Oxidation Characteristics of Water Soluble Fractions of Agro-Stalks with Focus on Function of Reactive Inorganics

R Zhao,Y Liu,F Behrendt,J Cai,F He,A Dieguez-Alonso

doi:10.18321/ectj1101

Abstract

In order to deepen the understanding of the thermochemical behavior of reactive inorganics, which play an important role in slagging and fouling during combustion of agro-stalks, the oxidation behavior of the water-soluble fraction of corn stover, wheat straw and rice straw was examined using a simultaneous thermogravimetric analyzer. The oxidation characteristics were discussed in combination with elemental analysis of water-soluble fractions. Results showed that reactive inorganics elements account for 30–40% in water-soluble fractions of the three agro-stalks and carbon was oxidized at two separate stages. Four stages were found during oxidation of water-soluble fractions – (1) devolatilisation of organics (100‒400 °C); (2) oxidation of char (400–650 °C); (3) oxidation of char with melting of salts or decomposition of carbonate (650–800 °C); (4) vaporization of KCl (800–1000 °C). This work provides a base study for an optimized design of combustion for agro-stalks and pharmaceutical waste.

Highlights

The annual consumption of biomass for energetic purposes currently accounts for 8‒14% of the world final energy consumption, and its share is increasing rapidly[1]
Most of the above named reactive inorganic elements in biomass can be extracted by washing with water and these combustion problems are alleviated by pre-treatment of alkali metal leaching [5, 11, 16,17,18,19,20,21,22]
Results show that the components and oxidation characteristics of the three materials are similar as following: 1) Water-soluble fractions (WSF) from agro-stalks are a mixture of ca. 35 wt% reactive inorganics (K, Cl, Ca, Mg, Na, S) and 65 wt% organics

Summary

Introduction

The annual consumption of biomass for energetic purposes currently accounts for 8‒14% of the world final energy consumption, and its share is increasing rapidly[1]. Problems related to ash, including alkali-induced slagging [8,9,10,11], corrosion [3, 12], particulate emission [1, 13], and ash nutrients solidification [6, 14] during direct combustion limit the efficient and clean energetic utilization of biomass. Most of the above named reactive inorganic elements in biomass can be extracted by washing with water and these combustion problems are alleviated by pre-treatment of alkali metal leaching [5, 11, 16,17,18,19,20,21,22]. The removal ratios of K, Cl, S with bath water washing at a constant temperature (25 °C) amount to 80, 90, and 90%, respectively [5]. These removal ratios can be further improved by grinding of the material, fully immersing or bathing using hot water [23], and the alkali of herbaceous biomass are easier to be extracted by water than those of woody biomass [18, 24]

Methods

Results

Conclusion