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 a thin layer of scale on the heating surface can cause high thermal resistance, reducing heat transfer efficiency, resulting in heat loss and fuel waste. Practice has proven that 1 mm 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, it can cause tube bulging, and in severe cases, boiler tube rupture, threatening personal safety. Scale is a complex salt containing halogen ions, which corrode iron at high temperatures. Analysis of iron-containing scale shows it contains about 20-30% iron. Scale corrosion makes the boiler inner wall brittle and continuously corrodes deeper into the boiler. Removing scale requires boiler shutdown, consumes manpower and resources, and causes mechanical damage and chemical corrosion to the boiler.
Therefore, preventing and removing scale are issues that must be addressed in water treatment.
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 it 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/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 descaling cleaner. Generally, control the solution concentration at 5-20%, which can also be determined by 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, 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 pretreatment cleaner. Generally, control the solution concentration at 2-5%, which can also be determined by the thickness of the scale. Cleaning can be done by long-term boiling without raising pressure, usually no less than 24-48 hours. After cleaning, immediately flush out the sludge and mud. For severely scaled equipment, this method may not completely dissolve the scale but softens it into mud. The boiler must then be opened to remove the mud using conventional chemical cleaning or mechanical methods, otherwise the mud will re-harden and be difficult to remove.
