Characterisation of meat and bone mill for coal co-firing

A most interesting solution for the disposal of meat and bone meal (MBM) is co-feeding with coal in combustion plants. MBM, is however, quite different from any other traditional or alternative solid fuel in terms of chemical composition, ash content and microstructural properties. Its effects on the performance of a boiler are largely unexplored. The present paper addresses the characteristics of MBM as alternative solid fuel and the effects of co-feeding MBM (6%) and coal (94%) in a utility boiler.A first activity consisted in the characterisation of the physico-chemical properties and the reactivity of MBM. The experimental campaign included ultimate and proximate analysis, granulometric analysis, ICP, SEM, XRD. An extensive campaign of isothermal and non isothermal thermogravimetric experiments was carried out to assess the reactivity of MBM upon pyrolysis, combustion and gasification and to obtain appropriate kinetic expressions.A second activity focused on co-firing of MBM and coal. Bottom and fly ashes were collected from an industrial boiler operated with MBM and coal. Ash samples were characterised by SEM, XRD, ICP, TGA and granulometric analysis. Results of this activity showed that MBM contributes mostly to bottom ash, however also the fly ashes are different from those typically encountered when the boiler is operated with coal alone. Differences concern the chemical composition and particle size distribution of ashes, in particular a large population of very fine particles characterised by perfectly spherical shape and non negligible carbon content is observed.