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 CO 2 -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/w d , with lower/upper 95% confidence intervals of 0.60% w/w d and 0.74% w/w d (class 3 of CEN Cl indicator). The average total chlorine can be simulated, using a reconciled SRF composition before shredding to <40 mm. The relative plastics vs paper mass ratios in particular result in an SRF with a 95% upper confidence limit for ash content marginally below the 20% w/w d deemed suitable for certain power plants; and a lower 95% confidence limit of net calorific value (NCV) at 14.5 MJ kg ar -1 . The data provide, for the first time, a high level of confidence on the effects of SRF composition on its chlorine content, illustrating interrelationships with other fuel properties. The findings presented here allow rational debate on achievable vs desirable MBT-derived SRF quality, informing the development of realistic SRF quality specifications, through modeling exercises, needed for effective thermal recovery. 1. INTRODUCTION Mechanical -biological treatment (MBT) plants employ mechanical processing (size reduction, air classification, and bioconversion (biodrying, composting, or anaerobic digestion)) to treat household and commercial waste. 1-5 Increasingly, MBT is used to generate a fuel product with market value: solid recovered fuel (SRF) or refuse-derived fuel (RDF). 4 SRF is becoming a major route for energy from waste (EfW/WtE) mainly throughout Europe. Removing excessive moisture by biodrying the waste improves its potential for thermal recovery, after suitable mechanical processing. 5-7 A major benefit of SRF is a potential incorporation of the biogenic content of the initial waste stream, a carbon dioxide (CO 2 )-neutral and alternative energy source, into the fuel. 2 Market uptake for SRF is contingent on assurances about the reliability of fuel composition in its supplied state, and the minimization of chemical residuals that might harm a process plant or compromise the environmental performance of the industrial facilities that accept SRF as a substitute fuel. Suitable quality management is imperative for SRF marketability, and the authors have reviewed the current state-of-the-art else- where. 4 The concentration of chlorine in SRF is key to fuel quality due to concern that elevated concentrations could exacerbate ash deposition in the convective part of boilers; 8 cause high-temperature corrosion (>500 °C) of boiler steel due 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/w d ) 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 study 16 simulated SRF properties and predicted total chlorine content from presumed stoichiometry, whereas another 18 adopted a probabilistic approach to predict- ing the total chlorine content of waste-derived fuels, using den- sity 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: October 9, 2011 Revised: December 15, 2011 Accepted: December 21, 2011 Published: December 21, 2011 Article pubs.acs.org/est © 2011 American Chemical Society 1923 dx.doi.org/10.1021/es2035653 | Environ. Sci. Technol. 2012, 46, 1923-1931