Coal gasification is a key technology for the clean and efficient utilization of coal, but it produces large volumes of coal gasification fine slag (CGFS) characterized by high water content and low residual carbon reactivity. Stockpiling or landfilling this waste occupies space, risks secondary environmental pollution, and wastes coal resources. Direct reuse is difficult because the ultrafine particle size prevents it from being re-fed into gasifiers.
In a study published in ENG. Chem. Eng., researchers at the East China University of Science and Technology investigated using a carbon-rich residue (CR, with a fixed carbon content of 81.21%) separated from CGFS. They combined this CR with a corn stalk (CS) powder modified by an NaOH-urea solution to act as a binder, producing briquetted carbon-rich residue (BCR) via hot-pressing.
The team systematically optimized the briquetting conditions. When the CS binder content was lower than 15%, the mixed materials exhibited severe delamination. Optimal mechanical strength was achieved at a 25% binder content. Two-factor orthogonal experiments revealed that the optimal hot-pressing temperature was 175 °C and the optimal pressure was 7.5 MPa. Under these conditions, all BCR samples exhibited drop strengths exceeding 99.7%.
The height-to-diameter (H/D) ratio significantly affected the briquettes' properties. The BCR-0.8 sample exhibited the best mechanical strength, with a compressive strength of 620.8 N. However, increasing the H/D ratio compressed the internal pores and weakened gasification reactivity. Therefore, the BCR-0.4 sample, with a compressive strength of 333.0 N, was identified as having the optimal comprehensive performance, balancing mechanical strength and gasification reactivity.
The briquetting process also improved gasification performance. At 1000 °C, the raw CR required 13.9 minutes to reach a 90% carbon conversion rate, whereas the BCR-0.2 sample required only 8.9 minutes, a reduction of 5.0 minutes.
Mechanistic analysis showed that during binder preparation, NaOH disrupts the intermolecular hydrogen bond network of the corn stalk, releasing lignin, while urea undergoes an amidation reaction to generate viscous amide-N active substances. During hot-pressing at 175 °C, the softened lignin coats the CR particles, and the amide components bind tightly to them, forming a dense structure through chemical bonding, physical filling, and hot-pressing synergy.
The authors note that the proposed hot-pressing route is compatible with existing coal chemical solid waste treatment lines. Laboratory-scale equipment can be scaled up to industrial continuous roller-molding units without modifying the main gasifier, significantly reducing equipment renovation costs. This strategy also reduces both solid waste landfill costs and raw material procurement costs.
DOI
10.1007/s11705-026-2707-x