Filters are an important part of many industrial facilities. They are used in power plants, cement factories or chemical plants, not to mention waste incineration plants. All of these facilities produce fine dust that must not be allowed to escape into the environment. Filters help to prevent this problem and remove fly ash, cement dust and other dust particles from the exhaust gases. Yet new requirements for many production facilities have led to two problems that are increasingly challenging for conventional filter media made of synthetic fibers.
First of all, the synthetic materials aren’t always sufficiently resistant to certain chemicals. Prolonged exposure to acidic or alkaline substances destroys the filter, which then has to be replaced. Another difficulty is the temperature resistance: high-performance synthetic materials typically cannot withstand temperatures higher than 250ºC for longer time periods. And even brief temperature fluctuations above this limit, known as peaks, can cause severe problems.
One example in which the filter’s temperature resistance is very important is during the recovery of energy from the exhaust gases of industrial facilities. In this process heat exchangers are used. To prevent them from becoming clogged, the exhaust gases flowing through them must be filtered first. However, the challenge is that the higher the exhaust gas temperature, the more efficient is the energy recovery – meaning the filter medium must be able to withstand higher temperatures. Many conventional dust filters cannot handle- this. The exhaust gases must therefore first be cooled down before they can be filtered and then fed into the recovery process. This leads to poor energy efficiency — and thus costs money.
Using carbon fibers leads to the fact that the filters can also withstand temperature peaks of up to 400 degree Celsius. “This is a huge advantage compared to more traditional textiles,” says Senior Manager Rainer Schmitt, who works in SGL Carbon’s research and development division at Central Innovation in Meitingen, Germany. Facilities operators using these new filters can extend the service life of their filter systems because of an significant reduction of damages caused by brief temperature peaks.
Another advantage of carbon-fiber filter media is their chemical resistance, especially at higher temperatures. Acids such as sulfuric acid and alkalis such as ammonia, both found in exhaust gases, can barely damage carbon-fiber filters—which is not the case for filters made of high-performance synthetic fibers.
Looking at the economics, we see a great advantage in using hybrid filtering media made of non-woven carbon-fiber textiles.
Senior Manager Dr. Rainer Schmitt, who works in Central Innovation at SGL Carbon
Yet another innovation on the filter market: hybrid structures based on non-woven carbon-fiber textiles. These involve a combination of carbon-fiber filter media with a mesh made of metal or continuous carbon fibers. These structures keep the filter textiles in shape and reinforce them, additionally. This results in the great advantage that these filters can be cleaned via backpulsing, something that isn’t possible for non-reinforced filters since they aren’t mechanically stable enough. With the insertion of metal supports, the filter medium also becomes pleatable. This allows a larger filtering area to be realized in a smaller space, for example in filter cartridges, which increases the filter’s dust absorption capacity.
There are a lot of potential application areas for these filters. The new filter media are ideal for filtering dust particles from gas flows as well as solid particles out of liquids. These reinforced non-woven textiles made of carbon fibers are especially useful with chemically aggressive fluids due to their chemical resistance.
SGL Carbon has already developed initial prototypes in cooperation with a partner in non-woven textile technology. These filter media are now being tested under real conditions for three to six months with selected customers. Schmitt is confident that the new filters offer many advantages compared to the synthetic fiber media alternatives currently available on the market: “The tests will now show our advantages in direct comparison.”