Biomass is a versatile energy resource that could be used as a sustainable energy resource in solid, liquid and gaseous form of energy sources. Torrefaction is an emerging thermal biomass pretreatment method that has an ability to reduce the major limitations of biomass such as heterogeneity, lower bulk density, lower energy density, hygroscopic behavior, and fibrous nature. Torrefaction, aiming to produce high quality solid biomass products, is carried out at 200-300 °C in an inert environment at an atmospheric pressure. The removal of volatiles through different decomposition reactions is the basic principle behind the torrefaction process. Torrefaction upgrades biomass quality and alters the combustion behavior, which can be efficiently used in the co-firing power plant. This paper presents a comprehensive review on torrefaction of biomass and their characteristics. Despite of the number of advantages, torrefaction is motivated mainly for thermochemical conversion process because of its ability to increase hydrophobicity, grindability and energy density of biomass. In addition to this, torrefied biomass could be used to replace coal in the metallurgical process, and promoted as an alternative of charcoal.

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A Comprehensive Review on Biomass Torrefaction

The recent concept of inherent safety uses the properties of a material or process to eliminate or reduce the risk thus removing or minimizing the hazard at the source as opposed to accept the hazard and looking to mitigate the effects. In this framework the control of particle size in dust explosion prevention and mitigation is recognized as a major inherent safety methodology. Indeed, the increase of particle size may allow significant reduction of particle reaction rate eventually reducing the risk. 
 
In this paper a novel model is developed to quantify the effect of particle size on dust reactivity in an explosion phenomenon. The model takes into account all of the steps involved in a dust explosion: internal and external heating, devolatilization reaction and volatiles combustion. Varying the dust size can establish different regimes depending on the values of the characteristic time of each step and of several dimensionless numbers (Damkohler number, Da; Biot number, Bi; thermal Thiele number, Th). Results from the model are reported in terms of the deflagration index (KSt) as a function of dust diameter in all regimes and at varying Da, Th and Bi. Comparison with experimental data from polyethylene explosion tests shows promising results. Finally, the results of the model are presented in the form of a dust explosion regime diagram, which is helpful to make a draft evaluation of the role of dust size on explosion behavior and severity.

Modelling the effect of particle size on dust explosion

Effects of particle size, dust concentration and dust-dispersion-air pressure on rock dust inertant requirement for coal dust explosion suppression in underground coal mines

Inhibition evaluation of ABC powder in aluminum dust explosion

Explosion severity of micro-sized aluminum dust and its flame propagation properties in 20 L spherical vessel

Explosion behaviors of typical light metal and carbonaceous dusts induced by different ignition energies were investigated based on systematic experiments in a Siwek 20 L vessel. Comparative analysis reveals that the explosion mechanism of carbonaceous dust is the volatile combustion, whereas the mechanism for light metal dust mainly features the surface heterogeneous oxidation. Influences of ignition energy on severity and flammability limit are much more significant for carbonaceous dust than light metal, especially for the powder with less volatile. An innovative approach was introduced to derive flame thickness from the pressure–time trace. The relation between explosion induction time and combustion duration of ignitor was also analyzed. Results show inappropriate ignition energy will cause under-/over-driving in the thermodynamic/kinetic characteristic measurements. In this way, a dimensionless parameter pressure ratio was introduced to evaluate the under-driving, while two methods by using flame thickness and induction time respectively, were proposed to evaluate over-driving. To improve the accuracy of dust explosion tests, authors advocate that explosion severity determination should be conducted at the critical ignition energy. Moreover, a comparison between the European and Chinese flammability limit determination procedures was also conducted, indicating that EN 14034-3 is suitable for light metal but not for carbonaceous, while GB/T 16425 appears to be slightly conservative for both carbonaceous and light metal dusts.

Experiment-based investigations on the effect of ignition energy on dust explosion behaviors

Experimental investigations of coal dust-inertant mixture explosion behaviors

An Extensive Discussion on Experimental Test of Dust Minimum Explosible Concentration

Experimental Investigation on Inerting Mechanism of Dust Explosion

An extensive investigation on experimental test of dust minimum explosible concentration (MEC) was carried out by using the Siwek 20 L vessel. Systematic data were reported on the MEC of various dusts and the influences of ignition energy, dust calorific value, moisture content and particle size were taken into account. It is found that the overly low or high ignition energy will result in unrealistic MEC results. To reliably measure MEC, the experimental tests should be preformed under the condition that the test result is independent of ignition energy. For the Siwek 20 L vessel, the 4-6 kJ is the most appropriate energy ranges to determine the MEC of various dusts. The more incombustible component contained in lower calorific value dust acts as a thermal sink in the ignition and heating process of dust cloud, and therefore, the higher MEC can be found in the MEC measurement of lower calorific value dust. Mo reover, due to the notable dust agglomeration, to validly measure MEC, the moisture content of test dust should not exceed 10 wt %. When the moisture content is lower than 10wt %, the MEC smoothly increases with the rise of moisture content. With the decrease of particle size, the measured MEC becomes lower, and the MEC has an approximate linear relation with particle size. The results reported in this work provide t he experimental basis and data guidance for the prevention and evaluation of dust explosion risk.

International Symposium on Safety Science and Engineering in China, 2012 (ISSSE-2012) An Extensive Discussion on Experimental Test of Dust Minimum Explosible Concentration

Zongshan Li

Papers

Experiment-based investigations on the effect of ignition energy on dust explosion behaviors

Experimental investigations of coal dust-inertant mixture explosion behaviors

An Extensive Discussion on Experimental Test of Dust Minimum Explosible Concentration

Experimental Investigation on Inerting Mechanism of Dust Explosion

International Symposium on Safety Science and Engineering in China, 2012 (ISSSE-2012) An Extensive Discussion on Experimental Test of Dust Minimum Explosible Concentration