The principal function of a Refuse Derived Fuel (RDF) system is to accept solid waste directly from the collection vehicle and to separate the solid waste into two fractions -- namely, combustible and non-combustible. The Refuse Derived Fuel (RDF) separation produces the “feedstock” for several types of back-end recovery systems, among which are included thermal and biological systems. The main components of a Refuse Derived Fuel (RDF) subsystem are usually any combination of size reduction, screening, magnetic separation, and density separation (e.g., air classification). The types and configurations of unit operations selected for the Refuse Derived Fuel (RDF) design depend on the types of secondary materials that will be recovered and on the desired quality of the recovered fuel fraction. The fuel quality must be specified by the designer or supplier of the thermal conversion system. Typically, systems that recover a combustible fraction from mixed MSW utilise size reduction, screening, and magnetic separation. Some designs and facilities have used screening, followed by size reduction (e.g., pre-trommel screening), as the fundamental foundation of the system design, while others have reversed the order of these two operations. A number of considerations enter into the determination and the selection of the optimum order of screening and size reduction for a given application. Among others, the considerations include composition of the waste. Other unit operations may also be included in the system design, including manual sorting, magnetic separation, air classification, and pelletization, as the need dictates for recovery of other materials and for achieving the desired specification of the solid fuel product.
