Analysis and comparison of four boilers
1. The first advantage of oil-fired boilers is less equipment investment. Fuel oil burns quickly, and there is no coking problem in the furnace. The furnace volume heat load is relatively high, which can be nearly double that of coal-fired boilers. In this way, the volume of the furnace is significantly reduced, and the boiler steel frame can be reduced accordingly. The ash content in the fuel is very small, and the ash content in the flue gas is very light to the tail heating surface. You can choose a higher flue gas velocity to strengthen the heat transfer on the tail heating surface, which can reduce the tail heating surface. There is no need for huge pulverizing equipment, and there is no need to build huge coal storage yards, ash storage yards, and powder storage bins. The fuel oil system is simple. The second advantage is that due to the low ash content in the oil, the wear of the equipment by fuel and flue gas is very light, and the workload of equipment maintenance and repair is small. The third advantage is that fuel oil does not require further processing, and it is convenient to transport as long as the temperature is increased, and it can be sent to the boiler by boosting the pump. As a result, fuel oil furnaces consume less electricity per ton of steam. The disadvantage of oil-fired boilers is that they consume a lot of valuable high-quality fuel. Fuel oil is an important chemical raw material. It is a pity to burn a large amount as fuel. In the current situation of energy shortage and high fuel oil prices, it is of great economic significance to not burn oil or burn less oil.
2. The chain furnace is a layer furnace with the most complete structure and the most reasonable combustion organization. Due to the high degree of mechanization, the labor intensity is not large, no complicated milling system is needed, the investment is relatively low, and the thermal efficiency of the boiler is high. Therefore, it is widely used in China for small and medium boilers below 65t / h. The disadvantage of a chain furnace is that it needs to burn coal of good quality, the boiler has lower thermal efficiency than a pulverized coal furnace, and the load adjustment is not as fast as a pulverized coal furnace. Therefore, a large boiler does not use a chain furnace. Most of the chain furnaces produced in our country are horizontal drum water tube boilers. The boiler barrels of the double boiler chain furnace are arranged vertically, and a convection tube bundle is connected between the upper and lower boiler barrels as an evaporation heating surface. The convection tube bundle is mostly arranged behind the superheater.
3. The pulverized coal obtained by pulverizing the coal of the pulverized coal boiler has very small particles. The pulverized coal per unit mass has a large surface area, can be well mixed with air, and burns completely. The mechanical incomplete combustion loss, the chemical incomplete combustion loss and the excess air coefficient of the furnace outlet are lower than the chain furnace, so the thermal efficiency of the pulverized coal furnace is higher than that of the chain furnace. The pulverized coal furnace is a chamber combustion furnace and adopts suspension combustion, so the load adjustment is faster than that of a chain furnace. Because the pulverized coal furnace has a complete pulverizing system, it can burn inferior coal, while the chain furnace not only has certain requirements for the particle size of the coal, but also requires low moisture content, ash content, high ash melting point, and does not have strong coking. Quality coal. However, the pulverized coal furnace requires huge and complicated pulverizing equipment, which occupies a large area, requires more investment, increases the power consumption of the plant, and makes the pulverizing system work more noisy. Serious, heavy maintenance workload. These are the disadvantages of pulverized coal furnaces. These advantages and disadvantages of pulverized coal furnaces determine that only large and medium-sized boilers can use pulverized coal furnaces to outweigh the disadvantages. Therefore, pulverized coal furnaces are only suitable for large and medium boilers, and small boilers are rarely used.
4. Due to the unique combustion method of the fluidized bed boiler, the lower part of the fluidized bed boiler always maintains a very thick material layer with a temperature of 850-950 ° C, which is equivalent to a large high-temperature heat storage pool. Fuel only accounts for about 5%, and the newly added fuel is immediately mixed with dozens of times of its own high-temperature materials, which can make any difficult-to-burn fuel quickly catch fire. Because the fuel circulates up and down in the fluidized bed boiler, its residence time is longer, and it provides sufficient combustion time for various fuels that are difficult to burn out. The fluidized bed boiler can burn extremely poor quality fuel, even if the ash content reaches 70%, the fuel with a calorific value of only 4200KJ / kg, and the volatile content is only 2% -3%, and the anthracite and carbon content are 15%. All the above slags can be well burned.
Because the materials in the fluidized bed have radiation, convection and heat conduction to the buried pipe at the same time, the heat transfer coefficient of the buried pipe is very high, which can reach 230-290W / (m2 / ℃), which is the water cooling of the pulverized coal furnace. 5-6 times the wall. Due to the ignition conditions of the newly added fuel in the fluidized bed, the combustion and exhaustion conditions are very good, and the combustion intensity is very high. It belongs to low-temperature intensified combustion. Its volumetric heat load can reach 1.7-2.1MW / m3, which is 10 Times. Therefore, the fluidized bed boiler furnace has a small volume, which is only about half that of other types of boilers of the same capacity, which can reduce metal consumption and equipment costs. The desulfurizing agent (limestone, dolomite) added at the same time as the fuel can desulfurize the fuel, which not only reduces the pollution of the flue gas to the atmosphere, but also helps to reduce the low temperature corrosion of the heated surface of the tail. The fluidized-bed boiler ash has the characteristics of low-temperature burning through, which is convenient for comprehensive utilization. The ash has been used to manufacture building materials, extract chemical products, and be used as farmland fertilizer. Due to the excellent fuel ignition and combustion conditions, there is no need to worry about extinguishing the fire due to the reduction of the furnace temperature at low load, so the load regulation performance is good, and the fluidized bed boiler can operate normally within the load range of 25% to 110%.
Although fluidized bed boilers have many advantages, they also have the following disadvantages: low boiler thermal efficiency. The thermal efficiency of fluidized bed boilers is usually 54% -68%. The main reason is that the mechanical incomplete combustion loss is large. Buried tubes in fluidized bed boilers are subject to rapid wear and tear due to the severe impact of the material. If no anti-wear measures are taken, the buried pipe with a wall thickness of 3.5mm will be worn through for 3-6 months. After the anti-wear measures are taken, the buried pipe can only run for 1-2 years, which significantly increases the maintenance cost. Large power consumption. In order to burn the fuel in a fluidized state, the raw coal is broken into particles below 8 mm and high-pressure air is used, so that the power consumption per unit evaporation of the fluidized bed boiler is about twice that of a pulverized coal furnace.