Investigation of ash deposition and corrosion during circulating fluidized bed combustion of high-sodium, high-chlorine Xinjiang lignite

A high-sodium, high-chlorine Xinjiang lignite was used as fuel in a 0.4 t/d circulating fluidized bed (CFB) test system to investigate ash deposition and corrosion characteristics using an air-cooled stainless steel probe. Different wall temperatures of the probe, exposed to the similar flue gas environment for 8 h, were achieved by adjusting cooling air flow separately at 1.0 m(3)/h, 3.0 m(3)/h and 5.0 m(3)/h. The probe wall temperature variation was analyzed, and deposited ash was characterized via a series of analytical techniques. Experimental results confirmed the disturbance of ash deposition to the heat flux through the probe, and this disturbance was enhanced due to the faster ash deposition rate at lower wall temperature. The selective deposition of mineral species including Na-, Cl-, K- and Mg-species occurred, resulting in a larger ash deposition amount on the lower-temperature probe. The corrosion caused by NaCl-rich deposited ash was accompanied with the oxidation of metallic matrix. It is found that the antioxidation of metals was in the order of Ni > Cr > Fe. During corrosion, metal chlorides with strong volatility were the main corrosion products, resulting in the presence of voids in deposited ash because of their release. This corrosion was accelerated at high temperatures and had repeatability.