Application of nanotechnology in the development of briquettes from selected biomass in Uganda

Abstract

The development of biomass briquettes remains relevant to communities in developing nations, as they offer a cost-effective and sustainable means of producing energy from solid waste. However, the low quality of the briquettes in comparison to traditional cooking fuels hampers their widespread adoption. The main objective of this research was to develop nanocomposite briquettes with improved ignition and combustion properties. The biochar matrix was obtained from Senna spectabilis, a fast-growing invasive species, while the nanocomposite binder incorporated Cellulose nanocrystals (CNC) from yellow thatching grass (Hyparrhenia filipendula) and Poly-vinyl alcohol (PVA). Novel biochar-CNC-PVA nanocomposite briquettes were developed using the solution casting method, with the CNC/PVA nanocomposite serving as a binder. A total of five biochar/binder nanocomposite briquette ratios were developed: 90:10, 80:20, 70:30, 60:40, and 50:50 and designated BCP (9/1), BCP (8/2), BCP (7/3), BCP (6/4), and BCP (5/5) respectively. The nanocomposite briquettes were characterized for thermal stability, mechanical properties, elemental composition, surface morphology, proximate composition, and combustion characteristics using standard scientific techniques. Thermogravimetric analysis was used to study the combustion characteristics of the nanocomposite briquette decomposition in an oxygen atmosphere at three heating rates of 5,10 and 20 °C/min. The kinetic parameters were determined using the Coats–Redfern method. A production facility for the nanocomposite fuels was modeled using ASPEN Plus software and the economic evaluation conducted using net present value (NPV) and Internal rate of return (IRR) analysis. The briquettes produced had a very low ash contents of less than 2 %, and low moisture content average of 8 %. The fixed carbon and volatile matter content of the briquettes were also within acceptable standards for biomass briquettes. The surface morphology of the briquettes showed a well-distributed nanocomposite binder in the biochar matrix. The nanocomposite fuel blends exhibited calorific values in the range of 16 to 27 MJ/kg, surpassing the calorific values of most organic binder-based biomass briquettes developed earlier. The ignition performance and combustibility indexes in oxy-combustion conditions were highest for the BCP (6/4) blend followed by BCP (8/2) nanocomposite blend. Therefore up to 40 % of the PVA-CNC binder can be added in the biochar matrix without affecting combustion performance. The kinetic studies also showed that the apparent activation energy was lowest for BCP (7/3), with a value of 13.30 kJmol-1 at a heating rate of 5 °C/min. The activation energy at a low heating rate was considered because the heating of the biomass particles occurs gradually, leading to a more effective heat transfer to the material bed and between the particles.

The selling price of the nanocomposite fuel, as determined from the techno-economic analysis, was $3/kg, accompanied by an NPV of $13.5 million and a projected payback period of 4.65 years. The calculated Internal rate of return (IRR) of the project is 82 %, indicating a robust level of economic viability.

In conclusion, this study provides a detailed protocol for the development of a nanocomposite briquette with improved ignition and combustion properties using locally available biomass and nanomaterials. The use of such briquettes can potentially offer a cost-effective and sustainable means of producing energy from solid waste in developing nations. Further research can focus on optimizing the fuel blends, conducting feasibility studies for scaling up production of nanocomposite briquettes and devising strategies to enhance consumer adoption.