• Energy Research

In light of the growing concerns over depleting energy resources, alternative renewable fuels such as biodiesel have been identified as a possible means of addressing this crisis. In biodiesel production, waste cooking oil (WCO) is seen as the ideal alternative feedstock to vegetable oils, which are part of the food chain. The need to obtain high quality biodiesel at minimal cost has driven the idea to use membrane reactors, which offers the ability to achieve both reaction and separation processes simultaneously. Design and optimization studies were conducted using sulphated zirconia pre-treated WCO as feed stock. Response surface methodology modelling was used to investigate the effect of reaction temperature, catalyst concentration and circulation flow rate in biodiesel production using membrane reactors. This is because limited data is available, particularly considering circulation flow rate effect on biodiesel production using membrane reactors. Experimental results also show that the higher the catalyst to WCO ratio the higher the free fatty acids (FFA) content. A maximum biodiesel yield of 92. 6 mole % was obtained at a temperature of 61°C, circulation flow rate of 26 mL/min using KOH catalyst concentration of 1.3 wt % over a TiO2/Al2O3 membrane. Upon membrane optimization, a biodiesel yield of 94.03 mol % was obtained at 58.5 °C, circulation flow rate of 18.78 ml/min and catalyst concentration of 1.24 wt %. This analysis clearly shows that RSM can be successfully used to model reacting membranes using temperature, catalyst concentration and circulation flow rate to achieve higher yields for biodiesel production.

Abstract This work shows work flows supported by experimental work to analyse the efficiency of a plasma system in biomass conversion processes. The most common set of problems encountered when using biomass-to-energy (BTE) processes relate to tar formation and product gas composition. However, using plasma technology to convert biomass provides a solution because it unlocks more energy than can be achieved by other BTE systems by using a heat supply derived from electricity. The research presented in this paper focuses on the conversion of biomass to chemical energy (in gaseous form) with the aid of the electrical energy supplied by a water-cooled nitrogen plasma torch. The authors conducted a series of experiments in a continuous pyrolysis set up in which wood pellets were converted to syngas in a small-scale laboratory nitrogen plasma torch reactor with a maximum power supply of 15 kW. The efficiency of the process was measured in terms of the carbon conversion to all product gases which changed from 43 to 77%, at temperatures ranging from 400 °C to 1000 °C respectively. The combined carbon monoxide and hydrogen mole concentration in the product gas (without nitrogen) was 86% at 1:1 ratio for all temperatures studied. Syngas yield increased with increase in temperature. The overall biomass conversion obtained increased from 46% to 82% for the temperatures 400 °C to 1000 °C respectively, with the balance comprising carbon-rich solid residue and liquid. The work flow shows that a plasma system can get to high temperatures but work is also degraded in the overall process. Exergy analysis shows that the work lost by the overall process decreases with increase in process temperature.

Abstract Background Engineers face increasing pressure to manage and utilize waste (whether of animal, human or municipal origin) in a sustainable way. We suggest that a solution to the problem of organic waste in rural communities lies in their being able to convert it to biogas technology. This would offer smallholders and farmers a long-term, cheap and sustainable energy source that is independent of the national electricity grid. However, although the technology involved in making biogas from waste has already been fully developed, there are obstacles impeding its adoption. First, there is a general ignorance about this source of energy among the very people who can most benefit from using it. Second, at present, South Africa has no regulatory framework to support the installation of biodigesters. Methods The research focused on the current gap between knowledge and need. The two objectives were raising general awareness of the many and varied benefits that biodigestion can offer, especially to rural communities, and demonstrating how it works. Using science events as a platform, the team introduced the concept of biodigestion, its functioning and uses, to their audiences, and then invited informal responses, which were recorded. The second stage, the case study, entailed the setting up of a small-scale (10 m3) household biodigester in the Muldersdrift community in Gauteng, South Africa. It was put into operation, using fresh cow dung as the feed. Members of the community were invited to watch every step of the process and afterwards were asked to participate in a more formal survey, which sought their opinions on whether biodigestion offers a power source the individual farmer could (and would) use. Results The results presented in this paper were derived from a comparison of the ‘before-and-after-installation’ responses of the persons interviewed. We found that the members of the Muldersdrift community who had been involved in both phases of the case study (explanation followed by experience of a hands-on educational example) had become more willing to adopt the technology. Conclusions The results justified our contention that, to ensure a greater adoption of biogas technology in South Africa, it is necessary to provide targeted communities with educational programmes and exposure to pilot plants.

The research shows theoretical calculations on the thermodynamics of digestion/gasification processes where glucose is used as a surrogate for biomass. The change in Enthalpy (∆H) and Gibbs Free Energy (∆G) is used to obtain the Attainable Region (AR) that shows the overall thermodynamic limits for digestion/gasification from 1 mol of glucose. Gibbs Free Energy and Enthalpy (G–H) plots were calculated for the temperature range 25–1500 °C. The results show the effect of temperature on the AR for the processes when water is in both liquid and gas states using 25 °C, 1 bar as the reference state. The AR results show that the production of CO, H2, CH4 and CO2 are feasible at all temperatures studied. The minimum Gibbs Free Energy becomes more negative from −418.68 kJ mol−1 at 25 °C to −3024.34 kJ mol−1 at 1500 °C while the process shifts from exothermic (−141.90 kJ mol−1) to endothermic (1161.80 kJ mol−1) for the respective temperatures. Methane and carbon dioxide are favoured products (minimum Gibbs Free Energy) for temperatures up to about 600 °C, and this therefore includes Anaerobic Digestion. The process is exothermic below 500 °C, and thus Anaerobic Digestion requires heat removal. As the temperature continues to increase, hydrogen production becomes more favourable than methane production. The production of gas is endothermic above 500 °C, and it needs a supply of heat that could be done, either by combustion or by electricity (plasma gasification). The calculations show that glucose conversion at temperatures around 700 °C favours the production of carbon dioxide and hydrogen at minimum G. Generally, the results show that the gas from high-temperature gasification (>~800 °C) typically carries the energy mainly in syngas components CO and H2, whereas at low-temperature gasification (<500 °C) the energy is carried in CH4. The overall analysis for the temperature range (25–1500 °C) also suggests a close relationship between biogas production/digestion and gasification as biogas production can be referred to as a form of low-temperature gasification.