Energy and environmental performance of a SRF-fired fluidized bed waste-to-energy plant

A methodology based on the ISO 14:031 guideline has been developed and applied to a full-scale fluidized bed waste to energy plant burning secondary recovered fuel (SRF). With reference to 3 years of operation, data on energy and environmental performance, on raw materials consumptions such as sand and diesel fuel, accidental reasons of plant shutdown have been acquired and analyzed. The obtained results have allowed to quantify the energy and environmental performance of the WtE plant under investigation by varying the amount, composition and characteristics of the inlet SRF. Indicated as SRF1 (year 2013), SRF2 (year 2014) and SRF3 (year 2015), their compositions was as follows: SRF1: Combusted waste = 88,110.22 tons/year; SRF composition = 78% of thickened SRF and 22% of fluff SRF; Low Calorific Value of the mixture = 20.2 MJ/kg. SRF2: Combusted waste = 79,906.44 tons/year; SRF composition = 86% of thickened SRF and 14% of fluff SRF; Low calorific value = 16.0 MJ/kg; SRF3: Combusted waste = 74,472.04 tons/year; SRF composition = 96% of thickened SRF and 4% of fluff SRF; Low Calorific Value of the mixture = 15.3 MJ/kg. The obtained results showed how, in terms of energy performance, the fluidized bed technology applied to SRF was able to guarantee adequate production of electricity (satisfying the market demands) showing certain flexibility with respect to the inlet SRF. In terms of net efficiency, the plant showed values in the range (12.1-16.6%), in line with similar installations. In terms of environmental performance, the adoption of such cleaning system based on SNCR (Selective Non Catalitic Reduction) + dry scrubbing + Fabric filter, generated emissions usually well below the limits set by the EU Directive 2000/76/EC as well as the Italian Law 133/2005 (more restrictive) with reference to all key parameters. While, in terms of plant shutdown, the majority of problems focused on the combustion chamber and the boiler. In contrast, mechanical and electrical cause, and those related to the control and instrumentation system, were of secondary importance. However, the fuel (in this case, the SRF) also was among the leading causes of frequent plant shutdown. Finally, the obtained results have been discussed also with reference to similar WtE plants such as Robbins (Chicago, USA), Lidköping (Sweden), Toshima (Tokyo, Japan), Madrid (Spain), Dundee (Scotland, UK) and Valene (Mantes la Jolie, France).