Sulphur recirculation for high temperature corrosion and dioxin abatement in Waste-to-Energy boilers

Paper i proceeding, 2018

Sulphur Recirculation is a new patented technology for reducing high temperature boiler corrosion and dioxin formation in Waste-to-Energy plants. SO2 is separated from a tail end wet scrubber using H2O2, producing a 15-25wt% H2SO4 solution, which is injected into the boiler producing SO2, thus creating a sulphur loop. The recirculated sulphur will increase the gas concentration of SO2 in the boiler and decrease the Cl/S ratio of the deposits and ashes, thus producing a less corrosive environment for the superheaters. Furthermore, the lower chlorine content of the boiler deposits also significantly decreased the dioxin formation rates as well as dioxin emissions. Sulphur Recirculation was initially demonstrated in pilot plant tests as well as full-scale tests at a Waste to Energy plant in Göteborg (Sweden) during nearly two months of operation. Babcock & Wilcox Vølund AB in Sweden has installed their Sulphur Recirculation technology in one of the two Waste-to Energy lines at Maabjerg Energy Center (MEC) in Denmark in order to combat high temperature corrosion and dioxin formation. This is the first commercial installation and it has been operating since mid-October 2016. Sulphur Recirculation decreased the high temperature corrosion rates of the superheaters in this full-scale installation by approximately 50%, which may increase green electricity production from combustion of biomass and waste in the future. Furthermore, the dioxin gas concentrations decreased by 72%. Sulphur Recirculation almost entirely decreased the need for costly road transports of effluent sulphate water for the Sulphur Recirculation line, since most sulphur from the waste now ends up in the ashes instead of creating a surplus dilute Na2SO4 solution. The sulphur content of the waste varies with time, which may create periods of sulphur surplus and deficit respectively. Most of these variations are being evened out by a storage vessel for H2SO4. These variations may facilitate a small market of waste sulphuric acid between plants in the future.