Co-combustion tests were performed in a lab-scale fluidised bed reactor, in order to define (a) the optimum percentage for substituting Greek lignite by waste wood, and (b) the operation conditions ensuring complete burnout of the fuel blends. Tests were performed at the experimental facility of the NTUA’s Steam Boilers and Thermal Plants Laboratory.
Pre-dried lignite, from Ptolemais reserve, and various waste wood species, i.e. uncontaminated wood, demolition timber and railway sleepers, were used to prepare the fuel blends. In all tests, the emissions in flue gases - CO, SO2, N2O, NOx, NO, NO2 and CxHy – were continuously monitored. Furthermore, a qualitative assessment for the ash deposition propensity, including measurements of the characteristic ash-fusibility temperatures of various fuel blends was accomplished.
The combustion efficiency, gaseous emissions and residual matter composition were measured for the various fuel blends, considering also the excess air ratio effects. Ash samples, collected during the co-combustion tests, were analysed, for heavy metals.
The results obtained, proved that waste wood addition in the fuel blend, up to a certain percentage, is feasible. Furthermore, the minimal ash content and sulphur percentage of waste wood contribute to the minimisation of ash agglomerates formation during the co-combustion with the low quality lignite.
Keywords: co-combustion, Greek lignite, waste wood, fluidised bed, emissions, ash agglomerates.