Temperature difference control method for steam pocket wall during cold start of boiler

Abstract

The invention discloses a boiler cold start steam drum wall temperature difference control method. According to the method, the steam drum wall temperature difference in different time periods of boiler cold start is controlled; the method specifically comprises the steps that in the boiler cold-state starting preparation stage, a steam condenser and a deaerator are washed in a tidal mode till the water quality of the steam condenser and the water quality of the deaerator reach the preset qualified standard; after the water quality of the deaerator is qualified, heating the deaerator, and controlling the water temperature of the deaerator according to a preset water temperature rising standard of the deaerator so as to control the steam pocket wall temperature difference generated when water enters the boiler; in the boiler cold-state starting temperature rising stage, the steam drum is filled with water through a water feeding pump until the water level just submerges a steam leading-out pipe opening in the top of the steam drum, the steam drum is soaked and preheated through water at the set temperature, and the water temperature is adjusted according to the steam drum wall temperature to control steam drum wall temperature difference generated in the boiler temperature rising and pressure rising initial stage; after the boiler is started and ignited in a cold state, the temperature of the steam pocket wall is controlled by designing metal heat transfer, saturated steam pressure and combustion control.

Description

Technical Field

[0001] The present invention relates to the technical field of generator sets, and particularly to a method for controlling the temperature difference of the steam drum wall during cold start-up of a boiler. Background Art

[0002] In a thermal power plant, if the boiler is a natural circulation boiler, there must be a steam drum. The steam drum is a large cylindrical metal container, which is usually suspended at the top of the boiler, horizontally arranged, independent of the furnace, not heated, but insulated.

[0003] The steam drum is the connection hub of the three processes of boiler heating, vaporization, and superheating, and also the demarcation point of these three processes. The steam drum is indispensable in a natural circulation boiler.

[0004] Modern thermal power plant units are all high-parameter and large-capacity units. When the boiler is in operation, the pressure inside the steam drum exceeds 25 MPa, and the saturation temperature of the water vapor inside the steam drum exceeds 350 °C. Therefore, the steam drum must bear huge pressure and high temperature. To meet the pressure safety requirements, the steam drum must be cast very thick. The wall thickness of the steam drum of a high-parameter and large-capacity unit boiler exceeds 200 mm; and because the steam drum must meet its functions and roles, the inner diameter φ of the radial cross-section of the steam drum is close to 2 meters, and the horizontal length is close to 20 meters. Therefore, the steam drum has a huge volume and mass, and the huge mass will have a huge heat storage capacity. Therefore, during the boiler start-up process of heating and pressurizing, the heat transfer of the steam drum metal is slow, that is, during the boiler start-up process of heating and pressurizing, due to the large metal mass and large wall thickness of the steam drum, a temperature difference will inevitably occur on the steam drum wall. The temperature difference includes the temperature difference between the inner and outer walls of the steam drum, the temperature difference between the upper and lower walls, the temperature difference between the left and right ends, etc.

[0005] According to the technical instructions of the casting manufacturer and domestic and international general experience, a certain temperature difference is allowed in the operation of the steam drum, but the wall temperature difference must be controlled within a certain range. Practice has proved that as long as the temperature difference between the upper and lower walls and the inner and outer walls of the steam drum does not exceed 50 °C, the additional temperature difference thermal stress generated will not damage the steam drum; during operation, a temperature difference of ≯40 °C is used as the safety control point.

[0006] In fact, during the boiler startup process, the temperature difference between the upper and lower walls of the steam drum is very likely to exceed this value, causing stress to occur inside the metal of the steam drum. Compressive stress is generated on the side with a higher temperature, and tensile stress is borne on the side with a lower temperature. If the temperature difference is too large, the internal stress of the steam drum will be too large, resulting in micro-cracks at the welds. Long-term use may lead to leakage. When the metal stress generated by the excessive temperature difference is too large, it will cause plastic deformation of the metal, resulting in permanent damage to the steam drum, and ultimately leading to equipment damage. The leakage of the steam drum not only affects the safe operation of the equipment but also may pose a threat to personal safety. At the same time, in order to control the temperature difference between the upper and lower walls of the steam drum during unit startup, a large amount of time will be consumed. Especially during the cold startup of the boiler, it is particularly difficult to control the wall temperature difference. There is also a situation where the wall temperature difference exceeds the limit during the hot startup of the boiler. However, relatively speaking, it is relatively easy to control the wall temperature difference during hot startup. The present invention only focuses on the difficult cold startup process. Summary of the Invention

[0007] A method, device, and storage medium for controlling the temperature difference between the upper and lower walls of a steam drum during cold startup of a boiler proposed by the present invention can at least solve one of the technical problems in the background art.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for controlling the temperature difference between the upper and lower walls of a steam drum during cold startup of a boiler controls the wall temperature of the steam drum at different time periods during the cold startup process of the boiler.

[0010] Furthermore, the specific time periods of the present invention include:

[0011] During the cold startup preparation stage of the boiler, the condenser and deaerator are flushed in a tidal form until the water quality of the condenser and deaerator reaches the preset qualified standard; after the water quality of the deaerator is qualified, the deaerator heating is started, and the water temperature of the deaerator is controlled according to the preset water temperature rising standard of the deaerator, so that the water temperature meets the water inlet requirements when the boiler is in its original cold state, and the wall temperature difference is not generated when the boiler is filled with water.

[0012] During the cold startup heating-up stage of the boiler, the steam drum is filled with water by the feed pump until the water level just reaches the steam outlet pipe opening at the top of the steam drum. The steam drum is soaked and preheated with water at a set temperature, and the water temperature is adjusted according to the wall temperature of the steam drum to control the wall temperature difference of the steam drum at the initial stage of boiler heating-up and pressure rising.

[0013] After the boiler is ignited during cold startup, the wall temperature of the steam drum is controlled by setting metal heat transfer, saturated steam pressure, and combustion control.

[0014] Furthermore, in the preparation stage of the cold startup of the boiler in the present invention;

[0015] The preparation stage is divided into two stages, specifically including: Hours 1-2: Flush the condenser, deaerator, and boiler;

[0016] Feed qualified demineralized water into the condenser. When the water level in the condenser meets the preset requirements, start the condensate pump to feed water into the deaerator, and flush the condenser and deaerator in a tidal form until the water quality of the condenser and deaerator is qualified; after the water quality of the deaerator is qualified, put into the deaerator heating, and control the water temperature of the deaerator, with the water temperature rising standard of the deaerator: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the steam drum < 50°C;

[0017] From the 3rd to the 6th hour: Start the feed water pump to feed water into the boiler, and flush the boiler by the tidal method until the boiler water quality is qualified. The deaerator continues to heat, and the water temperature of the deaerator is controlled according to the formula: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the steam drum < 50°C.

[0018] Furthermore, the water quality qualification standard in the preparation work for the cold start of the boiler described in the present invention is: the iron content in the condensate water ≤ 100 μg / L, and the iron content at the outlet of the deaerator ≤ 100 μg / L.

[0019] Furthermore, the method of the present invention also includes the method for controlling the wall temperature of the steam drum in the cold start-up heating stage of the boiler: Use the feed water pump to fill the steam drum with water until the water level reaches just above the steam outlet pipe at the top of the steam drum, so as to soak and preheat the steam drum with water at a certain temperature;

[0020] Among them, the soaking water temperature is selected as the wall temperature at the outlet of the economizer; the reference formula for the deaerator temperature rise standard is: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the steam drum < 50°C; the soaking time is 2 hours as a cycle, and soak continuously twice; after the first soaking time is up, drain 1 / 2 of the water in the boiler, and re-select water at a higher temperature according to the wall temperature of the steam drum, and then feed water into the boiler, repeating the first soaking operation.

[0021] Furthermore, the method for controlling the wall temperature of the steam drum after the boiler is ignited in the method of the present invention is:

[0022] a. Keep the high water temperature of the deaerator: The principle of the water temperature is that the water temperature of the deaerator - the wall temperature at the outlet of the economizer = 35°C to 40°C;

[0023] b. Keep the steam drum running at the highest safe water level: Control the steam drum water level to run at about +50 to +100 mm;

[0024] c. Conduct bottom blowdown of the boiler: For one or several lowest wall temperature points at the bottom of the steam drum, select the bottom blowdown valve corresponding to the temperature measurement point for blowdown;

[0025] d. Open the high-pressure bypass and low-pressure bypass of the unit 100%, and control the change of the boiler saturation temperature: Opening the high-pressure bypass and low-pressure bypass can effectively reduce the rising speed of the boiler pressure, control the rise of the boiler saturation temperature, reduce the heat release of the steam to the upper wall of the steam drum, and delay the rising speed of the upper wall temperature of the steam drum;

[0026] e. Open all drain valves of the boiler superheater heating surface;

[0027] f. Control the total boiler air volume: Keep the total boiler air volume at 30% - 40% BMCR, and adjust the secondary air distribution shape in the furnace to an equal distribution form;

[0028] g. Control the fuel quantity: In the initial stage of ignition, control the ignition fuel quantity, control the boiler heating rate, and strictly control the superheated steam temperature rise rate of the boiler at 1.5 - 2 °C / min; When the temperature difference between the steam drum walls is stable, the heating rate is controlled according to the unit startup requirements and is no longer restricted by this article;

[0029] h. Control the feed water flow regulation: Continuously feed water at a rate of < 316 t / g. When feeding water, confirm the closed state and tightness of the economizer recirculation valve.

[0030] As can be seen from the above technical solutions, the method for controlling the temperature difference between the steam drum walls during the cold start of the boiler of the present invention involves flushing the condenser, deaerator, and boiler until the water quality of the condenser and deaerator is qualified. After the water quality of the deaerator is qualified, the deaerator heating is put into operation, and the deaerator water temperature is controlled according to the preset deaerator water temperature rise standard to achieve the control of the temperature difference between the steam drum walls generated when the boiler is fed with water; Use the feed water pump to fill the steam drum with water until the water level just reaches the top of the steam outlet pipe of the steam drum. Soak and preheat the steam drum with water at a set temperature, and adjust the water temperature according to the steam drum wall temperature to control the temperature difference between the steam drum walls at the initial stage of boiler heating and pressure increase;

[0031] Through the above method, the solution of the present invention can effectively control the temperature difference between the steam drum walls within 40 °C during the unit startup process, far away from the maximum allowable value of 50 °C, ensuring the safe operation of the boiler steam drum and extending the service life of the steam drum.

[0032] After the boiler is ignited, the steam drum wall temperature can be controlled by designing metal heat transfer, saturated steam pressure, and combustion control, which can shorten the time of low boiler combustion rate, enabling the boiler not to be restricted by the metal wall temperature during the heating and pressure increase process, reducing the time of the unstable interval of low combustion rate, and making the startup process safer.

[0033] After adopting the solution of the present invention, the overall startup time of the unit is shortened, and the startup cost is saved. The time period for controlling the temperature difference between the steam drum walls after the boiler is ignited will not exceed 0.5 hours, saving a large amount of time compared with the traditional control process. Since it is no longer restricted by the temperature rise of the steam drum metal material, the startup process is accelerated, and various losses such as electric energy, fuel, steam, and manpower consumed during the startup process are greatly reduced. Therefore, the startup cost is saved. At the same time, because the startup process is accelerated, it means that the generator can be paralleled with the power grid faster, generating economic benefits, which can kill two birds with one stone. Brief Description of the Drawings

[0034] Figure 1 Schematic flow diagram of the method for controlling the temperature difference of the steam drum wall of the present invention;

[0035] Figure 2 Schematic diagram of the temperatures of various parts of the steam drum wall after the boiler is ignited. Specific implementation manner

[0036] 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.

[0037] The method for controlling the temperature difference of the steam drum wall during the cold start of the boiler of the present invention is implemented in 3 stages (steps): (Note: The grid dispatching generally notifies the unit grid connection time 24 hours in advance. The following uses 24 hours before grid connection as the time node for illustration. In actual operation, there is no strict requirement for the time node, and the step results are used as the guide).

[0038] As Figure 1 shown, the method for controlling the temperature difference of the steam drum wall during the cold start of the boiler described in this embodiment includes the following steps:

[0039] S100. Prepare for the cold start of the boiler;

[0040] S200. Soak and heat up the steam drum to prepare for boiler ignition;

[0041] S300. Ignite the boiler and at the same time control the steam drum wall temperature to complete the cold start of the boiler.

[0042] The following is a specific description of each step:

[0043] S100. Prepare for the cold start of the boiler;

[0044] After the boiler is shut down, to avoid corrosion, the water in the boiler is generally drained completely. Before the boiler is started, water is fed into the boiler again. When feeding water, the feed water passes through the feed water system, through the economizer and then into the steam drum. Since the steam drum is at the highest point of the water system, the water will first fill the pipes such as the water wall and the downcomer at the lower part of the boiler, and finally the water level rises and the visible water level in the steam drum can be gradually seen. When the water level in the steam drum rises from low to high and approaches "-50 mm" upward, the water level meets the ignition and operation conditions, and the water supply will stop. Because the boiler is in an unignited state at this time, the feed water is not heated when passing through the economizer, and when the feed water enters the steam drum, it first contacts the lower wall of the steam drum, and the lower wall of the steam drum is gradually heated and its temperature rises by the feed water with a certain temperature, while the upper wall of the steam drum does not contact the feed water and cannot be heated, gradually forming a temperature difference between the upper and lower walls of the steam drum. At this time, the temperature of the steam drum wall is low at the top and high at the bottom.

[0045] The preparation work for the cold start of the boiler is divided into two stages, specifically:

[0046] Preparation stage (hours 1 - 6):

[0047] First stage, hours 1 - 2: Conduct flushing of the condenser, deaerator, and boiler. Feed qualified demineralized water into the condenser. When the water level in the condenser meets the requirements, start the condensate pump to feed water into the deaerator. Flush the condenser and deaerator in a tidal form (fill the deaerator with water and then drain it all, repeating the two operations of filling and emptying) until the water quality of the condenser and deaerator is qualified. The water quality standards are shown in Table 1, and the qualified standards for the water quality of the condenser and deaerator are that the iron content in the condensate water ≤ 100 μg / L and the iron content at the outlet of the deaerator ≤ 100 μg / L.

[0048] Table 1 Low - pressure flushing water quality standards

[0049]

[0050] When the water quality of the deaerator is qualified, put the deaerator into heating and control the water temperature of the deaerator according to the water temperature rising standard of the deaerator: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the steam drum < 50°C.

[0051] Among them, the water in the deaerator is sent to the boiler through the feed water pump. Along the way, it passes through high - pressure heaters, economizers, and a large number of pipelines before entering the steam drum. At this time, because the equipment is in a cold state, after the water temperature of the deaerator rises, the water passes through the pipeline equipment along the way and will be absorbed by a large amount of heat by the pipeline and equipment along the way, resulting in a significant decrease in water temperature. Therefore, at this time, the feed water temperature is judged by the wall temperature at the outlet of the economizer. When the temperature difference between the temperature of the boiler room and the lowest wall temperature of the steam drum < 50°C, the wall temperature will not exceed the limit.

[0052] Second stage, hours 3 - 6: Start the feed water pump to feed water into the boiler and also use the tidal method to flush the boiler until the boiler water quality is qualified (qualified standard: the iron content in the boiler water ≤ 200 μg / L). The deaerator continues to heat to make the water temperature meet the requirements for water inlet when the boiler is in its original cold state, and control that there is no wall temperature difference when the water enters the boiler. Among them, the deaerator controls the water temperature according to the formula: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the steam drum < 50°C.

[0053] S200. Soak and heat up the steam drum to prepare for boiler ignition;

[0054] Heating - up stage: Soak and heat up the steam drum, in the stage of hours 7 - 10;

[0055] Use the feed water pump to fill the steam drum with water until the water level just reaches the steam outlet pipe opening at the top of the steam drum, so as to use the water at a certain temperature to soak and preheat the steam drum. The soaking water temperature is also selected as the wall temperature at the outlet of the economizer: the same reference formula is used for the temperature rise standard of the deaerator: 40°C < wall temperature at the outlet of the economizer - minimum wall temperature of the steam drum < 50°C. The soaking time is 2 hours as a cycle, and soak continuously for two times; after the first soaking time is up, drain 1 / 2 of the water in the boiler, re-select water at a higher temperature according to the wall temperature of the steam drum, then fill the boiler with water, and repeat the first soaking operation. After this process, the wall temperature of the boiler steam drum can reach 90°C.

[0056] Because soaking preheating is adopted, the steam drum is heated evenly and no temperature difference will be generated. If the unit startup time permits, this process can be continued, and the heating amplitude of the deaerator can be continuously increased. The water temperature of the deaerator can be increased to 160°C, and the wall temperature of the steam drum can even be preheated close to 100°C in advance.

[0057] S300. Ignite the boiler, and at the same time control the wall temperature of the steam drum to complete the cold start of the boiler;

[0058] After the boiler is ignited, in the initial stage of cold start, to control the heating rate of the boiler metal, the fuel input rate is controlled to be relatively low, the combustion in the boiler furnace is unstable, and in addition, the flame in the furnace cannot be evenly distributed during the initial stage of boiler combustion. Therefore, the combustion radiation heat received by the water walls at different parts is uneven. The water wall that receives less combustion radiation heat generates fewer bubbles and it is difficult to establish a natural circulation, resulting in a slow water flow rate in this part of the steam drum, and even a phenomenon of stagnation and backflow may occur. At this time, the water temperature in the steam drum remains unchanged, the lower wall of the steam drum cannot be heated by the feed water, and the temperature rise of the lower wall is slow; while the upper wall of the steam drum receives the heat release of the steam. Since the heat release coefficient of the steam is 2 - 3 times larger than that of the water, the temperature rise rate of the upper part of the steam drum wall is much higher than that of the lower part of the steam drum wall. The faster the pressure rise rate, the greater the wall temperature difference generated. At this time, the wall temperature of the steam drum is high at the top and low at the bottom, and this stage is also the stage where the wall temperature of the steam drum is most likely to exceed the limit and is the most difficult to control.

[0059] Control stage after the boiler is ignited, from the 11th hour to the 11.5th hour;

[0060] The following method can be adopted in this process to ensure that the wall temperature of the steam drum can be effectively controlled within 40°C, and gradually decreases and finally stabilizes.

[0061] Other measures of the generating unit are ready. Specifically, the measures include: coal feeding into the coal bunker, starting the boiler fan, using external heat supply to supply shaft seals to the steam turbine driven feed water pump set, evacuating the air, etc.; it is a series of very complicated works of multiple specialties.

[0062] After meeting the boiler ignition conditions, drain the drum water level to the ignition water level and then ignite the boiler. After the boiler is ignited, it starts to heat up and increase pressure, and the temperature difference across the drum wall will rapidly expand. This process is also the most difficult stage to control the temperature difference across the drum wall.

[0063] Among them, meeting the requirements for the ignition water level mainly targets the safe operation of the condensate pump and has no requirements for itself. It is stipulated that the condensate pump can be started only when the condenser water level > 425 mm, and the normal operating water level of the condenser is maintained at 700 - 775 mm.

[0064] During the process of the boiler igniting, heating up and increasing pressure, since the upper part of the drum is a steam space and the heat transfer coefficient of steam to the drum wall is large; the lower part of the drum is a water space and the heat release rate of water to the drum is slow. The temperature difference across the drum wall will show a situation where the temperature of the upper wall rises fast and the temperature of the lower wall rises slow, so a temperature difference will occur. Therefore, to control the temperature difference across the drum wall, heat transfer in the upper part is slowed down and heat transfer in the lower wall is accelerated, thereby reducing the drum temperature difference. Controlling the temperature difference across the drum wall is a series of methods and needs to be implemented from multiple perspectives such as designing metal heat transfer, saturated steam pressure, and combustion control.

[0065] Immediately after the boiler is ignited, the following methods are adopted:

[0066] a. Keep the deaerator water at a high temperature. The principle of the water temperature is: deaerator water temperature - economizer outlet wall temperature = 35°C - 40°C.

[0067] b. Keep the drum at the highest safe water level operation:

[0068] Control the drum water level to operate at about +50 - +100 mm.

[0069] c. Reasonably conduct blowdown at the bottom of the boiler:

[0070] As Figure 2 shown, for one or several lower wall temperature points of the drum, compare the temperatures of each part of the drum wall, obtain the lowest temperature point through comparison, and select the bottom blowdown valve corresponding to this temperature measuring point for blowdown to accelerate the water flow, promote the faster establishment of water circulation, so that the lower wall of the drum can be better heated, achieving the purpose of reducing the temperature difference between the upper and lower walls.

[0071] d. Open the high - pressure bypass and low - pressure bypass of the unit 100% to control the change of the boiler saturation temperature:

[0072] The opening of the high - pressure bypass and low - pressure bypass can effectively reduce the boiler pressure rising speed, thereby controlling the rise of the boiler saturation temperature, reducing the heat release of steam to the upper wall of the drum, and delaying the rising speed of the upper wall temperature of the drum.

[0073] e. Open all the drain valves of the boiler superheater heating surface:

[0074] Prevent water accumulation in the heating surfaces of the boiler causing steam lock, prevent steam lock from causing abnormal increase in steam pressure and overheating of pipelines, and keep the steam pipeline unobstructed.

[0075] f. Control the total air volume of the boiler:

[0076] Maintain the total air volume of the boiler at 30% to 40% BMCR, and adjust the furnace secondary air distribution shape to an even distribution form.

[0077] g. Control the amount of fuel:

[0078] The monitoring personnel's adjustment of the air volume, wind speed and wind temperature entering the boiler will not remain unchanged. They are different for different people. They are affected by their experience and equipment, which directly affects the adjustment of the boiler combustion process. The result of combustion adjustment affects the stability of combustion, and whether the combustion is stable affects the drum wall temperature.

[0079] In the initial stage of ignition, control the ignition fuel amount, control the boiler heating rate, and strictly control the boiler superheated steam temperature rise rate at 1.5-2℃ / min; when the drum wall temperature difference stabilizes, the heating rate is controlled according to the unit startup requirements and is no longer subject to this restriction.

[0080] h. Control water flow regulation:

[0081] When the boiler is started, the boiler combustion intensity, the heating range of the feed water by the economizer, the water temperature of the deaerator entering the economizer, the feed water flow control size, the feed water control method, etc., all of which will have a direct impact on the drum wall temperature;

[0082] Try to supply water continuously at a small flow rate, and make sure the economizer recirculation door is closed and tight when supplying water. Among them, continuous small flow is a relative concept. The steam-driven feedwater pump manufacturer sets it as: when the flow rate is continuously greater than 316t / h, it satisfies the minimum safe flow value for the steam-driven feedwater pump to close the steam pump recirculation door. Therefore, before it is less than 316t / g, it can be called a small flow rate.

[0083] Through the above measures, within 30 minutes after the boiler is ignited, the lowest wall temperature of the drum will quickly exceed 130℃, and the maximum temperature difference between the upper and lower walls of the drum will not exceed 40℃, and the wall temperature difference will gradually decrease, and finally the upper and lower wall temperatures will gradually become consistent, forming a "0" temperature difference. (Generally, the lower wall temperature of the drum is heated to above 110℃, the water temperature in the boiler has exceeded 100℃, reaching a saturated state, and the water vapor heat release coefficient tends to be consistent. In the subsequent process of the boiler continuing to increase temperature and pressure, the drum wall temperature difference gradually decreases)

[0084] In summary, the method for controlling the temperature difference of the steam drum wall during the cold start of the boiler according to the present invention involves flushing the condenser, deaerator, and boiler until the water quality of the condenser and deaerator is qualified. After the water quality of the deaerator is qualified, the deaerator heating is started, and the water temperature of the deaerator is controlled according to the preset water temperature rising standard for the deaerator, so as to control the temperature difference of the steam drum wall generated when the boiler is filled with water. The steam drum is filled with water by the feed water pump until the water level just reaches the steam outlet pipe opening at the top of the steam drum. The steam drum is soaked and preheated with water at a set temperature, and the water temperature is adjusted according to the steam drum wall temperature to control the temperature difference of the steam drum wall at the initial stage of boiler warming and pressure rising.

[0085] Through the above method, the present invention can effectively control the temperature difference of the steam drum wall within 40°C during the unit startup process, far away from the maximum allowable value of 50°C, ensuring the safe operation of the boiler steam drum and extending the service life of the steam drum.

[0086] After the boiler is ignited, the temperature of the steam drum wall can be controlled by designing metal heat transfer, saturated steam pressure, and combustion control, which can shorten the time of the boiler at low combustion rate, enabling the boiler not to be restricted by the metal wall temperature during the process of warming and pressure rising, reducing the time of the unstable interval at low combustion rate, and making the startup process safer.

[0087] After adopting the present invention, the overall startup time of the unit is shortened, and the startup cost is saved. The time period for controlling the temperature difference of the steam drum wall after the boiler is ignited will not exceed 0.5 hours, saving a large amount of time compared with the traditional control process. Since it is no longer restricted by the temperature rise of the steam drum metal material, the startup process is accelerated, and various losses such as electric energy, fuel, steam, and manpower consumed during the startup process are greatly reduced, thus saving the startup cost. At the same time, because the startup process is accelerated, it means that the generator can be paralleled with the power grid faster, generating economic benefits, which can kill two birds with one stone.

[0088] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0089] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; 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 recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A method for controlling the temperature difference of the steam drum wall during the cold start of a boiler, characterized in that, Control the drum wall temperature during different time periods in the cold start-up process of the boiler; Specifically include: During the preparation stage of the boiler cold start-up, flush the condenser and deaerator in a tidal form until the water quality of the condenser and deaerator reaches the preset qualified standard; After the water quality of the deaerator is qualified, put the deaerator into heating, control the water temperature of the deaerator according to the preset water temperature rising standard of the deaerator, make the water temperature meet the water inlet requirements when the boiler is in the original cold state, and control no wall temperature difference when the boiler takes in water; During the heating-up stage of the boiler cold start-up, use the feed water pump to fill the drum with water until the water level just exceeds the steam outlet pipe at the top of the drum. Use water at a set temperature to soak and preheat the drum, and adjust the water temperature according to the drum wall temperature to control the drum wall temperature difference generated in the initial stage of the boiler heating-up and pressure-boosting; After the boiler is ignited during the cold start-up, control the drum wall temperature by setting metal heat transfer, saturated steam pressure, and combustion control.

2. The method for controlling the temperature difference of the boiler drum wall during cold start-up according to claim 1, wherein The preparation stage of the boiler cold start-up; The preparation stage is divided into two stages, specifically including: The 1st - 2nd hour: Flush the condenser, deaerator, and boiler; Feed qualified demineralized water into the condenser. When the water level in the condenser meets the preset requirements, start the condensate pump to feed water into the deaerator, and flush the condenser and deaerator in a tidal form until the water quality of the condenser and deaerator is qualified; After the water quality of the deaerator is qualified, put the deaerator into heating and control the water temperature of the deaerator with the water temperature rising standard of the deaerator: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the drum < 50°C; The 3rd - 6th hour: Start the feed water pump to feed water into the boiler, and flush the boiler by the tidal method until the boiler water quality is qualified. The deaerator continues to heat, and the deaerator is calculated according to the formula: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the drum < 50°C, Control the water temperature.

3. The method for controlling the temperature difference of the steam drum wall during cold start-up of a boiler according to claim 3, characterized in that, The qualified standard of water quality in the preparation work of the boiler cold start-up is: the iron content in the condensate water ≤ 100 μg / L, and the iron content at the outlet of the deaerator ≤ 100 μg / L.

4. The method for controlling the temperature difference of the steam drum wall during cold start-up of a boiler according to claim 2, characterized in that, It also includes the method for controlling the drum wall temperature during the heating-up stage of the boiler cold start-up: Use the feed water pump to fill the drum with water until the water level just exceeds the steam outlet pipe at the top of the drum, so as to use water at a certain temperature to soak and preheat the drum; Among them, the soaking water temperature is selected as the wall temperature at the outlet of the economizer; The reference formula for the temperature rise standard of the deaerator: 40°C < the wall temperature at the outlet of the economizer - the lowest wall temperature of the drum < 50°C; The soaking time is 2 hours as a cycle, and soak continuously twice; After the first soaking time is up, drain 1 / 2 of the water in the boiler, re-select water at a higher temperature according to the drum wall temperature, and then feed water into the boiler, repeating the first soaking operation.

5. The method for controlling the temperature difference of the steam drum wall during cold start-up of a boiler according to claim 1, wherein The method for controlling the drum wall temperature after the boiler is ignited is: a. Keep the water temperature in the deaerator high: The principle of the water temperature is that the water temperature in the deaerator - the wall temperature at the outlet of the economizer = 35°C - 40°C; b. Keep the drum at the highest safe water level operation: Control the drum water level to operate at about +50 - +100 mm; c. Conduct bottom blowdown of the boiler: For one or several lowest temperature points on the lower wall of the drum, select the bottom blowdown valve corresponding to the temperature measuring point for blowdown; d. Open the high-pressure bypass and low-pressure bypass of the unit completely to control the change of the boiler saturation temperature: Opening the high-pressure bypass and low-pressure bypass can effectively reduce the rising speed of the boiler pressure, control the rise of the boiler saturation temperature, reduce the heat release of the steam to the upper wall of the steam drum, and delay the rising speed of the upper wall temperature of the steam drum; e. Open all the drain valves of the boiler superheater heating surface; f. Control the total boiler air volume: Keep the total boiler air volume at 30% - 40% BMCR, and adjust the secondary air distribution shape in the furnace to an equal distribution form; g. Control the fuel quantity: In the initial stage of ignition, control the ignition fuel quantity, control the boiler heating rate, and strictly control the superheated steam temperature rise rate of the boiler at 1.5 - 2 °C / min; When the temperature difference between the steam drum walls is stable, the heating rate is controlled according to the unit startup requirements and is no longer restricted by this item; h. Control the feed water flow regulation: Continuously feed water at a water volume of <316 t / g, and confirm the closed state and tightness of the economizer recirculation valve during water feeding.

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