High Temperature Corrosion in a 24 MW Waste-to-Energy Plant

Waste-to-energy (WTE) plants are utilized for the production of heat and electricity from municipal solid waste (MSW) and refuse derived fuel (RDF). Due to high chlorine content (0.5wt.%∼1.0wt.%) in MSW & RDF, high temperature corrosion is often observed on the superheater surfaces and correspondingly leads to a very low efficiency of 15%∼25% in practical WTE plants. To obtain information on the corrosion rate and high temperature corrosion mechanism, a full scale nine-month-long term corrosion test was therefore conducted in a heat and power generating WTE plant in Tianjin, China. The grate boiler with a capacity of 400 tons/d, runs at a burning temperature between 850∼900°C, flue gas temperature between 550∼650°C, steam temperature of 400°C, and steam pressure of 4MPa. The corrosion probes made of same metal alloy with heat exchanger were exposed on the surface of economizer, protector and superheater, respectively. The metal loss by corrosion was determined by measuring the distance from the inside of the ring to the interface between metal and oxide with a measuring microscope. The deposit characteristics as well as elemental compositions were determined using a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The objective of this work is to evaluate: 1) plant specific corrosion rate on different superheater materials and 2) relationship among chlorine content in the feedstock, chlorine gas emission before air pollutant clean system, and deposits composition. The results showed deposits characteristics depend on the probe location, metal materials, temperature and windward/leeward. Barely chlorine exists in the deposits, except for the outer surface of the deposits at 3^rd SH. The highest corrosion loss for 20G at 3^rd SH was calculated to be 2mm/year, based on the assumption of linear extrapolation of corrosion rate.