Sankar Bhattacharya

Thermogravimetric study of the combustion of Tetraselmis suecica microalgae and its blend with a Victorian brown coal in O2/N2 and O2/CO2 atmospheres

The combustion characteristics of microalgae, brown coal and their blends under O2/N2 and O2/CO2 atmospheres were studied using thermogravimetry. In microalgae combustion, two peaks at 265 and 485°C were attributable to combustion of protein and carbohydrate with lipid, respectively. The DTG profile of coal showed one peak with maximum mass loss rate at 360°C. Replacement of N2 by CO2 delayed the combustion of coal and microalgae. The increase in O2 concentration did not show any effect on combustion of protein at the first stage of microalgae combustion. However, between 400 and 600°C, with the increase of O2 partial pressure the mass loss rate of microalgae increased and TG and DTG curves of brown coal combustion shifted to lower temperature zone. The lowest and highest activation energy values were obtained for coal and microalgae, respectively. With increased microalgae/coal ratio in the blends, the activation energy increased due to synergy effect.

Application of the distributed activation energy model to the kinetic study of pyrolysis of the fresh water algae Chlorococcum humicola

Apart from capturing carbon dioxide, fresh water algae can be used to produce biofuel. To assess the energy potential of Chlorococcum humicola, the algas pyrolytic behavior was studied at heating rates of 5-20K/min in a thermobalance. To model the weight loss characteristics, an algorithm was developed based on the distributed activation energy model and applied to experimental data to extract the kinetics of the decomposition process. When the kinetic parameters estimated by this method were applied to another set of experimental data which were not used to estimate the parameters, the model was capable of predicting the pyrolysis behavior, in the new set of data with a R(2) value of 0.999479. The slow weight loss, that took place at the end of the pyrolysis process, was also accounted for by the proposed algorithm which is capable of predicting the pyrolysis kinetics of C. humicola at different heating rates.

Process modelling of dimethyl ether production from Victorian brown coal—Integrating coal drying, gasification and synthesis processes

Abstract Power plants using Victorian brown coal operate at low efficiency. Being reactive and spontaneously combustible, dried brown coals cannot be exported either. Synthesis of dimethyl ether (DME) is one option for the production of liquid fuel, an exportable product for power generation and transportation. This paper presents a steady-state process model for DME production using brown coal including drying, gasification and DME synthesis. The yield of the DME was a maximum for H 2 to CO molar ratio of 1.41 and 0.81 at the gasifier outlet and the DME reactor inlet respectively. A process efficiency of 32% and CO 2 emission of 2.91xa0kg/kg of DME was obtained. Improved yield of DME is achieved when CO 2 is removed from the fuel gas prior to feeding to the synthesis reactor. Integration of waste heat and design of appropriate catalyst for gasification and DME synthesis can result in further improvements in the process.

Sulfur Emission from Victorian Brown Coal Under Pyrolysis, Oxy-Fuel Combustion and Gasification Conditions

Sulfur emission from a Victorian brown coal was quantitatively determined through controlled experiments in a continuously fed drop-tube furnace under three different atmospheres: pyrolysis, oxy-fuel combustion, and carbon dioxide gasification conditions. The species measured were H(2)S, SO(2), COS, CS(2), and more importantly SO(3). The temperature (873-1273 K) and gas environment effects on the sulfur species emission were investigated. The effect of residence time on the emission of those species was also assessed under oxy-fuel condition. The emission of the sulfur species depended on the reaction environment. H(2)S, SO(2), and CS(2) are the major species during pyrolysis, oxy-fuel, and gasification. Up to 10% of coal sulfur was found to be converted to SO(3) under oxy-fuel combustion, whereas SO(3) was undetectable during pyrolysis and gasification. The trend of the experimental results was qualitatively matched by thermodynamic predictions. The residence time had little effect on the release of those species. The release of sulfur oxides, in particular both SO(2) and SO(3), is considerably high during oxy-fuel combustion even though the sulfur content in Morwell coal is only 0.80%. Therefore, for Morwell coal utilization during oxy-fuel combustion, additional sulfur removal, or polishing systems will be required in order to avoid corrosion in the boiler and in the CO(2) separation units of the CO(2) capture systems.

Nitrogen Oxides, Sulfur Trioxide, and Mercury Emissions during Oxy-fuel Fluidized Bed Combustion of Victorian Brown Coal

This study investigates, for the first time, the NOx, N2O, SO3, and Hg emissions from combustion of a Victorian brown coal in a 10 kWth fluidized bed unit under oxy-fuel combustion conditions. Compared to air combustion, lower NOx emissions and higher N2O formation were observed in the oxy-fuel atmosphere. These NOx reduction and N2O formations were further enhanced with steam in the combustion environment. The NOx concentration level in the flue gas was within the permissible limit in coal-fired power plants in Victoria. Therefore, an additional NOx removal system will not be required using this coal. In contrast, both SO3 and gaseous mercury concentrations were considerably higher under oxy-fuel combustion compared to that in the air combustion. Around 83% of total gaseous mercury released was Hg(0), with the rest emitted as Hg(2+). Therefore, to control harmful Hg(0), a mercury removal system may need to be considered to avoid corrosion in the boiler and CO2 separation units during the oxy-fuel fluidized-bed combustion using this coal.

Fermentable Sugars from Lignocellulosic Biomass: Technical Challenges

Lignocelluloses, the most abundant renewable biomass on earth, are composed mainly of cellulose, hemicellulose, and lignin. Both the cellulose and hemicellulose fractions are polymers of sugars and thereby a potential source of fermentable sugars. Lignin can be used for the production of chemicals, combining heat and power, or for other purposes. Energy crisis and environmental pollution drive the scientific community toward the potential exploitation of lignocellulosic biomass. To crack their complex structures various pretreatment technologies including biological, mechanical, chemical methods, and various other combinational methods are available. We cannot relate the best and common pretreatment method to all types of the lignocellulosic biomass. It mostly depends on the type of lignocellulosic biomass and the desired products. The final aim of pretreatments must be improvement in the hydrolysis rate of lignocellulosic biomass. Currently, there is a large scope to investigate and restore the challenges in the pretreatment processes which finally leads to develop the tailor-made effective pretreatment methods for diverse types of lignocellulosic biomass.