Abstract
Pakistan has proven huge coal reserves but still unable to harvest the energy due to unavailability of ingenious technology. Coal gasification is robust, efficient and environmental friendly technology but it is highly sensitive to the coal characteristics. Scant literature is available on the development of the coal gasification technology which suits the characteristics of indigenous coal reserves. This papers presents the simulation of entrained flow gasifier for using indigenous coal through process modeling software namely Aspen Plus® to evaluate various system flow steps within an entrained flow gasifier. General techniques have also been discussed for creating the equilibrium-bases simulations of gasification systems. Peng-Robinson equation was used to correlate the volume of species with respect to state variables (temperature and pressure). The effects of composition of different indigenous coals like Thar, Lakhra and Sonda were investigated through simulations along with O/C (Oxygen-to-Carbon) ratio. Parametric study revealed that the O/C ratio along with other related system parameters have great influence on the performance. Sulfur could be available in different forms in coal like pyrite, sulfate or organic sulfur so appropriate form of sulfur in feedstocks should be corrected for better accuracy of model results. The highest percentages of CO i.e. 44.2, 37.8, and 46.6% were obtained from Thar coal (air dried form), Lakhra coal and Sonda coal respectively at the 0.3 O/C ratio. The decrease in LHV and HHV (Lower and Higher Heating Values) of syngas was observed on increase of O/C ratio for all coal types. The composition of as received Thar coal gave maximum LHV (1.5x104 KJ/Kg) and HHV (1.78x104 KJ/Kg) at the 0.3 O/C ratio. The future work could be extended by simulating biomass composition in the developed model of gasifier in transient simulations.
Highlights
Pakistan has proven huge coal reserves but still unable to harvest the energy due to unavailability of ingenious technology
It was observed that increase in O/ C ratio decreases the CO mole fraction as shown in Fig.3 for all type of coals except Thar coal (AR) because of high moisture in parent coal from Thar coal field
Thar (AD), Sonda and Lakhra coals produced maximum mole fraction of CO of about 44.2, 46.6 and 37.8% respectively at O/C ratio 0.3 whereas maximum CO produced by Thar as received conditions (AR) of about 15% at 0.5 O/C ratio because of high moisture presence
Summary
Pakistan has proven huge coal reserves but still unable to harvest the energy due to unavailability of ingenious technology. Scant literature is available on the development of the coal gasification technology which suits the characteristics of indigenous coal reserves. This papers presents the simulation of entrained flow gasifier for using indigenous coal through process modeling software namely Aspen Plus® to evaluate various system flow steps within an entrained flow gasifier. The effects of composition of different indigenous coals like Thar, Lakhra and Sonda were investigated through simulations along with O/C (Oxygen-to-Carbon) ratio. The coal particles travel from different zones within the reaction chamber of entrained flow gasifier usually known as devitalization zone, drying zone, combustion zone, and gasification zone. The product gases formation, char and tar composition depend on the category of coal, heating rate, pressure, and temperature. The size of particles largely affects the overall reaction rate, quantity and quality of product syngas due to slow heat transfer rate and slow reaction time [6]
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