Subcritical unit rapid load increasing system and load increasing method thereof

Abstract

The invention provides a subcritical unit rapid load increasing system and a load increasing method thereof, and relates to the technical field of coal-fired power plant boilers, the subcritical unit rapid load increasing system comprises a coal-fired power plant boiler and a pulverizing device which are connected; the hearth is directly connected with a combustion assembly, and the combustion assembly is provided with a high-position combustor, a main combustor and a low-position combustor. An economizer is arranged at the lower part of the hearth tail flue; an inlet flue of the economizer is communicated with an external combustion device; a feed port of the coal feeder is butted with a discharge port of the coal hopper, and a discharge port of the coal feeder is connected with the coal mill; the first outlet pulverized coal pipe is communicated with the pulverized coal separator, the second outlet pulverized coal pipe is communicated with the main burner, and a pulverized coal return main pipe on the pulverized coal separator is communicated with the coal mill; a pulverized coal returning branch pipe on the pulverized coal separator is communicated with the pulverized coal returning storage hopper, a feeding port of the pulverized coal feeding and returning machine is in butt joint with a discharging port of the pulverized coal returning storage hopper, and a discharging port of the pulverized coal feeding and returning machine is connected with the coal mill. The problems that existing DCS control logic cannot change physical characteristics, and an independent pulverized coal storage bin is prone to explosion are solved, and the effect of rapid load rising is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired power plant boilers, and in particular to a rapid load increase system for a subcritical unit and a method for increasing the load thereof. Background Art

[0002] Driven by the energy transformation, it has become an inevitable trend to build a new power system with new energy as the main body. Although new energy has developed rapidly, due to its own characteristics, the proportion of power sources lacking regulation ability has gradually increased, which has made the problem of shortage of flexible grid resources increasingly prominent. In the current power supply system, coal power has become the only flexible resource with large-scale economic deep peak shaving ability in the short term due to its advantages such as mature technology, high reliability, and relatively good regulation performance. Subcritical units are an important part of coal power.

[0003] Currently, in order to improve the load increase rate of subcritical units, the industry mainly adopts technical means. First, the DCS control logic is optimized. By adjusting and optimizing the control logic of the unit's distributed control system (DCS), the method of tapping the potential of the unit itself is used. By reasonably optimizing the control parameters and control strategies, the response speed of the unit to load changes can be improved to a certain extent. Second, some coal-fired power units adopt the technical solution of setting up independent pulverized coal storage bins in the boiler. This solution can quickly transport the pulverized coal to the furnace when the unit needs to increase the load by pre-storing qualified pulverized coal, effectively solving the problem of grinding delay of the coal mill, and thus improving the peak shaving rate of the unit. Third, some units also adopt the method of coupling with molten salt energy storage. Utilizing the energy storage characteristics of the molten salt energy storage system, energy is stored when the unit load is low and released when the load needs to be increased, providing additional power support for the unit and realizing the improvement of the unit's flexible peak shaving ability.

[0004] However, although certain results have been achieved in improving the load increase rate of subcritical units, the following problems still exist:

[0005] 1) For the optimization of the DCS control logic, its improvement effect is restricted by the physical characteristics of the unit's thermal system. No matter how the control logic is optimized, it is difficult to break through the limitations of the unit's inherent physical characteristics and cannot meet the increasing demand for peak shaving rate of the future power grid.

[0006] 2) Starting from the structure, an independent pulverized coal storage bin is set in the boiler. Although the problem of the grinding delay of the coal mill is solved from the combustion side, for a subcritical unit, there are still serious potential fire safety hazards. Once pulverized coal leakage or explosion occurs, it will pose a great threat to the safe operation of the unit. In addition, the core restricting the safe and rapid load increase of the unit is the problem of the metal temperature change rate of the heating surface, which is jointly determined by the heat transfer on the working fluid side and the flue gas side of the heating surface. Therefore, the change rates of the determining factors on both sides need to be coordinated with each other. Relying solely on the design of an independent powder bin cannot solve the problem that the drastic change in the wall temperature of the heating surface affects the service life of the metal material.

[0007] 3) For the molten salt energy storage and thermal power unit coupling peak shaving technology, although it can effectively improve the flexible peak shaving ability of the unit, its total technology cost is extremely high. From the construction cost to the operation and maintenance cost, this technology faces huge economic pressure when it is widely promoted and applied, and it is difficult to be widely popularized. Summary of the Invention

[0008] The purpose of the present invention is to provide a rapid load increase system for a subcritical unit and its load increase method to alleviate the technical problems in the prior art that the DCS control logic cannot change the physical characteristics and the independent pulverized coal storage bin is prone to explosion.

[0009] A rapid load increase system for a subcritical unit provided by the present invention includes a coal-fired power station boiler and a coal pulverizing device connected to each other.

[0010] The coal-fired power station boiler includes a furnace and an economizer. The furnace is directly connected with a combustion assembly, and the combustion assembly is sequentially provided with a high-level burner, a main burner, and a low-level burner from top to bottom; an economizer is arranged at the lower part of the tail flue of the furnace, and the inlet flue of the economizer is communicated with an out-of-furnace combustion device.

[0011] The coal pulverizing device includes a coal hopper, a coal feeder, a coal mill, a pulverized coal separator, a return powder storage hopper, and a return powder feeder.

[0012] The coal hopper is arranged above the coal mill, the feed inlet of the coal feeder is butted with the discharge outlet of the coal hopper, and the discharge outlet of the coal feeder is connected with the coal mill.

[0013] The first outlet powder pipe on the coal mill is communicated with the pulverized coal separator, the second outlet powder pipe on the pulverized coal separator is communicated with the main burner, and the main return powder pipe on the pulverized coal separator is communicated with the coal mill; the return powder branch pipe on the pulverized coal separator is communicated with the return powder storage hopper, the feed inlet of the return powder feeder is butted with the discharge outlet of the return powder storage hopper, and the discharge outlet of the return powder feeder is connected with the coal mill.

[0014] Furthermore, a main pipe regulating baffle is arranged on the main return powder pipe, and a branch pipe regulating baffle is arranged on the return powder branch pipe; both the main pipe regulating baffle and the branch pipe regulating baffle are used to regulate the return powder flow rate.

[0015] Further, shut-off baffles are provided on the pipelines connecting the coal feeder's discharge port to the coal mill and the pipelines connecting the return powder feeder's discharge port to the coal mill. The shut-off baffles are used to control the raw materials fed into the coal mill.

[0016] Further, the main burner is located in the middle of the furnace and is connected to the second outlet powder pipe. The main burner is used to provide basic combustion for the unit; the low-level burner and the high-level burner are arranged on the upper and lower sides of the main burner. The low-level burner and the high-level burner are connected to the fuel delivery pipeline and are used to adjust the flame center height and the fuel supply during pulverized coal delay.

[0017] Further, the main burner is a multi-layer burner, and each layer of the burner is connected to a second outlet powder pipe, which is used to control the coal powder supply of each layer of the burner.

[0018] Further, quick cut-off valves and flow regulating valves are provided on the fuel delivery pipelines of the low-level burner and the high-level burner. The quick cut-off valves and the flow regulating valves are used to control the supply of fuel oil or gas.

[0019] Further, the out-of-furnace combustion device includes an independent combustion chamber. The burner in the combustion chamber adopts a swirl burner, and the fuel inlet of the swirl burner is connected to the fuel oil or gas supply pipeline; the out-of-furnace combustion device is used to make the flue gas evenly enter the inlet flue of the economizer and strengthen the outlet medium temperature of the economizer.

[0020] Further, the return powder feeder is a belt weighing feeder. Anti-slip patterns are provided on the surface of the belt of the return powder feeder, and retaining edges are provided on both sides of the belt of the return powder feeder to prevent the return powder from slipping during transportation.

[0021] The present invention also provides a method for quickly increasing the load of a subcritical unit, including the following steps:

[0022] Step 1: After the subcritical unit receives a load increase instruction, the high-pressure heater feed water bypass is opened, and the out-of-furnace combustion device operates. The input raw material amount of the out-of-furnace combustion device is adjusted according to the outlet medium of the economizer;

[0023] Step 2: The low-level burner or the high-level burner receives fuel oil or gas and operates. The low-level burner provides the fuel increment corresponding to the load; for the unit whose steam temperature has not reached the preset value, according to the steam temperature characteristics of the unit, the high-level burner operates;

[0024] At the same time, the output powder amount of the main burner is allocated according to the sharing method. The output increment of the coal mill is determined according to the load, and the coal feeding preferably uses the coal stored in the return powder storage hopper;

[0025] Step 3: When the coal feeding increase instruction of the coal mill reaches the stable increase of the outlet powder amount of the coal mill, the low-level burner and / or the high-level burner stops burning;

[0026] Step 4: After closing the high-pressure heater feed water bypass, close the out-of-furnace combustion device.

[0027] Step 5: Switch the coal supply in the coal pulverizing system from being supplied by the return powder storage hopper to being supplied by the coal bunker.

[0028] Step 6: After the unit load increase is completed and the load is stable, divert the return powder from the return powder branch pipe in the coal pulverizing system to the return powder storage hopper to the design value and wait for the next coal mill output.

[0029] Further, in Step 2, the apportionment method is that the powder feeding increment of the lower burner in the main burner is greater than that of the upper burner, that is, ΔF A > ΔF B > ΔF C > ΔF D > ΔF E ; where Δ represents the increment and F represents the fuel quantity of the combustion layer.

[0030] At the same time, the input raw material quantity of the coal mill does not exceed the rated input raw material quantity, that is, the input raw material quantity reaching the rated value does not participate in the fuel increment apportionment; in the later stage of load growth, the total fuel increment deducts the fuel used by the low-position burner or the high-position burner.

[0031] When the unit load stops growing, the input raw material quantity of the coal mill is evenly distributed.

[0032] Beneficial effects:

[0033] The present invention provides a subcritical unit rapid load increase system and its load increase method, including a coal-fired power station boiler and a coal pulverizing system connected thereto; the coal-fired power station boiler includes a furnace and an economizer, the furnace is directly connected with a combustion assembly, and the combustion assembly is sequentially provided with a high-position burner, a main burner, and a low-position burner from top to bottom; an economizer is arranged at the lower part of the tail flue of the furnace, and an out-of-furnace combustion device is communicated with the inlet flue of the economizer; the coal pulverizing system includes a coal bunker, a coal feeder, a coal mill, a pulverized coal separator, a return powder storage hopper, and a return powder feeder; the coal bunker is arranged above the coal mill, the feed inlet of the coal feeder is butted with the discharge outlet of the coal bunker, and the discharge outlet of the coal feeder is connected with the coal mill; the first outlet powder pipe on the coal mill is communicated with the pulverized coal separator, the second outlet powder pipe on the pulverized coal separator is communicated with the main burner, and the return powder main pipe on the pulverized coal separator is communicated with the coal mill; the return powder branch pipe on the pulverized coal separator is communicated with the return powder storage hopper, the feed inlet of the return powder feeder is butted with the discharge outlet of the return powder storage hopper, and the discharge outlet of the return powder feeder is connected with the coal mill.

[0034] The present invention realizes rapid fuel input by setting a low-level burner and a high-level burner and using fuel oil or gas as fuel, makes up for the pulverizing delay of the coal mill, avoids the explosion of an independent pulverized coal storage bin, and can quickly adjust the height of the flame center, enabling the unit to quickly respond to load change commands and significantly improving the load rate. The setting of the out-of-furnace combustion device ensures that the temperature of the medium at the outlet of the economizer and the flame center in the furnace are adjustable, taking into account the economy and safety of the unit operation; the overall system design considers the core elements restricting the load increase rate of the drum boiler, ensuring the safety of the heating surface when the unit increases the load. By storing fine coal particles in the pulverizing device and feeding them into the inlet of the coal mill, the response speed of the pulverizing device is rapidly increased, the usage amount of fast-acting fuel is reduced, or the system safety is improved because the system using stored pulverized coal is avoided;

[0035] In addition, the present invention is improved based on the existing unit system itself, and the cost is greatly reduced compared with the molten salt energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 It is a schematic structural diagram of a coal-fired power station boiler in a subcritical unit rapid load increase system provided by an embodiment of the present invention;

[0038] Figure 2 It is a schematic structural diagram of a pulverizing device in a subcritical unit rapid load increase system provided by an embodiment of the present invention;

[0039] Figure 3 It is a flowchart of a method for rapidly increasing the load of a subcritical unit provided by an embodiment of the present invention.

[0040] Reference Signs: 1 - Coal-fired power station boiler; 101 - Furnace; 102 - Economizer;

[0041] 2 - Pulverizing device; 201 - Coal hopper; 202 - Coal feeder; 203 - Coal mill; 204 - Pulverized coal separator; 205 - Return powder storage hopper; 206 - Return powder feeder; 207 - First outlet powder pipe; 208 - Second outlet powder pipe; 209 - Return powder main pipe; 210 - Return powder branch pipe; 211 - Main pipe regulating baffle; 212 - Branch pipe regulating baffle; 213 - Shut-off baffle;

[0042] 3 - Combustion assembly; 301 - High-level burner; 302 - Main burner; 303 - Low-level burner;

[0043] 4-Out-of-furnace combustion device. Specific implementation mode

[0044] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0045] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0046] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0047] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present invention is habitually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0048] In addition, the terms "horizontal", "vertical", "overhanging", etc. do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0049] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and defined, the terms "arrangement", "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0051] As Figure 1 、 Figure 2 shown, the present invention provides a subcritical unit rapid load increase system, including a coal-fired power station boiler 1 and a coal pulverizing device 2 which are connected;

[0052] The coal-fired power station boiler 1 includes a furnace 101 and an economizer 102. The furnace 101 is directly connected with a combustion assembly 3. The combustion assembly 3 is successively provided with a high-level burner 301, a main burner 302, and a low-level burner 303 from top to bottom; an economizer 102 is arranged at the lower part of the tail flue of the furnace 101, and the inlet flue of the economizer 102 is communicated with an out-of-furnace combustion device 4;

[0053] The coal pulverizing device 2 includes a coal hopper 201, a coal feeder 202, a coal mill 203, a pulverized coal separator 204, a return powder storage hopper 205, and a return powder feeder 206;

[0054] The coal hopper 201 is arranged above the coal mill 203. The feed inlet of the coal feeder 202 is butted against the discharge outlet of the coal hopper 201, and the discharge outlet of the coal feeder 202 is connected with the coal mill 203;

[0055] The first outlet powder pipe 207 on the coal mill 203 is communicated with the pulverized coal separator 204. The second outlet powder pipe 208 on the pulverized coal separator 204 is communicated with the main burner 302. The return powder main pipe 209 on the pulverized coal separator 204 is communicated with the coal mill 203;

[0056] The return powder branch pipe 210 on the pulverized coal separator 204 is communicated with the return powder storage hopper 205. The feed inlet of the return powder feeder 206 is butted against the discharge outlet of the return powder storage hopper 205, and the discharge outlet of the return powder feeder 206 is connected with the coal mill 203.

[0057] Specifically, the furnace 101 is the core space for combustion and is directly connected to the combustion assembly 3. The combustion assembly 3 includes a high-level burner 301, a main burner 302, and a low-level burner 303 arranged from the upper layer to the lower layer. The high-level burner 301 is mainly used to increase the steam temperature at critical moments under specific working conditions, such as when quickly increasing the load; the main burner 302, as the provider of basic combustion during the stable operation of the unit, continuously provides a stable energy output for the entire combustion process; the low-level burner 303 undertakes the main fuel increment task at the initial stage of load increase by virtue of its fast fuel input characteristic to make up for the pulverization delay of the coal mill. The high-level burner 301 and the low-level burner 303 using fuel oil or gas as fuel are arranged on the upper and lower sides of the main burner 302. The fuel input is rapid, and the combustion amount can be quickly increased instantly when the unit receives a load increase command, making up for the pulverization delay of the coal mill 203 from raw coal to pulverized coal, enabling the subcritical unit to quickly respond to the grid load change and improving the overall load increase rate. For example, when the grid power consumption peaks and the unit needs to quickly increase the load, the low-level burner 303 can operate quickly to enable the unit to quickly enter the load increase state.

[0058] A economizer 102 is arranged at the lower part of the tail flue of the furnace 101, and the inlet flue of the economizer 102 is connected to the out-of-furnace combustion device 4. The out-of-furnace combustion device 4 is an independent combustion chamber, adopting a swirl burner, with fuel oil or gas selected as fuel. High-temperature flue gas is generated through combustion and enters the inlet flue of the economizer 102 to strengthen the heat transfer process of the economizer 102. By inputting high-temperature flue gas into the inlet flue of the economizer 102, the out-of-furnace combustion device 4 enhances the heat transfer effect of the economizer 102. For units with steam turbine bypass high-pressure feedwater heaters, when the inlet water temperature of the economizer 102 drops, the out-of-furnace combustion device 4 can ensure that the outlet water temperature of the economizer 102 does not drop; for units without a steam turbine high-pressure feedwater heater bypass, the outlet water temperature of the economizer 102 can be raised to a reasonable upper limit, improving the safety of the boiler heating surface during the load increase process and ensuring the stable operation of the unit under different working conditions.

[0059] In the coal pulverizing device 2, the coal hopper 201 is located above the coal mill 203, providing the raw coal source for the coal mill 203. The feed inlet of the coal feeder 202 is precisely docked with the discharge outlet of the coal hopper 201. Through the control of the coal feeder 202, the raw coal can be stably transported to the coal mill 203. The coal mill 203 grinds the raw coal, and the generated pulverized coal is transported to the pulverized coal separator 204 through the first outlet powder pipe 207. The pulverized coal separator 204 is arranged in a separated high position, forming a relatively high drop; the pulverized coal separator 204 screens the pulverized coal. The qualified pulverized coal is transported to the main burner 302 through the second outlet powder pipe 208 to participate in combustion, while the pulverized coal that does not meet the particle size requirements is returned to the coal mill 203 through the main return powder pipe 209 for re-grinding. A return powder branch pipe 210 is arranged on the return powder pipeline of the pulverized coal separator 204, which is communicated with the return powder storage hopper 205. When the unit is operating stably, part of the return powder will enter the return powder storage hopper 205 through the return powder branch pipe 210 for storage. The feed inlet of the return powder feeder 206 is docked with the discharge outlet of the return powder storage hopper 205, and the discharge outlet is connected to the coal mill 203. When the unit increases the load, the return powder in the return powder storage hopper 205 is sent to the coal mill 203 after being metered by the return powder feeder 206.

[0060] The arrangement of the return powder storage hopper 205 and the return powder feeder 206 in the coal pulverizing device 2 stores the return powder during the stable operation of the unit. Since the particle size of the return powder is much smaller than that of the raw coal, when increasing the load, giving priority to using the return powder in the return powder storage hopper 205 can rapidly increase the output of the coal mill 203, shorten the grinding delay time of the coal mill 203, improve the response speed of the coal pulverizing device 2, timely provide sufficient pulverized coal for combustion, ensure the stable combustion during the load increase process of the unit, and further enhance the load increase capacity and operation stability of the unit.

[0061] It should be noted that the interior of the furnace 101 is provided with a screen superheater, a high-temperature superheater, a high-pressure reheater, a low-pressure reheater (low-temperature reheater) and a low-temperature superheater (the strip blocks from left to right inside the furnace 101 in the drawing) according to the conventional existing structure to assist in energy conversion and steam parameter regulation. The coal is ground into powder by the coal mill 203 and transported into the furnace 101 through the second outlet powder pipe 208, and then burns into flue gas and flows backward. The heat absorption of the furnace 101 part is mainly radiant heat absorption, and the subsequent heat transfer is mainly convective heat transfer; the screen superheater is semi-radiant and semi-convective. On the water side, it passes through the economizer 102, the water wall, the ceiling superheater, the low-temperature superheater, the screen superheater, the high-temperature superheater in sequence and goes to the high-pressure cylinder of the steam turbine to do work; the steam after doing work in the high-pressure cylinder passes through the low-pressure reheater and the high-pressure reheater in sequence and goes to the intermediate-pressure cylinder of the steam turbine to do work.

[0062] In the embodiment of the present invention, a main pipe adjustment baffle 211 is arranged on the main return powder pipe 209, and a branch pipe adjustment baffle 212 is arranged on the return powder branch pipe 210; both the main pipe adjustment baffle 211 and the branch pipe adjustment baffle 212 are used to adjust the return powder flow rate.

[0063] On the pipeline connecting the discharge port of the coal feeder 202 to the coal mill 203 and on the pipeline connecting the discharge port of the coal reclaimer 206 to the coal mill 203, shut-off baffles 213 are provided. The shut-off baffles 213 are used to control the raw materials fed into the coal mill 203.

[0064] Specifically, in the coal pulverizing process of the entire coal pulverizing device 2, a main pipe regulating baffle 211 and a branch pipe regulating baffle 212 are respectively installed on the main coal return pipe 209 and the branch coal return pipe 210. Both of these baffles are adjustable components, adopting the structural form of a gate valve or a shutter, and the opening degree of the baffle can be changed through manual or automatic control. The main pipe regulating baffle 211 is located on the main coal return pipe 209 and is responsible for overall regulation of the flow rate of the main coal return channel returning from the coal powder separator 204 to the coal mill 203; the branch pipe regulating baffle 212 is installed on the branch coal return pipe 210 and is mainly used for fine adjustment of the coal return flow rate diverted to the coal return storage hopper 205. By adjusting the opening degrees of these two baffles, the flow rate distribution of the coal return in different paths can be flexibly controlled. The regulation of the coal return flow rate by the main pipe regulating baffle 211 and the branch pipe regulating baffle 212 enables the coal pulverizing device 2 to better adapt to different unit operating conditions. When the unit load is stable, the coal return amount can be controlled by adjusting the baffles to ensure that the material concentration and grinding efficiency in the coal mill 203 are in the best state, improving the quality and output of the pulverized coal.

[0065] On the pipeline connecting the discharge port of the coal feeder 202 to the coal mill 203 and on the pipeline connecting the discharge port of the coal reclaimer 206 to the coal mill 203, shut-off baffles 213 are provided. The shut-off baffles 213 are gate valves or butterfly valves, and through electric, pneumatic or manual operation, the pipeline can be fully opened or closed, and the opening degree can be adjusted to a certain extent. During normal operation, the shut-off baffle 213 corresponding to the coal feeder 202 remains open to ensure that raw coal can be continuously transported to the coal mill 203; the shut-off baffle 213 corresponding to the coal reclaimer 206 is opened when coal return is required for grinding according to the system operating conditions and closed when not required, accurately controlling the type and quantity of raw materials fed into the coal mill 203. In addition, the shut-off baffles 213 can effectively control the raw materials fed into the coal mill 203, preventing unqualified raw materials from entering the coal mill 203 in case of abnormal situations such as a malfunction of the coal feeder 202 or a blockage in the coal return system, preventing damage to the coal mill 203 and ensuring the safe and stable operation of the equipment. During equipment maintenance, closing the corresponding shut-off baffles 213 can effectively isolate the equipment and prevent material leakage, providing a safe environment for the maintenance work.

[0066] In an embodiment of the present invention, the main burner 302 is located in the middle of the furnace 101 and is connected to the second outlet powder pipe 208. The main burner 302 is used to provide basic combustion for the unit. The low-level burner 303 and the high-level burner 301 are arranged on the upper and lower sides of the main burner 302. The low-level burner 303 and the high-level burner 301 are connected to the fuel delivery pipeline and are used to adjust the flame center height and the fuel supply during pulverized coal delay.

[0067] The main burner 302 is a multi-layer burner. Each layer of the burner is divided into multiple independent burners arranged at the corners of the boiler. Each independent burner is connected to a second outlet powder pipe 208 and is used to control the pulverized coal supply amount of each layer of the burner.

[0068] Quick cut-off valves and flow regulating valves are provided on the fuel delivery pipelines of the low-level burner 303 and the high-level burner 301. The quick cut-off valves and the flow regulating valves are used to control the supply of fuel oil or gas.

[0069] Specifically, in a coal-fired power plant boiler, the main burner 302 is located in the middle of the furnace 101 and is connected to the second outlet powder pipe 208 of the pulverized coal separator 204. Pulverized coal enters the main burner 302 through this pipeline. The main burner 302 is designed as a multi-layer structure. Each layer of the burner is divided into multiple independent burners arranged at the corners of the boiler. Each independent burner is connected to a second outlet powder pipe 208, that is, each layer of the burner corresponds to a pulverizing device 2. Considering costs, the number of pulverizing devices 2 can also be reduced. For example, the five-layer main burner 302 should originally correspond to five sets of pulverizing devices 2. Two sets of pulverizing devices 2 with increased coal return parts can be selected, and the remaining three sets are designed as conventional pulverizing structures. The low-level burner 303 is located below the main burner 302, and the high-level burner 301 is located above the main burner 302. They are both connected to independent fuel delivery pipelines. These fuel delivery pipelines are made of high-temperature and corrosion-resistant metal materials to ensure stable operation in a high-temperature, high-pressure, and corrosive combustion environment.

[0070] The main burner 302 is located in the middle of the furnace 101 and has a multi-layer structure. Each layer can independently receive pulverized coal, making the distribution of pulverized coal in the furnace 101 more uniform and the combustion more stable. The layout of the multi-layer main burner 302 increases the combustion area and intensity, provides continuous and stable basic combustion for the unit, and ensures the energy output of the unit under normal operating conditions. When the unit load is stable, the burners of each layer of the main burner 302 burn stably according to the set pulverized coal supply amount, maintaining the temperature and pressure stability in the furnace. The low-level burner 303 and the high-level burner 301 are arranged on the upper and lower sides of the main burner 302, and quick cut-off valves and flow regulating valves provided on their fuel delivery pipelines can control the supply of fuel oil or gas. When the unit needs to adjust the load or steam parameters, the fuel supply amounts of the low-level burner 303 and the high-level burner 301 can be adjusted to change the height of the flame center. In the initial stage of load increase, the fuel supply of the low-level burner 303 is increased to lower the flame center, strengthen the combustion intensity in the lower part, quickly increase the temperature in the furnace, and accelerate the steam generation speed; when the steam temperature needs to be increased, the high-level burner 301 is opened to raise the flame center and increase the heat absorption of the upper heating surface, thereby increasing the steam temperature.

[0071] Quick cut-off valves and flow regulating valves are installed on the fuel delivery pipelines of the low-level burner 303 and the high-level burner 301. The quick cut-off valve adopts an electromagnetic valve or a pneumatic valve and has the characteristic of quick response, capable of cutting off the fuel supply within an extremely short time. The flow regulating valve is an electric regulating valve, which drives the movement of the valve core through a motor to adjust the valve opening, thereby controlling the fuel flow rate and enabling the fuel supply to quickly respond to the change of the unit load. When receiving a load increase command, the quick cut-off valve quickly opens, and the flow regulating valve is adjusted to an appropriate opening, enabling the low-level burner 303, and / or, the high-level burner 301 (used when the steam temperature of the unit is insufficient) to quickly inject fuel, make up for the pulverizing delay of the coal mill, and accelerate the unit load increase speed.

[0072] In the embodiment of the present invention, the out-of-furnace combustion device 4 includes an independent combustion chamber. The burner of the combustion chamber adopts a swirl burner, and the fuel inlet of the swirl burner is connected to the fuel oil or gas supply pipeline; the out-of-furnace combustion device 4 is used to evenly introduce flue gas into the inlet flue of the economizer 102 and strengthen the outlet medium temperature of the economizer 102.

[0073] The coal return machine 206 is a belt weighing feeder. The surface of the belt of the coal return machine 206 is provided with anti-slip patterns, and the two sides of the belt of the coal return machine 206 are provided with edge guards to prevent the coal return from slipping during transportation.

[0074] Specifically, the out-of-furnace combustion device 4 has an independent combustion chamber, which is a relatively enclosed and high-temperature-resistant space made of special refractory materials and can withstand the thermal stress and chemical corrosion generated by high-temperature combustion. The fuel inlet is connected to the fuel oil or gas supply pipeline, and these supply pipelines continuously supply fuel oil or gas to the out-of-furnace combustion device 4. There is a unique swirl structure inside the out-of-furnace combustion device 4. When the fuel enters, a swirling air flow is formed, enabling the fuel to be fully mixed with air to achieve efficient combustion. The out-of-furnace combustion device 4 is connected to the inlet flue of the economizer 102 through a flue, ensuring that the flue gas generated by combustion can smoothly enter the economizer 102. These high-temperature flue gases uniformly enter the inlet flue of the economizer 102, increasing the contact area and heat transfer temperature difference between the heating surface of the economizer 102 and the high-temperature medium, thereby significantly enhancing the heat transfer effect of the economizer 102 and effectively increasing the outlet medium temperature of the economizer 102. For units with steam turbine bypass high-pressure feedwater heaters, it can ensure the stability of the outlet water temperature when the inlet water temperature of the economizer drops; for units without steam turbine high-pressure feedwater heater bypasses, it can raise the outlet water temperature to an appropriate range, improving the overall load-raising safety of the unit.

[0075] The coal return machine 206 is in the form of a belt weighing feeder. It includes a belt, a driving device, and a weighing sensor; the belt has anti-slip patterns on its surface, and the anti-slip patterns are usually in the form of regular protrusions or grooves and are evenly distributed on the surface of the belt. Sides are installed on both sides of the belt, and the sides are made of rubber or other flexible materials to form a relatively enclosed conveying channel. The driving device drives the belt to rotate, enabling the coal return to be conveyed from the coal return storage hopper 205 to the coal mill 203. The weighing sensor is used to monitor the weight of the coal return conveyed on the belt in real time. The anti-slip patterns and the sides ensure the stability of the coal return conveyance, reducing the weighing error caused by the coal return slipping or piling up, enabling the weighing sensor to accurately obtain the weight information of the coal return. It helps to achieve the control of the coal return supply amount to the coal mill 203.

[0076] The present invention also provides a method for quickly raising the load of a subcritical unit, as Figure 3 shown, including the following steps:

[0077] Step 1: After the subcritical unit receives a load-raising instruction, the high-pressure feedwater heater bypass is opened, and the out-of-furnace combustion device 4 operates. The input raw material amount of the out-of-furnace combustion device 4 is adjusted according to the outlet medium of the economizer 102;

[0078] Specifically, after the subcritical unit receives a load-raising instruction, the high-pressure feedwater heater bypass is immediately opened and put into use, and the out-of-furnace combustion device 4 is ignited and operated. The output (input raw material amount) of the out-of-furnace combustion device 4 is determined by the outlet medium temperature of the economizer, that is, the difference from the saturation temperature is kept small but sufficient.

[0079] Step 2: The low-level burner 303 receives fuel oil or gas, and the low-level burner 303 provides a fuel increment corresponding to the load; the high-level burner 301 receives fuel oil or gas, and for the unit whose steam temperature has not reached the preset value, the high-level burner 301 operates according to the steam temperature characteristics of the unit.

[0080] The coal powder output of the main burner 302 is allocated according to the sharing method. The output increment of the coal mill 203 is determined according to the load, and the coal feeding preferentially uses the coal stored in the return powder storage hopper 205.

[0081] Specifically, taking advantage of the fast fuel input of the low-level burner 303, the fuel increment corresponding to the load is mainly borne by it (the output of some coal mills 203 increases instantaneously due to the change of mill ventilation volume and the pulverized coal stored in the mill), until the incremental fuel of the coal mill 203 stably enters the furnace.

[0082] The coal powder quantities transmitted by multiple second outlet powder pipes 208 to the main burner 302 are allocated according to the sharing method; the sharing method is that the coal powder feeding increment of the lower burner in the main burner 302 is greater than that of the upper burner, that is, ΔF A >ΔF B >ΔF C >ΔF D >ΔF E ; where, Δ represents increment, F represents the fuel quantity of the combustion layer, and A, B, C, D, and E are the layers of the main burner 302.

[0083] Meanwhile, the input raw material quantity of the coal mill 203 does not exceed the rated input raw material quantity, that is, the input raw material quantity reaching the rated value does not participate in the fuel increment sharing; during the load increase process, the sharing ratio of the coal powder feeding increment of each layer of burner is combined with system simulation and on-site commissioning; in the later stage of load growth, the total fuel increment deducts the fuel used by the low-level burner 303 or the high-level burner 301; when the unit load stops growing, after the unit load stops growing, the output distribution of each coal mill 203 continues to be adjusted, and the adjustment principle at this time is that the output of each mill is balanced or in the normal operation combination.

[0084] Step 3: When the coal feeding increase command of the coal mill 203 reaches the stable increase of the coal powder quantity at the outlet of the coal mill 203, the low-level burner 303 and / or the high-level burner 301 stops burning.

[0085] Step 4: After closing the high-pressure heater feedwater bypass, then close the out-of-furnace combustion device 4.

[0086] Specifically, the high-pressure heater feedwater bypass and the out-of-furnace combustion device 4 gradually withdraw from operation in coordination. During the process, ensure that the medium temperature at the outlet of the economizer is reasonable to meet the safety requirements. The operation end time of the out-of-furnace combustion device 4 is later than the withdrawal time of the high-pressure heater feedwater bypass, which can be based on the system simulation and on-site commissioning of the actual unit.

[0087] Step 5: Switch the coal supply amount in the coal pulverizing device 2 from being supplied by the recycled powder storage hopper 205 to being supplied by the coal hopper 201;

[0088] Step 6: After the unit load increase ends and the load is stable, divert the recycled powder from the recycled powder branch pipe 210 in the coal pulverizing device 2 to the recycled powder storage hopper 205 to the design value, and wait for the next output of the coal mill 203.

[0089] Specifically, the recycled powder branch pipe 210 is always in use. During the load increase, as the fuel increases, the increased part preferentially uses the supply from the recycled powder storage hopper 205, and after stable operation, it is switched to the coal hopper 201. Since the particle size of the "recycled powder" entering the coal mill 203 is much smaller than that of the raw coal, it can make the output of the coal mill 203 increase rapidly (because the fineness of the pulverized coal at the outlet decreases, and for a dynamic separator, the separator speed can be appropriately reduced), shortening the grinding delay time of the coal mill 203.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A subcritical unit rapid load increase system, characterized in that: include: A connected coal-fired power station boiler (1) and a pulverizing device (2); The coal-fired power station boiler (1) comprises a furnace (101) and an economizer (102); the furnace (101) is directly connected to a combustion assembly (3); the combustion assembly (3) is provided with a high-position burner (301), a main burner (302) and a low-position burner (303) in order from top to bottom; the economizer (102) is provided at the lower part of the tail flue of the furnace (101); the inlet flue of the economizer (102) is connected to an external combustion device (4); The pulverizing device (2) comprises a coal hopper (201), a coal feeder (202), a coal mill (203), a pulverized coal separator (204), a return pulverized coal storage hopper (205) and a return pulverized coal feeder (206); The coal hopper (201) is arranged above the coal mill (203), the feed port of the coal feeder (202) is connected to the discharge port of the coal hopper (201), and the discharge port of the coal feeder (202) is connected to the coal mill (203); The first outlet powder pipe (207) on the coal mill (203) is in communication with the coal powder separator (204), the second outlet powder pipe (208) on the coal powder separator (204) is in communication with the main burner (302), and the return powder main pipe (209) on the coal powder separator (204) is in communication with the coal mill (203); The return powder branch pipe (210) on the coal powder separator (204) is connected to the return powder storage bucket (205), the feed port of the return powder machine (206) is connected to the discharge port of the return powder storage bucket (205), and the discharge port of the return powder machine (206) is connected to the coal mill (203).

2. The subcritical unit rapid load increase system according to claim 1, characterized in that: The powder return main pipe (209) is provided with a main pipe regulating baffle (211), and the powder return branch pipe (210) is provided with a branch pipe regulating baffle (212); the main pipe regulating baffle (211) and the branch pipe regulating baffle (212) are both used to regulate the powder return flow rate.

3. The subcritical unit rapid load increase system according to claim 1, characterized in that: A shutoff damper (213) is provided on the pipeline connecting the discharge port of the coal feeder (202) and the coal mill (203) and the pipeline connecting the discharge port of the coal powder recycling machine (206) and the coal mill (203). The shutoff damper (213) is used to control the raw materials fed into the coal mill (203).

4. The subcritical unit rapid load increase system according to claim 1, characterized in that: The main burner (302) is located in the middle of the furnace (101) and is connected to the second outlet powder pipe (208), and the main burner (302) is used to provide basic combustion for the unit; the low-position burner (303) and the high-position burner (301) are arranged on the upper and lower sides of the main burner (302), and the low-position burner (303) and the high-position burner (301) are connected to the fuel delivery pipeline, which is used to adjust the flame center height and the fuel supply during powder making delay.

5. The subcritical unit rapid load increase system according to claim 4, characterized in that: The main burner (302) is a multi-layer burner, and each layer of burners is connected to a second outlet powder pipe (208) for controlling the coal powder supply amount of each layer of burners.

6. The subcritical unit rapid load increase system according to claim 4, characterized in that: The fuel delivery pipelines of the low-position burner (303) and the high-position burner (301) are both provided with a quick shut-off valve and a flow regulating valve, and the quick shut-off valve and the flow regulating valve are used to control the supply of fuel oil or gas.

7. The subcritical unit rapid load increase system according to claim 1, characterized in that: The off-furnace combustion device (4) comprises an independent combustion chamber, the burner of the combustion chamber is a swirl burner, and the fuel inlet of the swirl burner is connected to the fuel oil or gas supply pipeline; the off-furnace combustion device (4) is used to make the flue gas evenly enter the inlet flue of the economizer (102) and enhance the outlet medium temperature of the economizer (102).

8. The subcritical unit rapid load increase system according to claim 1, characterized in that: The powder return machine (206) is a belt weighing feeder, the belt surface of the powder return machine (206) is provided with anti-slip grooves, and the belt sides of the powder return machine (206) are provided with ribs to prevent the powder return from slipping during the conveying process.

9. A method for rapidly increasing the load of a subcritical unit, characterized in that: The method uses the subcritical unit rapid load increase system according to any one of claims 1 to 8, and comprises the following steps: Step 1: After receiving a load increase instruction, the high-pressure heater feed water bypass of the subcritical unit is opened, the external combustion device (4) is operated, and the amount of raw materials input into the external combustion device (4) is adjusted according to the outlet medium of the economizer (102); Step 2, the low-position burner (303) or the high-position burner (301) receives fuel oil or gas, and the low-position burner (303) provides a fuel increment corresponding to the load; for a unit whose steam temperature does not reach a preset value, the high-position burner (301) is operated according to the steam temperature characteristics of the unit; The output powder quantity of the main burner (302) is apportioned according to the apportionment method, the output increment of the coal mill (203) is determined according to the load, and the coal stored in the return powder storage hopper (205) is preferentially used for coal supply; Step 3, when the coal feed increase instruction of the coal mill (203) is issued and the coal powder quantity at the outlet of the coal mill (203) increases steadily, the low-position burner (303) is exited, and / or the high-position burner (301) is burned; Step 4, closing the high pressure heater water bypass and then closing the external combustion device (4); Step 5, the coal supply in the pulverizing device (2) is switched from the coal return storage hopper (205) to the coal hopper (201); Step 6: After the load increase of the unit is completed and the load is stable, the return powder is diverted from the return powder branch pipe (210) in the pulverizing device (2) to the return powder storage bucket (205) to the designed value, and the next output of the coal mill (203) is awaited.

10. The method for rapid load increase of a subcritical unit according to claim 9, characterized in that: The apportionment method in step 2 is that the powder increment of the lower burner in the main burner (302) is greater than the powder increment of the upper burner, that is, ΔF A >ΔF B >ΔF C >ΔF D >ΔF E ; Wherein, Δ represents the increment, and F represents the amount of fuel in the combustion layer; At the same time, the amount of raw materials input to the coal mill (203) does not exceed the rated amount of raw materials input, that is, the amount of raw materials input that reaches the rated value does not participate in the fuel increment allocation; in the later stage of load growth, the total fuel increment deducts the fuel used by the low-level burner (303) or the high-level burner (301); When the unit load stops increasing, the amount of raw materials input into the coal mill (203) is evenly distributed.

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