Smoke path system of circulating fluidized bed boiler using contaminated coal with strong coal quality as fuel
By designing a three-flue structure and reasonably arranging the circulating fluidized bed boiler flue system of superheater, economizer and steam soot blower, the problem of contamination on the heated surface caused by strong contamination of coal is solved, and the stable operation and efficient heat transfer of the boiler are achieved.
Patent Information
- Application Number
- CN202422038733.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-22
- Publication Date
- 2025-07-29
- Estimated Expiration
- 2034-08-22
AI Technical Summary
When existing circulating fluidized bed boilers use coal-based coal as fuel, they are prone to contamination on the heated surface, resulting in unstable operation of the boiler system and corrosion on the heated surface.
A three-flue structure smoke system is designed, including a furnace, a cyclone separator, a descending flue, an upward flue and a tail flue. An empty flue is used to reduce the flue gas temperature, and a steam soot blower is installed in the empty flue. Combined with the reasonable arrangement of superheaters and economizers, circulating material erosion and steam soot blower are used to remove contamination.
It effectively avoids contamination of the heated surface, improves the operating stability and efficiency of the boiler, reduces steam consumption, reduces wear of the heated surface, and achieves efficient heat transfer performance and safe operation.
Smart Images
Figure CN223165561U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to a circulating fluidized bed boiler, in particular to a flue gas system of a circulating fluidized bed boiler using coal with strong fouling property as fuel. Background Art
[0002] The content of alkali metals sodium and potassium in some steam coals is much higher than that of other steam coals. The melting points of alkali metal compounds are usually within 800 °C, but the melting points of complex alkali metal sulfates are between 890 - 1210 °C. In a pulverized coal boiler, the flue gas temperature in the high-temperature zone of the furnace is usually above 1400 °C, which means that all alkali metals and their compounds in this kind of steam coal will sublime or melt in the boiler furnace and cause fouling on the heating surfaces of the boiler. Metal sodium oxide sublimes in a combustion environment above 700 - 800 °C and is easily condensed and attached to the tube screen wall surface and combines with carbon dioxide, alumina, iron oxide, etc. in the flue gas to form various sulfates, thus causing fouling. If the flue gas temperature is lower than 650 °C, fouling basically does not occur. How to design the flue gas system of a circulating fluidized bed boiler to avoid fouling has become a problem faced by boiler manufacturing enterprises. Summary of the Invention
[0003] The utility model provides a flue gas system of a circulating fluidized bed boiler using coal with strong fouling property as fuel, and solves the technical problem of how to overcome the fouling phenomenon on the heating surfaces in the boiler system.
[0004] The utility model solves the above technical problems through the following technical solutions:
[0005] A flue gas system of a circulating fluidized bed boiler using coal with strong fouling property as fuel includes a furnace and a cyclone separator. A downcomer is connected to the flue gas outlet of the cyclone separator, an upcomer is connected to the lower port of the downcomer, and the upper port of the upcomer is connected to the tail flue through a connecting flue. A high-temperature platen superheater and a medium-temperature platen superheater are arranged in the furnace. In the upcomer, a convection tube bundle and a low-temperature platen superheater are arranged in sequence along the upward direction from bottom to top. The downcomer is an empty flue, and steam soot blowers are arranged at intervals in the downcomer. An air superheater, a low-temperature economizer, and a high-temperature economizer are arranged in the tail flue. A slag discharge port is arranged at the bottom end of the downcomer.
[0006] The temperature in the furnace is 860 °C, the outlet flue gas temperature at the flue gas outlet of the separator is 880 °C, the outlet flue gas temperature at the lower end of the downcomer is 706 °C, the flue gas temperature at the inlet of the upcomer is 684 °C, the temperature after passing through the convection tube bundle in the upcomer is 630 °C, and the outlet flue gas temperature of the upcomer is 400 °C.
[0007] A dust hopper is provided at the lower end of the tail flue; a dust collector, an induced draft fan and a chimney are successively connected to the outlet of the tail flue.
[0008] In view of the characteristics that boilers burning coal with strong contamination tendency are prone to coking and contamination, the boiler of the present utility model adopts a three-flue structure; the designed downcomer of the rear flue is an empty flue, and the empty flue is used to reduce the flue gas temperature, so that contamination occurs in the empty flue, and an ash removal device is arranged in the empty flue to facilitate the removal of contamination; the rear flue adopts a steam-cooled wall structure. The flue gas first passes through the downcomer of the rear flue, then through the convection tube bundles of the upcomer of the rear flue, and then enters the low-temperature superheater and the tail heating surface, reducing the inlet flue gas temperature of the heating surface, thereby reducing the tube wall temperature. The tube wall temperature of the heating surface is lower than the slagging temperature of Zhundong coal, effectively avoiding the contamination and corrosion of the tube wall of the heating surface. Brief Description of the Drawings
[0009] Figure 1 It is a schematic diagram of the flue gas path structure of the present utility model. Detailed Embodiment
[0010] The present utility model will be described in detail below with reference to the drawings:
[0011] A flue gas system of a circulating fluidized bed boiler using highly contaminated coal as fuel, comprising a furnace 1 and a cyclone separator 2. A downcomer 4 is connected to the flue gas outlet 3 of the cyclone separator 2. An upcomer 5 is connected to the lower port of the downcomer 4. The upper port of the upcomer 5 is connected to the tail flue 7 through a connecting flue 6. A high-temperature platen superheater and a medium-temperature platen superheater 8 are arranged in the furnace 1. In the upcomer 5, a convective tube bundle 9 and a low-temperature platen superheater 10 are arranged in sequence along the upward direction from bottom to top. The downcomer 4 is an empty flue, and steam soot blowers 15 are arranged at intervals in the downcomer 4. An air superheater 11, a low-temperature economizer 12 and a high-temperature economizer 13 are arranged in the tail flue 7. A slag discharge port 14 is arranged at the bottom end of the downcomer 4. The high-temperature platen superheater and the medium-temperature platen superheater 8 are arranged in the furnace, and the low-temperature superheater 10 is arranged in the rear flue of the double flue. The advantages are that the heat transfer surface of the superheater is arranged in countercurrent as a whole, the heat transfer temperature difference is high, the system is simple, and the boiler cost is low. The outlet working medium temperature of the final heating surface in the furnace is controlled, and the working medium temperature is basically stable under various loads, not affected by desuperheating by spraying water, the wall temperature fluctuation is small, the screen will not deform, and the operation is safe. The high-temperature superheater is arranged in the furnace, and the low-temperature superheater is arranged in the rear flue of the double flue, which is beneficial to the reasonable distribution of radiant heat absorption and convective heat absorption of the boiler under various loads, so that the wall temperature of each stage of superheater is stable under load changes. In view of the high contamination characteristics of highly contaminated coal, steam soot blowers 15 with stronger soot blowing ability are selected. In addition, the soot blowing frequency needs to be determined according to the actual situation. The soot blowing method is to perform programmed soot blowing at fixed times in sequence along the flue gas flow, and intelligent selective additional soot blowing is carried out according to the location and severity of the ash accumulation, so as to effectively balance economy and safety. The overall performance of the boiler is improved, steam is saved while the wear of the heating surface is reduced. Steam soot blowers are installed at the inlet of each heating surface of the boiler. Long telescopic steam soot blowers are installed for the convective tube bundle and the low-temperature superheater, semi-telescopic steam soot blowers are installed for the economizer, and fixed steam soot blowers are installed for the air preheater. A certain number of long telescopic steam soot blowers (15) are arranged on both sides of the empty flue in the rear furnace. Since the fuel has a large moisture content, in order to avoid contamination of the air preheater, a warm air heater is installed at the air intake, and the exhaust gas temperature is designed to be appropriately high, considering to be about 140 °C, not lower than 135 °C.
[0012] The temperature in the furnace 1 is 860 °C, the temperature of the flue gas at the outlet of the separator flue gas outlet 3 is 880 °C, the temperature of the flue gas at the lower end outlet of the downcomer 4 is 706 °C, the temperature of the flue gas at the inlet of the riser 5 is 684 °C, and the temperature after passing through the convective tube bundle 9 in the riser 5 is 630 °C; the sublimation or melting of alkali metal compounds and complex alkali metal sulfates in strongly fouling coal mainly occurs in the furnace and the downcomer 4. When the flue gas enters the riser 5 and is cooled by the convective tube bundle 9, the flue gas temperature basically reaches below 630 °C, avoiding the temperature at which alkali metal compounds and complex alkali metal sulfates sublime or melt, and no fouling will be generated in the riser 5; since the downcomer 4 is an empty flue, the fouling and slagging in it can be cleaned by the steam soot blower 15; a large amount of solid circulating materials in the furnace continuously scour the heating surface. On the one hand, the circulating materials scour off the fouling layer formed on the surface of the heating surface, making it form finer solid particles, which cannot be separated after leaving the furnace and form fly ash; on the other hand, the circulating ash particles provide a rich adsorption surface, and the outer surface area of the particles is more than a thousand times that of the heating surface area. Therefore, the condensation of steam in the flue gas occurs on the surface or in the space of the circulating materials, and the small-diameter particles formed in this way can be separated from the circulating system and converted into fly ash; at the same time, the furnace material concentration and the bed mass flowing through the separator are greatly improved, ensuring that the furnace can achieve efficient heat transfer at a low bed temperature when burning coal with strongly fouling coal quality as fuel.
[0013] A hopper 16 is provided at the lower end of the tail flue 7; a dust collector 17, an induced draft fan 18 and a chimney 19 are successively connected to the outlet of the tail flue 7; the boiler adopts a low-temperature combustion mode, there is no problem of coking on the heating surface in the furnace, and the fluidized combustion in the furnace has a self-desulfurization effect. A limestone pneumatic conveying feed pipe is provided on the secondary air branch pipe. After adding an appropriate amount of limestone, the desulfurization efficiency in the furnace can be further improved, a large amount of SO2 and SO3 are removed, and the concentration of SO3 is much lower than that of other furnace types, and it is not easy to generate M3Fe(SO4)3 (M represents an alkali metal), avoiding the problem of high-temperature corrosion of the heating surface in the furnace.
Claims
1. A flue gas system of a circulating fluidized bed boiler using highly contaminated coal as fuel, comprising a furnace (1) and a cyclone separator (2), characterized in that, A downcomer (4) is connected to the separator flue gas outlet (3) of the cyclone separator (2). An upcomer (5) is connected to the lower port of the downcomer (4). The upper port of the upcomer (5) is connected to the tail flue (7) through a connecting flue (6). A high-temperature platen superheater and a medium-temperature platen superheater (8) are arranged in the furnace (1). In the upcomer (5), a convection tube bundle (9) and a low-temperature platen superheater (10) are arranged in sequence along the upward direction from bottom to top. The downcomer (4) is an empty flue, and steam soot blowers (15) are arranged at intervals in the downcomer (4). An air superheater (11), a low-temperature economizer (12) and a high-temperature economizer (13) are arranged in the tail flue (7). A slag discharge port (14) is arranged at the bottom end of the downcomer (4).
2. The flue gas system of a circulating fluidized bed boiler using highly contaminated coal as fuel according to claim 1, characterized in that, The temperature in the furnace (1) is 860 °C, the outlet flue gas temperature of the separator flue gas outlet (3) is 880 °C, the outlet flue gas temperature at the lower end of the downcomer (4) is 706 °C, the flue gas temperature at the inlet of the upcomer (5) is 684 °C, the temperature after passing through the convection tube bundle (9) in the upcomer (5) is 630 °C, and the outlet flue gas temperature of the upcomer (5) is 400 °C.
3. The flue gas system of a circulating fluidized bed boiler using highly contaminated coal as fuel according to claim 2, characterized in that, A dust hopper (16) is arranged at the lower end of the tail flue (7). A dust collector (17), an induced draft fan (18) and a chimney (19) are connected in sequence at the output port of the tail flue (7).