Characteristics of Smoldering on Moist Rice Husk for Silica Production

Shengtai Yan,Frank Behrendt,Dezheng Yin,Junmeng Cai,Thomas Schliermann,Fang He

doi:10.3390/su14010317

Abstract

In order to assess the possibility of silica production via smoldering of moist rice husk, experiments of washed (moist) rice husk (7 kg with moisture content of 51%) in a newly designed smoldering apparatus was performed. The temperature inside the fuel bed during smoldering was recorded, and characteristics of ash were analyzed. Results showed that the highest temperature in the middle of the naturally piled fuel bed was about 560.0 °C, lower than those in most of combustors. Some volatiles from the lower part of the fuel bed adhere to its upper ash during piled smoldering. Silica content and specific surface area of ash from smoldering of washed (moist) rice husk were 86.4% and 84.9 m2/g, respectively. Compared to our experiments, they are close to smoldering of unwashed rice husk (89.0%, 67.7 m2/g); different from muffle furnace burning (600 °C, 2 h) of washed (93.4%, 164.9 m2/g) and un-washed (90.2%, 45.7 m2/g) rice husk. The specific surface area is higher than those from most industrial methods (from 11.4 to 39.3 m2/g). After some improvements, the smoldering process has great potential in mass product of high quality silica directly from moist rice husk.

Highlights

Smoldering is slow, low-temperature, and flameless burning of porous fuels, which is an important and complex phenomenon [1,2]
The temperature first increases and stabilizes at a temperature of about 60 ◦ C. This is similar to the temperature of smoldering pine bark particle [39] and sewage sludge [4], which is different from the temperature of smoldering corn stalk powder [40] and corn flour [6]
Smoldering experiments with moist rice husk were performed in a self-designed apparatus to check its possibility for silica production

Summary

Introduction

Smoldering is slow, low-temperature, and flameless burning of porous fuels, which is an important and complex phenomenon [1,2]. The application of it in the field of waste-to-energy conversion such as sludge treatment [3], recovery of resources from waste streams [4], and biomass energy conversion [5] has attracted lots of attention in recent years. From an environmental point of view, these characteristics avoid the ash-related slagging/corrosion [8], making nutrients recovery easy via recycling of ash directly to farms [9] and reducing the pollution of solid waste. Open burning leads to air pollution because of the release of fine dust and incomplete combustion gases of CO, NOx , CH4 , poly-cyclic hydrocarbons (PAH) and soot [16]

Objectives

Methods

Results

Conclusion