An Energy-Saving Filtration Technology

When searching for potential savings, the supply of compressed air, which is indispensable for the industry, stands out as this form of energy is produced by the companies themselves and therefore its costs can be influenced in a direct way.

To realize these cost savings, specialists are needed for the various levels, from generation to purification and distribution to the required compressed air quality at the point of use. For example, Donaldson as one of the leading filter manufacturers succeeded in saving 460,000 kWh of electricity in the fiscal year 2021 through targeted actions in the supply of compressed air in its American plants (source: Donaldson Sustainability Report, Fiscal Year 2021). The focus of saving efforts has traditionally been on air compressors. Their electricity consumption is easy to track, and technological developments in compressors and their controls seem to be reaching their limits in terms of the significant design principles related to reducing electricity demand.

So where would you start if state-of-the-art generation is practiced, data is digitally recorded, and even leakages are controlled successfully in a well-designed compressed air network (Fig. 1)?

Preventing pressure losses is a permanent task and one of the most effective parameters on the way to greater energy efficiency. And filtration technology plays a decisive role in this. Even improved intake air filtration (Fig. 2) has an influence on the downstream filter components (Fig. 3) during the compression process and thus also on compressed air purification. By the time the energy carrier "compressed air" reaches the actuators, the pneumatic control elements, and, in many areas of application, its task as process air, a minimum of about six to several hundred application-specific filters can be assumed. And each filtration performance means pressure loss, which is compensated by the higher energy requirements of the compressors.

The influence of filtration technology on the energy requirement should therefore not be underestimated. Research and development at Donaldson recognized very early on that the interaction of filtration performance and differential pressure can be designed through the structure of the filter media in such a way that significant energy-saving potentials can be achieved.

The UltraPleat filtration technology (Fig. 4) uses a new structure of coated high-tech fibers, which are processed into a pleated filter medium with high separation efficiency of liquid particles and large absorption capacity for solid particles. The multi-layer structure of the new filter media has been designed to provide optimum fluidic conditions and, at the same time, a filter surface area that is over 400 % larger than that of wound filter media.

For the separation of oil aerosols, an efficiency of ≥ 99.9% is achieved according to ISO 12500-1:2007. The filter performance data according to ISO 12500-1 and ISO 12500-3:2009 have also been validated by an independent institute for energy and environmental research. The fact that it has been possible to achieve this high filtration performance while at the same time reducing the differential pressure by a further 50% underlines the successful development of this filtration technology for increasing energy efficiency and conserving resources (Fig. 5). A simple example calculation shows the great economic advantage of this technology: A differential pressure that is only 300 mbar lower for 8,000 operating hours saves around € 4,700 per UltraPleat filter per year (7 bar mains pressure, 110 kW installed compressor power, € 0.18/kWh).

The high efficiency of the innovative filter elements is fully exploited in the flow-optimized filter housings. A prerequisite for this, however, is the continuous monitoring of the differential pressure over the entire service life of the coalescence or particle filter elements. They should be replaced when the energy costs of the increasing differential pressure due to filtration performance reach the investment costs for a new filter element. The indication of the most economical replacement time is provided in the standard version by the economizer or by the economizer (Fig. 6), which continuously measures the differential pressure. The integrated microprocessor evaluates the measured data and compares the increasing energy costs due to the pressure drop with the costs for a new filter element. The most economical replacement time calculated in this way is indicated by light-emitting diodes and — if the digital control and maintenance requirements permit — transmitted to the higher-level control system of the compressed air station.

For larger compressed air volume flows, which require individual solutions with housings adapted to the application (Fig. 7), the question arises whether the measurement results of the DF-UltraPleat standard series can be "scaled up". Wolfgang Bongartz, Engineering Manager at Donaldson in Haan, comments: "Since test rigs are available at independent institutes, even for large filter capacities, we have a reliable database. The structure of the filters has been optimized for the different filter grades. With the validation of the new elements according to ISO 12500-1 and 12500-3, there is comprehensive comparability of the performance data. For the user, this translates into a long service life for the filter element with consistently low differential pressure - the decisive parameter for energy savings."

Extrapolated to the many millions of compressed air filters used worldwide, this is a factor for reducing CO₂ pollution that should not be underestimated, and "green electricity" does not come for free either (Fig. 8).

Only sophisticated filtration technology can achieve the necessary drying of compressed air up to sterile filtration at the point of consumption. The treatment concepts tailored to the application, which meet the requirements of ISO 8573-1:2010 with quality classes 1-2:1-2:1-2 and 0, use dryer systems equipped with UltraPleat energy-saving filters (Fig. 9).

For the economic use of adsorption dryers, the selection of the regeneration process, considering the operating conditions, is of decisive importance. If compressor heat is available, it can be used economically for regeneration in the so-called Heat of Compression (HOC) process. The cycle time here is 3.5-5.5 hours. If process heat is available, a further improvement in the energy balance is possible.

If, for example, a particularly high compressed air quality corresponding to the compressed air quality classes according to ISO 8573-1:2010 is not required for all consumers, this has an impact on the design of the central treatment and the compressed air network. Particularly high-quality levels can then be achieved more economically at the point of consumption by using the Ultrapac™ Smart purification system (Fig. 10). Ten sizes with nominal flow rates from 5 to 100 m³/h are available. The integrated UltraPleat prefilter retains solid particles and suspended solids as well as liquid aerosols (oil/water). The adsorption dryer adsorbs moisture down to a pressure dew point of -70 °C /-94 °F, at 70 % nominal load (standard -40 °C/-40 °F). In the final stage, remaining solid particles down to 0.01 μm are retained in the integrated UltraPleat after-filter.