Precautions for coal-fired boiler renovation
The long-standing problems of coal-fired boilers, such as large areas of pollutants, small individual capacity, emissions close to the ground, and mismatched main and auxiliary equipment, have been magnified once again. The transformation of coal-fired boilers will undoubtedly become the focus of urban air pollution control in the next step.The basic principle of converting a coal-fired boiler to an oil (gas) boiler.1. The renovated coal-fired boiler must meet the following conditions:① The original pressure parts of the boiler are basically intact and have value for continued use;② The water and gas system, as well as the supply and exhaust systems of the original boiler, should be basically intact.2. The renovated boiler should achieve the following objectives:① Maintain the original boiler rated parameters (such as steam pressure, steam temperature, return water temperature, etc.) unchanged;② Maintain or increase the original boiler output and efficiency.3. By means of renovation, the goal of eliminating smoke and dust is achieved, meeting environmental protection requirements.4. The boiler renovation plan must be simple, easy, with low investment, quick results, and short construction period. So the smaller the scope of boiler renovation, the better. It can only be achieved through boiler renovation and combustion devices, and the renovation part should not exceed the basic structural range of the boiler body.2、 Attention should be paid when converting coal-fired boilers to oil (gas) boilers.To switch to mechanized stratified combustion of fuel (gas) boilers, the front and rear arches should be removed first, while considering adding a bottom heating surface to replace the grate and prevent it from overheating and burning out.2. For small boilers that convert coal burning to fuel (gas) burning, i.e. from negative pressure combustion to micro positive pressure combustion, attention must be paid to the structure and sealing of the furnace wall.3. The selection and arrangement of burners are closely related to the form of the furnace, and it is necessary to ensure that the flames in the furnace are well filled and do not form blind spots in the airflow; Avoid interference between adjacent burner flames; Maintain the flame at the center of the furnace during low load to prevent the flame center from deviating from the symmetrical center of the furnace; The mixture of unburned gas must not come into contact with the heating surface to avoid incomplete combustion of the gas; High temperature flames should avoid high-speed erosion of the heating surface, and avoid excessive heat intensity on the heating surface that may cause overheating of the pipe wall. The layout of the burner should also consider the layout of the gas pipeline and the reasonable arrangement and use of the pipeline.4. The smoke velocity on the convective heating surface of a combustion oil and gas boiler is not limited by the condition of fly ash wear. The smoke velocity can be appropriately increased to increase the heat transfer coefficient of the convective heating surface; For boilers with overheated gas, without increasing the heating area, attention should be paid to the ability of the furnace steam water separator to ensure steam quality, especially for boilers with overheated gas.5. To prevent high-temperature corrosion, coal should be replaced with fuel because fuel contains organic metal elements such as sodium and vanadium. After combustion, the melting point of oxide eutectic crystals is very low, usually around 600 ℃, or even lower. After high-temperature sublimation in the furnace, this type of oxide forms corrosive high-temperature ash deposits on the heating surface at relatively low temperatures, and the corrosion rate is faster. Therefore, during the renovation, special coatings such as ceramics and silicon carbide should be coated on the surface of the heating surface that is prone to high-temperature corrosion. Materials with good high-temperature corrosion resistance can also be selected to improve their high-temperature corrosion resistance.6. To prevent explosions inside the furnace, when coal is converted into an oil (gas) furnace, if the atomization of the fuel is poor or the combustion of incomplete oil droplets (gas) is accumulated by hot gas in the furnace or tail, due to the risk of ignition, explosion, etc., explosion-proof doors should be installed in appropriate positions of the boiler. At the same time, ignition program control and extinguishing protection devices should be added to the automatic control to ensure the safe operation of the boiler.