Boiler adopts single drum natural circulation mode, which is generally divided into two shafts. The front axle is a general crane structure, surrounded by membrane walls. From bottom to top, there are primary air chamber, dense bed, suspension section, evaporation tube, high temperature superheater, low temperature superheater and high temperature economizer in turn. The rear axle adopts supporting structure, and low-temperature economizer and tubular air preheater are arranged from top to bottom. The two shafts are communicated through a vertical cyclone separator, and the lower part of the separator is connected with a material returning device and a slag cooler. Wear-resistant lining is installed in the combustion chamber and separator. ao tubular furnace wall is used in the front axle, light furnace wall is used in the rear axle, and eight steel columns bear the total weight of the boiler.
The boiler ignites (oil or gas) under the bed and burns in stages. The primary air rate accounts for 50-60%, and the fly ash circulation rate is low. Dry discharge of middle-temperature separated ash is discharged by water-cooled screw slag extractor, ash cooler and ash hopper of dust collector respectively. Furnace is the key to ensure the full combustion of fuel. Using turbulent bed, the fluidization speed is 3.5-4.5m/s, the furnace section is reasonably designed, and the thin lining (high alumina brick) is laid on the membrane wall tube of the furnace. Even if the boiler uses different fuels, the combustion efficiency can be kept above 98-99%.
The flue gas temperature at the inlet of the separator is about 450 degrees, and the inner diameter of the cyclone drum is small, so the structure is simplified, and only a thin anti-wear lining (silicon nitride brick) is needed in the drum. Its service life is long. The circulation ratio is about 10- 15.
The circulating ash conveying system is mainly composed of reflux pipe, reflux device, overflow pipe and slag cooler.
The adjustment process of bed temperature control system is automatic. In the whole range of load change, the bed temperature of dense bed is always kept at 860 degrees, which is the best desulfurization temperature. When the automatic control is not put into use, a constant hotbed can be maintained by manual operation.
Protecting the environment and saving energy are the primary considerations for the long-term development of all countries, and circulating fluidized bed boilers are developed based on this point, with high reliability, high stability and high availability. More and more attention has been paid to the best environmental protection characteristics and wide fuel adaptability, which are completely suitable for China's national conditions and development advantages.
Circulating fluidized bed boiler is a low-temperature combustion boiler. Fuel is sent to the furnace by the coal feeding system in front of the furnace, and primary air is sent to the combustion chamber from the lower part of the air distribution plate, mainly to ensure the laminar flow of materials; Secondary air is sent in stages and at multiple points along the height of the combustion chamber, mainly to increase the oxygen content of the combustion chamber to ensure the fuel to burn out; The tertiary air further strengthened the combustion.
Under the action of a certain fluidization wind speed, the materials in the combustion chamber are severely disturbed, and some solid particles leave the combustion chamber and enter the furnace with the high-speed airflow, among which the larger particles flow downward along the inner wall of the furnace due to gravity, and some smaller particles fly out of the furnace with the flue gas and enter the material separation device, forming a gas-solid two-phase flow in the furnace. The flue gas entering the separation device is subjected to solid-gas separation, and the separated particles are sent back to the combustion chamber along the return device at the lower part of the separation device. After the separated flue gas absorbs heat through the heating surface in the convection flue, because the circulating fluidized bed boiler is equipped with an efficient separation device, the separated particles are sent back to the furnace through the feeder, so that the ash concentration in the furnace of the boiler is high enough, which not only has the following advantages:
Radiation heat transfer mode, convection and heat transfer mode greatly improve the heat transfer coefficient of the furnace and ensure the boiler to reach the rated output.
Advantages of circulating fluidized bed boiler
1. Wide fuel adaptability
Circulating fluidized bed boilers can not only burn bituminous coal, anthracite, lean coal and lignite, but also burn inferior fuels such as gasification slag and coal gangue.
2. High efficiency of boiler
Because of the circulating separation device in the furnace, domestic manufacturers have continuously improved and perfected the separation device, and the separator efficiency is as high as 99%, the thermal efficiency of this boiler is also above 85%, and the combustion efficiency is above 98%.
3. A wide range of boiler load regulation
According to the operation situation of domestic users of circulating fluidized bed boilers, the boiler type operates within the load range of 30- 1 10%, and the steam temperature and pressure can be kept within the normal range.
4. The seal of the boiler is very reliable.
Because most domestic manufacturers adopt fully sealed membrane wall, the original expansion joint is cancelled, which not only improves the efficiency of boilers and furnaces, but also greatly improves the working environment of operators.
5. There are many anti-wear measures for boilers.
Due to the continuous development of domestic circulating fluidized bed boilers, the original headache wear problem has been basically solved, so that the continuous operation time of some circulating fluidized bed boilers has reached 4000 hours. According to the operation of more than 600 circulating fluidized bed boilers in China, some anti-wear measures adopted at present are reliable, such as spraying, design prevention, closely arranged pins and refractories, metal anti-wear tiles, reasonable pipeline avoidance and so on.
6. Adding limestone into the furnace can carry out desulfurization.
Because of the low combustion temperature of circulating fluidized bed boiler, it is very beneficial to desulfurization, and the separator efficiency of circulating fluidized bed boiler is high, and the desulfurizer limestone can be very fine, so the utilization rate of limestone is high. When the ratio of calcium to sulfur is 2, the desulfurization efficiency is above 85%. This greatly reduces the emission of SO2 and meets the requirements of environmental protection.
7. Reliable material return
At present, most circulating fluidized bed boilers in China use U-valve, which is an automatic non-mechanical feeder and the best material returning device in China. Some manufacturers also use technologies such as water cooling legs to ensure the reliable operation of boilers.
8. It is easy to realize the comprehensive utilization of ash.
The combustion process of circulating fluidized bed belongs to low temperature combustion. At the same time, the excellent burn-out conditions in the furnace make the boiler ash have low carbon content and good activity, which can be used as cement admixture or building materials. At the same time, burning Toya at low temperature is beneficial to extract rare metals from ashes.