Research on biomass energy usually focuses on the amount of energy produced, but how much energy is invested in this process? Tony Grift, a professor of agriculture and bioengineering at the University of Illinois, USA, said that it is also important to consider how much energy is invested in the production process, and this part is often overlooked.
Recently, as a co-author of a new study, Grift published a paper in the "Bioresources Technology Report" examining the bioconversion efficiency of two agricultural (by-product) products commonly used as biomass energy production-giant awn and bagasse .
"Our goal is to determine how much energy is required to prepare these materials. This is a comprehensive study of various pretreatment methods and their relationship with conversion efficiency." He explained.
These two materials were chosen because of their importance for energy production. Giant awn is a typical ornamental crop, but it has high biomass, is easy to grow and rarely requires nitrogen. Bagasse is a by-product left after sugar cane is pressed into sugar.
This research was done in collaboration with chemists at the University of California, Berkeley. Grift said that the interdisciplinary approach makes this research unique because it considers the entire energy balance. Researchers at the University of Illinois studied the energy consumption of collecting and pretreating materials, while chemists at the University of California at Berkeley focused on converting biomass into glucose for use in ethanol.
The researchers defined the percentage of inherent heating value (PIHV), which can measure the energy of biomass materials entering and leaving the production process. "It tells you that a certain amount of biomass contains a certain amount of energy. How much energy do you spend on processing? You don't want to spend more than 5% of the total energy value?" Grift said.
The researchers performed nine different methods of pretreatment on the two materials, giant awn and bagasse. Pretreatment methods include cutting, granulating, crushing and varying degrees of compression. Among the 9 treatment groups, 5 groups were giant awns, 3 groups were bagasse, and 1 group was a mixture of two products.
Grift explained that there are many reasons for preprocessing. After the crop is harvested, it needs to be transported to the processing plant. In order to improve transportation efficiency, the material must first go through a process called crushing, that is, it is shredded or cut into small pieces, and then compressed. The processed materials all release glucose through the same chemical process.
Harvesting and compression do not add much energy. The main source of energy consumption is crushing or size reduction. This brings energy consumption to 5%. "Smaller particle size makes compression easier. It is also beneficial for energy production because it provides a larger surface area for enzyme attachment during conversion. But crushing requires a certain amount of energy, so it needs to be weighed." Grift Say.
The researchers also evaluated the effects of particle size, compression level, and mixing on biomass conversion efficiency. The results show that crushing has a positive effect on the efficiency of giant awns, but it has no effect on bagasse, and granulation is the opposite. The researchers also found that the 50:50 mixture of these two materials has a higher conversion efficiency, but there is no significant difference compared to giant awn.
The results of the research can be used to help improve the production efficiency of biomass energy. Grift emphasized, "If you want to do something on a larger scale, it is very important to clarify these processes. These results are preliminary and should be tested in further research or may be extended to other products and Preprocessing method. "(Compiled by Wang Fang)
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