Flue gas compensation type coal wide load stable combustion system based on staged combustion and intelligent control and control method

Abstract

The application discloses a flue gas compensation type coal powder wide-load stable combustion system and a control method based on hierarchical combustion and intelligent regulation and control, and belongs to the technical field of coal-fired power generation. The system is composed of three modules of a burner, intelligent control and flue gas backflow. The burner adopts a double-ring fuel channel design, the inner ring sprays high-concentration coal powder and is equipped with an adjustable cyclone, and the outer ring is connected with a coal powder-flue gas mixed gas flow. The intelligent control module predicts the load through an LSTM neural network, and realizes accurate matching of air and coal in combination with PID regulation. The flue gas backflow module adopts adjustable oxygen concentration technology to maintain combustion intensity. Under the condition of 30%-40% low load, the system realizes the stable combustion effect of stabilizing the flame center temperature at 920±20 DEG C by means of optimizing the inner ring coal powder ratio to 75%-85%, improving the primary air temperature to 145-170 DEG C, compressing the secondary air volume ratio to 20%-30% and strengthening the cyclone field to 45 DEG, and cooperating with the flue gas backflow of 23%-25% oxygen concentration, and has the advantages of efficient combustion and low emission.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal-fired power generation, and particularly relates to a flue gas compensation type coal powder wide load (30%-100% rated load) stable combustion system based on staged combustion and intelligent control and a control method thereof. BACKGROUND

[0002] With the deepening of the reform of the electricity market, modern power grids have put forward higher technical requirements for the peak shaving capability of generating units. Generating units not only need to ensure the reliability of basic power generation functions, but also need to have dynamic adjustment capability to quickly respond to load fluctuations in the power grid, which poses a severe challenge to the wide load operation range of the units.

[0003] Traditional frequency modulation control strategies have significant technical defects when dealing with wide load adjustment. This is particularly true when the unit is in a low load condition: the decline in combustion stability leads to frequent extinguishing (oil / plasma assisted ignition is required), changes in coal quality can cause fluctuations in combustion efficiency, and dynamic response is slow, making it difficult to meet the rapid frequency modulation needs of the power grid. These problems not only cause a decline in the thermal efficiency of the unit and an increase in pollutant emissions, but also severely restrict the deep peak shaving capability of thermal power units, ultimately affecting the economy and flexibility of the power grid operation.

[0004] For the problem of poor combustion stability under low load conditions, although technologies such as micro-oil ignition and plasma ignition can improve the combustion conditions under low load conditions to some extent, their high operating costs and limited load adaptation range make it difficult to meet the economic and environmental requirements of modern power systems. More importantly, the traditional combustion system designed based on a fixed air-coal ratio is prone to combustion condition deterioration when the load changes rapidly, which not only exacerbates operational instability, but also leads to excessive carbon content in fly ash, directly conflicting with the current dual-carbon target.

[0005] Flue gas recirculation technology provides a new path to solve some problems. The recirculation of flue gas to the burner can dilute the oxygen concentration in the combustion zone and extend the residence time of the coal powder, which helps to improve the flame residence characteristics. At the same time, the reducing atmosphere formed by the recirculated flue gas can effectively inhibit the generation of NOx, and its dynamic adjustment characteristics can also balance the fluctuations in air-coal ratio. However, existing technologies such as the coal-fired power generating unit disclosed in Chinese patent CN119022295A achieve the recycling of high-temperature flue gas energy generated by the boiler through the design of a recirculation unit, but due to the lack of deep treatment of flue gas, system optimization of the burner structure and combustion strategy, and the absence of an intelligent control module, it is difficult to solve the problem of high carbon content in fly ash and overcome the hysteresis defect of the traditional feedback mechanism, and even the simple recirculation may lead to a decline in combustion efficiency. This highlights the need to develop a new system that integrates flue gas treatment, combustion optimization, and intelligent control.

[0006] Therefore, it is imperative to develop a new generation of wide-load stable combustion system. The ideal solution needs to break through the existing technical framework, integrate innovative technologies such as deep flue gas treatment, combustor structure optimization and intelligent control, and build a comprehensive solution with economic, adaptive and environmental performance, to provide reliable technical support for deep peak shaving of coal-fired units. SUMMARY

[0007] In view of the problems of poor combustion stability, slow dynamic response and high pollutant emission of traditional pulverized coal combustion system under low load condition, a flue gas compensation type pulverized coal wide-load stable combustion system and control method based on staged combustion and intelligent control are innovatively proposed. The system adopts a double-ring concentration gradient combustor structure to realize staged fuel supply, introduces an intelligent predictive control algorithm to improve the dynamic response capability of the system, and innovatively develops a flue gas oxygen-enriched back spraying technology to optimize the combustion environment. This technical solution effectively solves the industry problem that combustion stability and environmental performance are difficult to be considered together in wide-load operation of coal-fired units.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a flue gas compensation type pulverized coal wide-load stable combustion system based on staged combustion and intelligent control, comprising: a combustor module, including a multi-stage adaptive combustor and a swirl control assembly, the multi-stage adaptive combustor including a combustor main body, the front end of which is connected to a furnace combustion space, and a wind temperature adjusting unit is integrated inside; a concentric double-ring fuel channel including an inner ring fuel channel and an outer ring fuel channel for staged delivery of different states of fuel medium;

[0009] An intelligent control module, comprising: a combustion prediction submodule for predicting combustion load changes; a dynamic wind-coal matching submodule for adjusting the wind quantity and the coal powder supply ratio according to the real-time combustion condition; a central control unit connected with the combustor module and the flue gas backflow module to realize combustion parameter optimization and working condition closed-loop control;

[0010] A flue gas backflow module, comprising: a flue gas recovery unit for connecting the boiler tail flue and the outer ring fuel channel to extract and send part of the flue gas to the combustor; an oxygen concentration adjusting unit for adjusting the oxygen concentration in the backflow flue gas; a closed-loop temperature control unit based on the temperature feedback signal of the combustor outlet area to dynamically control the flue gas flow to maintain flame stability.

[0011] Further, the inner ring fuel channel is configured to inject a high-concentration coal powder gas flow with a coal powder concentration of ≥ 30 kg / kg air, and the end thereof is integrated with a primary air cyclone with an adjustable blade angle; the outer ring fuel channel is arranged around the inner ring fuel channel and is used to inject a coal powder-recirculated flue gas mixed gas flow, and is provided with a mixing flue gas pressure stabilizing chamber and is connected in a closed loop with the tail flue of the boiler through a flue gas recirculation interface; a primary air channel is arranged on the inner ring fuel channel, and a primary air flow adjusting valve group is arranged at the inlet of the channel; a secondary air channel is arranged on the outer ring fuel channel, and a secondary air flow adjusting valve group is arranged at the inlet of the channel.

[0012] Further, the combustion prediction sub-module comprises: a load prediction unit, which is internally provided with a load prediction model based on an LSTM neural network, the input variables of which include real-time power grid dispatching instructions and historical load data, and the output is a future 5-10 minute heat load prediction value; a combustion parameter pre-adjustment unit, which generates a primary air pressure correction amount ΔP and a coal powder concentration correction coefficient Kc according to the load prediction value; the dynamic wind-coal matching sub-module comprises: a temperature field monitoring unit, which is used to obtain a furnace temperature distribution standard deviation σ through optical temperature measuring devices in several regions of the furnace;

[0013] a wind flow control unit, which comprises a primary air PID adjusting system and a secondary air PID adjusting system, the primary air PID adjusting system synchronously adjusts the primary air flow and the cyclone blade angle according to the inner ring air pressure data of the burner; and the secondary air PID adjusting system dynamically optimizes the secondary air ratio parameter α by adjusting the opening degree of the secondary air channel;

[0014] a coal quality online analysis unit, which is used to detect the coal powder moisture content Wc and the volatile content Vc;

[0015] the central control unit controls the opening degree of the primary air adjusting valve group through a PID algorithm based on the ΔP, Kc signals and the σ, Wc, Vc data, calculates the secondary air flow ratio α and dynamically corrects the wind-coal ratio γ.

[0016] Further, the dynamic wind-coal matching sub-module is also provided with a secondary compensation mechanism: when the furnace temperature still has a continuous fluctuation greater than ± 40℃ after the main adjustment response, the coal powder fineness dynamic adjustment unit is automatically linked to realize the compensation of the combustion rate by adjusting the coal powder particle size distribution.

[0017] Further, the flue gas recirculation unit comprises:

[0018] a flue gas extraction pipeline, the inlet end of which is connected to the outlet side of the dust remover of the tail flue of the boiler, and the outlet end of which is connected to the mixing flue gas pressure stabilizing chamber of the outer ring fuel channel;

[0019] a high-efficiency electric dust removal device, which is arranged in the middle section of the flue gas extraction pipeline and is used to perform secondary dust removal treatment on the extracted flue gas, the temperature of the extracted flue gas being 200-300℃ and the flow ratio being 10%-30% of the total flue gas amount.

[0020] The oxygen concentration adjusting unit comprises an oxygen delivery branch pipe and a static mixer, which are used to incorporate oxygen into the backflow flue gas to make the mixed oxygen concentration reach 23%-25%;

[0021] The closed-loop temperature control unit comprises:

[0022] A thermocouple group is arranged in the region 500-800 mm downstream of the burner outlet along the burner axis direction, which is used to monitor the flame temperature distribution in real time;

[0023] An interlocking PID controller is triggered when the thermocouple detects that the center temperature of the flame is lower than 900℃, which triggers the maximum flow mode of the flue gas recovery unit, and controls the flue gas extraction amount to increase to 80%-100% of the rated flow;

[0024] A dynamic balance module is used to maintain the dynamic balance of the flue gas heat value and the combustion temperature by adjusting the valve opening degree of the oxygen delivery branch pipe based on the real-time flue gas temperature and oxygen concentration data through the PID algorithm.

[0025] Further, the swirler vane angle adjustment range is 15°-45°.

[0026] The application also discloses a stable combustion control method matched with the above-mentioned flue gas compensation type pulverized coal wide load stable combustion system. The method comprises the following steps:

[0027] S1. Low load stable combustion stage control:

[0028] a) Activate the high-concentration combustion mode of the burner, increase the mass proportion of the inner ring fuel channel to 75%-85%, and maintain the primary air temperature at 145-170℃ through the air temperature adjusting unit;

[0029] b) Adjust the secondary air quantity adjusting valve opening degree of the inner and outer ring fuel channels, so that the secondary air quantity accounts for 20%-30% of the total air supply quantity;

[0030] c) Increase the recirculated flue gas extraction ratio to 20%-30%, and make the mixed flue gas oxygen concentration reach 23%-25% through the oxygen concentration regulating assembly;

[0031] d) Drive the primary air swirler vane angle to increase to 45°, form a strong turbulent flow field with a swirl number >1.2, and maintain the center temperature of the flame at 920±20℃;

[0032] S2. Medium-high load transition stage control:

[0033] a) Receive the migration instruction output by the load prediction model, linearly increase the secondary air quantity to 40% within 5 minutes, reduce the primary air temperature to 120℃, reduce the flue gas flow to 15%, and no longer mix oxygen into the backflow flue gas;

[0034] b) The cyclone regulation assembly drives the primary air cyclone vane angle adjustment to 15°;

[0035] c) By monitoring the standard deviation sigma of the furnace temperature distribution in real time, the air-coal ratio gamma is dynamically corrected to constrain the temperature fluctuation amplitude to less than ±5℃;

[0036] d) The coal powder fineness adjustment unit is synchronously linked to reversely compensate the coal powder particle size distribution according to the flame height change.

[0037] Further, the low load stable combustion stage corresponds to a 30%-40% rated load range, and the medium-high load transition stage corresponds to a 40%-100% rated load range.

[0038] The beneficial effects of the present application are:

[0039] 1. The flue gas compensation type coal powder wide load stable combustion system based on staged combustion and intelligent control disclosed in the present application comprises three core modules of a burner, intelligent control and flue gas backflow, and through the synergistic effect of the double-ring concentration gradient burner structure optimization, intelligent control prediction algorithm and flue gas oxygenated back spraying compensation technology, the operation stability and reliability of the coal-fired unit under wide load conditions are effectively improved, and the technical bottlenecks of the traditional combustion system such as easy flameout under low load conditions, dynamic response lag and poor pollutant emission control are solved.

[0040] 2. The multi-fuel channel burner disclosed in the present application adopts a differentiated supply strategy of inner and outer ring fuel channels, cooperates with the accurate control of the primary air temperature and the secondary air volume ratio, optimizes the cyclone intensity and the flue gas backflow compensation mechanism, and builds a highly stable flame core temperature field structure. This design significantly improves the combustion stability under low load conditions, effectively suppresses the combustion oscillation phenomenon and reduces the risk of flameout. At the same time, the system integrates the flue gas recirculation technology and the dynamic oxygen concentration adjustment function, further enhances the controllability of the combustion process, and thus ensures efficient and continuous stable combustion of the equipment within a wide load range.

[0041] 3. The stable combustion system disclosed in the present application realizes dynamic optimization of the combustion process by using an intelligent control module. Its core lies in the synergistic control of the two sub-modules of combustion prediction and wind-coal dynamic matching. By analyzing the fuel characteristics and combustion demand in real time, the coal combustion efficiency and the overall thermal efficiency of the boiler are significantly improved. The system innovatively integrates the flue gas recirculation technology, which reduces the excess air coefficient and builds a low-oxygen reduction environment, thereby effectively inhibiting the generation of nitrogen oxides and achieving source reduction of pollutants. Cooperating with the precise regulation function of the closed-loop temperature control unit, the system further optimizes the combustion uniformity, significantly reduces the generation of unburned products, and comprehensively improves the environmental protection performance while ensuring the stability of combustion.

[0042] 4、The application innovatively integrates the coal quality online analysis unit and the combustion prediction submodule, constructs an intelligent adjustment system with autonomous adaptation capability, the system monitors the change of fuel characteristics in real time and automatically optimizes the combustion parameters, realizes the automation management from fuel identification to combustion regulation, and the intelligent dynamic response mechanism makes the unit show excellent stability when responding to dynamic load changes such as grid peak shaving, and effectively overcomes the regulation lag problem existing in the traditional control mode; more importantly, the system continuously accumulates operation experience through deep learning algorithm, continuously improves the adaptability to various complex working conditions, and provides reliable guarantee for flexible and efficient operation of thermal power generating units;

[0043] 5、The flue gas backflow module disclosed in the application realizes comprehensive optimization of the combustion system through multi-unit collaborative control, the flue gas recovery unit extracts and purifies the boiler tail flue gas, the oxygen concentration adjustment unit accurately adjusts the oxygen content of the mixed gas, and the closed-loop temperature control unit dynamically adjusts the operating parameters according to the real-time flame temperature, the technical scheme can significantly improve the combustion stability, effectively inhibit the generation of harmful gases, reduce the coking risk of equipment, realize clean combustion and double improvement of system reliability. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a structural schematic diagram of a multi-stage self-adaptive burner, wherein 1 is a burner main body, 2 is a furnace combustion space, 3 is an inner ring fuel passage, 4 is an outer ring fuel passage, 5 is a cyclone, 6 is a mixed flue gas pressure stabilization chamber, 7 is a primary air passage, 8 is a secondary air passage, and 9 is a feeding pipeline;

[0045] Figure 2 is a system flow block diagram of a flue gas compensation type coal powder wide load stable combustion system based on staged combustion and intelligent regulation and control;

[0046] Figure 3 is a biaxial time correlation diagram of fly ash carbon content and NOx emission concentration provided by the application example;

[0047] Figure 4 is a steam temperature fluctuation curve diagram with time provided by the application example. DETAILED DESCRIPTION

[0048] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be further described below in combination with the drawings and examples.

[0049] Example 1

[0050] The embodiment discloses a flue gas compensation type coal powder wide load stable combustion system based on staged combustion and intelligent regulation and control, which comprises a burner module, an intelligent control module and a flue gas backflow module.

[0051] The burner module comprises a multi-stage adaptive burner and a swirl control assembly, the multi-stage adaptive burner is composed of a burner body 1 and a concentric double-ring fuel passage, the front end of the burner body 1 is connected with a furnace combustion space 2, and a wind temperature adjusting unit is integrated in the burner module for regulating the primary air temperature.

[0052] The concentric double-ring fuel passage is coaxially arranged in the burner body 1 and comprises an inner ring fuel passage 3 and an outer ring fuel passage 4; the inner ring fuel passage 3 is used for injecting a high-concentration pulverized coal airflow with a coal concentration ≥ 30 kg / kg air, and the end of the inner ring fuel passage 3 is provided with a primary air swirl vane with an adjustable angle, the angle adjustment range of the swirl vane is limited to 15°-45°, and a servo driving mechanism is arranged to realize enhanced control of the swirl number being raised to > 1.2 under low load conditions.

[0053] The outer ring fuel passage 4 surrounds the inner ring fuel passage 3 and injects a mixed airflow of pulverized coal and recirculated flue gas with a coal concentration ≤ 15 kg / kg air; the outer ring fuel passage 4 is provided with a mixed flue gas pressure stabilizing chamber 6, the mixed flue gas pressure stabilizing chamber 6 is connected in a closed loop with a boiler tail flue, and the mixed flue gas pressure stabilizing chamber 6 injects the pulverized coal-recirculated flue gas mixed airflow at the outlet. The inner ring fuel passage 3 is provided with a primary air passage 7, a primary air volume adjusting valve group is arranged at the inlet of the passage, and the primary air volume adjusting valve group is used for providing accurate combustion air allocation for the high-concentration pulverized coal airflow; the outer ring fuel passage 4 is provided with a secondary air passage 8, a secondary air volume adjusting valve group is arranged at the inlet of the passage, and the secondary air volume adjusting valve group is used for regulating the dilution airflow supply of the mixed flue gas and the pulverized coal. The pulverized coal enters from a feeding pipeline 9 (the pulverized coal entering path is shown by an arrow in the figure) and is mixed with the primary air for combustion, the outer ring airflow enhances the combustion completeness, and the recirculated flue gas is injected through the pressure stabilizing chamber and realizes self-stable combustion with the high-concentration pulverized coal system. Figure 1

[0054] The intelligent control module is composed of a combustion prediction submodule, a dynamic wind-coal matching submodule and a central control unit.

[0055] The combustion prediction submodule integrates a load prediction unit and a combustion parameter pre-adjusting unit; the load prediction unit is internally provided with a load prediction model based on an LSTM (Long Short Term Memory) neural network, the input variables of the model include power grid dispatching instructions and historical load data, the training data set of the LSTM neural network model includes more than 2000 groups of boiler operating condition data, and the output is a heat load prediction value in the future 5-10 minutes; the combustion parameter pre-adjusting unit generates a primary air pressure correction amount ΔP and a pulverized coal concentration correction coefficient Kc according to the load prediction value.

[0056] ​The dynamic air-coal matching sub-module comprises a temperature field monitoring unit, an air volume control unit and a coal quality online analysis unit. The temperature field control unit is composed of a group of optical fiber temperature sensors arranged at the four corners of the furnace and an infrared thermal imager installed at the fire observation hole. The furnace temperature distribution standard deviation σ is obtained by the group of optical fiber temperature sensors. The air volume control unit realizes dynamic control through two sets of PID adjustment systems. The primary air adjustment valve group is based on the real-time air pressure data in the inner ring of the burner (measured by the air pressure sensor arranged in the inner ring fuel passage) to adjust the primary air delivery flow and link the blade angle change of the primary air swirler. The secondary air adjustment valve group adjusts the opening of the secondary air passage according to the combustion condition requirement to realize dynamic optimization of the secondary air ratio parameter a and ensure that the mixing efficiency of fuel and air is always in the best interval. The coal quality online analysis unit uses a laser-induced breakdown spectrometer (LIBS) to detect the moisture content Wc and volatile content Vc of the coal powder at the outlet of the coal feeder in real time, which is fed back to the central control unit to correct the air-coal ratio γ.

[0057] An additional secondary compensation mechanism is also provided in the dynamic air-coal matching sub-module. When there is still a sustained fluctuation of the furnace temperature greater than ±40℃ after the main adjustment (coal supply / air volume) response, the coal powder fineness dynamic adjustment unit is automatically linked, the coal mill parameter optimization program is started, the combustion rate is precisely compensated by adjusting the coal powder particle size distribution, and finally the combustion rate regulation closed loop from temperature monitoring to air-coal ratio correction to coal powder fineness compensation is completed. Generally, coarse coal powder can prolong the combustion period and raise the flame center temperature, and fine coal powder can accelerate the combustion reaction and reduce the flame height. When adjusting the coal powder fineness, the primary air pressure and the secondary air ratio need to be adjusted synchronously.

[0058] The data signals of each sub-module are collected and processed and then fed back to the central control unit: based on the ΔP and Kc signals of the combustion prediction sub-module, the opening of the primary air adjustment valve group is controlled by the PID algorithm, the secondary air volume ratio a is calculated according to the furnace temperature distribution standard deviation σ collected by the temperature field monitoring unit, and the air-coal ratio γ is dynamically corrected based on the output data Wc and Vc of the coal quality analysis unit.

[0059] The flue gas backflow module comprises a flue gas recovery unit, an oxygen concentration adjustment unit and a closed-loop temperature control unit, which corrects the flue gas mixing ratio by monitoring the flame temperature and finally determines the compensation oxygen concentration.

[0060] The flue gas recovery unit comprises a flue gas extraction pipeline and a flue gas purification device, wherein the inlet end of the flue gas extraction pipeline is connected to the outlet side of the dust collector of the tail flue of the boiler, the outlet end is connected to the mixing flue gas pressure chamber (flue gas inlet) of the outer ring fuel channel of the burner, the high-efficiency electric dust removal device is arranged in the middle section of the pipeline to reduce the dust content of the backflow flue gas, the extraction flue gas temperature is 200-300°C, and the mass flow accounts for 10%-30% of the total flue gas amount of the boiler. An electric flue gas backflow valve is arranged at the inlet of the mixing flue gas pressure chamber, and the backflow flow is adjusted by driving the valve plate opening degree of the servo motor (the flue gas backflow flow is measured by a flue gas flow meter).

[0061] The oxygen concentration adjusting unit comprises an oxygen delivery branch pipe connected with an oxygen generating system and a static mixer arranged downstream of the electric dust removal device, the oxygen is mixed into the backflow flue gas, the oxygen concentration of the mixed flue gas is controlled to reach 23%-25%, and the effect of inhibiting CO generation is achieved.

[0062] The closed-loop temperature control unit is composed of a temperature sensing network and an actuator, the temperature sensing network comprises a thermocouple group arranged in a ring array in the region 500-800 mm downstream of the outlet of the burner, the temperature distribution of the flame center is monitored in real time, the local temperature drop is inhibited, the actuator comprises a PID controller interlocked with the electric flue gas backflow valve, which is programmed to increase the flue gas extraction amount to 80%-100% of the set maximum flow when any thermocouple detection value is <900°C, and switch to proportional regulation mode to maintain thermal balance when the temperature returns to ≥900°C.

[0063] The flue gas backflow flow, oxygen concentration data and flame center temperature data are collected to the central control unit for further comprehensive regulation and control.

[0064] In the low load operation stage (30%-40% of the rated load) of the boiler, the combustion system executes the low load stable combustion strategy:

[0065] The burner module starts the high-concentration combustion mode, the mass ratio of the inner ring fuel channel coal powder is increased to the interval of 75%-85%, and the primary air temperature is stabilized in the range of 145-170°C through the integrated air temperature adjusting unit; the opening degree of the secondary air volume adjusting valve is adjusted, so that the proportion of the secondary air volume to the total air volume is compressed to 20%-30%; the flue gas backflow module is simultaneously enhanced, the recirculated flue gas extraction ratio is increased to 20%-30%, and the oxygen concentration regulation component mixes oxygen into the backflow flue gas to make the oxygen concentration reach the threshold of 25%; the cyclone regulation component drives the blade angle of the primary air cyclone to increase to 45°, forming a strong cyclone field to prolong the residence time of the coal powder, so that the flame center temperature is stabilized in the interval of 920±20°C.

[0066] When the load switches to the medium-high load (40%-100%) transition stage, the intelligent control module executes the dynamic transition program: after the central control submodule receives the operating condition migration instructions output by the load prediction model, it adjusts the system parameters in stages through the servo actuator - gradually increases the secondary air volume to 40% of the total air volume within a 5-minute time window, synchronously reduces the primary air temperature to 120℃, and linearly decreases the flue gas flow to 15% of the set value; as the load increases, the cyclone control assembly drives the primary air cyclone vane angle to adjust to 15°, weakening the cyclone intensity and improving the combustion intensity; the oxygen concentration control assembly no longer mixes oxygen into the backflow flue gas, returning to the normal air-assisted combustion condition; during the above adjustment process, the combustion prediction submodule real-time corrects the air-coal ratio parameter to ensure that the furnace temperature fluctuation amplitude is less than ±5℃.

[0067] The traditional boiler mainly has the following problems in low load operation condition: 1. easy to extinguish, need to burn oil / plasma auxiliary; 2. coal quality change will cause combustion efficiency fluctuation; 3. slow load response, cannot keep up with the grid speed. The present application solves the technical problems of traditional combustion system in low load stable combustion, dynamic response and pollution control through the deep combination of burner structure innovation (double-ring concentration gradient burner), intelligent control algorithm (LSTM prediction) and flue gas compensation strategy, and realizes a systematic breakthrough. Specifically, in terms of stable combustion: through the gradient grading combustion design of outer ring flue gas mixing pressure stabilization and inner ring high concentration pulverized coal jet, combined with the oxygen concentration inhibition effect of flue gas recirculation, the flame stability boundary of low load condition is significantly widened; for fuel fluctuation, based on the online composition monitoring of pulverized coal and the dynamic air-coal ratio self-correction algorithm, the real-time closed-loop optimization of combustion parameters with coal quality change is realized; for the problem of load response delay, LSTM neural network is used to predict the boiler operation trend in advance, and the dynamic response time is compressed to less than 30% of the traditional system through the pre-adjustment mechanism of burner cyclone intensity and secondary air ratio. The whole system solves the coupling problems of stable combustion, efficiency and response rate through the three-dimensional cooperation of structure-algorithm-gas circuit without external combustion aid.

[0068] Application example

[0069] Under the condition of 180 MW low load of a 600 MW supercritical once-through boiler, the flue gas compensation type pulverized coal wide load stable combustion system based on staged combustion and intelligent control shows significant regulation effect. The specific implementation process and operation effect are as follows:

[0070] 1. Combustion regulation implementation

[0071] In the pulverized coal distribution control link, the pulverized coal delivery proportion of the inner ring fuel passage is increased from 50% in the conventional condition to 80%, and the outer ring fuel passage is simultaneously adjusted and reduced to 20%, which significantly improves the ignition stability by strengthening the inner ring pulverized coal concentration effect.

[0072] The air distribution system executes a compound control strategy: the primary air temperature is heated to 160°C (33% higher than the conventional value of 120°C) by the air heater, which can reduce the moisture content of the pulverized coal to prevent pipe blockage and enhance the flowability of the pulverized coal, compensate for the delayed combustion caused by the increased concentration of the pulverized coal at low load, and accelerate the release of volatile matter in the pulverized coal to improve the stability of the ignition of the pulverized coal at low load. In combination with the 80% proportion of the inner ring of the pulverized coal, the problems of deposition or insufficient combustion of the pulverized coal due to insufficient temperature are effectively avoided, and the preheating process of the pulverized coal is accelerated; the secondary air volume is compressed to 25% of the total air volume, and the swirl vane angle is adjusted to 45°, which can limit the oxygen concentration in the combustion zone and inhibit the generation of NOx, and the low secondary air volume can reduce the flame diffusion range to concentrate the combustion heat and avoid excessive temperature fluctuations; in addition, in combination with the flue gas backflow (25%), an alternating region of hypoxia and hyperoxia is formed, and in combination with the adjustment of the swirl vane angle, the flue gas backmixing effect is enhanced, and the carbon content of the fly ash is reduced.

[0073] In summary, the primary air temperature (160°C) and the secondary air volume (25% of the total air volume) respectively undertake the core functions of optimizing the pulverized coal delivery / ignition and controlling the oxygen volume / flame shape at low load, and through systematic coordination with parameters such as the proportion of the inner ring of the pulverized coal and the swirl intensity, the dual improvement of low-load stable combustion and environmental protection performance is achieved.

[0074] The flue gas backflow module synchronously extracts 25% of the tail flue gas and mixes pure oxygen, and the oxygen concentration of the mixed medium is stabilized at 24%, which realizes staged combustion while ensuring the combustion intensity. The whole system cooperates with the primary air temperature control, secondary air volume adjustment, swirl intensity optimization, and flue gas oxygen-mixed backflow, and finally achieves the dual improvement of combustion stability and environmental protection performance at low load.

[0075] The temperature monitoring system tracks the thermal distribution of the furnace in real time through a temperature sensing network, and combines dynamic coal feeding adjustment to stabilize the flame center temperature measured by the temperature field control unit in the range of 900-940°C, and automatically triggers the pulverized coal fineness adjustment mechanism when the temperature fluctuation exceeds ±40°C.

[0076] 2. Dynamic load switching

[0077] During the transition phase of the load from 40% to 100%, the dynamic adjustment program of the air-coal ratio is started: the secondary air volume is gradually increased to 40% of the total air volume within 5 minutes, the flue gas backflow ratio is simultaneously reduced to 15%, the primary air temperature is adjusted to 120°C, the primary air swirler vane angle is adjusted to 15° to weaken the swirl intensity and improve the combustion intensity, and oxygen is no longer mixed into the backflow flue gas.

[0078] At low load, the NOx emission is less than 100 mg / Nm³ (conventional technology: more than 150 mg / Nm³), and the combustion efficiency is always greater than 98.5%.

[0079] 3. Comprehensive operation effectiveness

[0080] After 72 hours of continuous operation verification, the key performance indicators of the system are significantly optimized:

[0081] In terms of combustion stability, the flame shape remains stable without flash combustion / extinction phenomenon, and the carbon content of fly ash is reduced from 4.2% to 2.6% (see Figure 3 );

[0082] The environmental performance is improved, and the NOx emission concentration is reduced from 380 mg / Nm³ to 260 mg / Nm³, which is 42% lower than the traditional technology (see Figure 3 );

[0083] The energy efficiency index is improved, and the main steam temperature fluctuation range is <±5℃ (see Figure 4 ), and the boiler efficiency is improved by 2.1 percentage points compared with conventional low load operation;

[0084] This example verifies the superior performance of the wide load stable combustion system under low load conditions, and realizes the synergistic optimization of clean combustion and high efficiency operation.

[0085] The above shows and describes the basic principles, main features and advantages of the present application. However, the above only describes specific embodiments of the present application, and the technical features of the present application are not limited to this. Any other implementation derived by those skilled in the art without departing from the technical solution of the present application should be covered in the scope of the present application.

Claims

1. A flue gas compensation type pulverized coal wide load stable combustion system based on staged combustion and intelligent regulation and control, characterized in that, The application relates to a multi-stage self-adaptive burner module, which comprises a burner body, a concentric double-ring fuel channel, an intelligent control module, a flue gas backflow module and a central control unit. The burner body is connected with a furnace combustion space at a front end and is internally integrated with a wind temperature adjusting unit. The concentric double-ring fuel channel comprises an inner ring fuel channel and an outer ring fuel channel and is used for grading conveying of fuel media in different states. The intelligent control module comprises a combustion prediction sub-module, a dynamic wind-coal matching sub-module and a central control unit. The combustion prediction sub-module is used for predicting combustion load variation. The dynamic wind-coal matching sub-module is used for adjusting the wind volume and the coal powder supply ratio according to real-time combustion working conditions. The central control unit is connected with the burner module and the flue gas backflow module and realizes combustion parameter optimization. The flue gas backflow module comprises a flue gas recovery unit, an oxygen concentration adjusting unit and a closed-loop temperature control unit. The inner ring fuel channel is configured to spray high-concentration coal powder air flow with a coal powder concentration greater than or equal to 30 kg / kg air, and the tail end of the inner ring fuel channel is integrated with a primary air cyclone with adjustable blade angle. The outer ring fuel channel is arranged around the inner ring fuel channel and is used for spraying coal powder-recycled flue gas mixed gas flow, and the outer ring fuel channel is provided with a mixed flue gas pressure stabilizing chamber and is connected with a boiler tail flue in a closed loop through a flue gas recirculation interface. A primary air channel is arranged on the inner ring fuel channel, and a primary air volume adjusting valve group is arranged at the channel inlet. A secondary air channel is arranged on the outer ring fuel channel, and a secondary air volume adjusting valve group is arranged at the channel inlet. The combustion prediction sub-module comprises a load prediction unit and a combustion parameter pre-adjusting unit. The load prediction unit is internally provided with a load prediction model based on an LSTM neural network, input variables include real-time power grid dispatching instructions and historical load data, and output future 5-10 minute heat load prediction values. The combustion parameter pre-adjusting unit generates a primary air pressure correction amount Delta P and a coal powder concentration correction coefficient Kc according to the load prediction values. The dynamic wind-coal matching sub-module comprises a temperature field monitoring unit, a primary air PID adjusting system and a secondary air PID adjusting system.

2. The flue gas compensation type coal powder wide load stable combustion system based on hierarchical combustion and intelligent regulation according to claim 1, characterized in that, The temperature field monitoring unit is used for acquiring furnace temperature distribution standard deviation sigma through optical temperature measuring devices of several regions of the furnace. The wind volume control unit comprises the primary air PID adjusting system and the secondary air PID adjusting system. The coal quality online analysis unit is used for detecting coal powder moisture content Wc and volatile content Vc. The central control unit controls the opening degree of the primary air adjusting valve group through a PID algorithm based on the Delta P, Kc signals and the sigma, Wc and Vc data, calculates the secondary air volume ratio alpha and dynamically corrects the wind-coal ratio gamma. The dynamic wind-coal matching sub-module is further provided with a secondary compensation mechanism. The flue gas recovery unit comprises a flue gas extraction pipeline and a flue gas recirculation pipeline. The flue gas extraction pipeline is connected with the outlet side of a boiler tail flue dust remover at an inlet end and is connected with the mixed flue gas pressure stabilizing chamber of the outer ring fuel channel at an outlet end. The flue gas recirculation pipeline is connected with the mixed flue gas pressure stabilizing chamber of the outer ring fuel channel at an inlet end and is connected with the flue gas recovery unit at an outlet end. ​ ​ 3. The flue gas compensation type coal powder wide load stable combustion system based on hierarchical combustion and intelligent regulation according to claim 1, characterized in that, ​ 4. The flue gas compensation type coal powder wide load stable combustion system based on hierarchical combustion and intelligent regulation according to claim 1, characterized in that, ​ ​ The high-efficiency electric dust removal device is arranged in the middle section of the flue gas extraction pipeline and is used for secondary dust removal treatment of the extracted flue gas, the extracted flue gas has a temperature of 200-300 DEG C and a flow rate accounting for 10%-30% of the total flue gas amount; The oxygen concentration adjusting unit comprises an oxygen conveying branch pipe and a static mixer, and is used for mixing oxygen into the backflow flue gas, so that the mixed oxygen concentration reaches 23%-25%; The closed-loop temperature control unit comprises: A thermocouple group is arranged in the region 500-800 mm downstream of the burner outlet along the axial direction of the burner, and is used for real-time monitoring of the flame temperature distribution; When the thermocouple detects that the center temperature of the flame is lower than 900 DEG C, the interlocking PID controller triggers the maximum flow mode of the flue gas recovery unit, and controls the flue gas extraction amount to increase to 80%-100% of the rated flow rate; A dynamic balance module is used for adjusting the valve opening degree of the oxygen conveying branch pipe based on the real-time flue gas temperature and oxygen concentration data, so as to maintain the dynamic balance of the flue gas heat value and the combustion temperature.

5. The flue gas compensation type coal powder wide load stable combustion system based on hierarchical combustion and intelligent regulation according to claim 1, characterized in that, The cyclone vane angle adjustment range is 15°-45°.

6. A coal dust wide load stable combustion control method characterized by, It is based on the flue gas compensation type coal powder wide load stable combustion system according to any one of claims 1-5, comprising the following steps: S1. Low load stable combustion stage control: a) activate the burner high concentration combustion mode, increase the coal powder mass ratio of the inner ring fuel channel to 75%-85%, and maintain the primary air temperature at 145-170 DEG C through the air temperature adjusting unit; b) adjust the secondary air amount adjusting valve opening degree of the inner and outer ring fuel channels, so that the secondary air amount accounts for 20%-30% of the total air supply amount; c) increase the recirculated flue gas extraction ratio to 20%-30%, and make the mixed flue gas oxygen concentration reach 23%-25% through the oxygen concentration regulating component; d) drive the primary air cyclone vane angle to increase to 45°, form a strong turbulent flow field with a cyclone number >1.2, and maintain the flame center temperature at 920±20 DEG C; S2. Medium and high load transition stage control: Receive the migration instruction output by the load prediction model, linearly increase the secondary air amount to 40% within 5 minutes, reduce the primary air temperature to 120 DEG C, reduce the flue gas flow to 15%, and no longer mix oxygen into the backflow flue gas; b) the cyclone regulating component drives the primary air cyclone vane angle to adjust to 15°; c) dynamically correct the air-coal ratio γ by real-time monitoring of the standard deviation σ of the furnace temperature distribution, so as to constrain the temperature fluctuation amplitude to be less than ±5 DEG C; d) synchronously link the coal powder fineness adjusting unit, and inversely compensate the coal powder particle size distribution according to the flame height change.

7. The stable combustion control method of pulverized coal over a wide load according to claim 6, characterized by, The low load stable combustion stage corresponds to a 30%-40% rated load range, and the medium and high load transition stage corresponds to a 40%-100% rated load range.

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