Wrong fuel in your car? Something that can be expensive when it happens to cars involves a huge risk potential when filling chemicals. Unfortunately, accidents caused by confusing two different chemicals are not uncommon. However, there is a relatively simple means to avoid this type of problem: clamp-on ultrasonic systems can be used as media watchdogs.
The author: Jörg Sacher Press and Public Relations, Flexim
The photographs of a large-scale operation by the fire services in the Lower Saxony town of Bad Fallingbostel are still vividly remembered in Germany. Last October, a red alert was raised there after 10,000 l of nitric acid were accidentally pumped into a detergent tank containing 14,000 l of sodium hydroxide in the foodstuffs plant at Kraft Foods. This mix-up led to a violent exothermic reaction, nitrous gases escaped and at times the tank threatened to burst. At the beginning of 2012, a similar accident in Brühl near Bonn also caused quite a stir. Chlorine gas was released there after a sodium hypochlorite solution was inadvertently mixed with hydrochloric acid. In both cases, simple safety equipment could have detected the fatal mix-up in time and prevented the dangerous reaction.
External measurement of internal flow
“External measurement of internal flow” – this is the motto of Flexim, the measuring equipment manufacturers. In most applications it would be more accurate to say “External measurement of the internal flow quantity”. In fact, clamp-on ultrasonic technology is now widely used as a standard method for flow measurement and the same technology is also suitable for non-invasive media detection.
In contrast to flow measurement, it is not a question of measuring the transit-time difference when ultrasonic technology is used for analytical purposes; the aim is rather to determine the propagation velocity of sound in the medium concerned. Acoustic velocity is a substance-specific characteristic. For this reason, the acoustic measurement method can also be used for product identification. There are plenty of possible applications. The HPI meter is a combined instrument for simultaneous flow measurement and media detection that is specifically adapted to the needs of the oil and gas industry. HPI stands for hydrocarbon product identification. In principle, the HPI meter can be used at any filling station to differentiate between petrol and diesel. However, in everyday industrial applications, it tends to be found on transport pipelines or loading terminals where it simultaneously measures the flow rate, detects boundary layers between products arranged in series and reliably identifies the medium flowing inside. Similarly, the Piox S ultrasonic system is employed, for example, in CIP plants in the food industry to monitor cleaning cycles.
A danger detected is a danger less
In order to prevent accidents when handling chemicals, Germany’s Technical Rules for Hazardous Substances (TRGS) stipulate technical, organisational and personal protection measures. These measures include the use of left-hand threaded connections for filling sodium hypochlorite solution, chemical-analytical incoming inspections and adherence to the dual control principle by tank truck drivers and warehouse staff. However, accidents show that these precautions are obviously insufficient, or in many cases simply bypassed.
For statistical reasons alone, sodium hypochlorite poses a particular risk: it is a very common product which is also widely used under different names outside the chemical industry, for instance as Eau de Javel or liquid bleach for cleaning and disinfection.
When an employee died in Frankfurt in 2007 following a similar accident to the one in Brühl, the German Committee on Hazardous Substances (AGS) developed a concept for safe decanting of liquid bleach (Annex 4 TRGS 500). One of the requirements set out in this concept is that the filling pipe should be monitored by carrying out measurements with a pH electrode, for example, or by measuring the temperature. At the time, apparently, nobody thought to measure the sound velocity, yet the non-invasive, acoustic method has considerable advantages in day-to-day operations.
Austria was the first country to start using Piox S systems to guard against potentially risky filling operations. Flexim’s Austrian branch fitted two pilot plants with clamp-on ultrasonic technology in cooperation with the Vorarlberg Institute for Environment and Food Safety. In preliminary tests, institute experts discovered that pH and temperature measurements were unsuitable for the intended purpose: the electrodes for pH measurement are subject to extraordinary wear and tear by the medium and cause a huge amount of maintenance work, thereby interfering with operational processes. Temperature measurement has even greater disadvantages because it can only be observed after acid and caustics have been mixed which results in an exothermal reaction – in other words, when it’s too late. For this reason, the temperature monitor must be designed so that the filling and stored materials can react outside the storage tank before the filling material reaches it. In practical tests, this type of temperature measurement was inadequate to safely detect when the wrong product had been filled.
Active safety equipment
On the other hand, experts in Austria’s westernmost region had a very positive experience with non-invasive acoustic velocity measurements. Clamp-on ultrasonic systems were installed first at Collini in Hohenems and then at Schoeller in Hard. In both companies, sodium hypochlorite is an essential medium for production: Collini has developed into one of Europe’s leading groups of companies in the area of surface coatings for metals and plastics. Sodium hypochlorite is required to treat waste water in electroplating operations. Schoeller, a spinning group, produces a wide assortment of yarns from wool, cotton and synthetic fibres, using sodium hypochlorite to chlorinate the wool.
The active safety equipment set up in both pilot operations is designed so that it only opens the filling valve when the acoustic velocity value is in the desired range. This is determined by acoustic media detection. The filling valve closes automatically when the power is switched off. Since clamp-on ultrasonic transducers are simply fastened onto the filling pipe, they are not subject to any wear and tear by the medium flowing inside and they operate practically maintenance-free.
The most straightforward application where Piox S ultrasonic systems can be used as media watchdogs is when they prevent an acid or caustics tank from being filled with the wrong material. This type of protective equipment can be put into practice very easily. Regardless of concentration and temperature, the acoustic velocities of acids and caustics are far enough apart from one other for any errors during filling to be detected beyond doubt.
The situation is more complicated when it comes to ruling out a variety of potentially hazardous mixtures. This involves accurately measuring all relevant substances at various concentrations over a wide temperature range. Flexim carries out these investigations in-house and also cooperates on various research projects with the German, Austrian and Swiss authorities. Flexim engineers are currently implementing a complex safety system at a wholesaler of chemical products.
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