The effects of additives on deposit formation during co-firing of high-sodium coal with high-potassium and -chlorine biomass

In the last decades, the demand for alternative fuels has been growing due to carbon-neutral regulations. Co-firing coal with biomass potentially reduces greenhouse gases emission by replacing the portion of fossil fuels in the power generation sector. However, combining high-sodium coal with high-potassium and -chlorine biomass during co-firing can increase ash-related issues in the boiler's heat exchanger surfaces. Despite the fact that various additives have shown promising results in mitigating these issues, the effectiveness of these additives has not been clearly investigated yet. This study aims to evaluate the effectiveness of MgO, Al₂O₃, CaHPO₄, and SiO₂ additives during co-firing in several parameters. The study involves an experimental setup using a drop tube furnace and ash particle observation methods, including ash fusion temperature, thermogravimetric-differential thermal analysis, probe observation, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. The result shows that 1–6 wt% MgO, 1 wt% Al₂O₃, and 1–3 wt% CaHPO₄ are more effective than other additives in minimizing deposit formation. In addition, the mentioned additives decrease sodium (from 6.99 to 3.22–1.98 wt%) and potassium contents (from 4.51 to 4.11–1.49 wt%), increase ash melting temperature, and offer a cleaner probe surface with normal ash deposit weight. In comparison, the SiO₂ additive has a lower impact than other additives in overcoming ash-related problems in the boiler and could produce higher ash deposit weight.