Simulation And Evaluation Of Liguite Pyrolysis By Solid Heat Carrier Coupled With Gasification

Given that China is rich in lignite resource, and the coal-led energy structure will not be changed in a long term, how to use the lignite resource cleanly and efficiently has become a research hotspot. Supported by the State 863 projects, according to the features of the lignite itself, combined with the characteristics of the pyrolysis by solid heat carrier technology and the gasification technology, a process of lignite pyrolysis by solid heat carrier coupled with gasification was set up in this paper to find a clean and effective way to make full use of the pyrolysis resource and realize the classified utilization of the lignite resource.Simulation method is adopted in this paper to study the process of lignite pyrolysis by solid heat carrier coupled with gasification and a simulation process was set up by aspen plus, a professional chemical prosess simulation software, to conduct a series of calculations, including the sensitivity analysis, energy evaluation, material balance and economic evaluation with a view to provide a comprehensive evaluation of the process of lignite pyrolysis by solid heat carrier coupled with gasification as well as obtaining a theoretical foundation for the feasibility and rationality of the process.Through the sensitivity analysis, the optimum pyrolysis temperature and the optimum gasification technology were confirmed, and at the same time, the impact on the system of the different moisture content and ash content in lignite were also investigated. Through energy evaluation, the energy distribution tendency diagram was displayed and the thermal efficiency of the whole system was calculated, the ratio of char used in burning to meet the energy demand in drying unit and pyrolysis unit, the mass ratio between the solid heat carreier and the coal are specified and the mechanical energy consumption of the system is also computed. Through the material balance, the output of tar and coal gasification gas (CGG) was known, the amount of water that can be saved and the emission of the waste water that can be reduced were also calculated. Through the economic evaluation, the total investment of the project, the product costs, return on investment (ROI) and the static investment recovery period were evaluated.The research results proved that:the optimum pyrolysis tempereture is 550 ℃, the optimum gasification technology is BGL, and the more moisture content the lignite entails, the more energy consumption and the lower energy utilization efficiency of the whole system could be achieved. The drying unit and the pyrolysis unit are the main energy consumption units, which occupies respectively 49.3% and 36.1% of the whole energy consumption. The energy utilization efficiency of the whole system was as high as 86.3%. About 17% of the char produced from the pyrolysis unit was used in burning to meet the energy demand for the dying unit and the pyrolysis unit. The rest char was gasified as the gasification raw materials, and the mass ratio between the solid heat carrier and the row coal was 3:1, which was equal to 5:1 when the mass ratio was between the solid heat carrier and the dried coal. The mechanical energy consumption of the system was 1.2 MW, in other word, about 40 thousand kW·h per day. When the handle scale was 41.7 t/h, the tar output was 1.6 t/h, the CGG output was 25.7 t/h, about 8.9 t/h could be saved and 2.7 t/h emission of the waste water could be reduced in the coupled process. The cost of investment of the project was RMB 132.849 million, the product costs was RMB 133.59 million per year, the net margin was RMB 16.6 million per year, the ROI was 16.6% and the static investment recovery period was 8 years, however, the average ROI of the coal industry was around 14%-18%, the average static investment recovery period of the coal industry was about 9-11 years. Therefore the process of lignite pyrolysis by solid heat carrier coupled with gasification is feasible from the perspective of economy.All in all, the process of lignite pyrolysis by solid heat carrier coupled with gasification not only reached a high thermal efficiency, but also saved valuable water resource, and reduced the emission of the waste water through coupling the pyrolysis technology with the gasification technology. The process made full use of the moisture and the high value tar resource in the lignite, which enhanced the economic value of the lignite and achieved the maximium utilization of the chemical element. Thus, the process of lignite pyrolysis by solid heat carrier coupled gasification is one of the effective and economically feasible ways in using the lignite resource.