| Increasing the proportion of natural gas consumption in the energy consumption structure of China is an effective way to control the severe air pollution. To alleviate the problem of the insufficient reserves of natural gas in China, coal-based synthetic natural gas(SNG) is considered to be a promising option as a source of clean energy. In this paper, life cycle costing(LCC) and life cycle assessment(LCA) methods are used to analyse and evaluate the techno-economic and environmental performances as well as resource consumption of the SNG from life cycle perspective. Comparisons are conducted between SNG and other traditional energy utilization routes. Then, both the advantages and disadvantages of the SNG are illuminated and the results of analysis presented in this work could support the formulation of policies related to coal-based SNG.Coal gasification and methanation technologies are key technologies of a coal-based SNG process. BGL slagging gasification technology is more appropriate for a SNG plant as it has the following features: low steam and oxygen consumption, high cold gas efficiency and effective gas volume fraction, low investment, and little gasification wastewater. In terms of methanation technology, the TREMPTM and the CRG processes are most appropriate for a SNG plant. They all have long age of catalyst, mature technology, and by-produced high pressure steam which is good for enhancing the total energy efficiency of SNG production.In this paper, life cycle costing is made for SNG use in three main applications in residential sector: heating, household use, and public transport. Comparisons are conducted between SNG and coal, natural gas, liquefied petroleum gas(LPG), diesel, and methanol. The results show that SNG is a competitive option only for household use. The use of SNG for heating boilers or city buses is not as cost-effective as expected. The biggest shortcoming of SNG is the large amount of pollutants generated in the production stage which means a transfer of pollution from the urban areas to the regions where SNG is produced.Municipal heating by coal contributes considerably to the haze pollution in Chinese cities during cold period. SNG as an alternative for municipal heating is analyzed in comparison with coal. To target cleaner production, LCA methodology is used to analyze SNG contribution to haze pollutants and greenhouse gases(GHGs) emissions, as well as energy consumption. Compared to coal heating route, SNG heating route could reduce 44% of the haze pollutants emissions from life cycle perspective and up to 98% of the emissions in urban area. Thus, if municipal heating were entirely supplied by natural gas and SNG, there would be 52% less haze pollutants emissions in winter of Beijing. However, this “good” performance is at the cost of consuming 90% more coal and emitting 65% more GHGs than the coal heating route from life cycle point of view. To tackle the problems of haze pollutants transfer and the increase of GHGs emissions, the paper suggests implementing ecological compensation and carbon tax policies, as well as emissions trading scheme in the coal-based SNG industry.In many end use processes, the coal-derived electricity and SNG could replace each other. The coal-based SNG has a few shortcomings as mentioned above. How about the environmental performances and resource consumption of coal-based electricity for city use? Comparisons between electricity route and SNG route are conducted in applications of SNG for power generation, cooking, heating, cooling, and transit bus use by using LCA method. The results show that, compared to SNG route, electricity route could reduce 30-80% haze pollutants emissions, 6-73% GHGs emissions, 20-69% coal consumption. In terms of water consumption, electricity route based on air cooling technology could reduce 11-74%. Thus, it could conclude that electricity route is a cleaner and more resource-saving option than SNG route to supplement the clean energy supply for city. |
PDF Full Text Request