How to address heat pipe corrosion and scaling in the flue gas exchanger of industrial boilers?
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The figure below shows a heat pipe exchanger used in a refinery’s heater for heat exchange between flue gas and air. After more than a year of operation, the surface of the heat pipes became covered with soot, along with severe corrosion beneath the scale. Using conditionally burned medium residue oil, the flue gas inlet temperature is 180 degrees while the outlet temperature is above 80 degrees.
It seems that this issue is caused by the use of chemical descaling agents: these agents are directly added to the furnace during combustion, and once they adhere to the outer surface of the tube walls, they undergo significant chemical reactions – similar to a burning process – which effectively remove the carbon deposits from the tube surfaces. However, the by-products of these chemical reactions, along with the removed carbon deposits, rise upward with the smoke flow and accumulate around the heat pipes. Over time, this accumulation covers the heat pipes completely, severely reducing their heat exchange efficiency and leading to an increase in the exhaust temperature； Some also travel with the smoke to the chimney, where they eventually settle at its bottom.
It’s terrifying! Can it still exchange heat? It is recommended to thoroughly clean and wash it before putting it into use!
That’s right; in ordinary heating furnaces, soot blowers can be installed in the convection section of the furnace tubes, which allows for the timely removal of ash and dirt from the surface of these tubes. Practice has shown that this approach is quite effective. However, similar tests have also been conducted in the flue gas heat exchange section, with inconspicuous results. Primarily, flue gas at low temperatures contains a high amount of moisture, and most of the ash deposits form under conditions of wet flue gas. In this case, the tube can only be cleaned periodically. After cleaning, many signs of corrosion appeared on the surface of the heat pipe, with severe corrosion in some areas. How to do it as if?