Energy efficient filtration
August 1st 2007

The new Ultra-Filter industrial range from Donaldson,launched recently at the Hannover Fair,has made energy efficiency a priority.Tim McManan-Smith reports

ith nine design sizes, the new Ultra-Filter covers the performance spectrum from 35 to 1100m3/h flow rate and therefore the actual compressor outputs between 2 and 120kW.

Efficiency gains are achieved through a reduced pressure drop across the filter housing.This is due to the use of new media for the filter and coatings and newly designed ducting that encourages better flow through the filter housing.

Theses advances are patented by Donaldson and signal a major achievement in balancing the diametrically opposed aims of energy efficiency and high levels of filtration.

The question is: how to achieve the desired quality level stipulated in the ISO 8573-1 Standard, most economically? However, it is not an issue of direct energy consumption – after all the filtration task does not require connection to the power network. It is the indirect energy consumption which arises through differential pressure that is the important factor here.

Traditionally, if filters are effective, then they have a high pressure drop that increases the energy used by a compressor, but the new design enables lower pressure drops while retaining necessary levels of filtration.This differential pressure has consequential costs.As a rule of thumb, the user has to reckon with up to 10 % additional energy consumption for 1 bar additional differential pressure with a 7 bar system. Put into figures:With 100kW installed compressor output, utilisation of 8,000 annual operating hours and energy costs of 0.08 cent per kWh, this causes additional costs of € 6,400 per annum.

Improved flow control in the housing Optimisation of the flow control was an important objective for the Ultra- Filter developers: In order to minimise differential pressure in the housing, the possible 'soft' transitions and direction changes of the flow within the housing were considered in the design.

Extensive model test series and flow analyses formed the basis for this.

The core: new filter elements The targeted air flow into the element guarantees a turbulence-free, uniform flow to the filter medium – claimed to be a first in compressed air filtration technology. In addition, a new filter medium is used in the filters which repels oil and water at the surface, thus keeping a large cross sectional area available for the retention of particles and separation of liquid aerosols from the compressed air condensate.

The media: finest fibres The arrangement of the filter medium in the support sheath is also new.A pleating procedure is used here built on the optimisation of pleating height and number of pleats.This ensures that the flow area is kept as large as possible; at the same time a highest possible particle intake capacity is achieved.The latest media with the finest fleece from borosilicate fibres is used here.This fleece significantly aids low differential pressure over the total filter service life.At the same time Donaldson has succeeded in integrating the coalescent sheath within the stainless steel support sheath,necessary for the drainage of retained condensate droplets.For the practical operation of a filter this means that the coalescent sheath can not detach from the support body.

Pressure loss halved Pressure loss can be reduced by around 50 % through interaction of the design measures described here.

Common market filters demonstrate a pressure loss of 450 to 500mbar in wetted condition, with the new Ultra- Filters this is only around 250mbar.

With a flow rate of 1100m3/h the user saves more than € 1500 per annum on energy costs, if the differential pressure is just 200 mbar lower – severalfold the cost of the whole filter.The investment pays for itself within a few months even for replacing an existing filter housing.

Transparent costs The new Economizer integrated in the housing, enables continuous recording of the differential pressure. An integrated processor compares the associated higher energy costs with the costs of the filter element.The Economizer's program calculates the most costeffective replacement time for the filter element and LED's then signal that filter element replacement is necessary.The calculation looks at element cost which decreases over time, against energy cost which increases over time. Between these two figures there is an ideal time to change the filter that offers the best value for money. In addition, the Economizer enables the differential pressure signal to be called up via an analog interface (4-20mA).