Chlorine in waste-derived solid recovered fuel (SRF), co-combusted in cement kilns: A systematic review of sources, reactions, fate and implications

Solid recovered fuel (SRF), a partly biogenic form of waste-derived fuel, can be used for replacing fossil fuels in cement kilns. Higher SRF uptake is limited mainly by its chlorine (Cl) content. Here we present a systematic literature review (PRISMA methodology) on the challenges induced by Cl during SRF co-combustion in cement kilns. We show that mean Cl content in average commercially manufactured SRF is at 0.76 w/wd (± 0.14% w/wd, 95% confidence). Cl is widely dispersed amongst various chemical compounds present in several waste items—not just PVC. The variability around mean Cl in SRF is at 36.7% (CV), notably lower than that in MSW, indicating effective variability reduction because of mechanical processing of MSW into SRF. During co-combustion, most Cl remains within the kiln system causing operating problems and only a small percentage (0.7–13%) is incorporated in the clinker, making it stickier. A significant proportion is captured by the air pollution control system. State of the art engineering practices can result in suitable SRF quality assurance, largely preventing Cl-related problems in the kiln. Further investigation on the impact of fuel feeding systems, on effect of Cl speciation and on controlling the sources of Cl variability are needed to improve confidence in SRF uptake.