Non-Intrusive Flow Measurement with Ultrasonic Sensors - Important for EX Areas

EX areas are areas where an explosive atmosphere can potentially occur. This risk is particularly present where explosive substances such as powders or liquids are manufactured, processed, transported or stored. Especially in the chemical industry, with its often aggressive and toxic media, users, therefore, rely on non-intrusive measurement technology. New devices offer a high degree of flexibility with regard to media, aggregate states, pipe materials and dimensions, as well as pressure and temperature. The 'clamp-on' ultrasonic sensors used for this purpose are simply mounted on the outside of a pipe, usually even while the pipe is in operation. Flow measurement from the outside of the pipe means measuring from the safe side – without any wear caused by the medium, without any risk of leakage, and without any pressure loss and thus impairment of system availability.

Special Features of the EX Area

It is certainly a challenge to transport such advantages into potentially explosive atmospheres without having to make compromises in terms of measurement size and accuracy. For this purpose, current ultrasonic systems measure the flow according to the transit time difference method. From the difference in the transit time of ultrasonic signals that are radiated into the pipe with and against the direction of flow, the transducer calculates the average flow velocity of the medium and ultimately the volume flow. Inside the pressure-proof encapsulated housing, a powerful processor ensures the necessary measuring performance. The speedily measured value output (also directly into the IT system via Wi-Fi, for example) allows highly dynamic processes to be recorded in real time. Transducers and sensors are calibrated independently of each other in a patented process and without the influence of application-related disturbance variables. This ensures high measuring accuracy at all times – regardless of the combination in which the measuring system is used.

High Flexibility for Additional Applications

Such a 'clamp-on' device measures virtually anything that flows. In concrete terms, this means: The liquid metering devices are suitable for non-intrusive flow measurement of virtually all liquid media, from the thinnest pipe to the largest pipe – regardless of the pressure prevailing inside and over a wide temperature range. In conjunction with an appropriate sensor attachment for extreme temperatures, the flow of liquids can be measured non-intrusively in a temperature range from -190°C (for example, in the case of LNG) to over 600°C. The technology of the devices enables reliable flow measurement even of liquids with an increased solid or gas content.

Photo: 279photo



Focus on Sustainability: Using Water as a Refrigerant

In order to implement a functioning circular economy in its entirety in an ecologically sensible way, the CO2 emissions of the processing operations must be reduced in addition to increasing the recycling of plastics and the extensive use of recycled materials.

The basic problem of the plastics processing industry is a constantly necessary cooling requirement, mostly based on energy-intensive processes in combination with refrigerants that have a high greenhouse gas potential. Some plastics manufacturers now rely on water as a natural and, above all, CO2-neutral refrigerant in their cooling and refrigeration machines. For a functioning circular economy, it is not enough to optimise the material properties of the product in terms of sustainability. Extruders, injection moulding machines or even rollers – cooling plays a major role in the processing of plastics – it is even crucial for the overall quality that there are no major temperature fluctuations.

According to the International Institute of Refrigeration, eight per cent of global emissions are caused by the refrigeration industry alone, writes Angelika Thum of Efficient Energy in the trade journal 'Plastverarbeiter'. By switching to natural refrigerants such as water, air, ammonia, propane or CO2, direct emissions could be almost completely avoided. The corresponding refrigeration technologies are available, have already been tested in industry and can now cover the entire refrigeration demand.

Water – a Natural and Unproblematic Refrigerant

Operators of refrigeration systems using water no longer have to deal with issues such as the greenhouse potential, toxicity or explosiveness of the refrigerant. From the point of view of energy efficiency, too, water has an advantage over F-gases (fluorinated greenhouse gases) because of its high heat of evaporation.

Legislation to reduce the CO2 equivalents of F-gases has led and is leading to some refrigerants being banned outright and others probably being changed several times in less than ten years. This results in bottlenecks, price increases, increased maintenance of existing plants and, in case of doubt, limited operational safety. In addition, F-gases have to be transported, stored, made available and disposed of. All these points are eliminated when using water and help companies reduce their carbon footprint.

From this point of view, the concept of 'free cooling' is also very interesting. In this free cooling system, the compressor typically used is reduced in speed or switched off completely when the outside temperature is low enough. This saves the energy required and reduces the operating costs of the refrigeration system even further.

Photo: visoot


Regardless of Whether Liquids or Bulk Solids: In Future, Measurement Will Be Possible with Just One Device

The new generation of measuring instruments follows the principle of radically simplifying level measurement with radar devices. The development to this state of the art in measurement technology was already set in motion 20 years ago and now suppliers are finally doing away with the decision between bulk solids and liquids.

Since 2016, the manufacturer Vega from Schitach has consistently relied on 80 GHz technology in its developments, which is characterised by particularly precise signal focusing, great dynamics and a high level of protection against interference. In addition, a particularly narrow signal echo makes it possible to maintain very small distances between the sensor and the surface to be measured.

With the new generation of measuring devices (here the 'Vegapuls 6x'), this property has been refined to such an extent that a distinction between liquids and bulk solids is no longer relevant. Thus, it is possible to reduce the distance between the sensor and the surface in the silos from 80 cm to 30 cm and thus (economic advantage!) to better utilise the silo volume.

Redefining the SIL Level

Plant and machinery can pose risks that are so threatening that people and the environment must not be exposed to them under any circumstances. If such a hazard exists, the existing risks must be reduced to meet the safety requirement. One measure of this is the 'Safety Integrity Level' (SIL), which makes the risk reduction quantifiable. Ultimately, however, SIL is also quite clearly a device property.

Vega's application has also taken care of this aspect. Such 80-GHZ applications must be developed differently from the ground up if the requirements for functional safety according to higher SIL are to have an effect. The new radar chip achieves failure rates that exceed previous standards by a factor of ten. This is achieved primarily through innovative self-tests in which the test signal is fed into the very front of the antenna and thus the complete measurement chain from said antenna to the sensor is taken into account. This reduces the failure rate to almost zero, as the manufacturer points out.

Advantages for the Chemical Industry

And something else could be realised: For the chemical industry, the pressure and temperature range of the devices could be noticeably extended. This is achieved by the fact that the antennas, which were previously filled with plastics, can now also be filled with ceramics, making applications with temperatures from -196°C to +450°C and pressures between -1bar and +160bar possible.

The trend is clear: the users simply decide on the basis of their application how the device is configured. And in any case as uncomplicated as possible.

Photo: arborpulchra

Failures, Costs, Interrupted Production Processes: Easily Avoidable Through Surface Cleaning

 The production of high-quality parts is indeed daily business for the plastics processing industry. In production, it is not uncommon to fall back on the moulds of the customers. It is indispensable to treat the tools provided with care, because if damages occur, the reputation of the processing company naturally suffers. But that's not all: competitive pressure is also forcing thermoplastics processors to achieve maximum efficiency and constantly rising quality standards.

During thermoplastic processing, small amounts of the polymer, additives and pigments usually remain on the surface. Over time, this leads to deposits that also affect the surface quality of the parts. This threatens an increase in rejects - and creates a clear economic risk. In fact, just a few defective parts can affect an entire batch.

If such a batch is nevertheless delivered, there is a risk of consequences such as complaints or a poorer supplier rating. And in its worst case, the customer relationship is in jeopardy. The formation of such residues is a slow and steady process that is by no means always synchronous. For example, certain polymers, additives and pigments have a greater tendency to form deposits during long production cycles, others less so. Polyamides, PVC, acetals and numerous other substances, for example, accumulate more, polyolefins leave wax and trapped pigments on cavity surfaces.

How To Proceed With Maintenance?

The question of how to proceed with maintenance is by no means trivial. The differences in quality only become apparent in the final analysis. In order to reduce the unavoidable and often considerable maintenance costs and downtimes, the regular use of mould cleaners is recommended. The advantage is that plastics processors can save a lot of money, time and waste with a small amount of material and only a few minutes for regular cleaning.

What is particularly important to look out for? Checking for weld lines, bubbles and surface defects is still comparatively simple. This can be done directly at the machine and in a timely manner. Partially blocked vents (such as vent pins) can be much more difficult to detect. But they are very important in the process, because contaminated mould parts and tools can significantly impair filling. A good indication is also when an increasing surface gloss appears on structured surfaces - but this is often difficult to detect.

Source: Laurent Saleur (Chem-Trend) in the trade journal Plastverarbeiter 9/2021

Photo: Всеволод Чуванов


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