Effects of K⁺, Ca²⁺ and Fe³⁺ on the distribution, structure and quality of the pyrolysis products of Hefeng coal

The nitrate solution of K⁺, Ca²⁺ and Fe³⁺ was used to treat Hefeng demineralized coal (DC) separately. The weight loss and gas evolution of coal samples were studied by thermogravimetric analyzer. It is found that the total weight loss of treated coal samples decreases, while the concentration of CO₂ and H₂ increases for treated samples. Then the distribution variation of products during the pyrolysis process of treated coal samples were investigated in a fixed bed reactor together with the analyses of elemental analysis, FT-IR, simulated distillation and GC-MS. The results indicate that the char and gas yields of treated coal samples rise, while the tar yields decline. The unsaturation and condensation of corresponded char samples exhibit a decreasing tendency. Under the action of these metal components, the percentage of light component in the tar increases, especially by 22.4% due to the effect of iron species. GC-MS analysis exhibits that long chain alkanes occupy about 70% of the total relatively, leading to the high content of heavy component in tar, which can be catalytically cracked by K and Fe species.