Effect of demineralization on the physiochemical structure and thermal degradation of acid treated indigenous rice husk

Abstract

Energy generation from biomass presents some serious problems like slagging, fouling and corrosion of boilers.To address these problems, demineralization of biomass is performed using different leaching agents. This study is focused on determining the infl uence of leaching agents and leaching time on the physiochemical structure of rice husk during demineralization. Dilute (5% wt) solutions of HCl and H 2 SO 4 were used for the demineralization of rice husk separately with leaching time of 15, 60 and 120 minutes. It is shown that H 2 SO 4 exhibited higher removal of alkali and alkaline earth metals (AAEM) comparatively as depicted by the 34.2% decrease in ash content along with an increase of 7.10% in the heating value. The acid has been seen to induce more notable changes in physiochemical structure as depicted by the FTIR spectra and SEM micrographs. The thermal degradation behavior of the demineralized rice husk has also been reported.Keywords: demineralization, leaching agent, physiochemical structure, alkali and alkaline earth metals, thermal degradation. PRACTICAL APPLICATIONDue to depletion in fossil fuels reserves, increase in their price, greenhouse effect and environmental pollution, the current challenge to world is to reduce its dependence on fossil fuel by developing sustainable and renewable energy supply. Energy from biomass accounts for the largest renewable energy in the world 1 . Biomass is a lignocellulosic material mainly consisting of cellulose, hemicellulose, lignin, ash and extractives 2 . One important feature of biomass is that it contains alkali and alkaline earth metals (AAEM) such as potassium, sodium, magnesium, calcium, iron etc. 3 AAEM are the main inorganic content of biomass. They are generally present less than 1% and may go up to 15% depending on the biomass type 4 . High AAEM content in biomass leads to slagging and fouling of heat exchanger in the high temperature conversion system. Slagging and fouling is the deposition of ash on the heat transfer surface forming an insulating layer. This layer reduces the heat transfer as well as causes corrosion and erosion problems. This condition puts the threat on the safe operation of the thermal system and also increases the cost of operation and maintenance. The main contributors in slagging and fouling are potassium and sodium which lower the melting point of ash resulting in ash deposition on heat transfer surface 5-7 .Demineralization of biomass has demonstrated to be an effective process for reducing the slagging and fouling nature of it by reducing AAEM content and improving its fuel properties for high temperature processes. Leaching agents (water and different acids) are used to demineralize the biomass in different studies 2, 8-11 . Jiang 2013 17 et al. used deionized water, acetic acid, hydrochloric acid, sulphuric acid, nitric acid and prthophosphoric acid. It was found that sulphuric acid and nitric acid were able to remove more AAEM than other leaching agents. Asadieraghi et al. 2014 15 demineralized palm oil biomasses w...

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