Control method for octagonal tangent circle type coal-fired boiler unit FCB

Abstract

The invention discloses a control method for an octagonal tangent circle type coal-fired boiler unit FCB. The control method comprises the following steps that firstly, it is confirmed that the function of the unit FCB is normally input; step 2, judging whether a condition for triggering an FCB function is reached or not, and if so, entering step 3; 3, executing an FCB control program of the unit; and 4, judging whether the FCB control program of the unit is finished or not, if so, ending the FCB control program of the unit, and otherwise, returning to the step 3. The FCB control system is simple in structure and reasonable in design, an FCB control program is designed for the octagonal tangent circle type coal-fired boiler unit, and the safety and stability of unit operation are effectively improved; all the steps are combined to respond to unit faults quickly and safely, and further expansion of the situation is prevented; once the accident reason is confirmed and eliminated, the unit exits the FCB control program and restarts the rising load, so that a large amount of time and energy consumption are saved, and the economic loss caused by the fault is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of operating methods, and in particular relates to a control method for an octagonal tangential circle coal-fired boiler unit FCB. Background Art

[0002] FCB technology refers to the technology of rapid reduction of unit output. When the power grid or the unit itself fails, resulting in the disconnection of the unit from the power grid, the unit can quickly cut off most of the external power supply load in a very short time, while keeping the main equipment such as boilers and steam turbines running, and maintaining certain steam parameters, so that it can be quickly reconnected to the grid and carry load after the fault is eliminated, without the need to completely shut down the unit and then restart it. The core principle of FCB technology lies in the coordinated actions of multiple key systems such as the control system, steam turbine regulation system, and bypass system.

[0003] Octagonal tangential combustion technology is different from conventional units. The octagonal tangential combustion technology refers to the fuel being sprayed into the furnace from the burner located at the octagon of the furnace, forming eight tangential combustion flame airflows. The formed tangential flames make the coal powder rotate and burn in the furnace. These airflows interact and mix with each other in the furnace, prolonging the residence time of the coal powder in the furnace, thereby achieving more complete combustion.

[0004] During the FCB process of the unit, the regulation of the octagonal tangential coal-fired boiler needs to take into account multiple factors, including combustion stability, heat load distribution, steam temperature control, etc. For example, an octagonal tangential coal-fired boiler usually has multiple burners. When FCB occurs, it is necessary to quickly determine which burners to keep running and which need to be cut off according to the preset logic, so as to quickly reduce the combustion rate and maintain stable combustion in the furnace. Therefore, a control method for FCB of octagonal tangential coal-fired boiler units is needed to achieve automatic control, reduce the probability of non-stopping of the unit, enable the unit and the power grid to have rapid recovery capabilities, and improve operational safety and stability. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a control method for FCB of an octagonal tangential circle coal-fired boiler unit in view of the deficiencies in the above-mentioned prior art. The method has a simple structure and a reasonable design. An FCB control program is designed for the octagonal tangential circle coal-fired boiler unit, which effectively improves the safety and stability of the unit operation. The combined effect of various steps can quickly and safely respond to unit failures and prevent the situation from further escalating. Once the cause of the accident is confirmed and eliminated, the unit exits the FCB control program and restarts to increase the load, thereby saving a lot of time and energy consumption and reducing the economic losses caused by the failure.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a control method of an octagonal tangential circle coal-fired boiler unit FCB, characterized in that it comprises the following steps:

[0007] Step 1: Confirm that the FCB function of the unit is put into operation normally;

[0008] Step 2: Determine whether the conditions for triggering the FCB function are met. If so, proceed to step 3.

[0009] Step 3: Execute the unit FCB control procedure:

[0010] Step 301, the octagonal tangential-circle coal-fired boiler is stably burning at the minimum load, and at least one coal mill is reserved at each of the four corners of the octagonal tangential-circle coal-fired boiler; the mill group is automatically controlled for explosion-proof; and the outlet temperature of the boiler superheater and reheater is controlled:

[0011] Step 302: Automatic switching control of the auxiliary power system;

[0012] Step 303, automatic control of the steam turbine DEH system;

[0013] Step 304, automatic control of high and low pressure bypass and ERV valve system to prevent overpressure;

[0014] Step 305: Automatic control of the steam turbine auxiliary thermal system;

[0015] Step 4: Determine whether the unit FCB control program is completed. If so, end the unit FCB control program, otherwise return to step 3.

[0016] The above-mentioned control method of the FCB of an octagonal tangential coal-fired boiler unit is characterized in that: the specific method of automatic explosion-proof control of the grinding group in step 301 and the control of the outlet temperature of the boiler superheater and reheater includes:

[0017] Step 3011, adjusting the mixed flue gas temperature at the coal mill inlet, the flue gas temperature at the outlet, and the flue gas oxygen content;

[0018] Step 3012, adjusting the mixture temperature and flue gas oxygen content at the coal mill outlet;

[0019] Step 3013, close the cooling water regulating valve and put it back into automatic control after a delay.

[0020] The above-mentioned control method of FCB of an octagonal cut-circle coal-fired boiler unit is characterized in that: the octagonal cut-circle coal-fired boiler has 8 burners, each burner is connected to a coal mill, and the 8 coal mills are arranged in sequence along the circumferential direction. The tripping sequence of the coal mill unit is to trip one coal mill in sequence, every other sequence number, and every preset tripping time, and at least 4 coal mills are retained.

[0021] The above-mentioned control method of the FCB of an octagonal tangentially fired coal-fired boiler unit is characterized in that: the specific method of automatic switching control of the auxiliary power system in step 302 is:

[0022] Step 3021, the unit is connected to the grid in a unit wiring mode, and the circuit breakers on the high-voltage side and the low-voltage side are configured as synchronization points. After the FCB function of the unit is triggered, the interlock trips the remaining synchronization circuit breakers that are still in the closed state;

[0023] Step 3022: configure the unit startup power supply. After the unit FCB function is triggered, the plant power supply is switched from the high-voltage plant transformer to the high-voltage public transformer.

[0024] The above-mentioned control method of an octagonal tangential circle coal-fired boiler unit FCB is characterized in that: the specific method of automatic control of the steam turbine DEH system in step 303 is:

[0025] Step 3031, the steam turbine DEH exits the DCS remote control mode, and at the same time triggers the overspeed pre-protection action logic to control all the regulating valves of the steam turbine to interlock and close quickly; the steam turbine DEH system switches to the single valve speed control mode, waits for the steam turbine speed to be less than the speed threshold, and then controls to open the steam turbine medium pressure regulating valve group, and adjusts the steam turbine speed to maintain the speed setting value;

[0026] Step 3032: If the steam pressure of the reheat cold section of the steam turbine exceeds the first pressure threshold, the high-pressure regulating valve of the steam turbine is closed; after the steam pressure of the reheat cold section drops below the second pressure threshold or the generator grid connection signal is triggered, the high-pressure regulating valve of the steam turbine is opened at a set rate according to the instruction of the DEH speed controller, and works together with the medium-pressure regulating valve of the steam turbine to adjust the speed of the steam turbine to maintain the speed setting value;

[0027] Step 3033, the steam turbine DEH quickly opens the high-pressure cylinder exhaust ventilation valve and closes the check valve; after the generator set is connected to the grid again, the check valve is opened; after the high-pressure cylinder exhaust temperature is lower than the set temperature, the ventilation valve is closed after a preset delay.

[0028] The above-mentioned control method of the FCB of an octagonal tangential coal-fired boiler unit is characterized in that: the specific method of automatic control of the high and low pressure bypass and ERV valve system of the unit against overpressure in step 304 is:

[0029] Step 3041, the regulating valve group of the high and low pressure bypass system of the unit is switched to the unit island operation mode; at the same time, the steam pressure and temperature of the superheater and reheater are adjusted to the preset target values;

[0030] Step 3042: The boiler reheater system is equipped with an adjustable pneumatic safety valve ERV. After the FCB function of the unit is triggered, if the total coal quantity in the boiler at the moment of triggering is greater than the total coal quantity threshold, the adjustable pneumatic safety valve ERV is interlocked to open.

[0031] The above-mentioned control method of an octagonal tangential circle coal-fired boiler unit FCB is characterized in that: the specific method of automatic control of the turbine auxiliary thermal system in step 305 includes:

[0032] Step 3051: The unit is equipped with a steam source pipeline for supplying steam to the shaft seal of the reheat cold section. After the FCB function of the unit is put into operation, the isolation valve of the steam source pipeline for supplying steam to the shaft seal of the reheat cold section is interlocked and opened;

[0033] After the FCB function of the unit is triggered, the first regulating valve of the steam source pipeline for the reheat cold section steam supply to the shaft seal is opened by interlocking, and the mode is switched to automatic control mode, and the pressure of the steam supply main pipe of the shaft seal is adjusted to the value recommended by the manufacturer;

[0034] Step 3052: The unit is configured with a steam source pipeline for supplying reheat cold section steam to the deaerator, and the second regulating valve of the steam source pipeline for supplying reheat cold section steam to the deaerator is interlocked and opened to the opening threshold, and switched to the automatic control mode; the deaerator pressure is adjusted;

[0035] Step 3053, interlock and open the steam trap group of the main heat steam pipeline, the reheat steam pipeline and the steam extraction pipeline of the steam turbine, trigger the steam side trip logic of the high pressure heater and the low pressure heater, and interlock and close the steam extraction electric valve and the check valve of the steam turbine;

[0036] Step 3054, interlock and start the standby vacuum pump.

[0037] The above-mentioned method for controlling the FCB of an octagonal tangential-circle coal-fired boiler unit is characterized in that: the specific method of "confirming that the FCB function of the unit is normally put into operation" in step 1 is: the unit needs to meet the following conditions:

[0038] Condition 1a: The unit grid-connected switch is in the closed state;

[0039] Condition 1b: The active power of the unit is greater than the minimum stable combustion load;

[0040] Condition 1c: The CCS control mode of the unit has been put into normal operation.

[0041] The above-mentioned control method for FCB of an octagonal tangential circle coal-fired boiler unit is characterized in that: the specific method of "conditions for triggering the FCB function" in step 2 is: satisfying the following conditions:

[0042] Condition 2a: The FCB function of the unit has been put into normal operation;

[0043] Condition 2b: The generator is disconnected from the grid or the turbine trips.

[0044] The above-mentioned method for controlling FCB of an octagonal tangential-circle coal-fired boiler unit is characterized in that: the specific method of "judging whether the FCB control program of the unit is completed" in step 4 is: any of the following conditions must be met:

[0045] Condition 3a: The boiler has tripped;

[0046] Condition 3b, FCB action delay after the first fixed setting value;

[0047] Condition 3c: The unit CCS mode exit delay reaches the second fixed setting value, and the FCB does not trigger the action.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] 1. The invention has a simple structure, reasonable design, and is easy to implement and operate.

[0050] 2. The present invention designs an FCB control program for an octagonal tangential-circle coal-fired boiler unit. The octagonal tangential-circle coal-fired boiler unit has the characteristics of complex structure and difficulty in controlling operating parameters. Once a failure occurs in the unit, unplanned shutdown may cause serious economic losses and safety hazards. The introduction of the FCB control program effectively improves the safety and stability of the unit operation.

[0051] 3. The combined action of various steps in the unit FCB control program of the present invention can quickly and safely respond to unit failures and prevent the situation from further escalating by automatically controlling various systems, especially when the generator is off-grid or the turbine trips while the boiler side is still in normal operation.

[0052] 4. In the present invention, once the cause of the accident is confirmed and eliminated, the unit exits the FCB control program and restarts to increase the load, thereby saving a lot of time and energy consumption and reducing the economic losses caused by the failure, which is of great significance for reducing the operating cost of the octagonal tangential circle coal-fired boiler unit.

[0053] 5. In the FCB control program of the unit of the present invention, for the octagonal cut circle coal-fired boiler, it is necessary to maintain the minimum load stable combustion of the octagonal cut circle coal-fired boiler, and retain at least one coal mill at each of the four corners of the octagonal cut circle coal-fired boiler to prevent flameout and ensure stable combustion, and prevent the risk of explosion caused by insufficient or excessive fuel supply.

[0054] In summary, the present invention has a simple structure and a reasonable design. The FCB control program is designed for the octagonal tangential circle coal-fired boiler unit, which effectively improves the safety and stability of the unit operation. The combined effect of various steps can quickly and safely respond to unit failures and prevent the situation from further escalating. Once the cause of the accident is confirmed and eliminated, the unit exits the FCB control program and restarts to increase the load, thereby saving a lot of time and energy consumption and reducing economic losses caused by failures.

[0055] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The present invention is a flow chart of the method.

[0057] Figure 2 The invention discloses a schematic diagram of the installation of a coal mill for an octagonal tangential-circle coal-fired boiler.

[0058] Description of reference numerals:

[0059] 1- first coal mill; 2- second coal mill; 3- third coal mill;

[0060] 4-the fourth coal mill; 5-the fifth coal mill; 6-the sixth coal mill;

[0061] 7-the seventh coal mill; 8-the eighth coal mill. DETAILED DESCRIPTION

[0062] The method of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments of the present invention.

[0063] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0064] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0065] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0066] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0067] like Figure 1 As shown, a control method of an octagonal tangential circle coal-fired boiler unit FCB of the present invention comprises the following steps:

[0068] Step 1: Confirm that the FCB function of the unit is normally put into operation.

[0069] Specifically, the specific method of "confirming that the FCB function of the unit is normally put into use" in step 1 is: the unit needs to meet the following conditions:

[0070] Condition 1a: The unit grid-connected switch is in the closed state; the closing of the grid-connected switch means that the generator set has been connected to the grid and can start to transmit power to the grid. This is a key step for the generator set to transition from the no-load state to the grid-connected operation state, and is also an important part of achieving power balance and dispatch in the power system.

[0071] Condition 1b: The active power of the unit is greater than the minimum stable combustion load. When the active power of the unit is greater than the minimum stable combustion load, it means that the power output of the generator is large enough to maintain the stable combustion of the boiler and avoid safety accidents such as furnace fire extinguishing.

[0072] Condition 1c: The CCS control mode of the unit has been put into normal operation.

[0073] Step 2: Determine whether the conditions for triggering the FCB function are met. If so, proceed to step 3.

[0074] Specifically, the specific method of "conditions for triggering the FCB function" in step 2 is: meet the following conditions:

[0075] Condition 2a: The FCB function of the unit has been put into normal operation;

[0076] Condition 2b: Generator off-grid or turbine tripped. After the generator is off-grid, the power balance of the grid may be disrupted, resulting in fluctuations in grid frequency and voltage. If the capacity of the off-grid generator is large, it may lead to insufficient power supply in the local grid. After the turbine trips, the generator will lose its power source, resulting in power supply interruption. The turbine trip may be accompanied by damage to mechanical components, requiring shutdown for maintenance.

[0077] Step 3: Execute the unit FCB control procedure:

[0078] Step 301, the octagonal tangential circle type coal-fired boiler is stably burned at the minimum load, and at least one coal mill is retained at each of the four corners of the octagonal tangential circle type coal-fired boiler; the mill group is automatically controlled for explosion-proof; and the outlet temperature of the boiler superheater and reheater is controlled.

[0079] Specifically, the boiler's minimum load stable combustion means that the boiler master control cuts off the automatic control mode and maintains the fuel master control automatic control mode and the water supply automatic control mode; the fuel master control instruction target value is set to the minimum total coal amount required for the boiler to maintain low load stable combustion; the boiler feed water flow instruction and air supply volume instruction are both adjusted according to the minimum total coal amount.

[0080] In a possible embodiment, the boiler is a 350MW octagonal tangential circle coal-fired boiler, and the minimum total coal quantity of the 350MW octagonal tangential circle coal-fired boiler to maintain stable combustion at the minimum load is 210 t / h.

[0081] The octagonal tangential-circle coal-fired boiler adopts tangential-circle combustion and is equipped with 8 coal mills. The air-powder mixture produced from each coal mill is distributed into four coal powder branch pipes through the tower coal powder pipeline. These branch pipes each transport the mixture to the nozzles of a group of burners at a single angle position. There are 8 groups of burners, corresponding to 8 coal mills one by one. Each group has 4 burners, and 32 burners are arranged in 4 layers. The cold air from the blower enters the two-chamber air preheater. After heating, a part of it is mixed with the high-temperature furnace extracted from the vertical water-cooled wall area and the cold flue gas from the outlet of the induced draft fan and enters the coal mill to form a primary air that is sent into the burner nozzle along with the coal powder; the secondary air is sent into the furnace through the wind boxes arranged around the burner and the SOFA air nozzle arranged above the burner.

[0082] The octagonal cut-circle coal-fired boiler has 8 burners, each burner is connected to a coal mill, and the 8 coal mills are arranged in sequence along the circumferential direction. The tripping sequence of the coal mill units is to trip one coal mill in sequence, every other sequence number, and every preset tripping time, and at least 4 coal mills are retained.

[0083] At least one coal mill is reserved at each of the four corners of the octagonal tangential-circle coal-fired boiler to prevent flameout and ensure stable combustion. The coal mill is automatically controlled to prevent the risk of explosion caused by insufficient or excessive fuel supply.

[0084] In a possible embodiment, the arrangement order of the eight coal mills is as follows: Figure 2 As shown, the tripping sequence of the coal mills is the eighth coal mill 8 - the sixth coal mill 6 - the fourth coal mill 4 - the second coal mill 2, and the interval tripping time between each coal mill is 10s.

[0085] The octagonal tangential circle coal-fired boiler unit has the characteristics of complex structure and difficult control of operating parameters. Once a failure occurs in the unit, unplanned shutdown may cause serious economic losses and safety hazards. The introduction of the FCB function effectively improves the safety and stability of the unit operation.

[0086] Specifically, the specific method of the automatic explosion-proof control of the grinding group in step 301 includes:

[0087] Step 3011, adjusting the temperature of the mixed flue gas at the inlet of the coal mill, the temperature of the flue gas at the outlet, and the oxygen content of the flue gas; specifically, adjusting the temperature of the flue gas at the inlet of the coal mill by automatically adjusting the hot air regulating valve of the coal mill, and when the oxygen content of the flue gas at the inlet of the coal mill is higher than the set threshold value, the threshold value is set to 11%, and the hot air regulating valve of the coal mill is stopped from being opened;

[0088] Step 3012, adjust the mixture temperature and flue gas oxygen content at the coal mill outlet; specifically, adjust the flue gas temperature at the coal mill outlet by automatically adjusting the cold smoke regulating valve of the coal mill, increase the oxygen content adjustment feedforward of the flue gas at the coal mill outlet, and ensure that the oxygen content of the flue gas at the coal mill outlet is below the safety threshold when the operating conditions change, and the safety threshold is 12%.

[0089] Step 3013, close the desuperheating water regulating valve and put it back into automatic control after a delay. Specifically, the desuperheating water regulating valve includes: a superheated steam first-stage desuperheating water regulating valve, a superheated steam second-stage desuperheating water regulating valve and a reheated steam desuperheating water regulating valve;

[0090] The superheated steam first-stage desuperheating water regulating valve is overrun and closed, and automatically restarts after a certain delay, and the automatic setting value is the current temperature;

[0091] The superheated steam secondary desuperheating water regulating valve is overrun and closed, and automatically restarts after a certain delay, and the automatic setting value is the current temperature;

[0092] The reheat steam desuperheating water regulating valve is overrun and closed, and automatically restarts after a certain delay, and the automatic setting value is the current temperature. The above-mentioned certain delay time refers to a delay of 45s, and automatic control is restarted after the delay to protect the unit equipment and resume stable operation as soon as possible.

[0093] Step 302: Automatic switching control of the factory power system.

[0094] Specifically, the specific method of automatic switching control of the auxiliary power system in step 302 is:

[0095] Step 3021, the unit is connected to the grid in the form of unit connection, and the circuit breakers on the high-voltage side and the low-voltage side are configured as synchronization points. After the FCB function of the unit is triggered, the remaining synchronization circuit breakers that are still in the closed state are interlocked and tripped. Specifically, the unit generator-transformer group is connected to the reserved interval of the 400kV system in the form of unit connection, and the circuit breakers GCB and UCB are respectively set on the high-voltage side and the low-voltage side of the main transformer, which can be used as synchronization points of the generator-transformer group; after the FCB function of the unit is triggered, the remaining synchronization circuit breakers that are still in the closed state are interlocked and tripped. If the generator disconnection is caused by the opening of the UCB circuit breaker on the high-voltage side of the main transformer, the GCB circuit breaker on the high-voltage side of the main transformer will be interlocked and tripped.

[0096] After the FCB function of the unit is triggered, if the remaining synchronous circuit breakers are still in the closed state, it may cause abnormal fluctuations in current and voltage, causing damage to the unit equipment. Therefore, interlocking and tripping these synchronous circuit breakers can quickly cut off the abnormal current and protect the unit equipment from damage.

[0097] Step 3022: Configure the unit startup power supply. After the unit FCB function is triggered, the plant power supply is switched from the high-voltage plant transformer to the high-voltage public transformer. Specifically, the unit startup power supply is provided by the high-voltage public transformer connected to the reserved interval of the 110kV booster station; after the unit FCB function is triggered, the 6kV fast device and the fast-cut device are interlocked to switch the plant power supply from the high-voltage plant transformer to the high-voltage public transformer.

[0098] After the unit's FCB function is triggered, the unit needs to quickly adjust to the island operation state. At this time, switching the plant power supply from the high-voltage plant transformer to the high-voltage public transformer can ensure that the unit obtains a more stable and reliable power supply.

[0099] Step 303: Automatic control of the steam turbine DEH system.

[0100] Specifically, the specific method for automatic control of the steam turbine DEH system in step 303 is:

[0101] Step 3031, the steam turbine DEH exits the DCS remote control mode and triggers the overspeed pre-protection action logic at the same time, controlling all the regulating valves of the steam turbine to interlock and close quickly; the steam turbine DEH system switches to the single valve speed control mode, waits for the steam turbine speed to be less than the speed threshold, and then controls the opening of the steam turbine medium-pressure regulating valve group to adjust the steam turbine speed to maintain it at the speed setting value.

[0102] The speed setting value is 3000rpm. The speed threshold is 3030rpm.

[0103] Step 3032: If the steam pressure of the reheat cold section of the steam turbine exceeds the first pressure threshold, the high-pressure regulating valve of the steam turbine is closed, and the first pressure threshold is 0.966MPa; after the steam pressure of the reheat cold section drops below the second pressure threshold or the generator grid-connected signal is triggered, the high-pressure regulating valve of the steam turbine opens at a set rate according to the instruction of the DEH speed controller, and works together with the medium-pressure regulating valve of the steam turbine to adjust the speed of the steam turbine to maintain it at the speed setting value; the second pressure threshold is 0.828MPa, the set rate is 2.5% / s, and the speed setting value is 3000rpm.

[0104] Step 3033, the steam turbine DEH quickly opens the high-pressure cylinder exhaust ventilation valve and closes the check valve; after the generator and transformer group are connected to the grid again, the check valve is opened; after the high-pressure cylinder exhaust temperature is lower than the set temperature, the ventilation valve is closed after a preset delay. When the set temperature is 400°C, the preset time is 60s.

[0105] Step 304: Automatically control the high and low pressure bypass and ERV valve system to prevent overpressure.

[0106] When the pressure of the unit's main steam or reheated steam exceeds the design value, the high and low pressure bypass systems can open quickly to release excess steam to the condenser or other safe areas, and release it in time to avoid serious damage to key equipment such as boilers and turbines.

[0107] Step 3041, the regulating valve group of the unit's high and low pressure bypass system is switched to the unit's island operation mode; at the same time, the steam pressure and temperature of the superheater and reheater are adjusted to the preset target values.

[0108] When the power grid or line fails and the unit itself operates normally, the FCB function causes the unit's main transformer outlet switch to trip, but does not trip the steam turbine and boiler. The unit's high and low pressure bypass system regulating valve group switches to the unit's island operation mode.

[0109] The specific method for switching the regulating valve group of the unit's high and low pressure bypass system to the unit's island operation mode is: adjusting the high pressure bypass regulating valve and the low pressure bypass regulating valve.

[0110] In one possible embodiment, the high-pressure bypass regulating valve interlock is opened, the opening instruction is the pre-opening value of the high-pressure bypass regulating valve, and the automatic control mode is returned after a delay of 10 seconds to adjust the boiler superheater outlet pressure, and the target setting value is 18MPa. However, if the superheated steam outlet pressure is less than 18MPa at the moment when the high-pressure bypass regulating valve switches to the automatic state, the target setting value of the boiler superheater outlet pressure is locked to the actual superheater pressure at that moment. The target setting value change rate is 3MPa / min, the high-pressure bypass cooling water isolation valve interlock is opened, the high-pressure bypass cooling water regulating valve is switched to the automatic control mode, and the steam temperature after the high-pressure bypass regulating valve is adjusted, and the target setting value is 320℃.

[0111] In one possible embodiment, the low-pressure bypass regulating valve interlock is opened, and the opening instruction is the pre-opening value of the low-pressure bypass regulating valve. After a delay of 10 seconds, it returns to the automatic control mode to adjust the unit's reheat steam pressure, and the target setting value is 0.8MPa. However, if the reheat steam outlet pressure is less than 0.8MPa at the moment the low-pressure bypass regulating valve switches to the automatic state, the unit's reheat steam pressure target setting value is locked to the actual reheat steam pressure at that moment, and the target setting value change rate is 3MPa / min. The low bypass cooling water isolation valve interlock is opened, and the low bypass cooling water regulating valve is switched to the automatic control mode. The steam temperature after the low-pressure bypass regulating valve is adjusted, and the target setting value is 90°C.

[0112] Step 3042: The boiler reheater system is equipped with an adjustable pneumatic safety valve ERV. After the FCB function of the unit is triggered, if the total coal volume of the boiler at the moment of triggering is greater than the total coal volume threshold, the interlock opens the adjustable pneumatic safety valve ERV to assist in releasing the energy stored in the reheater system. For a 350MW octagonal tangential coal-fired boiler, the total coal volume threshold is 300t / h.

[0113] In one possible embodiment, the boiler reheater system is equipped with four safety valves, namely, an adjustable pneumatic safety valve ERV, with a capacity of 66.4%, and three mechanical safety valves, each with a capacity of 25.08%. When the steam pressure in the boiler or reheater exceeds the specified value, the safety valve can automatically open to discharge excess steam to prevent the boiler from overpressure operation and ensure the safe operation of the boiler. For the adjustable pneumatic safety valve ERV, when the steam pressure exceeds the set value, the pneumatic actuator receives a signal and drives the adjustable pneumatic safety valve ERV to open; when the steam pressure drops below the set value, the pneumatic actuator drives the adjustable pneumatic safety valve ERV to close.

[0114] Step 305: Automatically control the steam turbine auxiliary thermal system.

[0115] Specifically, the specific method for automatically controlling the turbine auxiliary thermal system in step 305 includes:

[0116] Step 3051, the unit is equipped with a steam source pipeline for supplying steam to the shaft seal of the reheat cold section. After the FCB function of the unit is put into operation, the isolation valve of the steam source pipeline for supplying steam to the shaft seal of the reheat cold section is interlocked and opened.

[0117] After the FCB function of the unit is triggered, the interlock opens the first regulating valve of the steam source pipeline for the reheat cold section steam supply to the shaft seal. The opening degree of the first regulating valve is 75%. When the opening degree before the first regulating valve is greater than 75%, the instruction is maintained unchanged and switched to automatic control mode, and the pressure of the steam supply main pipe for the shaft seal is adjusted to the manufacturer's recommended value.

[0118] The main function of the isolation valve is to isolate and cut off the steam flow. It is used to cut off the steam supply when necessary to prevent steam backflow or leakage.

[0119] The main function of the first regulating valve is to adjust and control the steam flow according to the demand for shaft seal steam and changes in system pressure to ensure stable operation of the shaft seal steam system.

[0120] Step 3052: The unit is configured with a steam source pipeline for the reheat cold section steam to supply the deaerator, and the second regulating valve of the steam source pipeline for the reheat cold section steam to supply the deaerator is interlocked and opened, and the second regulating valve is set to the opening threshold and switched to the automatic control mode; the opening threshold of the second regulating valve is 30%, and when the current opening of the second regulating valve is greater than 30%, the command is maintained unchanged. The second regulating valve is used to accurately adjust and control the steam flow and pressure entering the deaerator, improve thermal economy, protect the deaerator from damage, adapt to load changes, and assist in reducing the reheat steam pressure.

[0121] Adjust the deaerator pressure, and the target setting value of the deaerator pressure is 0.6MPa. If the deaerator pressure is greater than 0.8MPa when the regulating valve of the steam pipeline of the reheat cold section steam supply deaerator switches to the automatic state, the target setting value of the deaerator pressure is locked to the actual deaerator pressure at that moment.

[0122] Step 3053, interlocking and opening the drain valve group of the main hot steam pipe, reheat steam pipe and turbine extraction pipe, can assist in reducing the main reheat steam pressure, and quickly remove the possible accumulated water in the main hot steam pipe, reheat steam pipe and turbine extraction pipe during the boiler load reduction process, prevent the accumulated water from entering the turbine cylinder with the steam, and avoid the occurrence of turbine water ingress accidents; triggering the steam side tripping logic of the high-pressure heater and the low-pressure heater, interlocking and closing the turbine extraction electric valve and the check valve, can stop the operation of the heater, prevent the turbine speed from soaring due to the internal steam of the heater returning to the turbine, and can also prevent the cold steam from carrying drain water into the turbine cylinder, and wash and corrode the turbine blades and other components.

[0123] The execution of step 3053 can realize automatic control and protection of the steam system and improve the reliability and stability of the system.

[0124] Step 3054, interlock and start the standby vacuum pump.

[0125] Step 4: Determine whether the unit FCB control program is completed. If so, end the unit FCB control program, otherwise return to step 3.

[0126] Specifically, the specific method of "determining whether the unit FCB control program is completed" in step 4 is: any of the following conditions must be met:

[0127] Condition 3a: The boiler has tripped;

[0128] Condition 3b, FCB action delay after the first fixed setting value. For a 350MW octagonal tangential coal-fired boiler, the first fixed setting value is 300s. During this period, the unit can stabilize and the abnormal operating conditions can be preliminarily handled, thereby avoiding further damage that may be caused by the unit being in an unstable state for a long time. By setting a fixed setting value, the logical judgment of the FCB action can be made simpler and clearer, and it is easy to realize automatic control.

[0129] Condition 3c: The unit CCS mode exit delay reaches the second fixed setting value, and the FCB does not trigger the action.

[0130] In one possible embodiment, the second fixed setting value is 5s. In step 1, the CCS control mode of the unit has been put into normal operation. When the FCB control program of the unit is triggered, in step 303, when the DEH exits the DCS remote control mode, the DCS system can no longer control the DEH system through remote instructions. At this time, the DEH system switches to the local control mode, that is, it is separated from the coordinated control of the CCS system, and the CCS mode of the unit is correspondingly exited.

[0131] Once the cause of the accident is confirmed and eliminated, the unit exits the FCB control program and restarts to increase the load, thus saving a lot of time and energy consumption, which is of great significance for reducing the operating cost of the octagonal cut-circle coal-fired boiler unit.

[0132] In a specific embodiment, a 350MW supercritical unit of a power plant in Serbia is taken as an example. The boiler of the unit adopts a 350MW supercritical parameter transformer DC furnace, a single furnace, one-time reheating, balanced ventilation, semi-enclosed layout, octagonal tangential combustion, wet slag removal, all-steel frame, and a fully suspended structure tower boiler; the steam turbine adopts a supercritical, one-time intermediate reheating, two-cylinder and two-exhaust, condensing steam turbine; the generator adopts a water-hydrogen-hydrogen cooling, static excitation generator; the unit adopts a 100% full-capacity hydraulic control bypass system with the functions of adjustment, temperature reduction and pressure reduction, among which the high The high-pressure bypass regulating valve is arranged on the boiler side and has the function of a superheater safety valve; the boiler reheater system is equipped with four safety valves, including one adjustable pneumatic safety valve ERV with a capacity of 66.4% and three mechanical safety doors, each with a capacity of 25.08%; the unit's generator-transformer group is connected to the reserved interval of the 400kV system in the form of unit wiring, and circuit breakers GCB and UCB are respectively set on the high-voltage side and low-voltage side of the main transformer, both of which can be used as synchronization points for the generator-transformer group; the unit starting power supply is provided by the high-voltage public transformer connected to the reserved interval of the 110kV booster station.

[0133] Octagonal tangential coal-fired boiler uses an octagonal tangential coal-fired boiler. The layout order of 8 coal mills is as follows: Figure 2Before the FCB test at 100% rated load of the unit, the first coal mill 1, the second coal mill 2, the third coal mill 3, the fifth coal mill 5, the sixth coal mill 6, the seventh coal mill 7, and the eighth coal mill 8 in the boiler pulverizing system are in operation.

[0134] After the FCB function is triggered, the unit FCB control program is executed according to step 3, and the eighth coal mill 8 is tripped without delay interlocking, and the sixth coal mill 6 is tripped after an interval of 10s, and the second coal mill 2 is tripped after another interval of 10s. The first coal mill 1, the third coal mill 3, the fifth coal mill 5 and the seventh coal mill 7 remain in operation to ensure that the boiler maintains stable combustion operation with four corners cut into the circle.

[0135] The coal feed rate and related parameters of each grinding group before the unit FCB control program test are shown in Table 1, and the coal feed rate and related parameters of each grinding group after the unit FCB control program test are shown in Table 2.

[0136] Through the automatic adjustment of the hot air regulating valve and the cold smoke regulating valve at the coal mill inlet, the oxygen content of the flue gas at the outlet of the first coal mill 1, the third coal mill 3, the fifth coal mill 5 and the seventh coal mill 7 which remain in operation are stabilized to 11.0%, 6.8%, 10.4% and 7.4% respectively, all of which can be maintained within the safety threshold range of 12%.

[0137] The inlet temperatures of the first coal mill 1, the third coal mill 3, the fifth coal mill 5 and the seventh coal mill 7 which are kept in operation can be maintained within the range of no more than 550°C, and the outlet temperatures can be maintained within the range of 150-200°C to ensure stable combustion.

[0138] Table 1 Coal feed rate and related parameters of each grinding group before the unit FCB control program test

[0139]

[0140] Table 2 Coal feed rate and related parameters of each grinding group after the unit FCB control program test

[0141]

[0142] After the FCB control program is triggered, according to step 301, the desuperheating water regulating valve is closed and automatically put into automatic control after a delay, specifically: the first-stage desuperheating water regulating valve of superheated steam is overrun and closed, and automatically put into automatic control after a delay of 45 seconds, and the automatic setting value is the current temperature; the second-stage desuperheating water regulating valve of superheated steam is overrun and closed, and automatically put into automatic control after a delay of 45 seconds, and the automatic setting value is the current temperature; the reheating water regulating valve is overrun and closed, and automatically put into automatic control after a delay of 45 seconds, and the automatic setting value is the current temperature.

[0143] The main parameters of the unit before and after the FCB test at 100% rated load are shown in Table 3.

[0144] The minimum steady-fired load total coal target value of the 350MW octagonal cut-circle boiler is 210t / h. After the unit FCB function is triggered, the boiler feed water flow and air supply volume are adjusted according to the total coal command. The feed water flow is adjusted to 542t / h according to the total coal. During the test, the main reheat steam temperature and superheat degree of the unit are stable, with the highest main steam temperature of 544℃ and the lowest 539℃, the highest reheat steam temperature of 556℃ and the lowest 540℃, and the highest superheat degree of 44.4℃ and the lowest 23.9℃.

[0145] Before the unit's 100% rated load FCB test, the unit's power supply was provided by a high-voltage plant transformer with a power of 40380kW. After the FCB was triggered, the unit's power supply was quickly and stably switched to a high-voltage public transformer with a power of 40668kW. High-voltage public transformers usually have higher reliability and stability, and their power supply quality is better than that of high-voltage plant transformers. The electric auxiliary machines did not experience tripping events caused by plant voltage fluctuations. After the FCB was triggered, the generator power dropped from 350MW to 0MW, and the GCB circuit breaker interlocked and tripped. After completing the pre-grid inspection, the operator manually closed the UCB circuit breaker. After the generator was de-energized for 366s, the GCB circuit breaker was closed by the synchronization device and connected to the grid again. The initial load was 35MW.

[0146] After the FCB function of the unit is triggered, the turbine DEH exits the DCS remote control mode and triggers the overspeed pre-protection action logic at the same time, controlling all the regulating valves of the turbine to interlock and close quickly. The turbine speed rises to a maximum of 3132rpm and then quickly falls back. After the turbine speed is less than 3030rpm, the medium-pressure regulating valve opens and adjusts the turbine speed to 3000rpm; after being connected to the grid again, the turbine high-pressure regulating valve is unlocked and opened to 7.03%, and the turbine medium-pressure regulating valve is opened to 99.8%. After the unit is connected to the grid, the load is usually gradually loaded, with an initial load of 35MW.

[0147] After the FCB function of the unit is triggered, the high-pressure cylinder exhaust ventilation valve opens quickly, controlling the high-pressure cylinder exhaust check valve to close, effectively controlling the high-pressure cylinder exhaust temperature. The temperature was 309.5°C before the test, reached a maximum of 393.4°C during the test, and was 252.2°C after being connected to the grid again, preventing the risk of the turbine tripping due to the high high-pressure cylinder exhaust temperature.

[0148] Before the test, the total coal volume of the unit was 446.5t / h, which was greater than 300t / h. After the FCB was triggered, the adjustable pneumatic safety valve ERV of the boiler reheater system was opened, and the high-pressure bypass regulating valve and the low-pressure bypass regulating valve were opened to 100% opening, and then put into automatic control mode after a delay of 10 seconds. The pre-opening value of the high-pressure bypass regulating valve and the pre-opening value of the low-pressure bypass regulating valve were both 100%, and the excess steam was released to the condenser or other safe areas in time to avoid serious damage to key equipment such as boilers and turbines.

[0149] After the FCB action is triggered, the steam flow of the boiler will decrease rapidly. By adjusting the steam pressure and temperature of the superheater and reheater to the preset target values, the stability of the steam temperature can be ensured to prevent the equipment from being damaged due to excessive steam pressure. The boiler superheater outlet pressure and the unit reheat steam pressure are adjusted. When the boiler is connected to the grid again, the boiler superheater outlet pressure is 16.8MPa and the unit reheat steam pressure is 0.7MPa. During the process, the pressure control and bypass valve group operate stably.

[0150] After the FCB function of the unit is triggered, the turbine quickly and stably runs at 3000rpm, other auxiliary machines and valve interlocks of the turbine operate normally, and the subsystem automatically controls various parameters within a safe range.

[0151] Table 3 Main parameters of the unit before and after 100% rated load FCB test

[0152]

[0153]

[0154] 300s after the FCB is triggered, the unit's FCB control program is completed, marking a smooth transition from the fault to the emergency response stage. 366s after the FCB is triggered, the unit enters the grid-connected recovery stage. As the turbine speed stabilizes, the unit is connected to the grid again with load, and the initial load is 35MW. The setting of 35MW takes into account both the thermal stress limit of the unit after the FCB control program and the grid's demand for rapid power restoration.

[0155] During the initial operation after grid connection, the system parameters of the unit were stable without abnormal fluctuations, proving that the FCB control program can guide the unit to quickly resume stable operation after a fault, ensuring the safety and reliability of the unit in emergency situations, reducing downtime and economic losses, and providing strong support for the stable operation of the power grid.

[0156] The above description is only an embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A control method for FCB of an octagonal tangential coal-fired boiler unit, characterized in that: The following steps are involved: Step 1: Confirm that the FCB function of the unit is put into operation normally; Step 2: Determine whether the conditions for triggering the FCB function are met. If so, proceed to step 3. Step 3: Execute the unit FCB control procedure: Step 301, the octagonal tangential-circle coal-fired boiler is stably burning at the minimum load, and at least one coal mill is reserved at each of the four corners of the octagonal tangential-circle coal-fired boiler; the mill group is automatically controlled for explosion-proof; and the outlet temperature of the boiler superheater and reheater is controlled: Step 302: Automatic switching control of the auxiliary power system; Step 303, automatic control of the steam turbine DEH system; Step 304, automatic control of high and low pressure bypass and ERV valve system to prevent overpressure; Step 305: Automatic control of the steam turbine auxiliary thermal system; Step 4: Determine whether the unit FCB control program is completed. If so, end the unit FCB control program, otherwise return to step 3.

2. A control method for an octagonal tangential coal-fired boiler unit FCB according to claim 1, characterized in that: The specific method for automatic explosion-proof control of the grinding group in step 301 and the control of the outlet temperature of the boiler superheater and reheater includes: Step 3011, adjusting the mixed flue gas temperature at the coal mill inlet, the flue gas temperature at the outlet, and the flue gas oxygen content; Step 3012, adjusting the mixture temperature and flue gas oxygen content at the coal mill outlet; Step 3013, close the cooling water regulating valve and put it back into automatic control after a delay.

3. A control method for an octagonal tangential circle coal-fired boiler unit FCB according to claim 1 or 2, characterized in that: The octagonal cut-circle coal-fired boiler has 8 burners, each burner is connected to a coal mill, and the 8 coal mills are arranged in sequence along the circumferential direction. The tripping sequence of the coal mill units is to trip one coal mill in sequence, every other sequence number, and every preset tripping time, and at least 4 coal mills are retained.

4. The control method of an octagonal tangential circle coal-fired boiler unit FCB according to claim 1, characterized in that: The specific method of automatic switching control of the auxiliary power system in step 302 is: Step 3021, the unit is connected to the grid in a unit wiring mode, and the circuit breakers on the high-voltage side and the low-voltage side are configured as synchronization points. After the FCB function of the unit is triggered, the interlock trips the remaining synchronization circuit breakers that are still in the closed state; Step 3022: configure the unit startup power supply. After the unit FCB function is triggered, the plant power supply is switched from the high-voltage plant transformer to the high-voltage public transformer.

5. The control method of the FCB of an octagonal tangential circle coal-fired boiler unit according to claim 1 is characterized in that: The specific method of automatic control of the steam turbine DEH system in step 303 is: Step 3031, the steam turbine DEH exits the DCS remote control mode, and at the same time triggers the overspeed pre-protection action logic to control all the regulating valves of the steam turbine to interlock and close quickly; the steam turbine DEH system switches to the single valve speed control mode, waits for the steam turbine speed to be less than the speed threshold, and then controls to open the steam turbine medium pressure regulating valve group, and adjusts the steam turbine speed to maintain the speed setting value; Step 3032: If the steam pressure of the reheat cold section of the steam turbine exceeds the first pressure threshold, the high-pressure regulating valve of the steam turbine is closed; after the steam pressure of the reheat cold section drops below the second pressure threshold or the generator grid connection signal is triggered, the high-pressure regulating valve of the steam turbine is opened at a set rate according to the instruction of the DEH speed controller, and works together with the medium-pressure regulating valve of the steam turbine to adjust the speed of the steam turbine to maintain the speed setting value; Step 3033, the steam turbine DEH quickly opens the high-pressure cylinder exhaust ventilation valve and closes the check valve; after the generator set is connected to the grid again, the check valve is opened; after the high-pressure cylinder exhaust temperature is lower than the set temperature, the ventilation valve is closed after a preset delay.

6. A control method for an octagonal tangential circle coal-fired boiler unit FCB according to claim 1, characterized in that: The specific method for automatically controlling the high and low pressure bypass and ERV valve system to prevent overpressure in step 304 is as follows: Step 3041, the regulating valve group of the high and low pressure bypass system of the unit is switched to the unit island operation mode; at the same time, the steam pressure and temperature of the superheater and reheater are adjusted to the preset target values; Step 3042: The boiler reheater system is equipped with an adjustable pneumatic safety valve ERV. After the FCB function of the unit is triggered, if the total coal quantity in the boiler at the moment of triggering is greater than the total coal quantity threshold, the adjustable pneumatic safety valve ERV is interlocked to open.

7. A control method for an octagonal tangential circle coal-fired boiler unit FCB according to claim 1, characterized in that: The specific method of automatic control of the steam turbine auxiliary thermal system in step 305 includes: Step 3051: The unit is equipped with a steam source pipeline for supplying steam to the shaft seal of the reheat cold section. After the FCB function of the unit is put into operation, the isolation valve of the steam source pipeline for supplying steam to the shaft seal of the reheat cold section is interlocked and opened; After the FCB function of the unit is triggered, the first regulating valve of the steam source pipeline for the reheat cold section steam supply to the shaft seal is opened by interlocking, and the mode is switched to automatic control mode, and the pressure of the steam supply main pipe of the shaft seal is adjusted to the value recommended by the manufacturer; Step 3052: The unit is configured with a steam source pipeline for supplying reheat cold section steam to the deaerator, and the second regulating valve of the steam source pipeline for supplying reheat cold section steam to the deaerator is interlocked and opened to the opening threshold, and switched to the automatic control mode; the deaerator pressure is adjusted; Step 3053, interlock and open the steam trap group of the main heat steam pipeline, the reheat steam pipeline and the steam extraction pipeline of the steam turbine, trigger the steam side trip logic of the high pressure heater and the low pressure heater, and interlock and close the steam extraction electric valve and the check valve of the steam turbine; Step 3054, interlock and start the standby vacuum pump.

8. The control method of an octagonal tangential circle coal-fired boiler unit FCB according to claim 1, characterized in that: The specific method of "confirming that the FCB function of the unit is normally put into use" in step 1 is: the unit needs to meet the following conditions: Condition 1a: The unit grid-connected switch is in the closed state; Condition 1b: The active power of the unit is greater than the minimum stable combustion load; Condition 1c: The CCS control mode of the unit has been put into normal operation.

9. A control method for an octagonal tangential circle coal-fired boiler unit FCB according to claim 1 or 8, characterized in that: The specific method of "Conditions for triggering the FCB function" in step 2 is: meet the following conditions: Condition 2a: The FCB function of the unit has been put into normal operation; Condition 2b: The generator is disconnected from the grid or the turbine trips.

10. A control method for an octagonal tangential circle coal-fired boiler unit FCB according to claim 1 or 8, characterized in that: The specific method of "judging whether the unit FCB control program is completed" in step 4 is: any of the following conditions must be met: Condition 3a: The boiler has tripped; Condition 3b, FCB action delay after the first fixed setting value; Condition 3c: The unit CCS mode exit delay reaches the second fixed setting value, and the FCB does not trigger the action.

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