Coupling pulverized coal boiler low-load stable combustion and blending combustion system and control method

Abstract

The invention belongs to the field of coupling power generation, and provides a coupling pulverized coal fired boiler low-load stable combustion and blending combustion system and a control method. According to the system, cold air from a boiler primary air fan is divided into two paths, one path is directly conveyed to a cold air main pipe, and the other path is conveyed to a hot air main pipe after being preheated by a preheater; the coal mill correspondingly takes cold air and hot air from the cold air mother pipe and the hot air mother pipe, the cold air and the hot air are mixed to a set temperature and then enter the coal mill for pulverized coal drying, and the dried pulverized coal is conveyed to the pulverized coal boiler to enter a hearth for combustion; the biomass gasification furnace takes cold air and hot air from the cold air mother pipe and the hot air mother pipe correspondingly, and the cold air and the hot air enter the biomass gasification furnace after being mixed to a set temperature; the biomass material is gasified in the biomass gasification furnace to generate carbonized products, namely biomass charcoal and biogas; the carbonized product biomass charcoal is conveyed to a coal mill to be milled together with the raw coal, and then is blown to a pulverized coal boiler to enter a hearth for combustion; biogas directly enters the pulverized coal boiler and enters a hearth for combustion.

Description

Technical Field

[0001] The invention belongs to the field of coupled power generation, and in particular relates to a coupled pulverized coal boiler low-load stable combustion and blending system and a control method. Background Art

[0002] The statements in this section merely provide 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 can achieve negative carbon emissions when combined with carbon capture and storage technology. It can be seen that vigorously promoting biomass power generation is of strategic significance to global sustainable development. Coal-coupled biomass power generation technology plays a huge role in replacing fossil fuel consumption. This technology combines coal-fired power plants with biomass utilization to achieve complementary advantages, which helps reduce greenhouse gas emissions. It is an effective means to solve the overcapacity of coal-fired power generation, accelerate the transformation and upgrading of power generation, and gradually achieve green and low-carbon power generation.

[0004] Coal-biomass coupled power generation can generally be divided into three types: direct-fired coupled power generation, parallel-fired coupled power generation, and gasification-coupled power generation. Direct-fired coupled power generation: coal and biomass are mixed and burned in a boiler. Direct-fired coupling is divided into three schemes: (1) Coal and biomass are ground together and burned together; (2) Coal and biomass are ground differently and burned together; (3) Coal and biomass are ground differently and burned together, such as Figure 1 As shown. At present, coal-coupled biomass power generation mainly uses direct-fired coupling technology, which only requires slight changes to the original generator set. This coupling technology can effectively reduce the investment in unit modification, and the efficiency of biomass power generation is relatively high. However, direct-fired coupling has high requirements for biomass fuel, and various schemes have certain difficulties. Scheme 1 puts biomass into the coal mill of raw coal. It is usually necessary to dry the biomass and squeeze it into pellets. In addition, due to the presence of a large number of long fibers in the biomass, it is difficult to crush it to the same fineness as coal powder in the medium-speed coal mill and other coal mills that are crushed by grinding. The addition of biomass will significantly reduce the grinding output of the original coal mill, and the mixing ratio is only about 2%. Both Schemes 2 and 3 require the installation of biomass pretreatment equipment, which is usually mechanical cutting and crushing. The fineness of biomass powder is difficult to guarantee, and the life of the pretreatment equipment is short, requiring frequent maintenance and replacement.

[0005] like Figure 2 The parallel coupling power generation shown in the figure: that is, coal and biomass complete fuel pretreatment and pre-combustion in independent systems, and the generated steam shares a steam turbine system for power generation. Parallel coupling can screen and optimize adaptive combustion systems according to the characteristics of each fuel, and the coupling ratio of coal and biomass has no interference with the parallel power generation system. However, the parallel coupling system is complex and requires a separate incinerator and flue gas treatment system, which is too expensive.

[0006] like Figure 3 The gasification-coupled power generation shown in the figure is that the biomass is first pre-gasified, and the gas produced in the gasifier is mixed with the coal in the boiler for combustion. Since the gasifier has a strong adaptability to biomass fuels, gasification coupling reduces the requirements for fuel quality in the biomass conversion process. The crude synthesis gas produced by biomass gasification is introduced into a coal-fired boiler and coupled with coal for combustion. The original process equipment of the coal-fired power plant can be used in the later stage to achieve power generation and flue gas purification. However, gasification coupling requires the installation of a gasifier and a purification system, which requires a high investment, and the ash after gasification can usually only be recycled as organic fertilizer, and it is difficult to consume and utilize it locally.

[0007] In summary, the existing coupled power generation technology cannot simultaneously reduce carbon emissions when the unit is running at high load and solve the problems of boiler ignition and low-load stable combustion. Summary of the invention

[0008] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a coupled pulverized coal boiler low-load stable combustion and co-firing system and control method, which utilizes biomass gasification gas solid items to couple pulverized coal respectively, which can not only reduce the carbon emissions of the unit during high-load operation, but also solve the problems of boiler ignition and low-load stable combustion by co-firing biomass gas.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

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

[0011] A low-load stable combustion and mixed combustion system for a coupled pulverized coal boiler, comprising: a boiler primary fan, a preheater, a coal mill, a biomass gasifier, a pulverized coal boiler, a cold air main pipe and a hot air main pipe; the cold air from the boiler primary fan is divided into two paths, one of which is directly transmitted to the cold air main pipe, and the other is preheated by the preheater and then transmitted to the hot air main pipe;

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

[0013] The biomass gasification furnace takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, mixes them to the set temperature and then enters the biomass gasification furnace; the biomass material is gasified in the biomass gasification furnace to generate carbonized products, biochar and biogas; the carbonized product, biochar, is transported to the coal mill to be ground together with the raw coal, and then blown to the pulverized coal boiler to enter the furnace for combustion; the biogas directly enters the pulverized coal boiler and enters the furnace for combustion.

[0014] As an implementation mode, 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.

[0015] As an implementation mode, the biomass gasifier is connected to the second cold air sub-pipe and the second hot air sub-pipe respectively through the second air mixing pipe, the second cold air sub-pipe is connected to the cold air main pipe, and the second hot air sub-pipe is connected to the hot air main pipe.

[0016] As an implementation mode, the biomass gasification furnace is arranged in the operating layer between coal bunkers.

[0017] As an implementation mode, the carbonized product biochar is transported to the coal mill via a screw conveyor, and the screw conveyor is arranged at the bottom of the biomass gasification furnace.

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

[0019] A control method for a coupled pulverized coal boiler low-load stable combustion and blending system, comprising:

[0020] Start each coal mill one by one to complete the ignition process and load increase process of the boiler;

[0021] When the boiler starts to reduce its output from full load, the top burner is controlled to start shutting down until the load is reduced to the set percentage. When the boiler load is further reduced, the biomass gasifier is used to provide biomass gas for combustion support;

[0022] The air temperature and air 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 biochar at the bottom of the biomass gasifier. Combined with the combustion conditions of the corresponding layer burners, the biochar is matched and transported to the corresponding coal mill.

[0023] As an implementation method, if the boiler load drops to a set threshold, the pulverized coal burners of each layer are shut down in sequence until the boiler is shut down safely.

[0024] As an implementation method, if the boiler load gradually increases, the output of the biomass gasifier is gradually reduced until the biomass gasifier is shut down.

[0025] As an implementation method,

[0026] The calorific value of biomass gas is expressed as:

[0027]

[0028]

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

[0030] When the total air volume remains unchanged, by increasing the inlet air temperature, the consumption of biomass that needs to be burned in the oxidation zone to provide heat in the gasifier will be reduced, and the reduction of CO2 content in the biomass gas will make The same proportion increases, thereby increasing the calorific value of biomass gas; conversely, when the total air volume remains unchanged, by reducing the inlet air temperature, the biomass consumption increases and the calorific value of biomass gas decreases.

[0031] As an implementation method, assuming that the temperature of the hot air is T 热 , the hot air flow rate is M 热 , the temperature of the cold wind is T 冷 , the flow rate of cold air is M 冷 , then the temperature of the mixed air entering the biomass gasifier is Air volume is M 混 =M 热 +M 冷 .

[0032] The beneficial effects of the present invention are:

[0033] The present invention deeply couples the biomass gasification system with the coal powder preparation and combustion system, eliminates the fan of the ordinary gasifier, makes full use of the cold and hot air of the existing coal powder boiler, and increases the air temperature of the gasifier inlet air, 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 stabilize the combustion of coal powder, thereby reducing the minimum stable combustion load of the boiler and meeting the requirements of deep peak regulation of the power grid. The biomass carbonization product can be transported to the nearest coal mill for grinding and then sent into the furnace together with the coal powder for combustion, which efficiently utilizes the heat in the biomass charcoal.

[0034] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 This is the schematic diagram of direct combustion coupled power generation;

[0037] Figure 2 It is the schematic diagram of parallel coupled power generation;

[0038] Figure 3 This is the schematic diagram of gasification coupled power generation.

[0039] Figure 4 2 is a schematic diagram of the structure of a coupled pulverized coal boiler low-load stable combustion and blending system according to an embodiment of the present invention;

[0040] Figure 5 Schematic diagram of a pulverized coal burner according to an embodiment of the present invention. DETAILED DESCRIPTION

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

[0042] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

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

[0044] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

[0045] In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meanings of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

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

[0047] The coal mill takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, mixes them to the set temperature and then enters the coal mill to dry the coal powder, and the dried coal powder is sent to the corresponding burner of the coal powder boiler for combustion; the biomass gasifier takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, mixes them to the 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 product biochar is transported to the coal mill and ground together with the raw coal, and then blown to the coal powder boiler to enter the furnace for combustion; the biogas directly enters the coal powder boiler to enter the furnace for combustion.

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

[0049] The biomass gasifier is arranged in the operating layer of the coal bunker. The carbonized product, biochar, is transported to the coal mill through a screw conveyor, and the screw conveyor is arranged at the bottom of the biomass gasifier.

[0050] For example, a biomass gasifier is arranged in the operation layer of the coal bunker, and the biomass material is transported into the biomass gasifier for gasification through a belt or bucket elevator. The biomass gasifier takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, and enters the gasifier to work after mixing to a suitable temperature. The gasified biomass gas enters the biomass gas combustion gun set in the center of the coal powder burner at the bottom through a pipeline for combustion. Due to the good combustion stability of biomass gas, it can play a stable combustion effect when the boiler is under low load, which is conducive to reducing the minimum stable combustion load of the boiler. The carbonized product biochar generated at the bottom of the biomass gasifier is transported to the raw coal pipeline of the coal mill A or coal mill B corresponding to the bottom burner through the lower screw conveyor. After entering the coal mill, it is ground together with the raw coal, carried to the powder delivery pipeline by the mixed temperature wind, and enters the furnace through the corresponding coal powder burner for combustion.

[0051] The present invention deeply couples the biomass gasification system with the coal powder preparation and combustion system, eliminates the fan of the ordinary gasifier, makes full use of the cold and hot air of the existing coal powder boiler, and increases the air temperature of the gasifier inlet air, 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 stabilize the combustion of coal powder, thereby reducing the minimum stable combustion load of the boiler and meeting the requirements of deep peak regulation of the power grid. The biomass carbonization product can be transported to the nearest coal mill for grinding and then sent into the furnace together with the coal powder for combustion, which efficiently utilizes the heat in the biomass charcoal.

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

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

[0054] Combustion-supporting condition: When the boiler starts to reduce its output from full load, the top burner is controlled to start shutting down until the load is reduced to the set percentage. When the boiler load is further reduced, the biomass gasifier is used to provide biomass gas for combustion-supporting;

[0055] Real-time adjustment based on combustion conditions and flame conditions: adjust the wind temperature and air volume entering the biomass gasifier 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. Combined with the combustion conditions of the corresponding layer burners, the biochar is matched and transported to the corresponding coal mill.

[0056] Taking a 300MW coal-fired unit as an example, coal mills A to E correspond to the A to E burners from the bottom to the top of the burner area. Four biomass gasifiers are configured on the coal bunker operation layer between coal mills A and B. The biomass consumption of each gasifier is about 600kg / h and the gas production is about 1008Nm 3 / h, which shows the operation mode of the whole system under various working conditions. Figure 5 As shown, combined Figure 5 , the control process of the coupled pulverized coal boiler low load stable combustion and blending system is:

[0057] (1) Ignition conditions

[0058] When the boiler needs to be ignited, there is no hot flue gas to heat the cold air passing through the boiler air preheater, so it is necessary to heat the cold air by providing startup steam to the startup air heater to meet the pulverizer inlet temperature requirement of about 250-280°C. At this time, the pulverizer A at the bottom of the corresponding burner area is not put into operation first, biomass is fed into the biomass gasifier, the cold air regulating door corresponding to the biomass gasifier is closed, the corresponding hot air regulating door is gradually opened, the valve of the biomass gas outlet is opened, and the biomass in the biomass gasifier is ignited with an ignition device to start generating upper biomass gas, the main components of which are H2, CO and CH4, with a temperature of 250-360°C and a calorific value of 5-6MJ / Nm 3 , the biomass gas enters the surrounding Figure 2 The biomass gas ignition gun in the center of the pulverized coal burner is ignited, and after the combustion is stable, the coal mill A is started, hot air is introduced into the coal mill A, and raw coal is added. The air-powder mixture is generated in the coal mill A and sent to the attached Figure 2 The burner shown is ignited by the flame of the biomass gas and burns stably. At this time, the biomass charcoal in the biomass gasifier can be transported to the coal mill A through a screw conveyor, ground together with the raw coal, and then sent into the coal mill together with the air-powder mixture. Figure 2 The burners shown are fired together.

[0059] When the smoke temperature rises, gradually cut off the start-up heater to heat the cold air through the air preheater. When the hot air temperature exceeds 300℃, gradually open the cold air regulating door at the inlet of the biomass gasifier and the coal mill to adjust the inlet air temperature of the biomass gasifier and the coal mill. As the boiler load increases, gradually start the coal mills B, C, D, E, etc. to complete the boiler ignition process and load increase process.

[0060] (2) Combustion-supporting conditions

[0061] When the boiler starts to reduce its output from full load, the boiler burners will be shut down starting from the top E burner until the load is reduced to a set percentage (e.g. 30%), leaving only the A and B burners running. At this time, the corresponding coal mills are coal mill A and coal mill B. If the load is further reduced at this time, the boiler will be at risk of flameout due to the lower furnace temperature level and unstable combustion. At this time, open the hot air regulating door and cold air regulating door corresponding to the biomass gasifier, open the valve of the biomass gas outlet, and add biomass from the top of the gasifier. Ignite it with an ignition device, put the biomass gasifier into operation, and send the generated biomass gas to the surrounding Figure 2The biomass gas gun in the center of the pulverized coal burner shown in the figure burns, providing a stable combustion effect for the pulverized coal burner in layer A, thereby maintaining the stable combustion of the burners in layers A and B in the entire furnace. At the beginning, the hot air regulating door and the cold air regulating door corresponding to the biomass gasifier have a small opening, and only a small amount of biomass gas is needed for stable combustion. When the load is further reduced, the hot air regulating door and the cold air regulating door opening are gradually opened, and the feed amount of biomass material is increased, thereby increasing the output of the biomass gasifier, and using more biomass gas to maintain the stable combustion of the pulverized coal burner in layer A. If the boiler load is further reduced, the pulverized coal burners in layer B and layer A are shut down in turn until the boiler is safely shut down; if the boiler load is gradually increased, the output of the biomass gasifier is gradually reduced until the biomass gasifier is out of operation.

[0062] (3) Real-time adjustment based on combustion and flame conditions

[0063] (3.1) The air temperature entering the biomass gasifier can be adjusted by adjusting the opening of the hot air regulating door and the cold air regulating door corresponding to the biomass gasifier. When the total air volume remains unchanged and only the inlet air temperature is increased by changing the cold air and hot air regulating doors, the consumption of biomass that needs to be burned in the oxidation zone to provide heat in the gasifier will be reduced, and the CO2 in the biomass gas will also be reduced accordingly, and the calorific value of the biomass gas will be slightly increased. Conversely, when the total air volume remains unchanged, by reducing the inlet air temperature, the biomass consumption will increase and the calorific value of the biomass gas will be slightly reduced. Specific adjustment operations can be carried out according to the actual combustion situation.

[0064] Assume that the temperature of the hot air is T 热 , the hot air flow rate is M 热 , the temperature of the cold wind is T 冷 , the flow rate of cold air is M 冷 , then the temperature of the mixed air entering the biomass gasifier is Air volume is M 混 =M 热 +M 冷 .

[0065] When M 混 No change, 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 pis the heat capacity of the mixed gas. When the required biomass gas remains unchanged, the total heat required by the entire gasifier remains unchanged. The more heat the mixed temperature air brings in, the less heat the required biomass will generate in the oxidation zone. The less biomass is burned, the less CO2 content in the biomass gas will be. The unit calorific value of the biomass gas is H 生物质气 Will be improved.

[0066]

[0067] Ignoring the inert gases and carbon dioxide in small amounts in the atmosphere,

[0068]

[0069] in, Respectively represent the content of each component in the biomass gas. When the total air volume remains unchanged, by increasing the inlet air temperature, the biomass consumption that needs to be burned in the oxidation zone in the gasifier to provide heat will be reduced, and the reduction of CO2 content in the biomass gas will make The same proportion increases, thereby increasing the calorific value of biomass gas; conversely, when the total air volume remains unchanged, by reducing the inlet air temperature, the biomass consumption increases and the calorific value of biomass gas decreases.

[0070] (3.2) The air volume entering the biomass gasifier can be adjusted by adjusting the opening of the hot air regulating door and the cold air regulating door corresponding to the biomass gasifier. When the air temperature remains unchanged and the air intake is increased by only changing the cold air and hot air regulating doors, the supply of biomass materials will be increased, and the output of biomass gas in the gasifier will be significantly increased. On the contrary, when the air temperature remains unchanged and the air intake is reduced, the supply of biomass materials will be reduced, and the output of biomass gas in the gasifier will be significantly reduced. Specific adjustment operations can be carried out according to the actual combustion conditions.

[0071] Assume that the temperature of the hot air is T 热 , the hot air flow rate is M 热 , the temperature of the cold wind is T 冷 , the flow rate of cold air is M 冷 , then the temperature of the mixed air entering the biomass gasifier is Air volume is M 混 =M 热 +M 冷 .

[0072] When T 混 The opening of the hot air regulating door and the cold air regulating door are increased in the same proportion, then M 混 =M 热 +M 冷Increase, the amount of oxygen brought into the biomass gasifier by the mixed temperature wind increases, so that the consumption of biomass fuel increases linearly, so that the output of biomass gas in the gasifier is significantly increased, and the calorific value of biomass gas will also increase, but this increase is not a linear increase, and its formula relationship needs to be determined through experiments. Table 1 shows the data on the influence of the air intake volume on the gasification performance of a certain type of biomass gasifier.

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

[0074]

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

[0076] The present invention separates biomass into biomass gas and biomass charcoal through a biomass gasifier, and sends the biomass gas to an adjacent Figure 2 The biomass gas gun in the center of the pulverized coal burner shown in the figure burns, thereby achieving the purpose of ignition and stable combustion of the pulverized coal burner, at least the minimum stable combustion load of the boiler can be reduced from 30% to 20% or even lower, and the high calorific value biomass charcoal is transported to the coal mill for grinding and crushing, and then sent to the pulverized coal burner for combustion together with the pulverized coal, thereby recovering its heat. The biomass material is separated into biomass gas and biomass charcoal by the biomass gasifier and used separately, which can not only achieve the effect of stable combustion, but also fully utilize all the heat contained in the biomass.

[0077] After carbonization in the biomass gasifier, the long fibers in the biomass charcoal are destroyed by carbonization, so it can be better ground in the raw coal pulverizer, solving the problem that it is difficult to grind a large proportion of biomass in the raw coal pulverizer in direct-fired coupled power generation.

[0078] The biomass gasifier is a simple gasification system with no flue gas products, a simple system and low investment. It solves the problem of complex parallel coupling system, the need for separate incinerators and flue gas treatment systems, and excessive investment.

[0079] The biomass gasification furnace separates biomass materials into biomass gas and biomass charcoal for separate combustion. While achieving a stable combustion effect, it fully utilizes the combustion system, flue gas treatment system and pulverizing system of the coal-fired unit, solving the problem that gasification coupling requires the installation of a purification system, which requires high investment, and the ash after gasification can usually only be recycled as organic fertilizer, but is difficult to be consumed 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 of the coal-fired unit, thereby saving the consumption of biomass fuel, reducing the configuration of independent fans, and further improving the economy of the unit.

[0081] Take a 300MW coal-fired unit as an example. The coal mills A to E correspond to the A to E burners from the bottom to the top of the burner area. Four biomass gasifiers are configured on the coal bunker operation layer between coal mills A and B. The biomass consumption of each gasifier is about 600kg / h. After a single boiler is coupled with biomass gasification, the minimum stable combustion load of the boiler is reduced from 30% to 20%, the peak load capacity is increased by 10%, the deep adjustment time is 1000 hours, the on-grid electricity price is -0.08 yuan / kwh, and the power generation cost is 0.30 yuan / kwh. The total on-grid electricity fee saved by a unit during the negative electricity price period is (0.08+0.3)*300*1000*0.1*1000 / 10000=11.4 million yuan. Based on the calorific value of biomass of 3500kcal / kg and the price of 700 yuan / ton, the annual cost of biomass fuel is 4*600 / 1000*1000*700 / 10000=1.68 million, and the annual income is 11.40-168=9.72 million.

[0082] The investment in the project is about 8 million yuan, with an annual income of 9.72 million yuan, which has good economic benefits.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-load stable combustion and blending system for coupled pulverized coal boiler, characterized in that: include: Boiler primary fan, preheater, coal mill, biomass gasifier, pulverized coal boiler, cold air main pipe and hot air main pipe; the cold air from the boiler primary fan is divided into two paths, one of which is directly transmitted to the cold air main pipe, and the other is preheated by the preheater and then transmitted to the hot air main pipe; The coal mill takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, mixes them to the set temperature and then enters the coal mill for coal powder drying, and the dried coal powder is sent to the corresponding burner of the coal powder boiler for combustion; The biomass gasification furnace takes cold air and hot air from the cold air main pipe and the hot air main pipe respectively, mixes them to the set temperature and then enters the biomass gasification furnace; the biomass material is gasified in the biomass gasification furnace to generate carbonized products, biochar and biogas; the carbonized product, biochar, is transported to the coal mill to be ground together with the raw coal, and then blown to the pulverized coal boiler to enter the furnace for combustion; the biogas directly enters the pulverized coal boiler and enters the furnace for combustion.

2. The low-load stable combustion and blending system for coupled pulverized coal boiler according to 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 low-load stable combustion and blending system for coupled pulverized coal boiler according to claim 1, characterized in that: The biomass gasifier is connected to the second cold air sub-tube and the second hot air sub-tube respectively through the second air mixing tube, the second cold air sub-tube is connected to the cold air main tube, and the second hot air sub-tube is connected to the hot air main tube.

4. The low-load stable combustion and blending system for coupled pulverized coal boiler according to claim 1, characterized in that: The biomass gasification furnace is arranged in the operating layer of the coal bunker.

5. The low-load stable combustion and blending system for coupled pulverized coal boiler according to claim 1, characterized in that: The carbonized product biochar is transported to a coal mill through a screw conveyor, and the screw conveyor is arranged at the bottom of the biomass gasification furnace.

6. A control method for a coupled pulverized coal boiler low-load stable combustion and blending system as claimed in any one of claims 1 to 5, characterized in that: include: Start each coal mill one by one to complete the ignition process and load increase process of the boiler; When the boiler starts to reduce its output from full load, the top-layer burner is controlled to shut down until the load is reduced to the set percentage. When the boiler load is further reduced, the biomass gasifier is used to provide biomass gas for combustion support. The wind temperature and air 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 biochar at the bottom of the biomass gasifier. Combined with the combustion conditions of the corresponding layer burners, the biochar is matched and transported to the corresponding coal mill.

7. The control method according to claim 6, characterized in that: If the boiler load drops to the set threshold, the pulverized coal burners on each layer will be shut down in turn until the boiler is shut down safely.

8. The control method according to claim 6, characterized in that: If the boiler load gradually increases, the output of the biomass gasifier will be gradually reduced until the biomass gasifier is shut down.

9. The control method according to claim 6, characterized in that: The calorific value of biomass gas is expressed as: in, Respectively represent the content of each component in biomass gas; When the total air volume remains unchanged, by increasing the inlet air temperature, the consumption of biomass that needs to be burned in the oxidation zone to provide heat in the gasifier will be reduced, and the reduction of CO2 content in the biomass gas will make The same proportion increases, thereby increasing the calorific value of biomass gas; conversely, when the total air volume remains unchanged, by reducing the inlet air temperature, the biomass consumption increases and the calorific value of biomass gas decreases.

10. The control method according to claim 6, characterized in that: Assume that the temperature of the hot air is T 热 , the hot air flow is M 热 , the temperature of the cold wind is T 冷 , the flow rate of cold air is M 冷 , then the temperature of the mixed air entering the biomass gasifier is Air volume is M 混 =M 热 +M 冷 .

Images