Thermal desorption recycle–reduce–reuse technology (TDT-3R) is based on the low-temperature carbonization fuel pre-treatment principles. Clean coal samples were produced according to this method in an indirectly heated rotary kiln and were examined for their combustion efficiency and environmental performance. Raw material included coal and biomass, such as willow and straw. Investigations were realized via on-site measurements both in the clean coal procurement and combustion facilities and the characterization of end products and by-products.
Clean coals were proved to be less reactive than raw coal samples, while biomass chars increased the reactivity of fuel blends during combustion. In the clean coal production and combustion processes, flue gases emissions, such as CO, SO2, NO2, were particularly low, while polychlorinated dibenzo-p-dioxins and dibenzofuran emissions were in an order of magnitude less than anticipated from the EU legislation. Reduced total CO2 emissions are anticipated with the implementation of TDT-3R process compared to the conventional combustion of raw fuels. All ash leachates were accepted by the EPA-TCLP test, since none of them exceeded the EPA limits for safe disposal. The mercury content of all samples was very low and was reduced by about 90% after the leaching treatment. The pilot scale combustion tests demonstrated the major advantage offered by the TDT-3R process, which is the production of clean fuels with much lower pollutants content. High added value commercial application of the technology is feasible, provided that the ash content of raw fuel does not exceed 20% w/w. It is expected that the employment of produced clean coal originating from high-grade coal in combination with biomass derived materials may result in almost zero emission power plant operation.
Keywords: low-temperature carbonization, TDT-3R, CO2 reduction, heavy metals, dioxins, furans