The combustion and gasification behavior of the most common plastics is studied and compared with conventional fuels such as coal, peat, and wood. The aim is to give background data for finding the optimum conditions for co-combustion or co-gasification of a conventional fuel with a certain amount of plastic-derived fuel. Atmospheric or pressurized fluidized bed co-combustion of conventional fuels and plastics are considered to be promising future options. The plastics investigated were poly(ethylene) (PE), poly(propylene) (PP), poly(styrene) (PS), and poly(vinyl chloride) (PVC). Some of the samples had a print or color. The reference fuels were Polish bituminous coal, Finnish peat, and Finnish pine wood. PE, PP, and PS were found to burn like oil. The particles shrank to a droplet and burned completely during the pyrolysis stage, leaving no char. Printing and coloring left a small portion of ash. PVC was the only plastic that produced a carbonaceous residue, and its timescales for heating, devolatilization, and char burning were of the same order as those for peat and wood, and much shorter for the other plastics studied. An important result is that char from PVC contains less than 1% chlorine, 99% hydrocarbon. The gasification rate of PVC char (at 1 bar and 25 bar) was of the same order as that of char from coal. Peat-char and wood-char were gasified an order of magnitude faster.

No abstract

No abstract

No 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.