Staged combustion control method and system

Abstract

The invention discloses a staged combustion control method and system, and aims to solve the problem of oxygen-fuel ratio imbalance caused by inconsistent dynamic response of fuel and an oxidant in a combustion power change process. The method breaks down the regulation process of the fuel flow into at least one intermediate stage. And in each intermediate stage, the fuel flow is kept stable after approaching an intermediate target value, and the fuel flow of the next intermediate stage is continuously adjusted after the oxidant flow dynamically follows up until the actual oxygen-fuel ratio reaches a preset range. According to the scheme, the stability of the oxygen-fuel ratio in the transient process is ensured, the combustion efficiency is improved, and emission of harmful gas is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of combustion, in particular to a combustion control system and method. More specifically, it relates to a staged combustion control method and system. BACKGROUND

[0002] The combustion control system is a complex system with multiple variables, strong coupling and large time delay. The main input parameters of the combustion control system include the burner power, fuel flow, oxidant flow and fuel heat value, etc. The main output parameters of the combustion control system include the opening degree of each control valve, etc. There is a complex coupling relationship between the parameters, and the combustion control system is also affected by many external disturbances, such as fuel heat value fluctuation and pressure change, etc., which can significantly interfere with the stable operation of the combustion control system.

[0003] In industrial combustion applications, especially in oxy-fuel combustion applications, it is crucial to accurately control the ratio of fuel to oxidant (i.e. oxy-fuel ratio). The ideal oxy-fuel ratio can ensure complete combustion of the fuel to achieve the highest thermal efficiency. The power of the burner will be adjusted up or down according to the working condition. Affected by the pressure, delivery pipe diameter, control valve opening degree, etc. of the fuel and oxidant, the adjustment of the oxidant and the fuel will not be synchronized. If the proportion of the oxidant is too high, it will be easy to produce nitrogen oxides in the kiln, and take away heat. If the proportion of the fuel is too high, it will be easy to produce excess carbon monoxide in the kiln.

[0004] Currently, many combustion systems use automatic control schemes based on PID (proportional-integral-derivative). Most traditional burners use a relatively simple way to control the oxy-fuel ratio, which is difficult to accurately adjust the oxy-fuel ratio synchronously and stably according to the changes in the combustion working condition. For example, even if some of the burners use automatic control, the control algorithm is relatively backward and cannot achieve precise control of the oxy-fuel ratio. When facing load changes or fuel quality fluctuations, the combustion system cannot quickly respond and maintain the optimal oxy-fuel ratio. For example, the Chinese patent CN116282843A discloses a common cascade or ratio control system, in which the kiln temperature output is used to adjust the set point (SP) of the fuel flow, and the set point of the oxidant (such as oxygen) is obtained by multiplying the actual flow feedback value (PV) of the fuel by a fixed ratio (K). This control method can only maintain a certain oxy-fuel ratio under stable working conditions. Transient changes in the combustion working condition will cause the oxy-fuel ratio to be out of balance.

[0005] However, a key technical challenge in this field is the transient regulation process, i.e. when the system power needs to be increased or decreased. Due to the different physical conditions of the fuel and oxidant delivery pipe characteristics, valve actuator response speed, fluid pressure, etc., the actual flow of the two often cannot be synchronized, making it difficult to maintain a stable oxy-fuel ratio.

[0006] Under traditional PID control, when the system is instructed to quickly increase power, the fuel set point will be quickly raised. However, due to control lag and mechanical difference, the actual increase rate of oxidant flow often cannot keep up with the increase rate of fuel flow. This will cause the combustor to temporarily be in a "fuel-rich" or "oxygen-deficient" state during power climb, and the oxygen-fuel ratio will continuously be lower than the theoretical value. This transient imbalance in the ratio will cause incomplete combustion of the fuel, resulting in a large amount of carbon monoxide, not only wasting energy, but also causing serious environmental pollution and safety hazards. If the load mutation exceeds the system response capability (such as emergency load increase / decrease), it may cause short-term air-fuel ratio imbalance (such as black smoke or flameout). SUMMARY

[0007] The present application aims to solve the problem of air-fuel ratio imbalance caused by inconsistent dynamic response of fuel and oxidant during combustion, such as oxidant flow lag.

[0008] The present application provides an optimized method for controlling the air-fuel ratio. When the combustor power is increased, the fuel flow is first adjusted to an intermediate value and maintained stable; in this stable state, the oxidant flow is waited to rise to a matching value; after the oxidant flow meets the condition, the adjustment of the next stage is started. This step-by-step adjustment in stages ensures that the air-fuel ratio is always maintained at the target value. This avoids the air-fuel ratio being continuously low, reduces the production of harmful gases, and improves the combustion efficiency and adjustment accuracy.

[0009] The first aspect of the present application provides a staged combustion control method, the combustion control method comprising the steps of: S1: setting a combustor target power, thereby determining a fuel target flow; S2: splitting the range from the current fuel flow to the fuel target flow into at least one intermediate stage, each intermediate stage corresponding to a fuel intermediate flow; S3: for the at least one intermediate stage, performing: S3-1: adjusting the current fuel flow to approach the fuel intermediate flow, dynamically setting and monitoring the current oxidant flow based on the current fuel flow and the target air-fuel ratio; S3-2: when the current fuel flow reaches the fuel intermediate flow, maintaining the current fuel flow stable; S3-3: maintaining the stable state of the current fuel flow until the air-fuel ratio reaches a preset range; S3-4: after releasing the stable state of the current fuel flow, adjusting the current fuel flow to approach the next fuel intermediate flow or the fuel target flow.

[0010] Further, the preset range of the oxygen-fuel ratio in step S3-3 is 90% of the target oxygen-fuel ratio. That is, the current flow of the oxidant is allowed to fluctuate within a preset range, for example, the actual oxygen-fuel ratio is above 90% of the target oxygen-fuel ratio.

[0011] Further, in step S3-3, the oxygen-fuel ratio is maintained stable within a preset range.

[0012] Further, in step S2, the at least one intermediate stage is determined based on a preset power increment step or a preset number of stages. The "preset power increment step" refers to a fixed power adjustment amplitude pre-configured by a user or the system before performing the staged adjustment. The control unit divides the total power increase (i.e., the difference between the target power of the burner and the current power) by the preset "step" to calculate the total number of "intermediate stages" required. The power value corresponding to each "intermediate fuel flow" is the power value of the previous stage plus the fixed "step".

[0013] Further, after step S1, the method further comprises step S2-1: judging whether the target power of the burner satisfies a preset staged adjustment condition.

[0014] Further, the preset staged adjustment condition comprises: the target power of the burner is greater than or equal to a preset power threshold.

[0015] Further, the preset power threshold is 30% of the maximum power of the burner.

[0016] Further, if the preset staged adjustment condition is not satisfied, the combustion control method comprises the steps of: adjusting the current fuel flow to the target fuel flow at one time, and adjusting the current flow of the oxidant according to the target fuel flow and the target oxygen-fuel ratio.

[0017] Further, the method further comprises the step of: during step S3-1, if the current fuel flow exceeds the intermediate fuel flow to form an overshoot, the overshoot fuel flow is adopted as the intermediate fuel flow of the stage, and step S3-2 is performed based on the overshoot fuel flow. That is, the combustion control system does not attempt to adjust back. On the contrary, the control system accepts the overshoot value as the new stable point of the intermediate stage, and waits for the oxidant and fuel to be adjusted to match the oxygen-fuel ratio based on the overshoot value.

[0018] In a second aspect, the application provides a staged combustion control system, which comprises a fuel control device, an oxidant control device, a fuel flow monitoring device, an oxidant flow monitoring device, and a control unit. The control unit is configured to perform the combustion control method as described in the first aspect of the application.

[0019] Further, the control unit is configured to: A. receive a target power of the combustor, thereby determining a target fuel flow rate; B. divide a range from a current fuel flow rate to the target fuel flow rate into at least one intermediate stage, each of the intermediate stages corresponding to an intermediate fuel flow rate; C. for the at least one intermediate stage: C1. control the fuel control device to make the current fuel flow rate approach the intermediate fuel flow rate, and dynamically set and monitor the current oxidant flow rate based on the current fuel flow rate monitored by the fuel flow monitoring device and the target oxygen-fuel ratio; C2. when it is monitored that the current fuel flow rate reaches the intermediate fuel flow rate, maintain the current fuel flow rate stable; C3. maintain the stable state of the current fuel flow rate until the oxygen-fuel ratio calculated based on the current fuel flow rate monitored by the fuel flow monitoring device and the current oxidant flow rate of the oxidant flow monitoring device reaches a preset range; C4. control the fuel control device to approach a next intermediate fuel flow rate or the target fuel flow rate.

[0020] Further, in step C2, the current fuel flow rate is maintained stable by keeping the opening degree of the fuel control device unchanged.

[0021] In the above scheme, the control unit is used to determine the adjustment range and interval, calculate the total difference from the current fuel flow rate to the target fuel flow rate, and divide it into n intermediate stages, where n is greater than or equal to 1.

[0022] Specifically, taking power increase as an example, the n intermediate stages are executed in the manner of "first adjusting the fuel flow rate, maintaining the fuel flow rate stable, and waiting for the oxidant flow rate to adjust" step by step: The current oxidant flow rate can make the actual oxygen-fuel ratio always greater than or equal to 90% of the target oxygen-fuel ratio.

[0023] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects: Through the staged combustion control method and system, the technical scheme of the present application ensures that the actual oxygen-fuel ratio is always maintained near the target value during the entire transient process of the combustor power change, and effectively avoids the "rich fuel" state and the problem of continuously low oxygen-fuel ratio caused by oxidant lag under traditional PID control.

[0024] Since the oxygen-fuel ratio is accurately controlled, "oxygen deficiency" combustion is avoided, thereby significantly reducing harmful gases such as carbon monoxide (CO) generated by incomplete combustion, which is conducive to environmental protection and production safety.

[0025] The phased step-by-step adjustment mode makes the adjustment reference of each phase be confirmed, i.e. waiting for the realization of the oxidant flow, and realizes more accurate process control. BRIEF DESCRIPTION OF DRAWINGS

[0026] The advantages and spirits of the present application can be further understood through the following detailed description and drawings.

[0027] Figure 1 A timing chart of the conventional PID adjustment is shown.

[0028] Figure 2 A timing chart of the phased combustion control method adjustment of the present application is shown. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, the present application should not be understood as being limited to the following described embodiments, and the technical concept of the present application can be implemented in combination with other known technologies or other technologies having the same functions as those known technologies.

[0030] TERMINOLOGY In the following description of specific embodiments, in order to clearly show the structure and working mode, many directional words will be used for description, but the words of "front", "back", "left", "right", "outer", "inner", "outward", "inward", "axial", "radial" and the like should be understood as convenient words, and should not be understood as limiting words.

[0031] In the following description of specific embodiments, it should be understood that the directions or positional relationships indicated by the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the directions or positional relationships shown in the drawings, and are only for the convenience of simplifying the description, and are not intended to indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be understood as a limitation on the present application. In addition, when a first structure is described as being positioned "above" or "below" a second structure, it should be understood to mean that the first structure is positioned further away from or closer to the horizontal plane.

[0032] In addition, the terms "first", "second", "third", etc. are used only for the purpose of description, and are not intended to indicate or imply relative importance or quantity, and are not intended to limit the scope of the technical solutions indicated, but only to distinguish one technical feature from another technical feature in the technical solutions. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified. Similarly, the limiting words appearing in the text, such as "one", are not intended to limit the quantity, but to describe the technical features that have not appeared in the preceding text. Similarly, unless the noun is modified by a specific quantity, it should be considered to include both singular and plural forms in the text, that is, it can include a single technical feature or a plurality of technical features in the technical solutions. Similarly, the modifiers appearing before the numerals in the text, such as "about", "approximately", generally include the number, and its specific meaning should be understood in conjunction with the context.

[0033] It should be understood that in the present application, "at least one" means one or more, and "multiple" means two or more. "And / or" is used to describe the relationship between the associated objects, which means that there can be three relationships, for example, "A and / or B" can mean that there are three cases of only A, only B, and A and B at the same time, where A and B can be singular or plural. The character " / " generally represents that the front and rear associated objects are in an "or" relationship. "At least one of the following" or similar expressions means any combination of these items, including any combination of single or multiple items. For example, at least one of a, b or c can mean a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0034] However, the method disclosed in the present disclosure or other methods shown and / or described can be shown and / or described in the present disclosure as a series of actions or events. It should be understood that the order of the actions or events shown should not be interpreted in a limiting manner. For example, some actions can be performed in a different order and / or simultaneously with the actions or events shown and / or described in the present disclosure. In addition, not all shown actions are required to implement one or more aspects or embodiments of the present disclosure, and one or more actions of the present disclosure can be performed in one or more separate actions and / or stages.

[0035] In the present specification, the terms "unit", "piece", "object" and "module" represent a unit for processing at least one function and operation, and can be implemented by a hardware component or a software component and a combination thereof.

[0036] "Upstream" and "downstream" as described in this specification are defined with respect to the intended flow of fluid, the upstream end corresponding to the end closest to the introduction of fluid into the inlet, and the downstream end corresponding to the exit of fluid from the outlet or nozzle end.

[0037] The terms "high pressure" and "medium pressure" mean that the high pressure is higher than the medium pressure, so the difference between the two can be relatively small.

[0038] The terms "high temperature" and "low temperature" mean that the high temperature is higher than the low temperature, so the difference between the two can be relatively small.

[0039] PID controller (Proportional-Integral-Derivative Controller) is composed of three control links: proportional (P), integral (I), and derivative (D). The proportional link outputs control quantity according to the current deviation, the larger the deviation, the stronger the control effect. The integral link is used to eliminate the steady-state error of the system, which adjusts the control quantity by integrating the past deviation information. The derivative link predicts the trend of deviation change according to the rate of change of deviation, and gives control effect in advance to improve the dynamic response performance of the system.

[0040] As used herein, the term "fuel" refers to gaseous, liquid or solid fuel that can be used interchangeably or in combination. If it is at least partially in gaseous form, it can be introduced directly into the burner. If it is in liquid or solid form, it is introduced near the burner. The gaseous fuel can be natural gas (mainly methane), propane, hydrogen, synthetic gas, biomass gas or any other hydrocarbon and / or sulfur-containing and / or nitrogen-containing compound. The solid or liquid fuel can be any compound in the form of carbon and / or hydrocarbon and / or sulfur-containing. The person skilled in the art can determine the introduction method of gaseous, liquid or solid fuel as needed, and the present application does not intend to make any limitation.

[0041] As used herein, there is a direct quantitative relationship between the power of the burner and the fuel flow. The power of the burner (kW) usually refers to its ability to produce heat by burning fuel per hour, and the calculation formula is: Burner power = fuel consumption per hour × fuel heat value. The power is usually expressed in kilowatts (kW) or kilocalories per hour (kcal / h). The fuel flow can be expressed by the fuel consumption per hour (kg / h or Nm 3 / h).

[0042] As used herein, the oxygen-to-fuel ratio refers to the flow or volume ratio of oxidant to fuel in a combustion process, and is used to measure whether the ratio of the combustion system is at the stoichiometric ratio required for theoretical complete combustion. From a stoichiometric perspective, complete combustion refers to the complete reaction of the carbon-hydrogen components in the fuel with oxygen to produce CO2and water vapor, without the production of other byproducts (e.g., carbon monoxide, acetaldehyde, etc.). In order to achieve complete combustion, the ratio of fuel to oxygen must be at the stoichiometric ratio. For example, for the complete combustion of natural gas, the oxygen-to-fuel ratio is approximately 2.

[0043] As used herein, the terms "oxidant," "oxygen-enriched oxidant," and "comburent" refer to an oxidizing medium, such as air, oxygen-enriched air, or pure oxygen. The oxygen molar concentration of the oxygen-enriched oxidant can be at least 30%, at least 50%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99%. These oxygen-enriched oxidants are produced, for example, with cryogenic air separation units, or by vacuum swing adsorption processes, or any other source.

[0044] The operation of the fuel control valve and the oxidant control valve can be affected by a variety of environmental factors. These environmental factors include, for example, temperature, supply pressure, corrosive environments, dust and particulate matter, vibration and shock, air quality, dead band, valve aging, noise and vibration, etc. These factors can affect the performance of components such as the valve body, the sealing material, and the actuator. As a result, when the combustion control system outputs a target opening to the fuel control valve and the oxidant control valve, the actual opening of the fuel control valve / or the oxidant control valve can not match the target opening. At this point, the combustion control system needs to quickly make fine adjustments to achieve the target power.

[0045] Embodiments of the present application are described in detail below with reference to the attached drawing figures. Embodiments can be combined throughout the drawing figures. Like reference numerals can refer to like or corresponding elements throughout the several views of the drawing figures. The description of embodiments is not intended to be limited to any one or more of the figures, and the description of aspects can be combined with each other as well as with other aspects described herein. The description of aspects and embodiments is not intended to be limited to any one or more of the figures, and the description of aspects can be combined with each other as well as with other aspects described herein.

[0046] Unless clearly indicated otherwise, each aspect or embodiment defined herein can be combined with any other aspect or embodiment(s) defined herein. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature or features indicated as being preferred or advantageous.

[0047] The combustion control system is used to change the power of the burner by adjusting the fuel and oxidant supply within the burner as the operating conditions change. The operating conditions can include temperature fluctuations within the kiln or changes in the power setpoint, etc. The system and method of the present application are designed to respond to such changes to quickly bring the burner to and maintain the target power.

[0048] The delivery system of the burner mainly includes fuel delivery pipeline and oxidant delivery pipeline. On these delivery pipelines, valve group devices are usually installed along the pipeline. These valve group devices adjust the flow of fuel and oxidant by changing the cross-sectional area of the flow passage.

[0049] The combustion control system includes a programmable controller, also known as a PLC (Programmable Logic Controller) system. The PLC system can include multiple modular controllers to control each device or each subsystem. The combustion control system can be configured to ensure at least one of the following actions: obtaining data from at least one device, controlling according to flow meter data, adjusting and feeding back parameters, and transmitting data between each device or each subsystem.

[0050] As known by those skilled in the art, the combustion control system includes at least one of the following: a microcontroller, a microprocessor, a computer. The combustion control system communicates with each device or each subsystem. The information transmission mode includes but is not limited to radio frequency, WIFI, Bluetooth, etc.

[0051] The staged combustion control system in this application includes fuel control valves, oxidant control valves, fuel flow meters, oxidant flow meters, and control units as a whole.

[0052] The combustion control system also includes a storage and processing unit that can store and execute control algorithms. A variety of alternative combustion control systems are commercially available and known to those skilled in the art, and the present application does not make special limitations.

[0053] The following examples use the power of the burner's jet flame to represent the size of the flow. For example, a burner power of 300KW represents a gas flow of 30Nm 3 / h. Taking natural gas as an example, the theoretical oxygen combustion ratio of natural gas pure oxygen combustion is 2. In the following examples and comparative examples, natural gas is used as fuel, and oxygen (especially pure oxygen) is used as oxidant.

[0054] The production site needs to increase or decrease the power of the burner according to the working condition, at which time the control unit will issue instructions to adjust the opening of the flow control valves of the oxidant and the fuel respectively. Due to the different pressures of fuel and oxidant, the pipe diameters of the pipelines, and the adjustment amounts, when the power is increased or decreased respectively, the ratio of oxidant to fuel will deviate greatly.

[0055] If the oxidant flow is too high, nitrogen oxides will be produced in the kiln, and heat will be taken away. If the fuel flow is too high, a large amount of carbon monoxide will be produced in the kiln. Such improper ratio is not desirable.

[0056] Due to the delay and hysteresis, in the traditional PID regulation process, the oxygen-fuel ratio will be continuously maintained at a lower value, lower than the theoretical oxygen-fuel ratio 2.0, resulting in local carbon monoxide content exceeding the standard.

[0057] The inventors use the following method: during power adjustment, when the continued adjustment of one side flow will lead to oxygen-fuel ratio imbalance, the following steps are performed: (a) stop the adjustment action of that side; (b) after the flow of the other side is adjusted to the preset range, the stop state of step (a) is released (or "resume the adjustment action of that side").

[0058] Under certain working conditions, in order to quickly increase the flow of natural gas and oxygen, while reducing the turbulence caused by flame swing, if the target power ≤ 30% of the maximum power of the burner, the natural gas flow will be directly controlled by the target power, and the oxygen flow can be obtained based on the fuel target flow and the oxygen-fuel ratio.

[0059] Figure 2 The combustion control method of one embodiment of the present application is shown, and the timing diagram of the "staged adjustment" mode of the oxygen-enriched combustion burner of oxygen and natural gas is specifically shown.

[0060] The control unit receives a power increase instruction, and the target power is set to 1400 kW. In this embodiment, the maximum power of each burner is 2000 kW. The user sets the power to increase from 400 kW to 1400 kW (i.e. the target power of the burner), that is, the flow of natural gas needs to be increased from the current flow of 40 Nm 3 / h to the target flow of 140 Nm 3 / h. That is, the final and stable fuel flow value set by the user is 140 Nm 3 / h.

[0061] The control unit divides the total power increase, i.e. 1400 kW-400 kW = 1000 kW, into n intermediate stages. Those skilled in the art can determine the value of n. It can be known that the greater the value of n, that is, the more steps of staged adjustment, the smoother the adjustment process, and the longer the corresponding adjustment time. The smaller the value of n, the faster the adjustment speed. In this embodiment, n = 5 is taken as an example. The power adjustment interval of each stage is (1400-400) / 5 = 200 kW.

[0062] The corresponding natural gas flow will be increased from 40 Nm 3 / h to 140 Nm 3 / h in 5 steps.

[0063] The combustion control system performs adjustment in stages: First intermediate stage: the control unit sets the first fuel intermediate flow to 60 Nm 3 / h, i.e. Figure 2 The first fuel intermediate flow rate is the temporary, stage-wise set value for this intermediate stage.

[0064] The fuel control valve, as the fuel control device, is used to adjust the natural gas flow rate. The fuel flow meter, as the fuel flow monitoring device, monitors the current natural gas flow rate in real time. 3 / h. During this period, the control unit dynamically calculates the oxygen set value at each time point of this intermediate stage based on the feedback value of the current natural gas flow rate and the target oxygen-to-fuel ratio of 2:1, and outputs an instruction to adjust the oxidant control device (e.g., the oxidant control valve) to increase the oxygen flow rate. The oxidant flow meter, as the oxidant flow monitoring device, monitors the current oxygen flow rate in real time.

[0065] When the current fuel flow rate reaches 60 Nm 3 / h in advance, the opening of the fuel control valve remains unchanged, and the current fuel flow rate remains stable.

[0066] The stable state of the current fuel flow rate is maintained, and the current oxygen flow rate, which is still rising, is waited for to catch up until the current oxygen-to-fuel ratio reaches more than 90% of the target oxygen-to-fuel ratio. As shown in Figure 2 At the end of the first intermediate stage, the current oxygen-to-fuel ratio reaches about 1.97, and the current oxygen flow rate reaches 120 Nm 3 / h. Throughout the first intermediate stage, the oxygen-to-fuel ratio is maintained at more than 90% of the target oxygen-to-fuel ratio.

[0067] The second intermediate stage: after the current oxygen flow rate in the previous intermediate stage meets the condition, the natural gas set value is increased to the second fuel intermediate flow rate of 80 Nm 3 / h. The above-mentioned "adjust-pause-wait" process is repeated. As shown in Figure 2 In the second intermediate stage, the current oxygen-to-fuel ratio is maintained at about 1.96.

[0068] The subsequent stages: the natural gas set value is set to 100 Nm 3 / h, 120 Nm 3 / h, and 140 Nm 3 / h, respectively. In these stages, the current oxygen-to-fuel ratio is maintained at about 1.89, about 1.99, and about 1.93, respectively.

[0069] Finally, the current natural gas flow rate and the current oxygen flow rate both reach the target flow rates (140 Nm 3 / h and 280 Nm 3 / h), and the oxygen-to-fuel ratio is stabilized at more than 90% of the target oxygen-to-fuel ratio.

[0070] As shown in Figure 2As shown, the current oxygen-to-fuel ratio is always kept within the target range during the entire adjustment process of the present application, which is an efficient control, effectively avoiding Figure 1 the problems of continuous low oxygen-to-fuel ratio and excessive carbon monoxide.

[0071] Comparative Example Figure 1 A timing diagram of the power ramp-up process using the conventional PID adjustment method in the prior art is shown.

[0072] In this example, the user will set the power to be ramped up from a lower value (e.g. 400 KW) to 1400 KW at one time. The corresponding target flow rate of natural gas is 140 Nm 3 / h, and the corresponding target flow rate of oxygen is 280 Nm 3 / h.

[0073] During the adjustment process, the flow rate of natural gas is quickly ramped up to 140 Nm 3 / h. However, due to the hysteresis of pipeline characteristics, valve response, etc., at some stages, the actual flow rate of oxygen cannot catch up with the actual flow rate of natural gas.

[0074] This results in the actual oxygen-to-fuel ratio (R) being continuously low during most of the power ramp-up, for example, gradually ramping up from 1.37, 1.43, 1.38, 1.53, 1.75 to 1.96. This continuous "rich" or "oxygen-deficient" state will cause incomplete combustion of natural gas, resulting in a large amount of carbon monoxide. Until the flow rate of natural gas reaches the target value and stabilizes, the actual flow rate of oxygen gradually "catches up", so that the oxygen-to-fuel ratio eventually returns to 2.0.

[0075] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the present application. Any technical solution obtained by logical analysis, reasoning or limited experiments based on the conception of the present application should be within the scope of the present application.

Claims

1. A staged combustion control method, characterized in that, The combustion control method includes the following steps: S1: Set the target power of the burner to determine a target fuel flow rate; S2: Divide the range from the current fuel flow rate to the target fuel flow rate into at least one intermediate stage, each intermediate stage corresponding to an intermediate fuel flow rate; S3: Execute for at least one intermediate stage: S3-1: Adjust the current fuel flow rate to approach the intermediate fuel flow rate, and dynamically set and monitor the current oxidant flow rate based on the current fuel flow rate and the target oxygen-fuel ratio; S3-2: When the current fuel flow rate reaches the intermediate fuel flow rate, the current fuel flow rate is kept stable; S3-3: Maintain the current flow rate of the fuel at a stable state until the oxygen-fuel ratio reaches a preset range; S3-4: After releasing the current fuel flow rate from its stable state, adjust the current fuel flow rate to tend towards the next intermediate fuel flow rate or the target fuel flow rate.

2. The combustion control method according to claim 1, characterized in that, The oxygen-fuel ratio in step S3-3 is preset to be above 90% of the target oxygen-fuel ratio.

3. The combustion control method according to claim 1, characterized in that, In step S3-3, the oxygen-fuel ratio is kept stable within a preset range.

4. The combustion control method according to claim 1, characterized in that, In step S2, the at least one intermediate stage is determined based on a preset power increment step size or a preset number of stages.

5. The combustion control method according to claim 1, characterized in that, After step S1, step S2-1 is also included: determining whether the target power of the burner meets a preset phased adjustment condition.

6. The combustion control method according to claim 5, characterized in that, The preset phased adjustment conditions include: the target power of the burner is greater than or equal to a preset power threshold.

7. The combustion control method according to claim 6, characterized in that, The preset power threshold is 30% of the burner's maximum power.

8. A staged combustion control system, characterized in that, The combustion control system includes a fuel control device, an oxidant control device, a fuel flow monitoring device, an oxidant flow monitoring device, and a control unit, wherein the control unit is configured to perform the combustion control method as described in any one of claims 1 to 7.

9. The combustion control system according to claim 8, characterized in that, The control unit is configured to: A. Receive the target power of the burner to determine a target fuel flow rate; B. Divide the range from the current fuel flow rate to the target fuel flow rate into at least one intermediate stage, each intermediate stage corresponding to an intermediate fuel flow rate; C. For the at least one intermediate stage: C1. Control the fuel control device to make the current fuel flow rate approach the intermediate fuel flow rate, and dynamically set and monitor the current oxidant flow rate based on the current fuel flow rate monitored by the fuel flow monitoring device and in combination with the target oxygen-fuel ratio; C2. When the current fuel flow rate is detected to have reached the intermediate fuel flow rate, the current fuel flow rate is kept stable. C3. Maintain the current fuel flow rate in a stable state until the oxygen-fuel ratio calculated based on the current fuel flow rate monitored by the fuel flow monitoring device and the current oxidant flow rate monitored by the oxidant flow monitoring device reaches a preset range; C4. Control the fuel control device to move toward the next fuel intermediate flow rate or the fuel target flow rate.

10. The combustion control system according to claim 9, characterized in that, In step C2, the current fuel flow rate is kept stable by keeping the opening of the fuel control device constant.

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