Article pubs.acs.org/est
Solid Recovered Fuel: Influence of Waste Stream Composition and Processing on Chlorine Content and Fuel Quality Costas Velis,† Stuart Wagland,† Phil Longhurst,† Bryce Robson,‡ Keith Sinfield,‡ Stephen Wise,‡ and Simon Pollard*,† †
Centre for Energy and Resource Technology, Department of Environmental Science and Technology, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire MK43 0AL, U.K. ‡ Shanks Waste Management Ltd, Dunedin House, Mount Farm, Milton Keynes, Buckinghamshire, MK1 1BU, U.K. S Supporting Information *
ABSTRACT: Solid recovered fuel (SRF) produced by mechanical−biological treatment (MBT) of municipal waste can replace fossil fuels, being a CO2-neutral, affordable, and alternative energy source. SRF application is limited by low confidence in quality. We present results for key SRF properties centered on the issue of chlorine content. A detailed investigation involved sampling, statistical analysis, reconstruction of composition, and modeling of SRF properties. The total chlorine median for a typical plant during summer operation was 0.69% w/wd, with lower/upper 95% confidence intervals of 0.60% w/wd and 0.74% w/wd (class 3 of CEN Cl indicator). The average total chlorine can be simulated, using a reconciled SRF composition before shredding to 500 °C) of boiler steel due © 2011 American Chemical Society
to alkali chlorides and lower temperature melt deposits (300− 400 °C) in the presence of zinc and lead;9 generate high acid gases emissions (hydrogen chloride (HCl));10 and contribute to the formation of polychlorinated dibenzodioxins (PCDDs) (for [Cl] above 0.3% w/wd)11 during thermal recovery.12−14 Given these potential impacts and their effect on the marketability of SRF, residual chlorine content was selected by the European Committee for Standardisation (CEN) as the key technical performance indicator of SRF quality.15 Researchers have attempted to simulate the total chlorine content of SRF produced by (biodrying) MBT plants.16−18 Few validate their predictions by comparing theoretical with empirical data. One study16 simulated SRF properties and predicted total chlorine content from presumed stoichiometry, whereas another18 adopted a probabilistic approach to predicting the total chlorine content of waste-derived fuels, using density functions to describe concentrations in various material groups of waste. Here, a comprehensive analysis of the effects of input waste composition is presented in the context of the impact on the Received: Revised: Accepted: Published: 1923
October 9, 2011 December 15, 2011 December 21, 2011 December 21, 2011 dx.doi.org/10.1021/es2035653 | Environ. Sci. Technol. 2012, 46, 1923−1931
Environmental Science & Technology
Article
steps.21 In a predrying stage, the bulk moisture content Mb was determined on the sorted, reassembled, and shredded to
