1991

Fagernäs, Leena

Processes developed for biomass synthesis gas production during the 1980s are U-GAS, PEATGAS, High-Temperature- Winkler, MlNO, Omnifuel and CreusotLoire. Waste waters from the processes with wood, peat and wastes as raw materials have been studied in laboratory and pilot units and at demonstration plants. There is so far only one commercial biomass sygnas plant in operation in the world: the peat ammonia plant of Kemira Oy in Finland. In synthesis gas production, waste waters are formed in biomass drying, and in gas scrubbing and conversion. Major waste water impurities are solids, ammonia, cyanide, phenolics, benzene and polyaromatic compounds. Their concentrations are highly dependent on the gasification process used and on process conditions, such as pressure and temperature, gas treatment, amount of scrubbing water, and waste water recirculation. The waste waters from biomass gasification processes resemble those from coal gasification and coking and contain mainly the same impurity components, but in different ratios. The process waste waters require treatment before leading into water-courses or to a municipal purification plant, or before recirculation. The treatment is completely dependent on the concentration, amount and use of the waste water. Requirements set by the authorities and the maximum levels allowable in waste waters also vary in different regions and countries. Methods suited for the treatment of waste waters could be, on the basis of purification methods applied for coal-based waste waters, solids removal e.g. by centrifugation or filtration, ammonia removal by steam stripping and phenol removal by extraction, and, after pretreatment, treatment at a biological purification plant. When needed, activated carbon filtration, ion exchange or ozonation can be applied after the biological treatment. However, research activities are required to test and find methods suitable for the waste waters from biomass-based synthesis gas production.