

The invention provides an anaerobic fermentation gas automatic metering device and method based on a pressure method. The device comprises a reactor, a temperature sensor, a pressure sensor, an adsorption device, a one-way gas valve and a data processing module. In the metering process, by setting a pressure threshold value for metering the headspace gas of the reactor, when the pressure of the headspace gas reaches a preset pressure threshold value, the system automatically controls the on-off of a one-way air valve to release gas to recover the pressure of the headspace and meter the volume of the released gas, so that the system enters the next metering period; meanwhile, the influence of water vapor, purging gas, tail gas and standardization on metering is selectively compensated through a compensation algorithm of the data processing module, and therefore continuous and accurate gas flow metering is achieved. According to the invention, the adjustable resolution is realized by adopting a pressure method, and a high-precision sensing, intelligent algorithm and automatic control strategy are combined, so that an efficient, flexible and high-adaptability gas metering solution suitable for multiple application scenes is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of metering devices, and particularly relates to an automatic gas metering device and method based on the pressure method. Background Art

[0002] Anaerobic digestion is a technology widely used in the treatment of organic waste, which can effectively convert waste in agriculture, cities and industries into biogas. Biogas mainly consists of CH 4 and CO 2 and is an important source for the resource utilization of waste and the recovery of renewable energy. During the anaerobic digestion process, the methane production potential (BMP) of the material is a core evaluation index, aiming to evaluate the amount of methane gas that can be produced by a unit mass of organic fermentation material in an anaerobic environment. Ensuring the accuracy of gas measurement results is crucial for evaluating BMP tests, optimizing the anaerobic digestion process, and improving energy recovery efficiency.

[0003] Traditional gas measurement methods mainly rely on gas chromatography or gas sensors to measure gas concentration. It is necessary to manually collect gas and measure its volume to further calculate the total volume based on the concentration. However, this method not only cannot obtain the degradation kinetic curve of methane production, but also the manual measurement process is cumbersome, time-consuming, and has large errors. Compared with manual measurement, the main advantage of automatic measurement technology is that it can provide higher measurement accuracy and continuity, ensuring the consistency and reliability of data; at the same time, automatic measurement technology also greatly saves manual operation time, significantly improves work efficiency, and provides a more convenient and efficient tool for gas metering.

[0004] Currently, the automatic measurement method based on the pressure method measures the pressure before and after anaerobic fermentation using a pressure sensor while keeping the volume constant, and calculates the generated methane gas through the total pressure difference of the reactor. However, this method is limited by the volume of the reactor itself and the maximum pressure it can withstand, and has requirements for the volume of the reaction material and the headspace in the reactor, resulting in an increase in the error of the measurement result, poor repeatability, inability to accurately measure the generated gas, and inability to perform continuous feeding reactions with a large gas production volume.

[0005] Beaubien et al. (1988) published "Automated high-sensitivity gas metering system for biological processes" in *Biotechnol Bioeng*, which discloses a pressure method gas metering device that continuously releases the pressure of the headspace gas. By setting a three-way valve, the connection between the reactor and the gas collection bottle, and between the gas collection bottle and the external environment is controlled. The time for the gas collection bottle to communicate with the external environment is fixed, and the gas volume is calculated by measuring the number of times the gas collection bottle communicates with the external environment. However, this method is sensitive to the changes in daily atmospheric pressure and temperature, and is easily affected by the changes in the external environment, which affects the gas metering accuracy; at the same time, the fixed connection time with the outside makes it difficult to maintain the anaerobic environment in the reactor, affecting the normal progress of the anaerobic fermentation reaction; and the metering errors caused by water vapor, purge gas, and tail gas residues are not considered.

[0006] The invention patent CN102395864B discloses a device for measuring ultra-low gas flow. After the gas flows into the device, it enters the gas compartment and gradually accumulates. When the gas accumulates to a certain amount, it lifts the gas compartment to release the gas, and then returns to the initial state to continue collecting the gas. The device has a simple structure and can achieve accurate flow measurement. However, the resolution of the device is fixed, and the amount of gas released each time is constant, making it difficult to adapt to a wider flow rate range. At the same time, there is a metering interval in the device. When the gas compartment has not fallen, there is a situation where the gas is released without being metered, resulting in metering errors. In addition, when the gas volume is not enough to lift the gas compartment, metering cannot be carried out, and metering errors will also occur.

[0007] In summary, the current gas metering devices and methods all have the deficiencies of narrow application range, large metering errors, insufficient continuous measurement performance, and ineffective adjustment of resolution. Summary of the Invention

[0008] The present application invents an anaerobic fermentation gas automatic metering device and method based on the pressure method for metering the gas volume generated by anaerobic fermentation. The device and method are not only applicable to the gas volume metering of various reactors and reaction materials, but also have the ability of continuous measurement. The embedded compensation algorithm ensures the accuracy and precision of metering, thus ensuring the reliability of metering results; by adjusting the pressure release threshold, variable adjustment of the gas metering resolution is achieved to adapt to a wider gas flow range and meet the requirements of anaerobic digestion for gas production metering.

[0009] The gas automatic metering device of the present invention includes: At least one reactor with good mass transfer effect; At least one temperature sensor for monitoring the temperature of the headspace in the reactor; At least one pressure sensor for monitoring the pressure of the headspace in the reactor; At least one one-way gas valve for successively releasing the gas generated in the reactor to keep the internal air pressure of the reactor relatively stable; At least one adsorption device for containing a gas adsorption substance to adsorb acidic gases, wherein the adsorption process is based on an irreversible reaction; At least one data processing module for receiving data such as the pressure and temperature of the headspace in the reactor, controlling the opening and closing of the one-way gas valve according to the real-time pressure data, calculating the amount of gas released this time according to a specific compensation algorithm, and accumulating it to the change in the cumulative gas volume. At the same time, according to the experimental needs, the recorded gas volume can be converted into a BMP value and the data can be recorded; Wherein, the reactor is composed of a reaction bottle and a sealed bottle cap. Multiple pipeline interfaces and corresponding valve ports can be provided on the sealed bottle cap for supplementing substances into the reactor, setting other sensors (pH, gas components, etc.), or sampling, etc. The temperature sensor and pressure sensor are arranged in the reactor. The one-way gas valve is connected to a pipeline interface of the sealed bottle cap. The adsorption device can be arranged inside or outside the bottle mouth of the reaction bottle and is connected between the reaction bottle and the one-way gas valve to ensure that gases such as carbon dioxide are fully adsorbed.

[0010] When the one-way gas valve remains closed, the whole device is in a sealed state.

[0011] The adsorption device can use an alkaline substance to adsorb the carbon dioxide gas generated by the reaction. The reaction process is as follows: When CO 2 is in a small amount: CO 2 + 2OH - → CO 2- 3 + H 2 O, When CO 2 is in excess: CO 2 + OH - → HCO - 3 , This reaction is irreversible under the environmental conditions required for general anaerobic fermentation.

[0012] The present application invents an automatic metering device and method for anaerobic fermentation gas based on the pressure method. The metering method includes the following steps: Step 1, before the reaction starts, load the reactants to be monitored into the reactor, check whether there is air leakage after the device connection. If the device has good airtightness, purge it with an inert gas to create an anaerobic environment, start the device, and set the pressure threshold P 阈值 , where P 阈值To ensure that the selected pressure sensor can accurately monitor the values within the pressure change range, which is the resolution of gas metering of this device. Preferably, before the reaction, the reactor, reactants to be used, etc. are placed in the reaction environment respectively to stabilize the initial pressure and temperature; Step 2: Close the one-way gas valve. The temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor and record them as the initial temperature T R0 and the initial pressure P R0 ; Step 3: As anaerobic fermentation progresses, the substrates in the reactor are gradually decomposed and transformed by microorganisms, generating biogas (mainly a mixed gas of CH 4 and CO 2 ) and accumulating. Among them, the generated CO 2 is fully adsorbed by the alkaline substance in the adsorption device, and the remaining CH 4 volume is metered by the device of the present invention; Step 4: Select and enable the required compensation algorithm; the compensation algorithm includes one or more combinations of the following methods: standard condition conversion compensation algorithm, water vapor correction compensation algorithm, purge gas overestimation compensation algorithm, reactor tail gas compensation algorithm.

[0013] The process of metering the remaining CH 4 volume in Step 3 is as follows: The temperature sensor and pressure sensor monitor the temperature value and pressure value of the headspace in the reactor as the real-time temperature T R and the real-time pressure P R , and calculate the pressure change ΔP of the headspace in the reactor with the pressure value at the start of each metering The formula is as follows: , In the formula, ΔP is the pressure change amount in the reactor, P R is the real-time pressure value of the headspace in the reactor, is the initial pressure of the headspace in the reactor at the start of this metering.

[0014]

Gas volume metering algorithm

[0015] Calculate the amount of gas ΔV released during the i-th release at the current temperature according to the ideal gas volume formula. The formula is as follows: i The formula is as follows: , Wherein, ΔV i is the amount of gas released during the i-th release, and Δn i is the change in the amount of substance of the headspace in the reactor during this measurement, and V m is the molar volume of methane gas at temperature T at the end of this measurement, R is the ideal gas constant, and V Ri is the volume of the headspace in the reactor, and P R is the real-time pressure value of the headspace in the reactor at the end of this measurement, Ri is the initial pressure of the headspace in the reactor at the start of this measurement, and T is the real-time temperature of the headspace in the reactor at the end of this measurement, Ri is the initial temperature of the headspace in the reactor at the start of this measurement. is the initial temperature of the headspace in the reactor at the start of this measurement.

[0016] The specific processes of each compensation algorithm in Step 4 are as follows:

Standard condition conversion compensation algorithm

[0017]

Water Vapor Correction Compensation Algorithm

[0018] The content of dry gas f in the gas volume measured for the i-th time Di is calculated according to the formula: , In the formula, f Di is the content of dry gas in the gas volume measured for the i-th time, V vapi is the volume of water vapor in the gas volume measured for the i-th time, V gasi is the gas volume measured for the i-th time, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, P gasi is the pressure of the gas measured for the i-th time, Among them, the pressure of water vapor P in the gas volume measured for the i-th time vapi can be calculated according to the Antoine equation. The formula is as follows: , In the formula, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, T i is the temperature at the i-th measurement, and A, B, and C are Antoine constants. Therefore, the change in the volume of dry gas ΔV in the gas volume measured for the i-th time Di , and the formula is as follows: , In the formula, ΔV Di is the change in the volume of dry gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the i-th time, f Di is the content of dry gas in the gas volume measured for the i-th time.

[0019]

Purge Gas Overestimation Compensation Algorithm

[0020] Based on the residual ratio of the headspace purge gas and the volume of the headspace gas in the reactor during two adjacent measurements, calculate the amount of methane gas ΔV Ci in the gas volume during the i-th measurement. The formula is as follows, , where ΔV Ci is the amount of methane gas in the gas volume during the i-th measurement, ΔV i is the amount of gas released during the i-th measurement, V R is the volume of the headspace in the reactor, f Ni is the residual ratio of the headspace purge gas during the i-th measurement, and f N(i-1) is the residual ratio of the headspace purge gas during the (i - 1)-th measurement.

[0021]

Gas change cumulative calculation method

[0022] Repeat step 3 to record the next gas volume change.

[0023]

Reactor tail gas compensation algorithm

[0024] According to the enabling situation of the compensation algorithm, the amount of change in the volume of the unmeasured gas remaining in the reactor ΔV R is compensated and calculated, and is recorded as the amount of change in the volume of the unmeasured gas remaining in the reactor after compensation . Add to the cumulative gas production volume V ai in the previous i times. The formula is as follows: , In the formula, V a_end is the final cumulative gas volume of the reaction, V ai is the cumulative gas production volume in the previous i times, is the amount of change in the volume of the unmeasured gas remaining in the reactor after compensation.

[0025] The four compensation algorithms involved in steps 3 and 4 can be selected by the user according to the situation whether to enable them or not. The optimal solution is to enable all of them, but one or more compensation algorithms can also be enabled arbitrarily.

[0026] After calculating the cumulative gas volume, if it is a BMP experiment, the data processing module can also calculate the BMP value of the reactants based on the volatile solids (VS) content of the reaction materials. BMP is expressed as the volume of dry methane produced per kilogram of volatile solids (VS) fermentation converted to standard conditions (273.15 K and 101.33 kPa), and the unit is NmL / gVS.

[0027] The BMP experiment requires at least 2 groups of experiments (one group as a blank group to record the methane produced by the residual VS in the inoculum, and the other group as an experimental group to record the methane produced by the inoculum and reactants together). Each group of experiments should have at least 3 parallels. Before the experiment starts, measure the VS of the inoculum and reactants and input them into the data processing module.

[0028] The cumulative methane production in the experiment should be divided by the VS content added to the fermentation bottle. However, in the inoculum used in the fermentation bottle, there will be residual volatile solids that produce a certain amount of methane during anaerobic biodegradation. Therefore, this part of the methane production of the inoculum mud should be subtracted from the total methane production, and then divided by the VS content of the reactants to obtain the accurate methane production of the materials. The calculation formula is as follows: , In the formula, BMP s is the real-time methane production potential value of the reactants, V at is the cumulative methane gas production volume of the experimental group, V ab is the cumulative methane gas production volume of the blank group, m It is the amount of inoculum added in the experimental group, m Ib is the amount of inoculum added in the blank group, VS s is the VS content of the reactants, m s is the amount of reactants added in the experimental group. Beneficial effects

[0029] 1. Accurately measure the gas volume generated during the reaction process. The present invention uses high-precision temperature sensor and pressure sensor technologies to realize real-time acquisition of the headspace gas pressure and temperature in the reactor. Through the integrated standard condition conversion compensation algorithm, water vapor correction compensation algorithm, purge gas overestimation compensation algorithm, and reactor tail gas compensation algorithm, it can dynamically correct the gas volume measured during the reaction process, improve the accuracy and precision of gas measurement, and ensure the reliability of the data. At the same time, the four compensation algorithms can be selected by the user according to the actual situation whether to enable all of them, or any one or more of the compensation algorithms can be enabled arbitrarily, providing multiple measurement results for the user.

[0030] 2. Achieve full-automatic and continuous monitoring of reaction gases. Through an automated control system, the present invention precisely controls the opening and closing states of the one-way gas valves on the reactor, achieving precise control of gas release during the reaction process, thereby realizing full-automatic and continuous monitoring of the gases generated during the reaction process. The device of the present invention maintains the relative stability of the headspace pressure inside the reactor, avoids potential inhibition of the normal fermentation process caused by product accumulation, and prevents safety hazards caused by pressure increase. It is also applicable to gas metering in complex processes such as continuous anaerobic fermentation.

[0031] 3. Adjustable gas metering resolution. Under the condition of keeping the headspace volume of the reactor constant, by adjusting the threshold of pressure release, the amount of released gas per measurement is changed, realizing variable adjustment of gas metering resolution to adapt to a wider gas flow range, thereby meeting the diverse requirements for gas metering in different industrial scenarios and experimental needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Structural diagram of an automatic anaerobic fermentation gas metering device based on the pressure method of the present invention.

[0033] Figure 2 Algorithm flowchart of an automatic anaerobic fermentation gas metering method based on the pressure method of the present invention.

[0034] Figure 3 Comparison diagram of an automatic anaerobic fermentation gas metering method based on the pressure method of the present invention.

[0035] Figure 4 Cumulative BMP curve of the preferred Example 2 of the present invention.

[0036] Figure 5 Gas release situation in the early stage of the reaction of the preferred Example 2 of the present invention.

[0037] Figure 6 Gas release situation in the later stage of the reaction of the preferred Example 2 of the present invention.

[0038] 1 Reactor, 2 Temperature sensor, 3 Pressure sensor, 4 One-way gas valve, 5 Adsorption device, 6 Data processing module. SPECIFIC EMBODIMENTS

[0039] As Figure 1 shown, an automatic anaerobic fermentation gas metering device based on the pressure method includes at least one reactor 1; at least one temperature sensor 2; at least one pressure sensor 3; at least one one-way gas valve 4; at least one adsorption device 5; At least one data processing module 6, which is used to receive data such as the pressure and temperature of the headspace in the reactor 1, control the opening and closing of the one-way gas valve 4 according to the real-time pressure data, calculate the amount of gas released this time, and accumulate it to the change of the cumulative gas volume. According to the experimental needs, the recorded gas volume can be converted into BMP values and the data can be recorded; the temperature sensor 2, the pressure sensor 3, and the adsorption device 5 are arranged inside the top of the reactor 1, the one-way gas valve 4 is arranged outside the top of the reactor 1, and the temperature sensor 2, the pressure sensor 3, and the one-way gas valve 4 are electrically connected to the data processing module 6.

[0040] According to Figure 2 the described gas automatic metering algorithm process, before starting the metering, first confirm the enabling situation of the 4 compensation algorithms, and record the temperature and pressure of the headspace in the reactor at the initial time.

[0041] During the metering process, record the temperature and pressure of the headspace in the reactor at the start of the i-th metering and the temperature and pressure of the headspace in the reactor at the i-th release, and calculate the volume of gas released at the current temperature and pressure based on these two sets of data. Then, make the following judgments in sequence: "Whether the purge gas overestimation compensation algorithm is enabled", if the purge gas overestimation compensation algorithm is enabled, it is necessary to exclude the volume of purge gas contained in the metered gas volume, and use the calculation result as the metered gas volume; "Whether the water vapor correction compensation algorithm is enabled", if the water vapor correction compensation algorithm is enabled, it is necessary to exclude the volume of water vapor contained in the metered gas volume, and use the calculation result as the metered gas volume; "Whether the standard condition conversion compensation algorithm is enabled", if the standard condition conversion compensation algorithm is enabled, it is necessary to convert the metered gas volume to the gas volume under standard conditions.

[0042] After the above compensation calculations are completed, determine the final result value as the gas volume released at the i-th release, and accumulate it with the cumulative gas volume at the (i - 1)-th time to obtain the cumulative gas volume at the i-th time.

[0043] Repeat the above metering process until the reaction ends.

[0044] When the reaction ends, it is necessary to judge "whether the reactor tail gas compensation algorithm is enabled". If the reactor tail gas compensation algorithm is enabled, it is necessary to calculate the volume of gas in the headspace of the reactor that has not been metered, and add it to the cumulative gas volume at the i-th time to obtain the final cumulative gas volume. Otherwise, record the cumulative gas volume at the i-th time as the final cumulative gas volume.

Example 1

[0045] The device of the present invention is used to measure the cumulative methane production value. The metering scheme is not to release the generated gas during the fermentation process (traditional pressure metering method), and the cumulative methane production value of the substrate is obtained by measuring the pressure rise in the reactor.

[0046] Experimental setup: During the experimental setup, strategies such as reserving a large headspace volume or diluting the reaction substrate are needed to avoid the headspace pressure in the reactor reaching too high a level. A sufficiently large adsorption device needs to be used, equipped with sufficient alkaline substances to adsorb the acidic gases generated during the reaction.

[0047] For example, the total volume of the reactor is 2 L, the working volume is 0.5 L, and the fermentation temperature is 37 °C.

[0048] Its metering method includes the following steps: (1) Before the reaction starts, inoculum, substrate, nutrient solution, and water are loaded into the reactor. A sufficient amount of flaky NaOH is placed in the adsorption device. After checking for air leakage after connecting the device, if the device is hermetically sealed, an inert gas is purged into it to create an anaerobic environment, and the device is started. Set the pressure threshold P 阈值 to 100 kPa. Select to enable the water vapor correction compensation algorithm; (2) The one-way gas valve is closed, and the temperature and pressure sensors monitor the temperature and pressure in the reactor. The initial temperature T R0 and the initial pressure P R0 in the reactor are measured, and the partial pressure of water vapor P vap at this temperature is calculated; (3) Calculate the real-time pressure change in the headspace of the reactor. When ΔP ≥ P 阈值 , the one-way gas valve is opened to release the methane and other gases generated by the reaction to prevent safety problems caused by excessive pressure. Since only the water vapor correction compensation algorithm is enabled, the calculation formula for the cumulative amount of methane gas generated becomes: ,

[0049] In the formula, Δn is the change in the amount of substance of the cumulative gas in the reactor, V R is the volume of the headspace of the reactor, P R is the real-time pressure value in the reactor, P R0 is the initial pressure in the reactor, T R is the real-time temperature in the reactor, T R0 is the initial temperature in the reactor, V a is the cumulative amount of methane gas in the reactor, V m is the molar volume of methane gas under the current environment, f D is the content of dry gas, Pvap The pressure of water vapor in the measured gas volume, and R is the ideal gas constant.

[0050] This device is used to measure the cumulative methane production of a certain reactant during anaerobic fermentation. The measurement strategy is high-resolution without gas release (traditional pressure measurement method). During the measurement process, only the water vapor correction compensation algorithm is enabled, and finally the cumulative methane gas volume V of the reaction is recorded. a .

[0051]

Example 2

[0052] The device of the present invention is used to measure the BMP value of cellulose powder. The measurement scheme is to immediately release the part of the gas generated during the fermentation process and measure it, and finally accumulate the measured amount to obtain the BMP value of cellulose powder.

[0053] Preparation of fermentation materials: The inoculum for this experiment was taken from an operating anaerobic reactor, and its reactant was lignocellulosic biomass; the substrate was cellulose powder.

[0054] In the BMP experiment, the following reagents also need to be prepared as aids: The required reagents include: Acidic gas adsorption substances: commercial-grade flaky sodium hydroxide (NaOH), or NaOH solution with a certain concentration; If you want to adjust the pH of the mixture (inoculum, substrate, water, and nutrient solution), use the following reagents: 1N hydrochloric acid (HCl) solution, or 1N sodium hydroxide (NaOH) solution, or powdered sodium bicarbonate (NaHCO 3 ); In addition, a certain amount of nutrient solution is also required. The nutrient solution formula for nutrients and trace elements is as follows: A: 2.7 g of anhydrous potassium dihydrogen phosphate (KH 2 PO 4 ), 11.2 g of disodium hydrogen phosphate dodecahydrate (Na 2 HPO 4 ·12H 2 O), 5.3 g of ammonium chloride (NH 4 Cl). Dissolve the above reagents in distilled water and make up to a 0.5 L volumetric flask; B: 0.75 g of calcium chloride dihydrate (CaCl 2 ·2H 2 O), 1.0 g of magnesium chloride hexahydrate (MgCl 2 ·6H 2 O), 0.2 g of iron(II) chloride tetrahydrate (FeCl 2 ·4H 2 O). Dissolve the above reagents in distilled water and make up to a 0.5 L volumetric flask; C: 0.05 g of manganese(II) chloride tetrahydrate (MnCl 2 ·4H 2 O), 0.005 g of boric acid (H 3 BO 3 ), 0.005 g of zinc chloride (ZnCl 2 ), 0.003 g of copper(II) chloride (CuCl 2 ), 0.001 g of sodium molybdate dihydrate (Na 2 MoO 4 ·2H 2 O), 0.1 g of cobalt(II) chloride hexahydrate (CoCl 2 ·6H 2 O), 0.01 g of nickel(II) chloride hexahydrate (NiCl 2 ·6H 2 O), 0.005 g of sodium selenate (Na 2 SeO 3 ). Dissolve the above reagents in distilled water and make up to a 0.5 L volumetric flask; In the experiment, the ratio is made as required.

[0055] Experimental setup: The total volume of the reactor is 500 mL, the working volume is 400 mL, and the fermentation temperature is 37 °C. In this BMP experiment, a total of 2 parallel experimental groups are set up to test the background gas of the inoculum and the gas production of the substrate respectively: Table 1 Material characteristics and experimental setup table

[0056] Its measurement method includes the following steps: (1) Before the reaction starts, load the inoculum, substrate, nutrient solution and water into the reactor, place a sufficient amount of flaky NaOH in the adsorption device, check whether there is air leakage after connecting the device. If the device is airtight, purge it with an inert gas to create an anaerobic environment and start the device. Set the pressure threshold P 阈值 to 5 kPa. Select to enable the purge gas overestimation compensation algorithm, water vapor correction compensation algorithm, standard condition conversion compensation algorithm and reactor tail gas compensation algorithm.

[0057] (2) The one-way air valve is closed, and the temperature sensor and pressure sensor monitor the temperature inside the reactor and record it as the initial temperature T R0 which is 37°C, and the pressure inside the reactor is recorded as the initial pressure P R0 which is 104.8 kPa, and the partial pressure of water vapor at this temperature is 6.25993 kPa.

[0058] (3) Calculate the real-time pressure change of the headspace inside the reactor , and the headspace pressure change curve is as shown in Figure 5 and Figure 6 . When ΔP ≥ P 阈值 , the one-way air valve opens to release gases such as methane generated by the reaction to keep the pressure inside the reactor relatively constant. Calculate the change in the amount of methane gas in the headspace inside the reactor, add ΔV to the cumulative methane gas amount Va, close the one-way air valve, make the pressure of the headspace inside the reactor equal to the external environment, and re-record the pressure at this time as the initial pressure , and the temperature sensor re-records the temperature at this time as the initial temperature .

[0059] Calculate the amount of gas ΔV released for the i-th time at the current temperature according to the gas molar volume formula i , and the formula is as follows: ,

[0060] In the formula, ΔV i is the change in the volume of the gas in the headspace inside the reactor measured for the i-th time, Δn i is the change in the amount of substance in the headspace inside the reactor measured this time, V m is the molar volume of methane gas at the temperature T Ri at the end of this measurement, R is the ideal gas constant, V R is the volume of the headspace inside the reactor, P Ri is the real-time pressure value of the headspace inside the reactor at the end of this measurement, is the initial pressure of the headspace inside the reactor at the start of this measurement, T Ri is the real-time temperature of the headspace inside the reactor at the end of this measurement, is the initial temperature of the headspace inside the reactor at the start of this measurement.

[0061] Since the purge gas overestimation compensation algorithm is enabled, calculate the amount of methane gas ΔV in the gas volume measured for the i-th time based on the residual ratio of the purge gas in the headspace and the volume of the headspace gas in the reactor between two adjacent measurements, Ci , and the formula is as follows, ,

[0062] where, ΔV Ci is the amount of methane gas in the gas volume measured at the i-th measurement, and ΔV i is the amount of change in the gas volume of the headspace inside the reactor measured at the i-th measurement, V R is the volume of the headspace inside the reactor, f Ni is the residual ratio of the headspace purge gas at the i-th measurement, and f N(i-1) is the residual ratio of the headspace purge gas at the (i - 1)-th measurement.

[0063] Due to the activation of the water vapor correction compensation algorithm, according to the partial pressure law proposed by Dalton and the partial volume law proposed by Amagat, the amount of change in the volume of dry gas ΔV Di in the gas volume measured at the i-th measurement is as follows: ,

[0064] where, ΔV Di is the amount of change in the volume of dry gas in the gas volume measured at the i-th measurement, ΔV i is the amount of change in the gas volume measured at the i-th measurement, f Di is the content of dry gas in the gas volume measured at the i-th measurement, P vapi is the pressure of water vapor in the gas volume measured at the i-th measurement, and P gasi is the pressure of the gas measured at the i-th measurement.

[0065] Due to the activation of the standard condition conversion compensation algorithm, the amount of gas released at the standard condition ΔV i is calculated according to the gas molar volume formula, using the molar volume V ms of methane gas at the standard condition, and the formula is as follows: ,

[0066] where, ΔV_std i is the amount of change in the gas volume of the headspace inside the reactor measured at the i-th measurement under the standard condition, ΔV i is the amount of change in the gas volume of the headspace inside the reactor measured at the i-th measurement, P Ri is the real-time pressure value of the headspace inside the reactor at the end of this measurement, P 标 is the pressure under the standard condition, T Ri is the real-time temperature of the headspace inside the reactor at the end of this measurement, and T 标 is the temperature under the standard condition.

[0067] Therefore, the amount of change in the volume of the headspace gas inside the reactor at the i-th measurement after cumulative record compensation ΔV 补偿i , and the calculation formula for accumulating it to the cumulative gas production volume V ai in the previous i reactions becomes: ,

[0068] Wherein, V ai is the cumulative gas production in the previous i times, V a（i-1） is the cumulative gas production in the previous i - 1 times, ΔV 补偿i is the amount of change in the gas volume of the dry purge gas released in the i-th time under standard conditions, ΔV i is the amount of change in the volume of the overhead gas in the reactor measured in the i-th measurement, P 标 is the pressure under standard conditions, T 标 is the temperature under standard conditions, P Ri is the real-time pressure value of the overhead space in the reactor at the end of this measurement, T Ri is the real-time temperature of the overhead space in the reactor at the end of this measurement, P vapi is the pressure of water vapor in the gas volume measured in the i-th measurement, V R is the volume of the overhead space in the reactor.

[0069] Repeat step (3) to record the next change in methane gas volume.

[0070] (4) When the reaction ends, the one-way gas valve remains closed. If the reactor tail gas compensation algorithm is enabled, calculate the amount of unmeasured methane gas remaining in the reactor. The temperature sensor and pressure sensor monitor the real-time temperature T R1 in the reactor is 37 °C and the real-time pressure P R1 in the reactor is 106.1 kPa, calculate the amount of the remaining methane gas volume ΔV R in the reactor overhead space is 0.9665 mL, and accumulate it to the cumulative methane gas volume V a , ,

[0071] Wherein, V a_end is the final cumulative methane gas volume of the reaction, V ai is the cumulative methane gas volume of the previous measurement, ΔV R is the amount of change in the methane gas volume in the reactor overhead space.

[0072] (5) During the reaction process, the BMP value during the process can be calculated according to the real-time cumulative methane production of the blank group and the experimental group, ,

[0073] Wherein, BMP s is the real-time methane production potential value of the reactants, V at is the cumulative methane gas production of the experimental group, V ab is the cumulative methane gas production of the blank group, m ItThe amount of inoculum added in the experimental group, m Ib The amount of inoculum added in the blank group, VS s The VS content of the reactant, m s The amount of reactant added in the experimental group.

[0074] At the end of the reaction, the final cumulative methane gas volume V in the experimental group at is 893.9393 mL, and the final cumulative methane gas volume V in the blank group ab is 85.6116 mL. From this, the BMP value of the cellulose powder is calculated as follows ,

[0075] In the formula, V at is the final cumulative methane gas volume of the experimental group, V ab is the final cumulative gas change volume of the blank group, m It is the amount of inoculum added in the experimental group, m Ib is the amount of inoculum added in the blank group, VS s is the VS content of the reactant, m s is the amount of reactant added in the experimental group.

[0076] This device is used to monitor the BMP value of cellulose powder. The BMP change curve is as Figure 4 shown. The metering strategy adopts multiple releases of headspace gas production with a small resolution. During the metering process, a standard condition conversion compensation algorithm, a water vapor correction compensation algorithm, and a reactor tail gas compensation algorithm are enabled. Finally, the cumulative methane gas volume V of the reaction is recorded a_end is 893.9393 NmL, and the BMP is 361.7670 NmL / gVS.

[0077] Table 2 Table of changes in metered methane production in the experimental group

[0078] Table 3 Table of changes in cumulative methane production and BMP

[0079]

Example 3

[0080] Through the analysis of these data, it can be clearly seen that under different headspace volumes and pressure threshold conditions, the metering resolution of this gas automatic metering device changes, further demonstrating the flexibility and high adaptability of the present invention in different application scenarios, and providing a strong basis for selecting appropriate parameters according to specific requirements in practical applications.

Claims

1. An automatic metering method for anaerobic fermentation gas based on pressure method, characterized in that: The measuring method comprises the following steps: Step 1: Before the reaction starts, load the reactants to be monitored into the reactor and check whether there is any leakage after the device is connected. If the device is well sealed, purge inert gas into it to create an anaerobic environment, start the device, and set the pressure threshold P. 阈值 , where P 阈值 The selected pressure sensor can accurately monitor the value within the pressure variation range; Step 2: The data processing module controls the one-way gas valve to close, and the temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor and record them as the initial temperature T R0 and initial pressure P R0 ; Step 3, as the anaerobic fermentation in the reactor continues, the substrate in the reactor is gradually decomposed and transformed by microorganisms, biogas is generated and accumulated, the generated CO2 is fully adsorbed by the adsorption device, and the remaining CH4 volume is measured; Step 4, select and enable the required compensation algorithm; the compensation algorithm includes one or more combinations of the following methods: standard condition conversion compensation algorithm, water vapor correction compensation algorithm, purge gas overestimation compensation algorithm, reactor tail gas compensation algorithm.

2. A method according to claim 1, characterized in that The temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor to obtain the real-time temperature T R and real-time pressure P R and the pressure value at the beginning of each measurement Calculate the pressure change ΔP in the reactor headspace using the following formula: ， Where ΔP is the pressure change in the reactor, P R is the real-time pressure value of the headspace in the reactor, is the initial pressure of the headspace in the reactor at the beginning of this measurement; When ΔP ≥ P 阈值 When the temperature and pressure in the reactor are measured at the time of the ith release, they are T Ri and P Ri , the one-way valve is opened to release the gas produced by the reaction to keep the pressure in the reactor stable. According to the ideal gas equation, since the headspace volume is fixed, the change in the amount of substance Δn is calculated by monitoring the changes in the pressure and temperature of the headspace in the reactor. The formula is as follows: ， ， In the formula, P is pressure, V is volume, n is the amount of substance, R is the ideal gas constant, T is temperature, Δn i is the change in the amount of the headspace gas in the reactor measured for the i-th time, V R is the volume of the headspace in the reactor, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, is the initial pressure of the headspace in the reactor at the beginning of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, is the initial temperature of the headspace in the reactor at the beginning of this measurement; Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows, ， Where, ΔV i is the amount of gas released for the i-th time, Δn i V is the change in the amount of material in the headspace of the reactor measured this time, m T is the time when this measurement ends R1 The molar volume of methane gas at temperature.

3. A method as claimed in claim 2, characterized in that The standard condition conversion compensation algorithm is: convert the volume of the measured gas to the volume under standard conditions to ensure the consistency and comparability of different experimental data; calculate the amount of gas released for the i-th time under standard conditions ΔV according to the gas molar volume formula i , using the molar volume V of methane gas under standard conditions ms , the formula is as follows: ， In the formula, ΔV i is the change in the gas volume of the headspace in the reactor measured for the i-th time under standard conditions, ΔV i is the amount of gas released for the ith time, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, P 标 is the pressure under standard conditions, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, T 标 is the temperature under standard conditions.

4. A method as claimed in claim 2, characterized in that The water vapor correction compensation algorithm is as follows: considering that the liquid in the reactor is evaporated into water vapor and will also be measured by the device, resulting in a metering error, which affects the gas production; according to the partial pressure law proposed by Dalton and the partial volume law proposed by Amagat, the volume fraction of water is equivalent to the pressure fraction obtained by dividing the water vapor pressure by the total pressure; therefore, the dry gas content is calculated by subtracting the water content from the wet gas content; The dry gas content f in the gas volume measured for the i-th time Di Calculated according to the formula: ， In the formula, f Di is the dry gas content in the gas volume measured for the i-th time, V vapi is the volume of water vapor in the gas volume measured for the i-th time, V gasi is the gas volume measured for the ith time, P vapi is the pressure of water vapor in the i-th measured gas volume, P gasi is the pressure of the gas measured for the i-th time, ， Where P vapi is the pressure of water vapor in the i-th measured gas volume, T i is the temperature at the time of the i-th measurement, A, B, C are Antoine constants, Therefore, the volume change of dry gas in the gas volume measured for the i-th time is ΔV Di , the formula is as follows: ， Where ΔV Di is the volume change of dry gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the ith time, f Di is the content of dry gas in the gas volume measured for the i-th time.

5. A method as claimed in claim 2, characterized in that The purge gas overestimation compensation algorithm is as follows: in order to ensure the normal progress of anaerobic fermentation, inert gas needs to be purged into the reactor before the reaction starts to create an anaerobic environment; however, the purge gas will fill the reactor headspace, affecting the subsequent measurement of the metering gas production; the headspace purge gas residual ratio f at the i-th measurement Ni , the formula is as follows, , In the formula, f Ni is the residual ratio of headspace purge gas at the i-th measurement, ΔV i is the amount of gas released for the ith time, V R is the volume of the headspace in the reactor; Based on the headspace purge gas residual ratio and the reactor headspace gas volume during two adjacent measurements, the amount of methane gas in the gas volume measured for the i-th time, ΔV, is calculated. Ci , the formula is as follows, , Where, ΔV Ci is the amount of methane gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the ith time, V R is the volume of the headspace in the reactor, f Ni is the residual ratio of headspace purge gas at the i-th measurement; It also includes the gas change accumulation algorithm: Record the amount of gas released for the i-th time ΔV i , and added to the cumulative gas volume V produced in the previous i reactions ai , the formula is as follows: , Where V ai is the cumulative amount of gas produced in the previous i times, V a（i-1） is the cumulative amount of gas produced in the previous i-1 times, ΔV i is the amount of gas released for the i-th time. When the headspace pressure in the reactor is stable, the one-way gas valve is closed, and the temperature at this time is re-recorded by the temperature sensor and the pressure sensor as the initial temperature of the next gas release. , the pressure is the initial pressure of the next gas release ; Repeat step 3 to record the next change in gas volume.

6. A method according to claim 2, characterized in that The reactor tail gas compensation algorithm is as follows: when the reaction is finished, the one-way gas valve remains closed and the amount of gas remaining in the reactor that has not been measured is calculated; the temperature sensor and the pressure sensor monitor the temperature and pressure in the reactor as the real-time temperature T R and real-time pressure P R According to the ideal gas equation, the change in the amount of gas remaining in the reactor that has not been measured is calculated by monitoring the changes in the headspace pressure and temperature in the reactor. R , the formula is as follows: , In the formula, Δn R is the change in the amount of gas remaining in the reactor that has not been measured, V R is the volume of the reactor headspace, R is the ideal gas constant, P R is the real-time pressure value in the reactor, P R0 is the initial pressure in the reactor, T R is the real-time temperature in the reactor, T R0 is the initial temperature in the reactor, Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows, , Where, ΔV R is the volume change of the remaining unmeasured gas in the reactor, Δn R is the change in the amount of gas remaining in the reactor that has not been measured, V m T is the measurement time of this time R The molar volume of methane gas at the temperature; The amount of change in volume of the remaining unmeasured gas in the reactor ΔV according to the activation of the compensation algorithm R Perform compensation calculation and record the change in volume of the remaining unmeasured gas in the reactor after compensation. ,Will Add to the cumulative gas volume V generated in the previous i times ai , the formula is as follows: , Where V a_end is the final cumulative gas volume of the reaction, V ai is the cumulative amount of gas produced in the previous i times, It is the amount of volume change of the remaining unmeasured gas in the reactor after compensation.

7. An automatic anaerobic fermentation gas metering device based on a pressure method using the method according to any one of claims 1 to 6, characterized in that: include: at least one reactor; at least one temperature sensor; at least one pressure sensor; at least one one-way gas valve; at least one adsorption device; At least one data processing module, used to receive the pressure and temperature data of the head space in the reactor, and control the opening and closing of the one-way gas valve according to the real-time pressure data; The temperature sensor, pressure sensor, and adsorption device are arranged on the inner side of the top of the reactor, and the one-way gas valve is arranged on the outer side of the top of the reactor. The temperature sensor, pressure sensor, and one-way gas valve are electrically connected to the data processing module.

8. A metering device according to claim 7, characterized in that The one-way gas valve is used to release the gas generated in the reactor in sequence, so that the gas pressure inside the reactor remains stable; when the one-way gas valve is kept closed, the entire device is in a closed state.

9. A metering device as claimed in claim 7, characterized in that The reactor consists of a reaction bottle and a sealed bottle cap, and the sealed bottle cap is provided with multiple pipeline interfaces and corresponding valve ports for adding substances to the reactor or setting up other sensors or taking samples; the one-way gas valve is connected to a pipeline interface of the sealed bottle cap, and the adsorption device is arranged inside or outside the mouth of the reaction bottle, and is connected between the reaction bottle and the one-way gas valve to ensure that the gas to be adsorbed is fully adsorbed.

10. A metering device according to claim 7, characterized in that: The adsorption device uses alkaline substances to adsorb carbon dioxide gas generated by the reaction. The reaction process is: When CO2 is small: CO2+2OH - →CO 2- 3+H2O, When CO2 is in excess: CO2+OH - →HCO - 3.

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