A biomass powder hot air conveying and co-firing system and co-firing method

Abstract

The application discloses a biomass powder hot air feeding and blending combustion system, which comprises a stock bin, a belt conveyor, a dryer, a boiler, a burner, an air preheater and a dust collector. The air outlet end of the boiler is connected with the air preheater, and the flue gas outlet end of the air preheater is connected with the dust collector. The dust collector is connected with a flue gas discharge pipeline structure. The air preheater is assembled with a secondary air pipeline structure. The air inlet end of the dryer is assembled with an induced draft fan. The flue gas discharge pipeline structure and the secondary air pipeline structure controlled by a valve are connected with the air inlet end of the induced draft fan. The induced draft fan pumps the feeding hot air formed by the secondary air and the dust-collected flue gas into the dryer to dry the material. The application also discloses a blending combustion method based on the blending combustion system, which comprises the conveying of the biomass material and the controlled conveying of the secondary air and the dust-collected flue gas to realize the controlled blending combustion. The blending combustion efficiency of the biomass is greatly improved by the technical scheme.

Description

Technical Field

[0001] This invention belongs to the field of biomass co-firing technology, and particularly relates to a biomass powder hot air conveying co-firing system and co-firing method. Background Technology

[0002] Biomass is a zero-carbon emission renewable energy source and one of the potential alternatives to fossil fuels. Biomass energy has excellent advantages in diversified development, not only providing heat and electricity for domestic and industrial applications, but also serving as a major source of fuel for production and transportation.

[0003] In recent years, global gasification changes have intensified, and the task of carbon emission reduction has become increasingly challenging. The market for biofuels, which have good carbon reduction properties, has seen a surge in demand, and the co-firing of biomass into coal-fired power plants has become an important technical means.

[0004] Based on this, existing technologies regarding the use of biomass as co-firing fuel are widely reported, such as Chinese Patent Publication No. CN109386838 A, which discloses a biomass co-firing system and process. Specifically, this biomass co-firing system includes a biomass preparation system, a biomass metering system, a biomass conveying system, a central control room, and a boiler. The outlet of the biomass preparation system is connected to the inlet of the biomass conveying system, and the outlet of the biomass conveying system is connected to the inlet of the boiler. The biomass metering system is mounted on a conveyor belt and is used to weigh and measure the biomass powder and perform online calorific value analysis, transmitting the measured data to the central control room. In this disclosed combustion system, because the entire system is independent of the boiler fuel system, the lower ignition point of biomass allows for earlier ignition, saving ignition fuel and enhancing the boiler's load regulation characteristics. Furthermore, since the co-firing system is independently set up, the original unit can operate normally regardless of whether the system is in use.

[0005] However, most of the publicly available biomass combustion systems suffer from the following technical defects:

[0006] 1. Because a positive pressure pneumatic conveying method is adopted, the biomass crushed material is fed into the pneumatic conveying pipeline by a rotary feeder and the positive pressure pneumatic conveying is achieved by a Roots blower, which is a complex process.

[0007] 2. Rotary feeders are prone to backflow and difficulty in feeding. The fibers of biomass crushed material are easily entangled in the rotor of the rotary feeder, causing jamming.

[0008] 3. At the same time, due to the use of cold air to deliver pulverized coal, the flue gas temperature increases significantly, and the boiler thermal efficiency decreases considerably. Some patents consider hot air delivery of pulverized coal, but there are no technical measures to prevent the spontaneous combustion of biomass during transport and accumulated pulverized coal. Summary of the Invention

[0009] Based on the above background, the purpose of this invention is to provide a biomass powder hot air conveying and co-firing system.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A biomass powder hot air conveying and co-firing system includes a silo, a belt conveyor, a dryer, a boiler, a burner, an air preheater, and a dust collector. The belt conveyor is located at the discharge end of the silo, and the dryer is located at the discharge end of the belt conveyor.

[0012] The discharge end of the dryer is connected to a material passing fan, and the discharge end of the material passing fan is connected to a boiler.

[0013] The boiler is equipped with a burner, and the material feeding fan delivers the material to the burner.

[0014] The boiler's outlet is connected to an air preheater, and the air preheater's flue gas outlet is connected to a dust collector; the dust collector is connected to a flue gas duct structure.

[0015] The air preheater is equipped with a secondary air duct structure.

[0016] The air inlet of the dryer is equipped with an induced draft fan, and the exhaust duct structure and the secondary air duct structure are connected to the air inlet of the induced draft fan. The induced draft fan pumps the secondary air and the dust-removed flue gas to the dryer to dry the material.

[0017] The biomass powder hot air delivery and co-firing system also includes a first valve and a second valve for controlling the secondary air duct structure and the flue gas duct structure.

[0018] Preferably, the silo is an underground silo;

[0019] A spiral pushing structure is installed at the discharge port of the silo, which is used to assist in feeding biomass onto the belt conveyor.

[0020] Preferably, the air inlet end of the induced draft fan is equipped with a hot air feeding duct;

[0021] The secondary air duct structure and the smoke exhaust duct structure are respectively connected to the feeding hot air duct.

[0022] Preferably, the secondary air duct structure includes a secondary air inlet pipe connected to the air preheater, a secondary air outlet pipe connected to the air preheater's outlet end, and the secondary air outlet pipe connected to the boiler's inlet end.

[0023] The secondary air outlet pipe is connected to a first branch pipe, which is connected to the feeding hot air pipe.

[0024] Preferably, the flue gas duct structure includes a first flue gas duct connected to the flue gas outlet end of the boiler;

[0025] The first flue gas outlet pipe is connected to the flue gas inlet of the air preheater, and the flue gas outlet of the air preheater is connected to a second flue gas outlet pipe, which is connected to the flue gas inlet of the dust collector.

[0026] The dust collector is connected to a flue gas duct, which is connected to the feeding hot air duct via a second branch pipe.

[0027] Preferably, a first valve is installed on the first branch pipe, and a second valve is installed on the second branch pipe.

[0028] Preferably, a weighing sensor is installed on the belt for weighing the biomass.

[0029] Preferably, the desiccant is a drum dryer.

[0030] This invention also discloses a coagulation method based on the above-mentioned biomass powder hot air conveying and coagulation system, comprising the following steps:

[0031] (1) Feeding: After the biomass material is fed into the hopper, it is conveyed to the feed dryer by the belt conveyor;

[0032] The induced draft fan pumps the secondary air and the flue gas after dust removal into the dryer to dry the material;

[0033] After the material is dried, it is pumped into the boiler by a material conveying fan and then co-fired by the burner.

[0034] (2) Firing control:

[0035] 2.1 The measured temperature of the hot secondary air at the air preheater outlet is T1, and the measured temperature of the flue gas at the dust collector outlet is T2. The flue gas oxygen measurement point is marked as O2,2, and the flue gas CO measurement point is marked as CO2. The measured value of the hot secondary air oxygen is O. 2,1 The measured CO content was CO1.

[0036] 2.2 Add flow rate measurement points for hot secondary air and flue gas after dust removal, with measured values ​​Q1 and Q2 respectively. Control the opening of the first and second valves by the temperature and oxygen content of the mixed hot air. The specific control method is as follows:

[0037] The temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The setpoint for the hot air temperature, oxygen content, and CO content is T. p O 2, p, CO p ;

[0038] The specific heat capacities of hot secondary air and flue gas after dust removal are measured as c1 and c2, respectively. The biomass powder entering the furnace is measured as Qs, in kg / s.

[0039] The flow rate of the mixed hot air is measured as Q. The feed fan is controlled by frequency converter to effectively adjust the gas-solid ratio, i.e., to adjust Q, controlling the flow rate to the minimum level that does not cause blockage. These are known quantities in the calculation. Based on the laws of conservation of mass and energy, the following correlation is obtained:

[0040] Q1 + Q2 = Q;

[0041] Q1*O 2,1 +Q2*O 2,2 =Q*O2;

[0042] Q1*CO1+Q2*CO2=Q*CO;

[0043] c1*Q1*(T1-T)=c2*Q2*(T-T2);

[0044] The calculation shows that:

[0045] O2=(Q1*(O 2,1 -O 2,2 )+Q*O 2,2 ) / Q;

[0046] When O2 is higher than the set value O 2,p Then reduce Q1 by closing the first valve or opening the second valve.

[0047] CO=(Q*CO1+Q2*(CO2-CO1)) / Q;

[0048] When CO is higher than the set value CO p Then reduce Q2 by closing the second valve or opening the first valve.

[0049] T=(Q1*(c1*T1-c2*T2)+c2*T2*Q) / (Q1*(c1-c2)+c2*Q);

[0050] When T is higher than the set value Tp, Q1 is reduced by closing the first valve or opening the second valve.

[0051] Preferably, in step (2), O 2,1 =21%; the temperature of the mixed hot air is recorded as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The temperature of the mixed hot air should not exceed 200℃, the oxygen content should not exceed 10%, and the CO content should not exceed 0.02%.

[0052] The present invention has the following beneficial effects:

[0053] 1. The technical solution disclosed in this invention involves the direct conveying of crushed biomass material, which is simple, energy-efficient, and highly effective.

[0054] 2. Hot secondary air is mixed with flue gas from the dust collector outlet to dry the crushed biomass material. The temperature and oxygen content of the mixed flue gas are calculated by measuring the working fluid temperature and oxygen content in the two branches, and the temperature and oxygen content of the mixed hot air are controlled to avoid the accumulation of biomass powder and spontaneous combustion during the transportation process.

[0055] 3. The technical solution disclosed in this invention has a simple process, is energy-saving and reliable, and effectively avoids the jamming and blockage problems that are easily caused by positive pressure pneumatic conveying systems;

[0056] 4. Using hot air to deliver pulverized coal can avoid the problem of increased flue gas temperature and reduced boiler thermal efficiency caused by cold air delivery. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0058] Figure 1 This is a schematic diagram of the overall structure in an embodiment of the present invention.

[0059] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0061] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0062] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0063] Example 1: Biomass Powder Hot Air Conveying and Firing System

[0064] like Figure 1 As shown, a biomass powder hot air conveying and co-firing system includes a silo 1 (the silo 1 is an underground silo 1; to facilitate unloading and prevent biomass from bridging and making feeding difficult, a spiral pushing structure 10 is installed at the discharge port of the silo 1, following the existing discharge method. The spiral pushing structure 10 is used to assist the feeding of biomass onto the belt conveyor 2. Specifically, the spiral pushing structure 10 includes spiral pushing blades and a motor installed on the spiral pushing blades. During operation, it utilizes the spiral pushing blades to assist the feeding of materials in the same way as existing spiral pushing devices in terms of structure and principle).

[0065] Meanwhile, the biomass powder hot air conveying and co-firing system also includes a belt conveyor 2, a dryer 3, a boiler 6, a burner 7, an air preheater 8, and a dust collector 9. The belt conveyor 2 is installed at the discharge end of the silo 1 (according to the existing weighing method, a weighing sensor is installed on the belt conveyor 2 to realize the weighing of the biomass fed onto the belt conveyor 2), and the dryer 3 (the desiccant is a drum dryer 3) is installed at the discharge end of the belt conveyor 2.

[0066] Specifically, the discharge end of the dryer 3 is connected to the feed fan 5 (in the existing method, a frequency converter is installed inside the feed fan 5 for easy adjustment of the fan output). The discharge end of the feed fan 5 is connected to the boiler 6. Specifically, a burner 7 is installed inside the boiler 6, and the feed fan 5 feeds the material to the burner 7 (i.e., the discharge end of the feed fan 5 is connected to the burner 7 through a pipeline). Furthermore, in the existing method, pneumatic and manual gate valves and temperature measuring points can be installed on the pipeline, and a video monitoring system can be installed on the biomass burner 7 to monitor and prevent accidents caused by positive pressure or backfire in the furnace, which could lead to biomass ignition. In the event of system shutdown or an accident, the gate valves can be closed to isolate the biomass co-firing system.

[0067] The outlet of boiler 6 is connected to air preheater 8, and the outlet of air preheater 8 is connected to dust collector 9; dust collector 9 is connected to a flue gas duct structure; air preheater 8 is equipped with a secondary air duct structure, and the secondary air duct structure is connected to boiler 6.

[0068] The secondary air duct structure and the smoke exhaust duct structure are used to mix the secondary air with the high-temperature dust-removed flue gas to form a hot mixed air that is supplied to the dryer for drying the materials.

[0069] Meanwhile, the air inlet of the dryer 3 is equipped with an induced draft fan 4 (which introduces hot mixed air into the dryer 3). The exhaust pipe structure and the secondary air pipe structure are connected to the air inlet of the induced draft fan 4. The induced draft fan 4 pumps the secondary air and the dust-removed flue gas to the dryer 3 to dry the material.

[0070] Meanwhile, the biomass powder hot air feeding and co-firing system also includes a first valve 11 and a second valve 12 for controlling the secondary air duct structure and the flue gas duct structure. The first valve 11 and the second valve 12 control the amount of hot air / flue gas extracted.

[0071] Meanwhile, the air inlet end of the induced draft fan 4 is equipped with a feeding hot air duct; the secondary air duct structure and the smoke exhaust duct structure are respectively connected to the feeding hot air duct 106.

[0072] Example 2 Biomass Powder Hot Air Conveying and Firing System

[0073] like Figure 1 As shown, this embodiment, based on the structure of embodiment 1, specifically discloses the secondary air duct structure, the flue gas duct structure in the co-firing system, and the connection relationship between them and each component.

[0074] Specifically, the secondary air duct structure includes a secondary air inlet pipe 104 connected to the air preheater 8, a secondary air outlet pipe 102 connected to the air outlet end of the air preheater 8, and the secondary air outlet pipe 102 connected to the air inlet end of the boiler 6; the secondary air outlet pipe 102 is connected to a first branch pipe 103, and the first branch pipe 103 is connected to the feeding hot air duct 106.

[0075] Meanwhile, the flue gas duct structure includes a first flue gas pipe 101 connected to the flue gas outlet of boiler 6; the flue gas outlet of the first flue gas pipe 101 is connected to the flue gas inlet of air preheater 8, the flue gas outlet of air preheater 8 is connected to a second flue gas pipe 108, the second flue gas pipe 108 is connected to the flue gas inlet of dust collector 9; the dust collector 9 is connected to a flue gas pipe 105, the flue gas pipe 105 is connected to the feeding hot air pipe 106 through a second branch pipe 107.

[0076] A first valve 11 is installed on the first branch pipe 103, and a second valve 12 is installed on the second branch pipe 107.

[0077] During operation, biomass materials are fed into the hopper 1 and then conveyed to the dryer 3 via the belt conveyor 2. The induced draft fan 4 pumps the secondary air and the flue gas after dust removal into the dryer 3 to dry the materials.

[0078] After the material is dried, it is pumped into the boiler 6 by the feed fan 5 and co-fired by the burner 7. During this process, the flow rate and temperature of the feeding hot air (mixed air) are controlled by controlling the first valve 11 and the second valve 12.

[0079] Example 3: Calcination Method

[0080] like Figure 1 As shown, this embodiment discloses a coagulation method based on a biomass powder hot air conveying and coagulation system, including the following steps:

[0081] (1) Feeding: After the biomass material is fed into the hopper 1, it is conveyed to the feed dryer 3 by the belt conveyor 2;

[0082] The induced draft fan 4 pumps the secondary air and the flue gas after dust removal into the dryer 3 to dry the material;

[0083] After the material is dried, it is pumped into the boiler 6 by the material conveying fan 5 and then co-fired by the burner 7.

[0084] (2) Firing control:

[0085] 2.1 The temperature of the hot secondary air at the outlet of air preheater 8 is measured as T1, the temperature of the flue gas at the outlet of dust collector 9 is measured as T2, and the oxygen content measurement point in the flue gas is marked as O. 2,2 The flue gas CO measuring point is marked as CO2, and the measured value of the hot secondary air oxygen is O2. 2,1 The measured CO content was CO1 (the actual measured value was approximately 0). Specifically, the measured value of oxygen content in the hot secondary air was: O 2,1 =21%; the temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. Specifically, the temperature of the mixed hot air should not exceed 200℃, the oxygen content should not exceed 10%, and the CO content should not exceed 0.02%.

[0086] 2.2 Add flow rate measurement points for hot secondary air and flue gas after dust removal, with measured values ​​Q1 and Q2 respectively. Control the opening of the first valve 11 and the second valve 12 by the temperature and oxygen content of the mixed hot air. The specific control method is as follows:

[0087] The temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The setpoint for the hot air temperature, oxygen content, and CO content is T. p O 2, p, CO p ;

[0088] The specific heat capacities of hot secondary air and flue gas after dust removal were measured as c1 and c2 (in J / (kg·℃)), respectively. The biomass powder quantity Qs entering the furnace was measured (in kg / s).

[0089] The measured flow rate of the mixed hot air is Q. The feed fan 5 is controlled by a frequency converter to effectively adjust the gas-solid ratio, i.e., to adjust Q, controlling the flow rate to the minimum level that does not cause blockage. These are known quantities in the calculation. Based on the laws of conservation of mass and energy, the following correlation is obtained:

[0090] Q1 + Q2 = Q;

[0091] Q1*O 2,1 +Q2*O 2,2 =Q*O2;

[0092] Q1*CO1+Q2*CO2=Q*CO;

[0093] c1*Q1*(T1-T)=c2*Q2*(T-T2);

[0094] The calculation shows that:

[0095] O2=(Q1*(O 2,1 -O 2,2 )+Q*O 2,2 ) / Q;

[0096] When O2 is higher than the set value O 2,p Then Q1 is reduced by closing the first valve 11 or opening the second valve 12; this method achieves the adjustment in the first case.

[0097] CO=(Q*CO1+Q2*(CO2-CO1)) / Q;

[0098] When CO is higher than the set value CO p Then Q2 is reduced by closing the second valve 12 or opening the first valve 11; this method achieves the adjustment in the second case.

[0099] T=(Q1*(c1*T1-c2*T2)+c2*T2*Q) / (Q1*(c1-c2)+c2*Q);

[0100] When T is higher than the set value Tp, Q1 is reduced by closing the first valve 11 or opening the second valve 12 to achieve the adjustment in the third case.

[0101] The above measurement formulas and adjustment methods enable the entire system to be adjusted during the co-firing process.

[0102] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A biomass powder hot air conveying and co-firing system, characterized in that, It includes a silo, a belt conveyor, a dryer, a boiler, a burner, an air preheater, and a dust collector. The belt conveyor is installed at the discharge end of the silo, and the dryer is installed at the discharge end of the belt conveyor. The discharge end of the dryer is connected to a material passing fan, and the discharge end of the material passing fan is connected to a boiler. The boiler is equipped with a burner, and the material feeding fan delivers the material to the burner. The boiler's outlet is connected to an air preheater, and the air preheater's flue gas outlet is connected to a dust collector. The dust collector is connected to a smoke exhaust duct structure; The air preheater is equipped with a secondary air duct structure. The air inlet of the dryer is equipped with an induced draft fan, and the exhaust duct structure and the secondary air duct structure are connected to the air inlet of the induced draft fan. The induced draft fan pumps the secondary air and the dust-removed flue gas to the dryer to dry the material. The biomass powder hot air delivery and co-firing system also includes a valve structure for controlling the secondary air duct structure and the flue gas duct structure. The method for controlling the co-firing system is as follows: The measured temperature of the hot secondary air at the air preheater outlet is T1, the measured temperature of the flue gas at the dust collector outlet is T2, and the measured point for the flue gas oxygen content is marked as O. 2,2 The flue gas CO measuring point is marked as CO2, and the measured value of the hot secondary air oxygen is O2. 2,1 The measured CO content was CO1. Add flow rate measurement points for hot secondary air and flue gas after dust removal, with measured values ​​Q1 and Q2 respectively. Control the opening of the first and second valves by the temperature and oxygen content of the mixed hot air. The specific control method is as follows: The temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The calculated and set hot air temperature, oxygen content, and CO content are T. p O 2, p, CO p ; The specific heat capacities of hot secondary air and flue gas after dust removal were measured as c1 and c2, respectively, and the biomass powder feed rate Qs was measured. The flow rate of the mixed hot air is measured as Q. The feed fan is controlled by frequency converter to effectively adjust the gas-solid ratio, i.e., adjust Q to control the flow rate at the minimum level to avoid blockage. Based on the conservation of matter and energy, the following correlation is obtained: Q1 + Q2 = Q; Q1*O2,1+Q2*O2,2=Q*O2; Q1*CO1+Q2*CO2=Q*CO; c1*Q1*(T1-T)=c2*Q2*(T-T2); The calculation shows that: O2=(Q1*(O 2,1 -O 2,2 )+Q*O 2,2 ) / Q; When O2 is higher than the set value O 2,p Then reduce Q1 by closing the first valve or opening the second valve. CO=(Q*CO1+Q2*(CO2-CO1)) / Q; When CO is higher than the set value CO p Then reduce Q2 by closing the second valve or opening the first valve. T=(Q1*(c1*T1-c2*T2)+c2*T2*Q) / (Q1*(c1-c2)+c2*Q); When T is higher than the set value Tp, Q1 is reduced by closing the first valve or opening the second valve. Among them, O 2,1 =21%; the temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The temperature of the mixed hot air should not exceed 200℃, the oxygen content should not exceed 10%, and the CO content should not exceed 0.02%.

2. The biomass powder hot air conveying and co-firing system according to claim 1, characterized in that, The silo is an underground silo; A spiral pushing structure is installed at the discharge port of the silo, which is used to assist in feeding biomass onto the belt conveyor.

3. The biomass powder hot air conveying and co-firing system according to claim 1, characterized in that, The air inlet end of the induced draft fan is equipped with a hot air delivery pipe. The secondary air duct structure and the smoke exhaust duct structure are respectively connected to the feeding hot air duct.

4. The biomass powder hot air conveying and co-firing system according to claim 3, characterized in that, The secondary air duct structure includes a secondary air inlet pipe connected to the air preheater, a secondary air outlet pipe connected to the air preheater's outlet end, and the secondary air outlet pipe connected to the boiler's inlet end. The secondary air outlet pipe is connected to a first branch pipe, which is connected to the feeding hot air pipe.

5. The biomass powder hot air conveying and co-firing system according to claim 4, characterized in that, The flue gas duct structure includes a first flue gas pipe connected to the flue gas outlet end of the boiler. The first flue gas outlet pipe is connected to the flue gas inlet of the air preheater, and the flue gas outlet of the air preheater is connected to a second flue gas outlet pipe, which is connected to the flue gas inlet of the dust collector. The dust collector is connected to a flue gas duct, which is connected to the feeding hot air duct via a second branch pipe.

6. The biomass powder hot air conveying and co-firing system according to claim 5, characterized in that, The valve structure includes a first valve installed on a first branch pipe, and the valve structure also includes a second valve installed on a second branch pipe.

7. The biomass powder hot air conveying and co-firing system according to claim 1, characterized in that, The belt is equipped with a weighing sensor for weighing the biomass.

8. The biomass powder hot air conveying and co-firing system according to claim 1, characterized in that, The dryer is a drum dryer.

9. A method for co-firing biomass powder using the hot air conveying and co-firing system as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Feeding: After the biomass material is fed into the hopper, it is conveyed to the feed dryer by belt conveyor; The induced draft fan pumps the secondary air and the flue gas after dust removal into the dryer to dry the material; After the material is dried, it is pumped into the boiler by a material conveying fan and then co-fired by the burner. (2) Firing control: The measured temperature of the hot secondary air at the air preheater outlet is T1, the measured temperature of the flue gas at the dust collector outlet is T2, and the measured point for the flue gas oxygen content is marked as O. 2,2 The flue gas CO measuring point is marked as CO2, and the measured value of the hot secondary air oxygen is O2. 2,1 The measured CO content was CO1. Add flow rate measurement points for hot secondary air and flue gas after dust removal, with measured values ​​Q1 and Q2 respectively. Control the opening of the first and second valves by the temperature and oxygen content of the mixed hot air. The specific control method is as follows: The temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The setpoint for the hot air temperature, oxygen content, and CO content is T. p O 2, p, CO p ; The specific heat capacities of hot secondary air and flue gas after dust removal were measured as c1 and c2, respectively, and the biomass powder feed rate Qs was measured. The flow rate of the mixed hot air is measured as Q. The feed fan is controlled by frequency converter to effectively adjust the gas-solid ratio, i.e., adjust Q to control the flow rate at the minimum level to avoid blockage. Based on the conservation of matter and energy, the following correlation is obtained: Q1 + Q2 = Q; Q1*O2,1+Q2*O2,2=Q*O2; Q1*CO1+Q2*CO2=Q*CO; c1*Q1*(T1-T)=c2*Q2*(T-T2); The calculation shows that: O2=(Q1*(O 2,1 -O 2,2 )+Q*O 2,2 ) / Q; When O2 is higher than the set value O 2,p Then reduce Q1 by closing the first valve or opening the second valve. CO=(Q*CO1+Q2*(CO2-CO1)) / Q; When CO is higher than the set value CO p Then reduce Q2 by closing the second valve or opening the first valve. T=(Q1*(c1*T1-c2*T2)+c2*T2*Q) / (Q1*(c1-c2)+c2*Q); When T is higher than the set value Tp, Q1 is reduced by closing the first valve or opening the second valve.

10. The co-firing method according to claim 9, characterized in that, In step (2), O 2,1 =21%; the temperature of the mixed hot air is denoted as T, the oxygen content as O2, and the CO content as CO, to ensure that the biomass does not spontaneously combust. The temperature of the mixed hot air should not exceed 200℃, the oxygen content should not exceed 10%, and the CO content should not exceed 0.02%.

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