Abstract
Gasification under steam excess of the residual from mechanical treatment of municipal solid waste (RMT-MSW, refuse derived fuel (RDF)-type) was investigated in a laboratory batch reactor, equipped with a section for high-temperature gas equilibration. Experiments were performed with recirculation of the condensate and residual tars/oils, for closing of the process loop. Gas emissions were registered at 300–500 °C (pyrolysis; maximum at 390 °C) and 650–800 °C (gasification; maximum at 740 °C). Peak areas, equivalent to the gas volume, were in a general proportion of 55:45. Mass of tars and oils collected together with condensing steam was only equal to 0.15% of the average weight loss of the RMT-MSW. Ninety-seven percent of organic compounds, mainly naphthalene, phenanthrene and derivatives, was separable by a simple filtration. Concentration of metals in aqueous condensate was equal to 135 mg/dm3, 98.5% by mass was potassium and sodium ions. Concentration of NH4+ was equal to 2.49 g/dm3 (mostly carbonate). According to the thermodynamic evaluation, volume of the process gas was equal to 2.11 m3 (dry, 25 °C, 1 bar) per 1 kg of the dry waste. Standard enthalpy of the gas combustion was 24.6 MJ/kg of the dry waste; approximately 16% of this energy was due to endothermicity of the process.
Highlights
Considering gasification, a variety of processes may be applied for municipal solid waste (MSW) treatment; they are usually classified in view of the gasifying agent, reactor design, heat supply, pressure, temperature and form of solid residue [1]
The series was opened with discussion of results of gasifying experiments performed in the laboratory-scale in the two-stage fixed bed reactor with samples of original MSW and natural dolomite as catalyst for cracking of tars [7,8]
The dependence of the catalytic properties of granules on their composition were not investigated in the experiments, because the whole condensate as well as not-converted tars and oils were recirculated to the reactor
Summary
Considering gasification, a variety of processes may be applied for municipal solid waste (MSW) treatment; they are usually classified in view of the gasifying agent, reactor design, heat supply, pressure, temperature and form of solid residue [1]. It seems that interest in steam gasification of MSW gradually increases and there are new papers being presented with a more general insight into the process, e.g., into a route for energy recovery [16], analysis of the process performance [17] or exergy [18] This last one was based on the results of experiments in a semi-industrial fluidized bed gasifier, or conversion of MSW to SNG (Synthetic Natural Gas) [19]. We believe that the replacement of incineration by steam gasification transforms this traditional method of waste elimination in the “atmospheric open” flow reactor into a more advanced process of chemical refining of the waste to mineral/metal solid residue and producer gas (syngas). We recently discussed thermochemical cycles for some wastes, demonstrating equivalency of the initial and final states of both incineration and steam gasification [35]
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