Biomass gas staged combustion system and control method

Abstract

The invention discloses a biomass gas staged combustion system and a control method, the system comprises a staged combustor, a gas induced draft fan and an air blower, the gas induced draft fan is connected with the staged combustor through a gas main pipeline, a first-stage gas branch pipeline and a second-stage gas branch pipeline, the first-stage gas branch pipeline and the second-stage gas branch pipeline are connected in parallel, and the air blower is connected with the staged combustor. A first-stage fuel gas electric control valve is mounted on the first-stage fuel gas branch pipeline, and a second-stage fuel gas electric control valve is mounted on the second-stage fuel gas branch pipeline; the air blower is connected with the grading combustor through an air main pipeline, a first-stage air branch pipeline and a second-stage air branch pipeline, the first-stage air branch pipeline and the second-stage air branch pipeline are connected in parallel, and a first-stage air electric control valve is installed on the first-stage air branch pipeline; and a second-stage air electric control valve is mounted on the second-stage air branch pipeline. According to the invention, high-efficiency combustion and low-nitrogen emission are realized in a relatively wide load range.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass gasification gas burners, and more particularly to a biomass gas staged combustion system and a control method. Background Art

[0002] Biomass gas is a combustible gas produced by the gasification reaction of biomass raw materials (wood chips, bamboo, rice husks, fruit shells and other agricultural and forestry wastes) in a biomass gasifier. Biomass gas is a low calorific value combustible gas. At present, the main way to use biomass gas is to produce gas in a biomass gasifier to supply biomass gas boilers for combustion and heating. The nitrogen oxide emissions of biomass gas combustion systems are generally high. In order to achieve low-nitrogen combustion of biomass gas, premixed combustion and staged combustion are generally used to reduce nitrogen oxide emissions from combustion.

[0003] But there are still some problems:

[0004] (1) The air staged combustion method generally has the disadvantages of unstable partial load performance and poor load regulation performance: when the burner power is at a higher load state, the nitrogen oxide emissions can be effectively controlled. However, when the load fluctuates or the power is at a lower load state, the air staged distribution is often unreasonable, which makes the equivalent ratio of gas to air in the staged combustion unreasonable, resulting in a high flame temperature, increased nitrogen oxide emissions, or incomplete combustion, affecting the combustion efficiency.

[0005] (2) The use of fuel staged combustion still has the problem of unstable performance at some loads: when the load changes or the power is in a low load state, the fuel cannot be reasonably graded and adjusted, and the air corresponding to each level of fuel cannot be reasonably matched, resulting in an unreasonable equivalence ratio of each level of combustion, and the effect of low-nitrogen combustion cannot be achieved. It may even cause increased nitrogen oxide emissions and incomplete combustion.

[0006] (3) In order to ensure the fuel grading ratio control, it is necessary to install corresponding flow sensors on the gas main pipe and branch pipe to determine the flow of primary fuel and secondary fuel. However, biomass gas contains a large amount of tar, and tar precipitation often blocks the flow sensor, resulting in inaccurate flow measurement or failure of the flow sensor to work properly.

[0007] Therefore, providing a biomass gas staged combustion system and control method is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0008] In view of this, the present invention provides a biomass gas staged combustion system and control method, which adopts a combination of fuel staged control and staged combustion equivalence ratio control to enable the burner to achieve efficient combustion and low nitrogen emissions within a wider load range.

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

[0010] A biomass gas staged combustion system comprises a boiler body and a staged burner installed thereon, and also comprises a gas induced draft fan, a gas main pipeline, a primary gas branch pipeline, a secondary gas branch pipeline, a blower, an air main pipeline, a primary air branch pipeline and a secondary air branch pipeline, wherein the gas induced draft fan is connected to the staged burner through the gas main pipeline, the primary gas branch pipeline and the secondary gas branch pipeline, and the primary gas branch pipeline and the secondary gas branch pipeline are connected in parallel, a manual shut-off valve and two pneumatic shut-off valves are sequentially installed on the gas main pipeline along the gas flow direction, a primary gas electric regulating valve is installed on the primary gas branch pipeline, and a secondary gas electric regulating valve is installed on the secondary gas branch pipeline; the blower is connected to the staged burner through the air main pipeline, the primary air branch pipeline and the secondary air branch pipeline, and the primary air branch pipeline and the secondary air branch pipeline are connected in parallel, a primary air electric regulating valve is installed on the primary air branch pipeline; and a secondary air electric regulating valve is installed on the secondary air branch pipeline.

[0011] Furthermore, it also includes a flame detector, a NOx sensor, a gas draft fan inverter, a blower inverter and a programmable controller, wherein the flame detector is installed on the boiler body near the outlet of the staged burner; the NOx sensor is installed at the flue gas outlet of the boiler body; the gas draft fan inverter is electrically connected to the gas draft fan, and the blower inverter is electrically connected to the blower; the flame detector and the NOx sensor are electrically connected to the programmable controller respectively, and the programmable controller is electrically connected to the gas draft fan inverter, the blower inverter, the first-level gas electric regulating valve, the second-level gas electric regulating valve, the first-level air electric regulating valve, the second-level air electric regulating valve and the two pneumatic shut-off valves respectively.

[0012] A biomass gas staged combustion system control method is implemented using the biomass gas staged combustion system as described above, comprising the following steps:

[0013] 1) Determination of load ratio of staged burner

[0014] The load ratio of the staged burner is the ratio of the actual fuel flow of the gas induced draft fan to the designed rated flow of the gas induced draft fan;

[0015] 2) Determination of fuel staging ratio under different staging burner load ratio conditions

[0016] The staged burner includes a main combustion zone and a supplementary combustion zone, wherein the primary fuel is mixed with the primary air and then burned in the main combustion zone, the secondary fuel is mixed with the secondary air, and then mixed with the combustion products of the main combustion zone and then burned in the supplementary combustion zone, and the secondary fuel reburns with NO in the high-temperature flue gas generated by the combustion of the main combustion zone to reduce NO in the high-temperature flue gas of the main combustion zone and reduce the NOx concentration in the flue gas;

[0017] The ratio of primary fuel and secondary fuel is controlled by the primary gas electric regulating valve and the secondary gas electric regulating valve. The adjustment range of the primary fuel ratio is 80%-100%, and the adjustment range of the secondary fuel ratio is 0-20%. When the load ratio of the staged burner is ≤20%, the primary gas electric regulating valve is closed, and all combustion occurs in the supplementary combustion area. When the load ratio of the staged burner is greater than 20%, the ratio control relationship between the primary fuel and the secondary fuel satisfies the following formula:

[0018] α1=β-α2

[0019] 0≤α2≤α2max

[0020] Among them, α1 is the proportion of primary fuel to the total fuel, α2 is the proportion of secondary fuel to the total fuel, and α2max is the maximum proportion of secondary fuel;

[0021] α2max=0.2×β

[0022] Among them, β is the load ratio of the staged burner;

[0023] 3) Adjustment and control of fuel staging ratio

[0024] The emission limit of NOx is set by the programmable controller, and the concentration of NOx in the flue gas after combustion is obtained by feedback from the NOx sensor. The programmable controller compares the feedback value with the set emission limit. When the feedback value is higher than the emission limit, if the current load ratio of the staged burner is greater than 20%, it is adjusted by controlling the secondary fuel ratio, and the NOx concentration in the flue gas fed back by the NOx sensor is monitored at the same time. When the NOx concentration falls back to the set limit, the adjustment control is stopped; when the secondary fuel ratio has been adjusted to the maximum adjustable ratio under the corresponding load ratio condition, the adjustment control is stopped;

[0025] 4) Adjustment and control of air classification ratio

[0026] The programmable controller adjusts the opening of the primary air electric regulating valve and the secondary air electric regulating valve according to the operating frequency of the gas induced draft fan, the opening of the secondary gas electric regulating valve, the opening of the primary gas electric regulating valve and the equivalence ratio to achieve proportional control of the primary air and the secondary air.

[0027] Furthermore, the control method of the secondary fuel ratio is specifically as follows: the primary gas electric regulating valve and the secondary gas electric regulating valve are coordinated and adjusted to meet the secondary fuel ratio requirements under different graded burner load ratios, wherein both the primary gas electric regulating valve and the secondary gas electric regulating valve adopt regulating valves with equal percentage regulating characteristics of flow characteristics, so as to determine the gas flow of the pipeline where the gas regulating valves of each level are located according to the adjusted opening feedback signal;

[0028] Under different load ratios of graded burners, the valve opening adjustment control relationship of the first-stage gas electric regulating valve and the second-stage gas electric regulating valve satisfies the following formula:

[0029] φ1=β-0.2×φ2

[0030] 0≤φ2≤φ2max

[0031] Among them, φ1 is the opening of the first-stage gas electric regulating valve, φ2 is the opening of the second-stage gas electric regulating valve, and φ2max is the maximum opening of the second-stage gas electric regulating valve;

[0032] φ2max=β

[0033] Among them, β is the burner load ratio.

[0034] Furthermore, in step 1), the gas induced draft fan adopts a centrifugal fan, whose flow rate, rotation speed and operating frequency are in direct proportion, and the load ratio of the staged burner is determined by the ratio of the actual operating frequency of the gas induced draft fan to the operating frequency.

[0035] Furthermore, when the staged burner operates normally, the flame detector monitors the flame signal and feeds it back to the programmable controller in real time. When the flame goes out, the flame detector sends an alarm signal to the programmable controller, and the programmable controller closes the two pneumatic shut-off valves through a control signal.

[0036] It can be seen that the present invention provides a biomass gas staged combustion system and control method. Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) Different fuel grading ratios are determined according to different graded burner load ratios. Adjustment ranges are set for both primary and secondary fuels. Adjustments are made within the set adjustment ranges according to the NOx sensor feedback signal, effectively ensuring a lower NOx emission level under partial load conditions;

[0038] 2) By monitoring the operating frequency of the gas induced draft fan and the opening signal of the primary / secondary gas electric regulating valve, the load ratio of the graded burner and the primary / secondary gas flow data are indirectly calculated. There is no need to install a flow sensor on the gas pipeline, which can effectively avoid the influence of tar precipitation on the flow measurement accuracy;

[0039] 3) The NOx sensor monitors the NOx concentration generated by the combustion of the boiler in real time, and uses the monitoring signal as the basis for controlling the opening of the primary / secondary gas electric regulating valve, which can effectively control NOx emissions under partial load;

[0040] 4) The flame condition is monitored in real time based on the flame detector monitoring signal installed near the burner outlet of the boiler body. When a fault occurs and the flame goes out, the programmable controller closes the two pneumatic shut-off valves at the same time to increase the safety and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0042] Figure 1 The accompanying drawing is a schematic structural diagram of a biomass gas staged combustion system provided by the present invention;

[0043] Figure 2 The accompanying drawing is a flow chart of a biomass gas staged combustion system control method provided by the present invention. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] like Figure 1 , 2As shown, an embodiment of the present invention discloses a biomass gas staged combustion system, including a boiler body 1, a staged burner 2, a gas induced draft fan 3, a gas main pipeline 4, a primary gas branch pipeline 5, a secondary gas branch pipeline 6, a blower 7, an air main pipeline 8, a primary air branch pipeline 9 and a secondary air branch pipeline 10. The staged burner 2 is installed on the boiler body 1 to realize staged combustion to reduce the NOx content in the flue gas. The gas induced draft fan 3 is connected to the staged burner 2 through the gas main pipeline 4, the primary gas branch pipeline 5 and the secondary gas branch pipeline 6, and the primary gas branch pipeline 5 and the secondary gas branch pipeline 6 are connected in parallel. A manual shut-off valve 11 and two pneumatic shut-off valves 12 are sequentially installed on the gas main pipeline 4 along the gas flow direction, and a primary gas electric regulating valve 13 is installed on the primary gas branch pipeline 5. , a secondary gas electric regulating valve 14 is installed on the secondary gas branch pipe 6, wherein the manual shut-off valve 11 is used to manually close the gas main pipe 4, the pneumatic shut-off valve 12 is used to emergency shut off the gas main pipe 4 in case of system failure, flameout, etc., the primary gas electric regulating valve 13 and the secondary gas electric regulating valve 14 are used to adjust the fuel staging ratio; the blower 7 is connected to the staging burner 2 through the air main pipe 8, the primary air branch pipe 9 and the secondary air branch pipe 10, and the primary air branch pipe 9 and the secondary air branch pipe 10 are connected in parallel, and the primary air branch pipe 9 is installed with a primary air electric regulating valve 15; the secondary air branch pipe 10 is installed with a secondary air electric regulating valve 16, wherein the primary air electric regulating valve 15 and the secondary air electric regulating valve 16 are used to adjust the air staging ratio. The present invention combines fuel staging control with staging combustion equivalence ratio control, so that the staging burner 2 can achieve the functions of high-efficiency combustion and low nitrogen emission in a wider load range.

[0046] In order to improve the level of intelligence, it also includes a flame detector 17, a NOx sensor 18, a gas induced draft fan inverter 19, a blower inverter 20 and a programmable controller 21. The flame detector 17 is installed on the boiler body 1 near the outlet of the staged burner 2, and the NOx sensor 18 is installed on the flue gas outlet of the boiler body 1, which is used to feed back the real-time flame situation and flue gas NOx data to the programmable controller 21 in real time; the gas induced draft fan inverter 19 is electrically connected to the gas induced draft fan 3 to control the flow of the gas induced draft fan 3, and the blower inverter 20 is electrically connected to the blower 7 to control the flow of the blower 7; the flame detector 17 and the NOx sensor 18 are respectively electrically connected to the programmable controller 21, and the programmable controller 21 is respectively connected to the gas induced draft fan inverter 1 9. The blower inverter 20, the first-level gas electric regulating valve 13, the second-level gas electric regulating valve 14, the first-level air electric regulating valve 15, the second-level air electric regulating valve 16 and the two pneumatic shut-off valves 12 are electrically connected. The first-level gas electric regulating valve 13, the second-level gas electric regulating valve 14, the first-level air electric regulating valve 15, the second-level air electric regulating valve 16 feed back valve position signals to the programmable controller 21. The programmable controller 21 determines the ratio of fuel staging to air staging according to the valve position signals, and adjusts the valve position opening of the electric regulating valves (the first-level gas electric regulating valve 13, the second-level gas electric regulating valve 14, the first-level air electric regulating valve 15, the second-level air electric regulating valve 16) according to the data fed back by the NOx sensor 18 to control the ratio of fuel staging to air staging.

[0047] Of course, when the staged burner 2 is working normally, the flame detector 17 monitors the flame signal and feeds it back to the programmable controller 21 in real time. When the flame is extinguished, the flame detector 17 sends an alarm signal to the programmable controller 21, and the programmable controller 21 closes the two pneumatic shut-off valves 12 through the control signal to ensure system safety.

[0048] The embodiment of the present invention further discloses a biomass gas staged combustion system control method, which is performed using the biomass gas staged combustion system as described above, and includes the following steps:

[0049] 1) Determination of load ratio of staged burner 2

[0050] The load ratio of the staged burner 2 is the ratio of the actual fuel flow of the gas induced draft fan 3 to the designed rated flow of the gas induced draft fan 3; in this embodiment, the gas induced draft fan 3 adopts a centrifugal fan, and its flow, speed, and operating frequency are in a proportional relationship. The load ratio of the staged burner 2 is determined by the ratio of the actual operating frequency of the gas induced draft fan 3 to the power frequency (50Hz);

[0051] 2) Determination of fuel staging ratio under different staging burner 2 load ratio conditions

[0052] The staged burner 2 includes a main combustion zone and a supplementary combustion zone, wherein the primary fuel is mixed with the primary air and then burned in the main combustion zone, the secondary fuel is mixed with the secondary air, and then mixed with the combustion products of the main combustion zone and then burned in the supplementary combustion zone, and the secondary fuel reburns with NO in the high-temperature flue gas generated by the combustion of the main combustion zone to reduce the NO in the high-temperature flue gas of the main combustion zone and reduce the NOx concentration in the flue gas;

[0053] The ratio of the primary fuel and the secondary fuel is controlled by the primary gas electric regulating valve 13 and the secondary gas electric regulating valve 14, wherein the primary fuel ratio adjustment range is 80%-100%, and the secondary fuel ratio adjustment range is 0-20%. When the load ratio of the staged burner 2 is ≤20%, the primary gas electric regulating valve 13 is closed, and all combustion occurs in the supplementary combustion area. When the load ratio of the staged burner 2 is greater than 20%, the ratio control relationship between the primary fuel and the secondary fuel satisfies the following formula:

[0054] α1=β-α2

[0055] 0≤α2≤α2max

[0056] Among them, α1 is the proportion of primary fuel to the total fuel, α2 is the proportion of secondary fuel to the total fuel, and α2max is the maximum proportion of secondary fuel;

[0057] α2max=0.2×β

[0058] Among them, β is the load ratio of the staged burner;

[0059] When the secondary fuel ratio is adjusted within the set range, the primary fuel ratio can be calculated according to the above formula. Under different load ratios (30%-100%), the secondary fuel ratio adjustment range and the corresponding primary fuel ratio are shown in the following table:

[0060]

[0061]

[0062] 3) Adjustment and control of fuel staging ratio

[0063] The emission limit of NOx is set by the programmable controller 21, and the concentration value of NOx in the flue gas after combustion is obtained by feedback from the NOx sensor 18. The programmable controller 21 compares the feedback value with the set emission limit. When the feedback value is higher than the emission limit, if the current load ratio of the staged burner 2 is greater than 20%, the secondary fuel ratio is controlled to adjust, and the NOx concentration in the flue gas fed back by the NOx sensor 18 is monitored at the same time. When the NOx concentration falls back to the set limit, the adjustment control is stopped; when the secondary fuel ratio has been adjusted to the maximum ratio that can be adjusted under the corresponding load ratio condition, the adjustment control is stopped;

[0064] 4) Adjustment and control of air classification ratio

[0065] The programmable controller 21 adjusts the openings of the primary air electric regulating valve 15 and the secondary air electric regulating valve 16 according to the operating frequency of the gas induced draft fan 3, the opening of the primary gas electric regulating valve 13, the opening of the secondary gas electric regulating valve 14 and the equivalence ratio, thereby achieving proportional control of the primary air and the secondary air.

[0066] Specifically, the control method of the secondary fuel ratio is as follows: the primary gas electric regulating valve 13 and the secondary gas electric regulating valve 14 are coordinated and adjusted to meet the secondary fuel ratio requirements under different graded burner load ratios, wherein the primary gas electric regulating valve 13 and the secondary gas electric regulating valve 14 both adopt regulating valves with equal percentage regulating characteristics in flow characteristics, and the flow characteristics refer to the relationship between the relative flow and the relative stroke (opening) of the regulating valve, that is, the corresponding relationship between the ratio of the flow at a certain opening to the flow at the fully open state and the ratio of the stroke of the regulating valve at the corresponding opening to the stroke of the fully open state. The equal percentage regulating characteristic means that the relative stroke is proportional to the relative flow. Therefore, the gas flow of the pipeline where the gas regulating valves of each level are located is determined according to the adjusted opening feedback signal;

[0067] Under different load ratios of the graded burners 2, the valve opening adjustment control relationship of the first-stage gas electric regulating valve 13 and the second-stage gas electric regulating valve 14 satisfies the following formula:

[0068] φ1=β-0.2×φ2

[0069] 0≤φ2≤φ2max

[0070] Among them, φ1 is the opening degree of the first-stage gas electric regulating valve 13, φ2 is the opening degree of the second-stage gas electric regulating valve 14, and φ2max is the maximum opening degree of the second-stage gas electric regulating valve 14;

[0071] φ2max=β

[0072] Where, β is the load ratio of staged burner 2;

[0073] When the opening of the secondary gas electric regulating valve 14 is adjusted within the set range, the opening of the primary gas electric regulating valve 13 can be calculated according to the above formula. Under different load ratios (30%-100%), the opening adjustment range of the secondary gas electric regulating valve 14 and the corresponding opening of the primary gas electric regulating valve 13 are shown in the following table:

[0074]

[0075] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0076] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A biomass gas staged combustion system, comprising a boiler body and a staged burner installed thereon, characterized in that: It also includes a gas induced draft fan, a gas main pipeline, a first-level gas branch pipeline, a second-level gas branch pipeline, a blower, an air main pipeline, a first-level air branch pipeline and a second-level air branch pipeline. The gas induced draft fan is connected to the staged burner through the gas main pipeline, the first-level gas branch pipeline and the second-level gas branch pipeline, and the first-level gas branch pipeline and the second-level gas branch pipeline are connected in parallel. A manual shut-off valve and two pneumatic shut-off valves are sequentially installed on the gas main pipeline along the gas flow direction. A first-level gas electric regulating valve is installed on the first-level gas branch pipeline, and a second-level gas electric regulating valve is installed on the second-level gas branch pipeline; the blower is connected to the staged burner through the air main pipeline, the first-level air branch pipeline and the second-level air branch pipeline, and the first-level air branch pipeline and the second-level air branch pipeline are connected in parallel. A first-level air electric regulating valve is installed on the first-level air branch pipeline; and a second-level air electric regulating valve is installed on the second-level air branch pipeline.

2. A biomass gas staged combustion system according to claim 1, characterized in that: It also includes a flame detector, a NOx sensor, a gas draft fan inverter, a blower inverter and a programmable controller, wherein the flame detector is installed on the boiler body near the outlet of the staged burner; the NOx sensor is installed at the flue gas outlet of the boiler body; the gas draft fan inverter is electrically connected to the gas draft fan, and the blower inverter is electrically connected to the blower; the flame detector and the NOx sensor are electrically connected to the programmable controller respectively, and the programmable controller is electrically connected to the gas draft fan inverter, the blower inverter, the first-level gas electric regulating valve, the second-level gas electric regulating valve, the first-level air electric regulating valve, the second-level air electric regulating valve and the two pneumatic shut-off valves respectively.

3. A biomass gas staged combustion system control method, using the biomass gas staged combustion system according to claim 2, characterized in that: The following steps are involved: 1) Determination of load ratio of staged burner The load ratio of the staged burner is the ratio of the actual fuel flow of the gas induced draft fan to the designed rated flow of the gas induced draft fan; 2) Determination of fuel staging ratio under different staging burner load ratio conditions The staged burner includes a main combustion zone and a supplementary combustion zone, wherein the primary fuel is mixed with the primary air and then burned in the main combustion zone, the secondary fuel is mixed with the secondary air, and then mixed with the combustion products of the main combustion zone and then burned in the supplementary combustion zone, and the secondary fuel reburns with NO in the high-temperature flue gas generated by the combustion of the main combustion zone to reduce NO in the high-temperature flue gas of the main combustion zone and reduce the NOx concentration in the flue gas; The ratio of primary fuel and secondary fuel is controlled by the primary gas electric regulating valve and the secondary gas electric regulating valve. The adjustment range of the primary fuel ratio is 80%-100%, and the adjustment range of the secondary fuel ratio is 0-20%. When the load ratio of the staged burner is ≤20%, the primary gas electric regulating valve is closed, and all combustion occurs in the supplementary combustion area. When the load ratio of the staged burner is greater than 20%, the ratio control relationship between the primary fuel and the secondary fuel satisfies the following formula: α1＝β-α2 0≤α2≤α2max Among them, α1 is the proportion of primary fuel to the total fuel, α2 is the proportion of secondary fuel to the total fuel, and α2max is the maximum proportion of secondary fuel; α2max=0.2×β Among them, β is the load ratio of the staged burner; 3) Adjustment and control of fuel staging ratio The emission limit of NOx is set by the programmable controller, and the concentration of NOx in the flue gas after combustion is obtained by feedback from the NOx sensor. The programmable controller compares the feedback value with the set emission limit. When the feedback value is higher than the emission limit, if the current load ratio of the staged burner is greater than 20%, it is adjusted by controlling the secondary fuel ratio, and the NOx concentration in the flue gas fed back by the NOx sensor is monitored at the same time. When the NOx concentration falls back to the set limit, the adjustment control is stopped; when the secondary fuel ratio has been adjusted to the maximum adjustable ratio under the corresponding load ratio condition, the adjustment control is stopped; 4) Adjustment and control of air classification ratio The programmable controller adjusts the opening of the primary air electric regulating valve and the secondary air electric regulating valve according to the operating frequency of the gas induced draft fan, the opening of the secondary gas electric regulating valve, the opening of the primary gas electric regulating valve and the equivalence ratio to achieve proportional control of the primary air and the secondary air.

4. A biomass gas staged combustion system control method according to claim 3, characterized in that: The control method of the secondary fuel ratio is specifically as follows: the primary gas electric regulating valve and the secondary gas electric regulating valve are coordinated and adjusted to meet the secondary fuel ratio requirements under different graded burner load ratios, wherein both the primary gas electric regulating valve and the secondary gas electric regulating valve adopt regulating valves with equal percentage regulating characteristics of flow characteristics, so as to determine the gas flow of the pipeline where the gas regulating valves of each level are located according to the adjusted opening feedback signal; Under different load ratios of graded burners, the valve opening adjustment control relationship of the first-stage gas electric regulating valve and the second-stage gas electric regulating valve satisfies the following formula: φ1=β-0.2×φ2 0≤φ2≤φ2max Among them, φ1 is the opening of the first-stage gas electric regulating valve, φ2 is the opening of the second-stage gas electric regulating valve, and φ2max is the maximum opening of the second-stage gas electric regulating valve; φ2max=β Among them, β is the load ratio of the staged burner.

5. A biomass gas staged combustion system control method according to claim 3, characterized in that: In step 1), the gas induced draft fan adopts a centrifugal fan, whose flow rate, rotation speed and operating frequency are in direct proportion, and the load ratio of the staged burner is determined by the ratio of the actual operating frequency of the gas induced draft fan to the operating frequency.

6. A biomass gas staged combustion system control method according to claim 3, characterized in that: When the staged burner is operating normally, the flame detector monitors the flame signal and feeds it back to the programmable controller in real time. When the flame is extinguished, the flame detector sends an alarm signal to the programmable controller, and the programmable controller closes the two pneumatic shut-off valves through the control signal.

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