A biomass fuel staged pretreatment closed loop combustion optimization method

Abstract

This invention provides a closed-loop combustion optimization method for graded pretreatment of biomass fuel, belonging to the field of comprehensive utilization of biomass energy and thermal power generation technology. It can significantly alleviate or solve the problems of complex biomass fuel sources, large compositional fluctuations, insufficient targeting of single pretreatment processes, and the disconnect between pretreatment and combustion stages, making dynamic optimization based on combustion conditions difficult, leading to unstable combustion, high risk of slagging and corrosion, and limited blending ratios. This method includes online raw material detection and classification, graded pretreatment, zoned storage and dynamic proportioning, online combustion monitoring, and closed-loop feedback control, thereby improving the adaptability and blending ratio of biomass fuel and reducing the risks of slagging, corrosion, and pollutant emissions.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy comprehensive utilization and thermal power generation technology, specifically relating to a closed-loop combustion optimization method for staged pretreatment of biomass fuel. Background Technology

[0002] Reducing reliance on fossil fuels, increasing the proportion of renewable energy utilization, and reducing greenhouse gas emissions have become important development directions for the energy and power industry. Utilizing existing large-scale coal-fired power plants for biomass co-firing is considered a realistic approach that balances carbon reduction effects, engineering feasibility, and investment economics. Compared to building new independent biomass power generation projects, adapting existing coal-fired units' boilers, transmission, and control systems allows for faster large-scale replacement capacity. Therefore, this technological approach has high application value in the fields of comprehensive biomass energy utilization and thermal power generation.

[0003] From a more specific application perspective, while biomass fuels have a wide range of sources, including agricultural and forestry waste, woody raw materials, and other organic resources, their raw material properties naturally fluctuate significantly. Different batches exhibit marked differences in moisture content, particle size, ash content, alkali metal content, and lower heating value. Simultaneously, biomass generally suffers from low energy density, poor grindability, and insufficient stability during transportation and storage. When such fuels are directly introduced into coal-fired boiler systems, or when they undergo only simple crushing and drying before being blended in high proportions, it often leads to unstable fuel quality at the furnace, decreased pulverization and conveying performance, fluctuations in ignition and burnout characteristics, and deterioration of boiler thermal conditions. In particular, alkali metal components such as potassium and sodium in biomass ash are prone to inducing slagging, fouling, and corrosion on heating surfaces under high-temperature combustion conditions, affecting not only heat exchange efficiency but also adversely impacting unit safety, environmental protection, and continuous operation. Furthermore, the seasonality, regionality, and dispersed nature of biomass supply further increases the difficulty of implementing stable, high-proportion biomass blending in large-scale coal-fired units.

[0004] In existing technologies, most biomass co-firing treatment methods remain at the stage of single pretreatment or partial optimization. For example, some schemes only focus on crushing and screening, some only emphasize dehydration and drying, and others only improve the substitution rate through fixed-ratio co-firing. These technologies usually lack the ability to quickly identify, classify, evaluate, and grade and treat multi-source heterogeneous biomass feedstocks, making it difficult to select the most suitable pretreatment path based on the differences in feedstocks. At the same time, existing pretreatment and boiler combustion processes are often isolated, lacking a linkage feedback mechanism based on operational data such as furnace temperature field, flue gas composition, and ash characteristics. This makes it impossible to dynamically adjust pretreatment strategies, fuel formulations, and combustion parameters based on slagging risk, combustion stability, and pollutant emissions. The direct consequences of this are: insufficient adaptability of the system to complex fuel sources, limited improvement in biomass co-firing ratios, difficulty in simultaneously achieving boiler operation safety, economy, and environmental protection, and insufficient synergistic utilization of usable energy sources such as power plant waste heat.

[0005] To address this, a closed-loop combustion optimization method for staged pretreatment of biomass fuels is proposed. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art, and to provide a closed-loop combustion optimization method for staged pretreatment of biomass fuel.

[0007] This invention provides a closed-loop combustion optimization method for staged pretreatment of biomass fuels, comprising the following steps: S1: Online detection is performed on the biomass feedstock used for co-firing in coal-fired power generation units to obtain characteristic parameters that characterize the combustion adaptability of the biomass feedstock, and the biomass feedstock is classified and identified according to the characteristic parameters; S2: Based on the classification and identification results, the biomass raw materials are introduced into at least one pretreatment path for graded pretreatment to obtain at least one biomass pretreatment product; S3: The biomass pretreatment products obtained through different pretreatment paths are stored in separate areas, and the mixing ratio of each type of biomass pretreatment product with pulverized coal is determined and batching is performed in combination with the boiler operating status of the coal-fired power generation unit, the quality of coal fed into the furnace, the target blending strategy, and the inventory and quality information of each storage silo. S4: The prepared biomass pretreatment product and the pulverized coal mixture are fed into the boiler of the coal-fired power generation unit for combustion, and the combustion process is monitored online. S5: Based on the online monitoring results, perform closed-loop feedback control to dynamically adjust the scheduling of the graded pretreatment path, the ratio of mixed fuels, and / or the boiler combustion operating parameters.

[0008] Further, in step S1, the characteristic parameters include at least one of the following: moisture content, particle size distribution, ash content, alkali metal content, and lower heating value; after online detection, the biomass raw material is digitally identified by the control system of the coal-fired power generation unit, and the classification information of the biomass raw material is transmitted to the subsequent pre-processing scheduling stage.

[0009] Specifically, in step S2, the pretreatment path includes one or more of the following: physical shaping path, drying and upgrading path, and pyrolysis and carbonization path. The physical shaping path includes: removing impurities, crushing and screening the biomass raw material; after screening, the portion of the crushed biomass raw material with a particle size larger than the preset upper limit particle size is returned to the crushing process or enters the sorting process, the portion with a particle size within the preset particle size range is transported to the corresponding storage silo as qualified crushed material, and the portion with a particle size smaller than the preset lower limit particle size is transported to the corresponding storage silo.

[0010] Specifically, in step S2, the drying and upgrading path is used to process the biomass raw material with a moisture content greater than a preset moisture content threshold. The low-grade heat energy from the coal-fired power generation unit is used as the drying heat source to dry the biomass raw material, and selectively molding it after drying to obtain biomass pellets.

[0011] Preferably, the low-grade thermal energy of the coal-fired power generation unit includes medium- and low-temperature flue gas after the economizer at the tail end of the boiler and / or low-pressure steam extracted from the turbine; the drying process reduces the moisture content of the biomass raw material to below 15%; and the molding process yields cylindrical particles with a diameter range of 6 to 12 mm.

[0012] Specifically, the pyrolysis carbonization pathway is used to process the biomass feedstock selected by classification and / or the biomass feedstock selected according to control instructions, and to carry out pyrolysis treatment in a pyrolysis reactor under conditions of air isolation or limited oxygen supply to obtain biochar.

[0013] Furthermore, the temperature range of the pyrolysis treatment is 250–400°C; at least some of the alkali metals in the biochar obtained by the pyrolysis treatment are fixed, and the biochar is stored as an independent fuel in a biochar bin.

[0014] Further, in step S3, the partitioned storage includes setting up multiple storage bins, which are respectively used to store qualified crushed materials, biomass powder, biomass pellets, biochar and pulverized coal; the control system of the coal-fired power generation unit determines the material taking ratio of each storage bin according to the current boiler target load, coal quality analysis data, preset biomass substitution rate target and inventory and quality information of each storage bin, and controls the feeding device corresponding to each storage bin to take materials according to the material taking ratio and then mix them.

[0015] Furthermore, in step S4, the online monitoring includes at least one of the following: obtaining the temperature field distribution inside the boiler furnace of the coal-fired power generation unit through infrared thermography and / or acoustic thermography; monitoring the concentrations of O2, CO, NOx and SO2 in the flue of the boiler; and periodically or online analyzing the chemical composition of fly ash and slag to assess slagging and corrosion trends.

[0016] Specifically, in step S5, the closed-loop feedback control includes at least one of the following: When the pretreatment path includes a pyrolysis carbonization path and an increase in the alkali metal content in fly ash or slag is detected, indicating an increased risk of slagging, the proportion of biomass feedstock entering the pyrolysis carbonization path shall be increased. When combustion instability is detected, the total biomass blending ratio and / or the proportions of different biomass pretreatment products are adjusted; when the biomass blending ratio changes, the combustion air parameters of the coal-fired power generation unit are adjusted accordingly, including the ratio and velocity of primary and secondary air; and When the pretreatment path includes a drying and upgrading path, the drying temperature and / or residence time in the drying and upgrading path are adjusted in reverse according to the combustion effect.

[0017] The beneficial effects of this invention are as follows: Compared with existing technologies, this invention constructs an integrated technical system encompassing online raw material detection and classification, graded and targeted pretreatment, multi-fuel bin zoning and dynamic proportioning, online monitoring of the combustion process, and closed-loop feedback control. This system enables differentiated treatment of heterogeneous biomass raw materials with varying moisture content, particle size, ash content, alkali metal content, and calorific value, significantly improving the adaptability of biomass fuels to co-firing conditions in coal-fired power plants. Simultaneously, through the synergistic effect of pretreatment pathways such as physical shaping, drying and upgrading, and pyrolysis carbonization, the system enhances the stability of blended fuel quality and combustion, thus improving fuel efficiency. The invention increases the biomass co-firing ratio; furthermore, by online monitoring of the furnace temperature field, flue gas composition, and chemical composition of fly ash and slag during the combustion process, combined with dynamic adjustments to the pretreatment path, fuel ratio, and boiler combustion parameters, it can effectively reduce the risks of slagging, fouling, and corrosion, and improve boiler operation safety. In addition, the invention can also utilize the low-grade thermal energy and pyrolysis by-product gases of coal-fired power generation units to achieve energy cascade utilization, reduce pretreatment energy consumption, and suppress pollutant generation by optimizing fuel ratio and combustion air parameters, thereby improving the overall economy, stability, and environmental friendliness of the system. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps of a closed-loop combustion optimization method for staged pretreatment of biomass fuel according to a specific embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown in the figure, a closed-loop combustion optimization method for staged pretreatment of biomass fuel provided by a specific embodiment of the present invention includes the following steps: S1: Online detection is performed on biomass feedstock used for co-firing in coal-fired power generating units to obtain characteristic parameters that characterize the combustion adaptability of biomass feedstock, and the biomass feedstock is classified and labeled according to the characteristic parameters; S2: Based on the classification and identification results, the biomass raw materials are introduced into at least one pretreatment pathway for graded pretreatment to obtain at least one biomass pretreatment product; S3: Store the biomass pretreatment products obtained through different pretreatment paths in separate areas, and combine the boiler operating status of the coal-fired power generation unit, the quality of the coal fed into the furnace, the target blending strategy, and the inventory and quality information of each storage silo to determine the mixing ratio of various biomass pretreatment products with pulverized coal and execute the batching. S4: The mixture of pre-treated biomass products and pulverized coal is fed into the boiler of a coal-fired power generation unit for combustion, and the combustion process is monitored online. S5: Based on the online monitoring results, perform closed-loop feedback control to dynamically adjust the scheduling of the graded pretreatment path, the ratio of mixed fuels and / or boiler combustion operating parameters to improve the adaptability of biomass fuel and optimize combustion performance. In one implementation, the control system uses a preset rule base to analyze online monitoring data and generate control commands. The rule base includes at least: When the alkali metal content in fly ash and / or slag exceeds a preset threshold for multiple consecutive sampling periods, and / or its trend indicates a continuous increase in the risk of slagging, the proportion of biomass feedstock entering the pyrolysis carbonization path should be increased. When the CO concentration in the flue exceeds the preset upper limit, the temperature field fluctuation in the boiler furnace exceeds the preset range, or the flame center position deviates abnormally, it is determined that the combustion stability has decreased, and the blended fuel formula is recalculated to adjust the total biomass blending ratio and / or the ratio between different biomass pretreatment products. When the total biomass co-firing ratio changes relative to the previous control cycle, the control system adjusts the ratio and speed of the primary and secondary air in the boiler according to the preset mapping relationship. When continuous operating data indicates that the overall performance of combustion stability, pollutant emissions, and slagging risk in a certain target moisture content range is better than the current operating conditions, the control system feeds back the result to the drying and upgrading path to correct the drying temperature and / or residence time.

[0021] Preferably, combustion adaptability refers to the degree of matching between biomass raw materials and operational requirements such as transportation, storage, batching, ignition, stable combustion, burnout, slagging, and corrosion risk control under co-firing conditions in coal-fired power generating units; the degree of matching can be comprehensively characterized by the moisture content, particle size distribution, ash content, alkali metal content, lower heating value of the raw materials, as well as the combustion stability, temperature field distribution, flue gas composition, and ash characteristics after co-firing. The target blending strategy refers to the pre-set blending control targets and feed principles to meet the requirements of safe, economic and environmental operation of the boiler. The target blending strategy may include at least the total biomass substitution rate target, the blending ratio setting under different load conditions, the optimal ratio between different pretreatment products, the slagging risk control target and / or the pollutant emission control target. Quality information refers to the parameter information used to characterize the fuel availability and combustion characteristics in each storage bin, and may include at least one or more of the following: moisture content, particle size distribution, ash content, alkali metal content, lower heating value, whether it has undergone drying and upgrading treatment, whether it has undergone pyrolysis and carbonization treatment, and the combustion characteristics information formed therefrom. The control system can also combine the boiler target load, the coal quality analysis results, the inventory and quality information of each storage bin to prioritize the above rules in order to achieve linkage optimization between pretreatment scheduling, fuel ratio and boiler combustion conditions.

[0022] Specifically, by implementing differentiated treatment for biomass raw materials of different sources and qualities, the adaptability of biomass raw materials to the co-firing conditions of coal-fired power generation units is improved. During the combustion process, the pretreatment and batching strategies are dynamically adjusted based on online monitoring results to ensure the safe, stable and clean operation of the boiler.

[0023] Furthermore, biomass feedstocks can be agricultural and forestry waste, woody biomass, and other biomass fuels suitable for co-firing with coal-fired power plants. Since biomass from different sources varies significantly in terms of moisture content, particle size distribution, ash content, alkali metal content, and calorific value, online detection and classification can provide a basis for subsequent diversion to different pretreatment pathways, thereby avoiding the problems of poor adaptability, high energy consumption, and large fluctuations in combustion performance caused by using a single pretreatment process.

[0024] Furthermore, this invention does not limit the specific equipment structure, but focuses on defining the functional relationships, control relationships, and feedback logic between each process step. Those skilled in the art can select suitable detection instruments, crushing and screening equipment, drying equipment, forming equipment, pyrolysis reactors, storage devices, feeding devices, and control systems to implement the method of this invention based on the existing equipment conditions of the power plant.

[0025] Based on the above basic implementation method, in step S1, the characteristic parameters include at least one of the following: moisture content, particle size distribution, ash content, alkali metal content, and lower heating value; after online detection, the biomass raw materials are digitally identified by the control system of the coal-fired power generation unit, and the classification information of the biomass raw materials is transmitted to the subsequent pre-processing scheduling stage.

[0026] Furthermore, the online detection in step S1 can be completed by a rapid detection unit set on the raw material conveying path. The rapid detection unit can perform real-time measurement and data recording of each batch or continuous flow of biomass raw materials, and transmit the detection results to the control system so that the subsequent scheduling system can automatically classify the raw materials according to preset rules or algorithms.

[0027] In one specific embodiment, in step S2, the pretreatment path includes one or more of the following: physical shaping path, drying and upgrading path, and pyrolysis and carbonization path. The physical shaping path includes: removing impurities, crushing and screening the biomass raw material; after screening, the portion of the crushed biomass raw material with a particle size larger than the preset upper limit particle size is returned to the crushing process or enters the sorting process, the portion with a particle size within the preset particle size range is transported to the corresponding storage silo as qualified crushed material, and the portion with a particle size smaller than the preset lower limit particle size is transported to the corresponding storage silo.

[0028] In this embodiment, the physical shaping path serves as a basic pretreatment path, enabling uniform size shaping and impurity removal of biomass raw materials entering the system, thereby obtaining basic materials that meet the requirements for subsequent transportation, storage, and batching. By first removing ferromagnetic impurities and large debris, followed by coarse crushing and screening, the adverse effects of foreign matter on the operation of subsequent equipment can be reduced, and the impact of fuel particle size fluctuations on blending uniformity and combustion stability can be mitigated.

[0029] Furthermore, the crushing equipment in the physical shaping path can adjust the crushing parameters according to the initial particle size of the raw material, so that the material is crushed to below the uniform maximum size. After screening, the portion with a particle size within the preset particle size range is used as qualified crushed material and enters the corresponding storage bin for subsequent batching with other biomass pretreatment products and coal powder. The portion with an excessively large particle size is returned to crushing or enters manual sorting, which can avoid large particles from directly entering the storage bin and affecting the feeding stability. The portion with an excessively small particle size enters the corresponding storage bin separately, which can avoid repeated crushing and additional energy waste.

[0030] In another specific embodiment, in step S2, the drying and upgrading path is used to process the biomass raw material with a moisture content greater than a preset moisture content threshold. Low-grade heat energy from a coal-fired power plant is used as a drying heat source to dry the biomass raw material, and selective molding is performed after drying to obtain biomass pellets. The low-grade heat energy from the coal-fired power plant includes medium- and low-temperature flue gas after the economizer at the tail end of the boiler and / or low-pressure extraction steam from the turbine. The drying process reduces the moisture content of the biomass raw material to below 15%, and the molding process yields cylindrical pellets with a diameter range of 6 to 12 mm.

[0031] In this embodiment, the drying and upgrading path mainly targets biomass feedstocks with high moisture content, where direct co-firing would significantly affect pulverization and combustion efficiency. By utilizing the existing low-grade heat energy of the coal-fired power plant to dry the high-moisture feedstock, the moisture content of the feedstock can be effectively reduced, improving its calorific value utilization efficiency and combustion stability, while avoiding the introduction of additional high-quality heat sources that would increase system energy consumption.

[0032] Specifically, the drying device can employ equipment such as a rotary drying drum, allowing the material to exchange heat with the heat medium in a countercurrent or cocurrent manner, achieving dehydration without significantly damaging the fiber structure of the raw material. After drying, the material can be selected to enter a molding machine based on subsequent conveying and storage requirements. After being extruded under high pressure to form cylindrical granules, the bulk density and mechanical strength of the material can be significantly improved, along with its flowability and long-distance conveying performance.

[0033] Furthermore, by processing the dried raw materials into biomass pellets and storing them in corresponding storage silos, they can be mixed with qualified crushed materials, biochar, and pulverized coal during subsequent batching, thereby providing the control system with more fuel combination options and enabling it to flexibly select a better co-firing scheme according to the boiler's operating conditions.

[0034] In another specific embodiment, the pyrolysis carbonization pathway is used to process biomass feedstocks selected by classification and / or selected according to control instructions, and to carry out pyrolysis in a pyrolysis reactor under conditions of air isolation or limited oxygen supply to obtain biochar; the volatile gases generated by pyrolysis are purified and used as a supplementary and / or separately utilized drying heat source; the temperature range of the pyrolysis treatment is 250 to 400°C; at least a portion of the alkali metals in the biochar obtained by pyrolysis treatment are fixed, and the biochar is stored as an independent fuel in a biochar bin.

[0035] Furthermore, the pyrolysis carbonization pathway is mainly suitable for woody raw materials or other biomass raw materials that can obtain good combustion adaptability after pyrolysis. It can also be used to temporarily switch some raw materials to the pyrolysis carbonization pathway based on closed-loop control results to improve the overall combustion stability of the mixed fuel. Biochar obtained through pyrolysis has combustion characteristics closer to coal and helps reduce the risk of volatilization and deposition of some alkali metals in the high-temperature zone of the boiler.

[0036] Specifically, the volatile gases generated during pyrolysis, after purification, can be reused as an auxiliary heat source in the drying and upgrading process, achieving energy coupling and cascade utilization between different pretreatment paths; while the solid product, biochar, enters an independent storage silo to participate in subsequent blending. In this way, not only is the energy utilization efficiency of biomass feedstock improved, but the system's fuel regulation capability under different boiler loads and different blending ratios is also enhanced.

[0037] In another specific embodiment, in step S3, the partitioned storage includes setting up multiple storage bins, which are respectively used to store qualified crushed materials, biomass pellets, biochar and pulverized coal; the control system of the coal-fired power generation unit determines the material taking ratio of each storage bin according to the current boiler target load, coal quality analysis data, preset biomass substitution rate target and inventory and quality information of each storage bin, and controls the feeding device corresponding to each storage bin to take materials according to the material taking ratio and then mix them.

[0038] Furthermore, by storing the products obtained from different pretreatment paths in separate zones, fuels of different qualities and combustion characteristics can remain relatively independent before entering the boiler. This allows the control system to flexibly call upon these fuels according to real-time operational needs during subsequent batching processes, without having to pre-mix all raw materials, thereby improving the precision and adjustability of the batching.

[0039] Specifically, the optimization module in the control system can calculate the fuel extraction formula in real time based on the boiler target load, coal quality analysis data, biomass total substitution rate target, and inventory and quality information of each storage bin. For example, when the boiler is operating at a high and stable load, the proportion of biochar and biomass pellets in the mixed fuel can be appropriately increased; when a rapid response to load changes or improvement of ignition conditions is required, the proportion of qualified crushed material in the mixed fuel can be appropriately increased. The feeding device under each storage bin can adopt a variable frequency screw feeder or similar form to achieve precise feeding of various fuels. All extracted fuel can be preliminarily and uniformly mixed by a mixer before entering the conveying system to improve the consistency of the fuel composition entering the furnace.

[0040] In another specific embodiment, in step S4, online monitoring includes at least one of the following: obtaining the temperature field distribution inside the boiler furnace of the coal-fired power generation unit through infrared thermography and / or acoustic thermography; monitoring the concentrations of O2, CO, NOx and SO2 in the boiler flue; and periodically or online analyzing the chemical composition of fly ash and slag to assess slagging and corrosion trends.

[0041] Furthermore, the online monitoring system can be deployed in key areas such as the boiler furnace, flue, and ash collection points to continuously acquire data characterizing the combustion status, pollutant emissions, and slagging corrosion risk, and transmit the relevant monitoring data to the control system in real time for subsequent closed-loop feedback control.

[0042] Furthermore, by monitoring the temperature field distribution within the furnace, the location of the flame center, combustion uniformity, and the distribution of localized high-temperature areas can be determined. Continuous monitoring of O2, CO, NOx, and SO2 concentrations allows for the assessment of excess air coefficients, combustion completeness, and pollutant formation. Analysis of the chemical composition of fly ash and slag, particularly the alkali metal content, enables early prediction of slagging, fouling, and corrosion risks on boiler heating surfaces. Thus, the system can proactively adjust systems before risks escalate into actual failures.

[0043] In one specific implementation, in step S5, the closed-loop feedback control includes at least one of the following: when the pretreatment path includes a pyrolysis and carbonization path and an increase in the alkali metal content in fly ash or slag is detected, indicating an increased risk of slagging, the proportion of biomass raw materials entering the pyrolysis and carbonization path is increased; when combustion instability is detected, the total biomass blending ratio and / or the ratio between different biomass pretreatment products are adjusted; when the biomass blending ratio changes, the combustion air parameters of the coal-fired power generation unit are adjusted in a linked manner, including the ratio of primary and secondary air and the wind speed; when the pretreatment path includes a drying and upgrading path, the drying temperature and / or residence time in the drying and upgrading path are adjusted in reverse according to the combustion effect; in this specification, combustion instability can be characterized by at least one of the following: boiler furnace temperature Increased temperature field fluctuations, shift in flame center position, abnormal expansion of local high-temperature or low-temperature zones, increased CO concentration in flue gas, decreased burnout, or deviations of relevant parameters characterizing complete combustion and excess air coefficient from the preset operating range; increased slagging risk can be characterized by at least one of the following: continuously increasing alkali metal content in fly ash and / or slag, expansion of local high-temperature zones in the boiler furnace, ash and slag characteristic analysis results showing increased tendency for slagging, fouling, or corrosion on heating surfaces, or continuous deviations of relevant operating parameters from the preset safe operating range; based on combustion effect, it refers to the reverse correction of drying temperature and / or residence time in the drying and upgrading path based on one or more of the following: combustion stability, burnout, boiler furnace temperature field distribution, flue gas composition, slagging and corrosion trends, and pollutant emissions.

[0044] Specifically, the control system can compare the data obtained from online monitoring with preset safe operating ranges, economic operating ranges, and environmentally friendly operating ranges, and generate control commands based on rule base models, experience models, and / or intelligent algorithms. These control commands can be applied to raw material diversion and path scheduling at the front end of the pretreatment system, to mixing ratios in the fuel management stage, and to primary and secondary air regulation in the boiler combustion system, thus forming a closed-loop control mechanism that links multiple stages.

[0045] Furthermore, when the system determines that the alkali metal content in fly ash continues to rise and the risk of slagging increases, the proportion of raw materials sent to the pyrolysis and carbonization path can be increased to reduce the volatilization and deposition of alkali metals such as potassium and sodium during combustion by using the fixation effect of the pyrolysis process. When the system detects an increase in CO concentration or an aggravation of furnace temperature field fluctuations, indicating a decrease in combustion stability, the mixed fuel formula can be recalculated, the proportion of a certain biomass with large fluctuations can be appropriately reduced, or the ratio between different biomass pretreatment products can be adjusted to improve ignition and burnout conditions.

[0046] In one specific embodiment, the present invention is applied to a biomass co-firing scenario in a large-scale coal-fired power plant. Incoming biomass feedstock first enters the feedstock receiving area, where it undergoes preliminary cleaning (iron removal and removal of large debris) before entering the online detection area. This online detection area integrates a moisture content analyzer, particle size analyzer, ash content analyzer, alkali metal prediction detector, and low-calorific-value rapid estimation device. These devices are used to monitor the continuously flowing biomass feedstock in real time and transmit the results to the central control system. The central control system digitally identifies the feedstock based on preset classification thresholds. Feedstock with a moisture content greater than 35% is identified as suitable for the drying and upgrading path, while feedstock with an alkali metal content greater than 1.5% is identified as high-risk feedstock for slagging and suitable for the pyrolysis and carbonization path. The pretreatment system includes three process lines: a physical crushing and screening line, a waste heat drying and forming line, and a low-temperature pyrolysis and carbonization line. All identified biomass feedstock first enters the physical crushing and screening line, where it is crushed to a maximum particle size of less than 50mm in a hammer crusher, and then graded by a multi-layer vibrating screen. After screening, particles larger than the preset upper limit are returned to crushing or entered into manual sorting; particles with a diameter between 10 and 50 mm are transported to the corresponding storage bin as qualified crushed material; particles smaller than the preset lower limit are transported to the corresponding storage bin to avoid increased energy consumption caused by repeated crushing.

[0047] In this embodiment, biomass raw materials identified as high-moisture by online detection are introduced into a waste heat drying and forming line after physical crushing and screening. The drying heat source is low-grade thermal energy from a coal-fired power plant, specifically low-temperature flue gas after the economizer at the boiler tail and / or low-pressure extraction steam from the turbine, wherein the temperature of the low-temperature flue gas can be 120-200℃. The high-moisture biomass raw materials are in countercurrent contact with the heat medium in a rotary drying drum until the moisture content drops below 15%. The dried material is selectively fed into a forming machine according to subsequent batching requirements, where it is extruded under high pressure to form cylindrical particles with a diameter of 6-12mm, and then sent to a biomass pellet silo for storage. For woody raw materials selected by classification and / or some biomass raw materials selected according to control instructions, they are sent to a low-temperature pyrolysis carbonization line after completing the pre-treatment. The raw materials are pyrolyzed in a pyrolysis reactor under conditions of air isolation or limited oxygen supply, with the pyrolysis temperature controlled at 250-400℃. The volatile gases generated during pyrolysis are purified and then returned to the drying system as a supplementary heat source. The solid residue is biochar. At least some of the alkali metals in the obtained biochar are fixed and transported to the biochar silo for storage as an independent fuel.

[0048] Specifically, the system is equipped with multiple storage bins for storing qualified scrap, biomass pellets, biochar, and pulverized coal. The optimization module of the central control system calculates the fuel extraction formula in real time based on the current boiler target load, coal quality analysis data, preset biomass total substitution rate target, and inventory and quality information of each storage bin. It then controls the variable frequency screw feeders below each storage bin to precisely extract materials according to the formula. Before entering the boiler conveying system, the extracted qualified scrap, biomass pellets, biochar, and pulverized coal are first mixed in a mixer to form a mixed fuel for the boiler. The prepared mixed fuel is then fed into the burner area of ​​the coal-fired power plant boiler via an existing or modified conveying system for combustion. During combustion, monitoring systems deployed at key boiler locations operate continuously: acquiring the temperature field distribution within the boiler furnace through infrared and / or acoustic temperature measurement; continuously monitoring the concentrations of O2, CO, NOx, and SO2 in the flue; and periodically or online analyzing the chemical composition of fly ash and slag, especially the alkali metal content, to assess slagging and corrosion trends. All monitoring data is transmitted to the control system in real time. The intelligent control model in the control system compares the monitoring data with the preset safe operating range, economic operating range, and environmentally friendly operating range, and generates closed-loop control commands. When the alkali metal content in fly ash or slag is continuously increased, indicating an increased risk of slagging, the control system increases the proportion of raw materials entering the pyrolysis and carbonization path to enhance the fixation of alkali metals. When the CO concentration increases or the furnace temperature field fluctuates more, indicating unstable combustion, the control system recalculates the blended fuel formula and adjusts the total biomass blending ratio and / or the ratio between different biomass pretreatment products. When the biomass blending ratio changes, the control system adjusts the ratio and velocity of the primary and secondary air in the boiler to adapt to the rapid volatilization and ignition characteristics of biomass and to suppress NOx formation. When long-term operation results indicate a certain degree of dryness... When the biomass combustion effect is better, the control system feeds the result back to the drying and upgrading path, and reverses the set values ​​of drying temperature and residence time. Through the above implementation method, the classification and processing of multi-source heterogeneous biomass raw materials and the enhancement of adaptability can be realized. Through online monitoring and closed-loop feedback control during the combustion process, the combustion stability of biomass co-firing process can be improved, the risks of slagging, corrosion and pollutant emissions can be reduced, and the cascade utilization of low-grade heat energy in power plants can be realized. In contrast, a co-firing method that only performs conventional crushing and screening of biomass raw materials without drying and upgrading, pyrolysis and carbonization and closed-loop feedback control is used under similar boiler load and coal quality conditions.Compared with the comparative example, in the embodiments of the present invention, due to the classification and diversion of biomass raw materials of different qualities, and the linkage adjustment of pretreatment path, mixed fuel ratio and combustion air parameters in combination with online monitoring results, the boiler furnace temperature field distribution is more uniform, the CO concentration fluctuation is smaller, and the risk of alkali metal-related slagging in fly ash and slag is more easily controlled. This indicates that the method of the present invention has better overall performance in terms of combustion stability, slagging risk control and biomass co-firing adaptability.

[0049] To aid in a better understanding of the present invention, a more comprehensive and specific embodiment is described, in which the present invention provides a closed-loop combustion optimization method for staged pretreatment of biomass fuels, comprising the following steps: S1: Online detection is performed on biomass feedstock used for co-firing in coal-fired power generating units to obtain characteristic parameters that characterize the combustion adaptability of biomass feedstock, and the biomass feedstock is classified and labeled according to the characteristic parameters; S2: Based on the classification and identification results, the biomass raw materials are introduced into at least one pretreatment pathway for graded pretreatment to obtain at least one biomass pretreatment product; S3: Store the biomass pretreatment products obtained through different pretreatment paths in separate areas, and combine the boiler operating status of the coal-fired power generation unit, the quality of the coal fed into the furnace, the target blending strategy, and the inventory and quality information of each storage silo to determine the mixing ratio of various biomass pretreatment products with pulverized coal and execute the batching. S4: The mixture of pre-treated biomass products and pulverized coal is fed into the boiler of a coal-fired power generation unit for combustion, and the combustion process is monitored online. S5: Based on the online monitoring results, perform closed-loop feedback control to dynamically adjust the scheduling of the graded pretreatment path, the ratio of mixed fuels, and / or boiler combustion operating parameters to improve the adaptability of biomass fuel and optimize combustion performance.

[0050] In this embodiment, in step S1, the characteristic parameters include at least one of the following: moisture content, particle size distribution, ash content, alkali metal content, and lower heating value; after online detection, the biomass raw material is digitally identified by the control system of the coal-fired power generation unit, and the classification information of the biomass raw material is transmitted to the subsequent pre-processing scheduling stage; in step S2, the pre-processing path includes one or more of the following: physical shaping path, drying and upgrading path, and pyrolysis and carbonization path. The physical shaping path includes: removing impurities, crushing, and screening the biomass raw material; after screening, in the crushed biomass raw material, the portion with a particle size larger than the preset upper limit particle size is returned to the crushing process or enters the sorting process, the portion with a particle size within the preset particle size range is transported as qualified crushed material to the corresponding storage silo, and the portion with a particle size smaller than the preset lower limit particle size is transported to the corresponding storage silo; in step S2, the drying and upgrading path is used to process the biomass raw material with a moisture content greater than the preset moisture content threshold, utilizing... Low-grade heat energy from coal-fired power plants is used as a drying heat source to dry biomass feedstock, and selective molding is performed after drying to obtain biomass pellets. The low-grade heat energy from the coal-fired power plants includes medium- and low-temperature flue gas after the economizer at the boiler tail and / or low-pressure extraction steam from the turbine. The drying process reduces the moisture content of the biomass feedstock to below 15%, and the molding process yields cylindrical pellets with a diameter range of 6–12 mm. The pyrolysis carbonization path is used to process biomass feedstock selected by classification and / or selected according to control instructions. Pyrolysis is carried out in a pyrolysis reactor under conditions of air isolation or limited oxygen supply to obtain biochar. The volatile gases generated by pyrolysis are purified and used as a supplementary drying heat source and / or utilized separately. The temperature range of the pyrolysis process is 250–400 °C. At least some alkali metals are fixed in the biochar obtained by pyrolysis, and the biochar is stored as an independent fuel in a biochar bin.

[0051] Specifically, in step S3, the zoned storage includes setting up multiple storage bins, which are used to store qualified crushed materials, biomass pellets, biochar, and pulverized coal, respectively. The control system of the coal-fired power generation unit determines the material extraction ratio for each storage bin based on the current boiler target load, coal quality analysis data, preset biomass substitution rate target, and inventory and quality information of each storage bin. It then controls the feeding device corresponding to each storage bin to extract and mix the materials according to the extraction ratio. In step S4, online monitoring includes at least one of the following: obtaining the temperature field distribution inside the boiler furnace of the coal-fired power generation unit through infrared thermography and / or acoustic thermography; monitoring the concentrations of O2, CO, NOx, and SO2 in the boiler flue; and chemical analysis of fly ash and slag. The components are analyzed periodically or online to assess slagging and corrosion trends. In step S5, closed-loop feedback control includes at least one of the following: when the pretreatment path includes a pyrolysis and carbonization path and an increase in alkali metal content in fly ash or slag is detected, indicating an increased risk of slagging, the proportion of biomass feedstock entering the pyrolysis and carbonization path is increased; when combustion instability is detected, the total biomass blending ratio and / or the ratio between different biomass pretreatment products are adjusted; when the biomass blending ratio changes, the combustion air parameters of the coal-fired power generation unit are adjusted in a linked manner, including the ratio and velocity of primary and secondary air; when the pretreatment path includes a drying and upgrading path, the drying temperature and / or residence time in the drying and upgrading path are adjusted in reverse according to the combustion effect.

[0052] In summary, the embodiments disclosed herein have at least the following technical effects: This invention enables online detection, classification, and labeling of biomass raw materials, and diverts them to different pretreatment paths based on characteristics such as moisture content, particle size, alkali metal content, and calorific value. This allows for differentiated treatment of biomass from different sources and of different qualities, overcoming the problem that existing technologies only use a single crushing or drying process and are difficult to adapt to complex raw material fluctuations. This broadens the sources of usable biomass fuel and improves the adaptability and stability of raw material supply. This invention constructs a process system of "graded pretreatment - multi-fuel bin zoned storage - dynamic intelligent blending", which can flexibly determine the mixing ratio between qualified crushed materials, biomass pellets, biochar and pulverized coal according to the real-time load of the boiler, the quality of the coal fed into the furnace and the target blending strategy. This allows different fuel forms to complement each other's advantages, thereby improving the consistency of the quality of the blended fuel, enhancing ignition, stable combustion and burnout performance, and providing support for large coal-fired units to implement higher proportions of biomass blending. To address the issue of high potassium and sodium alkali metal content in biomass ash, which easily leads to slagging and corrosion at high temperatures, this invention addresses two main problems. First, it guides high-risk raw materials to appropriate treatment pathways through online detection and classification. Second, it fixes some alkali metals through pyrolysis and carbonization. Third, by combining monitoring of the chemical composition and alkali metal content of fly ash and slag, the proportion of pyrolysis pathways can be dynamically increased when the risk of slagging rises, thus reducing the risk of slagging, fouling, and corrosion on boiler heating surfaces from both the source and the operation process. This invention does not separate pretreatment from combustion. Instead, it dynamically optimizes pretreatment path weights, blending ratios, primary and secondary air parameters, and drying parameters by online monitoring of the furnace temperature field, flue gas composition, and ash characteristics, and feeding the monitoring results back to raw material scheduling, fuel ratio, and boiler combustion condition adjustment. Compared to existing technologies where pretreatment and combustion are independent, this invention enables proactive intervention, which is more conducive to maintaining safe, economical, and environmentally friendly boiler operation. This invention utilizes the low-grade thermal energy of the coal-fired power generation unit itself, such as the medium- and low-temperature flue gas after the economizer at the boiler tail and / or the low-pressure steam extracted from the turbine, to dry high-moisture biomass. Simultaneously, the volatile gases generated during pyrolysis, after purification, can be used as a supplementary drying heat source or utilized separately. This reduces the need for external heating sources, lowers the additional energy consumption in the pretreatment stage, and improves the overall energy utilization efficiency within the power plant.

[0053] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A closed-loop combustion optimization method for staged pretreatment of biomass fuel, characterized in that, Includes the following steps: S1: Online detection is performed on the biomass feedstock used for co-firing in coal-fired power generation units to obtain characteristic parameters that characterize the combustion adaptability of the biomass feedstock, and the biomass feedstock is classified and identified according to the characteristic parameters; S2: Based on the classification and identification results, the biomass raw materials are introduced into at least one pretreatment path for graded pretreatment to obtain at least one biomass pretreatment product; S3: The biomass pretreatment products obtained through different pretreatment paths are stored in separate areas, and the mixing ratio of each type of biomass pretreatment product with pulverized coal is determined and batching is performed in combination with the boiler operating status of the coal-fired power generation unit, the quality of coal fed into the furnace, the target blending strategy, and the inventory and quality information of each storage silo. S4: The prepared biomass pretreatment product and the pulverized coal mixture are fed into the boiler of the coal-fired power generation unit for combustion, and the combustion process is monitored online. S5: Based on the online monitoring results, perform closed-loop feedback control to dynamically adjust the scheduling of the graded pretreatment path, the ratio of mixed fuels, and / or the boiler combustion operating parameters.

2. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 1, characterized in that, In step S1, the characteristic parameters include at least one of the following: moisture content, particle size distribution, ash content, alkali metal content, and lower heating value; after online detection, the biomass raw material is digitally identified by the control system of the coal-fired power generation unit, and the classification information of the biomass raw material is transmitted to the subsequent pre-processing scheduling stage.

3. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 1, characterized in that, In step S2, the pretreatment path includes one or more of the following: physical shaping path, drying and upgrading path, and pyrolysis and carbonization path. The physical shaping path includes: removing impurities, crushing and screening the biomass raw material; after screening, the portion of the crushed biomass raw material with a particle size larger than the preset upper limit particle size is returned to the crushing process or enters the sorting process, the portion with a particle size within the preset particle size range is transported to the corresponding storage silo as qualified crushed material, and the portion with a particle size smaller than the preset lower limit particle size is transported to the corresponding storage silo.

4. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 3, characterized in that, In step S2, the drying and upgrading path is used to process the biomass raw material with a moisture content greater than a preset moisture content threshold. The low-grade heat energy from the coal-fired power generation unit is used as the drying heat source to dry the biomass raw material, and selectively molding it after drying to obtain biomass pellets.

5. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 4, characterized in that, The low-grade thermal energy of the coal-fired power generation unit includes medium- and low-temperature flue gas after the economizer at the tail end of the boiler and / or low-pressure steam extracted from the turbine; the drying process reduces the moisture content of the biomass raw material to below 15%; and the molding process yields cylindrical particles with a diameter range of 6 to 12 mm.

6. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 3, characterized in that, The pyrolysis carbonization pathway is used to process the biomass feedstock selected by classification and / or the biomass feedstock selected according to control instructions, and to carry out pyrolysis in a pyrolysis reactor under conditions of air isolation or limited oxygen supply to obtain biochar.

7. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 6, characterized in that, The temperature range of the pyrolysis treatment is 250 to 400°C; at least some of the alkali metals in the biochar obtained by the pyrolysis treatment are fixed, and the biochar is stored as an independent fuel in a biochar bin.

8. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 1, characterized in that, In step S3, the partitioned storage includes setting up multiple storage bins, which are respectively used to store qualified crushed materials, biomass powder, biomass pellets, biochar, and pulverized coal. The control system of the coal-fired power generation unit determines the material taking ratio of each storage bin based on the current boiler target load, coal quality analysis data, preset biomass substitution rate target, and inventory and quality information of each storage bin, and controls the feeding device corresponding to each storage bin to take materials according to the material taking ratio and then mix them.

9. The biomass fuel staged pretreatment closed-loop combustion optimization method according to claim 1, characterized in that, In step S4, the online monitoring includes at least one of the following: obtaining the temperature field distribution inside the boiler furnace of the coal-fired power generation unit by infrared thermometry and / or acoustic thermometry; monitoring the concentrations of O2, CO, NOx and SO2 in the flue of the boiler; and periodically or online analyzing the chemical composition of fly ash and slag to assess slagging and corrosion trends.

10. The biomass fuel staged pretreatment closed-loop combustion optimization method according to any one of claims 1 to 9, characterized in that: In step S5, the closed-loop feedback control includes at least one of the following: When the pretreatment path includes a pyrolysis carbonization path and an increase in the alkali metal content in fly ash or slag is detected, indicating an increased risk of slagging, the proportion of biomass feedstock entering the pyrolysis carbonization path shall be increased. When combustion instability is detected, the total biomass blending ratio and / or the proportions of different biomass pretreatment products are adjusted; when the biomass blending ratio changes, the combustion air parameters of the coal-fired power generation unit are adjusted accordingly, including the ratio and velocity of primary and secondary air; and When the pretreatment path includes a drying and upgrading path, the drying temperature and / or residence time in the drying and upgrading path are adjusted in reverse according to the combustion effect.

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