The Phase Inversion-based Coal-CO₂ Slurry (PHICCOS) feeding system : design, coupled multiscale analysis, and technoeconomic assessment

Abstract

The continuous conveying of a solid feedstock like pulverized coal into a pressurized environment is a challenging task required in multiple industrial processes. Plants based on pressurized, entrained-flow gasifiers (EFG) are a good example. EFGs are used to produce synthetic gas for the production of synthetic transportation fuels, chemicals, and for generating electricity in Integrated Gasification Combined Cycle (IGCC) power plants. The latter have also been proposed as an attractive platform for carbon dioxide capture. Commercially available feeding systems are based on coal-water slurry or lock hoppers. The earlier penalizes the plant efficiency and has feedstock limitations, while the latter is expensive and has pressure limitations. In this work, a coupled multiscale approach is applied, which combines system-level analysis, component-level modeling, and micron-scale particle phenomena, for the development and assessment of a novel coal feeding system. The proposed Phase Inversion-based Coal-CO₂ Slurry (PHICCOS) feeding system uses supercritical CO₂ with liquid-like density to feed pulverized coal into a high-pressure EFG. The challenge of preparing the coal-CO₂ slurry is addressed using phase inversion: a phenomenon associated with the hydrophobicity of liquid CO₂-coal mixtures. This allows for operation at ambient temperature and without the use of lock hoppers. Furthermore, the PHICCOS feeding system achieves very high feed pressures while reducing the moisture and ash content of the feedstock, which makes it especially attractive for low-rank and high-ash coal. The merits of the PHICCOS feeding system were demonstrated through technoeconomic analysis coupled with particle-level kinetics. The results of this work show the significant advantages of this system over alternative technologies, in particular for low-rank feedstock. Optimization was used to determine the operating conditions required for the best tradeoff between kinetics, thermodynamics, and costs. The effect of the uncertainty in critical design and operating parameters on the overall economics of a PHICCOS-fed plant were examined using Monte Carlo simulations. This work shows that the PHICCOS system can efficiently and economically feed pulverized coal into high-pressure reactors in plants equipped with carbon capture. Overall, the economics of the PHICCOS feeding system are better than those of commercial technologies for low-rank coal and are competitive with other solutions for high-rank coal. Furthermore, PHICCOS has unique operational advantages related to the very high feed pressures it can achieve and to its feedstock flexibility: cheap and widely available high-moisture and high-ash coal can be used to produce high value products. Keywords: Coal, CCS, Gasification, Feeding System, Multiscale Analysis.