04.03.2009 | Autor / Editor: S. Matthäus and R. Bunse / Dr. Enno Müller
Manufacturing or production processes which create organic or chemical dusts are extremely hazardous. As the security limits of primary explosion protection are rapidly reached and the risk of a dust explosion can not be excluded, a constructive explosion protection is essential.
An explosion is a violent expansion or bursting caused by a sudden release of energy from a very rapid reaction creating enormous temperature and pressure increases. Most common reactions are of flammable gases, vapours and cracked dusts -together with ambient oxygen. As a result of today’s production technologies and increased production capacities an explosion is a threat companies confront daily. Manufacturing or production processes which create organic or chemical dusts are extremely hazardous. Finer particles of dust caused by faster machines, automatic conveying systems and air cleaning equipment increase the risk of a dust explosion. The finer the dust particle, the more severe the explosion will be. International guidelines including ATEX 95 (valid for manufacturers of machines and plants) or ATEX 137 (valid for operating companies) require companies to consider the consequences of a dust explosion due to injured workers and damaged plants. In addition, the economic risk to the company due to plant shutdown, contaminated product or adverse publicity must be considered.
Special attention is placed on the elimination of the ignition source. The potential source of ignition is for example mechanical or electrically produced sparks, frictional heat, electrostatic charges (as, for example, the grounding systems offered by Kersting GmbH, a REMBE® ALLIANCE company), welding or other heat sources. Due to the high amount of potential ignition sources, it is easy to imagine the difficulty in eliminating them all. Similarly the removal of the fuel is impossible as this is the actual product or a waste product produced in the production process. As remaining measure the oxygen is completely removed. This can only be achieved through very expensive processing. The security limits here are also rapidly reached and the risk of a dust explosion can not be excluded. Therefore a constructive explosion protection is essential.
There are several ways to mitigate explosions: explosion pressure resistant construction, explosion isolation, automatic explosion suppressions, inerting, explosion venting, and others. Special advantages of explosion venting solutions are easy installation on existing facilities, minimal to no maintenance, and zero operating costs. The Q-Rohr®-3 from Rembe, for example, guarantees indoor explosion venting without any flame and dust propagation. It is maintenance-free, that means it does not cause any operational costs and is, therefore, more economical compared with active suppression systems. Even OEMs consider the simplified and cost-saving solution for the installation in new plants.
Safety for any Equipment Location
The Rembe solution consists of an integrated bursting disc which vents the explosion wave in a controlled manner into theQ-Rohr®-3. Flame gases with temperatures higher than 1500°C (2732°F) are cooled down to less than 90°C (195°F) via energy transfer within the special stainless steel mesh filter inlet. This leads to a reduction of the expanding gas volume as it extinguishes the flame. Additionally, the pressure rise and high noise level associated with a free vented explosion are reduced to negligible levels. The specially developed stainless steel mesh filter guarantees that no burned or unburned dust passes off the system, which is reusable immediately after cleaning. According to the manufacturer, the Q-Rohr®-3 system is the only indoor explosion device recognized worldwide by NFPA68 and accepted also by VDI-3673 and prEN 14797.
As previously explained, explosion isolation is an other way of explosion mitigation. One solution to protect interconnected equipment is to use quenchvalves that offer high speed closure of a fast acting pinch valve. The EXKOP® system is a good example for such a solution, that provides safe, economic and easy explosion, spark and flame front isolation. In this case, quench valve is triggered by a 100 % reliable signal from a maintenance-free triple-section bursting disc, explosion vents or by IR-, pressure or temperature sensors. The complete system is failsafe due to an integrated pressure storage tank and self-monitoring controller. In case of explosion the plant personnel can reset the system quickly and easily after inspection. Plant downtime is reduced to a minimum. Rembe developed their solution especially for applications with 1-2 quench valves. EXKOP® MINI fulfils these requirements in an ideal manner. Two separate inputs (bursting panels, explosion vents, spark detectors, etc.) can be combined with two quench valves. The use of the system is easy and works according to the manufacturer’s ‘one button easy handling’ philosophy. All events are observed by a ring storage memory.
The new protection concept developed by Rembe’s Safety Research and Development provides flame reduced venting of dust explosions. Industrial plants with low strength and the demand for large venting areas are protected safely and economically -flame propagation and heat are absorbed. The so-called Q-Box allows operators to position machines and equipment according to process requirements, and, as the manufacturer says, “is a cost-saving and flexible venting system for indoor-and outdoor applications.”
REMBE GmbH, SAFETY + CONTROL
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