Key links in the renovation of coal-fired boilers

(1)   Dismantle the auxiliary equipment of the original coal-fired boiler;

(2)   By calculating the heat transfer of the furnace, determine the geometric dimensions of the furnace and the center position of the furnace flame. Re pour the furnace. To avoid the center position of the flame, the original rear arch tube is raised on the basis of the original slope;

(3)   Install explosion-proof doors;

(4)   Conduct a water pressure test on the boiler body at 1.5 times the working pressure.

In general, efforts should be made to minimize changes to the pressure bearing components of the boiler body, and only partial modifications should be made to the furnace arch and wall.

Choose the correct matching burner

Taking into account various factors such as gas pressure, boiler back pressure resistance, air supply pressure, and pipeline resistance, a comprehensive consideration is given to selecting the appropriate burner.

Issues to be noted when converting coal-fired boilers into gas-fired boilers

(1)   Small boilers, which have been converted from coal-fired boilers to gas-fired boilers, have changed from negative pressure combustion to micro positive pressure combustion. Attention must be paid to the structure and sealing of the furnace walls;

(2)   To prevent ignition or incomplete combustion of fuel when converting coal-fired boilers to gas-fired boilers, explosion-proof doors should be installed in appropriate parts of the boiler, and ignition program control and flameout protection devices should be added to automation control to ensure safe operation of the boiler;

(3)   The selection and arrangement of burners are closely related to the form of the furnace, and should ensure that the flame inside the furnace is well filled and does not form blind spots for airflow; Avoid mutual interference of flames from adjacent burners; Maintain the flame at the center of the furnace during low load to avoid the flame center deviating from the symmetrical center of the furnace; The unburned gas air mixture should 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 to prevent excessive heat intensity and overheating of the pipe wall. The layout of the burner should also consider the reasonable arrangement of gas pipelines and air ducts, as well as the convenience of operation, inspection, and maintenance;

(4)   To convert a mechanized layered coal-fired boiler into a gas boiler, the front and rear arches should be removed first, and consideration should be given to adding a bottom heating surface to replace the grate and prevent it from overheating and burning out;

(5)   To prevent high-temperature corrosion, coal is replaced with fuel oil. Due to the presence of organic metal elements such as sodium and vanadium in fuel oil, the melting point of oxide eutectic crystals formed after combustion is very low, generally around 600 ℃ or even lower. After sublimating at high temperatures in the furnace, these oxides condense on the relatively low-temperature heating surface, forming corrosive high-temperature ash deposits, and the higher the temperature, the faster the corrosion. Therefore, during the renovation, special coatings such as ceramics and silicon carbide should be applied to the surface of the heating surface that is susceptible to high-temperature corrosion. Materials with good high-temperature corrosion resistance can also be selected to improve their high-temperature corrosion resistance;

(6)   The smoke velocity of the convective heating surface of a gas boiler is not limited by the wear conditions of fly ash. It is possible to increase the smoke velocity appropriately to increase the heat transfer coefficient of the convective heating surface. Without increasing the heating surface of the boiler, the pressure of the boiler can be increased. At this time, attention should be paid to the ability of the steam water separation device inside the boiler to ensure steam quality, which is particularly important for boilers with superheated gas.