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Complete fuel switching from heavy fuel oil (HFO) to bioliquid (BL) was demonstrated in a 100 MWe-capacity boiler with a tangential firing configuration. The BL from the residue of palm oil production successfully replaced HFO at the full load (103 MWe) with new atomizers and minor adjustments to the operating parameters. The detailed combustion and heat transfer characteristics of the two fuels were analyzed using computational fluid dynamics (CFD). Compared to the HFO firing case, more uniform distributions of the gas temperature and heat transfer rate were observed in the combustion zone for the BL firing case. The total heat transfer rate was slightly lower on the furnace wall (evaporator), but this disadvantage was offset by the increased convection in the downstream heat exchangers. Because of the low soot concentration, the contribution of convection in the BL-firing case was larger in the lower furnace. A significant reduction in SO x and NO x emissions was achieved due to the low S and N content of BL, which would be the main benefit of fuel switching, in addition to the minimization of greenhouse gas emissions. In the future, the CFD model established in this study could be applied to the evaluation of BL different candidates and various co-firing cases with HFO. [ABSTRACT FROM AUTHOR]

Abstract: Fast pyrolysis liquid or bio-oil has been used in engines with limited success. It requires a pilot fuel and/or an additive for successful combustion and there are problems with materials and liquid properties. It is immiscible with all conventional hydrocarbon fuels. Biodiesel, a product of esterification of vegetable oil with an alcohol, is widely used as a renewable liquid fuel as an additive to diesel at up to 20%. There are however limits to its use in conventional engines due to poor low temperature performance and variability in quality from a variety of vegetable oil qualities and variety of esterification processes. Within the European Project Bioliquids-CHP – a joint project between the European Commission and Russia – a study was undertaken to develop small scale CHP units based on engines and microturbines fuelled with bioliquids from fast pyrolysis and methyl esters of vegetable oil. Blends of bio-oil and biodiesel were evaluated and tested to overcome some of the disadvantages of using either fuel by itself. An alcohol was used as the co-solvent in the form of ethanol, 1-butanol or 2-propanol. Visual inspection of the blend homogeneity after 48h was used as an indicator of the product stability and the results were plotted in a three phase chart for each alcohol used. An accelerated stability test was performed on selected samples in order to predict its long term stability. We concluded that the type and quantity of alcohol is critical for the blend formation and stability. Using 1-butanol gave the widest selection of stable blends, followed by blends with 2-propanol and finally ethanol, thus 1-butanol blends accepted the largest proportion of bio-oil in the mixture. [Copyright &y& Elsevier]