Nonwoven manufacturing process consists of several steps. (Photo: Ahlstrom plant in Tampere, Finland)
By Noora Blasi, Marketing Communications Manager and Jan Kaukopaasi, Market Development Manager, Ahlstrom
Higher energy costs and ever increasing consumption demands worldwide have increased the focus on energy efficiency in many industries. One example is the power generating industry, which is driven by creating maximum efficiency, affordable electricity and low emissions. The consumption and production of energy will continue to rise globally and this article will highlight how correct filter selection at power plants can help to contribute to a reduction in energy consumption.
Many industrial applications have already been using nonwoven materials. Their usage has been increased due to the versatility and possibilities of designs and availability of new and improved raw materials. The process technologies and manufacturing capabilities also continue to improve, which make nonwovens even more suitable. Nonwovens offer a unique and compatible alternative in many industrial applications for paper, textile or woven materials. One key example of nonwovens used in Industrial applications is for air intake filters in gas turbine plants.
Nonwovens in detail
Overall filters made with nonwoven technologies are robust and provide high performance. Nonwovens are made with many different technologies including both dry and wet-laid manufacturing processes. Examples of dry-forming technologies are extruded nonwovens such as meltblown and spun-bonded media or carded and needle-punched filter media. All of these synthetic nonwoven media types have their advantages and disadvantages such as good pore-size for efficiency (meltblown) but poor strength for pleating the media into filters, or vice versa, good strength (spun-bond) but poor pore-sizes. Therefore these type of dry-formed nonwovens often have to be laminated together in order to reach better value propositions and overall filtration performance.
The wet-laid nonwoven manufacturing process is especially well suitable for making higher end filter media thanks to the flexibility of raw material usage. Longer synthetic fibers providing strength can therefore be mixed with finer fibers providing higher filtration efficiencies in one process step only. Furthermore, the natural porosity gradient of the fibers, which are formed during the so called dewatering step, enhances the depth filtration properties and therefore provides higher dust holding capacities and/or filter life. Special additional functionalities can furthermore be added with different chemicals and additives. These technologies can be further enhanced with features and functionalities including flame retardancy or hydrophobicity, which make them even more versatile. One important feature of synthetic based filter media is that opposed to cellulose based solutions, the fibers don’t swell, which under high humidity conditions can cause pore-size blockage and for the pressure drop over the filter media to rise increasing the energy demand.
Nonwoven filters are used in various industrial air and liquid applications and one good example is in air intake filtration systems at power generation plants. Filters play a key role in contributing to higher performance efficiency and higher energy and electricity output of the power plants. Two types of filter systems exist for gas turbine air intake applications, the so called self-cleanable (pulse-jet) and static system. The performance of pulse-jet systems relies on applying a back-pulse over the filter when the dust cake and pressure drop has built up releasing the dust cake and consequently reducing the pressure drop. The surface filtration properties can further be improved by coating the media with nano-fibers (200-300 nm diameter) using the so called electro-spinning technology. For pulse-jet applications good surface filtration properties are needed. In static applications, the typical set-up consists of a more open pre-filter followed by a higher efficiency fine filter, and in many instances also a so-called HEPA filter, which provides extremely high filter efficiencies.
How that is done
One key contributor to energy efficiency and optimal output at power plants is the air Intake system of the gas turbines. This step – the air intake system – of the power generation process takes a lot of energy to produce the clean air required for turbines to operate. As gas turbines are installed in many different environments worldwide, the requirements for air intake filter systems and the selection of the correct filters becomes crucial for the production of affordable energy.
Historically, the air filtration system has been equipped with products made with cellulose nonwoven, and they are still used in many locations. As there is a large correlation between the air quality (clean air) and the efficient output of the power plant, the performance requirements for filters have increased. Most critical performance requirements for filters today are:
- Higher filtration efficiency at the targeted pressure drop
- Increased dust holding capacity (DHC) especially for smaller hydro-carbon particles
- Strength for static but especially pulse-jet gas turbine applications
- Hydrophobicity especially under high humidity conditions
- Increased mechanical strength
Ahlstrom is a global leader in innovative fiber- based materials with capabilities that capture all main technologies used in the manufacture of nonwoven filter applications. The company has a long history in doing extensive research around this topic and has been able to combine several functionalities into one product to meet the performance requirements of industrial filtration media. Through its extensive research, the company is able to introduce new products to meet the growing need of even more sophisticated filter solutions.
Ahlstrom offers a complete product portfolio for the most demanding gas turbine end applications. In addition to a global portfolio of cellulose nonwovens, many of the higher-end product families are relying on synthetic based nonwovens. Examples are the three-layer Trinitex® media, corrugated and synthetic SafePulse™ media, and corrugated synthetic media coated with nano-fibers called NanoSafePulse. The company’s product offer is also well suited for other demanding industrial filter applications.
For more information visit www.ahlstrom.com