Large utility boiler system and method for flexible, high-efficiency combustion

Abstract

This invention relates to the field of large power plant boiler technology, specifically to a large power plant boiler system and method with flexible and efficient combustion technology, comprising: a boiler body; a pulverizing system; an air preheating system; an air supply system; and a dust removal system. The system controls the combined operation of the pulverizing system, air preheating system, and air supply system according to the boiler load status to achieve combustion stability and economic optimization under boiler start-up and shutdown, extremely low load, low load, and rapid load changes. Furthermore, it improves environmental performance and boiler operational reliability through a two-stage dust removal method involving high-temperature and low-temperature dust removal.

Description

Technical Field

[0001] This invention relates to the field of power plant boiler technology, specifically to a large power plant boiler system and method with flexible and efficient combustion technology. Background Technology

[0002] The large-scale development of photovoltaic and wind power new energy sources cannot be separated from the basic guarantee and system regulation of flexible coal-fired power. The coordinated development of coal-fired power and new energy sources is crucial. However, current coal-fired power plants are mainly constrained by the insufficient flexibility of their boilers, namely, their inadequacies in low-load stable combustion, rapid load change, start-up and shutdown peak shaving, and high efficiency over wide loads. This makes it difficult to meet the development needs of building a new energy system and a new power system.

[0003] Higher requirements are being placed on the new generation of coal-fired power units across the board. These are mainly reflected in: For newly built pulverized coal boilers burning bituminous coal, the minimum power output (Pe) under pure condensing operation should strive to reach 25% for deep peak shaving; at 50% and above load and 30% to 50% load, the load change rate should reach 2.2% and 1% of rated load / minute, respectively; at 30% load, the increase in coal consumption for power supply compared with rated load should strive to be controlled below 20%.

[0004] The new generation of coal-fired power units and pulverized coal boilers burning bituminous coal should strive to achieve a minimum power output (Pe) of 20% under pure condensing conditions; the load change rate at 50% and above load and 30% to 50% load should reach 4% and 2% of rated load / minute, respectively; and the increase in coal consumption for power supply at 30% load compared to rated load should be controlled to below 15%.

[0005] This demonstrates that the key aspects of improving the flexible and efficient performance of coal-fired power plant boilers are the deep peak shaving and start-stop peak shaving capabilities, rapid load change capabilities, and high energy efficiency operation over a wide load range. This project features an original design for the boiler combustion method. By optimizing the pulverizing, feeding, air preheating, and air supply methods of the boiler combustion system, it achieves two modes of configuration and operation: one for medium-to-high load operation and the other for low load and shutdown operation. This allows for seamless switching between these two modes, improving boiler flexibility and maintaining high energy efficiency at medium-to-low loads. In essence, this design constructs a large-scale coal-fired power plant boiler with a flexible and efficient dual-mode configuration suitable for dual-mode operation, referred to as a dual-mode boiler.

[0006] Depending on the unit type, coal quality characteristics, and heating type, currently in-service coal-fired power plants generate at least 25-40% of their rated load, with a load change rate of 0.8%-2.5% of rated load per minute. At 30% load, coal consumption increases by more than 25% compared to rated load. Conventional coal-fired power plants in operation with a capacity of 300MW or higher, using pulverized coal-fired boilers that burn bituminous coal, generally employ compact direct-fired pulverizing systems, rotary air preheaters, and low-temperature electrostatic precipitators. However, they suffer from the following shortcomings: ① The minimum power generation output for deep peak shaving is limited, making it unsuitable to start or stop peak shaving. The minimum power output for peak load regulation of the unit mainly depends on the boiler side. At low loads, the main problems with the boiler include: combustion stability, hydrodynamic safety, lifespan loss of thick-walled components and safety of components under strong thermal stress, main (reheat) steam temperature significantly lower than rated value, low flue gas temperature at the denitrification inlet preventing full-load denitrification, easy ash accumulation, blockage, and collapse on low-temperature heating surfaces, and difficulty in coordinated control. The most direct consequence is unstable combustion, which can easily lead to boiler flameout, affecting the safe operation of the boiler and the unit.

[0007] The main reasons for unstable boiler combustion include: low primary air pulverized coal concentration at low loads, large air leakage in the rotary air preheater, large primary / secondary air volume and low air temperature, resulting in decreased pulverized coal ignition and stable combustion capacity; reduced furnace combustion temperature and weakened flame support, making deep peak shaving impossible and unsuitable for start-up and shutdown peak shaving.

[0008] ②Limited ability to quickly adjust and change load rates Currently, coal-fired power units are slow to rapidly change load, mainly due to the inadequacy of boiler fuel regulation. In direct-fired pulverized coal systems, the entire process—from the coal feeder regulating fuel supply, through the pulverizer, the primary air fan delivering air and pulverized coal, to the ignition and combustion of the pulverized coal in the burner—is long, has high inertia, and a long time constant. This results in untimely supply response and boiler thermal lag, making it difficult to quickly respond to AGC power commands. The direct-fired pulverized coal system is most affected; increasing the amount of coal fed into the furnace requires a 5-10 minute pulverization cycle, leading to significant boiler thermal lag and an inability to quickly respond to unit load changes.

[0009] ③ The economic efficiency is significantly reduced over a wide load range. The significant increase in standard coal consumption for power supply under low-load conditions is mainly due to the combined effects of decreased boiler efficiency, increased turbine heat consumption, and increased plant power consumption. Ash accumulation and blockage on the boiler's tail-end heating surfaces cause blockage, wear, and corrosion of the denitrification catalyst packing and rotary air preheater heat exchange elements, while also increasing the power consumption of the forced and induced draft fans. Excessive air leakage in the rotary air preheater leads to high power consumption of the forced draft fan, a decrease in primary / secondary air temperature, and an increase in flue gas temperature, thus reducing boiler efficiency. At high boiler loads, the air preheater experiences significant air leakage and resistance, resulting in high power consumption for the forced draft fan, induced draft fan, and primary air fan. At low loads, the pulverizing system and forced draft system operate, increasing the plant power consumption and significantly raising coal consumption.

[0010] For every 1 percentage point decrease in boiler efficiency (e.g., from 94% to 93%), the standard coal consumption for power generation will increase by approximately 1% (about 3 gce / kWh). Among these factors, flue gas heat loss has the greatest impact on boiler efficiency; a 10°C increase in flue gas temperature leads to a approximately 0.5% decrease in boiler efficiency and an increase in standard coal consumption for power generation of approximately 1.5-1.6 gce / kWh. A 0.01% increase in plant power consumption leads to an approximately 0.03 gce / kWh increase in coal consumption for power generation. Conventional coal-fired power plant boiler system designs are ill-suited to meet the requirements of high efficiency across wide load ranges. Summary of the Invention

[0011] Technical problems to be solved The purpose of this invention is to provide a large-scale power plant boiler system and method with flexible and efficient combustion technology, which solves the following technical problems: ①Deep peak shaving limits the minimum power generation output reduction, making it unsuitable to start or stop peak shaving; ② The rate of rapid adjustment and change of load is limited; ③ The economic efficiency is significantly reduced over a wide load range.

[0012] (II) Technical Solution A flexible combustion dual-mode large power plant boiler system with wide load adaptability includes: Boiler body; pulverizing system, wherein the dual-mode pulverizing system includes: The central storage pulverizing unit is equipped with a coal mill, a coal powder silo, a bag filter, a pulverizer, and an exhaust fan. It is used to store coal powder in the coal powder silo after the coal mill is running, and the coal powder supply is regulated by the pulverizer and sent into the furnace for combustion by primary air. The direct-fired pulverizing unit is used to directly output pulverized coal from the coal mill to the furnace for combustion; The air preheating system has a dual-mode structure and includes: Indirect air preheater is used to preheat primary air; Rotary air preheater is used to preheat secondary air; The air supply system, including a primary air fan and a secondary air fan (i.e., the supply fan), has a dual-mode operation control system: When operating at low load, the main fan is stopped, and the primary fan provides primary and secondary air, which is preheated by the indirect air preheater. During medium- and high-load operation, the primary air fan and the secondary air fan operate in parallel. The primary air is preheated by the partition-type air preheater, and the secondary air is preheated by the rotary air preheater. The dust removal system is a two-stage series structure, including a high-temperature dust removal device and a low-temperature electrostatic precipitator / bag filter composite dust removal device. The high-temperature dust removal device is arranged before the denitrification device, and the low-temperature electrostatic precipitator / bag filter composite dust removal device is arranged before the flue gas desulfurization at the tail end of the boiler. The system controls the combined operation of the pulverizing system, air preheating system and air supply system according to the load status to optimize combustion stability and economy under extremely low load, low load and rapid load change, and improves environmental performance and boiler operation reliability through a two-stage dust removal method of high temperature dust removal and low temperature dust removal.

[0013] The central storage pulverizing unit provides continuous and stable pulverized coal supply under low unit load and boiler start-up and shutdown conditions. The pulverized coal silo decouples the pulverizer operation from the boiler load. The pulverizer is not started for pulverizing under low load, so that it can still maintain stable combustion and lower power generation output when the load is below 20% of the rated load. When the direct-fired pulverizing unit is put into operation under medium and high load, the medium-storage coal mill can be put into pulverizing and raise the pulverizing level when the coal powder level in the coal powder silo is low, so that the coal mill can operate in the economic operating range, thereby reducing the pulverizing power consumption and improving the combustion efficiency and equipment life. When operating at low load, the rotary air preheater is shut down and its inlet flue gas damper is closed. Only the indirect air preheater is used to preheat the primary and secondary air to reduce the temperature drop in the furnace caused by cold air entering the furnace, maintain stable combustion, reduce air leakage in the air preheater, and improve boiler efficiency.

[0014] The dust removal efficiency of the high-temperature dust removal device is not less than 50%, thereby pre-separating large particles of fly ash before the flue gas enters the denitrification catalyst layer, reducing the risk of wear, blockage and poisoning of the catalyst layer, and reducing ash accumulation and air leakage in the air preheater.

[0015] Preferably, the fly ash separated by the high-temperature dust removal device is heat-exchanged by a waste heat recovery device, and the waste heat is used to heat the boiler feedwater or preheat the primary air to reduce heat loss and improve the system thermal efficiency.

[0016] Preferably, the outlet separator of the coal mill adopts a multiphase flow high-efficiency separation structure. By optimizing the lower baffle of the separator, the outlet structure of the separator, and the air-coal pipeline, the coal powder separation efficiency and the output of the coal mill are improved, the system resistance is reduced, the accumulation of powder and blockage are eliminated, the equipment wear is reduced, and the nitrogen oxide emissions are reduced.

[0017] Preferably, the system has a hierarchical operation mode: Extremely low load and low load modes: The powder feeder and the indirect air preheater of the medium storage powder making unit are in operation; Medium-high load mode: The medium-storage type and direct-fired pulverizing unit are operated in combination. The direct-fired pulverizing unit is selected to carry the basic load and operate stably. The medium-storage type pulverizer undertakes the dynamic load adjustment function to improve the load rapid response adjustment capability. The indirect-containment type and rotary air preheater, primary air fan and secondary air fan operate simultaneously. To optimize combustion efficiency and plant power consumption across the entire load range.

[0018] Preferably, the pulverizing system, air preheating system and air supply system are automatically switched through a linkage control strategy, so that the boiler can maintain stable combustion and have rapid peak-shaving capability when the load changes rapidly.

[0019] Preferably, when the boiler is running at 30% load, the increase in coal consumption for power supply compared to the rated load operation does not exceed 15%, thereby achieving economy and adaptability throughout the entire process from start-up and shutdown, deep peak shaving to full-load operation.

[0020] A method for operating a large power plant boiler with flexible and efficient combustion technology, applied to a power plant boiler including the boiler body, a dual-mode pulverizing system, a dual-mode air preheating system, and a dual-mode air supply system, comprising: S1. Develop a load classification strategy, dividing the unit load range into low-load and medium-high-load operating condition zones; Powder making system switching control steps: When the boiler is started or stopped and the load is lower than the preset low load threshold, only the feeder in the medium storage pulverizing unit is operated to maintain boiler combustion and stabilize combustion using the pulverized coal already prepared in the pulverized coal silo. When the unit load reaches or exceeds the medium-high load threshold, the direct-fired pulverizing unit is gradually added, and the medium-storage and direct-fired pulverizing units are operated in combination until the two pulverizing units are operated in parallel to maximize the output and make the coal mill operate under economic conditions. S2. Air preheating system control: During the boiler start-up and shutdown to low load phase, the rotary air preheater is shut down, and only the indirect air preheater is used to preheat the primary and secondary air. At medium to high loads, the indirect air preheater and the rotary air preheater operate simultaneously, heating the primary air and secondary air independently, respectively. S3. Air supply control: During boiler start-up and shutdown and low-load phases, air is supplied only by the primary air fan; During medium-to-high load periods, secondary fans are started and run in parallel to optimize the air-to-coal ratio. Flue gas treatment and control: The high-temperature dust removal device is controlled to operate before the flue gas enters the denitrification system to capture coarse fly ash particles; Control the low-temperature dust removal device for efficient end-of-pipe dust removal; Linkage and feedback control: Based on closed-loop feedback of online load, oxygen content, temperature, and flue gas parameters, the system automatically switches between pulverizing and preheating system operating modes to maintain optimal combustion efficiency and emission levels.

[0021] Through the above steps, the boiler can achieve efficient and stable combustion across the entire load range, taking into account both energy saving and low emissions.

[0022] S4. In the linkage and feedback control steps, the main control system collects the furnace flue gas temperature, heating surface tube wall temperature, oxygen content and flue gas flow rate in real time, and uses a fuzzy logic control algorithm to realize the dual-mode system state switching with a response time of less than 30 seconds to meet the requirements of rapid peak shaving response.

[0023] S5. When the temperature of fly ash collected by the high-temperature dust removal device exceeds the set threshold, the waste heat recovery system is activated to use some of the heat for the waste heat boiler feedwater or primary air in order to achieve thermal balance optimization.

[0024] S6. During the extremely low load operation phase, a time-sharing and segmented pulverized coal feeding strategy is adopted to maintain the stability of the furnace heat load, and the furnace temperature is controlled by reducing the primary air volume and appropriately adjusting the return air circulation volume to achieve long-term stable combustion below 20% load.

[0025] At 30% unit load, the increase in coal consumption for power generation shall not exceed 15% of the rated operating condition, and the concentration of nitrogen oxide emissions shall remain below 50 mg / m³. 3 .

[0026] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are: Dual-mode pulverization (a hybrid pulverization system combining direct-fired and intermediate-storage pulverization) – Dual-mode pulverization is the core underlying technology supporting dual-mode boilers. The hybrid pulverization and feeding system fully leverages the flexibility of the intermediate-storage system and the simplicity of the direct-fired system, meeting the requirements for boiler start-up, stable combustion at low loads, deep adjustment, and economy. It also addresses the flexibility requirements for rapid load increases and decreases, while optimizing auxiliary equipment operation across a wide load range. The auxiliary equipment of the pulverization system and the air preheating system always operate within a highly efficient and economical range, reducing plant power consumption and coal consumption for power supply.

[0027] Through the buffering and decoupling effects of the pulverized coal silo, the low-inertia medium-storage pulverized coal feeding system plays a crucial role during boiler start-up and shutdown, extremely low load, low load, and rapid load changes. During boiler start-up and shutdown, and extremely low load, the pulverizer is shut down, significantly reducing the volume of primary and secondary air fed into the furnace at lower temperatures. This helps improve the overall furnace temperature and combustion stability, and also reduces plant power consumption at low and extremely low loads, improving economic efficiency and reducing coal consumption for power generation. The medium-storage pulverized coal feeding system also plays an important role in supporting the boiler, stabilizing combustion, and preventing interference at medium and high loads, facilitating rapid mill shutdown and load reduction while maintaining stable boiler combustion. The high-inertia direct-fired pulverized coal system, on the other hand, acts as an increment in coal supply at medium and high loads, meeting the coal consumption requirements at these loads and ensuring the boiler can operate at full capacity. Meanwhile, the high-inertia direct-fired pulverizing system handles the basic pulverized coal feed, while the low-inertia intermediate-storage pulverized coal feed system handles the additional pulverized coal feed required for load changes. This solves the technical problem of the long response time of the current direct-fired pulverizing system, which limits the unit's ability to rapidly change loads, thereby improving the boiler's ability to rapidly change loads. The design of the hybrid pulverizing system in the dual-mode boiler comprehensively, systematically, and holistically improves the stability, flexibility, and economy of the boiler combustion system, and enhances the boiler's start-up, shutdown, and peak-shaving capabilities.

[0028] Dual-mode air preheating (a hybrid air preheating system combining rotary and indirect-containment types) – Dual-mode air preheating is the second core technology and feature of dual-mode boilers, and is an essential option for retrofitting hybrid dual-mode pulverizing systems. The main component of hybrid air preheating is that the boiler's primary and secondary air preheaters utilize indirect-containment and rotary air preheaters respectively. The low-pressure, high-volume secondary air is preheated in a two-compartment rotary air preheater, while the high-pressure, low-volume primary air is preheated in a high-efficiency, leak-proof indirect-containment air preheater. This fully leverages the advantages of rotary air preheaters (compact layout, space saving) and indirect-containment air preheaters (leak-proof and less prone to clogging).

[0029] Because the primary and secondary air are preheated separately, this method is significantly superior to the conventional three-compartment or four-compartment rotary air preheater where both primary and secondary air are heated together. In the conventional mode, high-pressure primary air is very prone to leaking into low-pressure secondary air and negative-pressure flue gas, causing a large amount of hot air leakage, reducing the preheating effect of the air preheater, reducing boiler efficiency, increasing the power consumption of the primary air fan and induced draft fan, and affecting stable combustion at low loads. Due to the adoption of the dual-mode air preheating, only the partitioned air preheater and the intermediate storage coal feeding system are used at low loads, which increases the primary air temperature, improves the boiler's start-up and shutdown and stable combustion at low loads, enhances the boiler's deep peak-shaving capability and the economy of start-up and shutdown peak-shaving, and reduces the plant power consumption rate at low loads. Furthermore, the use of the rotary air preheater at medium and high loads significantly reduces air preheater leakage and also significantly reduces the plant power consumption rate of the boiler under medium and high load conditions, achieving the goal of high efficiency over wide loads.

[0030] (3) Dual-mode air supply (combined operation of primary and secondary air fans) --- Dual-mode air supply is the core technology and core feature of dual-mode boilers, and is a necessary option for the modification of hybrid dual-mode air preheating systems. When the boiler starts up and stops or is under low load, the primary air fan is stopped, and both primary and secondary air are supplied by the primary air fan and preheated through the partition air preheater. The gate-type isolation connecting damper of the hot primary air and hot secondary air main pipe is opened, and the secondary air is also supplied by the primary air. The coal storage silo is used for coal supply, and the coal mill is stopped, which greatly reduces the excess air volume entering the furnace when the boiler starts up and stops or is under low load, increases the furnace temperature, and enhances the stability of combustion. Under medium and high load, the air preheater is restored to dual-mode parallel operation, the primary air goes through the partition air preheater, and the secondary air goes through the rotary air preheater. The connecting damper of the hot primary and secondary air main pipe is closed, and the primary and secondary air fans operate in parallel.

[0031] (4) Dual-stage dust removal (high-temperature dust removal + low-temperature dust removal) --- The dust removal system adopts a combination of high-temperature dust removal (dust removal efficiency not less than 50%) and low-temperature electrostatic precipitator in series. High-temperature dust removal is arranged before the boiler denitrification device to solve the problems of wear, ash blockage, poisoning and ammonia escape of the denitrification catalyst layer, and at the same time solve the problems of wear, ash blockage, agglomeration and corrosion of the rotary air preheater and low-temperature economizer of the power plant boiler. Using a high-temperature dust collector to separate a portion of the large fly ash particles in the flue gas in advance helps to significantly improve the working environment of the boiler tail flue, reduce the wear of the heating surface, and in particular, significantly reduce the problem of high flue gas operating resistance caused by ash blockage of the denitrification catalyst layer and rotary air preheater. This significantly improves the reliability and economy of denitrification and air preheater, reduces the flow resistance of the flue gas system, reduces the power consumption of the forced draft fan, primary air fan and induced draft fan, and improves the overall performance of the boiler system. The fly ash removed by high-temperature dust removal is used to assist in the installation of a waste heat recovery device to reduce boiler heat loss. The use of high-temperature dust removal improves the cleanliness of subsequent heating surfaces, increases heat exchange efficiency, helps to increase hot air temperature, reduce flue gas temperature, and improve boiler efficiency and the dust removal efficiency of low-temperature dust collectors. Attached Figure Description

[0032] Figure 1 The diagram below shows the storage-type powder-making system of this invention patent. Figure 2 This is a schematic diagram of the smoke and flue gas system of this invention. Detailed Implementation

[0033] To better understand the purpose, structure, and function of this invention, the following detailed description, in conjunction with the accompanying drawings, provides an overview of a large-scale power plant boiler system and method based on flexible and efficient combustion technology.

[0034] Please see Figure 1-2The present invention will now be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] A large-scale power plant boiler system with flexible and efficient combustion technology is presented. This system employs a dual-mode boiler design, meaning the boiler system utilizes two different pulverizing and feeding, air preheating, and air supply modes (i.e., dual-mode pulverizing, dual-mode air preheating, and dual-mode air supply) for both medium-high and low load conditions. Simultaneously, it is equipped with a staged, series-connected two-stage dust removal system combining high-temperature and low-temperature dust removal to address issues such as ash accumulation, blockage, and wear in the denitrification catalyst layer and air preheater. The operating and adjustment methods are described under the following three conditions.

[0036] Boiler start-up and shutdown and extremely low load / low load conditions When the boiler is started up or shut down, or operating at extremely low or low loads, the coal mill, blower, and rotary air preheater are shut down. Only the medium-storage coal feeding system and the indirect air preheater are activated, with the primary air fan supplying coal and secondary air simultaneously.

[0037] The pulverized coal silo in a medium-speed mill-type pulverizing system stores the pulverized coal produced by the mill. The silo holds enough coal for 6-8 hours of rated load. During unit start-up and shutdown, extremely low load, and low load, only the feeder and the bottom two or one burners are operated to optimize the supply of primary air and a small amount of secondary air, increasing pulverized coal concentration and furnace flame temperature, and enhancing combustion stability. Because the direct-fired pulverizing system is shut down, boiler combustion is easily stabilized, while significantly reducing plant power consumption. When the unit rapidly increases or decreases load, the feeder is switched on or its speed is directly adjusted to quickly adapt to changes in external load. Furthermore, the pulverizers in both the medium-speed mill-type and direct-fired pulverizing systems always operate under economical conditions. Shutting down the pulverizers at low loads not only significantly reduces the pulverizing system's power consumption but also improves equipment lifespan and reliability.

[0038] During low-load boiler operation, the rotary air preheater is shut down, its inlet flue gas damper is closed, and the corresponding forced draft fan is stopped. The connecting dampers for the primary and secondary hot air headers are opened, and the primary and secondary air required for pulverized coal feeding and combustion are supplied by the indirect-flow air preheater. By shutting down two forced draft fans and all coal mills, a significant amount of unnecessary air intake is reduced, increasing the combustion temperature in the boiler furnace, enhancing the stability and burnout rate of pulverized coal combustion, and improving boiler combustion efficiency at low loads. By maximizing combustion efficiency and minimizing plant power consumption under different load conditions, the unit's deep peak-shaving capacity, start-stop peak-shaving capacity, and overall economy are effectively improved, thereby comprehensively enhancing the adaptability of the boiler combustion system across a wide load range.

[0039] (2) Medium and high load conditions At medium to high loads, additional direct-fired pulverizers, rotary air preheaters, and forced draft fans are added to achieve stable, high-volume combustion of pulverized coal and efficient preheating of air volume. During medium and high loads, the lower two layers of the central storage pulverizer system continue to operate, while the pulverizers corresponding to the upper and middle burners of the direct-fired pulverizer system are gradually added. The pulverizer operating conditions are matched to the boiler load, and the number of pulverizers in operation is determined based on the unit load, ensuring that the pulverizers operate in their high-efficiency range as much as possible. Simultaneously, the central storage pulverizer system can produce a large amount of pulverized coal at medium to high boiler loads, storing the produced pulverized coal in a silo for use during low loads or rapid load changes, ensuring stable and efficient operation at medium and high loads.

[0040] When the boiler is under medium and high load, a mixed preheating method is adopted. The primary air is supplied through a partition-type air preheater, and the secondary air is supplied through a rotary air preheater. The rotary air preheater is restarted, the inlet flue gas damper of the rotary air preheater is opened, the corresponding blower is started, and the connecting damper between the hot primary air header and the hot secondary air header is closed. This ensures an adequate supply of secondary air, reduces air leakage, and lowers the power consumption of the air supply system, enabling the boiler to maintain efficient and low-consumption combustion performance throughout a wide load operating range.

[0041] (3) Rapid load change conditions The intermediate storage pulverizing system stores 6-8 hours' worth of pulverized coal in its silos. The speed of the pulverizer or the number of pulverizers in operation is directly adjusted to deliver the pulverized coal to the boiler burners for combustion. This low-inertia intermediate storage pulverizer system can quickly respond to external peak-shaving demands, significantly improving the boiler's load change rate and enhancing the unit's start-up and shutdown peak-shaving capabilities. When the boiler experiences significant load changes, the pulverizers are activated or deactivated to adapt to these changes.

[0042] The dual-mode pulverizing system and the dual-mode air preheating system work together. Through the linkage control strategy of dual-mode pulverizing and dual-mode air preheating, the system can shut down the blower and coal mill during low-load stages, relying on only a small number of devices to maintain stable combustion, significantly reducing the plant's power consumption rate. Under conditions of rapid load changes, the synergistic effect of the central storage coal pulverizer and the indirect air preheater can achieve rapid coal supply and stable air support, thereby enabling the unit to have excellent peak-shaving and rapid response capabilities, meeting the flexible dispatching needs under the background of high proportion of new energy grid connection in modern power systems, while improving the reliability, stability and security of power system operation.

[0043] By integrating four innovative technologies—dual-mode pulverization, dual-mode air preheating, dual-mode air supply, and dual-stage dust removal—into a single boiler system, the system maintains combustion stability and high efficiency at low loads, ensures complete pulverized coal combustion and reduces energy consumption at medium and high loads, and improves the cleanliness of the tail flue and the long-term stability of the denitrification catalyst through the combination of high and low temperature dust removal. This comprehensive design not only significantly reduces boiler operating power consumption and maintenance costs but also enhances the unit's economy, environmental friendliness, and flexibility, meeting the high-efficiency operation requirements of power plant boilers across a wide load range.

[0044] The system employs a refined and optimized strategy for staged combustion at boiler start-up and shutdown, extremely low load, low load, medium load, and high load. During boiler start-up and shutdown, extremely low load, and low load operation, it primarily relies on a combination of a central storage pulverized coal silo and a partitioned air preheater to ensure stable combustion and reduced energy consumption. During medium and high load operation, it switches to full operation of direct-fired pulverizer, forced draft fan, and rotary air preheater to ensure efficient combustion of large quantities of pulverized coal. This staged mode meets the coal-fired power plant construction indicator system for the new generation of coal-fired power units, achieving a minimum power output (Pe) of 20% for deep peak shaving; a load change rate of 4% and 2.5% of rated load per minute at 50% and above load, and 30%–50% load, respectively; and controlling the increase in coal consumption for power supply at 30% load compared to rated load to below 15%.

[0045] A flexible combustion dual-mode boiler system for large power plants with wide load adaptability includes: Boiler body; pulverizing system, the dual-mode pulverizing system includes: The central storage pulverizing unit is equipped with a coal mill, a coal powder silo, a bag filter, a pulverizer, and an exhaust fan. It is used to store coal powder in the coal powder silo after the coal mill is running, and the coal powder supply is regulated by the pulverizer and sent into the furnace for combustion by primary air. The direct-fired pulverizing unit is used to directly output pulverized coal from the coal mill to the furnace for combustion; The air preheating system has a dual-mode structure and includes: Indirect air preheater is used to preheat primary air; Rotary air preheater is used to preheat secondary air; The air supply system, including a primary air fan and a secondary air fan (i.e., the supply fan), has a dual-mode operation control system: During low-load operation, the main fan is stopped, and the primary fan provides primary and secondary air, which is preheated by the indirect air preheater. During medium-to-high load operation, the primary air fan and the secondary air fan operate in parallel. The primary air is preheated by a heat exchange tube type air preheater, and the secondary air is preheated by a rotary air preheater. The dust removal system is a two-stage series structure, including a high-temperature dust removal device and a low-temperature dust removal device. The high-temperature dust removal device is arranged before the denitrification device, and the low-temperature dust removal device is arranged at the tail of the boiler. The system controls the combined operation of the pulverizing system, air preheating system, and air supply system according to the load status to optimize combustion stability and economy under boiler start-up and shutdown, extremely low load, low load, and rapid load change. It also improves environmental performance and boiler operation reliability through a two-stage dust removal method of high-temperature dust removal and low-temperature dust removal.

[0046] The central storage pulverizing unit provides continuous and stable pulverized coal supply under low unit load and boiler start-up and shutdown conditions. The pulverized coal silo decouples the pulverizer operation from the boiler load, thus enabling stable combustion and maintaining minimum power generation output even when the load is below 20% of the rated load. During operation at medium to high loads, the direct-fired pulverizing unit is added, and the medium-storage coal mill is put into operation when the coal powder level in the coal powder silo is low and the load is high, so that the coal mill operates in the economic operating range, thereby reducing pulverizing power consumption and improving combustion efficiency and equipment life. During low-load operation, the rotary air preheater is shut down and its inlet flue gas damper is closed. Only the indirect air preheater is used to preheat the primary and secondary air to reduce the temperature drop in the furnace caused by cold air entering the furnace, maintain stable combustion, reduce air leakage in the air preheater, and improve boiler efficiency.

[0047] The dust removal efficiency of the high-temperature dust removal device is not less than 50%, thereby pre-separating some fly ash before the flue gas enters the denitrification catalyst layer, reducing the risk of catalyst layer wear, blockage and poisoning, and reducing ash accumulation and air leakage in the air preheater.

[0048] The fly ash separated by the high-temperature dust removal device is heat-exchanged by a waste heat recovery device. The waste heat is used to heat the boiler feedwater or preheat the primary air to reduce heat loss and improve the system thermal efficiency.

[0049] The coal mill outlet separator adopts a multiphase flow high-efficiency separation structure. By optimizing the lower baffle of the separator, the separator outlet structure and the air-coal pipeline, the coal powder separation efficiency and coal mill output are improved, the system resistance is reduced, the accumulation of powder and blockage are eliminated, the equipment wear is reduced and the nitrogen oxide emissions are reduced.

[0050] The system has a tiered operation mode: Boiler start-up and shutdown, extremely low load and low load modes: operation of the pulverizer feeder and the indirect air preheater in the medium storage pulverizing unit; Medium and high load modes: The medium storage type and direct-fired pulverizing unit are operated in combination, and the direct-fired pulverizing unit is added. The indirect-wall type and rotary air preheater, primary air fan and secondary air fan are operated simultaneously. To optimize combustion efficiency and plant power consumption across the entire load range (including boiler start-up and shutdown).

[0051] The pulverizing system, air preheating system, and air supply system are automatically switched through a linkage control strategy to ensure that the boiler maintains stable combustion and has rapid peak-shaving capability when the load changes rapidly.

[0052] When the boiler is running at 30% load, the increase in coal consumption for power supply compared to the rated load operation does not exceed 15%, thus achieving economy and adaptability throughout the entire process from start-up and shutdown, deep peak shaving to full-load operation.

[0053] A flexible combustion boiler operation method with wide load adaptability, applied to a power plant boiler including the boiler body, a dual-mode pulverizing system, a dual-mode air preheating system, and a dual-mode air supply system, the method comprising: S1. Develop a load grading strategy. Based on the boiler load range, the operating conditions are divided into low load operation and medium-high load operation ranges. The low load operation range includes boiler start-up and shutdown (starting from zero or to zero load), extremely low load (0-20%), and low load (20%-30%). The medium-high load operation range includes medium load (30%-70%) and high load (70%-100%). Powder making system switching control steps: When the unit load is at the low load preset threshold, only the feeder in the medium storage pulverizing unit is operated to maintain boiler combustion and stabilize combustion using the pulverized coal already prepared in the pulverized coal silo. When the unit load reaches or exceeds the medium-high load threshold, add a direct-fired pulverizing unit, and operate the medium-storage and direct-fired pulverizing units in combination until the two pulverizing units are operated in parallel to maximize output and keep the coal mill operating in an economical condition. S2. Air preheating system control: During low-load periods, the rotary air preheater is shut down, and only the indirect air preheater is used to preheat the primary and secondary air. Conventional large power plant boilers typically use rotary air preheaters, while indirect air preheaters are used in smaller power plant boilers. This technology is the first to combine both types of air preheaters in the design of a large power plant boiler. This pioneering operating method has significant technical and economic implications.

[0054] During medium-to-high load periods, both the indirect-flow air preheater and the rotary air preheater operate simultaneously, independently heating the primary and secondary air respectively. Conventional power plant boiler designs typically employ only one type of air preheater, with large power plant boilers generally using rotary air preheaters, where primary and secondary air are heated through different compartments within the rotary air preheater. This technology proposes applying the indirect-flow air preheater to large power plant boilers for primary air heating, a pioneering design that utilizes different types of air preheaters for heating primary and secondary air. Furthermore, this technical solution proposes shutting down the rotary air preheater during low-load periods to reduce air leakage and fan power consumption, while activating it during high-load periods to independently heat the primary and secondary air, ensuring the large air volume required for pulverized air supply and furnace combustion, thus combining the advantages of both types of air preheaters.

[0055] S3. Air supply control: During low-load periods, only the primary air fan supplies air. Conventional operation during low-load periods involves both primary and secondary air fans running simultaneously. This approach suffers from difficulties in matching boiler airflow with fuel volume, leading to excess airflow causing lower combustion temperature and lower combustion efficiency. Furthermore, the fans deviate from their optimal design conditions, resulting in low efficiency, high power consumption, and potential fan competition causing boiler instability. Some operating methods involve shutting down only one fan, but this also reduces operational reliability and causes significant temperature differences in the exhaust gases from both sides. This innovative technology proposes shutting down the primary air fan during low-load periods, using the primary air fan to supply both primary and secondary air simultaneously. This ensures the fan operates within its high-efficiency range, and the airflow can be effectively controlled, improving boiler combustion efficiency and reducing fan power consumption.

[0056] During medium-to-high load periods, secondary fans are started and run in parallel to optimize the air-to-coal ratio. Flue gas treatment and control: The high-temperature dust removal device is controlled to operate before the flue gas enters the denitrification system to capture coarse fly ash particles; Control the low-temperature dust removal device for efficient end-of-pipe dust removal; Linkage and feedback control: Based on closed-loop feedback of online load, oxygen content, temperature, and flue gas parameters, the system automatically switches between pulverizing and preheating system operating modes to maintain optimal combustion efficiency and emission levels.

[0057] Through the above steps, the boiler can achieve efficient and stable combustion across the entire load range, taking into account both energy saving and low emissions.

[0058] S4. In the linkage and feedback control steps, the main control system collects the furnace flue gas temperature, heating surface tube wall temperature, oxygen content and flue gas flow rate in real time, and uses fuzzy logic control algorithm to realize the dual-mode system state switching with a response time of less than 30 seconds to meet the requirements of rapid peak shaving response.

[0059] S5. When the temperature of fly ash collected by the high-temperature dust removal device exceeds the set threshold, the waste heat recovery system is activated to use some of the heat to preheat the boiler feedwater or primary air in order to achieve thermal balance optimization.

[0060] S6. During the extremely low load operation phase, a time-sharing and segmented pulverized coal feeding strategy is adopted to maintain the stability of the furnace heat load, and the furnace temperature is controlled by reducing the primary air volume and appropriately adjusting the return air circulation volume to achieve long-term stable combustion below 20% load.

[0061] At 30% unit load, the increase in coal consumption for power supply shall not exceed 15% of the rated operating condition, and the nitrogen oxide emission concentration shall remain below 50 mg / m³. 3 .

[0062] Conventional large power plant boilers generally employ direct-fired pulverizing systems, while small power plant boilers typically use intermediate-storage pulverizing systems. In conventional technologies, direct-fired and intermediate-storage pulverizing systems are often operated in mutually exclusive or simple parallel configurations without coordination. This technical solution's "intermediate-storage + direct-fired dual-mode pulverizing" is the first application of dual-mode pulverizing combination in the design of a large power plant boiler, and it establishes a coordinated commissioning and complementary control strategy based on load gradients. Low load phase: Only the feeder of the medium storage pulverizer is operated (the coal mill is shut down). The coal powder stored in the coal powder silo is used for combustion in the furnace. Compared with the conventional medium storage system, the amount of primary air and secondary air with lower temperature fed into the furnace under low load is greatly reduced, which improves combustion stability, reduces plant power consumption, and enhances the high efficiency range over a wide load range. During medium to high load phases: gradually increase the number of direct-fired pulverizing units (in order of economic output of coal mills), and play an important role in supporting the coal supply, stabilizing combustion, and resisting interference through the pulverizing feed rate of the medium-storage pulverizer. At the same time, fine-tune and compensate for fluctuations in the output of the direct-fired pulverizer to achieve "uninterrupted load increase". Parallel operation optimization: When the dual-mode pulverizing system is in parallel operation, all coal mills are guaranteed to operate within the economic range of rated output, thus improving the economic efficiency of the pulverizing system. Dual-mode pulverization is not a simple superposition, but a synergistic control of "gradient operation + load complementarity + efficiency optimization", which solves the dual contradiction of "stable combustion and energy saving at low load" and "efficiency improvement and load stabilization at medium and high load".

[0063] Breaking away from the traditional model of independent operation of pulverizing, air preheating, and ventilation systems, a multi-system parameter precision coupling system with load grading as its core has been constructed. The distinct features are not simply the superposition of conventional technologies, but rather a synergistic effect of "1+1>2" formed through linkage control, ultimately achieving an organic unity of peak-shaving capacity, economy, environmental protection, and flexibility.

[0064] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A large-scale power plant boiler system with flexible and efficient combustion technology, characterized in that, include: Boiler body; The pulverizing system, wherein the pulverizing system is a dual-mode hybrid structure of medium storage and direct blowing, includes: The central storage pulverizing unit is equipped with a coal mill, a coal powder silo, a bag filter, a pulverizer, and an exhaust fan. It is used to store coal powder in the coal powder silo after the coal mill is running, and the coal powder supply is regulated by the pulverizer and sent into the furnace for combustion by primary air. The direct-fired pulverizing unit is used to directly output pulverized coal from the coal mill to the furnace for combustion; The air preheating system is a hybrid dual-mode structure combining rotary and partition types, including: Indirect air preheater is used to preheat primary air; Rotary air preheater is used to preheat secondary air; The air supply system, including a primary air fan and a secondary air fan (i.e., the supply fan), has a dual-mode operation control system: When operating at low load, the transport fan is stopped, and the primary fan is used to provide primary and secondary air, which is preheated by the indirect air preheater; During medium- and high-load operation, the primary air fan and the secondary air fan operate in parallel. The primary air is preheated by the partition-type air preheater, and the secondary air is preheated by the rotary air preheater. The dust removal system is a two-stage series structure, including a high-temperature dust removal device and a low-temperature dust removal device. The high-temperature dust removal device is arranged before the denitrification device, and the low-temperature dust removal device is arranged before the desulfurization device at the tail of the boiler. The system controls the combined operation of the pulverizing system, air preheating system and air supply system according to the load status to achieve combustion stability under extremely low load, low load and rapid load change, and improves environmental performance and boiler operation reliability through a two-stage dust removal method of high temperature dust removal and low temperature dust removal.

2. The large-scale power plant boiler system with flexible and efficient combustion technology according to claim 1, characterized in that, The central storage pulverizing unit provides continuous and stable pulverized coal supply under low unit load and boiler start-up and shutdown conditions. The pulverized coal silo decouples the pulverizer operation from the boiler load, thereby enabling stable combustion and maintaining a smaller power output when the load is below 20% of the rated load, and reducing boiler plant power consumption. When operating at medium to high loads, the direct-fired pulverizing unit is added, and the medium-storage coal mill is put into operation when the coal powder level in the coal powder silo is low and the boiler load is high, so that the coal mill operates in the economic operating range, thereby reducing pulverizing power consumption and improving combustion stability, economy and equipment life. When operating at low load, the rotary air preheater is shut down and its inlet flue gas damper is closed. Only the indirect air preheater is used to preheat the primary and secondary air to reduce the temperature drop in the furnace caused by cold air entering the furnace, maintain stable combustion, reduce air leakage in the air preheater, and improve boiler efficiency.

3. A large power plant boiler system with flexible and efficient combustion technology according to any one of claims 1 to 2, characterized in that, The dust removal efficiency of the high-temperature dust removal device is not less than 50%, thereby pre-separating large particles of fly ash before the flue gas enters the denitrification catalyst layer, reducing the risk of catalyst layer wear, blockage and poisoning.

4. A large power plant boiler system with flexible and efficient combustion technology according to claim 3, characterized in that, The fly ash separated by the high-temperature dust removal device is heat-exchanged by a waste heat recovery device, and the waste heat is used to heat the boiler feedwater or preheat the primary air.

5. A large power plant boiler system with flexible and efficient combustion technology according to any one of claims 1, characterized in that, The coal mill's outlet separator adopts a multiphase flow high-efficiency separation structure. By optimizing the lower baffle of the separator, the separator outlet structure, and the air-coal pipeline, the coal powder separation efficiency and coal mill output are improved, the system resistance is reduced, the accumulation of powder and blockage are eliminated, and the power consumption of pulverizing is reduced.

6. A large power plant boiler system with flexible and efficient combustion technology according to any one of claims 1, characterized in that, The system has a tiered operation mode: Boiler startup, extremely low load and low load modes: The feeder and indirect air preheater of the medium storage pulverizing unit are in operation; Medium-high load mode: The medium-storage type and direct-fired pulverizing unit operate in combination. The direct-fired pulverizing unit operates under basic load and is stable. The medium-storage type pulverizer undertakes the dynamic load adjustment function and improves the load rapid response adjustment capability. The partition-type air preheater and rotary air preheater, primary air fan and secondary air fan operate simultaneously. This aims to optimize combustion efficiency and boiler power consumption across the entire load range, thereby enhancing the dynamic load regulation characteristics of the boiler.

7. A large power plant boiler system with flexible and efficient combustion technology according to claim 6, characterized in that, The pulverizing system, air preheating system, and air supply system are automatically switched through a linkage control strategy, so that the boiler can maintain stable combustion and have rapid adjustment capability and flexibility when the load changes rapidly.

8. A large power plant boiler system with flexible and efficient combustion technology according to claim 7, characterized in that, When the boiler is running at 30% load, the increase in coal consumption for power supply compared to the rated load operation does not exceed 15%, thus achieving economy and adaptability throughout the entire process from start-up and shutdown, deep peak shaving to full-load operation.

9. A method for operating a large power plant boiler with flexible and efficient combustion technology, applied to a power plant boiler including a boiler body, a dual-mode pulverizing system, a dual-mode air preheating system, and a dual-mode air supply system, characterized in that, The method includes: S1. Develop a load grading strategy. The operating conditions are divided into boiler start-up and shutdown, extremely low load, low load, medium load, and high load based on the unit load range. Powder making system switching control steps: When the boiler is started up to the point where the load is lower than the preset low load threshold, only the pulverizer in the medium storage pulverizing unit is operated to maintain and stabilize the boiler combustion by using the pulverized coal already prepared in the pulverized coal silo. When the unit load reaches or exceeds the medium-high load threshold, the direct-fired pulverizing unit is gradually added, and the medium-storage and direct-fired pulverizing units are operated in combination until the two pulverizing units are operated in parallel to maximize the output and make the coal mill operate under economic conditions. S2. Air preheating system control: During low-load phases, the rotary air preheater is shut down, and only the indirect air preheater is used to preheat the primary and secondary air. During medium-to-high load periods, both types of air preheaters operate simultaneously, independently heating the primary and secondary air respectively. S3. Air supply control: During boiler start-up and shutdown and low-load phases, air is supplied only by the primary air fan; During medium-to-high load periods, secondary fans are started and run in parallel to optimize the air-to-coal ratio. Flue gas treatment and control: The high-temperature dust removal device is controlled to operate before the flue gas enters the denitrification system in order to capture large particles of fly ash; Control the low-temperature dust removal device for efficient end-of-pipe dust removal; Linkage and feedback control: Based on the closed-loop feedback of online load, oxygen content, temperature and flue gas parameters, the system automatically switches the operation mode of the pulverizing and preheating system to maintain optimal combustion efficiency and emission levels. Through the above steps, the boiler can achieve efficient and stable combustion across the entire load range, taking into account both energy saving and low emissions; S4. In the linkage and feedback control steps, the main control system collects the furnace flue gas temperature, heating surface tube wall temperature, oxygen content and flue gas flow rate in real time, and uses fuzzy logic control algorithm to realize the dual-mode system state switching with a response time of less than 30 seconds to meet the peak shaving rapid response requirements. S5. When the temperature of fly ash collected by the high-temperature dust removal device is higher than the set threshold, the waste heat recovery system is activated to use some of the heat to preheat the boiler feedwater or primary air in order to achieve thermal balance optimization. S6. During the extremely low load operation phase, a time-sharing and segmented pulverized coal feeding strategy is adopted to maintain the stability of the furnace heat load, and the furnace temperature is controlled by reducing the primary air volume and appropriately adjusting the return air circulation volume to achieve long-term stable combustion below 20% load. At 30% unit load, the increase in coal consumption for power generation shall not exceed 15% of the rated operating condition, and the concentration of nitrogen oxide emissions shall remain below 50 mg / m³. 3 .

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