The design, testing and analysis of a biofuel micro-trigeneration system

Abstract

Trigeneration and the use of biofuels are two research topics which are important in trying to help relieve global energy shortage and bring about a reduction in greenhouse gas emissions. Trigeneration produces electricity, cooling, and heating simultaneously using a single fuel source and can operate at a high efficiency rate. The use of biofuel provides a renewable and carbon neutral substitution for fossil fuels. This research thesis describes the development of a biofuel micro-trigeneration (BMT) system using raw vegetable oils and explores the feasibility of meeting the total energy demand of a typical household. The system was designed and constructed using a 6.5kW single cylinder diesel generator as the prime mover, two heat exchangers for recovering waste heat from the engine coolant and exhaust gas, and an absorption refrigerator driven by exhaust gas heat. Four raw vegetable oils: sunflower, rapeseed, jatropha and croton oils were preheated to 90℃ and used in the study. The system performance using the vegetable oils was compared to that of the gas oil. Experiments were carried out to determine the fuel properties of the oils, including viscosity, density, higher heating value and fatty acid components. Power generation, combined heat & power and trigeneration tests were also carried out. The experimental results reveal that the BMT system performed with a high efficiency of 65% for trigeneration at full load, and CO2 emissions was reduced by around 60% compared to single power generation mode. The exergy efficiency was also increased by approximately 5 points. An engine model was developed using DIESEL-RK software to study the engine performance and emissions using different fuel types. Optimizations were performed to improve the engine performance and emissions. A trigeneration system model was also developed using Dymola software and was used to predict the dynamic performance of the system parameters. These models and simulation studies were validated against experimental results and matched well with the experimental results; hence can be used to explore wider system design and performance considerations. Both the experimental and theoretical studies have proved the feasibility of the BMT system to meet the overall energy demand of a household user.