The Impact of Particles Comminution on Mechanical Durability of Wheat Straw Briquettes

Abstract

Briquetting is one of the recommended biomass agglomeration processes. The material subjected to briquetting gains valuable functional features related to higher energy density, appropriate moisture content, and increased bulk density. However, the briquettes need high mechanical durability to maintain high quality during transportation, loading, and other logistic steps before they will be delivered to the final consumer and utilized for energy purposes. The mechanical durability depends on many factors, including the particles comminution of the compacted biomass. Therefore, the aim of this study was to analyze the impact of particle comminution on the mechanical durability of wheat straw briquettes. The research was carried out in accordance with the international standard for solid biofuels PN-EN ISO 17831-1:2016-02. The briquettes were produced from three different fractions: 0–2 mm, 2–15 mm, and 15–45 mm. To obtain more data related to the mechanical durability of briquettes, the tests were also carried out outside the ISO standard conditions. During the investigations, the working chamber operation time was extended from 5 to 60 min, and the rotational speed of the working chamber was increased to 25 and 30 rpm, respectively. The results indicated that the mechanical durability index (Du) of briquettes decreases along with the increase in the particle size. According to the PN-EN ISO 17831-1:2016-02 standard, the highest mechanical durability was achieved for the 0–2 mm fraction (Du = 91.17%) followed by the 2–15 mm fraction (Du = 88.12%), and the lowest was achieved for the 15–45 mm fraction (Du = 84.48%). It was noticed that the increase in the working chamber operation time resulted in a decrease of the Du value. Moreover, the difference in mechanical durability (between t5 = 5 min and t60 = 60 min) was greater for a larger fraction (∆Du = 16.26% for 0–2 mm fraction, ∆Du = 21.04% for 2–15 mm fraction, and ∆Du = 23.43% for 15–45 mm fraction). It was also observed that the increase of the rotational speed of the working chamber caused a slight decrease in the value of the mechanical durability of briquettes for all investigated fractions.