Influences of Additives on Steam Gasification of Biomass. 1. Pyrolysis Procedure

Biomass gasification consists of two procedures: pyrolysis and char gasification. To better understand the influences of additives on the biomass gasification with steam, the two procedures were studied in part I and part 2, respectively. This paper is the part I of this series, where we focus on the influences of additives on the pyrolysis procedure of biomass gasification in a fixed-bed reactor. The additives used for this paper were alkali metal carbonates (Na2CO3 and K2CO3) alkaline earth metal oxides (CaO and MgO), transition metals (Ni and Fe2O3) natural ores (dolomite, olivine, and sepiolite) and clays (kaoline and diatomite). The results demonstrated that alkali metal carbonates (AMC), alkaline earth metal oxides (AEMO), dolomite, and sepiolite mainly increased the yields of permanent gases (H-2, CO2, etc.) and improved the quality of gaseous product by promoting the decomposition reactions of tat and light hydrocarbon (CnHm) and the gasification reaction of char; transition metals (TM) and olivine primarily enhanced reforming reactions of tar and CnHm to raise the yields of permanent gases (H-2, CO2, etc.) and upgrade the quality of gaseous product; clays played few roles in the conversion reactions of tar and CnHm. For AEMO, Fe2O3, dolomite, and olivine, these additives also display roles in improving the water-gas shift reaction to further raise the yields of H-2 and CO2. In addition, the pyrolysis procedure is further improved by the acts of these additives with increasing the temperature. On the basis of the properties of additives, TM should be selected as one portion of active ingredients of the composite catalyst, which could be used for promoting steam gasification of biomass to produce high-quality gas and increasing the overall efficiency of biomass gasification, to upgrade the quality of gaseous product; AMC or AEMO should be used as the promoter to enhance the steam gasification of carbon/char deposited on the catalyst.