Boiler separator outlet double-regulation flue gas cooling system and temperature control method

Abstract

The application discloses a boiler separator outlet double-regulation flue gas cooling system and a temperature control method, wherein the boiler separator outlet and the tail flue inlet are communicated through a membrane type cooling flue, the membrane type cooling flue is internally provided with a double-regulation anti-coking device, the double-regulation anti-coking device comprises a main cooling branch and a compensation mixing branch; the tail flue inlet is provided with a flue gas temperature measuring device and is connected with a DCS interlocking control system, the DCS interlocking control system is used for controlling the start and stop of a recirculation booster fan and a regulating valve of the compensation mixing branch according to the flue gas temperature signal measured by the flue gas temperature measuring device. Through the time-sharing double-stage regulation of the main cooling branch and the compensation mixing branch, the normal state relies on the water-cooled main branch to complete basic cooling, and the energy consumption is low; when the membrane type water-cooled heating area is covered with ash and the cooling capacity is insufficient, the flue gas temperature exceeds the standard, the low-temperature flue gas auxiliary branch is automatically put into operation for compensation, the temperature control capacity can be restored without shutdown and ash cleaning, and the shutdown frequency and the artificial ash cleaning workload are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of boiler flue gas cooling technology, specifically to a boiler separator outlet dual-regulation flue gas cooling system and temperature control method. Background Technology

[0002] When burning high-sodium coal, straw, bark, and other high-alkali metal fuels from Zhundong, the ash content is rich in Na2O and K2O, with a low initial deformation temperature and extremely strong adhesion. The high-temperature flue gas contains a large amount of gaseous alkali metal salts. When the flue gas temperature exceeds 650℃ and enters the tail convection heating surfaces such as the low-temperature superheater, economizer, and air preheater, the alkali metal vapors are very easy to condense on the tube wall to form a sticky bottom layer. The fly ash continues to adhere and grow coke lumps, causing flue blockage, a sharp drop in heat exchange efficiency, and a surge in soot blowing and maintenance workload.

[0003] Existing conventional technologies only set up a single water-cooled film cooling flue after the separator, relying on the water-cooled wall to absorb heat and reduce the flue gas temperature. However, after the boiler has been running for a long time, alkaline ash will continue to accumulate on the outer wall of the water-cooled heating surface, forming a heat insulation layer. The water-cooled heat exchange capacity gradually decreases, the flue gas cooling effect continues to deteriorate, and the flue gas temperature at the tail flue inlet gradually exceeds the standard. Summary of the Invention

[0004] The purpose of this invention is to provide a boiler separator outlet dual-regulating flue gas cooling system and temperature control method to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a boiler separator outlet dual-regulating flue gas cooling system and temperature control method, which is installed at the outlet of a cyclone separator and includes a tail flue and a tail convection heating surface. The boiler separator outlet and the tail flue inlet are connected by a membrane cooling flue. The membrane cooling flue is equipped with a dual-regulating anti-coking device, which includes a main cooling branch and a compensating mixing branch.

[0006] The main cooling branch includes a membrane water-cooled heating surface, forming a membrane cooling flue cooling section, and the membrane water-cooled heating surface is connected to the boiler water-cooled circulation device.

[0007] The compensation and mixing branch includes a low-temperature flue gas extraction main pipe, a recirculation booster fan, a recirculation duct, and an annular distribution manifold connected in sequence. The inlet of the low-temperature flue gas extraction main pipe is connected to the boiler flue gas outlet. A regulating valve is installed on the recirculation duct. A mixing nozzle is installed on the annular distribution manifold. The mixing nozzle corresponds to the outlet of the cooling section of the membrane cooling flue.

[0008] The tail flue inlet is equipped with a flue temperature measuring device and is connected to the DCS interlock control system. The DCS interlock control system uses the flue temperature signal measured by the flue temperature measuring device to control the start and stop of the recirculation booster fan and the regulating valve of the compensation mixing branch.

[0009] Furthermore, the inlet of the low-temperature flue gas extraction main pipe is connected to the dust collector outlet at the boiler flue gas outlet.

[0010] Furthermore, the number of the mixing nozzles is multiple sets, and the multiple sets of mixing nozzles are evenly distributed circumferentially along the outlet section of the membrane cooling flue.

[0011] Furthermore, the outlet of the mixing nozzle has a flow-guiding oblique cut structure and faces the mainstream direction of the flue gas in the membrane cooling flue.

[0012] Furthermore, the membrane cooling flue is provided with a removable insulation and maintenance layer corresponding to the outer side of the membrane water-cooled heating surface.

[0013] Furthermore, the DCS interlocking control system includes a delay adjustment module for delaying the start and stop of the compensation mixing branch.

[0014] A temperature control method for a boiler separator outlet dual-regulating flue gas cooling system, comprising the boiler separator outlet dual-regulating flue gas cooling system as described above, characterized by comprising the following steps:

[0015] S1. During normal boiler operation, all the high-temperature flue gas discharged from the cyclone separator enters the membrane cooling flue cooling section, where it continuously absorbs heat through the membrane water-cooled heating surface to achieve basic cooling of the flue gas, and the compensation mixing branch is completely closed.

[0016] S2. The flue gas temperature measuring device at the tail flue inlet collects the flue gas temperature in real time and uploads it to the DCS interlocking control system.

[0017] S3 and DCS interlocking control systems determine the smoke temperature threshold:

[0018] When the measured flue gas temperature is lower than the preset temperature threshold, the main cooling branch is kept in cooling mode, and the compensation mixing branch is kept off.

[0019] When the measured flue gas temperature is greater than or equal to the preset temperature threshold, the DCS interlock control system triggers the interlock program, opens the regulating valve, starts the recirculation booster fan, and the low-temperature flue gas at the boiler flue gas outlet is injected into the membrane cooling flue through the mixing nozzle to mix evenly with the high-temperature flue gas to complete the cooling.

[0020] S4. The flue gas temperature measuring device continuously monitors the flue gas temperature at the inlet of the tail flue. When the flue gas temperature drops below the preset temperature threshold, the interlocking program of the DCS interlocking control system automatically shuts down the recirculation booster fan and regulating valve, restoring independent operation of only the main cooling branch.

[0021] Furthermore, in step S3, the preset temperature threshold of the DCS interlocking control system is 650°C.

[0022] Furthermore, it also includes the following steps:

[0023] S5. When the boiler unit is shut down for maintenance, remove the removable insulation and maintenance layer of the membrane cooling flue and clean the ash from the membrane water-cooled heating surface.

[0024] The beneficial effects of this invention are as follows: This invention uses a two-stage time-sharing adjustment of the main cooling branch and the compensation mixing branch, so that the basic cooling is completed by the water-cooled main branch under normal conditions, resulting in low energy consumption; when the ash insulation and cooling capacity of the membrane water-cooled heating surface is insufficient and the flue gas temperature exceeds the standard, the low-temperature flue gas auxiliary road compensation is automatically activated, and the temperature control capability can be restored without stopping the machine for cleaning, which greatly reduces the frequency of machine shutdown and the amount of manual cleaning work.

[0025] The DCS interlocking control system sets a control threshold and automatically starts and stops the compensation branch based on the measured flue gas temperature signal from the flue gas temperature measuring device. No manual adjustment is required from the operator. It is adapted to the boiler's full load and variable operating conditions for stable temperature control and always keeps the flue gas temperature below the critical temperature for alkali metal condensation and coking. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0027] The components include: 1. Furnace; 2. Cyclone separator; 3. Membrane cooling flue; 4. Main cooling branch; 5. Compensating mixing branch; 6. Flue gas temperature measuring device; 7. Tail flue; 8. Tail convection heating surface; 9. Dust collector.

[0028] 41. Membrane water-cooled heating surface; 51. Low-temperature flue gas extraction header; 52. Recirculation booster fan; 53. Recirculation duct; 54. Regulating valve; 55. Annular distribution manifold; 56. Mixing nozzle. Detailed Implementation

[0029] 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 merely one embodiment of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0030] To make the objectives, technical solutions and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0031] In the following description, references to "an embodiment," "an embodiment," "an example," "example," etc., indicate that the described embodiment or example may include a particular feature, structure, characteristic, property, element, or limitation, but not every embodiment or example necessarily includes that particular feature, structure, characteristic, property, element, or limitation. Furthermore, the repeated use of the phrase "an embodiment according to this application," while possibly referring to the same embodiment, does not necessarily refer to the same embodiment.

[0032] like Figure 1 As shown, the present invention discloses a boiler separator outlet dual-regulating flue gas cooling system, which is installed at the outlet of cyclone separator 2, and includes a tail flue 7 and a tail convection heating surface 8. The feature is that the boiler separator outlet and the tail flue 7 inlet are connected by a membrane cooling flue 3, and the membrane cooling flue 3 is provided with a dual-regulating anti-coking device, which includes a main cooling branch 4 and a compensating mixing branch 5.

[0033] The main cooling branch 4 includes a membrane water-cooled heating surface 41, forming a cooling section of the membrane cooling flue 3. The membrane water-cooled heating surface 41 is connected to the boiler water-cooled circulation device. The wall of the membrane cooling flue 3 is a membrane cooling wall, and a cooling medium, which is water or steam, flows through the membrane cooling wall.

[0034] The flue gas outlet of furnace 1 is connected to the inlet of cyclone separator 2. All the high-temperature flue gas discharged from cyclone separator 2 enters the cooling section of the membrane cooling flue duct 3. The high-temperature flue gas transfers heat to the cooling medium in the membrane water-cooled heating surface 41 through both radiation and convection heat transfer, achieving basic cooling. Under most normal operating conditions, the flue gas temperature can be reduced to near or below the ideal value by the main water cooling circuit alone, significantly reducing the operating time of high-energy-consuming equipment such as recirculation fans. In other words, the main cooling branch 4 is a normal operating branch, driven by the boiler's original natural water circulation method, without adding extra energy consumption.

[0035] The compensating mixing branch 5 includes a low-temperature flue gas extraction main pipe 51, a recirculation booster fan 52, a recirculation duct 53 and an annular distribution manifold 55 connected in sequence. The inlet of the low-temperature flue gas extraction main pipe 51 is connected to the boiler flue gas outlet. A regulating valve 54 is installed on the recirculation duct 53. A mixing nozzle 56 is installed on the annular distribution manifold 55. The mixing nozzle 56 corresponds to the outlet of the cooling section of the membrane cooling flue duct 3.

[0036] The function of the compensating mixing branch 5 is to automatically activate and implement auxiliary cooling when the heat exchange capacity of the main cooling branch 4 is insufficient due to ash accumulation and the inlet flue gas temperature of the tail flue 7 exceeds the standard. It is an auxiliary working branch and is completely closed under normal conditions. Its working path is as follows: Low-temperature flue gas is drawn from the boiler flue gas outlet by the low-temperature flue gas extraction header 51, pressurized by the recirculation booster fan 52, sent into the recirculation air duct 53, and then into the annular distribution header 55. It is then sprayed into the main flue at the outlet of the cooling section of the membrane cooling flue duct 3 by the mixing nozzle 56 set on the annular distribution header 55. The low-temperature flue gas is mixed with the high-temperature flue gas, and the physical sensible heat of the low-temperature flue gas is used to reduce the overall flue gas temperature.

[0037] The tail flue 7 inlet is equipped with a flue temperature measuring device 6, which is connected to the DCS interlock control system. The DCS interlock control system uses the flue temperature signal measured by the flue temperature measuring device 6 to control the start and stop of the recirculation booster fan 52 and the regulating valve 54 of the compensation mixing branch 5.

[0038] Specifically, a flue gas temperature measuring device 6 is installed at the inlet of the tail flue duct 7 to monitor the flue gas temperature before it enters the tail convection heating surface 8 in real time, and the signal is connected to the DCS interlocking control system. The DCS interlocking control system compares the measured flue gas temperature with a preset threshold and automatically decides whether to activate or deactivate the compensation blending branch 5, realizing a main cooling branch 4 and compensation blending branch 5 operating in a time-sharing mode. Under normal conditions, only the main cooling branch 4 operates independently, and when the flue gas temperature exceeds the standard, the compensation blending branch 5 automatically activates.

[0039] When the measured flue gas temperature is less than the threshold, the recirculation booster fan 52 and the regulating valve 54 are closed, the compensation mixing branch 5 is completely closed, and only the main cooling branch 4 works independently.

[0040] When the measured flue gas temperature is greater than or equal to the threshold, the DCS interlock control system automatically starts the recirculation booster fan 52 and the regulating valve 54. The low-temperature flue gas is evenly injected into the main flue through the annular distribution box 55 and the mixing nozzle 56 to complete the mixing and cooling.

[0041] When the flue gas temperature drops below the threshold: the DCS interlock control system automatically shuts down the recirculation booster fan 52 and the regulating valve 54, closes the compensation mixing branch 5, and restores the independent operation of only the main cooling branch 4.

[0042] This invention uses a two-stage, time-sharing adjustment of the main cooling branch 4 and the compensation mixing branch 5 to achieve basic cooling by relying on the water-cooled main circuit under normal conditions, resulting in low energy consumption. When the membrane water-cooled heating surface 41 is ash-accumulated, has insufficient insulation and cooling capacity, and the flue gas temperature exceeds the standard, the low-temperature flue gas auxiliary circuit is automatically activated for compensation. Temperature control capability can be restored without stopping the machine for cleaning, which greatly reduces the frequency of machine shutdown and the amount of manual cleaning work.

[0043] The DCS interlocking control system sets a control threshold and automatically starts and stops the compensation branch based on the measured flue gas temperature signal from the flue gas temperature measuring device 6. No manual adjustment is required from the operator. It is adapted to the boiler's full load and variable operating conditions for stable temperature control and always keeps the flue gas temperature below the critical temperature for alkali metal condensation and coking.

[0044] In one embodiment, the inlet of the low-temperature flue gas extraction header 51 is connected to the outlet of the dust collector 9 at the boiler flue gas outlet. After the boiler flue gas is treated by the dust collector 9, a large number of fly ash particles in the flue gas are captured, ensuring that the recirculated low-temperature flue gas is free of coarse ash, avoiding clogging of the mixing nozzle 56, reducing wear on the impeller of the recirculation booster fan 52, lowering system maintenance costs, and ensuring the system's anti-coking effect. At the same time, it reduces the problem of fly ash deposition in pipe bends, valves, and other parts, which increases flow resistance and affects the precise control of the regulating valve 54.

[0045] In addition, the dust collector 9 is located at the end of the boiler tail flue 7, and the temperature of the flue gas has been significantly reduced after passing through the tail convection heating surface 8. The temperature of the flue gas extracted at the outlet of the dust collector 9 is much lower than the temperature of the flue gas extracted before the dust collector 9. The lower temperature of the recirculated flue gas means that the heat absorbed per unit volume of low-temperature flue gas is greater: the mixing and cooling efficiency is higher, and less recirculated flue gas is required to achieve the same cooling effect: the fan energy consumption is lower.

[0046] In one embodiment, the number of mixing nozzles 56 is multiple sets, which are evenly distributed circumferentially along the outlet cross-section of the membrane cooling flue 3. This is equivalent to arranging a surrounding cooling ring on the cross-section of the flue. This ensures that the low-temperature flue gas can cover the entire cross-section, eliminating cooling dead zones. Multiple jets are injected simultaneously and interact in the central region of the flue, significantly increasing the contact area between the low-temperature and high-temperature flue gas, achieving rapid and efficient mixing. In this embodiment, the mixing nozzles 56 are generally distributed in 8 to 12 sets at equal angles along the membrane cooling flue 3.

[0047] In one embodiment, the mixing nozzle 56 has a flow-guiding oblique-cut structure at its outlet, oriented towards the mainstream flue gas direction within the membrane cooling flue 3. This provides a smooth outlet path for the low-temperature flue gas, ensuring stable and concentrated airflow in a predetermined direction, avoiding energy loss and airflow turbulence caused by sudden changes in direction. Simultaneously, the oblique jet possesses both axial (along the flue direction) and radial (perpendicular to the flue direction) velocity components. This allows the low-temperature flue gas to rapidly penetrate towards the center of the flue (radial mixing, eliminating cross-sectional temperature differences) and continuously mix with the high-temperature flue gas along the flow direction (axial mixing, ensuring temperature drop throughout), achieving three-dimensional, dead-angle-free mixing and eliminating localized high-temperature zones at the outlet section of the membrane cooling flue 3. This prevents wall condensation corrosion caused by localized low temperatures and ensures effective cooling of the high-temperature zone at the center of the flue, further eliminating the risk of localized high-temperature dead zones and wall coking.

[0048] In one embodiment, a removable insulation and maintenance layer is provided on the membrane cooling flue 3, corresponding to the outer side of the membrane water-cooled heating surface 41. In this embodiment, the removable insulation and maintenance layer is connected to the membrane cooling flue 3 by bolts, clips, etc., and can be quickly disassembled and reassembled as a whole during maintenance without destructive removal. After removal, the water-cooled wall tubes that need to be cleaned can be directly and completely exposed, making it convenient to stop the machine and remove the alkaline ash accumulation on the outer wall of the membrane water-cooled heating surface 41.

[0049] In one embodiment, the DCS interlocking control system includes a delay adjustment module for delaying the start and stop of the mixing branch 5.

[0050] In this embodiment, the delay adjustment module is implemented in the DCS system using a software algorithm, and its basic judgment logic is as follows:

[0051] Activation Delay: When the measured smoke temperature first reaches or exceeds the preset threshold, no immediate action is taken; instead, a timer is started. Only after the smoke temperature is continuously monitored to be greater than or equal to the preset threshold and the preset delay time is reached will the activation command of the compensation mixing branch 5 be actually triggered.

[0052] Similarly, for the shutdown delay, when the measured smoke temperature first drops below the preset threshold, the branch is not immediately shut down; instead, another timer is started. Only after the smoke temperature is continuously monitored to be below the preset threshold and the preset delay time is reached will a shutdown command be issued.

[0053] The delay adjustment module filters out invalid short-term fluctuations, preventing frequent start-stop cycles of the branch circuits caused by small fluctuations in flue gas temperature. Simultaneously, it avoids the periodic disturbances to the flow and temperature fields within the flue gas duct caused by the frequent activation and deactivation of the compensation mixing branch 5. Without delay adjustment, frequent start-stop cycles of the branch circuits themselves would cause repeated fluctuations in flue gas temperature, forming a vicious cycle of positive feedback: measurement fluctuation → branch circuit action → flow field disturbance → further temperature fluctuations. The delay adjustment module breaks this vicious cycle, making the system operate more smoothly.

[0054] A temperature control method for a boiler separator outlet dual-regulating flue gas cooling system, comprising the boiler separator outlet dual-regulating flue gas cooling system as described above, includes the following steps:

[0055] S1. During normal boiler operation, all the high-temperature flue gas discharged from the cyclone separator 2 enters the cooling section of the membrane cooling flue duct 3, and continuously absorbs heat through the membrane water-cooled heating surface 41 to achieve basic cooling of the flue gas. The compensation mixing branch 5 is completely closed.

[0056] S2, The flue gas temperature measuring device 6 at the inlet of the tail flue 7 collects the flue gas temperature in real time and uploads it to the DCS interlocking control system.

[0057] S3 and DCS interlocking control systems determine the smoke temperature threshold:

[0058] When the measured flue gas temperature is lower than the preset temperature threshold, the main cooling branch 4 is kept in cooling mode and the compensation mixing branch 5 is kept off.

[0059] When the measured flue gas temperature is greater than or equal to the preset temperature threshold, the DCS interlock control system triggers the interlock program, opens the regulating valve 54, starts the recirculation booster fan 52, and the low-temperature flue gas at the boiler flue gas outlet is injected into the membrane cooling flue duct 3 through the mixing nozzle 56, and is uniformly mixed with the high-temperature flue gas to complete the cooling.

[0060] S4. The flue gas temperature measuring device 6 continuously monitors the flue gas temperature at the inlet of the tail flue 7. When the flue gas temperature drops below the preset temperature threshold, the interlocking program of the DCS interlocking control system automatically shuts down the recirculation booster fan 52 and the regulating valve 54, restoring only the main cooling branch 4 to independent operation.

[0061] In one embodiment, in step S3, the preset temperature threshold of the DCS interlocking control system is 650°C. When burning high-sodium coal, as long as the flue gas temperature is above 650°C, the heat transfer coefficient gradually decreases with prolonged operation, inevitably leading to ash accumulation and fouling. Biomass fuels also generally contain a large amount of alkali metals, which are easily released in gaseous form during combustion. 650°C is a critical control point within this range. When the flue gas temperature is above 650°C, the alkali metal vapor is in a gaseous state and has not yet undergone large-scale condensation; when the flue gas temperature is below 650°C, the alkali metal vapor begins to condense and deposit in large quantities. Therefore, controlling the inlet flue gas temperature of the tail convection heating surface 8 below 650°C can fundamentally prevent the condensation and coking of alkali metals on the tail convection heating surface 8.

[0062] In one embodiment, the step further includes:

[0063] S5. When the boiler unit is shut down for maintenance, remove the removable insulation maintenance layer of the membrane cooling flue 3 and clean the ash accumulated on the membrane water-cooled heating surface 41. Control the inlet flue gas temperature of the tail convection heating surface 8 below 650℃. Alkali metal vapors accumulate ash in the membrane cooling flue 3 and on the membrane water-cooled heating surface 41, affecting the heat exchange capacity of the main cooling branch 4. Quickly clean the ash through the removable maintenance layer.

[0064] The embodiments of the present invention are as follows:

[0065] The flue gas outlet of furnace 1 is connected to the inlet of cyclone separator 2. The outlet of cyclone separator 2 is connected to the inlet of tail flue 7 via membrane cooling flue 3. Tail flue 7 has a tail convection heating surface 8 inside. The membrane cooling flue 3 and tail flue 7 are arranged vertically side by side, and an ash hopper is set at the bottom for collecting ash. The flow direction of flue gas in membrane cooling flue 3 and tail flue 7 is U-shaped. This allows for a long-flow connection between the outlet of cyclone separator 2 and the inlet of tail flue 7 in a limited space, which is suitable for retrofitting existing boiler units with limited space. The flue gas temperature measuring device 6 is set at the bottom inlet of tail flue 7, i.e., the U-shaped bend outlet. It measures the temperature of the uniform flue gas after thorough mixing. Compared with the measurement value set before the bend, it can more accurately reflect the true temperature entering the tail convection heating surface 8, resulting in higher control accuracy. Its signal is connected to the DCS interlocking control system.

[0066] The inner wall of the cooling section of the membrane-cooled flue duct 3 is equipped with a membrane water-cooled heating surface 41. The membrane water-cooled heating surface 41 consists of multiple longitudinally arranged water-cooled pipes and flat steel connecting them, forming a membrane wall structure. The membrane water-cooled heating surface 41 is connected to the boiler's existing water-cooled circulation system via inlet and outlet headers, using boiler water as the cooling medium. As the high-temperature flue gas flows downwards, it undergoes radiative and convective heat exchange with the membrane water-cooled heating surface 41, achieving basic cooling. This is a normal operating branch, running continuously throughout the boiler's normal operation without consuming additional electrical energy.

[0067] The compensating blending branch 5 includes a low-temperature flue gas extraction main pipe 51, a recirculation booster fan 52, a recirculation duct 53, and an annular distribution manifold 55 connected in sequence. The inlet of the low-temperature flue gas extraction main pipe 51 is connected to the outlet of the dust collector 9 at the boiler flue gas outlet, extracting clean low-temperature flue gas after dust removal. A regulating valve 54 is installed on the recirculation duct 53. The annular distribution manifold 55 is an annular pipe structure with 12 sets of blending nozzles 56, evenly distributed at equal angles along the circumferential direction of the outlet section of the membrane cooling flue duct 3. The outlet of each blending nozzle 56 is a guide oblique cut structure, with the spray direction facing the mainstream flue gas direction of the membrane cooling flue duct 3. The compensating blending branch 5 is an auxiliary working branch, which is automatically activated only when the cooling capacity of the main cooling branch 4 is insufficient, and is completely closed under normal circumstances.

[0068] The DCS interlocking control system has a preset temperature threshold of 650℃ and a built-in delay adjustment logic. It also adds a fan and regulating valve 54 to the DCS interlocking control system in a recirculation manner.

[0069] A removable insulation and maintenance layer is provided on the outer side of the cooling section of the membrane cooling flue 3, corresponding to the outer side of the membrane water-cooled heating surface 41.

[0070] The temperature control method is as follows:

[0071] During normal boiler operation, the high-temperature flue gas discharged from cyclone separator 2 enters from the top of membrane-cooled flue duct 3. As it flows downward, it continuously absorbs heat through the membrane water-cooled heating surface 41, reducing the flue gas temperature to below approximately 650°C. The cooled flue gas continues to flow downward and then turns to flow into the tail flue duct 7, at which point the compensating blending branch 5 is completely closed.

[0072] The flue gas temperature measuring device 6 at the inlet of the tail flue 7 continuously collects the flue gas temperature in real time, and the signal is uploaded to the DCS interlock control system. The DCS interlock control system compares the measured flue gas temperature with the preset threshold of 650℃.

[0073] When the measured flue gas temperature is <650℃: Maintain only the main cooling branch 4 in operation, and shut down the compensation mixing branch 5.

[0074] When the measured flue gas temperature is ≥650℃: the DCS interlock control system triggers the interlock after confirming the preset delay time, opens the regulating valve 54 and starts the recirculation booster fan 52. The clean low-temperature flue gas from the outlet of the dust collector 9 is distributed by the annular distribution box 55 and injected into the membrane cooling flue 3 through 12 circumferentially distributed mixing nozzles 56 in an oblique direction via the guide oblique cutting structure.

[0075] When the DCS interlock control system detects that the flue gas temperature at the inlet of the tail flue 7 has steadily dropped below 650℃ and continues for a preset delay time, after confirming the shutdown delay, it automatically closes the regulating valve 54 and stops the recirculation booster fan 52, restoring the independent operation of only the main cooling branch 4.

[0076] After the boiler has been running continuously for a certain period of time, it is shut down for maintenance. The removable insulation maintenance layer is removed to expose the outer wall of the membrane water-cooled heating surface 41. Ash is cleaned from the water-cooled heating surface to restore the heat exchange capacity of the main circuit.

[0077] This invention normally relies on the water-cooled main circuit to complete the basic cooling, resulting in low energy consumption. When the water-cooled heating surface has insufficient heat insulation and cooling capacity, and the flue gas temperature exceeds the standard, the low-temperature clean flue gas auxiliary circuit is automatically activated for compensation. Temperature control capability can be restored without stopping the machine for cleaning, which greatly reduces the frequency of machine shutdown and the amount of manual cleaning work.

[0078] The annularly distributed multiple sets of mixing nozzles 56 ensure uniform mixing of low-temperature flue gas and high-temperature flue gas across the entire cross section, eliminating local high-temperature areas in the flue and completely eliminating the risk of local alkali ash melting, adhesion, and coking. The overall degree of fouling on the tail heating surface is significantly reduced, and the frequency of soot blowing is decreased.

[0079] With 650℃ at the tail inlet as the sole control threshold, the DCS interlocking control system automatically starts and stops the compensation branch, eliminating the need for manual adjustment by operators. It adapts to the boiler's full-load variable operating conditions for stable temperature control, always keeping the flue gas temperature below the critical temperature for alkali metal condensation and coking.

[0080] The recirculated flue gas is the same as that from the dust collector 9, free of coarse ash particles, and the multiple mixing nozzles 56 are not prone to clogging during long-term operation. Since the main cooling branch 4 is a closed water circulation system, the high-temperature flue gas flows through the membrane cooling flue duct 3, exchanging heat with the water-cooled walls, but the flue gas does not enter the interior of the water-cooled walls. The compensating mixing branch 5 is an independent flue gas pipeline system driven by a fan, drawing low-temperature flue gas from downstream and then sending it into the membrane cooling flue duct 3 through the mixing nozzles 56. The main and auxiliary lines are physically isolated; when the compensating mixing branch 5 is shut down, there is no backflow of low-temperature flue gas, and it does not interfere with the heat exchange operation of the main cooling branch 4.

[0081] This system can be directly installed at the outlet of the cyclone separator of a circulating fluidized bed or biomass boiler. The water-cooled heating surface is compatible with the original water circulation system of the boiler, requiring minimal modification work. New boilers can be integrated into the design.

[0082] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A boiler separator outlet dual-regulating flue gas cooling system, installed at the outlet of a cyclone separator, comprising a tail flue and a tail convection heating surface, characterized in that: The boiler separator outlet and the tail flue inlet are connected by a membrane cooling flue. The membrane cooling flue is equipped with a dual-adjustment anti-coking device, which includes a main cooling branch and a compensating mixing branch. The main cooling branch includes a membrane water-cooled heating surface, forming a membrane cooling flue cooling section, and the membrane water-cooled heating surface is connected to the boiler water-cooled circulation device. The compensation and mixing branch includes a low-temperature flue gas extraction main pipe, a recirculation booster fan, a recirculation duct, and an annular distribution manifold connected in sequence. The inlet of the low-temperature flue gas extraction main pipe is connected to the boiler flue gas outlet. A regulating valve is installed on the recirculation duct. A mixing nozzle is installed on the annular distribution manifold. The mixing nozzle corresponds to the outlet of the cooling section of the membrane cooling flue. The tail flue inlet is equipped with a flue temperature measuring device and is connected to the DCS interlock control system. The DCS interlock control system uses the flue temperature signal measured by the flue temperature measuring device to control the start and stop of the recirculation booster fan and the regulating valve of the compensation mixing branch.

2. The boiler separator outlet dual-regulating flue gas cooling system according to claim 1, characterized in that: The inlet of the low-temperature flue gas extraction main pipe is connected to the dust collector outlet at the boiler flue gas outlet.

3. The boiler separator outlet dual-regulating flue gas cooling system according to claim 1, characterized in that: The number of mixing nozzles is multiple sets, and the multiple sets of mixing nozzles are evenly distributed circumferentially along the outlet section of the membrane cooling flue.

4. The boiler separator outlet dual-regulating flue gas cooling system according to claim 3, characterized in that: The mixing nozzle outlet has a flow-guiding oblique cut structure and faces the mainstream direction of flue gas in the membrane cooling flue.

5. A boiler separator outlet dual-regulating flue gas cooling system according to claim 1, characterized in that: The membrane cooling flue is provided with a removable insulation and maintenance layer corresponding to the outer side of the membrane water-cooled heating surface.

6. The boiler separator outlet dual-regulating flue gas cooling system according to claim 1, characterized in that: The DCS interlocking control system includes a delay adjustment module for delaying the start and stop of the compensation mixing branch.

7. A temperature control method for a boiler separator outlet dual-regulating flue gas cooling system, comprising the boiler separator outlet dual-regulating flue gas cooling system according to any one of claims 1-6, characterized in that: Includes the following steps: S1. During normal boiler operation, all the high-temperature flue gas discharged from the cyclone separator enters the membrane cooling flue cooling section, where it continuously absorbs heat through the membrane water-cooled heating surface to achieve basic cooling of the flue gas, and the compensation mixing branch is completely closed. S2. The flue gas temperature measuring device at the tail flue inlet collects the flue gas temperature in real time and uploads it to the DCS interlocking control system. S3 and DCS interlocking control systems determine the smoke temperature threshold: When the measured flue gas temperature is lower than the preset temperature threshold, the main cooling branch is kept in cooling mode, and the compensation mixing branch is kept off. When the measured flue gas temperature is greater than or equal to the preset temperature threshold, the DCS interlock control system triggers the interlock program, opens the regulating valve, starts the recirculation booster fan, and the low-temperature flue gas at the boiler flue gas outlet is injected into the membrane cooling flue through the mixing nozzle to mix evenly with the high-temperature flue gas to complete the cooling. S4. The flue gas temperature measuring device continuously monitors the flue gas temperature at the inlet of the tail flue. When the flue gas temperature drops below the preset temperature threshold, the interlocking program of the DCS interlocking control system automatically shuts down the recirculation booster fan and regulating valve, restoring independent operation of only the main cooling branch.

8. The temperature control method for a boiler separator outlet dual-regulating flue gas cooling system according to claim 7, characterized in that: In step S3, the preset temperature threshold of the DCS interlocking control system is 650℃.

9. The temperature control method for a boiler separator outlet dual-regulating flue gas cooling system according to claim 7, characterized in that: It also includes the following steps: S5. When the boiler unit is shut down for maintenance, remove the removable insulation and maintenance layer of the membrane cooling flue and clean the ash from the membrane water-cooled heating surface.

Images