Hot primary air graded heating system of positive pressure direct blowing pulverizing system and operation method

Abstract

The invention discloses a hot primary air graded heating system of a positive-pressure direct-blowing coal pulverizing system and an operation method, and the system comprises a flue gas-air heat exchanger, a flue gas leading pipeline, a flue gas backflow pipeline, and an air pre-heater, a hot primary air pipeline and a coal pulverizing system which are connected in sequence, an air flow channel inlet of the flue gas-air heat exchanger is connected with a hot primary air outlet of the air pre-heater through a hot primary air pipeline; the flue gas and air heat exchanger is provided with an air flow channel and a flue gas flow channel which are isolated from each other, an air flow channel outlet of the flue gas and air heat exchanger is connected with a hot primary air inlet of the coal pulverizing system through a hot primary air pipeline, and the flue gas leading and conveying pipeline is connected with a flue smoke taking opening and a flue gas flow channel inlet of the flue gas and air heat exchanger. The flue gas backflow pipeline is connected with a flue gas flow channel outlet of the flue gas and air heat exchanger and a flue flue gas backflow opening; the temperature of hot primary air can be effectively increased, waste heat of high-temperature flue gas in front of the coal economizer can be fully recycled, and meanwhile the adaptability of the system to coal type changes and load fluctuations is enhanced.

Description

Technical Field

[0001] This invention pertains to hot air heating technology in boiler pulverizing systems within the field of thermal power generation, specifically relating to a positive pressure direct-fired pulverizing system with graded heating of primary hot air and its operation method. Background Technology

[0002] In positive pressure direct-fired pulverizing systems of thermal power plants, the temperature of the hot primary air has a crucial impact on the drying output, pulverized coal fineness, and subsequent boiler combustion efficiency. Currently, the industry generally uses an air preheater (hereinafter referred to as "air preheater") as the sole heating device for the hot primary air. Ambient air exchanges heat with boiler exhaust gas through the air preheater to form hot primary air that meets the initial requirements of the pulverizing system, which is then delivered to the pulverizing system for pulverized coal drying and transportation.

[0003] However, with the continuous development of thermal power generation technology and increasingly stringent environmental protection requirements, the traditional method of relying solely on air preheaters to heat primary air has gradually revealed the following problems: Limited primary air temperature increase: The heat exchange efficiency of the air preheater is limited by its own structural design, the temperature difference between flue gas and air, and factors such as ash accumulation and wear, making it difficult to further increase the outlet temperature of the primary air. When the boiler burns coal with high moisture content, the primary air temperature heated by the air preheater alone cannot meet the drying capacity requirements of the pulverizing system, resulting in excessive moisture content in the pulverized coal and affecting the stability and economy of subsequent boiler combustion.

[0004] Waste of heat in boiler flue gas: As an important heat exchange device at the tail end of the boiler, the boiler flue gas at its inlet still has a relatively high temperature (usually 350-450℃). However, in traditional systems, this part of high-temperature flue gas only heats the feedwater in the economizer before entering the air preheater, where it exchanges heat with the air before being discharged. Due to the limited heat exchange temperature difference in the air preheater, the large amount of heat contained in this part of high-temperature flue gas is not fully utilized, resulting in energy waste and reducing the thermal efficiency of the entire boiler system.

[0005] Poor system adaptability: When the boiler load changes or the moisture content, calorific value and other characteristics of the coal fluctuate greatly, the air preheater alone cannot quickly and flexibly adjust the temperature of the primary hot air, resulting in unstable operating parameters of the pulverizing system, which in turn affects the overall operating efficiency and safety of the boiler.

[0006] The existing patent CN115468181A discloses a medium-speed mill direct-fired pulverizing system suitable for ultra-high moisture lignite. It addresses the problem that traditional systems cannot raise the primary air temperature to approximately 400℃, resulting in insufficient drying capacity, low boiler efficiency, and poor adaptability. This system focuses on meeting the extremely high primary air temperature requirements of specific coal types and mill types, enhancing the drying output of the medium-speed mill for ultra-high moisture lignite. The system employs a two-stage series heating approach using a rotary air preheater and a tubular air preheater to heat the primary air. The heating flue gas for the tubular air preheater comes from the boiler bypass flue gas outlet. After heating the primary air, this bypass flue gas merges with the main flue gas and enters the rotary air preheater together, ensuring the safe and economical operation of the pulverizing system and improving its adaptability to ultra-high moisture lignite, thereby broadening the coal source selection. However, it does not explicitly emphasize residual heat recovery.

[0007] Therefore, how to design a hot primary air heating system that can further increase the temperature of the hot primary air, make full use of the waste heat from boiler flue gas, and enhance the system's adaptability has become a technical problem that urgently needs to be solved in the field of positive pressure direct blowing pulverizing systems. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a staged heating system for primary air in a positive pressure direct-fired pulverizing system. This system achieves staged heating of the primary air by adding a flue gas-air heat exchanger after the air preheater. This effectively increases the temperature of the primary air, fully recovers and utilizes the waste heat from the high-temperature flue gas before the economizer, and enhances the system's adaptability to changes in coal type and load fluctuations. It overcomes the problems of limited temperature rise, wasted exhaust heat, and poor system adaptability inherent in prior art that relies solely on the air preheater to heat the primary air.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a hot primary air staged heating system for a positive pressure direct-fired pulverizing system, comprising a flue gas air heat exchanger, a flue gas inlet pipeline, a flue gas return pipeline, and an air preheater, a hot primary air pipeline, and a pulverizing system connected in sequence. The air inlet of the flue gas air heat exchanger is connected to the hot primary air outlet of the air preheater via the hot primary air pipeline. The flue gas air heat exchanger is provided with mutually isolated air channels and flue gas channels. The air outlet of the flue gas air heat exchanger is connected to the hot primary air inlet of the pulverizing system via the hot primary air pipeline. The flue gas inlet pipeline connects the flue gas outlet of the flue gas duct to the flue gas inlet of the flue gas air heat exchanger. The flue gas return pipeline connects the flue gas outlet of the flue gas air heat exchanger to the flue gas return outlet of the flue gas air heat exchanger.

[0010] Furthermore, the flue gas inlet is located in the main flue gas duct of the boiler before the economizer, and the flue gas return outlet is set on the main flue gas duct of the boiler after the economizer. The flue gas inlet pipeline is used to introduce the high-temperature flue gas before the economizer into the flue gas duct of the plate heat exchanger, and the flue gas return pipeline is used to send the low-temperature flue gas after heat exchange in the flue gas air heat exchanger back to the main flue gas duct of the boiler.

[0011] Furthermore, the flue gas air heat exchanger is a plate heat exchanger made of 316L stainless steel or ND steel.

[0012] Furthermore, a flue gas flow regulating valve is installed on the flue gas delivery pipeline.

[0013] Furthermore, a first temperature sensor is installed between the air preheater outlet and the air flow channel inlet of the flue gas air heat exchanger, and a second temperature sensor is installed between the air flow channel outlet of the flue gas air heat exchanger and the pulverizing system inlet.

[0014] Furthermore, the flue gas air heat exchanger is equipped with an online soot blowing device in its flue gas flow channel.

[0015] Secondly, the present invention provides a method for operating the hot primary air staged heating system of the positive pressure direct blowing pulverizing system, comprising: In the primary heating stage, ambient air enters the air preheater and exchanges heat with the boiler flue gas after heat exchange in the economizer for the first time, raising the temperature to the set temperature and forming primary hot air. In the secondary heating stage, the primary hot primary air enters the air flow channel of the flue gas air heat exchanger through the hot primary air pipeline, and the high-temperature flue gas before the economizer enters the flue gas flow channel of the flue gas air heat exchanger through the flue gas duct. Inside the flue gas air heat exchanger, the high-temperature flue gas and the primary hot primary air undergo a second heat exchange, further heating the primary hot primary air to form secondary hot primary air that meets the high dryness requirements of the pulverizing system. The flue gas recirculation and hot primary air conveying process involves sending the low-temperature flue gas, after heat exchange in the flue gas air heat exchanger, back to the main flue gas pipeline of the boiler after the economizer through the flue gas recirculation pipeline. The flue gas then enters the air preheater for further heat exchange or enters the desulfurization and denitrification system for treatment. The secondary hot primary air is conveyed to the pulverizing system through the hot primary air pipeline for the drying and conveying of pulverized coal.

[0016] Furthermore, based on the difference between the hot primary air temperature at the outlet of the flue gas air heat exchanger collected by the second temperature sensor and the set temperature, the flue gas flow regulating valve on the flue gas delivery pipeline is automatically adjusted: when the actual temperature is lower than the set temperature, the opening of the flue gas flow regulating valve is increased; when the actual temperature is higher than the set temperature, the opening of the flue gas flow regulating valve is decreased.

[0017] Furthermore, in the operation method of the primary air staged heating system of the positive pressure direct-fired pulverizing system, ambient air enters the air preheater and exchanges heat with the flue gas for the first time, raising the temperature to 250-300℃ to form primary hot primary air; in the secondary heating stage, the flue gas temperature taken from the economizer is 350-450℃, which further heats the primary hot primary air to 320-380℃; in the flue gas recirculation and hot primary air conveying stage, the temperature of the low-temperature flue gas after heat exchange in the flue gas air heat exchanger drops to 300-350℃.

[0018] In addition, the present invention can also provide a coal-fired power generation unit that adopts the positive pressure direct-fired pulverizing system hot primary air staged heating system.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: the flue gas air heat exchanger adopts a plate heat exchanger, which has an air flow channel and a flue gas flow channel, and the air flow channel and the flue gas flow channel are isolated from each other and can exchange heat; the inlet of the air flow channel is connected to the hot primary air outlet of the air preheater through a hot primary air pipeline, and the outlet of the air flow channel is connected to the hot primary air inlet of the pulverizing system through a hot primary air pipeline, forming a staged heating channel for the hot primary air; one end of the flue gas inlet pipeline is connected to the main flue gas pipeline of the boiler before the economizer, and the other end is connected to the flue gas flow channel inlet of the flue gas air heat exchanger, which is used to introduce the high-temperature flue gas before the economizer into the flue gas flow channel of the flue gas air heat exchanger; the positive pressure direct-fired pulverizing system hot primary air staged heating system of the present invention, through innovative staged heating design, effectively solves the defects of the traditional hot primary air heating system, and achieves the goals of energy saving, high efficiency and stable operation, which has important practical value and broad prospects for promotion.

[0020] Furthermore, a flue gas flow regulating valve is installed on the flue gas inlet pipeline to facilitate control of the flue gas flow entering the flue gas air heat exchanger and adjust the heating temperature of the hot primary air. The flue gas flow regulating valve can adjust the amount of flue gas entering the flue gas air heat exchanger in real time according to the pulverizing system's requirements for the hot primary air temperature and the changes in the flue gas temperature before the economizer, thereby achieving precise control of the staged heating temperature of the hot primary air.

[0021] Furthermore, in the hot primary air duct, a first temperature sensor is installed between the air preheater outlet and the flue gas air heat exchanger air channel inlet, and a second temperature sensor is installed between the flue gas air heat exchanger air channel outlet and the pulverizing system inlet. These sensors monitor the temperature of the hot primary air before and after staged heating to ensure the stability of system operating parameters. The first and second temperature sensors are used to collect the hot primary air temperature at the air preheater outlet and the hot primary air temperature at the flue gas air heat exchanger outlet, respectively, and transmit the temperature signals to the system control unit to provide data for the adjustment of the flue gas flow regulating valve.

[0022] Furthermore, the flue gas air heat exchanger is equipped with an online soot blowing device to prevent fly ash in the boiler flue gas from depositing in the flue gas air heat exchanger's flue gas air heat exchanger, which would affect the heat exchange efficiency. The online soot blowing device can periodically or according to the pressure difference signal of the flue gas air heat exchanger to clean the flue gas air heat exchanger, ensuring the smooth flow of the flue gas air heat exchanger and maintaining the high-efficiency heat exchange performance of the plate heat exchanger.

[0023] Furthermore, the air flow channel and flue gas flow channel of the flue gas air heat exchanger are both made of corrosion-resistant and high-temperature resistant metal materials, such as 316L stainless steel or ND steel, to adapt to the high temperature (350-450℃) and corrosive environment of boiler flue gas and extend the service life of the plate heat exchanger. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings are only schematic and are used to help illustrate the system structure of the present invention. The actual dimensions and installation positions of each component can be adjusted according to specific engineering requirements.

[0025] Figure 1 This is a schematic diagram of the hot primary air grading and heating system of the positive pressure direct blowing pulverizing system of the present invention; In the diagram: 1-Air preheater; 2-Hot primary air duct; 3-Pulverizing system; 4-Flue gas air heat exchanger; 5-Flue gas inlet duct; 6-Flue gas return duct; 7-Boiler flue shaft before economizer; 8-Boiler flue gas main duct after economizer; 9-Flue gas flow regulating valve; 10-First temperature sensor; 11-Second temperature sensor; 12-Online soot blowing device. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, a positive pressure direct-fired pulverizing system with a primary air staged heating system includes an air preheater 1, a primary air duct 2, and a pulverizing system 3 connected in sequence. The primary air duct 2 is used to transport the primary air heated by the air preheater 1 to the pulverizing system 3. The system also includes a flue gas air heat exchanger 4, a flue gas inlet duct 5, and a flue gas return duct 6.

[0028] Among them, the flue gas air heat exchanger 4 adopts a plate heat exchanger, which has mutually isolated air flow channels and flue gas flow channels. Both the air flow channels and flue gas flow channels are made of 316L stainless steel to adapt to high temperature and corrosive environment. The inlet of the air flow channel is connected to the hot primary air outlet of the air preheater 1 through the hot primary air pipeline 2, and the outlet of the air flow channel is connected to the hot primary air inlet of the pulverizing system 3 through the hot primary air pipeline 2, forming a staged heating channel for the hot primary air.

[0029] The flue gas-air heat exchanger 4 can be implemented using a plate structure, a shell-and-tube structure, or other forms of heat exchange structure. For example, it can be implemented by setting multiple layers of metal plates or tube bundles to form independent airflow channels and flue gas flow channels, thereby ensuring that the two media complete heat transfer in a non-mixing state. The flue gas inlet pipeline 5 can be understood as a pipeline system used to guide high-temperature flue gas into the flue gas-air heat exchanger 4, which can be implemented by setting a fan or other power device to transport the flue gas. As a preferred embodiment, the flue gas inlet pipeline 5 can also be equipped with a flow regulating device, such as a manual valve or an automatic control valve, to achieve flexible control of the flue gas flow rate. In addition, the flue gas return pipeline 6 can be understood as a pipeline system used to reintroduce the low-temperature flue gas after heat exchange into the main flue gas pipeline of the boiler, which can be implemented by setting a conveying device to achieve the flue gas return operation.

[0030] One end of the flue gas inlet pipe 5 is connected to the boiler flue duct 7 before the economizer (i.e., the economizer inlet flue gas pipe), and the other end is connected to the flue gas inlet of the plate heat exchanger. A flue gas flow regulating valve 9 is installed on the flue gas inlet pipe 5 to control the amount of high-temperature flue gas entering the flue gas inlet. One end of the flue gas return pipe 6 is connected to the flue gas outlet of the plate heat exchanger, and the other end is connected to the boiler flue gas main pipe 8 after the economizer (i.e., the economizer outlet flue gas pipe), so that the low-temperature flue gas after heat exchange can return to the original flue gas system.

[0031] This application achieves staged heating of the primary air by introducing a flue gas air heat exchanger 4 and its supporting flue gas inlet pipe 5 and flue gas return pipe 6. Specifically, it utilizes the high-temperature flue gas before the economizer as a secondary heating source, breaking through the temperature limitations of traditional single air preheater heating. At the same time, through the flue gas return design, the low-temperature flue gas after heat exchange is reintroduced into the boiler system, reducing heat loss. This not only solves the problem of limited temperature rise of the primary air but also effectively recovers the waste heat from boiler exhaust, enhancing the system's adaptability to different coal types and load changes.

[0032] The system itself preheats the ambient air through the air preheater 1 to form primary hot primary air, which enters the airflow channel of the flue gas air heat exchanger 4 via the primary hot primary air duct 2. Simultaneously, the high-temperature flue gas before the economizer is introduced into the flue gas flow channel of the flue gas air heat exchanger 4 through the flue gas inlet duct 5. In the flue gas air heat exchanger 4, the airflow channel and the flue gas flow channel are isolated from each other, ensuring efficient heat exchange between the high-temperature flue gas and the primary hot primary air in a non-mixed state, thereby achieving secondary heating of the primary hot primary air to form secondary hot primary air that meets the requirements of the pulverizing system. The low-temperature flue gas after heat exchange is returned to the main boiler flue gas duct after the economizer through the flue gas return duct 6 to continue participating in subsequent heat exchange processes or to be treated in the desulfurization and denitrification system. The secondary hot primary air is transported to the pulverizing system 3 via hot primary air duct 2 for the drying and transport of pulverized coal. Through a staged heating mechanism, it effectively overcomes the temperature limitations of traditional single air preheater heating, while simultaneously recovering and utilizing waste heat from boiler flue gas. This significantly increases the upper temperature limit of the hot primary air and reduces heat loss. Furthermore, it enhances the system's adaptability to different coal types and load variations, addressing issues such as limited hot primary air temperature increase, wasted boiler flue gas heat, and poor system adaptability.

[0033] The flue gas flow regulating valve 9 is a device that dynamically controls the flow rate of high-temperature flue gas through the flue gas delivery pipeline 5. It can be implemented using an electric, pneumatic, or manual regulating valve. In practical applications, the flue gas flow regulating valve 9 precisely controls the flue gas flow rate by changing its opening degree. When the pulverizing system needs to increase the temperature of the hot primary air, the opening degree of the regulating valve 9 is increased to increase the supply of high-temperature flue gas entering the flue gas-air heat exchanger 4, thereby enhancing the heat exchange intensity with the primary hot primary air. Conversely, when the temperature of the hot primary air is too high, the opening degree of the regulating valve 9 is reduced to decrease the flue gas input and prevent overheating. Based on the flow regulation mechanism, the flue gas delivery process is transformed from a fixed flow mode to an adjustable mode, effectively overcoming the temperature adaptability defects caused by the uncontrollable flow rate in the original design. The flue gas flow regulating valve 9, together with the flue gas delivery pipeline 5 and the flue gas-air heat exchanger 4, ensures that the temperature of the hot primary air can respond quickly to fluctuations in boiler load or changes in coal moisture content, thereby improving the system's operational reliability and environmental adaptability.

[0034] In addition, in the hot primary air duct 2, a first temperature sensor 10 is installed between the outlet of the air preheater 1 and the inlet of the air flow channel of the plate heat exchanger to collect the primary hot primary air temperature at the outlet of the air preheater 1; a second temperature sensor 11 is installed between the outlet of the air flow channel of the plate heat exchanger and the inlet of the pulverizing system 3 to collect the secondary hot primary air temperature at the outlet of the plate heat exchanger; an online soot blowing device 12 is also installed on the flue gas flow channel of the plate heat exchanger. The online soot blowing device 12 adopts the compressed air soot blowing method and can automatically start the soot blowing operation according to the pressure difference signal before and after the flue gas flow channel to prevent fly ash deposition.

[0035] By installing a first temperature sensor 10 between the outlet of the air preheater 1 and the inlet of the air channel of the flue gas air heat exchanger 4, the hot air status during the primary heating stage can be captured in real time. This allows the system to accurately assess the primary heating effect before the hot air enters the secondary heating stage, providing a preliminary basis for subsequent adjustments. A second temperature sensor 11 is installed between the outlet of the air channel of the flue gas air heat exchanger 4 and the inlet of the pulverizing system 3. This sensor directly acquires the final hot air temperature that meets the pulverizing requirements. This monitoring point is adjacent to the inlet of the pulverizing system 3, ensuring a strong correlation between temperature data and the coal powder drying process. Based on the monitoring data from these two temperature sensors, the system can dynamically adjust operating parameters according to the actual temperature, thereby maintaining a stable output of hot air temperature when coal type changes or load fluctuates, ensuring the efficient and reliable operation of the pulverizing system. Furthermore, this temperature monitoring scheme is closely integrated with the structural design of the entire primary hot air staged heating system. By precisely locating the temperature monitoring point, it effectively supports the system's dynamic adjustment capability and solves the problem of hot air temperature deviating from the set range due to a lack of real-time temperature monitoring.

[0036] The online soot blowing device 12 is a device that can automatically remove ash accumulation inside heat exchange equipment. It can be implemented using various methods such as steam soot blowing, sonic soot blowing, or mechanical vibration. In practical applications, the main purpose of the online soot blowing device 12 is to remove ash deposits in the flue gas duct in real time, avoid thermal resistance accumulation, and thus ensure the stability of heat exchange efficiency. During the operation of the flue gas air heat exchanger 4, ash carried by high-temperature flue gas will continuously accumulate in the flue gas duct, forming a heat insulation layer that directly hinders heat transfer. By integrating the online soot blowing device 12 into the flue gas duct, the blowing action can be automatically triggered during system operation to promptly remove the ash accumulation on the inner wall of the duct. This design allows the primary hot air to continuously obtain sufficient heat exchange during the secondary heating stage, ensuring that the temperature of the secondary hot air is accurately maintained within the drying threshold range required by the pulverizing system. When the boiler load fluctuates or high-moisture coal is burned, the online soot blowing device 12 can significantly improve the dynamic response capability and operational reliability of the system, fundamentally solving the problem of temperature runaway caused by ash accumulation.

[0037] The flue gas intake port is the location where high-temperature flue gas is extracted from the main flue gas duct of the boiler. It can be located on the flue gas flow path before the economizer to ensure the acquisition of high-temperature flue gas. The flue gas return port is the location where low-temperature flue gas, after heat exchange, is returned to the main flue gas duct of the boiler. It is usually located on the flue gas flow path after the economizer to avoid interfering with the normal heat exchange process of the economizer. The flue gas delivery pipeline 5 is the pipeline structure used to guide high-temperature flue gas into the flue gas-air heat exchanger 4. It can be made of high-temperature resistant materials and equipped with an insulation layer to reduce heat loss. The flue gas return pipeline 6 is the pipeline structure used to transport low-temperature flue gas back to the main flue gas duct of the boiler. Its design needs to consider the matching of flue gas flow rate and pressure to ensure the stable operation of the system. By accurately locating the flue gas intake port and the flue gas return port, the problems of insufficient high-temperature flue gas acquisition and system process interference are effectively solved. The flue gas intake is located on the main boiler flue gas duct before the economizer, directly capturing the high-temperature flue gas before it has undergone heat exchange with feedwater. This provides a sufficient heat source for the flue gas-air heat exchanger 4, ensuring that the primary hot air receives adequate heating during the secondary heating stage. The flue gas return outlet is located on the main boiler flue gas duct after the economizer, allowing the low-temperature flue gas after heat exchange to be returned to the temperature-matching region, avoiding interference with the economizer's heat exchange process and maintaining the stability of the boiler's tail flue gas flow. The flue gas inlet duct 5 guides the high-temperature flue gas to the heat exchange location, achieving efficient heat exchange with the primary hot air and significantly enhancing waste heat utilization efficiency. The flue gas return duct 6 ensures a closed-loop system for the flue gas. After the low-temperature flue gas is safely returned to the main flue, it can continue to participate in the air preheater's heat exchange or subsequent treatment, preventing the risk of flue gas leakage and ensuring that the overall boiler thermal efficiency is not affected.

[0038] This system is applied in the positive pressure direct-fired pulverizing system of a thermal power generating unit. The specific operation process is as follows: Primary heating: Ambient air enters the air preheater 1 and exchanges heat with the flue gas at the outlet temperature of the economizer 13, which is about 300°C. The air is heated to 280°C to form primary hot air. The first temperature sensor 10 collects the temperature in real time and transmits it to the system control unit. Secondary heating: Primary hot air enters the air flow channel of the plate heat exchanger through the primary hot air duct 2; at the same time, high-temperature flue gas with a temperature of about 400°C in front of the economizer 13 enters the flue gas flow channel of the plate heat exchanger through the flue gas duct 5. The system control unit adjusts the opening of the flue gas flow regulating valve 9 to 60% according to the target temperature (set to 350°C) collected by the second temperature sensor 11, so that the high-temperature flue gas and the primary hot air can fully exchange heat in the plate heat exchanger. Temperature control and flue gas recirculation: After heat exchange, the temperature of the primary hot air rises to 350°C and is transported to the pulverizing system 3 through the primary hot air pipeline 2 to meet the drying requirements of the unit when burning bituminous coal with 20% moisture content; while the high-temperature flue gas in the flue gas flow channel 42 drops to 320°C after heat exchange and is sent back to the boiler flue gas main pipeline 8 after the economizer through the flue gas recirculation pipeline 6, and enters the air preheater 1 for heat exchange again along with the subsequent flue gas, and is finally discharged after being treated by the desulfurization and denitrification system; Maintenance and Adjustment: During operation, when the pressure difference across the flue gas duct exceeds the set value (1.5 kPa), the online soot blowing device 12 will automatically start to clean the flue gas duct and ensure heat exchange efficiency. When the moisture content of the coal used for combustion decreases to 12%, the system control unit will reduce the opening of the flue gas flow regulating valve 9 to 30% based on the feedback from the second temperature sensor 11, so that the secondary hot primary air temperature is stabilized at 320℃, and the coal powder is prevented from drying out excessively.

[0039] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A hot primary air staged heating system for a positive pressure direct-blown pulverizing system, characterized in that, It includes a flue gas air heat exchanger (4), a flue gas inlet pipe (5), a flue gas return pipe (6), and an air preheater (1), a hot primary air pipe (2), and a pulverizing system (3) connected in sequence. The air inlet of the flue gas air heat exchanger (4) is connected to the hot primary air outlet of the air preheater (1) through the hot primary air pipe (2). The flue gas air heat exchanger (4) is provided with mutually isolated air channels and flue gas channels. The air outlet of the flue gas air heat exchanger (4) is connected to the hot primary air inlet of the pulverizing system (3) through the hot primary air pipe (2). The flue gas inlet pipe (5) connects the flue gas outlet to the flue gas inlet of the flue gas air heat exchanger (4). The flue gas return pipe (6) connects the flue gas outlet of the flue gas air heat exchanger (4) to the flue gas return outlet of the flue gas air heat exchanger (4).

2. The positive pressure direct-blown pulverizing system hot primary air staged heating system according to claim 1, characterized in that, The flue gas inlet is located in the main flue gas pipeline of the boiler before the economizer, and the flue gas return outlet is set on the main flue gas pipeline of the boiler after the economizer. The flue gas inlet pipeline (5) is used to introduce the high-temperature flue gas before the economizer into the flue gas flow channel of the plate heat exchanger. The flue gas return pipeline (6) is used to send the low-temperature flue gas after heat exchange through the flue gas air heat exchanger (4) back to the main flue gas pipeline of the boiler.

3. The hot primary air staged heating system of the positive pressure direct-blown pulverizing system according to claim 1, characterized in that, The flue gas air heat exchanger (4) adopts a plate heat exchanger and is made of 316L stainless steel or ND steel.

4. The hot primary air staged heating system of the positive pressure direct-blown pulverizing system according to claim 1, characterized in that, A flue gas flow regulating valve (9) is installed on the flue gas delivery pipeline (5).

5. The hot primary air staged heating system for positive pressure direct blowing pulverizing according to claim 1, characterized in that, A first temperature sensor (10) is installed between the outlet of the air preheater (1) and the inlet of the air channel of the flue gas air heat exchanger (4), and a second temperature sensor (11) is installed between the outlet of the air channel of the flue gas air heat exchanger (4) and the inlet of the pulverizing system (3).

6. The hot primary air staged heating system for positive pressure direct-blown pulverizing according to claim 1, characterized in that, The flue gas air heat exchanger (4) is equipped with an online soot blowing device (12) in the flue gas flow channel.

7. The method of operating the hot primary air staged heating system of the positive pressure direct-blown pulverizing system as described in any one of claims 1-6, characterized in that, include: In the primary heating stage, ambient air enters the air preheater (1) and exchanges heat with the boiler flue gas after heat exchange in the economizer for the first time, raising the temperature to the set temperature and forming primary hot air. In the secondary heating stage, the primary hot primary air enters the air flow channel of the flue gas air heat exchanger (4) through the primary hot air duct (2), and the high-temperature flue gas before the economizer enters the flue gas flow channel of the flue gas air heat exchanger (4) through the flue gas duct (5); inside the flue gas air heat exchanger (4), the high-temperature flue gas and the primary hot primary air undergo a second heat exchange, further heating the primary hot primary air to form secondary hot primary air that meets the high dryness requirements of the pulverizing system; The flue gas is returned to the boiler flue gas main pipeline after the economizer through the flue gas return pipeline (6) and the low temperature flue gas after heat exchange in the flue gas air heat exchanger (4) enters the air preheater (1) together with the flue gas for heat exchange again or enters the desulfurization and denitrification system for treatment. Secondary hot primary air is transported to the pulverizing system through the hot primary air pipeline (2) for the drying and transportation of pulverized coal.

8. The operating method of the hot primary air staged heating system of the positive pressure direct-blown pulverizing system according to claim 7, characterized in that, Based on the difference between the outlet hot primary air temperature of the flue gas air heat exchanger (4) collected by the second temperature sensor and the set temperature, the flue gas flow regulating valve on the flue gas delivery pipeline is automatically adjusted: when the actual temperature is lower than the set temperature, the opening of the flue gas flow regulating valve is increased; when the actual temperature is higher than the set temperature, the opening of the flue gas flow regulating valve is decreased.

9. The operating method of the hot primary air staged heating system of the positive pressure direct-blown pulverizing system according to claim 7, characterized in that, The operation method of the primary air staged heating system of the positive pressure direct blowing pulverizing system is characterized in that the ambient air enters the air preheater (1) and exchanges heat with the flue gas for the first time, and is heated to 250-300℃ to form primary hot primary air; in the secondary heating stage, the flue gas temperature taken from the economizer is 350-450℃, and the primary hot primary air is further heated to 320-380℃; in the flue gas recirculation and hot primary air conveying stage, the temperature of the low-temperature flue gas after heat exchange through the flue gas air heat exchanger (4) drops to 300-350℃.

10. A coal-fired power generation unit, employing the positive pressure direct-fired pulverizing system hot primary air staged heating system as described in any one of claims 1-6.

Images