The structure design of the hot blast stove is based on the selected steam capacity parameters and the fuel conditions, which comprehensively considers various factors to ensure the safe and economical operation of the hot blast stove. Under these conditions, the hot blast stove can meet various safety and environmental protection standards for long-term operation. Of course, there is a certain margin for all kinds of parameters in the design, which will cause some abnormal operation. Firstly, the hot stove should work in accordance with the principle of heat balance. For example, when the hot stove exceeds the rated load by 10%, the economy and safety of the hot stove can be basically guaranteed. The main operating conditions of hot blast stove are fuel characteristics, feed water temperature and air leakage.
CHANGES IN FUEL CHARACTERISTICS
Fuel composition has many effects on the operation of hot blast stove. For example, the amount of volatile matter will affect the ignition and combustion of fuel. The content and property of ash will affect unburned loss, contamination and wear of heating surface, slagging of furnace, etc. The size of moisture not only affects the ignition, combustion and corrosion of heating surface, but also causes significant changes in flue gas temperature, heat transfer and heat loss of hot blast stoves in different areas. The properties of moisture and excess air in the furnace are similar to those of flue gas temperature, heat transfer and heat loss of exhaust gas at the outlet of the furnace. They are all smoke after increasing the combustion of each kilogram of fuel. Gas volume and theoretical combustion temperature reduction. But the specific heat capacity of water is much larger than that of air, so the influence is much more serious. When the moisture content in fuel increases, the theoretical combustion temperature decreases significantly, so does the flue gas temperature at the outlet of the furnace. The reduction of radiation heat transfer and the increase of convective heat transfer are much greater than that of the increase of excess air in the furnace. These conditions will make the hot blast stove operation regulation range exceed the original design value.
II. Change of Feed Water Temperature
Reduction of turbine load or decoupling of high-pressure heater will reduce feed water temperature. Especially in the early stage of unit operation, when high-pressure heater has not been put into operation, the unit will start operation. This phenomenon often occurs. At this time, if the same amount of fuel is used, the evaporation of hot blast stove will decrease, or the amount of fuel will increase at the same amount of evaporation. Therefore, the operation of hot blast stove will be affected by the decrease of feed water temperature and the increase of fuel quantity, that is, the heat absorption in convection zone will increase, the heat absorption of convection superheater will increase, the heat absorption of economizer will increase, the outlet flue gas temperature will decrease, and the outlet air temperature of air preheater will decrease.
3. Change Caused by Air Leakage in Hot Stove
The influence of furnace air is the same as that of increasing excess air coefficient in furnace, but the influence and harm of leakage of cold air is greater than that of hot air. The location of leakage is different, and the influence is also different. For example, the leakage near the burner or the lower part of the furnace will affect the ignition and combustion of fuel, as well as the theoretical combustion temperature, thereby reducing the flue gas temperature at the outlet of the furnace. If the air leakage is in the upper part of the furnace, it will mainly reduce the outlet flue gas temperature of the furnace. The air leakage in each part of the convective flue will reduce the flue temperature and heat transfer temperature and pressure in this part and the future flue, thus reducing the heat absorption in each part. If the air leakage point is close to the outlet of hot blast stove, the exhaust gas temperature may be lower than the original level, but the heat loss of exhaust gas will increase. In summary, hot blast stove operation should pay close attention to the location and size of air leakage, take necessary measures to increase the tightness of hot blast stove, modern hot blast stoves mostly use membrane water wall structure, which can effectively reduce air leakage of hot blast stove.
The influence of the above non-design conditions on the operation of hot blast stoves is often possible, and the operation management departments of hot blast stoves should take measures to avoid the occurrence as far as possible. If the influence is great and endangers the normal operation of the hot blast stove, it is necessary to carry out technical transformation of the hot blast stove. After detailed calculation, the size of the heating surface should be adjusted, the height of the furnace should be increased if necessary, the combustion device should be improved, the anti-wear ability of the convective heating surface should be improved, and the auxiliary equipment should be improved. In this regard, domestic and foreign hot stove workers also have a lot of successful experience.
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