Assessment of explosion risk for wood dust in a ventilation-dust separation installation, by determining the concentration of total dust in suspension inside of the installation

Most of combustible dusts present both fire and explosion hazard. Explosion may occur at certain concentrations of dust mixed with air and in the presence of an ignition source. The threat posed by this real danger was confirmed by the events that took place in economic units such as: feed factories, wood products, textile industry, steel, etc. Among the parameters of explosiveness of combustible dust, which can cause an explosion, we mention: maximum explosion pressure, lower explosion limit, explosive index, minimum ignition energy, electrical resistivity of dust, minimum ignition temperature of dust layer and cloud, particle size and concentration of dust in suspension. The current paper presents the results of determinations of combustible wood dust concentrations, performed at an important economic unit, manufacturing veneer and wood panels, at a dusting ventilation installation composed of fan, cyclone and textile filter. These determinations were made in the pipe connecting the fan and the bag filter, to assess possible danger of explosion in the pipe, by relating the measured concentration to the lower explosion limit (concentration of wood dust).

Efficiency of gas discharge methods for odor control in municipal wastewater transportation and treatment systems

В процессе транспортировки и очистки сточных вод в воздух выделяются дурнопахнущие вещества, среди которых одним из наиболее трудноудаляемых является сероводород. Для очистки воздуха от дурнопахнущих веществ используются различные методы, в том числе газоразрядные (плазменные, ионизационные), которые хорошо зарекомендовали себя в других областях промышленности. Вентиляционные выбросы, образующиеся при обработке и очистке сточных вод, имеют ряд особенностей: высокая влажность, высокая концентрация сероводорода, потенциальная взрывоопасность. Эти свойства ограничивают возможность использования газоразрядных методов для очистки данного типа вентиляционных выбросов. Описывается специфика применения газоразрядных методов при очистке воздуха на очистных сооружениях канализации и канализационных насосных станциях. Приведены возникающие при этом технические сложности. In the process of wastewater transportation and treatment malodorous substances are released into the air; among them hydrogen sulfide being one of the most difficult to remove. Various methods are used to remove malodorous substances from the air, including gas-discharge (plasma, ionization) methods that have proven remarkably effective in other industries. Vent emissions generated during wastewater treatment are specified by high humidity, high concentration of hydrogen sulfide, potential explosion hazard. These properties limit the possible use of gas discharge methods for the purification of this type of vent emissions. The specificity of applying gas discharge methods for air purification at the wastewater treatment facilities and wastewater pumping stations is described. The arising technical difficulties are presented.

A change in the air temperature inside a 20-liter chamber when air is added from the receiver

Introduction. One of the reasons for the overestimation of the explosion hazard of dust inside a (20 ± 2)-liter chamber is the elevated initial temperature of the air suspension. The initial temperature is also raised by the process of filling the pre-emptied chamber with air from the receiver, used to distribute dust over the chamber. In this work, an increase in the air temperature inside an 18.7-liter chamber was identified in an experiment for the case of addition of air from the receiver.The methodology of an experiment. The air temperature in the chamber was measured at the time when the air from the receiver was added using a WR 5/20 thermoelectric converter (a thermocouple). The thermocouple junction was located at the distance of 70 mm from the inner wall of the chamber. The thermocouple signal was processed by an MCLab PRO programmable logic controller (the time resolution is 1 ms).Research results. The measuring instruments recorded an increase in the temperature of the thermocouple junction by +14 degrees. Due to the comparability of the inertia of the thermocouple (3 s) and the characteristic time of air cooling by the chamber walls (5 s), the measurement results underestimated the real value of a jump in the air temperature inside the chamber. Measurement results were refined using a simple model of heat transfer between the objects involved in the process (thermocouple junction – air – chamber wall) that entailed the exponential relaxation of the temperature difference over time. As a result, an estimated increase in the initial temperature inside the chamber of +30 degrees was identified.Results and discussion. The temperature jump by +30 degrees makes a noticeable contribution to the total jump in the initial temperature, which was previously tied solely to the burnout of the ignition source (+80 degrees).Conclusions. Given the known increase in the temperature inside the chamber caused by the burnout ofa standard ignition source (2 kJ), the real value of the initial temperature of the environment can reach 135 °C in the course of studying dust in a (20 ± 2)-liter chamber.

Simulation of Possible Fire and Explosion Hazards of Clean Fuel Vehicles in Garages

Clean fuel is advocated to be used for sustainability. The number of liquefied petroleum gas (LPG) and hydrogen vehicles is increasing globally. Explosion hazard is a threat. On the other hand, the use of hydrogen is under consideration in Hong Kong. Explosion hazards of these clean fuel (LPG and hydrogen) vehicles were studied and are compared in this paper. The computational fluid dynamics (CFD) software Flame Acceleration Simulator (FLACS) was used. A car garage with a rolling shutter as its entrance was selected for study. Dispersion of LPG from the leakage source with ignition at a higher position was studied. The same garage was used with a typical hydrogen vehicle leaking 3.4 pounds (1.5 kg) of hydrogen in 100 s, the mass flow rate being equal to 0.015 kgs−1. The hydrogen vehicle used in the simulation has two hydrogen tanks with a combined capacity of 5 kg. The entire tank would be completely vented out in about 333 s. Two scenarios of CFD simulation were carried out. In the first scenario, the rolling shutter was completely closed and the leaked LPG or hydrogen was ignited at 300 s after leakage. The second scenario was conducted with a gap height of 0.3 m under the rolling shutter. Predicted results of explosion pressure and temperature show that appropriate active fire engineering systems are required when servicing these clean fuel vehicles in garages. An appropriate vent in an enclosed space such as the garage is important in reducing explosion hazards.

Assessment of the risks of using hydrogen instead of carbon-containing fuels in the ferrous metallurgy

The Paris Agreement, adopted in December of 2015 at the 21st session of the UNFCCC Conference of the Parties and effected from November of 2016, coordinates the efforts of states to reduce greenhouse gas (GHG) emissions, including carbon dioxide. One of its largest emitters to the atmosphere is the metallurgical industry. Among the proposed ways to reduce carbon dioxide emissions is the widespread use of hydrogen in the ferrous metallurgy. An overview of the problems that the ferrous metallurgy will face when replacing carbon-containing fuels with hydrogen is presented. It was noted that the use of hydrogen in the ferrous metallurgy contains such technological risks as high cost in comparison with currently used fuels and reducing agents; explosion hazard and corrosion activity, the need for a radical reconstruction of thermal units when using hydrogen instead of traditional for the ferrous metallurgy natural, coke and blast furnace gases, as well as solid fuels. It is shown that minimizing these risks is not always possible or economically feasible, and the result of using hydrogen in the ferrous metallurgy instead of carbon-containing fuel from the point of view of reducing greenhouse gas emissions may be low with a significant increase of economic and social risks.

The Fire and Explosion Hazard of Coloured Powders Used during the Holi Festival

During the world-famous Holi festival, people throw and smear each other with a colored powder (Holi color, Holi powder, Gulal powder). Until now, adverse health and environmental effects (skin and eye irritation, air pollution, and respiratory problems) have been described in the available literature. However, the literature lacks data on the flammable and explosive properties of these powders during mass events, despite the fact that burns, fires, and explosions during the Holi festival have taken place many times. The aim of the article is to present the fire and explosion parameters of three currently used Holi dust and cornflour dust types as reference dust. The minimum ignition temperature of the dust layer and dust cloud, the maximum explosion pressure and its maximum rate of growth over time, the lower explosion limit, the limit of oxygen concentration, and the minimum ignition energy were determined. Tests confirmed that the currently available Holi powders should be classified as flammable dusts and low-explosive dusts. The likelihood of a fire or explosion during mass incidents involving a Holi dust-air mixture is high.

Fire and Explosion Hazard during Depressurization of Equipment with Ammonia

The statistics of fires and explosions of ammonia in the sphere of its circulation (production, storage, use) indicate the relevance of studies aimed at preventing emergency situations, localization, and elimination of accidents consequences. Equally important are studies on the development of assessments of accidents consequences associated with the release and spillage of ammonia from the equipment in various aggregate state. When ammonia is released, the resulting mixture of the product with air can vary in density from the formation of gas-air clouds with a density below the air density to buoyancy and excess air density, depending on the release conditions (pressure and temperature in the equipment; the sizes of the hole through which ammonia enters the surrounding space; the location of the hole in the equipment (gas or liquid phase). When the liquid ammonia leaks out, the spills are formed, from the surface of which the product evaporates especially rapidly in the first moments after the spill. Based on the computational and analytical studies, the design schemes and formulas were proposed for determining the parameters of the explosion: excess pressure and impulse of the undisturbed (incident) and reflected from the obstacles of the blast wave, as well as the nature of the destruction depending on the distance from the epicenter of the explosion, caused by the depressurization of equipment with ammonia. An accident scenario is considered, according to which the ammonia with a mass of 100 kg, when depressurizing, breaks out from the equipment of an industrial refrigerator. Ammonia vapors mix with the air to form a cloud that ignites and explodes. As an example, the overpressure and impulse during explosion of ammonia at a distance of 30 m from the epicenter of the explosion were determined. According to the empirical formula for estimating the distances from the epicenter of the explosion to a given place, the levels of the consequences of building destruction (complete, medium, small, moderate damage) can be established.