Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures

Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process.

Analysis of Spontaneous Ignition of Grass: Chemical Oxidation and Water Vapor Sorption

Self-heating of biomass by chemical oxidation, which can cause spontaneous ignition, is a safety and management concern. This process can be accelerated by aerobic fermentation and water vapor sorption. The chemical oxidation and water vapor sorption of grass were studied in a laboratory oven, measuring the variations in weight and the internal temperature of a sphere with grass within a flexible polymeric network. Both processes were simulated to prove that the proposed mathematical model could fit the experimental data. It was observed that the water vapor sorption capacity of the grass was high, so the experimental increase in the internal temperature of a spherical body was around 47 K, from 73°C to 120°C. This fact can be very important because the chemical oxidation of grass accelerates at high temperatures. For scaling, simulation programs were used to study the sorption and oxidation processes with an increase in internal temperature in spherical bodies and infinite plane slabs. These results can be used to obtain those of other geometric symmetries by interpolation. It was deduced that at 70°C and with vapor sorption, the ignition time can be around 3 days to 5 days, while without vapor sorption, the ignition times can be around 110 days to 140 days. For 35°C the ignition times with vapor sorption can be around 12 days to 18 days, while without vapor sorption the ignition times can be around 3700 days to 4500 days. These results can be of interest for warehouses of similar biomass and for forestry research and management groups of wildfires. Graphical Abstract

Behavior Characteristics of Hazardous Gas and Scattering Coal Dust in Coal Storage Sheds

This study has comprehensively analyzed the ventilation system of an indoor coal storage shed using computational fluid dynamics (CFD). In addition, the effects of the plan to improve the ventilation system were investigated by synthesizing the results. First, the velocity of inlet wind entering through the natural ventilation system was measured. Then, the concentration of carbon monoxide inside the coal storage shed was measured at the spontaneous combustion of coal. The boundary conditions were set using the measurement results. The characteristics of carbon monoxide concentration, ventilation volume, and behavior of scattering dust were analyzed. According to the CFD analysis results, the upper recirculation strength increased as the flow rate of external air increased. The flow-stagnation area occurred on the center wall. In particular, the concentration of carbon monoxide was high in the flow-stagnation area. When the inflow velocity was 2.0 m/s, a risk of 30 ppm or more occurred in the area near the second-floor workspace and central retaining wall. When ventilation dropped sharply, coal dust emissions decreased to 14.5%. Thus, ventilation must be secured by installing a natural ventilation system, in case spontaneous ignition occurs in many cells or the ventilation sharply decreases. Finally, in order to improve the ventilation system, the effect on the additional installation of natural ventilation and the use of mobile blowers was analyzed. Finally, in order to improve the ventilation system, the effect on the additional installation of natural ventilation and the use of mobile blowers was analyzed. As a result of the analysis, we concluded that using a mobile blower is more effective than a method of additionally installing a natural ventilation device. Carbon monoxide may be locally diluted, and ventilation volume additionally secured.

Improvement of the Thermocouple Method for Testing Energy-Intensive Emulsions for Compatibility with the Sulfide Ores

The results are presented concerning improving the thermostatic method for studying the chemical compatibility of modern industrial emulsion explosives based on the ammonium nitrate with surrounding materials, the increased reactivity of which can lead to spontaneous ignition and even explosion. An assessment of the compatibility of emulsion explosives with sulphide ores was conducted using an original thermocouple methodology developed at the D. Mendeleyev University of Chemical Technology of Russia, fixation of the thermal effects of the interaction of shell-free explosives based on the ammonium nitrate with sulfide minerals. Improved thermocouple method allows to determine chemical compatibility of the industrial explosives with the reactive rocks. It is distinguished by the possibility of continuous recording of the thermocouple measurements during tests using an oscilloscope and combines the reliability of the results with small laboratory weights of the test samples (no more than 20 g, which ensures safety testing). Temperature measurement accuracy is ± 2 °С. It is concluded that the method used is able to identify the cases of the most dangerous interaction from the practice point of view using the emulsion explosives when the pyrite content in the ore exceeds 85 %. The results of experiments on the applicability of thermocouple measurements to testing low-activity rocks, highly reactive pyrite ores, mixed sulfide ores of medium activity, as well as on the identification of the main regularities of heat release during the interaction of emulsion explosives with the sulfide ores are considered.

Physical-and-chemical calculations of safe mode of propane transportation

The key criteria used to assess fire-and-explosive hazard of any facility are: flash point, self-ignition temperature and minimum ignition energy. This article addresses how fire-and-explosive hazard criteria can be used to forecast emergency situations while transporting great quantities of flammable substance – propane, based upon ambient environment temperature. Calculations that were made have led to a conclusion that fire-and-explosive safety concentration mode for propane handling will be: lower concentration value is equal to 1.27 % or under than that value; upper concentration value is equal to 13.96 % or greater than that value. When selecting safe transportation and storage conditions for self-igniting combustible substances, great attention is given to relationship between environment, mass of substance transported and time-period to spontaneous ignition. For propane, the safe self-ignition temperature is deemed to be less than 360°C. Calculations for theoretical experiment regarding propane transportation were made based upon three critical temperature values: 1) 25 °C+10 °C - initial starting point when ambient temperature is 25 °C (roadway temperature is disregarded because ambient temperature is not high enough); 2) 60 °C+10 °C – point of arrival where ambient temperature is 60 °C; 3) 470 °C – propane self-ignition temperature. This helped us to figure out that propane can be stored and transported safely if the minimal electric ignition source is under 4*10−6 Joule.

Characteristics of Porous YAG:Ce Nano-Powders Phosphor Fabricated by a Solution Combustion Synthesis

A cerium-doped YAG (Y3Al5O12) phosphor is used as a rare-earth element phosphor for blue light absorption and yellow light emission for a white light source. A solution combustion synthesis, which is a method for producing nano-powder, is a reaction that is spontaneous ignition by reaction heat released through oxidation/reduction reaction between metal nitrate and fuel. Since the reaction speed is fast and it does not go through a separate firing process, it is a method of easily synthesizing nano-powder by simple process. In this study, YAG:Ce nano-powders were prepared by using various fuels in the combustion synthesis method. Depending on the kind of the additive fuel, the reaction of the combustion synthesis process was different, and the shape of the powder particles according to the fuels was also different. The agglomerated particles of nanoparticles were observed and the characteristics of YAG:Ce powders synthesized under various conditions were analyzed.

An Automated Solution for Controlling Random Fires on Coal Yards

In spite of recent moves to wean the world of fossil fuels, coal remains the main source of power in many countries. Coal yards are prone to spontaneous ignition, a problem faced in every country that stores or transports coal. Depending on the environment – temperature, ventilation, and the rank of the coal – heating and self-ignition can be a longer or shorter process, but the possibility can never be entirely dismissed. A plethora of studies have modelled this oxidation behaviour and proposed countermeasures. Most often, human intervention is necessary, which is both slow and dangerous for the firefighters involved. In this study, we propose to build a complete firefighting solution which is mounted on a number of towers sufficient to cover the area of an open coal yard, complete with redundancy. Each tower includes an inexpensive infrared detector, software to identify areas of elevated temperature, and a water dispenser. The heat detection software calculates the parameters to position the water dispenser so that it covers the area. A prototype has been built from inexpensive components to demonstrate the effectiveness at detecting and extinguishing arising fires. This work has been conducted in collaboration with the managers of the coal yard of a power plant.