Ash Melting Behavior of Rice Straw and Calcium Additives

Veronika Chaloupková,Petr Hutla,Tatiana Ivanova,Monika Špunarová

doi:10.3390/agriculture11121282

Veronika Chaloupková, Petr Hutla + Show 2 more

Open Access

https://doi.org/10.3390/agriculture11121282

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Abstract

Rice straw is potentially an appropriate feedstock material for biofuel production, since a huge amount of this postharvest residue is generated every year. The transformation of such agricultural biomass into densified products with a higher energy value and their subsequent combustion is associated with several questions. One of them is that rice straw exhibits a large formation of ash during combustion; thus, it is essential to know the nature of its ash melting behavior. Generally, during the combustion of straw biomass, ash sintering occurs in relatively low temperatures, resulting in the damaging of heating equipment. This negative aspect can be overcome by the addition of calcium-based additives. This paper aimed to study the ash melting behavior at a laboratory scale and to determine the ash melting points of rice straw mixed with calcium carbonate (CaCO3) and calcium hydroxide (Ca(OH)2) in different proportional ratios. The standardly produced ash samples from the rice straw obtained from Cambodia were constantly heated up in a muffle furnace, and characteristic temperatures of ash melting, i.e., shrinkage, deformation, hemisphere, and flow temperature, were recorded. The results showed that increasing the additive ratio did not bring linear growth of the melting temperatures. The addition of 1% CaCO3 showed an optimal positive impact of higher ash melting temperatures, and thus a better ability to abate the sintering of the rice straw ash.

Highlights

Worldwide, there is increasing energy consumption, and biomass serves as a suitable alternative to fossil fuels to cover this expanding energy demand on small- and large-scale levels, together with a solution to international commitments to reduce carbon dioxide emissions [1,2]
The aim of this paper was to study the ash melting behavior of RS ash mixed with calcium additives such as CaCO3 and Ca(OH)2 during the continuous heating in laboratory conditions to determine the characteristic temperatures of ash melting points and to find a more suitable additive for the production and thermal utilization of biofuels based on RS biomass
The present research provides complementary information on the behavior of rice ash mixed with two calcium additives in three different fraction rates during continuous heating in laboratory conditions, and gives an idea of how the material could behave during combustion

Summary

Introduction

There is increasing energy consumption, and biomass serves as a suitable alternative to fossil fuels to cover this expanding energy demand on small- and large-scale levels, together with a solution to international commitments to reduce carbon dioxide emissions [1,2]. RS with such a high annual production is considered as the most abundant agriculture lignocellulosic residue not competing a food production with great energy potential [12,14,15,16]. This plant material consists mainly of complex carbohydrates such as cellulose and hemicelluloses, and their energy is possible to recover by different pathways like combustion, pyrolysis, gasification, anaerobic digestion, and other biochemical conversion processes [7,8,17]. The transformation of these agricultural residues into solid biofuels with improved parameters and a higher energy density, as well as their subsequent thermochemical conversion, is associated with several operating challenges

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