Circulating fluidized bed boiler
By suspending the superheater in the furnace in the circulating fluidized bed boiler and a large pitch water-cooled pipe bundle is arranged in the rear shaft flue, the contamination and alkali metal corrosion problems during combustion of high-sodium-potassium coal are solved, and the long-term reliability and low-cost technical transformation and optimization of the boiler are achieved.
Patent Information
- Application Number
- CN202323456137.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-18
- Publication Date
- 2025-03-25
- Estimated Expiration
- 2033-12-18
AI Technical Summary
When using high-sodium-potassium coal, it is difficult to achieve long-term reliability without reducing the boiler's steam temperature maintenance ability when existing circulating fluidized bed boilers are burned, and there are problems of contamination, alkali metal corrosion, inconvenience in maintenance and technical transformation and optimization that cannot be applied to the put into operation units.
A circulating fluidized bed boiler is designed, with all superheaters suspended inside the furnace, and a large-pitch water-cooled pipe bundle is arranged in the high smoke temperature area of the rear shaft flue to cool down, and a screen-type heating surface is set inside the furnace to avoid contamination.
It effectively avoids contamination on the heated surface and corrosion of alkali metals, improves the boiler's steam temperature, ensures the reliability of long-term continuous operation, and is suitable for technical transformation and optimization of put into operation units.
Smart Images
Figure CN222669976U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of boilers, in particular to a circulating fluidized bed boiler. Background Art
[0002] After years of exploration and research, the industry has gained an in-depth understanding of the characteristics of high-sodium-potassium coal. The contamination ability of high-sodium coal is strongly correlated with the flue gas temperature: when the flue gas temperature is lower than 650°C, the contamination of the heated surface is light or even non-existent; the contamination rapidly intensifies in the flue gas temperature range of 650°C to 700°C; and the contamination is serious when the flue gas temperature is above 700°C.
[0003] Due to the flushing of high-concentration circulating ash inside the furnace of the circulating fluidized bed boiler, the heating surfaces in the furnace are not easily contaminated. The main contamination area is the high-temperature section of the rear shaft flue. The strong contamination area above 650°C in the rear shaft of the conventional circulating fluidized bed boiler is usually arranged with superheater convection heating surfaces. Once contamination and blockage occur, it will seriously affect the main steam parameters of the boiler. In addition, the wall temperature of the superheater is usually high, and some power plants have already experienced alkali metal corrosion problems.
[0004] Based on the above research conclusions, the industry has developed a series of solutions to prevent heating surface contamination in response to the problems of circulating fluidized bed boilers. The main situations are as follows:
[0005] (1) Use a cooling air flue to reduce the inlet flue gas temperature of the superheater convection heating surface in the tail shaft to below 650°C. This solution requires a large heating surface area to achieve its purpose because the cooling flue itself has limited heat exchange capacity. The reduction of the inlet flue gas temperature of the superheater convection heating surface also affects the heat exchange of the superheater convection heating surface itself. It also requires a large number of heating surfaces to increase the steam temperature. The overall area occupied is large and the cost is high, so it cannot be applied to power plant boiler technical transformation projects.
[0006] (2) The pitch of the superheater convection heating surface in the high-temperature area of the tail shaft is directly increased, which prolongs the contamination cycle. As the boiler runs longer, the contamination of the heating surface will gradually increase, and the boiler's ability to reach steam temperature will gradually decrease. After contamination, the high wall temperature of the superheater is also prone to alkali metal corrosion. In order to increase the heat absorption of the superheater, it is necessary to increase the number of longitudinal rows of the convection heating surface, which increases the overall height of the rear shaft and is limited by space. It is also difficult to apply to power plant boiler technical transformation projects.
[0007] (3) The water-cooled evaporator tube bundle is arranged in the high-temperature zone of the tail shaft to reduce the inlet flue gas temperature of the superheater convection heating surface to below 650°C. In this scheme, the superheater convection heating surface is arranged in the low-temperature zone. The reduction of the inlet flue gas temperature of the superheater convection heating surface also affects the heat exchange of the superheater convection heating surface itself. A large number of heating surfaces need to be added to increase the steam temperature, which reduces the boiler's steam temperature maintenance capacity and increases costs.
[0008] (4) The high temperature area of the tail shaft is cooled by water-cooled screens, and an external bed is used to increase the heat absorption of the superheater. The overall heat exchange capacity of the tail screen heating surface of this solution is limited, and a large number of water-cooled screens need to be added. The external bed heat exchanger is inconvenient to repair, and the later operation and maintenance of the boiler are difficult.
[0009] (5) Low-temperature flue gas recirculation. This solution leads the clean flue gas after dust removal back to the entrance of the rear shaft flue, mixes it with the high-temperature flue gas and cools it to below 650°C before entering the convection heating surface. This solution is relatively simple, but the required amount of low-temperature recirculated flue gas exceeds 30% of the boiler flue gas volume. In order to ensure that the convection heating surface of the rear shaft is not worn, the cross-section of the rear shaft flue needs to be greatly increased, which is costly. In addition, after the flue gas temperature at the entrance of the superheater convection heating surface is reduced, the boiler's steam temperature maintenance capacity is significantly reduced.
[0010] In summary, the existing technical solutions for preventing high-sodium-potassium coal contamination generally have problems such as high cost, gradual decrease in steam temperature maintenance capacity as the boiler is put into operation for a longer time, alkali metal corrosion after contamination of the convection heating surface, inconvenient maintenance, and inability to be applied to technical transformation and optimization of units already in operation. Utility Model Content
[0011] In order to overcome the deficiencies of the prior art, the utility model provides a circulating fluidized bed boiler to solve the problem in the prior art that it is difficult to achieve long-term reliability of the circulating fluidized bed boiler at low cost and without reducing the boiler's steam temperature retention capacity.
[0012] The technical solution adopted by the utility model to solve the above problems is:
[0013] A circulating fluidized bed boiler comprises a wind chamber and a furnace which are interconnected, and also comprises a rear vertical shaft flue which is connected to the furnace. A superheater is arranged in the furnace.
[0014] As a preferred technical solution, the superheater includes one or more of a high-temperature superheater, a medium-temperature superheater, and a low-temperature superheater.
[0015] As a preferred technical solution, it also includes a water-cooled tube bundle arranged in the rear vertical shaft flue.
[0016] As a preferred technical solution, it also includes an economizer arranged in the rear vertical shaft flue, and the economizer is arranged below the water-cooled tube bundle.
[0017] As a preferred technical solution, it also includes an air preheater arranged in the rear vertical shaft flue.
[0018] As a preferred technical solution, the water-cooling tube bundle is a serpentine tube structure.
[0019] As a preferred technical solution, a separator is provided in the connecting pipe between the furnace and the rear shaft flue.
[0020] As a preferred technical solution, the separator includes separator A and separator B.
[0021] As a preferred technical solution, the separator and water-cooled tube bundle are steam-cooled membrane wall structures, and the economizer and air preheater are steel plate structures.
[0022] As a preferred technical solution, the furnace is a structure surrounded by membrane walls.
[0023] Compared with the prior art, the utility model has the following beneficial effects:
[0024] (1) All superheaters are suspended inside the furnace. The high-concentration circulating ash inside the furnace can prevent the heating surface from being contaminated and coked. The heat exchange temperature and pressure in the furnace are higher, which is conducive to improving the boiler's ability to reach steam temperature.
[0025] (2) The high smoke temperature area of the rear shaft flue is cooled by arranging a large pitch water-cooled tube bundle to avoid bridging and blocking the channel and alkali metal corrosion on the convection heating surface. The water-cooled tube bundle has no direct impact on the boiler steam temperature. Even if contamination occurs, it will not affect the boiler steam temperature from reaching the standard. The water-cooled tube bundle is arranged in the space occupied by the convection heating surface of the conventional circulating fluidized bed boiler superheater, which does not increase the boiler cost and can ensure the reliability of long-term continuous operation of the boiler. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 It is a structural schematic diagram of the utility model.
[0027] Marks and their corresponding names in the attached drawings: 1-wind chamber, 2-furnace, 3-high temperature superheater, 4-medium temperature superheater, 5-low temperature superheater, 6-separator A, 7-separator B, 8-rear vertical shaft flue, 9-water-cooled tube bundle, 10-economizer, 11-air preheater. DETAILED DESCRIPTION
[0028] The present invention will be further described in detail below in conjunction with the embodiments and drawings, but the implementation manner of the present invention is not limited thereto.
[0029] Example 1
[0030] like Figure 1 As shown, the utility model proposes a circulating fluidized bed boiler burning high-sodium-potassium coal, which can effectively avoid the influence of contamination on steam temperature at a relatively low cost; avoid the reduction of steam temperature maintenance capacity caused by too low flue gas temperature at the inlet of the superheater convection heating surface; avoid alkali metal corrosion caused by contamination of the convection heating surface of the rear superheater, and at the same time can be highly adapted to the technical transformation and optimization of the currently operated units.
[0031] The utility model proposes a circulating fluidized bed boiler burning high-sodium-potassium coal. By implementing this scheme, a high proportion of high-sodium-potassium coal can be blended or purely burned at a relatively low cost without reducing the boiler's steam temperature maintenance capacity, thereby ensuring the long-term reliability of the circulating fluidized bed boiler burning high-sodium-potassium coal. At the same time, it can also be applied to the technical transformation of most of the boilers that have been put into operation and burn high-sodium-potassium coal.
[0032] The principle of CFB boiler is a public technology, and the utility model will not repeat it. The utility model provides a circulating fluidized bed boiler burning high sodium potassium coal, such as Figure 1 As shown,
[0033] 1. A circulating fluidized bed boiler burning high sodium potassium coal, generally composed of a wind chamber, a furnace, a cyclone separator, a tail shaft flue, a water-cooled evaporation tube bundle, an economizer, an air preheater, a superheater and other components. A return device is provided below the cyclone separator to return the separated solid materials to the furnace. The furnace is surrounded by a membrane wall, and the separator and the rear shaft flue adopt a steam-cooled membrane wall structure. A fuel supply device and a secondary air duct are provided at the lower part of the furnace, and a fluidized bed is provided at the bottom of the furnace, and an ignition device and primary air are provided at the fluidized bed.
[0034] 2. The heating surfaces of the low-temperature superheater, medium-temperature superheater and high-temperature superheater are all arranged inside the furnace in a screen-type structure. Because there is a large amount of circulating ash flushing inside the furnace during the operation of the circulating fluidized bed boiler, even if high-sodium-potassium coal is burned, there will be no problems such as coking and contamination on the screen-type heating surfaces inside the furnace.
[0035] 3. The tail shaft is no longer equipped with superheater convection heating surfaces. Instead, water-cooled tube bundles, economizers, air preheaters and other convection heating surfaces are arranged from top to bottom. Large-pitch water-cooled tube bundles with serpentine tube structures are used in high-temperature areas to reduce the flue gas temperature. The large pitch of the water-cooled tube bundles can avoid bridging and blocking the channel, thereby increasing resistance and affecting boiler output; the wall temperature of the water-cooled tube bundles is relatively low, which can avoid alkali metal corrosion of the tube wall after contamination; the water-cooled tube bundles have no direct impact on the boiler steam temperature, and even if contamination occurs, it will not affect the boiler steam temperature from meeting the standard; the water-cooled tube bundles are arranged in the space occupied by the convection heating surface of the conventional circulating fluidized bed boiler superheater, without increasing the boiler cost.
[0036] 4. The boiler steam-water system includes economizer, drum, water cooling system, low-temperature superheater, medium-temperature superheater, high-temperature superheater and their connecting pipes. The feed water flows through the economizer and then enters the drum. The boiler water in the drum enters the water-cooled heating surface such as the furnace water-cooled wall and water-cooled tube bundle through the downcomer, and is heated to become a steam-water mixture. It returns to the drum for steam-water separation, and the separated boiler water (saturated water) enters the downcomer to participate in the next cycle. The separated saturated steam flows through the cooling cyclone separator, the rear shaft flue wall, the low-pass, medium-pass, and high-pass, and is then drawn out after being heated and sent to the high-pressure cylinder of the steam turbine to perform work.
[0037] 5. When the boiler is running, the fuel enters the furnace and burns. The hot flue gas generated by the combustion transfers part of the heat to the water-cooled wall of the furnace, and then flows through the cyclone separator for gas-solid separation. The relatively clean flue gas enters the rear shaft flue, and flows through the water-cooled tube bundle, economizer, and air preheater arranged in the rear flue in turn to release heat before leaving the boiler. After passing through the tail flue gas purification system, it enters the chimney and is discharged into the atmosphere.
[0038] The utility model provides a circulating fluidized bed boiler burning high sodium potassium coal, which has the following characteristics:
[0039] The overall structure of the boiler includes: wind chamber 1, furnace 2, high-temperature superheater 3, medium-temperature superheater 4, low-temperature superheater 5, separator A6, separator B7, rear vertical shaft flue 8, water-cooled tube bundle 9, economizer 10, and air preheater 11.
[0040] The furnace is composed of a full-membrane water-cooled wall structure. The water-cooled tube panel heating surface, superheater heating surface, coal feeding port and secondary air port are arranged along the width direction of the furnace. At the bottom of the furnace, there is a water-cooled air chamber formed by bending water-cooled wall tubes. The air chamber is connected to the under-bed ignition air duct. Each ignition air duct is equipped with an oil burner for heating the bed material. The return interface of the return device, the secondary air interface and the slag discharge port are arranged on the rear wall of the furnace along the width direction.
[0041] Preferably, a cyclone separator is used for gas-solid separation, and a return device is arranged at the lower end of each cyclone separator to return the material separated by the cyclone separator directly to the furnace through the return device.
[0042] Preferably, a screen-type superheater heating surface is used, all of which are arranged inside the furnace. During the operation of the circulating fluidized bed boiler furnace, a large amount of circulating ash is flushed, which can avoid contamination of the superheater heating surface. This solves the problem of contamination of high-sodium-potassium coal affecting the boiler steam temperature and avoids alkali metal corrosion of the superheater convection heating surface.
[0043] Preferably, a rear vertical flue is used, and a water-cooled tube bundle, economizer, and air preheater are arranged in order from top to bottom. A water-cooled tube bundle with a serpentine tube structure is used to cool the high-temperature area. At the same time, the water-cooled tube bundle is arranged with a larger pitch, which can effectively resist the contamination problem caused by burning high-sodium-potassium coal, reduce the impact of contamination on boiler operation, and ensure the long-term operation reliability of the boiler.
[0044] Preferably, all superheater heating surfaces (low-temperature superheater, medium-temperature superheater, high-temperature superheater) adopt a screen-type heating surface structure and are arranged inside the furnace;
[0045] Preferably, the cyclone separator adopts steam cooling or adiabatic type to perform gas-solid separation;
[0046] Preferably, the tail flue wall is steam-cooled or heat-insulated; a water-cooled tube bundle is arranged in the high smoke temperature zone of the boiler tail shaft;
[0047] Preferably, the boiler tail shaft economizer may be arranged in a single stage or multiple stages, or in a graded arrangement, and an SCR space may be arranged or reserved between the upper and lower economizers.
[0048] The utility model proposes a circulating fluidized bed boiler scheme for burning high-sodium-potassium coal. Aiming at the contamination and corrosion characteristics of high-sodium-potassium coal, the layout of the heating surface of the circulating fluidized bed boiler is replanned, which can achieve the following effects:
[0049] (1) All superheaters are suspended inside the furnace. The high-concentration circulating ash inside the furnace can prevent the heating surface from being contaminated and coked. The heat exchange temperature and pressure in the furnace are higher, which is conducive to improving the boiler's ability to reach steam temperature.
[0050] (2) The high smoke temperature area of the rear shaft flue is cooled by arranging a large pitch water-cooled tube bundle to avoid bridging and blocking the channel and alkali metal corrosion on the convection heating surface. The water-cooled tube bundle has no direct impact on the boiler steam temperature. Even if contamination occurs, it will not affect the boiler steam temperature from reaching the standard. The water-cooled tube bundle is arranged in the space occupied by the convection heating surface of the conventional circulating fluidized bed boiler superheater, which does not increase the boiler cost and can ensure the reliability of long-term continuous operation of the boiler.
[0051] Example 2
[0052] like Figure 1 As shown, as a further optimization of Example 1, based on Example 1, this embodiment also includes the following technical features:
[0053] Smoke and wind side:
[0054] Most of the air coming out of the primary fan is heated by the air preheater 11, and then enters the water-cooled air chamber 1 at the bottom of the furnace through the ignition air duct under the bed, and then enters the furnace 2 through the hood on the air distribution plate, so that the bed material is evenly fluidized and forms a gas-solid two-phase flow passing through the furnace upward. In order to ensure sufficient combustion residence time, the furnace cross-sectional velocity is set to 4.5-5m / s. The fuel is fed into the dense phase area at the bottom of the furnace from the feed port arranged on the front wall, fully mixed with the air and the fluidized high-temperature bed material, and ignited and burned. The air coming out of the secondary fan is heated by the air preheater 11, and then fed into the furnace through the secondary air ports arranged on the front and rear walls of the furnace, which supplements sufficient combustion air for fuel combustion, and causes strong disturbances in the flow field in the furnace, ensuring the burnout of the fuel and reducing the generation of carbon monoxide CO.
[0055] The furnace adopts a water-cooled membrane wall structure. The furnace is arranged with a screen-type high-temperature superheater 3, a medium-temperature superheater 4, a low-temperature superheater 5 and a suitable water-cooled heating surface. By reasonably matching the heating surface area, the temperature above the secondary air inlet on the furnace is controlled at 870-890°C. The height from the upper secondary air inlet to the furnace outlet is not less than 20 meters to ensure that the fuel has sufficient residence and combustion time.
[0056] The flue gas produced by combustion carries a large amount of solid particulate materials and turns through the furnace top. It passes through the flue gas outlet located on the upper part of the rear wall water-cooled wall and enters the separator A6 and separator B7 (separator A6 and separator B7 are preferably steam-cooled cyclone separators) for gas-solid separation. To ensure the separation efficiency, the inlet flue gas velocity of the separator is 25-30m / s, and the rising speed of the separator section is 5-7m / s. Most of the particles are separated and returned to the furnace through the return feeder. After separation, the clean flue gas containing a small amount of fly ash enters the rear shaft flue 8. In the high flue gas temperature area of the rear shaft flue, a water-cooled tube bundle 9 is used, and the transverse pitch of the tube bundle is 200mm. The flue gas temperature is reduced to below 550℃ through the water-cooled tube bundle. Then, after the flue gas enters the economizer 10 and air preheater 11 arranged under the water-cooled tube bundle, the flue gas temperature has dropped to about 130-150℃.
[0057] Soda side:
[0058] The boiler steam-water system includes an economizer 10, a boiler drum, a water cooling system, a water cooling tube bundle 9, a high-temperature superheater 3, a medium-temperature superheater 4, a low-temperature superheater 5, a separator A6, a separator B7 and connecting pipes, and a rear vertical shaft flue 8 and its pipes.
[0059] The boiler feed water is first introduced into the economizer inlet header at the tail flue, and then flows upward in counterflow through the horizontally arranged economizer tube group 10 to enter the economizer outlet header, and then enters the boiler drum from the drum head through the economizer outlet pipe. The feed water is introduced into the boiler drum water space, and enters the water-cooled wall and the water-cooled tube bundle 9 inlet header through the centralized downcomer and the downcomer connecting pipe. The boiler water is heated to become a steam-water mixture in the process of flowing upward through the furnace water-cooled wall 2 and the water-cooled tube bundle 9, and is introduced into the boiler drum through the steam-water outlet pipe through the respective upper outlet headers for steam-water separation. The separated water re-enters the boiler drum water space and is recycled, and the separated saturated steam is led out from the steam connecting pipe at the top of the boiler drum.
[0060] If the water-cooled tube bundle area of cyclone separator A6, separator B7 and rear shaft flue 8 is steam-cooled, after the saturated steam is drawn out from the boiler drum, it will be introduced into the cyclone separator A6 and separator B7 inlet headers through the saturated steam connecting pipe, and after being heated by the cyclone separator, it will enter the cyclone separator A6 and separator B7 outlet headers, and then introduced into the wall-wrapped inlet header of the water-cooled tube bundle area of the rear shaft flue 8 through the connecting pipe, and after being heated by the rear shaft flue 8, it will be introduced into the rear shaft flue wall-wrapped outlet header, and then introduced into the low-temperature superheater 5, the medium-temperature superheater 4 and the high-temperature superheater 3 in turn through the connecting pipe, and then merged into the superheater outlet header, and finally the qualified superheated steam is drawn out from the high-temperature superheater 3 outlet header.
[0061] If separator A6, separator B7 and rear vertical shaft flue 8 are insulated or steam-cooled, after the saturated steam is drawn out from the boiler drum, it will be directly introduced into the low-temperature superheater 5, the medium-temperature superheater 4 and the high-temperature superheater 3 in sequence through the saturated steam connecting pipe and then merged into the superheater outlet header. Finally, qualified superheated steam is drawn out from the high-temperature superheater 3 outlet header.
[0062] The superheater system adopts flexible water spray cooling as a means of regulating steam temperature and protecting the heating surface pipes at all levels. The whole superheater system is arranged with two levels of water spray. The first level desuperheater is arranged on the pipeline from the outlet of the low-temperature superheater 5 to the inlet of the medium-temperature superheater 4, controlling and adjusting the outlet steam temperature of the medium-temperature superheater; the second level desuperheater is located on the connecting pipeline between the medium-temperature superheater 4 and the high-temperature superheater 3, controlling and adjusting the outlet steam temperature of the high-temperature superheater 3.
[0063] As described above, the utility model can be implemented well.
[0064] The above is only a preferred embodiment of the utility model and does not limit the utility model in any form. According to the technical essence of the utility model, within the spirit and principles of the utility model, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the utility model.
Claims
1. A circulating fluidized bed boiler, characterized in that: It comprises a wind chamber (1) and a furnace (2) which are interconnected, and also comprises a rear vertical shaft flue (8) which is connected to the furnace (2), and a superheater is arranged in the furnace (2); It also includes a water-cooling tube bundle (9) arranged in the rear vertical shaft flue (8); It also includes an economizer (10) disposed in the rear vertical shaft flue (8), and the economizer (10) is disposed below the water-cooled tube bundle (9); It also includes an air preheater (11) disposed in the rear shaft flue (8); A separator is provided in the connecting pipe between the furnace (2) and the rear vertical shaft flue (8); The separator comprises a separator A (6) and a separator B (7), wherein the separator A (6) comprises a separator A outlet header, and the separator B (7) comprises a separator B outlet header, and the separator A outlet header and the separator B outlet header are respectively connected to the rear vertical shaft flue (8).
2. A circulating fluidized bed boiler according to claim 1, characterized in that: The superheater includes one or more of a high-temperature superheater (3), a medium-temperature superheater (4), and a low-temperature superheater (5).
3. A circulating fluidized bed boiler according to claim 1, characterized in that: The water cooling tube bundle (9) is a serpentine tube structure.
4. A circulating fluidized bed boiler according to claim 1, characterized in that: The separator and the water-cooled tube bundle (9) are steam-cooled membrane wall structures, and the economizer (10) and the air preheater (11) are steel plate structures.
5. A circulating fluidized bed boiler according to any one of claims 1 to 3, characterized in that: The furnace (2) is a structure surrounded by membrane walls.