CO2 gasification of chars prepared from wood and forest residue

The CO2 gasification of chars prepared from Norway spruce and its forest residue was investigated in a thermogravimetric analyzer (TGA) at slow heating rates. The volatile content of the samples was negligible; hence the gasification reaction step could be studied alone, without the disturbance of the devolatilization reactions. Six TGA experiments were carried out for each sample with three different temperature programs in 60 and 100% CO2. Linear, modulated, and constant-reaction rate (CRR) temperature programs were employed to increase the information content available for the modeling. The temperatures at half of the mass loss were lower in the CRR experiments than in the other experiments by around 120 degrees C. A relatively simple, well-known reaction kinetic equation described the experiments. The dependence on the reacted fraction as well as the dependence on the CO2, concentration were described by power functions (n-order reactions). The evaluations were also carried out by assuming a function of the reacted fraction that can mimic the various random pore/random capillary models. These attempts, however, did not result in an improved fit quality. Nearly identical activation energy values were obtained for the chars made from wood and forest residues (221 and 218 kJ/mol, respectively). Nevertheless, the forest residue char was more reactive; the temperatures at half of the mass loss showed 20-34 degrees C differences between the two chars at 10 degrees C/min heating rates. The assumption of a common activation energy, E, and a common reaction order, v, on the CO2, concentration for the two chars had only a negligible effect on the fit quality

Potential applications of nanotechnology in thermochemical conversion of microalgal biomass

The rapid decrease in fossil reserves has significantly increased the demand of renewable and sustainable energy fuel resources. Fluctuating fuel prices and significant greenhouse gas (GHG) emission levels have been key impediments associated with the production and utilization of nonrenewable fossil fuels. This has resulted in escalating interests to develop new and improve inexpensive carbon neutral energy technologies to meet future demands. Various process options to produce a variety of biofuels including biodiesel, bioethanol, biohydrogen, bio-oil, and biogas have been explored as an alternative to fossil fuels. The renewable, biodegradable, and nontoxic nature of biofuels make them appealing as alternative fuels. Biofuels can be produced from various renewable resources. Among these renewable resources, algae appear to be promising in delivering sustainable energy options. Algae have a high carbon dioxide (CO2) capturing efficiency, rapid growth rate, high biomass productivity, and the ability to grow in non-potable water. For algal biomass, the two main conversion pathways used to produce biofuel include biochemical and thermochemical conversions. Algal biofuel production is, however, challenged with process scalability for high conversion rates and high energy demands for biomass harvesting. This affects the viable achievement of industrial-scale bioprocess conversion under optimum economy. Although algal biofuels have the potential to provide a sustainable fuel for future, active research aimed at improving upstream and downstream technologies is critical. New technologies and improved systems focused on photobioreactor design, cultivation optimization, culture dewatering, and biofuel production are required to minimize the drawbacks associated with existing methods. Nanotechnology has the potential to address some of the upstream and downstream challenges associated with the development of algal biofuels. It can be applied to improve system design, cultivation, dewatering, biomass characterization, and biofuel conversion. This chapter discusses thermochemical conversion of microalgal biomass with recent advances in the application of nanotechnology to enhance the development of biofuels from algae. Nanotechnology has proven to improve the performance of existing technologies used in thermochemical treatment and conversion of biomass. The different bioprocess aspects, such as reactor design and operation, analytical techniques, and experimental validation of kinetic studies, to provide insights into the application of nanotechnology for enhanced algal biofuel production are addressed

Integrated Concept for Municipal Solid waste Valorization: Pre-Pilot Experience

Municipal solid waste (MSW) is considered to be one of the critical issues in developing countries. To manage this waste in a sustainable way, it is necessary to develop integrated processes to find its multiple utilization pathways. Hydrothermal carbonization (HTC) of MSW integrated with power generation and nutrient recovery could be a plausible solution to the wet waste handling problem in a densely populated country like Bangladesh. In this study, MSW sampled from a landfill of Dhaka city revealed the presence of high amount of organic waste (~ 74 w/w%). This facilitated the concept of waste valorization through nutrient recovery. The heating value of the MSW was found to be 14.7 MJ/kg (on dry basis) making it a suitable source for power generation. HTC experiments on the waste showed a retention of almost ~83% of the energy in biocoal. Based on these results, an integrated biorefinery having a capacity of processing all the MSW generated in Dhaka, can produce 45 MWe power with 3.2 ton/day of K and 0.9 ton/day of Ca as by-product. These results would be further evaluated in a pilot-scale demonstration in 2020.2562605Energy, Power and Research Council, Government of People’s Republic of Banglades

Preliminary understanding on the ash behavior of algae during co-gasification in an entrained flow reactor

Algae are considered as a promising alternative fuel to produce energy due to its advantages such as high production yield, short growth cycle and flexible growing environment. Unfortunately, ash-related issues restrict its thermochemical utilization due to the high ash content and especially the high alkali metal concentration. In this paper, the gasification performance and ash behavior were experimentally analysed for three macro- and micro-algal species. Clear differences in the proximate and ultimate compositions were found between the cultivated algae used in this study and macroalgae (seaweed) harvested from the marine environments. Algal biomass generally contained higher Na and P contents than lignocellulosic biomass. Microalgae also had a relatively high mineral content due to the impurities in the harvesting process which included centrifugal pumping followed by sedimentation. Co-gasification of 20 wt% algae with softwood was investigated using an entrained flow reactor. The addition of both macroalgal species Derbersia tenuissima and Oedogonium to softwood had a limited influence on the gas yields and carbon conversion. On the other hand, the addition of the microalgal species Scenedesmus significantly decreased the main gas yields and carbon conversion. Moreover, the addition of algae clearly changed the residual ash composition of the base fuel. Finally, a preliminary understanding of the ash behavior of the tested algae blends was obtained through the analysis of the fuel ashes and the collected residual ashes. Fouling and corrosion were presumably occurred during the co-gasification of wood/macroalgae blends in view of the high alkali metal content. Microalga Scenedesmus had a high mineral content which could potentially capture the alkali metal in the ash and mitigate fouling when gasified with softwood. The growing environment and harvesting method were found to be significantly affecting the ash behavior implying the need for careful consideration regarding co-gasification process.Youjian Zhu, Philip J. van Eyk, Christoffer Boman, Markus Broström, Kawnish Kirtania, Patrycja Piotrowska, Dan Bostrom, Rocky de Nys, Sankar Bhattacharya, Francesco G. Gentili, Peter J. Ashma

Comparative assessment of the thermochemical conversion of freshwater and marine micro- and macroalgae

The aim of this study was to investigate differences in the thermochemical conversion properties of freshwater and marine algae as well as micro- and macroalgae on the production of biogas, bio-oils, and biochar. The pyrolysis process of all samples involved three main stages consisting of the evaporation of bound water, primary pyrolysis reactions, and the slow decomposition of the remaining carbonaceous matter. There were no obvious differences in the thermal behavior between freshwater micro- and macroalgae, with similar thermogravimetric and apparent specific-heat profiles. However, the marine alga exhibited significantly different thermal behavior to the freshwater algae. The marine alga showed a very significant endothermic reaction of bound water releasing and a dramatic high-temperature endothermic reaction, which were not observed in any of the freshwater algae. The evolution of primary volatiles showed CO2 and CO as the dominant volatiles for all species of algae. At the heating rate of 60 °C/min, the maximum liquid yield for the pyrolysis of the marine Ulva ohnoi was 55 wt %, while the range of 70–75 wt % could be achieved for the pyrolysis of the three species of freshwater algae. The bio-oils collected after heating of the samples to 500 °C under slow and fast heating rates indicated that alcohols (including phenols) and carboxylic acids were the dominant components in the bio-oils produced from the three species of freshwater algae, while nitrogen-containing organics and phenols were overwhelming in the oil from the marine alga. The bio-oils produced at two heating rates presented only minor differences in the bio-oil composition and compound contents