Filter systems are for all of us an everyday companion, even though not an obvious one. Starting with the fume hood in the kitchen or for drinking water, for wastewater, for swimming pools or at gas stations. Certainly, also for many different industries filter systems are – due to current environmental protection guidelines – mandatory by law and necessary. Like in other fields, also here the so-called Life Cycle Costs are an important factor when it comes to the choice of the material and these LCC definitely vote for the use of Duplex stainless steels.
Wastewater Treatment Plants
Within Europe austenitic grades like 1.4307 (304L) or 1.4404/1.4432 (316L) or 1.4571 (316TI) are commonly used for the wastewater treatment plant due to their corrosion resistant characteristics. Only for some exceptions, Duplex grades are used instead.
As the worldwide water consumption increases constantly, more water resources are needed, in example fresh water catchment through seawater desalination plants. In dependence of the production methods almost all available Duplex grades and 6-Mo-steels (1.4539, 1.4529, 1.4547 etc.) are used. Each of these plants are unique and for their construction always special profiles in special grades have to be utilized.
In swimming pools where the human skin gives enough protection against all kinds of „damages“ caused by the pool water, different stainless steels are needed which are resistant against the particular water composition. The grade that is used the most for the production of indoor and outdoor pools is currently 1.4404 (316L). However, there are some examples where this grade has its limits, for example when the water is of high temperature or has a high content of chlorides. To avoid the risk of stress corrosion cracking in these cases, often 6-Mo-steels and sometimes Duplex steels are used instead. Salt water, thermal or therapy pools are some examples, just to name a few.
Pulp and Paper Industry
Everyone uses paper each day in various forms such as newspaper, writing or printing paper, handkerchiefs, napkins or toilet paper and others.
It is likely that the consumption of paper will remain constant or even raise worldwide, nevertheless the digital era. The average consumption in Europe is per person and year of 150-190 kilograms. Worldwide it is around 57 kilograms. In Africa, the average consumption is just about seven to eight kilograms.
During paper production, the process water – also called white water – is highly corrosive. Based on the use of waste-paper, sodium hydroxide, soaps and hydrogen peroxides are utilized for production when “Deinking” (removal of the printer’s ink from the waste-paper). That is why this is an excellent example for the necessary of filter systems, as very aggressive media is being applied.
Depending on the exact application, almost all Duplex grades, which are usual and available in the market, are used in many different product forms. To these belong standard profiles for the structural part, but also custom-made special profiles for processing machines.
Many goods of our everyday-use are shipped by vessel from Asia to Europe. On the other hand, many products from Europe are exported and transported worldwide by freight- and container ships.
In addition, holidays on cruise liners are very popular and therefore constantly increasing, as a result in future the quantity of shipping traffic will raise in the coming years. Unfortunately, this brings negative consequences for the environment due to more pollution from the gigantic ships, more waste (key word “plastic carpets”) and spill after naval accidents. Especially the air pollution is to emphasize when talking about filter systems. The worldwide CO2 emission caused by shipping traffic increases annually and exceeds the one caused by car traffic multiple times.
Also by using heavy oil, many other polluting particles enter the environment. To reduce this air pollution, partly premium fuels are used or so called “scrubber” – smoke washer – are installed in the ships. For this application, only high-alloyed materials such as Duplex steels in grade 1.4462 (2205) or 1.4410 (2507), austenitic steels in grades 1.4539 (904L), 1.4529 (926) and 1.4547 (254 SMO) or nickel-based alloys are considered.
Chemical plants are usually obliged to run own sewerage treatment plants to comply with strict environmental protection guidelines. Subject to the composition of the wastewater, more or less the same standards can be set as for the conventional wastewater treatment.
The filter systems for the exhaust air can be compared – at least partly – with those for the shipping industry. Duplex grades, 6-Mo-grades and nickel-based alloys are used here, too.
Especially for these unusual grades, the availability of standard and special profiles do quite often challenge the equipment manufacturer. Montanstahl has proved to be a reliable partner, who not only can satisfy the demand for special profiles but also for small batches with different production technologies.