Process Simulation and exergy analysis for integrated brown coal pyrolysis gasification For the production of ethylene glycol

摘要

This paper introduces a novel process for the utilisation of low-rank coal through the integration of pyrolysis and entrained-flow gasification by using Aspen Plus. In this process, an initial mild pyrolysis of the coal is proposed to reduce simultaneously the moisture content down to nearly zero and produce coal gas which has a similar property with gasification syngas. Subsequently, the water-free semi-coke derived from pyrolysis would be sent to an entrained-flow gasifier (or mixed with additive/high-ash bituminous coal together) for co-gasification. By doing so, the ash is expected to melt easily and form a sufficiently thick layer protecting the refining lines in a gasifier. Regarding the syngas derived from gasifier, it passes through cleaning step and water gas shift reactor before mixing with the pyrolysis-derived coal gas to reach a molar ratio of 2 for H_2 to CO in the final gas product. Such a ratio is essential for the downstream synthesis of ethylene glycol which has a much higher value than other coal-derived chemicals. In this paper, the results for two typical brown coal samples were reported. The optimized conditions for their semi-coke gasification were clarified. The energy efficiency for such a system was analysed and compared to the traditional brown coal pre-drying system as well. The results show that higher exergy efficiency can be achieved for the proposed pyrolysis-gasification integration process.