Effect of heterogeneity of organic solid wastes on gasification behavior and efficiency

Gasification is a promising technology for organic solid wastes (OSWs) utilization. However, OSWs heterogeneity causes significant temperature fluctuation in gasifier, which thus affects gasification reactions and leads to decreases in gasification efficiency. This has been demonstrated in other studies, but the key influencing factors are not clear. Our study combines computational fluid dynamics (CFD) simulations to quantitatively analysis the effect of heterogeneity of OSWs on gasification behavior and to propose equivalent ratio under dry-ash-free basis (ERdaf) as a more accurate parameter. Four different kinds of OSWs with totally different composition and fuel properties are investigated. The largest temperature difference is obtained in oxidation zone, reaching 358 K. Basing on the difference of moisture and ash contents of different OSWs, equivalent ratio (ER) is optimized and a new parameter ERdaf is proposed to better describe the actual air supplied to combustible portion of OSWs. The factor affecting temperature difference in drying and pyrolysis zone is moisture content, while the factor in oxidation and reduction zone changes to ERdaf. High ERdaf feedstocks, such as food waste, tend to undergo over-oxidation process and result in low syngas calorific value of 39.46 % compared to proper ERdaf feedstock biomass. While, low ERdaf feedstocks, such as polymer, produce the highest syngas tar content, which is 29 times than that of biomass. Therefore, temperature fluctuation causes great influences on gasification behavior and efficiency. It can be solved by homogenization pretreatments of feedstocks such as torrefaction or conjunctions with thermal energy storage technologies in gasifier.