Steam explosion, unlike other hydrothermal pretreatment technologies, which characterized by physical tearing effects is the most cost-effective and widely used method for pretreating lignocellulosic materials. Because the severity factor originates from hydrothermal pretreatment processes, it cannot represent the effects in the instantaneous decompression, but depicts those in the high-temperature cooking. No breakthroughs can be seen in previous studies on the severity factor.

Researchers with Institute of Process Engineering, Chinese Academy of Sciences (IPE) established multiscale models based on the analysis of physical tearing in instantaneous decompression. They optimized moisture content of materials by maintain temperature and optimized chip size with discharge port area. The chip size, moisture content of materials, and discharge port area are then incorporated into the severity factor.

In their work, researchers first set up the model assumption and established a brittle fracture criterion for materials. Then they established energy conservation equation and momentum conversion equation. Based on these theories, they analyzed physical tearing in instantaneous decompression and also considered particle size, moisture content, and discharge port area.

Results indicated that moisture content and holding pressure were key factors that affected physical tearing. The chip size of materials that were pretreated by steam explosion was not randomly chosen but restricted by specific equipment requirements. Based on the experimental data researchers established a novel severity factor on the basis of chip size, discharge port area, and moisture content.

The severity factor enriched with chip size, moisture content, and discharge port area represents the effects of high-temperature cooking on steam explosion and the physical tearing effects of instantaneous decompression. Such representations enable the comprehensive interpretation of the mechanism of steam explosion technology, and guide equipment design and process parameter selection for steam explosion under a given set of materials, products, and treatment targets.

This work was financially supported by the National Basic Research Program and National Key Project of Scientific and Technical Supporting Programs. The paper was published in Chemical Engineering Science.