Quality of deposits during grate combustion of corn stover and wood chip blends

• Published in: Fuel (Guildford) 2013-02, Vol.104, p.476-487
• Main Authors: Aho, Martti, Paakkinen, Kari, Taipale, Raili
• Format: Article
• Language: English
• Subjects: Applied sciences; Biomass; Corrosion; Deposits; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuels; Grate combustion; Natural energy; Triticum aestivum
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2012.05.057

► New data on Cl deposition and alkali chlorides formation during corn stover firing. ► Corn stover was found to be corrosive to power plant superheaters at grate combustion conditions. ► Problem solution concept must be developed to ensure safe burning of corn stover in power plants. There is need to increase efficiency of electricity production in grate combustion (GC). This will lead, however, to higher steam temperatures and make superheaters more susceptible to corrosion. Corn stover (CS) is one of the most abundant agro-biomass residues available to energy production on a global scale and GC power plants are best suited to its combustion. The focus in this study was the quality of deposits during GC of CS blended with wood chips. CS is a difficult fuel at least due to its high chlorine content (up to 1wt%). After a thorough fuel analysis (also with wheat straw, for comparison), combustion tests were conducted with a 100kW grate reactor, where gas temperature versus residence time can resemble that in a full scale GC power plant furnace. Flue gas composition, alkali chloride mass flow, mass deposition, and deposition of chlorine and other key elements at critical positions of two superheater simulators were measured. Corrosivity of deposit, if estimated only from the maximum chlorine concentration found in deposits, reached maximum already with 20±3% portion of CS on energy basis (which was the lowest portion of CS in the tests). However, further increase of the portion of CS in the blend was found to increase the overall mass deposition and also Cl mass deposition through this way. Because corrosion reactions consume elemental chlorine, the corrosivity (metal loss) at superheater area can increase as a function of CS portion in range >20% CS. Ash problems found on the grate were mostly due to the high mineral content in CS. These minerals originated mainly from the soil (during the harvesting stage), which led to higher ash melting temperatures compared to wheat straw ash.