A quick start and stop heat accumulation type partition heating and heat preservation system for a drum boiler and a control method thereof

Abstract

The application discloses a kind of quick start and stop heat accumulation type zoned heat tracing heat preservation systems and control methods of drum boiler, belong to thermal power plant boiler technical field, system is by waste heat storage heat supply unit, zoned heat tracing pipe network and intelligent control system composition.Control process is divided into five steps: unit is extinguished and stops early and opens large flow branch, utilizes boiler exhaust to be heat accumulator and completes boiler pressure relief;After steam drum pressure drops to threshold, use small flow branch closed loop control valve to supplement heat, according to wall temperature data correction cooling rate;After heat charging, heat accumulator gives heat to zoned heat tracing, and the wall temperature difference is stabilized by adjusting the cylinder supply opening;When heat accumulation is insufficient, automatically switch to auxiliary steam to maintain equipment standby;Before unit restart, whole domain strengthens heat tracing and eliminates wall temperature gradient, and the system is drained after boiler ignition and pressure rise meets the standard and standby.This application is adapted to unit deep peak shaving scene, ensures that the safety of drum boiler start and stop process is controllable, improves operation flexibility and thermal energy utilization efficiency.

Description

Technical Field

[0001] This invention belongs to the field of boiler technology for thermal power plants, specifically relating to a rapid start-up and shutdown regenerative zoned heat tracing and insulation system and control method for a steam drum boiler. Background Technology

[0002] With the continuous advancement of the construction of new power systems, the operation mode of 300MW-class subcritical drum boilers, as the main units for grid peak shaving, is undergoing profound changes. Frequent start-ups and shutdowns, as well as off-peak shutdowns for standby at night, have become the norm. This not only places higher demands on the economic efficiency of boiler operation but also poses a severe challenge to the safety of thick-walled pressure-bearing components.

[0003] Currently, steam drum boilers generally face two major technical challenges during rapid start-up and shutdown for peak shaving. First, there is significant room for improvement in thermal energy utilization efficiency. During the rapid depressurization phase at the beginning of shutdown, the boiler inevitably discharges a large amount of high-temperature, high-pressure, high-quality steam into the atmosphere; in the subsequent cooling phase, the steam drum still retains a high-temperature saturated working fluid, and the heat energy it contains is dissipated naturally through the furnace walls. Effective recovery and cascade utilization of these two portions of heat energy would significantly reduce the overall energy consumption during unit shutdown. Second, the thermal fatigue life of the steam drum is severely threatened. During depressurization, cooling, and rapid start-up and shutdown, the significant differences in heat dissipation conditions and heating rates between the upper and lower drums can easily lead to temperature differences between the upper and lower walls approaching or even exceeding safe reference values. This excessive temperature difference generates enormous thermal stress within the steam drum metal, which, over time, will cause fatigue damage, and may even lead to deformation or cracking and leakage of the steam drum, severely shortening the equipment's service life and endangering unit safety. Summary of the Invention

[0004] This invention provides a rapid start-up and shutdown regenerative zoned heat tracing and insulation system and control method for steam drum boilers, aiming to break through existing technical bottlenecks and achieve safe, flexible and efficient operation of steam drum boilers under complex peak-shaving conditions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A rapid start-stop thermal storage zoned heat tracing and insulation system for a steam drum boiler includes a waste heat storage steam supply unit, a zoned heat tracing pipeline network, and an intelligent control system. The waste heat storage steam supply unit includes a heat accumulator body, and parallel-connected high-flow-rate charging branch, low-flow-rate charging branch, heat release branch, and condensate level control component. The inlet of the high-flow-rate charging branch is connected to the steam exhaust pipe of the steam drum safety valve, the inlet of the low-flow-rate charging branch is connected to the saturated steam outlet of the steam drum, and the outlets of both the high-flow-rate charging branch and the low-flow-rate charging branch are connected to the bottom of the heat accumulator body. The heat release branch is led out from the top of the heat accumulator body, passes through a pressure stabilizing valve, and is connected in parallel with the plant auxiliary steam pipeline before entering the intelligent control system as a heat tracing source. The zoned heat tracing pipeline network is laid on the outer surface of the thick metal wall of the steam drum, and includes an independent upper cylinder first axial parallel pipe array and a lower cylinder second axial parallel pipe array; the two ends of the two pipe arrays respectively converge into a semi-circular steam inlet header and an outlet header, and the upper steam inlet header and the lower steam inlet header are each connected to an independent steam supply branch, and each branch is equipped with an electric regulating valve. The input end of the intelligent control system is connected to the steam drum wall temperature measuring point, the accumulator pressure / liquid level measuring point, and the pressure / flow measuring point of each pipeline, and the output end is connected to the valve motor of each branch. The system has a built-in standard shutdown cooling curve model and zonal control logic, which can realize the full-process control of cascade heating, zonal heat tracing temperature difference adjustment, steam source switching, rate protection and automatic start and stop of the system.

[0006] A further improvement of the present invention is that the heat accumulator body is a pressure vessel, the tank is pre-filled with deoxygenated saturated water, a steam distributor and a liquid level control valve are installed at the bottom, a steam-water separator and an emergency pressure relief valve are installed at the top, and the outside of the tank is covered with a high-temperature resistant insulation layer.

[0007] A further improvement of the present invention is that the high-flow-rate heating branch is equipped with a large-diameter regulating valve and a throttling orifice plate for high-flow-rate exhaust steam heating during the rapid depressurization stage at the beginning of shutdown; the low-flow-rate heating branch is equipped with a small-diameter electric regulating valve and a high-precision flow sensor for controllable low-flow-rate continuous heating and heat storage during the shutdown cooling stage.

[0008] A further improvement of the present invention is that the heat tracing pipelines of the first axial parallel tube array and the second axial parallel tube array are laid flat along the steam drum axis; when encountering obstacles such as tube seats or lifting lugs on the surface of the steam drum, the heat tracing pipeline adopts a three-dimensional spatial bend bypass structure, and the inner diameter of the pipeline remains consistent before and after bypassing.

[0009] A further improvement of the present invention is that each group of outlet headers is independently equipped with a thermodynamic condensate drain valve, and the outlet of the condensate drain valve is collected into the main condensate drain pipeline and connected to the unit condensate recovery system; the condensate drain valve and liquid level regulating valve of the heat storage body are connected to the unit condensate system to realize the full recovery of condensate during the heat tracing and heat storage process.

[0010] A further improvement of the present invention is that the intelligent control system is based on a PLC controller, and is equipped with a data acquisition module and an execution output module; the data acquisition module is connected to the power plant DCS system to read the steam drum wall temperature, pressure and accumulator operating parameters; the execution output module controls the opening and closing status and degree of each valve; the system receives remote shutdown and restart commands issued by the DCS and outputs execution signals for valve adjustment and audible and visual alarms.

[0011] A control method for a rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler includes the following steps: Step S1: Rapid depressurization and heat charging in the initial stage of shutdown: After the unit is disconnected and the boiler is shut down, the system receives the shutdown signal, fully opens the valves of the high-flow heat charging branch, and closes all heat tracing branches; the high-temperature exhaust steam is sent to the heat accumulator for condensation and heat release after being throttled and depressurized, completing the initial large-capacity heat storage, while meeting the requirements for rapid depressurization of the boiler. Step S2: Controllable Continuous Charging for Heat Storage in the Medium-Pressure Stage: When the steam drum pressure drops to the set value, the high-flow-rate charging branch is closed and switched to low-flow-rate charging branch operation; the opening of the charging valve is adjusted in a closed loop with the allowable cooling rate of the steam drum as the control target, and saturated steam in the steam drum is continuously extracted to supplement the heat storage; no active heating is activated in this stage, and correction is only made by adjusting the charging rate when the wall temperature difference exceeds the standard; when the accumulator pressure reaches the design upper limit or the steam drum temperature drops to the set value, all charging branches are closed. Step S3: Low-pressure stage waste heat release and heat tracing: When the steam drum wall temperature drops to the set value and the accumulator is fully charged, the system switches to heat release mode, opens the accumulator heat release branch to supply steam to the heat tracing network, and executes zoned temperature difference closed-loop control; by adjusting the opening of the upper and lower cylinder steam supply branches, the wall temperature difference is controlled within the safe threshold, and the cooling rate is controlled as needed or the hot standby temperature is maintained. Step S4: Steam source switching during extended shutdown: When the pressure inside the accumulator drops to the switching threshold, the heat release branch of the accumulator is shut off, and the system automatically switches to plant auxiliary steam supply to maintain the zoned temperature control logic and the hot standby temperature range. Step S5: Preheating before boiler start-up: Within the preset time before receiving the unit restart command, the system exits the temperature difference fine-tuning logic, uniformly increases the opening of the upper and lower cylinder steam supply branches, strengthens the heat tracing throughout the entire area, and uniformly increases the temperature of the thick wall of the steam drum and eliminates the residual wall temperature gradient. Step S6: Automatic system shutdown after ignition: After the boiler is successfully ignited and the internal pressure of the steam drum rises to the set shutdown threshold, all steam supply valves are gradually closed, the pipeline drain valves are opened to drain residual steam and water, and the heat tracing system shuts down and enters standby mode.

[0012] A further improvement of the present invention is that, in step S2, the first safe temperature difference threshold is set to 35°C. When the temperature difference between the upper and lower walls exceeds the safe threshold, the wall temperature is corrected by adjusting the heat charging rate. After the temperature difference falls back to within 30°C, normal heat charging is resumed. The heat storage termination condition is that the heat storage pressure reaches the design upper limit.

[0013] A further improvement of the present invention is that, in step S3, the closed-loop control logic of the zoned temperature difference is as follows: when the temperature difference between the upper and lower walls is greater than 35°C and the upper wall temperature is higher than the lower wall temperature, the opening of the lower cylinder steam supply branch is increased and the opening of the upper cylinder branch is simultaneously decreased; when the temperature difference is reversed, reverse adjustment is performed; when the temperature difference is less than or equal to 35°C, the valve opening is adjusted as needed to control the cooling rate or maintain the target hot standby temperature.

[0014] A further improvement of the present invention is that, in step S4, the steam source switching pressure threshold of the heat accumulator is 0.4 MPa; the normal hot standby temperature range is 160~180℃; when the standby time exceeds 48h, the heat preservation temperature is lowered to 120℃ to reduce energy consumption.

[0015] Compared with the prior art, the present invention has at least the following beneficial technical effects: First, this invention achieves tiered recovery and utilization of boiler waste heat, resulting in significant energy savings and reduced consumption. The invention employs a two-stage heating structure with parallel high-flow and low-flow heating branches, enabling phased recovery of boiler waste heat. The high-flow heating branch connects to the boiler drum safety valve exhaust pipe, while the low-flow heating branch connects to the boiler drum saturated steam outlet. This adheres to the energy utilization principle of "high-temperature storage, low-temperature use," effectively storing and reusing redundant boiler exhaust waste heat. The waste heat steam stored in the waste heat storage steam supply unit provides a stable heat source for equipment heating, effectively replacing traditional auxiliary steam, significantly reducing auxiliary steam consumption during unit operation, fully tapping the potential of boiler waste heat utilization, improving overall unit energy efficiency, and demonstrating excellent energy-saving benefits.

[0016] Secondly, this invention enables proactive and controllable cooling of the steam drum, significantly optimizing equipment protection and extending the service life of core equipment. The innovative design of this invention features a zoned heat tracing network. Independent axial parallel tube arrays are laid on the thick-walled outer surface of the steam drum, with the upper cylinder having a first axial parallel tube array and the lower cylinder having a second axial parallel tube array. Each tube array is equipped with an independent steam supply branch and an electric regulating valve, enabling independent and differentiated heat tracing control of the upper and lower cylinders of the steam drum. Combined with the zoned control logic of the intelligent control system, the steam drum cooling rate can be precisely controlled, stabilizing the maximum temperature difference between the upper and lower walls within 35°C. This effectively slows down the cooling rate during boiler start-up and shutdown and maintains stable steam drum metal wall temperature according to operational needs. This effectively avoids the problem of thermal stress concentration caused by excessive temperature differences in the thick-walled metal during rapid start-up and shutdown of the steam drum boiler, significantly reducing thermal fatigue damage to the thick-walled metal. This fundamentally protects the core pressure-bearing equipment of the steam drum, effectively extending its service life and improving the safety and stability of unit operation.

[0017] Third, the equipment modification is simple and adaptable, and the system operation is highly safe and reliable. The overall structure of this invention is simple and reasonable, requiring no structural modifications to the core pressure-bearing components of the boiler, such as the steam drum. Only matching heat tracing pipelines are laid on the external surface of the steam drum, which will not adversely affect the structural strength or pressure-bearing performance of the boiler's pressure-bearing components. Simultaneously, this invention adopts an external heat tracing design, with the steam heat tracing medium circulating only in the external pipe network and heat storage unit, without entering the boiler's internal circulation system. The physical operating boundaries of the equipment are clear, effectively avoiding safety hazards such as medium cross-flow, internal pipeline contamination, and pressure-bearing structure failure, resulting in extremely high system operational safety. Furthermore, the overall modification work is minimal and the modification difficulty is low, making it suitable for the upgrading needs of existing steam drum boiler units and highly applicable. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall structure and connection of the system of the present invention; Figure 2 This is a flowchart of the control method of the present invention. Detailed Implementation

[0020] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0021] In the description of this invention, it should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0022] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0024] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] Example 1 like Figure 1 As shown, the present invention provides a rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler. Following the principle of "high-temperature storage and low-temperature use" for cascaded energy utilization, it proposes an overall system scheme, which is composed of three core parts: a waste heat storage steam supply unit, a zoned heat tracing pipeline network, and an intelligent control system.

[0027] 1. Waste heat storage steam supply unit The unit consists of a heat accumulator body, a high-flow heat storage branch and a low-flow heat storage branch (used to recover waste heat from exhaust steam at different times during shutdown), a heat release branch, and condensate and liquid level control equipment.

[0028] The heat accumulator body is a pressure vessel designed to recover waste heat from unit shutdown for 0-8 hours. It is pre-filled with deoxygenated saturated water, and has a steam distributor and liquid level control valve at the bottom, and a steam-water separator and emergency pressure relief valve at the top. The entire tank is covered with a high-temperature resistant insulation layer.

[0029] High-flow-rate heat charging branch: The inlet end is connected to the steam drum safety valve, equipped with a large-diameter regulating valve and a throttling orifice plate, and the outlet is connected to the bottom of the heat accumulator; This branch corresponds to the rapid depressurization stage of the boiler in the initial stage of shutdown, and can receive a large flow of high-temperature exhaust steam. After being throttled and depressurized to the pressure of the heat accumulator, it is bubbled into the water in the tank to complete the large-capacity heat storage.

[0030] Small flow rate charging branch: Connected in parallel to the large flow rate charging branch, the inlet end is connected to the saturated steam outlet of the steam drum, equipped with a small-diameter electric regulating valve and a high-precision flow sensor, and the outlet is connected to the bottom of the accumulator; corresponding to the slow cooling stage in the middle of the shutdown, the saturated steam in the steam drum is continuously extracted and stored in the accumulator in a small-opening controllable throttling manner, and the steam extraction rate is strictly matched with the allowable cooling rate of the steam drum.

[0031] Heat release branch: It is drawn from the steam space at the top of the heat accumulator, passes through the pressure regulating valve, and is connected in parallel with the plant auxiliary steam pipeline before entering the intelligent control system, outputting saturated steam that meets the heat tracing requirements.

[0032] Drainage and level control equipment: A drain valve is installed after the pressure stabilizing valve and connected to the unit's condensate system. The normal water level in the tank is maintained by a level regulating valve. Each outlet header is equipped with an independent thermodynamic drain valve. The outlets of the drain valves are collected into the main drainage pipeline and connected to the unit's condensate recovery system to achieve full recovery of the heated condensate.

[0033] 2. Zoned heat tracing network It is laid on the outer surface of the thick metal wall of the steam drum and adopts an independent partition design for the upper and lower cylinders.

[0034] The pipeline network includes a first axial parallel pipe array corresponding to the upper cylinder of the steam drum and a second axial parallel pipe array corresponding to the lower cylinder. The two sets of pipe arrays are independent of each other.

[0035] The heat tracing pipelines of each group of pipe arrays are laid flat along the axial direction of the steam drum, and the two ends converge into the semi-circular steam inlet header and the steam outlet header, respectively; the upper steam inlet header and the lower steam inlet header are each connected to an independent steam supply branch, and an electric regulating valve is installed on the branch.

[0036] When encountering obstacles such as pipe seats and lifting lugs on the surface of the steam drum, the heat tracing pipeline adopts a three-dimensional spatial bend structure, with the inner diameter of the pipeline remaining consistent before and after the bend. A layer of highly thermally conductive mortar is filled between each heat tracing tube bundle and between the heat tracing tube bundle and the outer wall of the steam drum to reduce contact thermal resistance and enhance heat transfer.

[0037] 3. Intelligent Control System The intelligent control system is based on a PLC controller, and is equipped with a data acquisition module and an execution output module. The data acquisition module is connected to the power plant's DCS control system and can read operating parameters such as the steam drum wall temperature and pressure distribution, the accumulator temperature, pressure and steam supply status, and auxiliary steam pressure and temperature.

[0038] The output module can control the on / off status or opening degree of each regulating valve, shut-off valve, drain valve and pressure stabilizing valve in the waste heat storage steam supply unit.

[0039] The PLC controller can automatically calculate the temperature difference between the upper and lower walls of the steam drum based on the data obtained from the acquisition module. It has a built-in standard shutdown cooling curve model and zone control logic, which can realize full-process automated control functions such as automatic control of cascade heating, closed-loop adjustment of the temperature difference between the upper and lower zones, steam source switching, audible and visual alarms, boiler start-up pre-charging and automatic system shutdown.

[0040] The system supports receiving remote commands such as shutdown and restart issued by the unit's DCS, and outputs execution signals such as valve opening adjustment and audible and visual alarm prompts. It can achieve data exchange and linkage operation with the power plant's main control system.

[0041] Example 2 like Figure 2 As shown, the present invention provides a control method for a rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler, comprising: Step S1: Rapid depressurization and heat charging stage during initial shutdown. This stage occurs during the initial disconnection of the unit and the initial shutdown of the boiler. Upon receiving the boiler shutdown signal, the PLC controller fully opens the valves of the high-flow-rate heat charging branch. At this time, all heat tracing branches are not operational. During this stage, high-temperature exhaust steam is depressurized through the orifice plate and then sent to the accumulator at a high flow rate for condensation and heat release, rapidly increasing the temperature and pressure of the saturated water in the tank, completing the initial large-capacity heat storage, and simultaneously meeting the boiler's rapid depressurization requirements.

[0042] The system is preset with a first safe temperature difference threshold of 35℃ and a second alarm temperature difference threshold of 45℃ (which can be modified according to actual needs). When the temperature difference exceeds the first safe threshold, the temperature difference between the upper and lower walls is reduced by adjusting various regulating valves. When the alarm threshold is reached, an alarm is triggered, and the operator manually takes over the system to perform the corresponding emergency operation.

[0043] Step S2: When the PLC controller reads that the steam drum pressure has dropped to about 8 MPa (corresponding to a saturation temperature of about 295℃), it closes the high-flow-rate charging branch and switches to the low-flow-rate precision charging branch. At this time, with the steam drum cooling rate ≤5℃ / h (default value, which can be modified according to actual conditions) as the control target, the opening of the low-flow-rate charging valve is adjusted in a closed loop to continuously draw saturated steam from the steam drum to replenish the heat accumulator.

[0044] During this stage, the system does not perform active heat tracing. When the absolute temperature difference ΔT between the upper and lower walls is detected to be greater than 35°C and the upper wall temperature is higher than the lower wall temperature, the system reduces the upper wall temperature by appropriately increasing the regulating valve of the small-flow-rate heat charging branch, thereby correcting the temperature imbalance between the upper and lower walls. Once the temperature difference falls back to within 30°C, the regulating valve is closed. When the accumulator pressure reaches the design upper limit or the steam drum temperature drops to 200°C, all heat charging branches are shut down.

[0045] Step S3: When the steam drum wall temperature drops below 200℃ and the accumulator is fully charged, the system switches to heat release mode and starts the heat release branch of the accumulator to supply steam. Implement zoned temperature difference closed-loop control: When the temperature difference between the upper and lower walls of the steam drum ΔT > 35℃ and Tupper > Tlower (Tupper represents the average temperature of the upper wall of the steam drum, and Tlower represents the average temperature of the lower wall of the steam drum), increase the opening of the lower cylinder electric regulating valve and simultaneously decrease the opening of the upper cylinder; when ΔT > 35℃ and Tupper < Tlower, adjust in the opposite direction; when ΔT ≤ 35℃, adjust the cooling rate or maintain the steam drum temperature by adjusting the opening of the upper and lower cylinder regulating valves according to the actual start-up and shutdown needs of the power plant.

[0046] Step S4: When the pressure inside the accumulator drops to 0.4 MPa, close the shut-off valve at the accumulator outlet, automatically switch to the plant auxiliary steam branch for steam supply, and continue to maintain the zoned temperature control logic to ensure that the steam drum remains stable in the hot standby range of 160~180℃. If the standby time exceeds 48 hours, the insulation temperature can be lowered to around 120℃.

[0047] Step S5: 30 to 120 minutes before receiving the unit restart command, the system exits the temperature difference fine-tuning logic, uniformly increases the opening of the upper and lower cylinder electric regulating valves to over 80%, strengthens the heat tracing across the entire area, uniformly increases the overall temperature of the thick wall of the steam drum, and eliminates the residual wall temperature gradient.

[0048] Step S6: After ignition, the system automatically shuts off. When the boiler ignition is successful and the internal pressure of the steam drum is built up to 0.5MPa, all steam supply valves are gradually closed, the pipeline drain valves are opened to drain the residual steam and water, and the heat tracing system shuts off and enters standby mode.

[0049] Example 3 The present invention will be further described in detail below with reference to specific embodiments. This embodiment takes a 300MW subcritical drum boiler of a power plant as an example. The boiler drum has an inner diameter of φ1800mm, a wall thickness of 90mm, a straight section length of 19800mm, a design pressure of 18.3MPa, and a rated operating saturation temperature of about 360℃. This system is used to implement peak shaving, shutdown, and heat preservation.

[0050] 1. Configuration of thermal storage steam supply unit system: The heat accumulator is designed with an effective volume of 25 m³ and a design pressure of 1.6 MPa. It is constructed of Q245R steel plate, a material specifically for pressure vessels. The tank is pre-filled with deoxygenated saturated water at an initial water level of 60% of the tank height. A microporous steam distributor with a level regulating valve is installed at the bottom, while a steam-water separator and an emergency pressure relief valve are located at the top. The outer wall of the tank is covered with a 150 mm thick aluminum silicate insulation layer, with a surface heat loss ≤110 W / m². 2 .

[0051] The heat accumulator is equipped with two parallel charging branches, which can recover the waste heat from exhaust steam in stages at different times: High-flow-rate heat charging branch: The inlet is connected to the exhaust manifold of the steam drum safety valve, with a pipe specification of DN100. An electric shut-off valve and a fixed throttling orifice plate are configured in sequence, and the outlet is connected to the steam distributor at the bottom of the accumulator. The maximum designed flow rate is 15t / h, which can throttle the high-temperature exhaust steam of 10~18MPa to 1.2~1.5MPa and then bubble it into the tank, which is suitable for the rapid pressure relief condition at the beginning of shutdown.

[0052] Small-flow precision heat charging branch: Connected in parallel to the large-flow heat charging branch, the inlet is connected to the saturated steam outlet pipe of the steam drum, the pipe specification is DN25, and an electric regulating valve and a flow sensor are configured in sequence. The outlet is connected to the steam distributor of the heat accumulator. The flow rate adjustment range is 0.2~1.0t / h, which can accurately match the allowable cooling rate of the steam drum and realize controllable continuous heat storage.

[0053] The heat release branch is led out from the steam space at the top of the heat accumulator. The pipeline specification is DN50 and equipped with a pressure regulating valve. The outlet steam pressure is stabilized at 0.9MPa (corresponding to a saturation temperature of about 175℃). The parameters are adapted to the heat tracing requirements. The outlet of the heat release branch is connected in parallel with the plant auxiliary steam pipeline (0.8~1.0MPa) and then enters the intelligent control system. After that, the steam is connected to the heat tracing pipeline network. A shut-off valve is installed on the auxiliary steam branch.

[0054] The drain at the bottom of the accumulator and the drain in the heat release branch pipeline are both connected to the unit's condensate recovery system, and the water level in the tank is maintained in a reasonable range of 60% to 70% through the level regulating valve.

[0055] 2. Zoned heat tracing network The pipeline network is laid entirely on the metal outer wall of the steam drum, and adopts a completely independent partitioned structure for the upper and lower sections: The first axial parallel tube array in the upper cylinder and the second axial parallel tube array in the lower cylinder each contain 12 seamless No. 20 steel heat tracing pipes with a diameter of 25×3mm. The pipes are evenly laid out along the axis of the steam drum, and the effective heat tracing length of a single pipe is 19,500mm.

[0056] Each group of pipe arrays has a semi-circular inlet steam header and a semi-circular outlet steam header at both ends, with the header specifications being φ76×6mm. The upper and lower inlet steam headers are each connected to an independent steam supply branch, and each branch is equipped with an electric regulating valve, which can independently adjust the steam supply flow of the two branches to achieve zoned temperature control.

[0057] When the pipeline encounters obstacles such as pipe seats or lifting lugs on the steam drum wall, a three-dimensional spatial bend bypass structure is adopted. The inner diameter of the bypass section remains unchanged to avoid uneven flow caused by sudden changes in the flow cross section. The bypass section is simultaneously filled with high thermal conductivity mud paste to ensure heat exchange continuity.

[0058] All heat tracing pipes are filled with a high thermal conductivity mud layer between them and the outer wall of the steam drum, and between the gaps in the heat tracing pipe bundles. The thermal conductivity of the mud is ≥5W / (m·K), and the filling thickness is 10~15mm, which greatly reduces the contact thermal resistance and enhances the heat transfer effect.

[0059] Each of the two sets of outlet headers is equipped with a thermodynamic steam trap at its lowest point. The steam trap outlets are collected into the main steam trap pipeline and connected to the unit's condensate recovery system.

[0060] 3. Intelligent Control System The system is based on a PLC controller, and is equipped with a data acquisition module and an execution output module.

[0061] Data acquisition terminal: Connected to the power plant's DCS control system, it can read operating parameters such as steam drum wall temperature and pressure distribution, accumulator temperature, pressure and steam supply status, and auxiliary steam pressure and temperature.

[0062] Output terminal: can independently control the on / off status and opening degree of large flow heat charging shut-off valve, small flow heat charging regulating valve, heat release pressure stabilizing valve, upper and lower heat tracing branch electric regulating valve, auxiliary steam shut-off valve, drain valve, etc.

[0063] Control and Communication: The system is connected to the power plant's DCS system and can receive remote commands such as shutdown and restart, and upload operating data and alarm signals. The system has a built-in standard shutdown cooling curve model for this type of unit, with preset control thresholds: first safe temperature difference 35℃, second alarm temperature difference 45℃, cooling rate limit 5℃ / h, heat accumulator switching pressure 0.5MPa, and system exit pressure 0.4MPa. All parameters can be modified locally or remotely by operation and maintenance personnel.

[0064] Implementation process During a nighttime peak-shaving shutdown, the system operated fully automatically. The specific steps are as follows: 1. Step S1: Rapid depressurization and heating during initial shutdown After the unit is disconnected and the boiler is shut down, the power plant's DCS sends a shutdown trigger signal to this system, and the system automatically starts operation. The system fully opens the electric shut-off valve of the high-flow-rate heating branch and closes all valves of the heating branch throughout. The high-temperature exhaust steam (12~18MPa, 330~360℃) in the steam drum is depressurized by the orifice plate and then bubbled into the accumulator water at a flow rate of approximately 12t / h. The steam condenses and releases heat to quickly heat the saturated water in the tank, while simultaneously fulfilling the boiler's rapid depressurization requirements.

[0065] At the end of this stage, the pressure inside the accumulator can rise from the initial 0.1 MPa to 1.1 MPa, and the water temperature inside the tank can rise to 184°C; the pressure in the steam drum can drop to 8.1 MPa.

[0066] 2. Step S2: Controllable continuous charging heat during the medium-pressure stage When the system detects that the steam drum pressure drops to 8 MPa, it automatically shuts down the high-flow-rate heating branch and switches to the low-flow-rate precision heating branch. The system uses a closed-loop control mechanism to maintain a steam drum cooling rate of ≤5℃ / h, keeping the opening of the low-flow-rate electric regulating valve stable at 10%~15% and the extraction steam flow rate maintained at 0.7~0.9 t / h. This continuously sends saturated steam from the steam drum into the accumulator to replenish heat storage, converting the naturally dissipated heat into usable stored energy.

[0067] When the temperature difference between the upper and lower walls of the steam drum exceeds the first safety threshold, the system automatically increases the opening of the small-flow charging valve to 20% to accelerate the steam extraction rate from the upper wall. After the temperature difference returns to the safe range, the valve returns to its original opening and continues to charge and store heat.

[0068] When the steam drum wall temperature drops to 200℃ or the pressure inside the accumulator rises to 1.48MPa, reaching the design upper limit for heat storage, the system shuts down all charging branches, and the continuous charging phase ends.

[0069] 3. Step S3: Waste heat release and heat tracing during the low-pressure stage When the average wall temperature of the steam drum drops below 200℃, the natural cooling trend accelerates, and the accumulator has completed its charging. The system automatically opens the accumulator's heat release branch, and the steam, after being stabilized by the pressure regulating valve, is sent to the zoned heat tracing network, entering the heat release and heat tracing mode. At this time, the system can automatically control the stabilized steam pressure and temperature according to the actual wall temperature of the steam drum to match the actual cooling or insulation requirements.

[0070] This stage implements zoned temperature difference closed-loop control: when the temperature difference between the upper and lower walls is >35℃, the opening of the two heat tracing valves is adjusted in the opposite direction to increase the steam supply on the low-temperature side and decrease the steam supply on the high-temperature side; when the temperature difference is ≤35℃, the valves are kept at a low opening to control the cooling rate at approximately 2℃ / h.

[0071] During this stage, the waste heat recovered by the heat accumulator is used for steam supply throughout the process. The average opening degree of the valves in the upper and lower heat tracing branches is about 7%, and the temperature difference between the upper and lower walls of the steam drum is stable in the range of 22~28℃.

[0072] 4. Step S4: Switching Steam Source for Extended Shutdown The system detected that the pressure of the heat accumulator dropped to the switching threshold of 0.4MPa and executed the "open first, close later" switching logic: first, slowly open the auxiliary steam branch valve of the plant, and after the main pipe pressure stabilizes, slowly close the heat accumulator heat release branch valve.

[0073] After switching to auxiliary steam supply, the system continues to maintain zoned temperature control logic, and the drum wall temperature remains stable in the hot standby range of 160~170℃.

[0074] 5. Step S5: Thermal pre-charging before furnace start-up The system received the unit restart command from the DCS and set it to ignite after 60 minutes. The system automatically exited the temperature difference fine-tuning logic and synchronously increased the opening of the electric regulating valves of the upper and lower cylinder heat tracing branches to over 85%, thereby enhancing heat tracing and heat exchange throughout the entire area and uniformly increasing the overall temperature of the thick-walled steam drum.

[0075] After 60 minutes of pre-charging, the overall temperature of the thick wall of the steam drum increases uniformly, the temperature difference between the upper and lower walls is controlled within a reasonable range, and the residual temperature gradient is basically eliminated, creating optimal conditions for rapid hot start-up.

[0076] 6. Step S6: The system automatically exits after ignition. After successful boiler ignition, the system monitors the internal pressure of the steam drum in real time. When the pressure rises to 0.5 MPa, it determines that the steam drum's own heat generation capacity is sufficient, and gradually closes the upper and lower heat tracing branch valves and auxiliary steam valves. At the same time, it opens the pipeline drain bypass valve to drain the residual steam and condensate in the pipes. After all valves are closed and the drain is drained, the system automatically enters standby mode.

[0077] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. 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 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 rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler, characterized in that, This includes waste heat storage steam supply units, zoned heat tracing pipelines, and intelligent control systems; The waste heat storage steam supply unit includes a heat accumulator body, and parallel-connected high-flow-rate charging branch, low-flow-rate charging branch, heat release branch, and condensate level control components. The inlet of the high-flow-rate charging branch is connected to the steam exhaust pipe of the steam drum safety valve, the inlet of the low-flow-rate charging branch is connected to the saturated steam outlet of the steam drum, and the outlets of both the high-flow-rate charging branch and the low-flow-rate charging branch are connected to the bottom of the heat accumulator body. The heat release branch is led out from the top of the heat accumulator body, passes through a pressure stabilizing valve, and is connected in parallel with the plant auxiliary steam pipeline before entering the intelligent control system as a heat tracing source. The zoned heat tracing pipeline network is laid on the outer surface of the thick metal wall of the steam drum, and includes an independent upper cylinder first axial parallel pipe array and a lower cylinder second axial parallel pipe array; the two ends of the two pipe arrays respectively converge into a semi-circular steam inlet header and an outlet header, and the upper steam inlet header and the lower steam inlet header are each connected to an independent steam supply branch, and each branch is equipped with an electric regulating valve. The input end of the intelligent control system is connected to the steam drum wall temperature measuring point, the accumulator pressure / liquid level measuring point, and the pressure / flow measuring point of each pipeline, and the output end is connected to the valve motor of each branch. The system has a built-in standard shutdown cooling curve model and zonal control logic, which can realize the full-process control of cascade heating, zonal heat tracing temperature difference adjustment, steam source switching, rate protection and automatic start and stop of the system.

2. The rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to claim 1, characterized in that, The heat accumulator body is a pressure vessel with pre-filled deoxygenated saturated water inside. A steam distributor and a liquid level control valve are installed at the bottom, and a steam-water separator and an emergency pressure relief valve are installed at the top. The outside of the tank is covered with a high-temperature resistant insulation layer.

3. The rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to claim 1, characterized in that, The high-flow-rate heating branch is equipped with a large-diameter regulating valve and a throttling orifice plate for high-flow-rate exhaust steam heating during the rapid depressurization phase at the initial stage of shutdown; the low-flow-rate heating branch is equipped with a small-diameter electric regulating valve and a high-precision flow sensor for controllable low-flow-rate continuous heating and heat storage during the shutdown cooling phase.

4. The rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to claim 1, characterized in that, The heat tracing pipelines of the first axial parallel tube array and the second axial parallel tube array are laid flat along the steam drum axis; when encountering obstacles such as tube seats or lifting lugs on the surface of the steam drum, the heat tracing pipeline adopts a three-dimensional spatial bend bypass structure, and the inner diameter of the pipeline remains consistent before and after bypassing.

5. A rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to claim 1, characterized in that, Each group of outlet headers is equipped with an independent thermodynamic steam trap at its outlet. The outlets of the steam traps are collected into the main condensate drain line and connected to the unit's condensate recovery system. The steam trap and level regulating valve of the heat accumulator body are connected to the unit's condensate system to achieve full recovery of condensate during the heat tracing and heat storage process.

6. The rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to claim 1, characterized in that, The intelligent control system is based on a PLC controller, and is equipped with a data acquisition module and an execution output module. The data acquisition module is connected to the power plant's DCS system to read the steam drum wall temperature, pressure and accumulator operating parameters. The execution output module controls the on / off status and opening degree of each valve. The system receives remote shutdown and restart commands issued by the DCS and outputs execution signals for valve adjustment and audible and visual alarms.

7. A control method for a rapid start-up and shutdown regenerative zoned heat tracing and insulation system for a steam drum boiler according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1: Rapid depressurization and heat charging during initial shutdown: After the unit is disconnected and the boiler is shut down, the system receives the shutdown signal, fully opens the high-flow heat charging branch valves, and closes all heat tracing branches; High-temperature exhaust steam is throttled and depressurized before being sent to the heat accumulator for condensation and heat release, completing the initial large-capacity heat storage while meeting the boiler's rapid depressurization requirements. Step S2: Controllable Continuous Charging for Heat Storage in the Medium-Pressure Stage: When the steam drum pressure drops to the set value, the high-flow-rate charging branch is closed and switched to low-flow-rate charging branch operation; the opening of the charging valve is adjusted in a closed loop with the allowable cooling rate of the steam drum as the control target, and saturated steam in the steam drum is continuously extracted to supplement the heat storage; no active heating is activated in this stage, and correction is only made by adjusting the charging rate when the wall temperature difference exceeds the standard; when the accumulator pressure reaches the design upper limit or the steam drum temperature drops to the set value, all charging branches are closed. Step S3: Low-pressure stage waste heat release and heat tracing: When the steam drum wall temperature drops to the set value and the accumulator is fully charged, the system switches to heat release mode, opens the accumulator heat release branch to supply steam to the heat tracing network, and executes zoned temperature difference closed-loop control; by adjusting the opening of the upper and lower cylinder steam supply branches, the wall temperature difference is controlled within the safe threshold, and the cooling rate is controlled as needed or the hot standby temperature is maintained. Step S4: Steam source switching during extended shutdown: When the pressure inside the accumulator drops to the switching threshold, the heat release branch of the accumulator is shut off, and the system automatically switches to plant auxiliary steam supply to maintain the zoned temperature control logic and the hot standby temperature range. Step S5: Preheating before boiler start-up: Within the preset time before receiving the unit restart command, the system exits the temperature difference fine-tuning logic, uniformly increases the opening of the upper and lower cylinder steam supply branches, strengthens the heat tracing throughout the entire area, and uniformly increases the temperature of the thick wall of the steam drum and eliminates the residual wall temperature gradient. Step S6: Automatic system shutdown after ignition: After the boiler is successfully ignited and the internal pressure of the steam drum rises to the set shutdown threshold, all steam supply valves are gradually closed, the pipeline drain valves are opened to drain residual steam and water, and the heat tracing system shuts down and enters standby mode.

8. The control method according to claim 7, characterized in that, In step S2, the first safe temperature difference threshold is set to 35℃. When the temperature difference between the upper and lower walls exceeds the safe threshold, the wall temperature is corrected by adjusting the heat charging rate. Normal heat charging resumes after the temperature difference drops back to within 30℃. The heat storage termination condition is that the heat storage pressure reaches the design upper limit.

9. The control method according to claim 7, characterized in that, In step S3, the closed-loop control logic for zoned temperature difference is as follows: when the temperature difference between the upper and lower walls is greater than 35°C and the upper wall temperature is higher than the lower wall temperature, the opening of the lower cylinder steam supply branch is increased and the opening of the upper cylinder branch is simultaneously decreased; when the temperature difference is reversed, reverse regulation is performed; when the temperature difference is less than or equal to 35°C, the valve opening is adjusted as needed to control the cooling rate or maintain the target hot standby temperature.

10. The control method according to claim 7, characterized in that, In step S4, the steam source switching pressure threshold of the heat accumulator is 0.4 MPa; the normal hot standby temperature range is 160~180℃. When the standby time exceeds 48h, the insulation temperature is lowered to 120℃ to reduce energy consumption.

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