Combustion and emission characteristics of optimised yellow grease methyl ester in an oil burner applications

Abstract

Yellow grease is an abundant non-edible waste cooking oil that has potential to be converted into biodiesel fuel for utilisation in the industrial liquid fuel burner. A single or two-stage acid and base catalysed transesterification process is usually used to produce this fuel and commonly affected by high Free Fatty Acid (FFA) contents and other several factors which can be enhanced to achieve high yield production. At present, research on converting oil with high FFA value using the single-stage base catalysed transesterification process is very limited due to incompliant of fuel physical properties with the biodiesel standard. Besides that, the utilisation of biodiesel as the industrial liquid fuel burner using yellow grease-based biodiesel have not yet been evaluated and reported in the literature. This study aimed to investigate the optimum production of Grease Methyl Ester (GME) from yellow grease with FFA value of 2.01% which is compliant to the American Society for Testing Materials (ASTM) D6751. This study was also evaluated the combustion and emission characteristics of various GME biodiesel blends for use in the industrial liquid fuel burner. The Central Composite Face Centred model was applied on three transesterification factors in terms of the weight of Potassium Hydroxide (KOH) catalyst from 1.0 wt.% to 2.0 wt.%, Methanol (MeOH) to yellow grease molar ratio from 6.0 to 12.0 and reaction temperature from 45 oC to 65 oC for maximising the percentage of GME yield. Design- Expert V10 software was used to plan the experiments with six axial points, three centre points and two replications. For the fuel combustion, all GME biodiesel fuel blends (B10, B30, B50, B75 and B100) were atomised using the Delavan Type W 60o angle nozzle at 1.5 GPH which was installed on the BTL-10 light industrial fuel burner and combusted inside a concentric cylindrical combustion chamber from equivalence ratio (O) 0.8 to 1.4. The results show that the quadratic regression model generated from the Response Surface Methodology analysis is effective to explain the outcome of all transesterification factors and excellent to predict the yield of GME as close to the actual experimental data. GME yield is able to be optimised by 97.61% when using 1.33 wt.% of KOH, 6.05 MeOH to yellow grease molar ratio and reaction temperature at 45oC. Besides that, several tests on the fuel physical properties of GME show promising compliance with the ASTM D6751. As for the fuel combustion, increasing GME content from 10% to 100%, it reduces the average combustor wall temperature between 0.26% to 15.37%, average Nitrogen Oxide between 4.76% to 12.70%, average Carbon Monoxide between 10.23% to 30.77%, average Sulphur Dioxide between 23.81% to 95.24% and average Carbon Dioxide between 1.43% to 8.91%. Such reduction is due to the high value of oxygen content, kinematics viscosity, surface tension and flash point as well as low value of gross calorific, nitrogen and sulphur contents than Petroleum Diesel Fuel (PDF). This finding is beneficial in providing relevant information for decent production of GME and promising usage as an alternative fuel in the industry with comparable performance to PDF.