A flexible bed material adding system for a peak-shaving unit

Abstract

The application discloses a kind of peak-shaving unit bed material flexible adding system, belong to thermal power technology field, system contains bottom ash storehouse, drum screening machine, bucket elevator, limestone powder bin before furnace, switching tee valve, positive and negative rotation scraper conveyor, main bed feeding pipe, external bed feeding pipe, electric plugboard feeding valve, primary cold air sealing air pipe line, gas lock type feeder, hot secondary air sealing air pipe line, PLC control cabinet, material level meter, temperature transmitter, pressure transmitter and bin top purging device.Combination application drum screening machine, bucket elevator, limestone powder bin before furnace, switching tee valve, positive and negative rotation scraper conveyor are applied to CFB unit bed material addition in order of "screening→promotion→buffer / direct sending→two-way distribution".Realize multistage cooperation, old benefit and functional reuse of powder bin before furnace, two-way distribution based on positive and negative rotation scraper conveyor, multistage combined sealing for high-temperature positive pressure condition.

Description

Technical Field

[0001] This invention relates to the field of thermal power technology, and in particular to a flexible bed material addition system for peak-shaving units. Background Technology

[0002] In the power industry, in response to the national "dual carbon" target and to enhance the grid's capacity to absorb new energy sources, large thermal power units need to undergo "flexibility retrofitting." After each overhaul or emergency repair, circulating fluidized bed (CFB) units must have hundreds of tons of bed material added to the combustion chamber (main bed) and external heat exchanger (external bed) before they can be restarted.

[0003] Currently, there are three main similar existing technical solutions in the industry: Option 1: Manual / loader loading. A loader is used to scoop up the bed material and pour it directly into the furnace or the manhole of an external bed. This method is extremely inefficient (<10t / h), labor-intensive, and generates severe dust; it has been phased out.

[0004] Option 2: Tanker truck + pneumatic conveying solution. This involves using specialized tanker trucks to blow the bed material into the furnace using compressed air. However, the equipment is past its service life, pipelines are prone to detachment, posing significant safety hazards such as high-pressure injuries, and maintenance costs are high. The conveying capacity of a single tanker truck is only 10-15 t / h.

[0005] Option 3: Conventional scraper feeder solution. This involves using the existing scraper feeder on site to feed material from the silo to the furnace. The conveying capacity is typically below 20t / h, the equipment is prone to aging and failure (scraper jamming, guide rail wear), and it cannot simultaneously supply material to both the main feeder and the external feeder; adding material from both sides takes as long as 50-56 hours.

[0006] The relevant technologies have the following drawbacks: 1. Low efficiency in adding power, failing to meet the needs of deep peak shaving. Existing technologies (manual, pneumatic, conventional scraper conveyors) generally have a conveying capacity of less than 20 t / h, and their unreasonable equipment layout and cumbersome switching result in a single addition taking 50-100 hours. The direct consequence is that the preparation time from the completion of maintenance to ignition and startup of the unit far exceeds the 24-hour response time limit required by the power grid for deep peak shaving. In scenarios where new energy generation is booming and the power grid urgently needs rapid peak shaving from thermal power, these units can only "look at the grid with envy." Power plants not only face the grid's "two detailed rules" assessment (losses of tens of thousands of yuan per hour), but may also lose the opportunity to generate electricity during periods of high electricity prices in the spot market.

[0007] 2. Poor equipment reliability, frequent malfunctions, and high maintenance costs. Conventional scraper conveyors suffer from severe wear on guide rails, chain jamming, and aging and failure of tank trucks and pipelines. Root cause analysis: Existing technology is not specifically designed for the characteristics of bed materials (high hardness, high abrasiveness). The guide rails are made of ordinary materials, have an unreasonable structure, and lack a pre-screening process, exacerbating wear from large particles. Consequences: Annual maintenance and labor costs exceed 150,000 yuan. Core components need to be replaced every 6-8 months, requiring a 2-3 day downtime for replacement. More seriously, the conveying system frequently malfunctions during bed material addition, causing interruptions and forcing power plants to resort to manual shoveling, further extending the start-up cycle and creating a vicious cycle.

[0008] 3. Significant safety hazards and heavy reliance on manpower. Tanker truck transportation carries risks of high-pressure pipeline rupture and hose detachment causing injury; manual / forklift solutions pose risks of mechanical injury, high-temperature burns, and occupational diseases caused by dust. Furthermore, existing solutions require a large number of personnel (8-10 people) for 24-hour monitoring, operation, and troubleshooting, resulting in high labor costs and management challenges. Consequences: Power plant safety production faces significant pressure; during peak summer seasons, temporarily deploying a large number of personnel for bed material replenishment can disrupt other operation and maintenance work. Summary of the Invention

[0009] This invention provides a flexible bed material addition system for peak-shaving units, solving the core technical problems of low addition efficiency, long start-up cycles, poor equipment reliability, and significant safety hazards in existing circulating fluidized bed (CFB) unit bed material addition systems after maintenance or emergency repairs. It shortens the long downtime caused by bed material addition in large CFB units, reducing the overall addition time from the current 50-100 hours to less than 24 hours, thus meeting the grid's flexibility requirements for deep peak shaving of thermal power units.

[0010] According to one aspect of this disclosure, a flexible bed material addition system for a peak-shaving unit is provided, the system comprising: a bottom ash silo 1, a drum screen 2, a bucket elevator 3, a limestone powder silo in front of the furnace 4, a switching three-way valve 5, a forward and reverse scraper conveyor 6, a main bed feed pipe 7, an external bed feed pipe 8, an electric slide gate feed valve 9, a primary cold air sealing duct 10, an airlock type feeder 11, a hot secondary air sealing duct 12, a PLC control cabinet 13, a level gauge 14, a temperature transmitter 15, a pressure transmitter 16, and a silo top purging device 17. Among them, the limestone powder silo in front of the furnace 4 is used as a buffer silo for supplementing bed material during the bed material addition process; The bottom ash silo 1 serves as the source of bed material storage, and the drum screen 2 is installed below the discharge port of the bottom ash silo 1. The undersize material outlet of the drum screen 2 is connected to the feed inlet of the bucket elevator 3; the discharge outlet of the bucket elevator 3 is connected to the inlet of the switching three-way valve 5, and the two outlets of the three-way valve are respectively connected to the feed inlet of the top feed scraper of the bottom ash silo 1 and the feed inlet of the forward and reverse scraper conveyor 6. The bottom outlet of the limestone powder silo 4 in front of the furnace can be directly connected to the inlet of the forward and reverse scraper conveyor 6 via a chute, or it can be connected to the second line of the three-way valve via an external conveyor in the middle. The two ends of the forward and reverse scraper conveyor 6 are connected to the main bed feed pipe 7 and the external bed feed pipe 8, respectively. Electric slide gate feed valves 9 are installed at the ends of both feed pipes. A primary cold air sealing air duct 10 is connected to the electric slide gate feed valve 9. An airlock type feeder 11 is connected in series between the discharge port of the forward and reverse scraper conveyor 6 and the inlet of the primary cold air sealing air duct 10. A hot secondary air sealing air duct 12 is connected below the cold air sealing air ducts 10 of the main bed feed pipe 7 and the external bed feed pipe 8. The PLC control cabinet 13 is connected to the motors, frequency converters, level gauges 14, temperature transmitters 15, pressure transmitters 16 and the silo top purging device 17 of each device through cables.

[0011] In one possible implementation, the bottom ash silo 1 serves as the source of bed material storage, and its discharge port is switched via a drum screen 2: when slag discharge is required, the drum screen 2 directly discharges the bottom slag; when bed material supply is required, the qualified bed material is screened out and enters the subsequent equipment.

[0012] In one possible implementation, the forward and reverse scraper conveyor 6 includes a drive motor 61, a reducer 62, a head wheel 63, a tail wheel 64, a scraper chain 65, a trough 66, an NM400 wear-resistant guide rail 67, a main bed discharge port 68, and an external bed discharge port 69. The drive motor 61 is a variable frequency motor, which can realize forward and reverse rotation control. The reducer 62 is connected to the drive motor 61. The head wheel 63 and the tail wheel 64 are installed at both ends of the trough 66. The scraper chain 65 is wrapped around the head wheel 63 and the tail wheel 64. The bottom of the trough 66 is laid with NM400 wear-resistant guide rail 67. The guide rail adopts a combination structure of steel base and NM400 wear-resistant material. The cross section is convex and the straightness is ≤0.5mm / m. When the drive motor 61 rotates forward, the scraper chain 65 drives the bed material to move towards the main bed discharge port 68. When it rotates in reverse, the bed material moves towards the external bed discharge port 69.

[0013] In one possible implementation, the structure of the limestone powder silo in front of the furnace is as follows: The top of the bin is equipped with a bed material inlet pipe 42, the bottom of the bin is equipped with a bed material outlet pipe 44, the inner wall of the bin is lined with wear-resistant inner lining plate 45, and the top of the bin is equipped with a compressed air purging device 17.

[0014] In one possible implementation, the system further includes a high-temperature sealing device for the feed port: An electric slide gate feeder valve 9 is installed at the connection between the main bed feed pipe 7 or the external bed feed pipe 8 and the furnace 100. A cold air main valve 101 and a cold air pressure gauge 102 are installed on the primary cold air sealing air duct 10 and connected to the sealing air interface of the electric slide gate feed valve 9. Pressure data and temperature data are sent to the PLC control cabinet 13 through the installed pressure transmitter 16 and temperature transmitter 15.

[0015] In one possible implementation, the control flow of the system includes: Preparation and Switching: The operator selects "Bed Material Addition Mode" on the touch screen of PLC control cabinet 13. There are two operating modes: If "Cache First, Add Later" is selected, the three-way valve is switched to the channel connecting to the bottom ash silo 1, and the electric valve on the bottom bed material discharge pipe 44 of the limestone powder silo 4 in front of the furnace is automatically closed by the PLC, waiting for the material level signal monitored in real time by the material level gauge 14; If "Add Directly" is selected, the three-way valve is switched to the channel connecting to the forward and reverse scraper conveyor 6. Screening and Lifting: Open the slide valve of the bottom ash silo 1, the bed material falls into the drum screen 2, the drum screen 2 rotates, and the screened material falls into the feed port of the bucket elevator 3; large pieces of material are discharged from the end of the drum; the bucket elevator 3 starts, and the bed material is sent to the designated destination through the switching three-way valve 5 by centrifugal force; Buffering and Material Level Control: If the buffer mode is selected, on the side of the bottom ash silo, this function is generally used to repair the downstream equipment of the bucket elevator 3, empty the material inside the bucket elevator, and reduce the load on the equipment. At this time, the material level gauge 14 monitors the bed material height in the limestone powder silo 4 in front of the furnace in real time. When the material level reaches the high level set value, the PLC control cabinet (13) suspends the branch feeding and conveying equipment and keeps the bucket elevator 3 in a stopped state; when it is necessary to switch to the "bed material adding mode" again, the PLC automatically controls the priority to open the bottom bed material discharge pipe 44 of the limestone powder silo 4 in front of the furnace. The electric valve discharges material to the forward and reverse scraper conveyor 6. When the material level in the current limestone powder silo 4 drops to the low set value, the bucket elevator 3 is restarted, and the front limestone powder silo 4 and its branch supplementary bed material system are activated as needed. Bidirectional material distribution: According to the dispatching instructions, the operator selects "main bed addition" or "external bed addition". If the main bed addition is selected, the PLC control cabinet 13 controls the drive motor 61 of the forward and reverse scraper conveyor 6 to rotate forward, and the scraper chain 65 conveys the bed material to the main bed outlet 68. It reaches the electric slide plate feed valve 9 through the main bed feed pipe 7. At the same time, the cold air main valve 101 automatically opens to supply air to the lower part of the airlock feeder 11. The electric slide plate feed valve 9 opens and sends the bed material into the furnace 100 through the main bed feed pipe 7. If the external bed addition is selected, the drive motor 61 reverses, and the bed material is conveyed to the external bed outlet 69.

[0016] In one possible implementation, the control flow of the system further includes: Multi-stage sealing protection works continuously: In the first stage, the electric slide gate feeder 9 and the airlock feeder 11, together with the 15KPa sealing air provided by the primary cold air sealing air duct 10, form a positive pressure air seal at the feed port to prevent high-temperature flue gas from leaking out; the pressure transmitter 16 monitors the differential pressure in real time, and if the differential pressure is lower than 3KPa, it will alarm and adjust the valve opening. In the second stage, the airlock feeder 11 pushes the material to form a continuous material seal, blocking the hot flue gas from flowing back from the downstream. In the third stage, the hot secondary air sealing duct 12 injects 250°C hot air into the feed pipe, forming an air curtain inside the duct. The temperature transmitter 15 monitors the valve body temperature. If it exceeds 120°C, an alarm is triggered and the cold air flow is increased. Through the three-stage sealing, the system achieves fully sealed operation, and the equipment failure rate is reduced to less than 0.3 times per month.

[0017] In one possible implementation, the control flow of the system further includes: Once the required bed material is added, the operator issues a stop command, and the PLC control cabinet 13 automatically stops the machine in reverse order: first, the electric slide gate feed valve 9 is closed, and after a 30-second delay, the main cold air valve 101 is closed; the three-way valve is switched to the channel connecting to the bottom ash silo 1; then, after a 30-second delay, the forward and reverse scraper conveyor 6 is stopped; after a 10-second delay, the drum screen 2 is stopped; and finally, after a 30-second delay, the bucket elevator 3 is stopped; the silo top blowing device 17 is briefly activated again to remove residual bed material in the silo, and the system returns to standby mode.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. Corresponding to low addition efficiency: The total output of the system is ≥35t / h, which is 1.75 times that of the traditional scraper conveyor (20t / h). It can shorten the bed material addition time of a 300MW CFB unit from 50-100 hours to less than 24 hours (actually measured 22 hours), meeting the requirements of deep peak shaving of the power grid.

[0019] 2. In response to poor equipment reliability and high maintenance costs: NM400 wear-resistant guide rail (67), pre-screening (2) and wear-resistant liner (45) are adopted, the life of core components is extended by more than 1 times (≥18 months), the running resistance is reduced by 25%-30%, and the annual maintenance and labor costs are saved by more than 120,000 yuan.

[0020] 3. In response to safety hazards and high labor costs: The fully sealed automated operation requires only 1-2 people for remote monitoring, reducing manual input by more than 80% and eliminating safety hazards such as dust and high pressure.

[0021] The proposed solution, combining a bucket elevator and a reversible scraper conveyor, along with single three-way switching and multi-stage sealing, is a systematic solution addressing the pain points of existing technologies. It is highly integrated and original. While there are possible alternatives in some details—for example, the drum screen 2 can be replaced by a vibrating screen, but vibrating screens occupy a larger area and generate more noise; the airlock feeder 11 can be replaced by a double-layer flap airlock valve, but this results in intermittent discharge; and the electric slide gate feeder 9 can be replaced by a rotary feeder valve, but slide gate valves are more suitable for granular materials and offer better sealing. Attached Figure Description

[0022] Figure 1 This is a diagram of the overall system structure of the present invention.

[0023] Figure 2 This is a top view of the overall system of the present invention.

[0024] Figure 3 This is a structural diagram of a forward and reverse rotating scraper conveyor.

[0025] Figure 4 This is a top view of a forward and reverse rotating scraper conveyor.

[0026] Figure 5 This is a structural diagram of the scraper chain of a forward and reverse scraper conveyor.

[0027] Figure 6 For forward and reverse scraper conveyors from Figure 3 Schematic diagram of the front wheel in the AA direction.

[0028] Figure 7 For forward and reverse scraper conveyors from Figure 3 Schematic diagram of NM400 wear-resistant guide rail in the BB direction.

[0029] Figure 8 This is a schematic diagram of a high-temperature sealing device for the feed inlet.

[0030] Figure 9 This is a magnified view of a portion of the powder silo in front of the furnace.

[0031] The components include: 1. Bottom ash silo; 2. Drum screen; 3. Bucket elevator; 4. Furnace front limestone powder silo; 5. Three-way reversing valve; 6. Forward and reverse scraper conveyor; 7. Main bed feed pipe; 8. External bed feed pipe; 9. Electric slide gate feed valve; 10. Primary cold air sealing duct; 11. Airlock type feeder; 12. Hot secondary air sealing duct; 13. PLC control cabinet; 14. Level gauge; 15. Temperature transmitter; 16. Pressure transmitter; 17. Silo top purging device. 61. Drive motor; 62. Reducer; 63. Head wheel; 64. Tail wheel; 65. Scraper chain; 66. Tank; 67. NM400 wear-resistant guide rail; 68. Main bed discharge port; 69. External bed discharge port; 42. Bed material feed pipe (from switching three-way valve); 43; 44. Bed material discharge pipe (to forward and reverse scraper); 45. Wear-resistant lining plate inside the silo; 101. Cold air main valve; 102. Cold air pressure gauge; 100. Furnace (main bed or external bed). Detailed Implementation

[0032] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0033] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0034] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0035] The technical terms used in this application are as follows: Circulating fluidized bed (CFB) units: a highly efficient and clean coal-fired power generation technology. Its core is that solid materials (fuel and bed material) are fluidized and combusted under the action of airflow. It is widely used in 300MW and above thermal power units.

[0036] Bed material: During the start-up or operation of the CFB unit, a layer of inert solid particles (such as river sand, slag, quartz sand, etc.) is laid at the bottom of the combustion chamber. The particle size is usually required to be between 0.1-10mm, which is used for heat storage, stable combustion and heat transfer.

[0037] Main bed: The main combustion chamber of a CFB boiler, which is the primary area for fuel combustion and fluidization.

[0038] External bed: short for external heat exchanger, a component unique to large CFB units, used for heat exchange and temperature regulation of circulating ash, usually located on both sides of the boiler.

[0039] Deep peak shaving refers to the practice of thermal power units operating stably or starting and stopping rapidly under low load conditions according to grid demand, in order to balance the volatility of renewable energy generation such as wind power and photovoltaic power. Deep peak shaving requires that the time from unit startup to full-load grid connection typically does not exceed 24 hours.

[0040] Reversible scraper conveyor: A type of chain conveyor whose drive motor can rotate in both directions, thereby controlling the movement direction of the scraper chain. By changing the direction of rotation, a single device can feed material to two different discharge ports.

[0041] Airlock: A device that can continuously convey materials while also sealing off and isolating air or gas. Common forms include rotary feed valves or screw feeders, where a small gap is maintained between the rotor and the housing, relying on the material itself to form a material seal while preventing gas from flowing through.

[0042] NM400 wear-resistant material: a high-strength wear-resistant steel plate with a Brinell hardness of over 400HBW. It has good wear resistance and a certain degree of toughness and is often used in guide rails, liners and other components under high wear conditions.

[0043] PLC control: Programmable Logic Controller, used for the automated control of industrial equipment. This system uses a PLC to realize functions such as sequential start-up, speed regulation, and fault interlock shutdown of various devices.

[0044] A flexible bed material addition system for a thermal power deep peak-shaving unit includes a bottom ash silo 1, a drum screen 2, a bucket elevator 3, a limestone powder silo in front of the furnace 4, a switching three-way valve 5, a forward and reverse scraper conveyor 6, a main bed feed pipe 7, an external bed feed pipe 8, an electric slide gate feed valve 9, a primary cold air sealing duct 10, an airlock-type feeder 11, a hot secondary air sealing duct 12, a PLC control cabinet 13, a level gauge 14, a temperature transmitter 15, a pressure transmitter 16, and a silo top purging device 17. The bottom ash silo 1, originally used for storing boiler bottom ash, now serves as a bed material storage source. Its discharge port achieves functional switching via the drum screen 2—when ash discharge is needed, the drum screen 2 directly discharges the bottom ash; when bed material supply is needed, the screened qualified bed material enters subsequent equipment. The limestone powder silo 4 in front of the furnace is used as a buffer silo for supplementing bed material during bed material addition; it is equipped with a bed material inlet pipe 42 at the top and a bed material outlet pipe 44 at the bottom. The silo top blowing device 17 is used to blow away residual dust in the silo after the addition is completed.

[0045] The rotary drum screen 2 is installed below the discharge port of the bottom lime silo 1. It has a drive power of 5.5kW, a screening efficiency of ≥90%, and a processing capacity of ≥40t / h, ensuring that the bed material particle size is controlled within the range of 0.1-10mm. The undersize outlet of the rotary drum screen 2 is connected to the feed inlet of the bucket elevator 3. The bucket elevator 3 has a drive power of 18.5kW, a lifting capacity of ≥35t / h, and a lifting height of up to 40m. The discharge port of the bucket elevator 3 is connected to the inlet of a switching three-way valve 5. The two outlets of this three-way valve are connected to the top feed inlet of the limestone powder silo 4 in front of the furnace, and the feed inlet of the forward and reverse scraper conveyor 6, respectively. By switching the three-way valve 5, the bed material can be either first fed into the limestone powder silo 4 in front of the furnace for buffering, or directly supplied to the forward and reverse scraper conveyor 6. The bottom outlet of the limestone powder silo 4 in front of the furnace can be directly connected to the inlet of the forward and reverse scraper conveyor (6) via a chute, or it can be connected to the second path of the three-way valve via an external conveyor in the middle (to avoid excessive conveying distance of a single forward and reverse scraper conveyor and improve the system's service life). The forward and reverse scraper conveyor 6 has a driving power of 15kW, a conveying capacity of 35t / h, and an operating resistance coefficient of ≤0.18. Its two ends are connected to the main bed feed pipe 7 and the external bed feed pipe 8, respectively. Electric slide gate feed valves 9 are installed at the ends of both feed pipes. A primary cold air sealing air duct 10 is connected to the electric slide gate feed valve 9, with an air volume of about 300Nm³ / h and an air pressure of 15KPa. An airlock type feeder 11 is connected in series between the outlet of the forward and reverse scraper conveyor 6 and the inlet of the primary cold air sealing air duct 10. A hot secondary air sealing duct 12 is connected below the cold air sealing duct 10 of the main bed feed pipe 7 and the external bed feed pipe 8. The air volume is about 1100 Nm³ / h, the air pressure is 10 kPa, and the air temperature is 250℃. The PLC control cabinet 13 is connected to the motors, frequency converters, level gauges 14, temperature transmitters 15, pressure transmitters 16, and silo top purging devices 17 of each device via cables.

[0046] The specific structure of the forward and reverse scraper conveyor 6 is shown in the attached figure. Figure 2 As shown, it includes a drive motor 61, a reducer 62, a head wheel 63, a tail wheel 64, a scraper chain 65, a trough 66, NM400 wear-resistant guide rails 67, a main bed discharge port 68, and an external bed discharge port 69. The drive motor 61 is a variable frequency motor, capable of forward and reverse rotation control. The reducer 62 is connected to the drive motor 61. The head wheel 63 and tail wheel 64 are installed at both ends of the trough 66, and the scraper chain 65 is wrapped around the head wheel 63 and tail wheel 64. The bottom of the trough 66 is covered with NM400 wear-resistant guide rails 67. The guide rails adopt a combination structure of steel base and NM400 wear-resistant material, with a convex cross-section and a straightness ≤0.5mm / m. When the drive motor 61 rotates forward, the scraper chain 65 drives the bed material to move towards the main bed discharge port 68; when rotating in reverse, the bed material moves towards the external bed discharge port 69.

[0047] The renovation and reuse of existing limestone powder silo 4 in front of the furnace, such as Figure 3As shown. A bed material inlet pipe 42 is installed at the top of the bin, and a bed material outlet pipe 44 is installed at the bottom of the bin. The inner wall of the bin is lined with wear-resistant inner lining plate 45, with a thickness of 10mm and material 16Mn. A compressed air purging device 17 is installed on the top of the bin.

[0048] High-temperature sealing device for feed port, such as Figure 4 As shown. An electric slide gate feed valve 9 is installed at the connection point between the main bed feed pipe 7 or the external bed feed pipe 8 and the furnace 100. A main cold air valve 101 and a cold air pressure gauge 102 are installed on the primary cold air sealing air duct 10 and connected to the sealing air interface of the electric slide gate feed valve 9. A pressure transmitter 16 and a temperature transmitter 15 are installed at appropriate locations. The furnace back pressure is 10 kPa, the flue gas temperature is 950°C, and the sealing air pressure is 15 kPa, ensuring a pressure difference ≥ 5 kPa.

[0049] When the system is in operation, preparation and switching are performed first. The operator selects "Bed Material Addition Mode" on the touch screen of PLC control cabinet 13, and the system automatically sets the switching three-way valve 5 to the required position. There are two operating modes: if "Buffer First, Add Later" is selected, the three-way valve is switched to the channel connecting to the bottom ash silo 1, and the electric valve on the bottom bed material discharge pipe 44 of the limestone powder silo 4 in front of the furnace is automatically closed by PLC control, waiting for the material level signal monitored in real time by the level gauge 14; if "Direct Addition" is selected, the three-way valve is switched to the channel connecting to the forward and reverse scraper conveyor 6. The silo top blowing device 17 can be turned on briefly (about 10 seconds) before adding begins to remove residual dust in the silo.

[0050] The material is then screened and lifted. The gate valve of the bottom ash silo 1 is opened, and the bed material falls into the drum screen 2. The drum screen 2 rotates, screening out qualified fine materials with a particle size ≤10mm, which fall into the feed inlet of the bucket elevator 3; larger pieces of material are discharged from the end of the drum. The bucket elevator 3 starts, using centrifugal force to send the bed material to the designated destination via the switching three-way valve 5. The overall conveying capacity reaches over 35t / h.

[0051] In the buffering and level control stage, if the buffering mode is selected, this function is generally used on the bottom ash silo side for maintenance of downstream equipment of bucket elevator 3, emptying the accumulated material inside the bucket elevator, and reducing the load on the equipment. At this time, the level gauge 14 monitors the bed material height in the limestone powder silo 4 in front of the furnace in real time. When the material level reaches the high level set value (80% full), the PLC control cabinet 13 pauses the branch feeding conveyor and keeps the bucket elevator 3 in a stopped state. When it is necessary to switch back to the "bed material addition mode", the electric valve on the bottom bed material discharge pipe 44 of the limestone powder silo 4 in front of the furnace is opened first through PLC automatic control to discharge the material to the forward and reverse scraper conveyor 6. When the material level of the current limestone powder silo 4 drops to the low level set value (10% full), the bucket elevator 3 is restarted, and the front limestone powder silo 4 and its branch supplement bed material system are activated as needed. When feeding material in both directions, the operator selects "Main Bed Addition" or "External Bed Addition" according to the scheduling instructions. If Main Bed Addition is selected, the PLC control cabinet 13 controls the drive motor 61 of the forward and reverse scraper conveyor 6 to rotate forward, and the scraper chain 65 conveys the bed material towards the main bed outlet 68, reaching the electric slide gate feed valve 9 via the main bed feed pipe 7. At the same time, the main cold air valve 101 automatically opens, supplying air to the lower part of the airlock feeder 11. The electric slide gate feed valve 9 opens, sending the bed material into the furnace 100 through the main bed feed pipe 7. If External Bed Addition is selected, the drive motor 61 reverses, and the bed material is conveyed towards the external bed outlet 69. Actual modification verification shows that after adopting this system, the total bed material addition time for a single 300MW CFB unit can be shortened from the original 50-100 hours to less than 22 hours.

[0052] Multi-stage sealing protection operates continuously. In the first stage, the electric slide gate feeder 9 and the airlock-type feeder 11, together with the 15 kPa sealing air supplied by the primary cold air sealing duct 10, form a positive pressure air seal at the feed inlet, preventing the leakage of high-temperature flue gas. The pressure transmitter 16 monitors the differential pressure in real time; if the differential pressure is lower than 3 kPa, an alarm is triggered and the valve opening is adjusted. In the second stage, the airlock-type feeder 11 pushes the material to form a continuous material seal, blocking the backflow of hot flue gas from downstream. In the third stage, the hot secondary air sealing duct 12 injects 250°C hot air into the feed pipe, forming an air curtain within the duct. The temperature transmitter 15 monitors the valve body temperature; if it exceeds 120°C, an alarm is triggered and the cold air flow rate is increased. Through this three-stage sealing, the system achieves fully sealed operation, reducing the equipment failure rate to less than 0.3 times per month.

[0053] Once the required bed material is added, the operator issues a shutdown command. The PLC control cabinet 13 automatically shuts down in reverse sequence: first, the electric slide gate feed valve 9 is closed; after a 30-second delay, the main cold air valve 101 is closed; the three-way valve is switched to the channel connecting to the bottom ash silo 1; then, after a 30-second delay, the forward and reverse scraper conveyor 6 stops; after a 10-second delay, the drum screen 2 stops; and finally, after a 30-second delay, the bucket elevator 3 stops. The silo top blowing device 17 briefly restarts to remove residual bed material from the silo, and the system returns to standby mode. With the core components made of NM400 wear-resistant material, the service life is extended from 6-8 months to over 18 months, saving over 120,000 yuan in annual maintenance and labor costs, and reducing labor input by 80%.

[0054] The main points of protection in this application are as follows: 1. Multi-stage collaborative conveying system structure: The drum screen 2, bucket elevator 3, limestone powder silo in front of the furnace 4, switching three-way valve 5, and forward and reverse scraper conveyor 6 are combined in the order of "screening → lifting → buffering / direct delivery → bidirectional distribution" and applied to the bed material addition of the CFB unit.

[0055] 2. Reuse and functional reuse structure of the furnace front powder silo: By installing switching three-way valves (5a, 5b) on the feed pipe and discharge pipe of the original limestone powder silo 4 respectively, and in conjunction with the silo top purging device 17, the same silo can switch between "limestone powder conveying" and "bed material buffering" modes, realizing multiple uses of one silo.

[0056] 3. Bidirectional distribution structure based on forward and reverse scraper conveyor: A scraper conveyor 6 with a drive motor that can rotate forward and reverse is adopted. The main bed discharge port 68 and the external bed discharge port 69 are respectively set at both ends of the trough. By changing the direction of the motor, the material can be fed to the main bed or the external bed.

[0057] 4. Multi-stage combined sealing device for high temperature and positive pressure conditions: including ① electric slide gate feeder 9 working with primary cold air sealing duct 10 to form an air seal; ② airlock type feeder 11 using material seal to block flue gas backflow; ③ hot secondary air sealing duct 12 forming an air curtain inside the duct.

[0058] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A flexible bed material addition system for peak-shaving units, characterized in that, The system includes: bottom ash silo (1), drum screen (2), bucket elevator (3), limestone powder silo in front of furnace (4), switching three-way valve (5), forward and reverse scraper conveyor (6), main bed feed pipe (7), external bed feed pipe (8), electric slide plate feed valve (9), primary cold air sealing air duct (10), airlock type feeder (11), hot secondary air sealing air duct (12), PLC control cabinet (13), level gauge (14), temperature transmitter (15), pressure transmitter (16), and silo top purging device (17). Among them, the limestone powder silo in front of the furnace (4) is used as a buffer silo for supplementing bed material during the bed material addition period; The bottom ash silo (1) serves as the source of bed material storage, and the drum screen (2) is installed below the discharge port of the bottom ash silo (1); The undersize outlet of the drum screen (2) is connected to the feed inlet of the bucket elevator (3); the discharge outlet of the bucket elevator (3) is connected to the inlet of the switching three-way valve (5), and the two outlets of the three-way valve are respectively connected to the feed inlet of the top feed scraper of the bottom ash silo (1) and the feed inlet of the forward and reverse scraper conveyor (6). The bottom outlet of the limestone powder silo (4) in front of the furnace can be directly connected to the feed inlet of the forward and reverse scraper conveyor (6) through a chute, or it can be connected to the second line of the three-way valve through an external conveyor in the middle. The two ends of the forward and reverse scraper conveyor (6) are connected to the main bed feed pipe (7) and the external bed feed pipe (8), respectively. Electric slide gate feed valves (9) are installed at the ends of the two feed pipes. A primary cold air sealing air duct (10) is connected to the electric slide gate feed valve (9). An airlock feeder (11) is connected in series between the discharge port of the forward and reverse scraper conveyor (6) and the inlet of the primary cold air sealing air duct (10). A hot secondary air sealing air duct (12) is connected below the cold air sealing air duct (10) of the main bed feed pipe (7) and the external bed feed pipe (8). The PLC control cabinet (13) is connected to the motor, frequency converter, level gauge (14), temperature transmitter (15), pressure transmitter (16) and silo top purging device (17) of each device through cables.

2. The flexible bed material addition system for peak-shaving units according to claim 1, characterized in that, in, The bottom ash silo (1) serves as the source of bed material storage. Its discharge port is switched through the drum screen (2): when slag needs to be discharged, the drum screen (2) directly discharges the bottom slag; when bed material needs to be supplied, the qualified bed material screened out enters the subsequent equipment.

3. The flexible bed material addition system for peak-shaving units according to claim 1, characterized in that, The forward and reverse scraper conveyor (6) includes a drive motor (61), a reducer (62), a head wheel (63), a tail wheel (64), a scraper chain (65), a trough (66), an NM400 wear-resistant guide rail (67), a main bed discharge port (68), and an external bed discharge port (69). Among them, the drive motor (61) is a variable frequency motor, which can realize forward and reverse control. The reducer (62) is connected to the drive motor (61). The head wheel (63) and tail wheel (64) are installed at both ends of the trough (66). The scraper chain (65) is wrapped around the head wheel (63) and tail wheel (64). The bottom of the trough (66) is laid with NM400 wear-resistant guide rail (67). The guide rail adopts a combination structure of steel base and NM400 wear-resistant material. The cross section is convex and the straightness is ≤0.5mm / m. When the drive motor (61) rotates forward, the scraper chain (65) drives the bed material to move towards the main bed outlet (68). When it rotates in reverse, the bed material moves towards the external bed outlet (69).

4. The flexible bed material addition system for peak-shaving units according to claim 1, characterized in that, The structure of the limestone powder silo (4) in front of the furnace is as follows: The top of the bin is equipped with a bed material inlet pipe (42), the bottom of the bin is equipped with a bed material outlet pipe (44), the inner wall of the bin is covered with wear-resistant lining plate (45), and the top of the bin is equipped with a compressed air purging device (17).

5. The flexible bed material addition system for peak-shaving units according to claim 1, characterized in that, The system also includes a high-temperature sealing device for the feed inlet: An electric slide gate feeder valve (9) is installed at the connection between the main bed feed pipe (7) or the external bed feed pipe (8) and the furnace (100). A cold air main valve (101) and a cold air pressure gauge (102) are installed on the primary cold air sealing air duct (10) and connected to the sealing air interface of the electric slide gate feed valve (9). The pressure data and temperature data are sent to the PLC control cabinet (13) through the installed pressure transmitter (16) and temperature transmitter (15).

6. The flexible bed material addition system for peak-shaving units according to claim 1, characterized in that, The control flow of the system includes: Preparation and switching: The operator selects "bed material addition mode" on the touch screen of the PLC control cabinet (13). There are two operating modes: If "buffer first and then add" is selected, the three-way valve is switched to the channel connecting the bottom ash silo (1), and the electric valve on the bottom bed material discharge pipe (44) of the limestone powder silo (4) in front of the furnace is automatically closed by the PLC, and the material level signal monitored in real time by the material level gauge (14) is waited for. If "direct addition" is selected, the three-way valve is switched to the channel connecting the forward and reverse scraper (6). Screening and Lifting: Open the slide valve of the bottom ash silo (1), and the bed material falls into the drum screen (2). The drum screen (2) rotates, and the screened material falls into the feed port of the bucket elevator (3). Large pieces of material are discharged from the end of the drum. The bucket elevator (3) is started, and the bed material is sent to the designated destination by centrifugal force through the switching three-way valve (5). Buffer and level control: If the buffer mode is selected, on the side of the bottom lime silo, this function is generally used to repair the downstream equipment of the bucket elevator (3), empty the accumulated material inside the bucket elevator, and reduce the load on the equipment; at this time, the level gauge (14) monitors the bed material height in the limestone powder silo (4) in front of the furnace in real time. When the material level reaches the high level set value, the PLC control cabinet (13) pauses the branch feeding conveyor and keeps the bucket elevator (3) in a stopped state; when it is necessary to switch to the "bed material addition mode" again, the electric valve on the bottom bed material discharge pipe (44) of the limestone powder silo (4) in front of the furnace is opened first through the automatic control of the PLC to discharge the material to the forward and reverse scraper conveyor (6). When the material level of the current limestone powder silo (4) drops to the low level set value, the bucket elevator (3) is restarted and the front limestone powder silo (4) and its branch supplement bed material system are activated as needed; Two-way material distribution: According to the scheduling instructions, the operator selects "add main bed" or "add external bed". If the main bed is selected, the PLC control cabinet (13) controls the drive motor (61) of the forward and reverse scraper conveyor (6) to rotate forward. The scraper chain (65) conveys the bed material to the main bed outlet (68) and reaches the electric slide plate feed valve (9) through the main bed feed pipe (7). At the same time, the cold air main valve (101) automatically opens to supply air to the lower part of the airlock feeder (11). The electric slide plate feed valve (9) opens and sends the bed material into the furnace (100) through the main bed feed pipe (7). If the external bed is selected, the drive motor (61) rotates in reverse and the bed material is conveyed to the external bed outlet (69).

7. A flexible bed material addition system for peak-shaving units according to claim 6, characterized in that, The control flow of the system also includes: Multi-stage sealing protection works continuously: First stage, the electric slide gate feeder (9) and the airlock feeder (11) work together with the 15KPa sealing air provided by the primary cold air sealing air duct (10) to form a positive pressure air seal at the feed port to prevent high temperature flue gas from leaking out; the pressure transmitter (16) monitors the differential pressure in real time, and if the differential pressure is lower than 3KPa, it will alarm and adjust the valve opening; The second stage is a lock-type feeder (11) that pushes materials to form a continuous material seal, blocking the hot flue gas that flows back from the downstream. The third stage, the hot secondary air sealing duct (12) injects 250°C hot air into the feed pipe to form an air curtain in the duct. The temperature transmitter (15) monitors the valve body temperature. If it exceeds 120°C, it will alarm and increase the cold air flow. Through the three-stage sealing, the system achieves fully sealed operation and the equipment failure rate is reduced to less than 0.3 times per month.

8. A flexible bed material addition system for peak-shaving units according to claim 6, characterized in that, The control flow of the system also includes: After the bed material is added to the required level, the operator issues a stop command, and the PLC control cabinet (13) automatically stops the machine in reverse order: first, the electric slide gate feed valve (9) is closed, and after a delay of 30 seconds, the main cold air valve (101) is closed; the three-way valve is switched to the channel connecting the bottom ash silo (1); then the forward and reverse scraper machine (6) is stopped after a delay of 30 seconds; the drum screen machine (2) is stopped after a delay of 10 seconds; and finally the bucket elevator (3) is stopped after a delay of 30 seconds; the top cleaning device (17) is turned on briefly to remove the residual bed material in the silo, and the system returns to standby status.

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