The Messer Group produces industrial gases at temperatures of up to minus 196 degrees Celsius, which demands a reliable and powerful cooling circuit. Thanks to a measuring and metering system with integrated corrosion measurement section from ProMinent, the company can now achieve constant minus temperatures by the prevention of corrosion and sedimentation in the cooling water.
Noble gases are so called because of their chemical similarity to noble metals and, like noble metals, they are also highly inert. This is just one of the reasons why they are often used as blanket gases in industry. The Messer Group has been producing industrial gases at its air separation facilities for more than a century. Noble gases, such as neon, xenon, krypton, argon and helium, are already present in the air, but only in very small quantities. 99% of the air is made up of nitrogen and oxygen and an air separation system separates the various elements and extracts the gases from the air.
Industrial gas production at low minus temperatures
At the start of the process the air is cleaned and compressed at a pressure of approximately 6 bar. This compressive force generates heat that must be reduced as the gas mixture has to be cooled rapidly until it liquefies. Heat exchangers lower the temperature – initially to minus 180 degrees Celsius to pre-cool the air, then the mixture is filled into a high separation column, where the temperature continues to fall to minus 196 degrees Celsius. As the elements in the air have different boiling points, oxygen, for instance, liquefies at minus 183 degrees Celsius, this enables them to be separated from one another. The droplets that form with the steam fall to the sieve floor of the column, whilst the other elements in the compressed air continue to rise as gases. Argon condenses at minus 186 degrees Celsius for example.
Protection against corrosion and sedimentation in the cooling water
A powerful cooling circuit is essential for air separation as it produces and precisely controls the low minus temperatures that are needed. This is why the Messer Group took the decision to install a panel-mounted measuring and metering system with integrated corrosion measurement section from ProMinent.
"The system controls the cooling water circuit and prevents the growth of algae, bacteria and fungi by adding biocides and inhibitors", explains Mr. Siebert, Sales Engineer at ProMinent. If left, these can cause corrosion and sedimentation to form in pipes and heat exchangers and consequently reduce the efficiency of the system, or even worse damage the cooling system. Particularly in heat transfer zones, it doesn't take long for a biofilm to form. Mr. Siebert adds, "Of course it is important for all processes that the right pH value is maintained."
Reliable measurement of pH value, conductivity and corrosion
This is where ProMinent's system proves its worth: it can measure pH values at two points reliably and accurately. This dual pH value measurement improves reliability and guarantees the correct pH value at all times. An alarm is triggered if the values at the two measurement points should drift apart. The system also monitors conductivity using inductive sensors that help to ensure almost maintenance-free operation. This measurement is particularly important, as make-up water has to be continuously added to the cooling water to replace the water that has evaporated or leaked away. This process increases the salt concentration, resulting in scaling and corrosion. By measuring the conductivity of the cooling water by induction, the salt content can be measured reliably and blowdown can be initiated as required. Corrosion is also monitored using three coupons placed along the corrosion measurement section.
delta® diaphragm metering pumps keep cooling water germ-free – fully automatically
The Messer Group also uses three delta® diaphragm metering pumps. Based on optoDrive® drive technology, these pumps meter even the smallest quantities with high precision and, instead of releasing the feed chemical drop by drop, they release it into the pipe in a continuous stream, ensuring that it mixes with the cooling water. Suction lances fitted with level switches are used to convey the feed chemical from the containers to the pumps. Depending on the measurement values, the diaphragm metering pumps release the biocides chlorine and bromine and an inhibitor into the cooling water – fully automatically.
Everything from a single source
"All of the components of the system are supplied by ProMinent, helping to keep the cost to the Messer Group low. The individual components were mounted on a PE panel wired ready for connection with a drip tray on a stainless steel stand," explains Mr. Siebert adding, "The high quality standards of ProMinent combined with high-precision, almost maintenance-free components were what attracted the Messer Group. By using a customised measuring and metering system, this industrial gas company can significantly reduce its costs. Due to the high quality of the cooling water, they have to add less fresh water and need far fewer chemicals. Both of these aspects not only save money, but also protect the environment – definitely a winning combination."
Picture: Customised, ready-wired metering system. DULCOTEST® type sensors, DULCOMETER® control and delta® solenoid metering pumps with optoDrive® regulated solenoid drive, together with the required containers, form a single unit that can assimilate your work without any installation effort.