Experimental measurement of particle size effects on the self-heating ignition of biomass piles: Homogeneous samples of dust and pellets

Biomass can become an important fuel source for future power generation worldwide. However biomass piles are prone to self-heating and can lead to fire. When storing and transporting biomass, it is usually in the form of pellets which vary in diameter but are on average in the order of 7 mm. However, pellets tend to break up into smaller particles and into dust down to the µm size. For self-heating, size of particles is known to matter but the topic is poorly studied for biomass piles. This work presents an experimental study on the self-heating ignition behaviour of different particle sizes of wheat biomass. We study for the first time homogeneous samples from the dust scale to pellet diameter size, ranging from diameters of 300 µm to 6.5 mm. Experiments are done in an isothermal oven to find minimum ignition temperatures as a function of sample volume. The results are analysed using Frank-Kamenetskii theory. For the homogeneous biomass samples studied, we show that particle diameter variation does not bring a large change in self-heating ignition behaviour. The present work can be used to help quantify size effects on biomass ignition and help address the safety problems of biomass fires

Ignition sensitivity of solid fuel mixtures

Due to both environmental concerns and the depletion of the reserves of fossil fuels, alternative and more environmentally friendly fuels, such as biomass and waste products, are being considered for partial or full fossil fuel replacement. The main disadvantage of these products is their lower energy density compared to fossil fuels. To deal with this several heat and power generation facilities are co-firing fuel mixtures. These processes involve mixtures of flammable dusts whose ignitability and explosibility characteristics are not known and therefore present un-quantified safety risk to the new technologies. This study reports on these risks and on the reactivity characteristics of two and three components dust mixtures of coal/sewage-sludge/torrefied-wood-pellet. In particular chemical composition, ignition sensitivity parameters (including minimum ignition energy, minimum ignition temperature on a layer, minimum explosive concentration) and flame speed have been determined. In all cases the measured parameters for the mixtures were within the range defined by the lower and upper value of the constituent. However, the expected values do not agree with the experimentally obtained ones, providing more relaxed values than the ones needed on this facilities

Steam exploded pine wood burning properties with particle size dependence

Power generation using waste material from the processing of agricultural crops can be a viable biomass energy source. However, there is scant data on their burning properties and this work presents measurements of the minimum explosion concentration (MEC), flame speed, deflagration index (Kst), and peak pressure for pulverised pine wood and steam exploded pine wood (SEPW). The ISO 1 m3 dust explosion vessel was used, modified to operate on relatively coarse particles, using a hemispherical dust disperser on the floor of the vessel and an external blast of 20 bar compressed air. The pulverized material was sieved into the size fractions <500 μm, <63 μm, 63–150 μm, 150–300 μm, 300–500 μm to study the coarse particles used in biomass power generation. The MEC (Ø) was measured to be leaner for finer size fraction with greater sensitivity of explosion. The measured peak Kst was 43–122 bar m/s and the maximum turbulent flame speeds ∼1.4–5.4 m/s depending on the size distribution of the fraction. These results show that the steam exploded pine biomass was more reactive than the raw pine, due to the finer particle size for the steam exploded biomass

Current Wildland Fire Patterns and Challenges in Europe: A Synthesis of National Perspectives

Changes in climate, land use, and land management impact the occurrence and severity of wildland fires in many parts of the world. This is particularly evident in Europe, where ongoing changes in land use have strongly modified fire patterns over the last decades. Although satellite data by the European Forest Fire Information System provide large-scale wildland fire statistics across European countries, there is still a crucial need to collect and summarize in-depth local analysis and understanding of the wildland fire condition and associated challenges across Europe. This article aims to provide a general overview of the current wildland fire patterns and challenges as perceived by national representatives, supplemented by national fire statistics (2009–2018) across Europe. For each of the 31 countries included, we present a perspective authored by scientists or practitioners from each respective country, representing a wide range of disciplines and cultural backgrounds. The authors were selected from members of the COST Action “Fire and the Earth System: Science & Society” funded by the European Commission with the aim to share knowledge and improve communication about wildland fire. Where relevant, a brief overview of key studies, particular wildland fire challenges a country is facing, and an overview of notable recent fire events are also presented. Key perceived challenges included (1) the lack of consistent and detailed records for wildland fire events, within and across countries, (2) an increase in wildland fires that pose a risk to properties and human life due to high population densities and sprawl into forested regions, and (3) the view that, irrespective of changes in management, climate change is likely to increase the frequency and impact of wildland fires in the coming decades. Addressing challenge (1) will not only be valuable in advancing national and pan-European wildland fire management strategies, but also in evaluating perceptions (2) and (3) against more robust quantitative evidence

Two-dimensional model of smouldering combustion using multi-layer cellular automaton: The role of ignition location and direction of airflow

Smouldering combustion is one of the most common and persistent fire hazards of reactive porous media, such as biomass. In this work, a two-dimensional multi-layer cellular automaton has been developed to study the process of smouldering and the roles of both the ignition location and the direction of airflow for generic biomass. Three different configurations are studied: line front, with forward and opposed airflow respectively, and radial front. The first two configurations simulate ignition of one edge of the sample, while the radial front simulates ignition of a spot at the centre of the sample. The resulting spread patterns of line vs. radial front are significantly different. Furthermore, when smouldering occurs with similar characteristics, where both line front and radial front are self-sustained, the smouldering radial front has a higher growth rate than the line front. However, in the studied cases where enough oxygen is always available for oxidation, the direction of the airflow does not influence the spread of the smouldering front, and the line front with forward and opposed airflow present similar behaviour. Finally, two non-zero minimum values have been detected for self-sustained spread according to the moisture of the fuel (probability of drying) and its tendency for thermal degradation (probability of pyrolysis). This model provides a powerful but simple way of reproducing the complex dynamics of smouldering processes which can be used to investigate different scenarios

Simulation of fingering behavior in smoldering combustion using a cellular automaton

Smoldering is the slow, low-temperature, flameless burning of porous fuels and the most persistent type of combustion phenomena. It is a complex physical process that is not yet completely understood, but it is known that it is driven by heat transfer, mass transfer, and fuel chemistry. A specific case of high interest and complexity is fingering behavior. Fingering is an instability that occurs when a thin fuel layer burns against an oxygen current. These instabilities appear when conduction rather than convection is the dominant mode of heat transfer to the fuel ahead and the availability of oxygen is limited during the combustion of a thin fuel, such as paper. The pattern of the fingers can be characterized through the distance between them and their width, and can be classified into three different regimes: isolated fingers, tip-splitting fingers, or no fingers forming and a smooth continuous front. In this paper, a multilayer cellular automaton based on three governing principles (heat, oxygen, and fuel) is shown to reproduce all the regimes and the details of finger structures observed in previous experiments. It is shown how when oxygen is not limited, a smooth smoldering front is formed. If the oxygen speed decreases beyond a critical value, fingers appear first as tip-splitting fingers and later as isolated fingers, increasing the distance between them and decreasing their thickness. The oxygen consumed during oxidation influences these critical values with a positive correlation. This cellular automaton provides an alternative approach to simulate smoldering combustion in large systems over long times. That the model is able to reproduce the complex pattern formation seen in a fingering experiment validates the model. In the future, we could apply the model in various other geometries to make predictions on the outcome of smoldering combustion processes

Ignition Sensitivity of Coal / Waste /Biomass Mixtures

Due to environmental concerns and depleting reserves of fossil fuels, alternative, environmentally friendly fuels such as biomass and waste products are being considered for partial or full fossil fuel replacement. A particular problem of waste materials such sewage sludge is the low energy density and to deal with this several heat and power generation facilities are working with fuel mixtures, such as coal-biomass, coal-sewage sludge or even biomass-sewage sludge. These processes effectively involve mixtures of flammable powders whose iginitability and explosibility characteristics are not known and therefore present un-quantified safety risks to the new technology. This study reports on these risk and reactivity characteristics of the individual components and of two or three component powder mixtures of coal / sewage-sludge / torrified-wood-pellet. In particular the chemical composition, ignition sensitivity parameters (including minimum ignition energy, minimum ignition temperature on a layer), minimum explosive concentration and flame speed, have been determined. In all cases the measured parameters mixtures were within the range defined by the lower and upper value components and no synergistic or antagonistic effects were noted

Resolving the Polarized Dust Emission of the Disk around the Massive Star Powering the HH 80-81 Radio Jet

Here we present deep (16 μJy beam-1), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protostar driving the HH 80-81 radio jet. The observations clearly resolve the disk oriented perpendicularly to the radio jet, with a radius of ≃0.″171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R ≲ 170 au. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼0.″1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 μm. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with the self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.Fil: Girart, J. M.. Instituto de Estudios Espaciales de Cataluña; EspañaFil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Li, Z. Y.. University of Virginia; Estados UnidosFil: Yang, H.. University of Virginia; Estados UnidosFil: Estalella, R.. Universidad de Barcelona; EspañaFil: Anglada, G.. Instituto de Astrofísica de Andalucía; EspañaFil: Anez López, N.. Instituto de Ciencias del Espacio (ice); EspañaFil: Busquet, G.. Instituto de Estudios Espaciales de Cataluña; EspañaFil: Carrasco González, C.. Instituto de Radioastronomía y Astrofísica (irya-unam); MéxicoFil: Curiel, S.. Universidad Nacional Autónoma de México; MéxicoFil: Galvan Madrid, R.. Instituto de Radioastronomía y Astrofísica (irya-unam); MéxicoFil: Gómez, J. F.. Instituto de Astrofísica de Andalucía; EspañaFil: Gregorio Monsalvo, I. De. European Southern Observatory Santiago; Chile. Atacama Large Millimeter-submillimeter Array; ChileFil: Jiménez Serra, I.. Queen Mary University Of London; Reino UnidoFil: Krasnopolsky, R.. Academia Sinica; República de ChinaFil: Marti, J.. Universidad de Jaén; EspañaFil: Osorio, M.. Instituto de Astrofísica de Andalucía; EspañaFil: Padovani, M.. Osservatorio Astrofisico Di Arcetri; ItaliaFil: Rao, R.. Academia Sinica; República de ChinaFil: Rodriguez, L. F.. Instituto de Radioastronomía y Astrofísica; MéxicoFil: Torrelles, J. M.. Instituto de Estudios Espaciales de Cataluña; España. Consejo Superior de Investigaciones Científicas; Españ