Abstract
Co-pelletization of waste biomass and microalgae is an attractive option for using bioenergy efficiently. This work investigates the potential of microalgae as a binder to improve the energy consumption and physical and thermal properties of a novel pellet. Wood waste biomass was blended with microalgae in proportions of 15%, 30%, and 50% to investigate its properties using a single pelleting device and thermodynamic analysis. The results showed that, under the conditions of temperature (80–160 °C), pressure (120–200 MPa), and moisture content (6%–14%), blending microalgae can effectively increase the bulk density and mechanical durability of the pellets by 9%–36% and 0.7%–1.6%, respectively, and can significantly reduce the energy consumption of pelleting by 23.5%–40.4%. Blending microalgae can significantly reduce the energy consumption of pelleting by 23.5%–40.4%. Moreover, when the amount of Chlorella vulgaris powder (CVP) is 50%, a maximum bulk density (BD) of 1580.2 kg/m3, a durability (DU) of 98%, and a minimum energy consumption of 25.2 kJ/kg were obtained under the optimum conditions of temperature (120 °C), pressure (120 MPa), and moisture content (10%), respectively. Besides, the interaction between the microalgae and sawdust does exist, and their effect on the co-combustion process is inhibitive (0–300 °C) and accelerative (300–780 °C). When the amount of microalgae was 15%, the average activation energy of the pellet was a minimum value, which was 133.21 kJ/mol and 134.60 kJ/mol calculated by the Kissinger–Akahira–Sunose method and Ozawa–Flynn–Wall method, respectively. Therefore, the energy consumption, physical, and thermal properties of the novel pellet could be improved and meet the ISO standard (International Organization for Standardization of 17225, Geneva, Switzerland, 2016) by blending 15% of microalgae. Overall, the use of microalgae as a binder can indeed improve pellet quality, and it can be considered a significant way to utilize microalgae in the future.
Highlights
Microalgae, as the third generation of bioenergy feedstock, has many important applications in the industrial field, such as water pollution control and flue gas CO2 fixation [1]
Considering the economics of raw materials, the high content of Chlorella vulgaris powder (CVP) seems to improve pellet quality, the proportions of CVP higher than 50% will greatly increase the cost of the pellet fuel
The results show that blending CVP could reduce the activation the phenomenon was similar to that reported by Cao et al [47]
Summary
Microalgae, as the third generation of bioenergy feedstock, has many important applications in the industrial field, such as water pollution control and flue gas CO2 fixation [1]. From a purely economical viewpoint, worldwide microalgae production is mostly dedicated to the extraction of low-volume, high-value chemicals, such as carotenoids and ω-3 fatty acids, which could be sold at a high price [2]. The extraction of such low-volume, high-value chemicals is precluded when microalgae are of interest in effluent treatment for the removal of nitrogen and phosphorus [3]. New alternatives must be pursued, such as high-volume, low-value products. When compared with current methods of obtaining biofuels (consisting of several upstream and downstream technologies), the value of NER is generally within the range of 0.20–0.86 [4], that is, none of the known microalgae-based routes can produce biofuels competitively. Direct combustion is one of the high-volume, low-value ways of using bioenergy for large-scale use. Pelletization turns raw material at a certain temperature and pressure into a regular shape, which can increase the energy density of the biomass raw material by about
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