Abstract
Thermodynamic equilibrium analysis is used to investigate the transformation of metals during the co-gasification of municipal solid waste (MSW) and gypsum (CaSO4). Aspen Plus is combined with Thermo-calc to develop a process model that considers the conversion of metals. The effect of air ratio, temperature, and feed mass ratio (MSW to gypsum) on the syngas evolution and mineral transformation behavior is investigated. The results showed that temperatures below 1050°C, air ratio < 0.4, and MSW to CaSO4 feed mass ratio > 2.5 prevented the gypsum sulfur transformation to sulfur dioxide. About 90 wt% of the products were gases comprising 22% CO and 19% H2. At about 900°C the major minerals formed were CaS (alabandite), melilite, anorthite, rankinite, nepheline, and wollastonite. Melilite, a calcium silicate of aluminum and magnesium, dominated over all other silicates. However, at temperatures > 1000°C, these minerals transform into a more stable calcium orthosilicate (CaSiO4) and molten oxysulfide. Above 1200°C all metals in MSW were transformed into molten oxides. The results show that syngas and minerals can be recovered during the co-gasification of MSW and gypsum revealing the synergetic benefits of co-processing two different low-value waste materials.
