(511h) Plant-Wide Modeling and Techno-Economic Optimization of Processes for Producing Bio-Coal Briquettes, Biochar, and Building Materials By Using Coal Refuse and Woody Biomass

There are millions of tonnes of coal refuse, that are low-quality coal with high content of ash and other undesired materials, that have piled up in many parts of the world as an undesired product of the coal mining process[1]. This has resulted in environmental issues, such as greenhouse gas (GHG) emissions like SOx and CO₂ when this coal refuse ignites on its own due to exothermic pyrite oxidation, acid mine drainage when acidic constituents leach into water bodies, among several others. Due to these issues, there is a need to find mitigation methods by utilizing this coal refuse. This research investigates the following three products for the co-utilization of coal refuse with biomass: bio-coal briquette, biochar, and building materials. While these products are commercially produced, they are mainly produced from either higher quality coal or biomass, but not by synergistic use of coal refuse and biomass. This work develops models of conceptual processes for producing these three products. It also develops models of potential alternative process routes. Economic models are developed, and techno-economic analysis (TEA) is undertaken by using Aspen Process Economic Analyzer (APEA). This work seeks to make several contributions. For the first time, to the best of our knowledge, this work investigates a novel synergistic use of coal refuse and biomass for the co-production of the three products. It should be noted that the analysis of bio-coal briquette production from only biomass has been investigated in the existing literature. For biochar, while slow pyrolysis is well studied, this work investigates a complete economic assessment for all three pyrolysis products and takes into account their contributions towards capital and operating costs. For producing building materials, two alternative pathways, one using the column flotation mechanism and another using the chain-type traveling grate furnace (CTGF), are considered and evaluated. A thorough economic analysis of these products is also not currently available in the open literature.

Bio-coal briquettes are produced through a torrefaction process at temperatures between 200°C-300°C, that helps to decrease the moisture levels of the woody biomass. This process is followed by pelletization to generate the briquettes with a moisture content of 7 wt.%. For this case, two scenarios are considered: biomass-to-coal ratios of 1:0 (i.e., biomass only) and 1:1. The bio-coal briquette torrefaction reactor is modeled by considering a two-stage reactor[2]. Biochar is produced by a slow pyrolysis process set at a temperature of 500°C at 1 atm[3]. The heavy and light volatiles from the pyrolysis process are separated using absorbers to obtain syngas and bio-oil[4]. For the case of building materials, two scenarios are considered. These include using the column flotation method (CFM) to separate ash from the coal refuse, yielding clean coal, fly ash, and light weight aggregate (LWA). The other option that is evaluated is a CTGF to burn the coal refuse directly. Since syngas is generated while burning the coal refuse, part of it is used for power generation.

Mass and energy balances from Aspen Plus V14^® models are exported to APEA to carry out TEA. The TEA results are compared regarding their net present value (NPV), payout period, and internal rate of return (IRR). Sensitivity studies are carried out with respect to uncertainties in the raw material prices and plant scale-ups. To summarize, this presentation will provide an in-depth discussion of the technical and economic modeling for production of bio-coal briquette, biochar, and building materials by using biomass and coal refuse. Results from uncertainty analyses will also be presented.

References

[1] W. H. Buttermore, E. J. Simcoe, and M. A. Maloy, “Characterization of Coal Refuse (No. FE-1218-T3; 159).” West Virginia Univ., Morgantown (United States). Coal Research Bureau, 1979.

[2] R. B. Bates and A. F. Ghoniem, “Biomass Torrefaction: Modeling of Volatile and Solid Product Evolution Kinetics,” Bioresource Technology, vol. 124, pp. 460–469, Nov. 2012, doi: 10.1016/j.biortech.2012.07.018.

[3] D. Chen, Y. Li, K. Cen, M. Luo, H. Li, and B. Lu, “Pyrolysis Polygeneration of Poplar Wood: Effect of Heating Rate and Pyrolysis Temperature,” Bioresource Technology, vol. 218, pp. 780–788, Oct. 2016, doi: 10.1016/j.biortech.2016.07.049.

[4] A. Dutta, A. Sahir, and E. Tan, “Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbon Fuels: Thermochemical Research Pathways with In Situ and Ex Situ Upgrading of Fast Pyrolysis Vapors,” 2015.