Avoidance Of Dangerous Electrostatic Discharges In Production Plants

In all industrial areas where flammable liquids or fine-grained, combustible bulk materials are filled, mixed or loaded, explosive atmospheres may form. In fact, such discharges are ubiquitous. However, what usually happens harmlessly in everyday life can have devastating consequences in an industrial environment - for example, when conveyor belts cause permanent friction. An earthing technique to minimise risk is therefore elementary.

The ignition hazard resulting from uncontrolled discharges in real applications depends on their form and the energy emitted. A distinction is usually made between:

  • Tuft discharges occur when charged objects made of insulating material approach conductive objects. Due to the comparatively low energy density, this form of discharge can be reduced to a non-ignitable level by deliberately reducing the insulating surfaces.
  • Corona discharges, which can form at field strengths of 3 MV/m and above on sharp edges or corners of conductive materials, also pose a relatively low ignition hazard.
  • Spark discharge is the abrupt discharge between two charged objects. This is considered the most common source of electrostatic ignition and is avoided by earthing all conductive objects.
  • The most energetic type of discharge is the sliding brush discharge, which typically occurs on thin insulating material surfaces such as foils or coatings. If the high amounts of energy generated by friction are released during a sudden discharge, they are capable of igniting all explosive atmospheres based on flammable liquids, gases or dusts.
  • The fifth, industrially relevant type of discharge, the bulk material cone discharge, occurs when silos are filled with highly charged, insulating bulk material. The strength of the discharges, which occur between the upper part of the bulk cone and conductive silo walls, depends to a large extent on the grain size, conductivity and filling speed of the bulk material. (Stephan Schultz, R. Stahl, in technical journal "PROCESS", 7/2021)

The standard "EN IEC 600792" and the "Technical Rule for Hazardous Substances 727" contain a number of different recommendations and regulations for the avoidance and safe discharge of dangerous electrostatic potentials. The regulations stipulate that all conductive equipment and objects must be earthed or have an equipotential bonding connection in order to limit charging to a safe level. Electrostatic earthing is considered to be ensured when the resistance of objects and materials to earth is less than one mega-ohm.

Observe Wear And Maintenance!

In principle, the prescribed electrostatic earthing can be realised with the help of simple cables and suitable pliers. However, especially in areas where mobile containers such as tank trucks, tank wagons or FIBCs ("Flexible Intermediate Bulk Containers") are filled or emptied with flammable substances, passive earthing is risky. Due to frequent connection and disconnection of the clamps, abrasive ground contact or accidental rolling over of the cables with vehicles, the components are subject to high mechanical stresses. Even minor damage to the cables or contact elements can render a safety device ineffective.

In addition, corrosion, dirt or coatings lead to impairments of the conductivity between clamps and the object to be earthed. With passive, i.e. not actively monitored earthings, there is also the danger that interruptions of the conductive connection remain undetected.

Even though the monitoring of permanently installed earthing connections has not been a priority safety measure so far, this topic is becoming increasingly important due to the trend towards plant modularisation. It is therefore becoming a necessity for plants that use a large number of earthed applications such as filling and mixing stations or operate machines connected via pipe systems.

Photo:  Jens Rother


Digital Transformation Of Companies: Greenfield Restart Or Transformation?

It is becoming increasingly clear to many companies that they can no longer avoid a reorganisation, specifically a digitalisation. What is still going well now will almost certainly be obsolete in a good ten years time and will simply no longer (be able to) happen in the same way in an ‘Internet of Things’ (IoT). What is initially evident today in communication, like the increasing importance of websites and social media (also for b2b), will also apply to production in the foreseeable near future.

To approach the whole thing fundamentally and anew – on a greenfield site – or to implement it in a transformation is one of the most important decisions for companies. But it has to be made if you still want to be in a good position in ten years' time. There will be no ‘business as usual’. These two approaches are often referred to as ‘brownfield’ (converting the existing in small steps) or ‘greenfield’ (starting new and smart on a greenfield site).

The obvious brownfield approach builds on the existing product range, machinery and IT systems and develops them further. And it serves the purpose of safeguarding past investments worth billions while still making the company future-proof.

A greenfield transformation is quite different: here, a kind of smart factory is created, starting with ‘state of the art’ networked machines and IT systems. This undoubtedly ideal approach will probably only come into consideration for very few companies, and not only from a financial point of view. It is more feasible to tackle new product generations or a specific production process with modern systems throughout. A ‘greenfield light’, so to speak, in which definable areas are transformed and repositioned.

Smart Maintenance Versus High Initial Costs

Those who can plan and implement a project from scratch have a great advantage: old systems and usually inadequate possibilities for data acquisition and even more so data exchange do not have to be laboriously upgraded to the new level. The components are then based on the latest technologies and can be seamlessly integrated and feature modern interfaces, sensors or machines. The advantage is thus quickly defined: One can draw from the best resources, is maximally flexible and thus future-proof.

The downside, however, writes Larry Terwey in the trade journal ‘MM Maschinenmarkt’, is that all systems and components have to be purchased from scratch – so the initial investment is very high.  This is especially true when it comes to a smart factory where products and components first have to be newly developed. On the other hand, companies that opt for this approach can expect significantly lower maintenance costs, according to Terwey. This is because modern systems facilitate remote access and pave the way for IoT scenarios such as remote repair and remote software deployment.

Transforming The Inventory

Many companies do not want to lose sight of their inventory, often millions were invested in the past that entrepreneurs would like to protect – this is especially true in the manufacturing industry. Instead of purchasing new equipment, they, therefore, prefer to upgrade their machines to smart devices. The products are retrofitted with sensors or communication technology, for example, which does not have to be negative. Companies that proceed in this way often even make faster progress, quickly gather essential information and gain valuable experience. Even something like the installation of sensors for temperature, pressure, air quality or the like can bring a clear gain in information.

Ultimately, there is no right or wrong, no better or worse. Because the complete answer can only be found between a differentiated, analytical approach and a precise calculation, as well as project planning created according to individual company goals, the technical status quo and the budget framework.

Photo: zapp2photo


 E-mobility: New hybrid company car for Weserland

For the first time, Weserland is using a company car with plug-in hybrid technology for its daily commutes within the city of Hannover. In addition, we are testing an electric forklift for loading and unloading in the warehouse.

With the company car, we also want to make a contribution to significantly less noise and lower particle pollution in the city centre.
For more than 80 per cent the vehicle is used for the daily commute.The lithium-ion high-voltage battery offers a purely electric range of up to 65 km and can be easily recharged at home or at our newly installed in-house charging station. This is ideal for commuting.

For the occasional necessary business trips outside Hannover, the conventional drive comes into play. thus we also have the necessary flexibility in terms of range.The lithium-ion high-voltage battery offers a purely electric range of up to 65 km and can be easily recharged at home or at our newly installed in-house charging station. This is ideal for commuting.

For the occasionally necessary business trips outside Hannover, the conventional drive comes into play. This gives us the additional flexibility we need in terms of range. So for us, a plug-in hybrid vehicle is the perfect alternative to an all-electric car.

Of course, the lower CO2 impact on the climate is an important factor. However, it is debatable from how many kilometres onwards othe vehicle achieves a positive CO2 balance – obviously depending on the number of kilometres driven electrically. It is difficult to predict whether this will be achieved within the working life of two years as a company car – but we will actively monitor it.

So far, a maximum of one tank filling per month has been necessary. And there have even been months in which no refuelling was necessary at all. In the past, at least two fillings per month were necessary for the same mileage.

New quality in the warehouse with electric forkliftsE-Forklifter

We also tested an electric forklift. With one battery charge, we got well beyond one day, with several vehicles being loaded and unloaded. Our colleagues were particularly impressed by the low noise level in the warehouse. The difference in noise in the hall is enormous compared to our gas-powered forklifts. The driving performance also attracted positive attention. The electric control is very precise everywhere.

After this all-round positive impression, we will turn to electric versions in the future – after the current leasing contracts will expire.

We are also planning to use company e-bikes for interested colleagues. Of course, these can then be charged at Weserland and thus also contribute to reducing emissions in the city.

Photos: Oliver Bär

Until When Is It Safe To Continue Operating GRP Tanks Without Replacing Them?

Tanks and pipelines made of glass-fibre reinforced plastic (GRP) are extremely popular in plant construction. The reason for this is the material's high resistance to a variety of aggressive media. Components made of GRP are therefore particularly suitable for use in the chemical industry.

Over the years, however, various influences can impair its serviceability.  This is because the components are constantly subjected to chemical, thermal and mechanical stress - which naturally leaves corresponding traces in the long run. 200,000 operating hours - about 23 years - is the calculated service life of GRP tanks.

GRP is only one fifth as dense as steel, but it can withstand high mechanical loads. It consists of a multi-layer, very strong laminate with low weight. Another advantage is that more flexible geometries are possible during production than with components made of other materials. Plant operators benefit not only from the particularly long service life but also from the material's nominal mechanical values, which enable high load inputs and the absorption of large agitator loads. With these and other properties, constructions made of steel perform noticeably worse.

Condition Assessment Of Durable GRP Tanks And Pipes

For an effective condition assessment of a GRP tank, both an external and an internal visual inspection are necessary.  This can reveal various damage patterns, such as cracks or deformations - but also the so-called osmotic blistering. These changes are caused by the penetration of the medium into the laminate, where it exposes the glass fibres and can also attack the substance through acids or alkalis that form. If the process progresses, the glass fibres can even dissolve completely, resulting in the destabilisation of containers. It is important that operators of industrial plants receive a reliable basis for decision-making with such detailed tests.

If even clearer, more detailed statements on the condition of the glass fibres in the material are required, the use of a scanning electron microscope coupled with an energy dispersive X-ray analyser (SEM-EDX) makes sense. This requires very little sample material so that a diameter of 20 to 30 mm is sufficient for the core hole. It is also advantageous that the very small holes created by sampling can be closed again with little effort. It is certain that with proper inspection, GRP components can be operated even after their expected service life. Service providers can make recommendations on further operation, replacement or refurbishment by means of laboratory analysis.

 This text is based on a longer article in the trade journal "CHEMIE TECHNIK" from March 2021.


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