Integration of pyrolysis and entrained-bed gasification for the production of chemicals from Victorian brown coal - Process simulation and exergy analysis

- Pyrolysis-gasification process is exergy efficient compared to drying-gasification.
- Moisture in Victorian brown coal negates the process exergy efficiency monotonously.
- 20 wt.% black coal with Victorian brown coal is the optimum blending ratio.

This paper introduces a novel process for the integration of pyrolysis and entrained-flow gasification for the as-mined Victorian brown coal containing 65 wt.% moisture. An initial mild pyrolysis of coal is proposed to reduce moisture content, and produce multiple products including char, tar and hydrogen-rich coal gas. Subsequently, the resulting water-free char is subjected to an entrained-flow gasifier, upon the blending of silica additive or high-ash bituminous coal. The resultant syngas passes through a cleaning unit and water gas shift reactor before mixing with the pyrolysis-derived gas to reach a target H2/CO molar ratio of 2.0 that is essential for the synthesis of a number of chemicals. In this paper, process simulation and exergy analysis were conducted to prove the advantages of the proposed process against the conventional drying-gasification combination. The results show that, the proposed pyrolysis-gasification integration process for Victorian brown coal possesses an exergy efficiency 4.5% higher than the drying-gasification process, and 1.5% higher than the drying case for another lignite containing 25 wt.% moisture. A prior removal of 20% of the inherent moisture can further improve the exergy efficiency by 4% for Victorian brown coal. The addition of 20% of black coal is the optimum ratio to improve the ash slagging propensity, as well as improve exergy efficiency compared to the conventional drying-gasification process.