A fan mill boiler slag waste heat coupled pulverizing drying system and working method

Abstract

The present application belongs to the field of waste heat coupling pulverizing, and discloses a slag waste heat coupling pulverizing and drying system of a fan mill powder boiler and a working method. The slag waste heat coupling pulverizing and drying system is characterized by that a sealed high-temperature steel belt cold slag heat exchange machine is connected to the slag discharge port of the furnace body of the boiler, and a slag high-temperature heat exchange cavity and an inert drying air side heat exchange cavity are arranged in the cold slag heat exchange machine and isolated from each other. In the process of conveying the high-temperature slag by the steel belt, the sensible heat of the slag is transferred to the inert drying air through the slag side heat exchange tube bundle, the metal partition plate and the air side heat exchange tube bundle. In this way, the slag and the drying medium are prevented from directly contacting each other, the originally lost slag waste heat is converted into the heat required for the pulverizing and drying, and the utilization rate of the slag waste heat is improved.

Description

Technical Field

[0001] This invention belongs to the field of waste heat coupled pulverization, specifically relating to a waste heat coupled pulverization and drying system and working method for pulverized coal boiler slag. Background Technology

[0002] Pulverized coal boilers using lignite typically employ direct-fired pulverizing systems. Because lignite has a high base moisture content, after the raw coal enters the fan mill, it requires a high-temperature drying medium to complete the crushing, drying, and pulverized coal conveying. Existing fan mill pulverizing systems mostly employ a three-medium drying method consisting of high-temperature flue gas from the furnace, hot air from the air preheater, and low-temperature flue gas. By adjusting the flow rates of each medium, the mixed drying medium achieves the required temperature and flow rate for the fan mill.

[0003] The main heat source for existing three-medium drying systems is high-temperature flue gas extracted from the furnace, with temperatures typically reaching 900–1100℃. The extraction of large amounts of high-temperature flue gas from the furnace reduces the effective heat available for radiative heat exchange, increasing boiler heat loss and unit coal consumption for power generation. Simultaneously, the high-temperature flue gas conveying pipelines are typically characterized by large diameters, long distances, and numerous bends, making them prone to pipe wall wear, burning, and leaks during operation, generating significant flow resistance and increasing the energy consumption of auxiliary equipment such as primary air fans and induced draft fans. Especially during deep peak shaving and low-load operation, the furnace flue gas temperature decreases, leading to problems such as insufficient mixed medium temperature, inadequate raw coal drying, and reduced coal mill output in existing drying systems.

[0004] Furthermore, existing drying media contain oxygen-containing media such as hot air from air preheaters, resulting in a generally high oxygen content in the mixed media. Lignite is characterized by high volatile matter content, easy oxidation, and high susceptibility to spontaneous combustion. When pulverized coal accumulates in the pulverizer or pulverized coal pipeline, the high oxygen content easily increases the risk of spontaneous combustion and deflagration. To ensure operational safety, existing systems typically require nitrogen inerting or fire extinguishing equipment, increasing equipment investment and operating and maintenance costs. When the raw coal has high moisture content or undergoes significant changes in coal quality, existing three-media drying systems may also experience insufficient drying heat, reduced drying output, and limited unit load.

[0005] High-temperature slag produced during boiler combustion is typically discharged from the bottom of the furnace, with an initial temperature reaching 850–980℃. Existing boilers mostly use water-cooled steel belt slag coolers to cool the high-temperature slag. The sensible heat of the slag is carried away by the cooling water and is usually dissipated through cooling towers and other equipment, failing to be effectively utilized. While some existing slag waste heat recovery devices can utilize slag heat to generate low-pressure steam or heat feedwater, the temperature of the obtained heat medium is relatively low, making it difficult to directly meet the high-temperature drying medium requirements of fan mills. Therefore, slag waste heat recovery systems and pulverizing and drying systems are usually still independent of each other.

[0006] Because the slag cooling system and the pulverizing and drying system are set up separately, there is a certain degree of duplication in the configuration of heat exchange equipment, conveying pipelines, fans and control devices. This not only results in a large footprint and complex system structure, but also makes it difficult to coordinate and adjust according to the unit load, raw coal moisture content, slag temperature and drying medium temperature and oxygen content. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of existing fan-operated pulverized coal boilers where the slag waste heat recovery system and the pulverizing and drying system are independent, resulting in low sensible heat utilization rate of slag, large amount of high-temperature flue gas extraction, high oxygen content of drying medium, and unstable pulverizing and drying output under wide load conditions. This invention provides a fan-operated pulverized coal boiler slag waste heat coupled pulverizing and drying system and its working method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a slag waste heat coupled pulverizing and drying system for a fan-operated pulverized coal boiler, comprising a boiler body, wherein the furnace slag discharge port of the boiler body is connected to a sealed high-temperature steel belt cold slag heat exchanger, wherein the sealed high-temperature steel belt cold slag heat exchanger is provided with a slag high-temperature heat exchange chamber and an inert drying air-side heat exchange chamber that are isolated from each other, wherein the slag high-temperature heat exchange chamber is provided with a steel belt conveying mechanism for conveying slag and a slag-side heat exchange tube bundle, wherein the inert drying air-side heat exchange chamber is provided with a wind-side heat exchange tube bundle, wherein the slag-side heat exchange tube bundle and the wind-side heat exchange tube bundle are connected by a metal partition for heat exchange, wherein the cold air inlet of the inert drying air-side heat exchange chamber is connected to a booster circulating fan, and the hot air outlet is connected to a total drying medium mixing chamber, wherein the total drying medium mixing chamber is connected to the hot air header of the air preheater, the high-temperature flue gas extraction header of the furnace and the low-temperature cold flue gas mixing duct, wherein the total drying medium mixing chamber is provided with a multi-layer staggered porous flow equalization mixing partition, and wherein the outlet of the total drying medium mixing chamber is connected to the drying medium inlet of several fan-operated coal mills through a distribution header; The sensing points installed at the sealed high-temperature steel belt cold slag heat exchanger, the main drying medium mixing chamber, and the fan coal mill, as well as the regulating valves installed at each medium inlet, are respectively connected to the DCS coupling control equipment.

[0009] A further improvement of the present invention is that the high-temperature heat exchange chamber of the slag is located above the heat exchange chamber of the inert drying air side, the steel belt conveyor is located above the heat exchange tube bundle of the slag side, the heat exchange tube bundle of the air side is arranged in the opposite direction of the flow of the inert drying air, and the heat exchange tube bundle of the slag side and the heat exchange tube bundle of the air side are respectively attached to both sides of the metal partition.

[0010] A further improvement of the present invention is that the cold air inlet of the inert drying air-side heat exchange chamber is connected to the booster circulating fan through the inert cold air duct, and a filter and a cold air make-up valve are provided on the inert cold air duct; the hot air outlet of the inert drying air-side heat exchange chamber is connected to the total drying medium mixing chamber through the high temperature coupling drying duct.

[0011] A further improvement of the present invention is that the high-temperature coupled drying duct, the hot air main pipe of the air preheater, the high-temperature flue gas extraction main pipe of the furnace, and the low-temperature cold flue gas mixing duct are respectively connected to the total drying medium mixing chamber, and regulating valves capable of independently adjusting the flow rate of the corresponding medium are respectively provided on the high-temperature coupled drying duct, the hot air main pipe of the air preheater, the high-temperature flue gas extraction main pipe of the furnace, and the low-temperature cold flue gas mixing duct.

[0012] A further improvement of the present invention is that the total drying medium mixing chamber is a vertical cylindrical pressure-bearing chamber, and three layers of porous flow equalization mixing baffles are arranged along the height direction of the total drying medium mixing chamber. The through holes of adjacent two layers of porous flow equalization mixing baffles are arranged alternately, and a conical outlet connected to the distribution header is provided at the bottom of the total drying medium mixing chamber.

[0013] A further improvement of the present invention is that the main distribution pipe is connected to branch drying air ducts corresponding to several fan coal mills, and each branch drying air duct is connected to the drying medium inlet of the corresponding fan coal mill, so as to distribute the drying medium output from the main drying medium mixing chamber to several fan coal mills.

[0014] A further improvement of this invention is that the sensing points include a temperature sensing point located at the hot air outlet of the sealed high-temperature steel belt cold slag heat exchanger, temperature sensing points located at the inlets of each medium in the total drying medium mixing chamber, an oxygen-temperature composite measuring point located at the outlet of the total drying medium mixing chamber, and a temperature sensing point located at the drying medium inlet of each fan coal mill; the DCS coupled control equipment adjusts the operating frequency of the booster circulating fan and the opening degree of the regulating valve at each medium inlet according to the medium temperature, oxygen content, pressure, and flow rate collected by the sensing points.

[0015] Secondly, the present invention provides a method for operating a pulverized coal boiler slag waste heat coupled pulverization and drying system, comprising the following steps: The high-temperature slag generated by the boiler body enters the high-temperature heat exchange chamber of the sealed high-temperature steel belt cold slag heat exchanger through the furnace slag discharge port. The high-temperature slag is transported by the steel belt conveyor and the heat of the high-temperature slag is transferred to the air-side heat exchange tube bundle through the slag-side heat exchange tube bundle and metal partition. Cold air is sent into the inert drying air-side heat exchange chamber by a booster circulating fan, so that the cold air exchanges heat with the high-temperature slag in a countercurrent flow through the air-side heat exchange tube bundle to form slag heat exchange hot air. Hot air from the slag heat exchanger, hot air from the air preheater conveyed by the air preheater hot air header, high-temperature flue gas from the furnace conveyed by the furnace high-temperature flue gas extraction header, and low-temperature cold flue gas conveyed by the low-temperature cold flue gas mixing duct are sent into the total drying medium mixing chamber and mixed through multi-layer staggered porous flow equalization mixing baffles to obtain a mixed drying medium. The operating parameters of the slag heat exchange hot air and the mixed drying medium are collected by the sensing points and sent to the DCS coupling control equipment. The DCS coupling control equipment adjusts the operating frequency of the booster circulating fan and the opening of the regulating valve at each medium inlet. The mixed drying medium is distributed to several fan mills via a distribution header, and the raw coal entering the fan mills is dried and ground using the mixed drying medium.

[0016] A further improvement of this invention lies in the following specific method for adjusting the operating frequency of the booster circulating fan and the opening degree of the regulating valves at each medium inlet via a DCS coupling control device: When the unit load is 70% to 100% of the rated load, close the regulating valve on the high-temperature flue gas extraction main pipe in the furnace and increase the slag heat exchange hot air flow rate output by the sealed high-temperature steel strip cold slag heat exchanger. When the unit load is 40% to 70% of the rated load, keep the regulating valve on the furnace high-temperature flue gas extraction main pipe closed and increase the air preheater hot air flow rate delivered by the air preheater hot air main pipe. When the unit load is less than 40% of the rated load, open the regulating valve on the high-temperature flue gas extraction main pipe of the furnace, and make the opening of the regulating valve not exceed 15%, so as to use the high-temperature flue gas in the furnace to supplement the heat of the mixed drying medium.

[0017] A further improvement of this invention is that the DCS coupled control device adjusts the mixed drying medium according to the moisture content and volatile matter content of the raw coal. Specifically, when the moisture content of the raw coal increases, the flow rate of the slag heat exchange hot air output by the sealed high-temperature steel belt cold slag heat exchanger is increased; when the volatile matter content of the raw coal increases, the upper limit of the oxygen content control of the mixed drying medium is reduced; when the sealed high-temperature steel belt cold slag heat exchanger experiences a fault shutdown signal, the regulating valve on the furnace high-temperature flue gas extraction main pipe is opened, so that the hot air from the air preheater, the furnace high-temperature flue gas, and the low-temperature cold flue gas mix to form the drying medium.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention connects a sealed high-temperature steel belt cold slag heat exchanger to the slag discharge port of the boiler body. Within the cold slag heat exchanger, separate high-temperature slag heat exchange chambers and inertial drying air side heat exchange chambers are installed. During the steel belt transport process, the high-temperature slag transfers sensible heat to the inert drying air via slag-side heat exchange tube bundles, metal baffles, and air-side heat exchange tube bundles. This avoids direct contact between the slag and the drying medium, while converting the originally lost slag waste heat into the heat required for pulverization and drying, thus improving the utilization rate of slag waste heat. The slag heat exchange hot air, air preheater hot air, high-temperature furnace flue gas, and low-temperature cold flue gas are concentrated and mixed in the total drying medium mixing chamber. The mixture is then diverted, disturbed, and homogenized by multi-layered, staggered, porous flow-equalizing mixing baffles, improving the uniformity of temperature and composition distribution of the drying medium and reducing local temperature deviations. By adjusting the supply ratio of different media, the dependence on high-temperature furnace flue gas can be reduced, and the oxygen content of the mixed drying medium can be lowered using low-oxygen flue gas, thereby balancing the raw coal drying capacity with the operational safety of the pulverizing system. The mixed drying medium is fed into several fan-operated coal mills through the distribution header, enabling centralized air supply and coordinated operation of multiple coal mills. The DCS coupled control equipment adjusts the booster circulating fan and the regulating valves at each medium inlet according to the parameters collected by the sensor points, which helps to adapt to changes in unit load and coal quality, maintain the stability of the pulverizing and drying process, and reduce system energy consumption and operation and maintenance costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the internal structure of the total drying medium mixing chamber in this invention; The components include: 1. Boiler body; 2. Furnace slag discharge port; 3. Sealed high-temperature steel belt cold slag heat exchanger; 4. Dry slag conveyor belt; 5. Slag-side heat exchange tube bundle; 6. Inertial drying air-side heat exchange chamber; 7. Filter; 8. Raw coal feed hopper; 9. Cold air make-up valve; 10. Inertial cold air duct; 11. Booster circulating fan; 12. High-temperature coupled drying duct; 14. Air preheater hot air header; 16. Furnace high-temperature flue gas extraction header; 18. Low-temperature cold flue gas mixing duct; 20. Distribution header; 21. Branch drying duct; 24. Fan pulverizer; 25. Pulverized coal primary air duct; 26. Layered burner; 27. Sensor points; 28. DCS coupled control equipment. Detailed Implementation

[0020] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0021] Example 1: See Figure 1This embodiment provides a fan-driven pulverized coal boiler slag waste heat coupled pulverization and drying system, including a boiler body 1, a sealed high-temperature steel belt cold slag heat exchanger 3, a booster circulating fan 11, a main drying medium mixing chamber, a distribution header 20, several fan-driven coal mills 24, and a DCS coupled control device 28.

[0022] The bottom of the boiler body 1 is provided with a furnace slag discharge port 2, which is sealed to the top of the sealed high-temperature steel belt cold slag heat exchanger 3, so that the high-temperature slag generated by combustion in the boiler body 1 can directly enter the sealed high-temperature steel belt cold slag heat exchanger 3 through the furnace slag discharge port 2, thereby reducing the heat loss of the high-temperature slag during the transfer process.

[0023] The sealed high-temperature steel belt slag heat exchanger 3 has an internal structure consisting of a vertically arranged and isolated high-temperature slag heat exchange chamber and an inertial drying air-side heat exchange chamber 6. The high-temperature slag heat exchange chamber is located above the inertial drying air-side heat exchange chamber 6, and contains a steel belt conveyor mechanism and multiple sets of slag-side heat exchange tube bundles 5. The steel belt conveyor mechanism, located above the slag-side heat exchange tube bundles 5, receives the high-temperature slag falling from the furnace slag discharge port 2 and slowly moves the high-temperature slag along the steel belt conveyor mechanism.

[0024] An air-side heat exchange tube bundle is installed inside the inertial drying air-side heat exchange chamber 6, arranged counter-currently along the flow direction of the inertial drying air. The slag-side heat exchange tube bundle 5 and the air-side heat exchange tube bundle are respectively attached to both sides of a metal partition, isolating the high-temperature slag heat exchange chamber from the inertial drying air-side heat exchange chamber 6, while heat transfer is achieved through the metal partition. No intermediate heat exchange medium such as cooling water or heat transfer oil is placed between the slag-side heat exchange tube bundle 5 and the air-side heat exchange tube bundle, thereby shortening the heat transfer path and reducing temperature loss during the heat exchange process.

[0025] The steel belt conveyor transports the high-temperature slag in the opposite direction to the flow of the inert drying air within the air-side heat exchange tube bundle, creating a counter-current heat exchange between the slag and the inert drying air. As the high-temperature slag moves, it passes through different temperature zones sequentially, while the inert drying air enters from the end containing the low-temperature slag and exits from the end containing the high-temperature slag. This allows the inert drying air to gradually absorb the sensible heat from the slag and reach the temperature required for pulverization and drying.

[0026] The slag-side heat exchange tube bundle 5 and the air-side heat exchange tube bundle are made of 310S high-temperature resistant austenitic alloy material to improve the oxidation resistance, corrosion resistance and high-temperature resistance of the heat exchange tube bundle in the high-temperature slag environment, so that the heat exchange tube bundle can withstand high-temperature conditions of close to 1000℃ for a long time.

[0027] The sealed high-temperature steel belt slag heat exchanger 3 adopts a negative pressure sealing structure, with an airlock at its bottom and a dry slag conveyor belt below it. After heat exchange and cooling, the slag is discharged through the airlock and falls onto the dry slag conveyor belt for outward transport. The gap sealing structure of the steel belt conveyor mechanism, together with the airlock, forms a double sealing structure to reduce the entry of external air into the high-temperature slag heat exchange chamber or the inertial drying air side heat exchange chamber 6 through the slag discharge point, thus preventing external air infiltration from causing a drop in the temperature of the heat exchange hot air.

[0028] The cold air inlet of the inertial drying air-side heat exchange chamber 6 is connected to the booster circulating fan 11 via the inertial cold air duct 10. One end of the inertial cold air duct 10 is connected to the outdoor environment. A filter, which can be an F9 grade fine air filter, is installed at the inlet of the inertial cold air duct 10 to remove particulate matter and impurities entering the system. A cold air supply valve 9 is also installed on the inertial cold air duct 10, located between the filter and the booster circulating fan 11, to regulate the flow rate of cold air entering the inertial drying air-side heat exchange chamber 6.

[0029] The outlet of the booster circulating fan 11 can be connected to the cold air inlet of the inert drying air side heat exchange chamber 6 via an expansion joint. The expansion joint is used to absorb the thermal expansion displacement of the air duct caused by temperature changes and to reduce the transmission of vibration from the booster circulating fan 11 to the sealed high-temperature steel belt cold slag heat exchanger 3.

[0030] The hot air outlet of the inertial drying air-side heat exchange chamber 6 is connected to the main drying medium mixing chamber via the high-temperature coupled drying duct 12. The high-temperature coupled drying duct 12 is equipped with a regulating valve for adjusting the flow rate of the hot air used for slag heat exchange, and temperature and pressure sensing points are installed on its wall. The inner wall of the high-temperature coupled drying duct 12 can be lined with alumina wear-resistant and high-temperature resistant castable material to improve the wear resistance and high-temperature resistance of the duct under high-temperature dust-laden medium conditions.

[0031] During operation, the high-temperature slag (850–980°C) generated by the boiler body 1 enters the high-temperature slag heat exchange chamber through the furnace slag discharge port 2. The high-temperature slag moves slowly on the steel belt conveyor, transferring heat to the slag-side heat exchange tube bundle 5 and the metal partition. Outdoor ambient temperature air is filtered and its flow rate is regulated by the cold air supply valve 9 before being sent to the inertial drying air-side heat exchange chamber 6 by the booster circulating fan 11. The cold air flows through the air-side heat exchange tube bundle, undergoing counter-current heat exchange with the high-temperature slag. After absorbing the sensible heat of the slag, it forms slag heat exchange hot air with a temperature of 350–450°C. After releasing sensible heat, the temperature of the slag drops to below 60°C and is discharged through the airlock and dry slag conveyor belt.

[0032] The main drying medium mixing chamber is connected to the high-temperature coupling drying duct 12, the air preheater hot air header 14, the furnace high-temperature flue gas extraction header 16, and the low-temperature cold flue gas mixing duct 18, thereby forming a four-heat source mixing structure.

[0033] The high-temperature coupled drying duct 12 is used to send the slag heat exchange hot air generated by the sealed high-temperature steel strip cold slag heat exchanger 3 into the total drying medium mixing chamber. The air preheater hot air header 14 is used to send the hot air generated by the air preheater into the total drying medium mixing chamber. The furnace high-temperature flue gas extraction header 16 is connected to the furnace high-temperature flue gas area of ​​the boiler body 1, and is used to supplement the total drying medium mixing chamber with furnace high-temperature flue gas when the slag heat exchange hot air cannot meet the drying heat requirements. The low-temperature cold flue gas mixing duct 18 can be led out from the low-temperature flue gas duct before the electrostatic precipitator, and is used to transport low-temperature cold flue gas into the total drying medium mixing chamber to regulate the temperature, oxygen content and flow rate of the mixed drying medium.

[0034] Each of the high-temperature coupled drying duct 12, the air preheater hot air header 14, the furnace high-temperature flue gas extraction header 16, and the low-temperature cold flue gas mixing duct 18 is equipped with a regulating valve capable of independently adjusting the flow rate of the corresponding medium. Among them, the regulating valve on the furnace high-temperature flue gas extraction header 16 can be a bidirectional metal hard-seal flue gas flow limiting and shut-off valve, which can close the furnace high-temperature flue gas extraction header 16 when furnace high-temperature flue gas is not needed, and open the furnace high-temperature flue gas extraction header 16 when under low load or when the cold slag heat exchange equipment fails.

[0035] The high-temperature coupling drying duct 12, the air preheater hot air header 14, the furnace high-temperature flue gas extraction header 16, and the low-temperature cold flue gas mixing duct 18 can be connected along the tangential direction of the total drying medium mixing chamber, so that each medium enters the total drying medium mixing chamber and forms a rotating flow, thereby improving the mixing uniformity of media with different temperatures and different compositions.

[0036] See Figure 2 The main drying medium mixing chamber can be configured as a vertical cylindrical pressure-bearing chamber, with a medium inlet at the top connected to each medium path and a tapered outlet at the bottom. The tapered outlet is connected to the distribution header 20 to centrally guide the mixed drying medium into the distribution header 20.

[0037] Three layers of porous flow-equalizing mixing baffles are arranged along the height direction inside the main drying medium mixing chamber. The three layers of porous flow-equalizing mixing baffles are spaced apart from each other, and the through holes on adjacent layers of porous flow-equalizing mixing baffles are arranged alternately. After each stream of medium enters the main drying medium mixing chamber, it passes through the three layers of porous flow-equalizing mixing baffles in sequence. Under the action of flow diversion, disturbance and remixing in the through holes, turbulent mixing is formed, thereby reducing the temperature deviation of the medium at the outlet of the main drying medium mixing chamber.

[0038] In one specific structure, the porosity of the porous flow equalization mixing baffle is 45%, the diameter of the total drying medium mixing chamber is 4.2m, and the total height is 6.5m. After the various media are mixed by the three layers of porous flow equalization mixing baffles, the temperature deviation of the media at different positions of the outlet cross-section of the total drying medium mixing chamber can be controlled within ±8℃.

[0039] The outlet short pipe section of the main drying medium mixing chamber is equipped with an oxygen-temperature composite measuring point for simultaneously collecting the temperature and oxygen content of the mixed drying medium. The main drying medium mixing chamber can also be equipped with pressure and flow sensing points to collect the pressure and flow rate of the mixed drying medium.

[0040] The main distribution pipe 20 is connected to several branch drying ducts, and each branch drying duct corresponds to a number of fan mills 24. Each branch drying duct is sealed to the drying medium inlet of the corresponding fan mill 24, so that the mixed drying medium output from the main drying medium mixing chamber can be sent to the corresponding fan mill 24 through the main distribution pipe 20 and each branch drying duct.

[0041] Each fan mill 24 is equipped with a raw coal feed hopper at its top, which is used to feed high-moisture lignite into the fan mill 24. A drying medium inlet is provided on the side of the fan mill 24. The low-oxygen, high-temperature mixed drying medium enters the fan mill 24 through the drying medium inlet and comes into contact with the raw coal inside the fan mill 24 to simultaneously complete the crushing, grinding and drying of the raw coal.

[0042] The pulverized coal outlet of the fan mill 24 is connected to the stratified burner inside the boiler body 1 via a pulverized coal primary air duct. The dried and ground pulverized coal is carried by the mixed drying medium, sent through the pulverized coal primary air duct to the stratified burner, and then enters the furnace of the boiler body 1 for combustion.

[0043] In one specific pipe diameter configuration, the nominal diameter of the high-temperature coupled drying duct 12 is DN2800, the nominal diameter of the hot air main pipe 14 of the air preheater or the hot air branch pipe drawn from it is DN2200, the nominal diameter of the low-temperature cold flue gas mixing duct 18 is DN2600, and the nominal diameter of the furnace high-temperature flue gas extraction main pipe 16 is DN3000. The above pipe diameters can be adjusted according to the boiler capacity, the number of fan mills 24, the moisture content of the raw coal, and the required flow rate of the drying medium.

[0044] Sensing points are installed at the sealed high-temperature steel belt cold slag heat exchanger 3, the main drying medium mixing chamber, and each fan mill 24. These sensing points include a temperature sensing point at the hot air outlet of the sealed high-temperature steel belt cold slag heat exchanger 3; temperature sensing points at the points where the high-temperature coupled drying duct 12, the hot air header 14 of the air preheater, the high-temperature flue gas extraction header 16 of the furnace, and the low-temperature cold flue gas mixing duct 18 connect to the main drying medium mixing chamber; an oxygen-temperature composite measuring point at the outlet of the main drying medium mixing chamber; and temperature sensing points at the drying medium inlet of each fan mill 24.

[0045] The sensing points may also include slag temperature measuring points, medium pressure measuring points, medium flow measuring points, unit load measuring points, raw coal moisture measuring points, raw coal volatile matter measuring points, furnace outlet flue gas temperature measuring points, furnace outlet flue gas humidity measuring points, and NOx concentration measuring points. Each sensing point can output a 4-20mA standard analog signal, which is connected to the DCS coupling control equipment 28 via a signal line.

[0046] The regulating valves, cold air supply valves 9, and booster circulating fans 11 at each medium inlet are connected to the DCS coupling control device 28. The DCS coupling control device 28 receives parameters such as slag temperature, hot air temperature, mixed drying medium temperature, mixed drying medium oxygen content, medium pressure, medium flow rate, raw coal moisture content, raw coal volatile matter content, and unit load collected by each sensing point, and outputs control signals according to the preset control program.

[0047] The DCS coupled control device 28 adjusts the opening of the cold air supply valve 9, the operating frequency of the booster circulating fan 11, the opening of the regulating valve on the high-temperature coupled drying duct 12, the opening of the regulating valve on the hot air header 14 of the air preheater, the opening of the regulating valve on the high-temperature flue gas extraction header 16 of the furnace, and the opening of the regulating valve on the low-temperature cold flue gas mixing duct 18 through output control signals, thereby performing closed-loop regulation of the flow ratio of slag heat exchange hot air, air preheater hot air, high-temperature flue gas in the furnace, and low-temperature cold flue gas.

[0048] The DCS coupling control device 28 can be equipped with a load-adaptive adjustment module, an oxygen-temperature coupling adjustment module, and a fault interlock protection module. The load-adaptive adjustment module is used to adjust the flow rate of each medium according to the unit load; the oxygen-temperature coupling adjustment module is used to synchronously adjust each regulating valve according to the temperature and oxygen content of the mixed drying medium; the fault interlock protection module is used to switch the system operation mode when a fault occurs in the sealed high-temperature steel belt cold slag heat exchanger 3, the booster circulating fan 11, or related measuring points.

[0049] The DCS coupling control device 28 can also be connected to a human-machine interface and report module to display real-time data of each measuring point, the opening degree of the regulating valve, the operating frequency of the booster circulating fan 11 and system alarm information, and record the oxygen-temperature change curve of the mixed drying medium, the unit load curve, the combustion abnormality warning information and the NOx change curve.

[0050] Example 2: During the operation of the boiler body 1, combustion in the furnace produces high-temperature slag with a temperature of 850-980℃. The high-temperature slag continuously falls into the high-temperature heat exchange chamber of the sealed high-temperature steel belt cold slag heat exchanger 3 through the furnace slag discharge port 2, and is received and transported by the steel belt conveyor mechanism.

[0051] The high-temperature slag moves slowly along the steel belt conveyor, transferring heat to the slag-side heat exchange tube bundle 5 during the movement. The slag-side heat exchange tube bundle 5 further transfers heat to the air-side heat exchange tube bundle through metal partitions. After releasing sensible heat, the temperature of the high-temperature slag gradually decreases to below 60°C and is discharged to the dry slag conveyor belt through the airlock at the bottom of the sealed high-temperature steel belt cold slag heat exchanger 3.

[0052] Simultaneously, the booster fan 11 operates, causing outdoor ambient temperature air to pass sequentially through the filter and the cold air supply valve 9. The filter removes dust and particulate matter from the cold air, and the cold air supply valve 9 adjusts the cold air flow rate according to the control signal issued by the DCS coupled control device 28.

[0053] The booster circulating fan 11 delivers filtered and flow-regulated cold air into the inertial drying air-side heat exchange chamber 6. The cold air flows through the air-side heat exchange tube bundle and forms counter-current heat exchange with the high-temperature slag on the steel belt conveyor. After absorbing the sensible heat of the slag, the cold air rises to form slag heat exchange hot air at 350-450°C, and is then sent into the main drying medium mixing chamber through the high-temperature coupled drying air duct 12.

[0054] The 280-340℃ hot air generated by the air preheater is sent into the total drying medium mixing chamber through the air preheater hot air header 14; the 900-1100℃ high-temperature flue gas extracted from the boiler furnace is sent into the total drying medium mixing chamber through the high-temperature flue gas extraction header 16; and the 120-160℃ low-temperature cold flue gas extracted from the low-temperature flue gas duct before the electrostatic precipitator is sent into the total drying medium mixing chamber through the low-temperature cold flue gas mixing duct 18.

[0055] After the slag heat exchanger hot air, air preheater hot air, high-temperature furnace flue gas, and low-temperature cold flue gas enter the main drying medium mixing chamber, they flow sequentially through multiple layers of staggered porous flow equalization mixing baffles. The porous flow equalization mixing baffles divert, agitate, and remix the various media, ensuring that media with different temperatures and oxygen contents are fully mixed to form a mixed drying medium.

[0056] The oxygen-temperature composite measuring point at the outlet of the total drying medium mixing chamber collects the temperature and oxygen content of the mixed drying medium in real time, while the pressure and flow sensing points collect the pressure and flow rate of the mixed drying medium, respectively. All operating parameters are transmitted to the DCS coupled control device 28.

[0057] The DCS coupling control device 28 adjusts the operating frequency of the booster circulating fan 11 and the opening degree of each regulating valve on the high-temperature coupling drying duct 12, the air preheater hot air header 14, the furnace high-temperature flue gas extraction header 16, and the low-temperature cold flue gas mixing duct 18 according to parameters such as the temperature of the mixed drying medium, oxygen content, unit load, raw coal moisture and raw coal volatile matter, so as to control the temperature of the mixed drying medium at 340-400℃ and the oxygen content of the mixed drying medium within 8%.

[0058] The mixed drying medium that meets the temperature and oxygen content requirements enters the distribution header 20 from the conical outlet at the bottom of the total drying medium mixing chamber, and is then distributed by the distribution header 20 to the branch drying ducts corresponding to several fan coal mills 24.

[0059] Raw coal enters the fan mill 24 through the raw coal feed hopper. The mixed drying medium enters the fan mill 24 through the drying medium inlet and comes into full contact with the raw coal. While grinding the raw coal, the fan mill 24 uses the heat carried by the mixed drying medium to remove moisture from the raw coal.

[0060] The pulverized coal formed by grinding and drying is carried by a mixed drying medium and sent into the stratified burner inside the boiler body 1 through the pulverized coal primary air duct. Because the oxygen content of the mixed drying medium is limited, the possibility of pulverized coal accumulation, spontaneous combustion, or deflagration in the fan mill 24 and the pulverized coal primary air duct can be reduced, and the conversion of nitrogen-containing volatiles into NOx precursors during the pulverized coal drying process can be reduced.

[0061] During system operation, each sensor point continuously collects parameters such as slag temperature, slag heat exchange hot air temperature, mixed drying medium temperature and oxygen content, inlet temperature of each fan mill 24, raw coal moisture content, raw coal volatile matter content, and unit load. The DCS coupled control equipment 28 continuously adjusts the flow rate of each medium according to the real-time operating conditions to maintain the stable drying output of the fan mill 24.

[0062] Example 3: When the unit load is 70% to 100% of the rated load, the slag discharge of the boiler body 1 is relatively large, and the sealed high-temperature steel belt cold slag heat exchanger 3 can generate sufficient slag heat exchange hot air. The DCS coupling control device 28 closes the regulating valve on the furnace high-temperature flue gas extraction main pipe 16, stops the extraction of high-temperature flue gas from the boiler furnace, and increases the opening of the regulating valve on the high-temperature coupling drying air duct 12 and the operating frequency of the booster circulating fan 11 to increase the supply of slag heat exchange hot air.

[0063] Within this load range, slag heat exchange hot air is used as the main drying heat source, and the temperature and oxygen content of the mixed drying medium are regulated by the hot air from the air preheater and the low-temperature cold smoke, so that the temperature of the mixed drying medium is stabilized at 345-395℃ and the oxygen content is controlled within 8%.

[0064] When the unit load is 40% to 70% of the rated load, the DCS coupled control device 28 keeps the regulating valve on the furnace high-temperature flue gas extraction main pipe 16 closed, and appropriately increases the opening of the regulating valve on the air preheater hot air main pipe 14 according to the outlet temperature of the total drying medium mixing chamber, thereby increasing the proportion of air preheater hot air in the mixed drying medium and thus compensating for the change in the heat supply of slag heat exchange hot air.

[0065] When the unit load is less than 40% of the rated load, the slag discharge and residual heat of the slag in the boiler body 1 decrease. The DCS coupled control device 28 opens the regulating valve on the furnace high-temperature flue gas extraction header 16, ensuring that the opening of the regulating valve does not exceed 15%, and supplements a small amount of furnace high-temperature flue gas into the total drying medium mixing chamber. At the same time, it adjusts the flow rates of the hot air from the air preheater and the hot air from the slag heat exchange to ensure that the temperature of the mixed drying medium meets the drying requirements of the fan mill 24.

[0066] When the moisture content of the raw coal increases, the DCS coupled control device 28 increases the opening of the regulating valve on the high-temperature coupled drying air duct 12 and increases the operating frequency of the booster circulating fan 11, so that more cold air enters the inert drying air side heat exchange chamber 6 for heat exchange, thereby increasing the flow rate of hot air for slag heat exchange and the drying heat sent to the fan mill 24.

[0067] When the volatile matter content of raw coal increases, the DCS coupled control device 28 lowers the control limit of oxygen content in the mixed drying medium, and maintains a low-oxygen drying environment in the fan mill 24 by increasing the low-temperature cold flue gas flow, adjusting the hot air flow of the air preheater, and adjusting the hot air flow of the slag heat exchanger.

[0068] When the sealed high-temperature steel belt cold slag heat exchanger 3 experiences a fault shutdown signal, the DCS coupling control device 28 triggers the fault interlock protection program, closes or reduces the regulating valve on the high-temperature coupling drying duct 12, and opens the regulating valve on the furnace high-temperature flue gas extraction main pipe 16, so that the hot air from the air preheater, the high-temperature flue gas from the furnace, and the low-temperature cold flue gas mix to form a drying medium, thereby switching the system to the traditional three-medium drying operation mode, maintaining the operation of the fan mill 24, and avoiding unit shutdown due to the fault of the sealed high-temperature steel belt cold slag heat exchanger 3.

[0069] Example 4: This embodiment uses a 600MW lignite-fired unit as an example to illustrate the system's equipment parameters and operating performance.

[0070] The sealed high-temperature steel belt cold slag heat exchanger 3 has an effective heat exchange length of 22m, a total heat exchange area of ​​1280㎡ on the slag side, and a total counter-current heat exchange area of ​​1060㎡ on the air side. The booster circulating fan 11 has a rated air volume of 125000Nm³ / h, a pressure boost of 2200Pa, and is equipped with a variable frequency motor with a power of 1120kW.

[0071] Under the condition that the outdoor cold air temperature is 25℃, the temperature of the cold air can be raised to about 410℃ after heat exchange in the inert drying air side heat exchange chamber 6. The temperature of the hot air for slag heat exchange can be maintained in the range of 350~450℃. A single sealed high temperature steel belt cold slag heat exchanger 3 can recover about 12.8MW of slag waste heat power.

[0072] Under rated load operating conditions, the system uses slag-heated hot air as the main drying heat source, which can reduce the amount of high-temperature flue gas extracted from the furnace by about 85%. According to calculations, the unit's coal consumption for power generation can be reduced by about 3.2g / kWh, saving more than 11,000 tons of standard coal per year, and the overall thermal efficiency of the boiler can be increased by about 1.75%.

[0073] When the moisture content of the raw coal reaches 42%, the slag heat exchange hot air can provide stable high-temperature drying heat for the fan mill 24. The drying output of the fan mill 24 does not decrease significantly, and there is no need to expand or modify the original high-temperature flue gas extraction pipeline in the furnace.

[0074] By reducing the amount of high-temperature flue gas extracted from the furnace and the flow rate of high-temperature flue gas transported over long distances, the overall resistance of the system duct can be reduced by about 1500Pa, the power consumption rate of the 600MW unit can be reduced by about 0.42 percentage points, and the annual power consumption can be saved by about 2.6 million kWh.

[0075] Since the oxygen content of the mixed drying medium can be stably controlled within 8%, the risk of spontaneous combustion and deflagration of high volatile lignite in the fan mill 24 and the primary air duct of pulverized coal can be reduced, and the separately installed nitrogen inerting fire extinguishing system can be reduced or eliminated, thereby reducing equipment investment and operation and maintenance costs.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A pulverized coal boiler slag waste heat coupled pulverization and drying system, characterized in that, The boiler body (1) is connected to a sealed high-temperature steel belt cold slag heat exchanger (3) at the furnace slag discharge port (2) of the boiler body (1). The sealed high-temperature steel belt cold slag heat exchanger (3) is equipped with a slag high-temperature heat exchange chamber and an inert drying air-side heat exchange chamber (6) that are isolated from each other. The slag high-temperature heat exchange chamber is equipped with a steel belt conveying mechanism for conveying slag and a slag-side heat exchange tube bundle (5). The inert drying air-side heat exchange chamber (6) is equipped with an air-side heat exchange tube bundle. The slag-side heat exchange tube bundle (5) and the air-side heat exchange tube bundle are connected by a metal partition for heat exchange. The cold air inlet of the inert drying air side heat exchange chamber (6) is connected to the booster circulating fan (11), and the hot air outlet is connected to the total drying medium mixing chamber. The total drying medium mixing chamber is connected to the hot air header (14) of the air preheater, the high temperature flue gas extraction header (16) of the furnace and the low temperature cold flue gas mixing duct (18) respectively. The total drying medium mixing chamber is equipped with multi-layer staggered porous flow equalization mixing baffles. The outlet of the total drying medium mixing chamber is connected to the drying medium inlet of several fan coal mills (24) through the distribution header (20). The sensing points set at the sealed high-temperature steel belt cold slag heat exchanger (3), the main drying medium mixing chamber and the fan coal mill (24) and the regulating valves set at each medium inlet are respectively connected to the DCS coupling control equipment (28).

2. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The high-temperature heat exchange chamber of slag is located above the heat exchange chamber (6) on the inert drying air side, and the steel belt conveyor is located above the heat exchange tube bundle (5) on the slag side. The heat exchange tube bundle on the air side is arranged in the opposite direction of the flow of the inert drying air. The heat exchange tube bundle (5) on the slag side and the heat exchange tube bundle on the air side are respectively attached to the two sides of the metal partition.

3. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The cold air inlet of the inert drying air-side heat exchange chamber (6) is connected to the booster circulating fan (11) through the inert cold air duct (10). The inert cold air duct (10) is equipped with a filter and a cold air supply valve (9). The hot air outlet of the inert drying air-side heat exchange chamber (6) is connected to the total drying medium mixing chamber through the high temperature coupling drying duct (12).

4. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The high-temperature coupled drying duct (12), the air preheater hot air main pipe (14), the furnace high-temperature flue gas extraction main pipe (16), and the low-temperature cold flue gas mixing duct (18) are respectively connected to the total drying medium mixing chamber. The high-temperature coupled drying duct (12), the air preheater hot air main pipe (14), the furnace high-temperature flue gas extraction main pipe (16), and the low-temperature cold flue gas mixing duct (18) are respectively equipped with regulating valves that can independently adjust the flow rate of the corresponding medium.

5. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The main drying medium mixing chamber is a vertical cylindrical pressure-bearing chamber. Three layers of porous flow equalization mixing baffles are arranged along the height direction of the main drying medium mixing chamber. The through holes of the two adjacent layers of porous flow equalization mixing baffles are arranged alternately. The bottom of the main drying medium mixing chamber is provided with a conical outlet that is connected to the distribution header (20).

6. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The main distribution pipe (20) is connected to branch drying ducts corresponding to several fan mills (24). Each branch drying duct is connected to the drying medium inlet of the corresponding fan mill (24) to distribute the drying medium output from the total drying medium mixing chamber to several fan mills (24).

7. The pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 1, characterized in that, The sensing points include temperature sensing points set at the hot air outlet of the sealed high-temperature steel belt cold slag heat exchanger (3), temperature sensing points set at the inlets of each medium in the total drying medium mixing chamber, oxygen-temperature composite measuring points set at the outlet of the total drying medium mixing chamber, and temperature sensing points set at the inlets of the drying medium in each fan coal mill (24). The DCS coupled control device (28) adjusts the operating frequency of the booster circulating fan (11) and the opening degree of the regulating valve at each medium inlet according to the medium temperature, oxygen content, pressure and flow rate collected by the sensing points.

8. A method for operating a fan-milled pulverized coal boiler slag waste heat coupled pulverizing and drying system, based on the fan-milled pulverized coal boiler slag waste heat coupled pulverizing and drying system according to claim 1, characterized in that, Includes the following steps: The high-temperature slag generated by the boiler body (1) enters the high-temperature heat exchange chamber of the sealed high-temperature steel belt cold slag heat exchanger (3) through the furnace slag discharge port (2). The high-temperature slag is transported by the steel belt conveyor and the heat of the high-temperature slag is transferred to the air-side heat exchange tube bundle through the slag-side heat exchange tube bundle (5) and the metal partition. The cold air is sent into the inert drying air-side heat exchange chamber (6) by the booster circulating fan (11), so that the cold air exchanges heat with the high temperature slag in a countercurrent manner through the air-side heat exchange tube bundle to form slag heat exchange hot air. The hot air from the slag heat exchanger, the hot air from the air preheater main pipe (14), the high-temperature flue gas from the furnace high-temperature flue gas extraction main pipe (16), and the low-temperature cold flue gas from the low-temperature cold flue gas mixing duct (18) are sent into the total drying medium mixing chamber and mixed through multi-layer staggered porous flow equalization mixing baffles to obtain a mixed drying medium. The operating parameters of the slag heat exchange hot air and the mixed drying medium are collected by the sensing points and sent to the DCS coupling control device (28). The DCS coupling control device (28) adjusts the operating frequency of the booster circulating fan (11) and the opening degree of the regulating valve at each medium inlet. The mixed drying medium is distributed to several fan mills (24) via the distribution header (20) to dry and grind the raw coal entering the fan mills (24).

9. The working method of a fan-operated pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 8, characterized in that, The specific method for adjusting the operating frequency of the booster circulating fan (11) and the opening degree of the regulating valves at each medium inlet using the DCS coupling control device (28) is as follows: When the unit load is 70% to 100% of the rated load, close the regulating valve on the furnace high-temperature flue gas extraction main pipe (16) and increase the slag heat exchange hot air flow rate output by the sealed high-temperature steel strip cold slag heat exchanger (3). When the unit load is 40% to 70% of the rated load, keep the regulating valve on the furnace high-temperature flue gas extraction main pipe (16) closed and increase the air preheater hot air flow rate delivered by the air preheater hot air main pipe (14). When the unit load is less than 40% of the rated load, open the regulating valve on the furnace high-temperature flue gas extraction main pipe (16) so that the opening of the regulating valve does not exceed 15%, and use the furnace high-temperature flue gas to supplement the heat of the mixed drying medium.

10. The working method of a fan-operated pulverized coal boiler slag waste heat coupled pulverization and drying system according to claim 8, characterized in that, The DCS coupled control device (28) adjusts the mixed drying medium according to the moisture content and volatile matter content of the raw coal. When the moisture content of the raw coal increases, the flow rate of the slag heat exchange hot air output by the sealed high-temperature steel belt cold slag heat exchanger (3) is increased. When the volatile matter content of the raw coal increases, the upper limit of the oxygen content control of the mixed drying medium is reduced. When the sealed high-temperature steel belt cold slag heat exchanger (3) has a fault shutdown signal, the regulating valve on the furnace high-temperature flue gas extraction main pipe (16) is opened, so that the hot air of the air preheater, the furnace high-temperature flue gas and the low-temperature cold smoke are mixed to form a drying medium.

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