Ash Melting Behavior of Rice Straw and Calcium Additives

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.

Impact of Torrefaction on Fuel Properties of Aspiration Cleaning Residues

“…In sample WT-275-30, the ash content was 24.14% wt. Such a high ash content can be problematic, depending on the type of combustion device, as was observed during the processing of residues from rice cleaning [ 56 ]. The reason for the increase in ash content is the loss of mainly moisture but also oxygen and hydrogen during torrefaction.…”

A Review of the Sustainable Utilization of Rice Residues for Bioenergy Conversion Using Different Valorization Techniques, Their Challenges, and Techno-Economic Assessment

“…The rice husk contains approximately 75% organic volatile matter, and the remaining 25% of its weight is converted into ash, which is known as rice husk ash (RHA), during the incineration process [ 119 ]. The high ash content, which has a range of 9–22% [ 120 , 121 , 122 ], and remaining chemical make-up of RH mean that rice husk combustion faces some challenges. For instance, the high amount of silica and sulphur, along with alkali metals and alkaline earth metals, present in RH poses a threat to its combustion, as it leads to the low melting temperature of ash followed by slag generation and fouling [ 120 , 122 , 123 ].…”

“…The high ash content, which has a range of 9–22% [ 120 , 121 , 122 ], and remaining chemical make-up of RH mean that rice husk combustion faces some challenges. For instance, the high amount of silica and sulphur, along with alkali metals and alkaline earth metals, present in RH poses a threat to its combustion, as it leads to the low melting temperature of ash followed by slag generation and fouling [ 120 , 122 , 123 ]. Moreover, it has been found that the influence of ash on thermal behaviour is directly related to the amount of potassium in the feedstock.…”