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FEATURE SAFETY SOLUTIONS STAYING GROUNDED IN MATERIALS CONVEYING


Pneumatic conveying systems can generate vast quantities of electrostatic charge. Here, James Grimshaw, marketing manager at Newson Gale, looks at the top five ways of addressing the issue


neumatic conveying systems are an effective method of moving granular and powdered bulk materials within a production process. However, it is not without its risks, with the most serious being a build-up of static electricity especially if the material being processed is combustible and has an appreciable portion of fine powder or granules. In fact, the potential for an explosion


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increases dramatically with all fine powders that have a low MIE (minimum ignition energies). Within pneumatic conveying systems, these materials will regularly reach the MEC (minimum explosive concentration) along the entire conveying system. In this situation, a common source of ignition, explosion and fire is electrostatic discharge. The risk is exacerbated because pneumatic systems can move a large amount of material at speed, which can result in vast amounts of static electricity being generated. This is caused by the friction of the particles against the equipment as it travels. It is the most common cause of electrostatic build up and is known as tribo-electrification caused by the contact and separation of the powder with the walls of the processing equipment. Here are our top 5 tips for avoiding


electrostatic explosion in pneumatic conveying systems: 1. Set up a dedicated static grounding solution from the start The most effective method of ensuring pneumatic conveying systems that move materials with a low MIE don’t accumulate static electricity is to provide a dedicated static grounding solution. For example, our EarthRite Multipoint II is a multi-channel static earthing system that can monitor the simultaneous earthing of up to eight individual pieces of equipment at risk of discharging electrostatic sparks. It is ATEX/IECEx/cCSAus certified and these international standards identify when equipment exceeds earth resistance levels outlined in codes of practice including CLC/TR 60079-32-1 and NFPA 77. When required, EarthRite Multipoint II is capable of stopping the flow of product and alerting personnel to a potential hazard if a component loses its connection to ground, avoiding an electrostatic explosion occurring. This is particularly important where grounding connections


32 MARCH 2020 | PROCESS & CONTROL


can’t be visually checked because operators may not know that the connection has been lost, resulting in a build-up of electrostatic charge. 2. Check all grounding clips after clearing material clogs Pneumatic Conveying Systems are susceptible to clogging when the material/air velocity drops below a certain level, which means the powder cannot be carried along the pipeline and a blockage develops. As such they require regular maintenance to ensure free flow. However, disassembling elements of the system can result in bonding and grounding connections being missed or not correctly re-connected when it is put back together. That means the equipment is not earthed and this can result in build-up of electrostatic charge. When disassembling equipment for


whatever reason, we always recommend that all earthing connections are checked. It is prudent to keep a written record of the type and location of earthing points so that they can be verified correct following any works.


The Earth-Rite MULTIPOINT II system ensures that all parts of a pneumatic conveying system have continuity through to ground with a resistance connection of less than 10 Ohms. In many cases, this can reduce the need for manual human intervention to check that grounding clips are in place. The system has cCSAus, ATEX and IECEx approval for use in hazardous atmospheres and meets all current EC directives


Newson Gale is part of Hoerbiger Safety Solutions


assembly have become isolated from a true earth ground. 4. Recheck all grounding clips after


3. Carry out regular inspection for


vibration stresses Pneumatic systems usually have elevated


levels of vibration due to the movement of the product within the pipework. This flow-induced vibration can cause a few issues at elbows and other areas where pipework changes direction. Resonance vibration can also occur in straight lengths of pipework. The consequence of vibration is stress fractures, loosening and deterioration of mechanical connections, including grounding clips. As part of a regular maintenance programme, we always recommend that grounding clips are checked for tightness and structural integrity. Vibration can also degrade assembly connections, so it is important to ensure that no parts in the


The table above shows the Minimum Ignition Energy (MIE) of a range of common powders. MIE represents a measure of the lowest amount of energy conveyed by an electrostatic spark that will ignite these dispersed fuels in air


The multi-channel static earthing system can monitor the simultaneous earthing of up to eight individual pieces of equipment at risk of discharging electrostatic sparks


cleaning and maintenance Regular examination of bonding straps between the metal pipework and duct sections should be carried out in order to check that they haven’t been dislodged by cleaning and maintenance operations. In a recent incident a process operator working on a pneumatic conveying system received a significant static shock. Although the operator was unharmed, the severity of the incident warranted a full system shutdown. An inspection of that section of duct found that it was not suitably grounded as a result of a single grounding clip that hadn’t been properly installed after a clean down operation. When you consider that one misplaced grounding clip can result in a potential explosion with injury or worse, along with loss of assets and missed customer orders, there is a need to be constantly vigilant against static electricity. 5. Corrosion can weaken grounding connections Some pneumatic systems operate in production facilities that have aggressive environments. This can result in bonding connections facing accelerated corrosion. Industrial atmospheres are generally the most aggressive in terms of corrosion and so particular attention should be paid to grounding connections in these environments.


Newson Gale https://bit.ly/39dvpHf


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