Synergies Between Biomass and Solid Recovered Fuel in Energy Conversion Processes

Abstract

Solid recovered fuels (SRFs) derived from commercial/industrial and municipal solid waste-type streams containing high heat value plastics offer a number of synergies for biomass combustors. This article covers technical and operational synergies to increase biomass combustion efficiency in a grate fired system typical for waste-to-energy technology. The transfer of laboratory results to pilot scale is presented by a new approach based on experimental data in laboratory scale and a mathematical model using key combustion parameters. Agreement between the experimental data and the mathematical model is sufficient to use the model for scale up. Because of the sometimes poor biomass fuel quality in biomass combustion facilities, the following unfavorable operating conditions occur: fouling and slagging on the furnace and boiler walls. These effects lead to lower operating hours due to more frequent cleaning cycles. The low- and medium-priced biomass available from the market has very low heat values (5 GJ/t) and high alkali metal content. Biomass availability in most European Union (EU) countries lead to an increased amount of low-grade biomass fed into grate-type combustors. Efforts of the American Chemistry Council, the Institute of Technical Chemistry, and PlasticsEurope have assessed the synergies through laboratory-scale experiments and have continued to demonstrate the biomass and SRF synergies on a large-scale pilot grate-type incinerator. This article points out that primary air preheat influences energy efficiency of the total process for the combustion of wet biomasses positively. Local combustion behavior of the wet biomass will depend on the degree of mixing and the moisture content. Results from this pilot scale confirm that SRF addition of 20–40 wt% lead to more homogeneous combustion behavior and an increase of energy efficiency from 2% to 3% absolutely.