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The Performance Evaluation of Low Rank Coal - to - SNG Process with Upgraded Drying Concepts by Aspen Plus Simulation
- Author(s)
- He Chunyang
- Advisor
- Hyung-Taek Kim
- Department
- 일반대학원 에너지시스템학부
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2012-02
- Language
- eng
- Alternative Abstract
- Natural gas is the fuel of choice worldwide and represents an important pillar of energy supply in the form of electricity and for covering heat demand. However consumption and price of natural gas are rising steadily throughout the entire world, bringing about the need to develop and seek technologies like SNG. Coal-to-SNG technology is promising for countries with significant proven reserves of coal but scarce natural gas. Modern coal gasification and methanation technologies constitute an excellent opportunity to address energy and environmental challenges for producing SNG in an economically attractive way. The idea of using low rank coal to produce SNG is mostly due to the abundant of low rank coal reserves. It has low mining strip ratio and good quality in terms of sulfur and ash content. The purpose of this work is to develop a model for the utilization of SNG plant from low rank coal using Aspen plus simulator. This model, which is involved in the Shell coal gasification process (SCGP) and Haldor Topsoe’s Recycle energy-efficient methanation process (TREMPTM), is the combination of some advanced technologies and would be flexible enough for future development. In order to evaluate the effect of low rank coal on this plant, IBC coal (Indonesian lignite) is chosen as the input feedstock of gasification. IBC coal has lower ash content (2.27%) and sulfur content (0.06%), but has higher moisture content (34.05%) and oxygen content (19.59%) compared with high rank coal. Present investigation focuses on the evaluation of low rank coal to SNG plant, the comparison of two drying concepts in terms of energy input and the upgrading of the simulation plant. Firstly, five processes are simulated according to the literatures and report from the commercial case. The two main parts, which are gasification process and methanation process, have a good match with the commercial case. Fuel preparation process and gas cleaning process are the simple simulation model based on some experimental data, and the water gas shift reaction process has a higher CO conversion (>98%). These processes have a good performance to support the establishment of low rank coal to SNG plant. Secondly, after each process is simulated, they are combined together and IBC coal is fed into the simulation system for evaluating the performance of low rank coal on the coal to SNG plant. The parameters for the evaluation are cold gas efficiency (CGE) and carbon conversion (CC) of gasifier, syngas composition and end-product purity. Sensitivity analysis is conducted, in order to indicate the effect of oxidant index and steam index on the evaluating parameters. According to the sensitivity analysis and when the ratio of oxygen to drycoal is equal to 0.91, which is the value when it has the same temperature range and heat loss with Illinois #6, CC and CGE of IBC coal reach 99.8% and 78.6%, respectively (Illinois #6: CC=99.4%, CGE=80.0% when oxygen/dry coal uses the reference data.). The SNG purity of end-product is 83.5%. Thirdly, two drying concepts, which are the conventional and recycle syngas drying processes, are introduced into the drying system. The recycle syngas drying concept, which has a high temperature and pressure, can reduce the energy consumption (123.82 Gcal/hr) compared to the conventional drying concept (177 Gcal/hr), and also saves a lot of fuel for heating up the drying system. Fourthly, in order to meet the requirement for improving the product purity and reducing the greenhouse gas emission, the concept of conventional carrier gas is replaced by carbon dioxide and the optimal concepts from the sensitivity analysis are used. Finally, based on the developed models, the coal to SNG plant is upgraded into a low rank coal to SNG plant and the end-product purity is also improved, which improves the CH4 purity of the end-product from 83.5% to 94%, and the oxygen/drycoal ratio is decreased to 0.78. The CO2 content (5.2%) in the syngas from the gasifier is lower than the original case (7.7%) that uses N2 as the carrier gas.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 3. Theses(Master)
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