A near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit

Abstract

The present application belongs to the technical field of peak regulation of thermal power units, and particularly relates to a near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit. The method comprises a deep regulation preparation stage, a deep regulation stage and a post-deep regulation recovery stage; in the deep regulation preparation stage, bed material replacement and overall soot blowing are performed, and various protections are exited; in the deep regulation stage, the unit power is controlled to enter the range of deep regulation, and the boiler and auxiliary equipment are gradually controlled to be shut down, the steam turbine unit is reduced to a set value, and the steam turbine unit is operated with near-zero power output; in the post-deep regulation recovery stage, the boiler and auxiliary equipment are restarted, the steam turbine unit is gradually increased in power output, and the thermal power unit is recovered to a normal operating state. The present application can adapt to the peak regulation demand of the power grid, ensure the unit to be operated at a low load for 1-2 hours without being disconnected from the grid during the peak period of new energy power generation, and high-levelly accommodate new energy, and also can obtain deep peak regulation compensation to meet the profit requirement of the power plant.

Description

Technical Field

[0001] The present invention belongs to the technical field of peak regulation of thermal power units, and in particular relates to a near-zero-depth peak regulation control method based on a subcritical circulating fluidized bed unit. Background Art

[0002] In recent years, with the rapid development of renewable energy generation, the power system has experienced dual peaks and peaks, as well as randomness on both sides. This has had a significant impact on the system. To address the instability of renewable energy generation and the volatility of extreme weather, thermal power plants urgently need a method for deep peak regulation.

[0003] Based on the range of peak load, thermal power generation peak shaving can generally be categorized as basic peak shaving and deep peak shaving. Given the current high demand for grid peak shaving, basic peak shaving is no longer applicable. Commonly used technologies for deep peak shaving of thermal power generation units include deep load variation, thermal-electric decoupling, and unit start-stop peak shaving. Using start-stop peak shaving for thermal power generation units is relatively costly, and frequent starts and stops can shorten the unit's lifespan. Thermal-electric decoupling peak shaving is only suitable for use with extraction steam units during the heating season and has certain limitations. Therefore, deep load variation peak shaving has become the primary method for peak shaving of thermal power generation units.

[0004] Compared to traditional pulverized coal boilers, circulating fluidized bed (CFB) boilers naturally offer greater operational flexibility than traditional pulverized coal boilers. Furthermore, CFB boiler units offer ample heat storage capacity. Leveraging this high heat storage capacity, the unit can be started directly with coal when load increases are needed, significantly reducing startup costs. By implementing high-parameter peak-shaving, the boiler can be shut down without shutting down the generator or disconnecting the generator, achieving deep peak-shaving at near-zero load, creating greater room for renewable energy consumption. This allows the unit to quickly resume operation when renewable energy load decreases, rapidly responding to grid load increases and significantly improving peak-shaving flexibility. Therefore, during the CFB boiler's simmering and peak-shaving process, improving the safety and convenience of both peak-shaving and peak-raising operations, and ensuring safe and stable operation during this period, are key challenges for CFB units participating in grid-wide deep peak-shaving. Summary of the Invention

[0005] In order to further ensure the safe and stable operation of the circulating fluidized bed unit during the furnace stewing and fire suppression process, the present invention decomposes the near-zero peak regulation period of the thermal power unit into a pre-deep regulation preparation stage, a deep regulation stage and a post-deep regulation recovery stage; in the pre-deep regulation preparation stage, bed material replacement and comprehensive soot blowing are carried out, and various protections are exited; in the deep regulation stage, the unit power is controlled to enter the deep regulation range, and the boiler and its auxiliary equipment are gradually controlled to stop operating, the turbine unit is reduced to the set value, and the turbine unit operates with a load of near zero output; in the post-deep regulation recovery stage, the boiler and its auxiliary equipment are restarted, and the turbine unit gradually increases its output, so that the thermal power unit returns to normal operating state.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit, the method comprising a pre-deep regulation preparation stage, a deep regulation stage, and a post-deep regulation recovery stage.

[0008] The pre-deep adjustment preparation stage includes the following operations in sequence: bed material replacement; full soot blowing; control of boiler bed pressure; starting the fuel oil system for circulating standby; exiting the unit for protection; switching the auxiliary steam system steam source and the auxiliary power system to the adjacent unit; shutting down the furnace desulfurization system and closing the compressed air pneumatic door;

[0009] The deep adjustment stage includes the following operations in sequence: controlling the unit load and boiler bed temperature; shutting down the coal feeding and slag discharge systems; closing the superheating and reheating desuperheating water valves; controlling the primary air flow rate and performing a large air volume disturbance on the boiler; shutting down the primary and secondary fans and one induced draft fan when monitoring the bed temperature to show a downward trend and the flue gas oxygen content rises to a preset threshold; shutting down all induced draft fans when monitoring the CO content to drop to the lowest; switching the turbine from sequence valve to single valve operation; controlling the main steam pressure and main steam temperature; reducing the unit load; starting the air cooling fan to control the unit back pressure; adjusting the feed water pump output and the water supply valve opening to control the change of the steam drum water level; opening the economizer recirculation door when the steam drum stops supplying water; adjusting the induced draft fan inlet and outlet plug-in doors and the primary and secondary air dampers to control the furnace negative pressure; stopping the deep adjustment when the key parameters trigger the safety boundary and entering the recovery stage;

[0010] The recovery phase after deep adjustment includes the following operations in sequence: opening each air and smoke damper to establish an air channel; checking the CO content in the air chamber, return feeder air chamber and economizer inlet, and starting the induced draft fan when it is not within the preset threshold; after monitoring the CO content and finding no change, starting the primary and secondary fans; after adjusting the boiler primary air volume to the minimum fluidizing air volume, starting the coal feeder, adopting a point-to-point coal feeding method, and continuing to feed coal after confirming that the coal can be burned, gradually increasing the coal feed amount to normal load, and performing the remaining operations in accordance with grid-connected operations.

[0011] Furthermore, in the pre-deep adjustment preparation stage, the boiler bed pressure is controlled at 7.5-8Kpa to ensure that the sum of the boiler bed pressure and the furnace differential pressure is not less than 8.5Kpa; the exit unit protection includes exiting the large interlocking protection of the boiler electric load, the boiler exiting the total air volume protection, and the boiler exiting the minimum fluidizing air volume protection.

[0012] Furthermore, in the deep adjustment stage, the unit load is controlled to 130-150MW, and the boiler bed temperature is above 900℃; the preset threshold of the flue gas oxygen content is 8%; the main steam pressure is controlled to be no more than 16Mpa, the variation range of the main steam pressure is less than 0.05MPa, and the main steam temperature is not lower than 538±5℃; the unit load is reduced to 3-5MW; the unit back pressure is controlled to 4-5KPa; the steam drum water level is controlled to ±50mm; the furnace negative pressure is controlled to be within 500Pa; key parameters include boiler heat storage, main steam temperature, main steam pressure, reheat steam temperature, bed temperature and bed pressure.

[0013] Furthermore, in the recovery phase after deep adjustment, the preset threshold value of the CO content is 12.5-74.2%.

[0014] Furthermore, in the recovery stage after deep adjustment, if no ignition occurs when coal feeding is started and the bed temperature drops rapidly, the primary air volume is immediately reduced to the minimum fluidizing air volume, and an oil gun is used to assist combustion; the slag cooler is started to reduce the bed pressure to 6KPa; and the unit ignition and startup operations are carried out.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention utilizes the characteristics of the circulating fluidized bed unit and implements a high-parameter pressure-fire peak-shaving method. The furnace is shut down without stopping the unit and the generator is not disconnected. The minimum load and near-zero depth peak-shaving are used to give more space for the consumption of new energy. After the grid peak-shaving, the unit can quickly return to the normal operating level, reducing the operation time when the unit is connected to the grid and greatly improving flexibility. This method can effectively reduce the operating steps of the operating personnel, greatly reduce the possibility of misoperation, and improve the safety and convenience of the pressure-fire and fire-raising operation of the circulating fluidized bed boiler during the furnace-simmering pressure-fire process, thereby ensuring the safe and stable operation of the unit during the pressure-fire peak-shaving period.

[0017] (2) The present invention can adapt to the peak-shaving demand of the power grid. During the peak period of renewable energy power generation, it can ensure that the unit can operate at low load for 1-2 hours without being disconnected from the grid, thereby absorbing renewable energy at a high level. At the same time, it can also obtain deep peak-shaving compensation to meet the profit requirements of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 3D schematic diagram of the circulating fluidized bed unit of the present invention;

[0019] Figure 2 This is a sequential control logic diagram for the preparatory stage before deep adjustment of the present invention;

[0020] Figure 3 This is a sequential control logic diagram for the deep adjustment stage of the present invention;

[0021] Figure 4 This is a sequential control logic diagram of the recovery stage after deep adjustment of the present invention. DETAILED DESCRIPTION

[0022] To facilitate understanding of the present invention, the present invention will be described more fully below.

[0023] Example

[0024] A deep adjustment study was conducted on a 300MW subcritical CFB boiler (DG1070 / 17.4-Ⅱ2 boiler) in a power plant in Shanxi. Figure 1 As shown, this boiler features single-stage reheating, a single furnace, an open-air layout, balanced ventilation, and an all-steel frame structure. The main body of the boiler consists of a membrane-type water-cooled hearth, three cooling cyclone separators, and an aft shaft. The aft shaft houses the superheater, reheater, and economizer. A return feeder is located beneath the cyclone separator. The front wall of the furnace is equipped with six panels each of medium-temperature superheater tube panels, high-temperature superheater tube panels, and high-temperature reheater tube panels, while the rear wall houses two water-cooled evaporator panels. Four belt coal feeders are located at the front of the boiler. The bottom of the furnace is a water-cooled plenum, flanked by primary and secondary air outlets for the air preheater. The lower duct houses an underbed duct igniter, and six drum-type slag coolers are located beneath the rear water-cooled wall of the furnace.

[0025] like Figures 2 to 4 As shown, a near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit includes a pre-deep regulation preparation stage, a deep regulation stage, and a post-deep regulation recovery stage, wherein:

[0026] The preparatory stage before deep adjustment includes the following operations in sequence: bed material replacement; full soot blowing; controlling the boiler bed pressure to 7.5-8KPa, ensuring that the sum of the boiler bed pressure and the furnace differential pressure is not less than 8.5KPa; starting the fuel oil system for circulating standby; disabling the large interlocking protection of the boiler and the electric load, the total air volume protection of the boiler, and the minimum fluidizing air volume protection of the boiler; cutting the steam source of the auxiliary steam system and the auxiliary power system to the adjacent unit; shutting down the desulfurization system in the furnace and closing the compressed air pneumatic door;

[0027] The deep regulation stage comprises the following operations in sequence: controlling the unit load to be 130-150 MW, the boiler bed temperature to be above 900 DEG C; stopping the coal feeding and slag discharging system; closing the superheating and reheating desuperheating water valve; controlling the primary air flow, and performing a primary large air flow disturbance to the boiler; when the bed temperature has a downward trend and the flue gas oxygen content rises to 8%, stopping the primary air fan, the secondary air fan and one induced draft fan; when the CO content decreases to the minimum, stopping all induced draft fans; switching the steam turbine from the sequence valve to the single valve operation; controlling the main steam pressure to be not more than 16 MPa, the variation range of the main steam pressure to be less than 0.05 MPa, and the main steam temperature to be not less than 538 DEG C ± 5 DEG C; reducing the unit load to 3-5 MW; starting the air cooling fan, and controlling the unit back pressure to be 4-5 KPa; adjusting the water pump output and the water regulating door opening degree, and controlling the steam drum water level to be ± 50 mm; when the steam drum stops feeding water, opening the economizer recirculation door; adjusting the induced draft fan inlet and outlet flapper door and the primary and secondary air dampers, and controlling the furnace negative pressure to be within 500 Pa; when the boiler heat storage, the main steam temperature, the main steam pressure, the reheated steam temperature, the bed temperature and the bed pressure trigger the safety boundary, stopping the deep regulation and entering the recovery stage;

[0028] The recovery stage after the deep regulation comprises the following operations in sequence: opening the air flaps, and establishing the air passage; checking the CO content of the air chamber, the return feeder air chamber and the economizer inlet; when the CO content is not within 12.5-74.2%, starting the induced draft fan; after monitoring the CO content without change, starting the primary and secondary air fans; after adjusting the primary air flow of the boiler to the minimum fluidization air flow, starting the coal feeder, adopting the point coal feeding mode, confirming that the coal can be combusted, continuously feeding the coal, gradually increasing the coal feeding amount to the normal load, and performing the remaining operations according to the grid connection operation. If the coal does not ignite and the bed temperature rapidly decreases when the coal is started, the primary air flow is reduced to the minimum fluidization air flow, and the oil gun is started to assist combustion; the cold slag device is started to reduce the bed pressure to 6 KPa; and the unit ignition starting operation is performed.

[0029] The above-described embodiments only express the specific implementation cases of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation on the scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit, comprising a pre-deep regulation preparation stage, a deep regulation stage, and a post-deep regulation recovery stage, characterized in that: The pre-deep adjustment preparation stage includes the following operations in sequence: bed material replacement; full soot blowing; control of boiler bed pressure; starting the fuel oil system for circulating standby; exiting the unit for protection; switching the auxiliary steam system steam source and the auxiliary power system to the adjacent unit; shutting down the furnace desulfurization system and closing the compressed air pneumatic door; The deep adjustment stage includes the following operations in sequence: controlling the unit load and boiler bed temperature; shutting down the coal feeding and slag discharge systems; closing the superheating and reheating desuperheating water valves; controlling the primary air flow rate and performing a large air volume disturbance on the boiler; shutting down the primary and secondary fans and one induced draft fan when monitoring the bed temperature to show a downward trend and the flue gas oxygen content rises to a preset threshold; shutting down all induced draft fans when monitoring the CO content to drop to the lowest; switching the turbine from sequence valve to single valve operation; controlling the main steam pressure and main steam temperature; reducing the unit load; starting the air cooling fan to control the unit back pressure; adjusting the feed water pump output and the water supply valve opening to control the change of the steam drum water level; opening the economizer recirculation door when the steam drum stops supplying water; adjusting the induced draft fan inlet and outlet plug-in doors and the primary and secondary air dampers to control the furnace negative pressure; stopping the deep adjustment when the key parameters trigger the safety boundary and entering the recovery stage; The recovery phase after deep adjustment includes the following operations in sequence: opening each air and smoke damper to establish an air channel; checking the CO content in the air chamber, return feeder air chamber and economizer inlet, and starting the induced draft fan when it is not within the preset threshold; after monitoring the CO content and finding no change, starting the primary and secondary fans; after adjusting the boiler primary air volume to the minimum fluidizing air volume, starting the coal feeder, adopting a point-to-point coal feeding method, and continuing to feed coal after confirming that the coal can be burned, gradually increasing the coal feed amount to normal load, and performing the remaining operations in accordance with grid-connected operations.

2. The near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit according to claim 1 is characterized in that: During the pre-deep adjustment preparation stage, the boiler bed pressure is controlled at 7.5-8KPa to ensure that the sum of the boiler bed pressure and the furnace differential pressure is not less than 8.5KPa; the exit unit protection includes exiting the large interlocking protection of the boiler electric load, the boiler exiting the total air volume protection, and the boiler exiting the minimum fluidizing air volume protection.

3. The near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit according to claim 1 is characterized in that: During the deep adjustment stage, the unit load is controlled to 130-150MW, and the boiler bed temperature is above 900℃; the preset threshold of the flue gas oxygen content is 8%; the main steam pressure is controlled to be no more than 16Mpa, the variation range of the main steam pressure is less than 0.05MPa, and the main steam temperature is not lower than 538±5℃; the unit load is reduced to 3-5MW; the unit back pressure is controlled to 4-5KPa; the steam drum water level is controlled to ±50mm; the furnace negative pressure is controlled within 500Pa; key parameters include boiler heat storage, main steam temperature, main steam pressure, reheat steam temperature, bed temperature and bed pressure.

4. The near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit according to claim 1 is characterized in that: During the post-deep adjustment recovery phase, the preset threshold value of CO content is 12.5-74.2%.

5. The near-zero depth peak regulation control method based on a subcritical circulating fluidized bed unit according to claim 1 is characterized in that: During the recovery phase after deep adjustment, if no ignition occurs when coal feeding is started and the bed temperature drops rapidly, immediately reduce the primary air volume to the minimum fluidizing air volume and simultaneously use an oil gun to assist combustion; start the slag cooler to reduce the bed pressure to 6KPa; and proceed according to the unit ignition and startup operation.

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