Supachita Krerkkaiwan, Sasithorn Buranatrevedhya, Jaggapan Sanduang and Suneerat Fukuda*
Abstract: In this study, fast pyrolysis characteristics of a sub-bituminous (SB) coal were investigated using a high temperature drop tube furnace (HT-DTF). Effect of pyrolysis temperature (850, 1000 and 1300°C) on product distribution (char, soot and gas yield) as well as the gas composition was investigated. The product chars were characterized for the intrinsic combustion reactivity under isothermal condition at 550°C using a TGA and for surface properties using BET analysis and SEM. The results showed that, with increasing temperature, char yield decreased while gas and soot significantly increased especially at above 1000°C, suggesting the occurrence of secondary reactions. The disappearance of hydrocarbon gases (CH4 + C2 HC gases) and sharp decrease of CO2 with a significant increase of CO and H2 at above 1000°C strongly suggests the reactions of hydrocarbon fractions with CO2 and steam. The DTF char prepared at 1300°C gave the highest intrinsic combustion reactivity at 50% char conversion with R50 and t50 of 66 × 10-4 s-1 and 80 s, respectively. This might be due to its high surface area and highly porous structure. However, the char prepared at lower temperatures had lower burnout time, tb, which may be due to the difference in pore structural change with conversion.
Keywords: Fast pyrolysis, sub-bituminous coal, drop tube furnace, coal, char.
Pongchai Uppapongchai, Theerawute Srisutham, Awassada Phongphiphat, Chiraporn Auechalitanukul and Sirintornthep Towprayoon
Abstract: This study examined the possibility of using rice husk char as a catalyst in the catalytic tar conversion process. Four types of catalysts were prepared and tested in this study: three of them were prepared by calcining rice husk under N2 atmosphere at 400, 600, 700°C, and one was prepared by coating nickel on 700°C-calcined rice husk (10% by weight). Key elemental components in these catalysts were carbon and silicon (as SiO2). Characteristics including surface areas, total pore volumes and mean pore diameters were analyzed for all catalysts. Tar conversion tests, divided into 2 parts: using naphthalene as a simulated tar and using actual tar from RDF pyrolysis, were conducted in a 5-cm-diameter quartz reactor that was controlled at 600°C under N2 atmosphere. Results showed that catalyst prepared at higher temperature could convert more of naphthalene into useful H2 and CH4. This could be due to higher surface area and total pore volume. Nickel-coating on calcined rice husk showed to increase the performance on naphthalene conversion compared to uncoated catalyst around 5%. Nevertheless, experimental results were not yet sufficient to draw a conclusion on the catalytic effects on conversion of actual tar. Further investigations are required.
Keywords: RDF; RDF gasification; catalytic tar conversion; rice husk, catalyst.
Janewit Wannapeera, Nakorn Worasuwannarak, Hideaki Ohgaki and Kouichi Miura*
Abstract: Preparation of a carbon fiber precursor from an extract produced from a solvent treatment of rice straw, which we call Soluble, was examined by using an air blowing and a N2 purge methods at 120-360°C. Small weight change was observed during the air blowing, whereas only evaporation of the small-molecular-weight compounds was observed duringthe N2 purge treatment. Changes of functional groups during the treatments were measured by an in-situ FTIR spectroscopy. Significant change of pyrolysis behaviors was observed after treating Soluble by the air blowing. The melting point of Soluble was also found to increase significantly after the air blowing treatment. The modification of Soluble structure through the cross-linking reactions among the low-molecular-weight compounds were judged to play an important role on causing such significant changes.
Keywords: carbon fiber precursor, biomass derived extract, air blowing treatment, N2 purge treatment.
C. Dejtrakulwong and S. Patumsawad*
Abstract: From energy and environment problems the renewable energy is attractive to replace the fossil fuel. The biomass downdraft gasification process is interested for clean energy production. The downdraft gasification model was developed to predict the compositions of product gas and also study the effect of operational parameters by considering three modules that consist of equilibrium drying-pyrolysis module, sequence equilibrium oxidation module, and kinetic reduction module. This model was developed by using MATLAB with the iterative Newton-Raphson’s numerical method. The main assumptions are: all gases are ideal and pressure is constant. This work focuses the influences of moisture content and air to fuel ratio on temperature and gas composition of each zones by varying from 0 to 40% for moisture content and from 1.4 to 3 for air to fuel ratio. The model validation shows a good agreement with the experimental data. The temperature of all zones decreased with the moisture content increasing while increased with the air to fuel ratio increasing. The calorific value of final product gas increased from 4.39 to 4.79 MJ/Nm3 along the increasing of moisture content while decreased from 6.71 to 3.48 MJ/Nm3 along the increasing of air to fuel ratio.
Keywords: Modeling, Downdraft gasification, Equilibrium model, Synthesis gas, Renewable energy.
Nakorn Worasuwannarak*, Arthit Phopiyanukror and Janewit Wannapeera
Abstract: Torrefaction is one of the thermal treatment techniques at relative low temperature range of 200 – 300°C in an inert atmosphere, which aims to improve the fuel properties attractively for further utilization such as combustion, gasification and/or co-combustion. It was found that the energy density as well as the higher heating value (HHV) was increased progressively at higher torrefaction temperature and at longer holding time. This is due to the increase in carbon content and decrease in oxygen content in the biomass. However, few studies have been conducted to examine the effect of oxygen concentrations at temperature below 300°C. There still remains a need to study the influence of different oxygen concentrations on the thermal reactivity during the torrefaction as well as their effects on the chemical properties of the torrefied biomass. In this study, woody biomass (Leucaena Leucocephala) was torrefied at 220, 240, and 260°C under the oxygen concentration of 2, 5, 10, and 22%. The gas formation rate during the torrefaction under the different oxygen concentrations was also examined in detail by using TG-MS technique. It was found that the different oxygen concentrations affected significantly the reactivity of biomass during the torrefaction especially at 260°C. At 260°C, the high oxygen concentration affected significantly the chemical properties of the torrefied biomass. The results obtained from the study provide the basic information for the design of torrefaction process.
Keywords: Biomass, torrefaction, pyrolysis.