A promising approach to co-processing calcium-rich coal and an aqueous condensate from biomass carbonization

The pretreatment of biomass via torrefaction and low-temperature carbonization produces a high-quality biochar that is more favorable to co-gasification and/or co-combustion with coal. However, the production of biochar is the consequence of dehydration and devolatilization reactions that result in the simultaneous formation of an aqueous condensate (AQ) containing small amounts of organic contaminants. The arbitrary discharge of such a wastewater fraction would cause serious environmental pollution. In this paper, we specifically address this issue. A potential approach has been proposed for the disposal of AQ in combination with gasification (or combustion) of calcium-rich coals. During the operation of blending coal and AQ, most of the organic contaminants in AQ can be physically or chemically adsorbed onto the surface of coal and can thereby be co-gasified or co-combusted together with coal. The most attractive technical benefit of the proposed approach is that such a combination has synergistic effects during co-gasification and co-combustion of the binary mixtures of calcium-rich coal and the AQ. The same effects can also be achieved using a calcium-deficient coal by co-processing it with an AQ solution containing dissolved shell wastes. In addition, both the indigenous crystalline calcite minerals in coal and the dissolved shell wastes show good desulfurization performance during combustion.