Abstract
Microwave torrefaction of oat hull was conducted to enhance its physicochemical properties. A bench-top reactor with an internal stirrer was used for oat hull pretreatment at temperatures of 225 °C, 255 °C, and 285 °C, and residence times of 3, 6, and 9 min, respectively. Results showed that a high temperature level at 3 min residence time or severe torrefaction increased calorific values by up to 35% of its original value, while decreasing mass yield down to 60.77%. Severe torrefaction further decreased moisture absorption, moisture content, and grinding energy consumption but decreased energy yield and bulk density. Residence time had no significant effect on biomass physicochemical changes; however, production cost may be significantly increased by longer residence times. It was also concluded that increased microwave power levels from 400 to 650 W decreased energy consumption by shortening processing times, resulting in a positive economic impact of the process. Moderate and severe torrefaction significantly enhanced biomass fuel properties, and short residence times are recommended in order to decrease electricity consumption. In addition, microwave pretreatment enhances biomass in a similar way to conventional torrefaction, but at a faster processing time. Moreover, the liquid fraction as a by-product may represent a valuable product for the food industry.
Highlights
IntroductionA by-product of the milling process, represents up to 25% of the total weight of the grain [1]
Accepted: 12 July 2021Oat hull, a by-product of the milling process, represents up to 25% of the total weight of the grain [1]
Under high power level (>750 W), the energy consumption slightly increased with no significant decrease in processing time, but it tended to damage the reactor vessel and components
Summary
A by-product of the milling process, represents up to 25% of the total weight of the grain [1]. Due to its high fiber content and low-quality nutritive value for animals, this by-product is of low economic value in the region. Agricultural by-products could be utilized as a source of renewable energy, which are considered carbon neutral [2]. Some of the major problems associated with the use of biomass for energy production are high moisture content, hydrophilic nature, and low heating values [3,4]. One of the possible solutions to this problem could be the use of torrefaction, which is a thermochemical process that improves the fuel characteristics of biomass [5]. As described by Basu [6], temperature is the most important parameter within the torrefaction process
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