The Effect of Rice Straw Gasification Temperature on the Release and Occurrence Modes of Na and K in a Fluidized Bed

Abstract

Rice straw gasification was carried out in a laboratory fluidized bed reactor system from 600 to 800 • C in order to well-understand the release and occurrence mode of alkali metals as a function of temperature during the gasification process. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was applied to analyze the original rice straw and obtained fly ash at different temperatures. The results show that the Water-Soluble, Ammonium acetate-Soluble, Hydrochloric acid-Soluble, and Aluminosilicate Combination-Soluble modes of the Na and K contents in rice straw decreased in sequence. The content of Water-Soluble salts of Na and K accounts for more than 50%, while the content of the Aluminosilicate Combination-Soluble mode is the lowest: less than 5%. The release rate of Na appears to be consistent but nonlinear, increasing with gasification conversion ranges between 50.2% and 70.8%, from which we can deduce that temperature is not the only factor that impacts Na emission. The release of K can be divided into two stages at 700 • C. At the first stage, the release rate of K is almost invariable, ranging from 23.3% to 26%. At the second stage, the release rate increases sharply: up to 55.9%. The concentration and the proportion of the Water-Soluble, Ammonium acetate-Soluble, and Hydrochloric acid-Soluble modes of Na in fly ash decrease with a temperature increase. The release of K can be explained as follows: one path is an organic form of K converted into its gaseous phase; the other path is a soluble inorganic form of K that is volatile at a high temperature. With a temperature increase, the Aluminosilicate Combination-Soluble mode of both Na and K increases.

Thermochemical Conversion of Rice Straw

“…1. High silica content of about 73.65% SiO 2 of rice straw ash was also reported by Chen et al (2017). Silica from ash can be used to treat effluents containing heavy metals (i.e.…”

Novel Model for the Release and Condensation of Inorganics for a Pressurized Fluidized-Bed Gasification Process: Effects of Gasification Temperature

“…Both experimental measurement − and chemical equilibrium calculation ,, have been conducted for the release of alkali metals during biomass gasification. It is well known that factors including gasifier type, gasification conditions, feedstock impurities, ,, tars, and bed materials , can affect the release of alkali metals during biomass gasification. In terms of the condensation of inorganics during gas cooling, studies are generally performed based on thermodynamic equilibrium calculations.…”