System and control method for coupling low-load stable combustion and blending combustion of pulverized coal boiler

Abstract

The present application belongs to the field of coupling power generation, and provides a system and a control method for coupling a pulverized coal boiler low-load stable combustion and blending combustion. The system comprises two paths of cold air from a boiler primary air fan, one of which is directly transmitted to a cold air main pipe, and the other is transmitted to a hot air main pipe after being preheated by a preheater; a coal mill respectively takes cold air and hot air from the cold air main pipe and the hot air main pipe, mixes them to a set temperature, and then enters the coal mill for drying of the pulverized coal and sending the dried pulverized coal to the furnace of the pulverized coal boiler for combustion; a biomass gasifier respectively takes cold air and hot air from the cold air main pipe and the hot air main pipe, mixes them to a set temperature, and then enters the biomass gasifier; biomass material is gasified in the biomass gasifier to generate carbonized products of biomass charcoal and biogas; the carbonized product of biomass charcoal is transported to the coal mill to be ground together with raw coal, and then is blown to the pulverized coal boiler for combustion in the furnace; and the biogas is directly introduced into the pulverized coal boiler for combustion in the furnace.

Description

Technical Field

[0001] This invention belongs to the field of coupled power generation, and particularly relates to a coupled pulverized coal boiler low-load stable combustion and co-firing system and control method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Biomass energy is a renewable energy source that can replace coal, oil, and natural gas. It has low sulfur and nitrogen content, produces near-zero carbon emissions, and, when combined with carbon capture and storage technologies, can achieve negative carbon emissions. Therefore, vigorously promoting biomass power generation is of strategic significance to global sustainable development. Coal-coated biomass power generation technology plays a significant role in replacing fossil fuel consumption. This technology combines coal-fired power plants with biomass utilization, achieving complementary advantages, helping to reduce greenhouse gas emissions, and is an effective means to address overcapacity in coal-fired power generation, accelerate the transformation and upgrading of power generation, and gradually achieve green and low-carbon power generation.

[0004] Coal-to-biomass power generation can generally be divided into three types: direct combustion coupled power generation, parallel coupled power generation, and gasification coupled power generation. Direct combustion coupled power generation: that is, coal and biomass are mixed and burned in a boiler. Direct combustion coupled power generation is divided into three schemes: (1) coal and biomass are ground and burned in the same furnace; (2) coal and biomass are ground separately and burned in the same furnace; (3) coal and biomass are ground separately and burned in different furnaces, such as Figure 1 As shown. Currently, coal-fired biomass power generation mainly utilizes direct combustion coupling technology, which requires only slight modifications to existing generator sets. This coupling technology can effectively reduce investment in unit modifications, and biomass power generation has high efficiency. However, direct combustion coupling has high requirements for biomass fuel, and various schemes have certain difficulties. Scheme 1 feeds biomass into the coal mill of raw coal. Usually, the biomass needs to be dried and extruded into pellets. However, due to the large amount of long fibers in biomass, it is difficult to crush it to a fineness comparable to coal powder in medium-speed coal mills or other grinding mills. The addition of biomass will significantly reduce the grinding output of the original coal mill, and the blending ratio is only about 2%. Schemes 2 and 3 both require the installation of biomass pretreatment equipment, usually mechanical cutting and crushing. It is difficult to guarantee the fineness of biomass powder, and the pretreatment equipment has a short lifespan and requires frequent maintenance and replacement.

[0005] like Figure 2 The parallel-coupled power generation system shown involves coal and biomass undergoing fuel pretreatment and pre-combustion in independent systems, with the generated steam sharing a single turbine system for power generation. Parallel coupling allows for the selection and optimization of adaptive combustion systems based on the characteristics of each fuel, and the coal-to-biomass coupling ratio has no impact on the parallel power generation system. However, parallel-coupled systems are complex, requiring separate incinerators and flue gas treatment systems, resulting in excessively high investment costs.

[0006] like Figure 3 The gasification-coupled power generation shown involves pre-gasifying biomass, where the resulting gas is mixed with coal in a boiler for combustion. Because gasifiers are highly adaptable to biomass fuels, gasification-coupled power generation reduces the fuel quality requirements of the biomass conversion process. The crude syngas produced from biomass gasification is fed into a coal-fired boiler for coupled combustion with coal. The subsequent stages can utilize existing equipment in the coal-fired power plant for power generation and flue gas purification. However, gasification-coupled power generation requires a gasifier and purification system, resulting in high investment costs. Furthermore, the ash residue from gasification is typically only recovered as organic fertilizer and is difficult to utilize locally.

[0007] In summary, existing coupled power generation technologies cannot simultaneously reduce carbon emissions during high-load operation of the unit and solve the problems of boiler ignition and stable combustion at low loads. Summary of the Invention

[0008] To address the technical problems mentioned above, this invention provides a coupled pulverized coal boiler low-load stable combustion and co-firing system and control method. It utilizes biomass gasification gas and solid phases to couple pulverized coal, which can reduce carbon emissions during high-load operation of the unit and solve the problems of boiler ignition and low-load stable combustion by co-firing biomass gas.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] The first aspect of the present invention provides a coupled pulverized coal boiler low-load stable combustion and co-firing system.

[0011] A coupled pulverized coal boiler low-load stable combustion and co-firing system includes: a boiler primary air fan, a preheater, a coal mill, a biomass gasifier, a pulverized coal boiler, a cold air header and a hot air header; the cold air from the boiler primary air fan is divided into two paths, one of which is directly delivered to the cold air header, and the other is preheated by the preheater and then delivered to the hot air header.

[0012] The coal mill draws cold air from the cold air header and hot air from the hot air header respectively, mixes them to the set temperature, and then enters the coal mill for coal powder drying. The dried coal powder is then sent to the corresponding burner of the coal pulverized boiler for combustion.

[0013] The biomass gasifier draws cold air from the cold air header and hot air from the hot air header, respectively, mixes them to a set temperature, and then enters the biomass gasifier. The biomass material is gasified in the biomass gasifier to generate carbonized products, biochar and biogas. The carbonized products, biochar, are transported to a coal mill and ground together with the raw coal, and then blown into a pulverized coal boiler for combustion in the furnace. The biogas directly enters the pulverized coal boiler for combustion in the furnace.

[0014] In one embodiment, the coal mill is connected to a first cold air sub-pipe and a first hot air sub-pipe via a first air mixing pipe. The first cold air sub-pipe is connected to a cold air main pipe, and the first hot air sub-pipe is connected to a hot air main pipe.

[0015] In one embodiment, the biomass gasifier is connected to a second cold air sub-pipe and a second hot air sub-pipe via a second air mixing pipe. The second cold air sub-pipe is connected to a cold air main pipe, and the second hot air sub-pipe is connected to a hot air main pipe.

[0016] In one implementation, the biomass gasifier is arranged in the operating layer between the coal bunkers.

[0017] In one embodiment, the carbonization product, biochar, is conveyed to a coal mill via a screw conveyor located at the bottom of the biomass gasifier.

[0018] A second aspect of the present invention provides a control method for a coupled pulverized coal boiler low-load stable combustion and co-firing system.

[0019] A control method for a coupled low-load stable combustion and co-firing system of a pulverized coal boiler includes:

[0020] Each coal mill is started one by one to complete the boiler ignition and load increase process;

[0021] When the boiler starts to reduce its output from full load, the top burner is shut down until the load drops to a set percentage. When the boiler load decreases further, biomass gas is provided by the biomass gasifier for combustion assistance.

[0022] The temperature and volume of the air entering the biomass gasifier are adjusted according to the combustion conditions of the biomass gasifier, thereby adjusting the calorific value of the biomass gas and generating biochar at the bottom of the biomass gasifier. The biochar is then matched and fed into the corresponding coal mill based on the combustion conditions of the corresponding burner.

[0023] In one implementation method, if the boiler load drops to a set threshold, the pulverized coal burners on each floor are shut down sequentially until the boiler is safely shut down.

[0024] As one implementation method, if the boiler load gradually increases, the output of the biomass gasifier is gradually reduced until the biomass gasifier is taken out of service.

[0025] As one implementation method, life

[0026] The expression for the calorific value of biomass gas is:

[0027]

[0028]

[0029] in, These represent the content of each component in the biomass gas;

[0030] With the total air volume remaining constant, increasing the inlet air temperature reduces the amount of biomass consumed in the oxidation zone of the gasifier to provide heat. This reduction in CO2 content in the biomass gas will... Increasing the inlet air temperature proportionally increases the calorific value of biomass gas; conversely, when the total air volume remains constant, decreasing the inlet air temperature increases biomass consumption and decreases the calorific value of biomass gas.

[0031] As one implementation method, the temperature of the hot air is assumed to be T. 热 The flow rate of the hot air is M. 热 The temperature of the cold air is T. 冷 The airflow rate of the cold air is M. 冷 The temperature of the mixed air entering the biomass gasification furnace is then... Air volume is M 混 =M 热 +M 冷 .

[0032] The beneficial effects of this invention are:

[0033] This invention deeply couples the biomass gasification system with the pulverized coal preparation and combustion system, eliminating the blower of a conventional gasifier, fully utilizing the hot and cold air from existing pulverized coal boilers, and increasing the inlet air temperature of the gasifier. This reduces the biomass consumption in the oxidation zone of the gasifier, thereby correspondingly reducing the CO2 content in the biomass gas and increasing its calorific value. The combustion-supporting effect of the biomass gas can also stabilize the combustion of pulverized coal, thus lowering the minimum stable combustion load of the boiler and meeting the requirements of deep peak shaving in the power grid. The biomass carbonization products can be transported to a nearby coal mill for grinding and then fed into the furnace for combustion along with the pulverized coal, efficiently utilizing the heat in the biomass char.

[0034] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 This is a schematic diagram of direct-fired coupled power generation.

[0037] Figure 2 This is a schematic diagram of parallel coupled power generation.

[0038] Figure 3 This is a schematic diagram of gasification coupling power generation.

[0039] Figure 4 This is a schematic diagram of the low-load stable combustion and co-firing system of a coupled pulverized coal boiler according to an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of a pulverized coal burner according to an embodiment of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0045] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0046] like Figure 4As shown, an embodiment of the present invention provides a coupled pulverized coal boiler low-load stable combustion and co-firing system, comprising: a boiler primary air fan, a preheater, a coal mill, a biomass gasifier, a pulverized coal boiler, a cold air header, and a hot air header; the cold air from the boiler primary air fan is divided into two paths, one of which is directly delivered to the cold air header, and the other is preheated by the preheater (for example, preheated to 350°C to 380°C) and then delivered to the hot air header;

[0047] The coal mill draws cold and hot air from the cold and hot air main pipes respectively, mixes them to a set temperature, and then enters the coal mill for coal powder drying. The dried coal powder is then sent to the corresponding burner of the pulverized coal boiler for combustion. The biomass gasifier draws cold and hot air from the cold and hot air main pipes respectively, mixes them to a set temperature, and then enters the biomass gasifier. The biomass material is gasified in the biomass gasifier to generate carbonized products, biochar and biogas. The carbonized biochar is transported to the coal mill and ground together with the raw coal, and then blown into the pulverized coal boiler for combustion in the furnace. The biogas directly enters the pulverized coal boiler for combustion in the furnace.

[0048] Specifically, the coal mill is connected to a first cold air sub-pipe and a first hot air sub-pipe via a first air mixing pipe. The first cold air sub-pipe is connected to a cold air main pipe, and the first hot air sub-pipe is connected to a hot air main pipe. The biomass gasifier is connected to a second cold air sub-pipe and a second hot air sub-pipe via a second air mixing pipe. The second cold air sub-pipe is connected to a cold air main pipe, and the second hot air sub-pipe is connected to a hot air main pipe.

[0049] The biomass gasifier is located in the operating layer between the coal bunkers. The carbonization product, biochar, is transported to the coal mill via a screw conveyor, which is located at the bottom of the biomass gasifier.

[0050] For example, a biomass gasifier is arranged in the operating layer between coal bunkers. Biomass feed is transported into the biomass gasifier via belt conveyor or bucket elevator for gasification. The biomass gasifier draws cold air from the cold air header and hot air from the hot air header, mixes them to a suitable temperature, and then enters the gasifier for operation. The gasified biomass gas enters the biomass gas combustion gun located in the center of the lowest pulverized coal burner through pipelines for combustion. Due to the good combustion stability of biomass gas, it can achieve a stable combustion effect when the boiler is under low load, thus helping to reduce the minimum stable combustion load of the boiler. The carbonized product biomass char generated at the bottom of the biomass gasifier is transported by the lower screw conveyor to the raw coal pipeline of the corresponding coal mill A or coal mill B of the lowest burner. After entering the coal mill, it is ground together with the raw coal, then carried by the mixed warm air to the pulverized coal delivery pipeline, and enters the furnace for combustion through the corresponding pulverized coal burner.

[0051] This invention deeply couples the biomass gasification system with the pulverized coal preparation and combustion system, eliminating the blower of a conventional gasifier, fully utilizing the hot and cold air from existing pulverized coal boilers, and increasing the inlet air temperature of the gasifier. This reduces the biomass consumption in the oxidation zone of the gasifier, thereby correspondingly reducing the CO2 content in the biomass gas and increasing its calorific value. The combustion-supporting effect of the biomass gas can also stabilize the combustion of pulverized coal, thus lowering the minimum stable combustion load of the boiler and meeting the requirements of deep peak shaving in the power grid. The biomass carbonization products can be transported to a nearby coal mill for grinding and then fed into the furnace for combustion along with the pulverized coal, efficiently utilizing the heat in the biomass char.

[0052] The control method based on the above-described coupled pulverized coal boiler low-load stable combustion and co-firing system includes:

[0053] Ignition mode: Start each coal mill one by one to complete the boiler ignition and load increase process;

[0054] Combustion-assisted operation: When the boiler starts to reduce its output from full load, the top burner is controlled to shut down until the load drops to a set percentage. When the boiler load decreases further, biomass gas is provided by the biomass gasifier for combustion assistance.

[0055] Real-time adjustments are made based on combustion and flame conditions: the air temperature and volume entering the biomass gasifier are adjusted according to the combustion conditions of the biomass gasifier, thereby adjusting the calorific value of the biomass gas and generating biomass char at the bottom of the biomass gasifier. Then, in combination with the combustion conditions of the corresponding burners, the biomass char is matched and transported to the corresponding coal mill.

[0056] Taking a 300MW coal-fired unit as an example, coal mills A through E correspond to the burners in layers A through E of the burner area, from the bottom to the top. Four biomass gasifiers are configured on the coal bunker operating layer between coal mills A and B. Each gasifier consumes approximately 600 kg / h of biomass and produces approximately 1008 Nm³ of gas. 3 / h indicates the operating mode of the entire system under various working conditions. The structure of the pulverized coal burner is as follows: Figure 5 As shown, combined with Figure 5 The control process of the low-load stable combustion and co-firing system of the coupled pulverized coal boiler is as follows:

[0057] (1) Ignition condition

[0058] When the boiler needs ignition, there is no hot flue gas to heat the cold air passing through the boiler air preheater. Therefore, it is necessary to provide starting steam to the start-up air heater to heat the cold air, thereby meeting the coal mill inlet temperature requirement of approximately 250–280℃. At this time, the coal mill A at the bottom of the corresponding burner area is not started. Biomass feed is fed into the biomass gasifier, the corresponding cold air regulating valve of the biomass gasifier is closed, and the corresponding hot air regulating valve is gradually opened. The valve of the biomass gas outlet is opened, and the biomass feed in the biomass gasifier is ignited using the ignition device. Biomass gas is then generated in the upper part, with the main components being H2, CO, and CH4, at a temperature of 250–360℃ and a calorific value of 5–6 MJ / Nm³. 3 The biomass gas enters the attached Figure 2 The biomass gas ignition gun in the center of the pulverized coal burner is ignited. After combustion stabilizes, coal mill A is started, hot air is introduced into coal mill A, and raw coal is fed in. A mixture of air and coal is generated in coal mill A and sent to the auxiliary... Figure 2 The burner shown is stably combusted after being ignited by the biomass gas flame. At this point, the biomass char from the biomass gasifier can be conveyed to coal mill A via a screw conveyor, ground together with raw coal, and then fed into the gasifier along with the air-coal mixture. Figure 2 The burners shown are burning together.

[0059] As the flue gas temperature rises, the warm air heater is gradually shut off, and the cold air is heated via the air preheater. Once the hot air temperature exceeds 300℃, the cold air regulating dampers at the inlet of the biomass gasifier and coal mill are gradually opened to adjust the inlet air temperature. As the boiler load increases, coal mills B, C, D, and E are gradually started to complete the boiler ignition and load increase process.

[0060] (2) Combustion-supporting conditions

[0061] When the boiler begins to reduce its output from full load, the boiler burners start shutting down from the top E layer burners until the load drops to a set percentage (e.g., 30%), leaving only the A and B layer burners operating. At this point, the corresponding coal mills are coal mill A and coal mill B. Further reducing the load at this stage would lead to unstable combustion due to the decreased furnace temperature, posing a risk of boiler flameout. At this point, the hot and cold air regulating dampers for the biomass gasifier are opened, the biomass gas outlet valve is opened, and biomass is fed into the gasifier from the top. The gasifier is then ignited using an ignition device, and the generated biomass gas is sent to the auxiliary... Figure 2The biomass gas lance in the center of the pulverized coal burner provides stable combustion for the pulverized coal burners in layer A, thus maintaining stable combustion in both layers A and B of the furnace. Initially, the hot and cold air regulating dampers corresponding to the biomass gasifier are opened relatively small, requiring only a small amount of biomass gas for stable combustion. As the load further decreases, the openings of the hot and cold air regulating dampers are gradually increased, and the biomass feed rate is also increased, thereby increasing the output of the biomass gasifier and using more biomass gas to maintain stable combustion in the pulverized coal burners in layer A. If the boiler load decreases further, the pulverized coal burners in layers B and A are shut down sequentially until the boiler is safely shut down; if the boiler load gradually increases, the output of the biomass gasifier is gradually reduced until the biomass gasifier is taken out of service.

[0062] (3) Make real-time adjustments based on the combustion and flame conditions.

[0063] (3.1) By adjusting the opening of the hot and cold air regulating dampers corresponding to the biomass gasifier, the air temperature entering the biomass gasifier can be adjusted. When the total air volume remains constant, increasing the inlet air temperature by changing the hot and cold air regulating dampers reduces the consumption of biomass that needs to burn in the oxidation zone to provide heat within the gasifier, and the CO2 in the biomass gas will also decrease accordingly, resulting in a slight increase in the calorific value of the biomass gas. Conversely, when the total air volume remains constant, decreasing the inlet air temperature increases biomass consumption, resulting in a slight decrease in the calorific value of the biomass gas. Specific adjustments can be made based on the actual combustion conditions.

[0064] Assume the temperature of the hot air is T. 热 The flow rate of the hot air is M. 热 The temperature of the cold air is T. 冷 The airflow rate of the cold air is M. 冷 The temperature of the mixed air entering the biomass gasification furnace is then... Air volume is M 混 =M 热 +M 冷 .

[0065] When M 混 Keep it unchanged, increase M 热 Then M 冷 Decrease, T 混 Increase the heat Q brought into the biomass gasifier by the mixed-temperature air. 混 =c p ×M 混 ×T 混 Increase, where c pThis refers to the heat capacity of the mixed gas. When the required biomass gas volume remains constant, the total heat required by the entire gasifier remains constant. The more heat brought in by the mixed air, the less heat is needed for the biomass to burn in the oxidation zone. Less biomass is burned, the lower the CO2 content in the biomass gas, and thus the lower the unit calorific value (H) of the biomass gas. 生物质气 It will improve.

[0066]

[0067] If we ignore the small amounts of inert gases and carbon dioxide in the atmosphere, then

[0068]

[0069] in, These represent the content of each component in the biomass gas. With the total air volume remaining constant, increasing the inlet air temperature reduces the amount of biomass consumed in the oxidation zone of the gasifier to provide heat. This reduction in CO2 content in the biomass gas will... Increasing the inlet air temperature proportionally increases the calorific value of biomass gas; conversely, when the total air volume remains constant, decreasing the inlet air temperature increases biomass consumption and decreases the calorific value of biomass gas.

[0070] (3.2) By adjusting the opening of the hot air regulating damper and cold air regulating damper corresponding to the biomass gasifier, the air volume entering the biomass gasifier can be adjusted. When the air temperature remains constant, increasing the air volume by changing the hot and cold air regulating dampers corresponds to increasing the supply of biomass feedstock, thus significantly increasing the biomass gas production in the gasifier. Conversely, when the air temperature remains constant and the air volume is reduced, the supply of biomass feedstock is reduced, thus significantly reducing the biomass gas production in the gasifier. Specific adjustments can be made according to the actual combustion conditions.

[0071] Assume the temperature of the hot air is T. 热 The flow rate of the hot air is M. 热 The temperature of the cold air is T. 冷 The airflow rate of the cold air is M. 冷 The temperature of the mixed air entering the biomass gasification furnace is then... Air volume is M 混 =M 热 +M 冷 .

[0072] When T 混 If the openings of the hot air regulating door and the cold air regulating door remain unchanged, and the openings are increased proportionally, then M... 混 =M 热 +M 冷Increasing the air intake volume leads to a greater amount of oxygen introduced into the biomass gasifier, resulting in a linear increase in biomass fuel consumption. This, in turn, significantly increases the biomass gas yield and calorific value within the gasifier. However, this increase is not linear and requires experimental verification to establish the relevant formula. Table 1 shows the impact of air intake volume on gasification performance for a specific type of biomass gasifier.

[0073] Table 1. Data on the impact of air intake rate on gasification performance of a certain type of biomass gasifier.

[0074]

[0075] (3.3) The biomass char produced at the bottom of the biomass gasifier has a calorific value of about 28 MJ / kg and a low volatile content. It needs to be fed into the corresponding coal mill A or coal mill B according to the combustion conditions of the burners in layers A and B.

[0076] This invention separates biomass into biogas and biochar using a biomass gasifier, and sends the biogas into an auxiliary gasifier. Figure 2 The biomass gas gun in the center of the pulverized coal burner, as shown, ignites and stabilizes the pulverized coal burner, reducing the boiler's minimum stable combustion load from 30% to 20% or even lower. High-calorific-value biomass char is fed to a coal mill for grinding and crushing, then fed into the pulverized coal burner along with the pulverized coal, thus recovering its heat. The biomass is separated into biomass gas and biomass char in a biomass gasifier for separate utilization, achieving both stable combustion and full utilization of the heat inherent in the biomass.

[0077] After carbonization in the biomass gasifier, the long fibers in the biomass char are destroyed by carbonization, so they can be better ground in the raw coal mill, solving the problem that it is difficult to blend biomass in a large proportion in the raw coal mill in direct-fired cogeneration.

[0078] Because biomass gasification furnaces only perform simple gasification without producing flue gas byproducts, the system is simple and requires low investment. This solves the problem of complex parallel coupling systems that require separate incinerators and flue gas treatment systems, resulting in excessively high investment.

[0079] Biomass gasification furnaces separate biomass into biogas and biochar for co-firing. While achieving stable combustion, they make full use of the combustion system, flue gas treatment system, and pulverizing system of coal-fired units. This solves the problems of gasification coupling requiring the installation of purification systems, resulting in high investment costs, and the fact that the ash residue after gasification can usually only be recycled as organic fertilizer and is difficult to dispose of locally.

[0080] The biomass gasifier in this scheme is fully coupled with the coal-fired unit, and the air intake also utilizes the hot air from the coal-fired unit, thereby saving biomass fuel consumption, reducing the need for independent fan configuration, and further improving the unit's economic efficiency.

[0081] Taking a 300MW coal-fired unit as an example, coal mills A through E correspond to the burners in layers A through E of the burner area from the bottom to the top. Four biomass gasifiers are configured on the coal bunker operating layer between coal mills A and B, with each gasifier consuming approximately 600 kg / h of biomass. After coupling a single boiler with biomass gasification, the minimum stable combustion load of the boiler is reduced from 30% to 20%, peak-shaving capacity is increased by 10%, deep-shaving time is 1000 hours, the grid-connected electricity price is -0.08 yuan / kWh, and the power generation cost is 0.30 yuan / kWh. Therefore, the total grid-connected electricity cost saved by a single unit during the negative price period is (0.08 + 0.3) * 300 * 1000 * 0.1 * 1000 / 10000 = 11.4 million yuan. Based on a biomass calorific value of 3500 kcal / kg and a price of 700 yuan / ton, the annual cost of biomass fuel consumption is 4*600 / 1000*1000*700 / 10000 = 1.68 million yuan, and the annual revenue is 11.4 million - 1.68 million = 9.72 million yuan.

[0082] The project has an investment of approximately 8 million yuan and an annual return of 9.72 million yuan, demonstrating good economic benefits.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coupled pulverized coal boiler low-load stable combustion and co-firing system, characterized in that, include: The boiler includes a primary air fan, preheater, coal mill, biomass gasifier, pulverized coal boiler, cold air header and hot air header; the cold air from the primary air fan is divided into two paths, one of which is directly delivered to the cold air header, and the other is preheated by the preheater and then delivered to the hot air header. The coal mill draws cold air from the cold air header and hot air from the hot air header respectively, mixes them to the set temperature, and then enters the coal mill for coal powder drying. The dried coal powder is then sent to the corresponding burner of the coal pulverized boiler for combustion. The biomass gasifier draws cold air from the cold air header and hot air from the hot air header, mixes them to a set temperature, and then enters the biomass gasifier. The biomass material is gasified in the biomass gasifier to generate carbonized biochar and biogas. The carbonized biochar is transported to a coal mill and ground together with the raw coal, and then blown into a pulverized coal boiler for combustion in the furnace. The biogas directly enters the pulverized coal boiler for combustion in the furnace. Each coal mill is started one by one to complete the boiler ignition and load increase process; When the boiler starts to reduce its output from full load, the top burner is shut down until the load drops to a set percentage. When the boiler load decreases further, biomass gas is supplied by the biomass gasifier for combustion assistance. The air temperature and volume entering the biomass gasifier are adjusted according to the combustion situation in the biomass gasifier, thereby adjusting the calorific value of the biomass gas and generating biochar at the bottom of the biomass gasifier. The biochar is then matched and fed into the corresponding coal mill based on the combustion situation of the corresponding burner.

2. The coupled pulverized coal boiler low-load stable combustion and co-firing system as described in claim 1, characterized in that, The coal mill is connected to the first cold air sub-pipe and the first hot air sub-pipe respectively through the first air mixing pipe. The first cold air sub-pipe is connected to the cold air main pipe, and the first hot air sub-pipe is connected to the hot air main pipe.

3. The coupled pulverized coal boiler low-load stable combustion and co-firing system as described in claim 1, characterized in that, The biomass gasifier is connected to a second cold air sub-pipe and a second hot air sub-pipe via a second air mixing pipe. The second cold air sub-pipe is connected to a cold air main pipe, and the second hot air sub-pipe is connected to a hot air main pipe.

4. The coupled pulverized coal boiler low-load stable combustion and co-firing system as described in claim 1, characterized in that, The biomass gasifier is located in the operating layer of the coal bunker.

5. The coupled pulverized coal boiler low-load stable combustion and co-firing system as described in claim 1, characterized in that, The carbonization product, biochar, is conveyed to the coal mill via a screw conveyor located at the bottom of the biomass gasification furnace.

6. A control method for a coupled pulverized coal boiler low-load stable combustion and co-firing system as described in any one of claims 1-5, characterized in that, include: Each coal mill is started one by one to complete the boiler ignition and load increase process; When the boiler starts to reduce its output from full load, the top burner is shut down until the load drops to a set percentage. When the boiler load decreases further, biomass gas is supplied by the biomass gasifier for combustion assistance. The air temperature and volume entering the biomass gasifier are adjusted according to the combustion situation in the biomass gasifier, thereby adjusting the calorific value of the biomass gas and generating biochar at the bottom of the biomass gasifier. The biochar is then matched and fed into the corresponding coal mill based on the combustion situation of the corresponding burner.

7. The control method as described in claim 6, characterized in that, If the boiler load drops to the set threshold, the pulverized coal burners on each floor will be shut down sequentially until the boiler is safely shut down.

8. The control method as described in claim 6, characterized in that, If the boiler load gradually increases, the output of the biomass gasifier should be gradually reduced until the biomass gasifier is taken out of service.

9. The control method as described in claim 6, characterized in that, The expression for the calorific value of biomass gas is: + + + + + =1 in, , , , , , These represent the content of each component in the biomass gas; With the total air volume remaining constant, increasing the inlet air temperature reduces the amount of biomass consumed in the oxidation zone of the gasifier to provide heat. This reduction in CO2 content in the biomass gas will... , , Increasing the inlet air temperature proportionally increases the calorific value of biomass gas; conversely, when the total air volume remains constant, decreasing the inlet air temperature increases biomass consumption and decreases the calorific value of biomass gas.

10. The control method as described in claim 6, characterized in that, Assuming the temperature of the hot air is The flow rate of the hot air is The temperature of the cold air is The airflow rate of the cold air is The temperature of the mixed air entering the biomass gasification furnace is then... Air volume is .

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