A method for operation control of a CO₂ cycle catalytic biomass gasification polygeneration unit

Abstract

This invention discloses an operation control method for a CO₂ circulating catalytic biomass gasification polygeneration unit, relating to the field of distributed biomass energy utilization and process control technology. The method includes the following steps: inerting and purging are performed based on the gas supply and atmosphere control unit to determine the unit's operating boundaries; during the pyrolysis stage, active sites are constructed in situ on the carbon through alkali metal Na / K dosage control; during the gasification stage, recycled CO₂ and / or purified flue gas are introduced and the CO₂ / steam ratio is controlled to drive the reaction unit to stably produce gas and generate biochar as a byproduct; tar and dust are controlled through staged condensation-filtration-switchable catalytic cracking; a micro gas chromatography calibration dataset is established and sensor array data is fused; soft measurement and closed-loop control are used to adjust the feed rate, bed temperature, and recycled CO₂ ratio; and emergency shutdown is executed when safety interlock conditions such as backfire, CO leakage, and pressure difference abnormalities are triggered. This method solves the problems of large calorific value fluctuations, easy tar blockage, and high monitoring and control costs in distributed biomass gasification, achieving improved efficiency and safe and stable operation.

Description

Technical Field

[0001] This invention relates to the field of distributed utilization and process control technology of biomass energy, specifically providing an operation control method for a CO2 circulating catalytic biomass gasification polygeneration device. Background Technology

[0002] Low-value biomass resources such as crop straw and forestry residues are abundant and scattered. If they are disposed of by open burning or extensive dumping, it will not only cause environmental pollution, but also put pressure on the management of burning bans. The distributed polygeneration pathway of biomass gasification-heating / drying-biochar carbon sequestration can achieve "on-site treatment and on-site energy use" in county or rural scenarios.

[0003] However, existing distributed biomass gasification devices generally suffer from the following problems: fluctuations in the moisture content and ash content of the raw materials lead to unstable reactor temperature fields and large fluctuations in the calorific value of the produced gas; tar and dust are prone to condensation and adhesion at the cold end, causing pipeline blockage; online component analysis equipment is costly and difficult to maintain, resulting in a lack of reliable monitoring and closed-loop control in rural areas; at the same time, there is a lack of engineering control methods for CO2 / flue gas resource recovery and catalyst dosage window, which can easily introduce slagging, corrosion or safety risks. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide an operation control method for a CO2 circulating catalytic biomass gasification polygeneration device. Through an integrated strategy of "CO2 / flue gas reuse + Na / K in-situ active site catalysis + staged tar removal + micro GC calibration soft measurement + safety interlock closed-loop control", the distributed system can operate stably for a long time, while taking into account both efficiency improvement and safety.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for operating and controlling a CO2 circulating catalytic biomass gasification polygeneration device, comprising: inerting and purging the device based on a gas supply and atmosphere control unit and establishing a switching logic between a start-up mode and an operating mode; heating the reaction unit in the start-up mode and forming catalytic carbon containing alkali metal active sites in the pyrolysis stage; introducing recycled CO2 and / or flue gas as a gasifying agent and controlling the CO2 / steam ratio in the operating mode to drive catalytic gasification to generate syngas and produce biochar as a byproduct; performing staged condensation, filtration, and switchable catalytic cracking of the syngas through a condensation and tar control unit to obtain purified fuel gas; establishing a micro gas chromatography calibration dataset through an analysis and digitization unit and fusing sensor array data to obtain soft measurement results of the lower heating value of the syngas and the H2 / CO ratio; and using a closed-loop control strategy based on the soft measurement results to adjust the feed rate, bed temperature, and recycled CO2 ratio, and performing an emergency shutdown when safety interlock conditions are triggered.

[0006] In a preferred embodiment, the gas supply and atmosphere control unit includes an inerting gas channel and a vaporizing agent channel. The inerting gas channel introduces N2 or Ar into the reaction unit to reduce the outlet oxygen content to below 0.8%. The vaporizing agent channel uses a mass flow controller to perform closed-loop control of the flow rates of recycled CO2, supplemented CO2, and steam, and uses a pressure sensor to control the reactor's micro-negative pressure at -200 to -800 Pa.

[0007] In a preferred embodiment, the catalytic carbon forming alkali metal active sites comprises: adding Na2CO3 and / or K2CO3 at 0.2-2.0% of the dry biomass mass, or adding biomass ash at a rate of 0.1-1.5% Na / K based on the soluble sodium and potassium content in the ash; forming a Char-Na / Char-K structure during the pyrolysis stage at 350-550℃, and accelerating the Boudouard reaction during the CO2-assisted gasification stage at 700-900℃.

[0008] In a preferred embodiment, the staged condensation-filtration and switchable catalytic cracking includes: setting a primary high-temperature filtration section (280-400°C), a secondary condensation section (80-150°C), and a tertiary condensation section (10-40°C), and configuring a catalytic cracking bypass after the secondary or tertiary condensation section. When the online estimated tar index exceeds the threshold, the catalytic cracking bed is activated and the bed temperature is controlled at 650-850°C.

[0009] In a preferred embodiment, the analysis and digitization unit uses intermittent measurements from a micro gas chromatograph as a reference and continuous measurements from an NDIR / thermal conductivity / electrochemical sensor as observations. Kalman filtering is used for time synchronization and noise reduction to obtain soft measurement results for lower heating value, H2 / CO ratio, and tar index. Model predictive control (MPC) or fuzzy control algorithms are used to output control quantities for the proportion of recycled CO2, steam flow rate, and feed rate.

[0010] The technical solution provided by this invention has the following beneficial effects: (1) By synergistic control of CO2 / flue gas reuse and Na / K in-situ active sites, CO generation and carbon conversion rates are improved, thereby enhancing gasification efficiency; (2) By using a staged condensation-filtration-switchable catalytic cracking linkage control, the risk of blockage caused by tar and dust is reduced, making it suitable for long-term operation; (3) By fusing the micro GC calibration dataset with the sensor array, low-cost online soft measurement and closed-loop control can be achieved, reducing heat value fluctuations and improving safety; (4) Through safety interlocking logic such as backfire, CO leakage, and pressure difference abnormality, rapid isolation and inerting venting are achieved to reduce on-site operational risks; (5) It can be linked with biochar yield and fixed carbon content to form a carbon sequestration ledger, which facilitates subsequent carbon accounting and operation and maintenance management. Attached Figure Description

[0011] Figure 1 This is a schematic flowchart of the operation control method for a CO2 circulating catalytic biomass gasification polygeneration unit according to the present invention. Detailed Implementation

[0012] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention. Example

[0013] like Figure 1 As shown in the figure, the operation control method of a CO2 circulating catalytic biomass gasification polygeneration unit provided in this embodiment includes the following steps: S1: Device operation boundary determination and inerting purging.

[0014] First, read the temperature, pressure, differential pressure, O2 and CO sensor signals to complete valve position self-test and communication self-test; then open the inert gas (N2 or Ar) channel to purge the reaction unit, condensation section and sampling pipeline until the oxygen content at the reactor outlet is less than 0.8%; at the same time, maintain the reactor at a slight negative pressure of -200 to -800 Pa by using an induced draft fan or vacuum pump to suppress the escape of combustible gas.

[0015] S2: Pyrolysis heating and construction of in-situ Na / K active sites.

[0016] The pretreated biomass (preferably with a moisture content ≤20%) is fed into the reaction unit, and the heating rate is controlled at 2-10℃ / min to enter the pyrolysis stage at 350-550℃. Na2CO3 and / or K2CO3 (or 0.1-1.5% Na / K based on biomass ash) are added at 0.2-2.0% of the dry biomass mass to form a Char-Na / Char-K structure by complexing the alkali metal with the carbon group. Then, the temperature is further increased to 700-900℃ to enter the CO2-assisted catalytic gasification stage.

[0017] S3: CO2 circulating gasification and staged tar removal.

[0018] In operation, recycled CO2 and supplementary CO2 are introduced, with steam added at a steam / CO2 molar ratio of 0.1–0.6. The recycled CO2 can come from combustion exhaust gas or CO2 by-products from biogas purification. Before reuse, it undergoes dust removal, dehydration, and temperature regulation to ensure a dust content ≤10 mg / Nm³, a dew point ≤0℃, and a volume fraction ≥85%. The generated syngas sequentially passes through a high-temperature filtration section at 280–400℃ to remove fly ash and heavy tar aerosols, and then enters a secondary condensation section at 80–150℃ and a tertiary condensation section at 10–40℃ for graded recovery of condensate. When the tar index exceeds the threshold, the catalytic cracking bypass is activated, and the cracking bed temperature is controlled at 650–850℃ to further reduce tar residue.

[0019] S4: Micro GC calibration soft measurement and closed-loop control.

[0020] A standard mixed gas with at least five concentration gradients was prepared using H2, CO, CH4, CO2, and light hydrocarbons as target components to establish a micro gas chromatograph calibration dataset for on-site sensor zero-point, range, and cross-interference correction. During operation, the micro gas chromatograph outputs intermittent component data at 10–30 min intervals, while the sensor array outputs continuous data at 1–5 s intervals. Kalman filtering was used for time synchronization and noise reduction, and the estimated values ​​of lower heating value, H2 / CO ratio, and tar index were calculated. Closed-loop control adopted Model Predictive Control (MPC) or fuzzy control algorithm. Under constraints such as T_bed∈[750,900]℃, O2<1.0%, and ΔP_bed<3kPa, the control quantities of CO2 reuse ratio, steam flow rate, and feeder speed were output to ensure that the lower heating value fluctuation is ≤±10%.

[0021] S5: Safety interlock and emergency stop.

[0022] When the following conditions are detected: reactor outlet O2 ≥ 2.0%, gas pipeline CO leakage concentration ≥ 50 ppm, condensation / filtration section pressure difference ΔP ≥ 5 kPa, or backfire signal, the safety interlock is triggered: the gasifying agent and feed valves are closed, inert gas is continuously purged, and the gas is switched to the flare or safety burner. At the same time, alarm and shutdown events are recorded for easy traceability and maintenance.

[0023] The above embodiments can be implemented in whole or in part by software, hardware, firmware or other arbitrary combinations; all modifications or substitutions made by those skilled in the art within the scope of the technology disclosed in this invention should be covered within the protection scope of this invention.

Claims

1. A method for operating and controlling a CO2-cycle catalytic biomass gasification combined production unit, characterized in that, include: The device is inerted and purged based on the gas supply and atmosphere control unit, and a switching logic between the start-up mode and the operation mode is established. In the start-up mode, the reaction unit is heated and catalytic carbon containing alkali metal active sites is formed during the pyrolysis stage; In the operation mode, recycled CO2 and / or flue gas are introduced as gasification agents and the CO2 / steam ratio is controlled to drive catalytic gasification to generate syngas and produce biochar as a byproduct. The synthesis gas is subjected to staged condensation, filtration and switchable catalytic cracking through condensation and impurity removal and tar control unit to obtain purified fuel gas; By analyzing and establishing a micro gas chromatography calibration dataset using a digital unit and fusing sensor array data, soft measurement results of the lower heating value of syngas and the H2 / CO ratio were obtained. Based on the soft measurement results, a closed-loop control strategy is adopted to adjust the feed rate, bed temperature and CO2 recycling ratio, and to perform an emergency shutdown when the safety interlock conditions are triggered.

2. The operation control method according to claim 1, characterized in that, The gas supply and atmosphere control unit includes an inert gas channel and a vaporizing agent channel. The inert gas channel introduces N2 or Ar into the reaction unit to reduce the outlet oxygen content to below 0.8%. The vaporizing agent channel uses a mass flow controller to perform closed-loop control of the flow rates of recycled CO2, supplementary CO2 and steam, respectively, and uses a pressure sensor to control the reactor's micro-negative pressure at -200 to -800 Pa.

3. The operation control method according to claim 2, characterized in that, The catalytic carbon forming alkali metal active sites comprises: adding Na2CO3 and / or K2CO3 at 0.2-2.0% of the dry biomass mass, or adding biomass ash at a Na / K ratio of 0.1-1.5% based on the soluble sodium and potassium in the ash; forming a Char-Na / Char-K structure by complexing the alkali metal with the carbon groups during the pyrolysis stage at 350-550℃; and accelerating the Boudouard reaction during the CO2-assisted gasification stage at 700-900℃.

4. The operation control method according to claim 1, characterized in that, The recycled CO2 is obtained from CO2 by-products of combustion exhaust gas or biogas purification. Before recycling, it undergoes dust removal, dehydration, and temperature regulation to ensure that the dust content is ≤10mg / Nm³, the dew point is ≤0℃, and the volume fraction of recycled CO2 is ≥85%.

5. The operation control method according to claim 1, characterized in that, The staged condensation-filtration and switchable catalytic cracking include: A primary high-temperature filtration section is set up, with a filtration temperature of 280-400℃ to intercept fly ash and heavy tar aerosols. A two-stage condensation section is set up with a condensation temperature of 80-150℃ to recover heavy tar; A three-stage condensation section is set up with a condensation temperature of 10–40°C to recover light condensate; A catalytic cracking bypass is configured after the secondary or tertiary condensation section. When the online estimated tar index exceeds the preset threshold, the catalytic cracking bed is activated and the bed temperature is controlled at 650-850℃.

6. The operation control method according to claim 1, characterized in that, The establishment of the micro gas chromatography calibration dataset includes: preparing a standard mixed gas with no less than 5 concentration gradients using H2, CO, CH4, CO2 and light hydrocarbons as target components; periodically calibrating the standard mixed gas using micro gas chromatography to obtain a calibration coefficient matrix for zero-point and range correction of the on-site sensor.

7. The operation control method according to claim 6, characterized in that, The soft measurement results were obtained in the following manner: Intermittent measurements from a micro gas chromatograph were used as reference values, while continuous measurements from an NDIR / thermal conductivity / electrochemical sensor were used as observation values. Kalman filtering was used to synchronize and denoise the multi-source data, and the estimated values ​​of the lower heating value of syngas, H2 / CO ratio and tar index were calculated.

8. The operation control method according to claim 7, characterized in that, The closed-loop control strategy adopts model predictive control (MPC) or fuzzy control algorithm. Under the constraints of T_bed∈[750,900]℃, O2<1.0%, and ΔP_bed<3kPa, it calculates and outputs the control quantities of CO2 reuse ratio, steam flow rate, and feed screw feeder speed, so that the low heating value fluctuation is ≤±10%.

9. The operation control method according to claim 1, characterized in that, The safety interlock conditions include at least: reactor outlet O2 ≥ 2.0%, or gas pipeline CO leakage concentration ≥ 50 ppm, or condensation / filtration section pressure difference ΔP ≥ 5 kPa, or detection of backfire pressure fluctuation peak ≥ set threshold; when any safety interlock condition is met, an emergency shutdown is performed, including closing the gasifying agent and feed valves, opening the inerting gas valve for continuous purging, switching the gas to the flare or safety burner, and recording the alarm event.

10. The operation control method according to claim 1, characterized in that, The method also includes calculating carbon sequestration based on biochar emissions and fixed carbon content, and packaging the tCO2e emission reduction per unit of raw material with operating data to generate a traceable digital ledger.

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