Replacement of an SCR DENOX system by a highly efficient SNCR in a waste-to-energy plant in the Netherlands

摘要

Since 1996 Attero has been operating an integrated waste processing plant in Wijster/ Netherlands. The plant includes a sorting facility and an incineration plant. Each of the three combustion lines was originally equipped with a catalyst (SCR) for NO_x reduction. However, in this plant the catalysts have two functions: denitrification of flue gases and oxidisation of dioxins. Because of the ageing of the catalyst elements, the oxidisation of dioxins has already been realised with active carbon for some years. Within the next years the catalyst elements used for denitrification would have had to be replaced as well. Apart from the ageing of the catalysts, the high consumption of natural gas for reheating the flue gases is another negative aspect of SCR. When the plant was designed in 1992, it could not be anticipated that soon Selective Non-catalytic Reduction (SNCR) could reach NO_x levels comparable to SCR which represented the state-of-the-art technology at that time. Meanwhile, the SNCR process is referred to by the European Commission as "Best Available Technology Reference" (BREF) for waste-to-energy plants. Hence, SNCR is acknowledged as generally reliable, technically fully developed and as an economical process for NO_x removal. Because of the significantly more favourable cost-benefit ratio of the SNCR technology, Attero decided to close down the SCR plants in the three combustion lines and replaced them with SNCR. Regardless of the economic advantages, a key factor for this decision was, of course, that emission levels would lie within or even below the limits set by the authorities.