Characterisation of Solid Recovered Fuels for Direct Co-firing in Large-Scale PF Power Plants

Solid Recovered Fuels are solid fuels prepared from high calorific fractions of non-hazardous waste materials intended to be co-fired in coal power plants and industrial furnaces (CEN/TC 343). They are composed of a variety of materials of which some, although recyclable in theory, may be in a form that makes their recycling an unsound option. The SRF with a typical size range of 3 mm through 25 mm are to be directly co-fired in an existing pulverised coal power plant. In comparison to pulverised coal, the particle size distribution of the SRF is of several magnitudes higher, resulting in a different burnout behaviour. Size reduction of the SRF to a fraction similar to coal is not economically feasible. The aim here is, therefore, the direct co-firing of the solid recovered fuels in the boilers without any further size reduction. This approach, however, bears the risk of incomplete combustion if the injection points of the solid recovered fuels are not optimally selected.

Accordingly, the prediction of the burner levels, at which the solid recovered fuels should be injected and whether or not a complete combustion will be achieved under full load condition, is the primary objective of this dissertation. In this research work, laboratory experiments have been conducted to forecast the success of co-firing the SRF in a commercial pulverised coal power plant. It involves the analyses of the fuel and its intermediate chars generated at conditions comparable to boiler conditions to determine some characteristic parameters, namely the burnout time, the aerodynamic lift velocity, the drag coefficient and the apparent densities. The data gathered from the laboratory experiments are transferred to boiler conditions to determine the particle trajectories and the maximum distance likely to travel before they are completely converted in the boiler. Different scenarios are examined and based on the results the best boiler injection points are predicted. Furthermore, an on-site measurement is conducted during the co-firing investigation at a 600 MWel lignite power plant and the emission results are compared with the base line configuration.