I. Hazards of scale in electric heating steam boilers
Scale in electric heating steam boilers directly threatens the safety of the boiler device and its service life, because the thermal conductivity of scale is very low. The thermal conductivity of scale is hundreds of times smaller than that of metal. Therefore, even if a not very thick layer of scale forms on the heating surface, due to high thermal resistance, its thermal efficiency decreases, causing heat loss and wasting fuel. Practice has proven that a 1 mm thick layer of scale on the boiler heating surface can increase coal consumption by about 1.5-2%. Scale on the heating surface can cause local overheating of metal tube walls. When the wall temperature exceeds the allowable limit for operation, it can cause tube bulging, and in severe cases, lead to boiler tube bursts, threatening personal safety. Scale is a complex salt containing halogen ions, which corrodes iron at high temperatures. Analysis of iron-containing scale shows it contains about 20-30% iron. Scale erosion makes the inner wall of the boiler brittle and continuously corrodes deeper into the boiler. Removing scale requires boiler shutdown, consumes manpower and materials, and causes mechanical damage and chemical corrosion to the boiler.
Therefore, preventing and removing scale are problems that must be solved in water treatment work.
II. Removal methods of scale in electric heating steam boilers:
1. Mechanical descaling method: When there is scale or sludge in the boiler, shut down the boiler, drain the water, let the boiler cool, and use water flushing or a spiral wire brush to remove it. If the scale is very hard, high-pressure water jet cleaning or power- or hydraulic-driven tube cleaners can be used. This method is only suitable for cleaning steel tubes, not copper tubes, as tube cleaners can easily damage copper tubes.
2. Conventional chemical descaling method: Based on the equipment material, choose a safe and powerful scale removal cleaning agent. Generally, control the solution concentration at 5-20%, which can also be determined according to the thickness of the scale. After cleaning, first drain the waste liquid, then rinse with clean water, then fill with water and add about 3% of the water volume of neutralizer, soak and boil for 0.5-1 hour, drain the residual liquid, and rinse with clean water once or twice.
3. Special chemical descaling method: For sulfate and silicate scale, or mixed sulfate and silicate scale, use a special scale pretreatment cleaning agent. Generally, control the solution concentration at 2-5%, which can also be determined according to the thickness of the scale. Cleaning can be done by boiling the boiler without raising pressure for a long time, generally not less than 24-48 hours. After cleaning, immediately flush out the sludge and mud. For equipment with severe scaling, this method cannot completely dissolve and remove the scale, but only softens and muddies it. The boiler must be opened and the mud residue removed using conventional chemical cleaning methods or mechanical methods, otherwise the mud residue will re-harden and become difficult to remove.
