Fireside Corrosion in Reducing Waste Incineration Environments

Abstract The corrosion behavior of a carbon steel covered with synthetic ashes and an actual ash has been investigated under reducing and oxidizing atmospheres. It has become clear that HCl content has a great influence on the corrosion rate of the carbon steel covered with NaCl-KCl and NaCl-KCl-Na2SO4-K2SO4 in the reducing atmosphere. When the HCl content in the reducing gas was 0.2%, a severe corrosion attack was observed at 350°C and 400°C. This corrosion is considered to be due to NaCl-KCl-FeCl2 hot corrosion. In the oxidizing atmosphere the corrosion was slight at all temperatures tested. The corrosion rate of the carbon steel covered with an actual ash was faster in the oxidizing atmosphere than that in the reducing atmosphere. Because heavy metal chlorides of low melting point existed in the actual ash, the oxygen accelerated the corrosion. Although CuO, PbO or ZnO additions to the NaCl-KCl salt mixture did not accelerate the corrosion in the reducing atmosphere, these oxides remarkably increased the corrosion rate in the oxidizing atmosphere. These oxides can form eutectic mixtures having low melting points in the oxidizing atmosphere. Such mixtures result in the molten salt corrosion that can be more severe than attack by HCl and chlorine gases.