The use of low calorific value or high sulphur content coal mixed with biomass is interesting due to the complementary properties of the two fuels since, as opposed to the typical characteristics of low quality coals, biomass has low ash and sulphur contents and a high volatile concentration that is favourable to a clean combustion of the coals under consideration.
Within the scope of this concept, NTUA's Steam Boilers and Thermal Plants Laboratory (NTUA-LSB) performed a series of experiments in a lab-scale Bubbling Fluidised Bed Combustor (BFBC), using the fossil fuels of Megalopolis pre-dried lignite and Göttelborn hard coal with biomass material, i.e. Wood matter from pressed oil-stone (WPOS) and straw. During the trials, the applicability limits of the coal partial substitution by biomass as a function of the excess air ratio were determined, taking also into account the special features of the combustion technology used. In this way, the effects on combustion behaviour, flue gas emissions, volatiles release, residual matter and the ash tendency for agglomerates and deposits formation were thoroughly examined. The obtained results showed that co-combustion is technically feasible and could be extended in large-scale firing installations, provided that difficulties arising mainly from the ash melting in high temperatures can be industrially confronted.
Keywords : co-combustion, fossil fuels, lignite, Wood matter from pressed oil-stone (WPOS), straw, fluidised bed, emissions, ash agglomerates.