Nano fibre could cut compressed air energy costs

London - Technology company Nano-porous Solutions Ltd (NPSL), based in Gateshead, has won a Carbon Trust grant to develop and commercialise a hollow fibre-based system that could provide the compressed air industry with more energy efficient ways of reducing its environmental impact.

NPSL, which was set up by Colin Billiet, former chief executive of domnick hunter group,  was awarded £250,000 under the Carbon Trust’s Applied Research Scheme to develop its technology. This is based on a new regenerative adsorbent hollow fibre, which could potentially halve the energy consumption of conventional compressed air treatment systems.

Compressed air generation accounts for 10% of the total electricity used by UK industry, with up to 20% of this energy taken up by air treatment systems that remove contaminants in compressed air  before use,  explains Neil McPherson, business development director for NPSL: “Given that there are around 85,000 air compressors currently used in manufacturing processes today, even if only a fraction of these were to convert to the new technology, the energy savings would be enormous."

The recently formed company said it expects to employ up to 20 people within the next 18 months. The ramp-up is to include pilot-scale manufacture of the fibre, which was originally developed at the University of Bath. NPSL then plans to move into commercial-scale manufacturing for a worldwide market.

"Applications for the nano-porous adsorbent hollow fibres are numerous and our work is already attracting a huge amount of interest from many sectors, including the compressed air industry," said McPherson. “Key markets will include the pharmaceutical, health care, environmental, volatile organic compounds recovery/recycle, life support, medical, and food & beverage sectors.”

The technology

Compressed air is widely used throughout manufacturing industries as a safe and reliable source of energy. However, the quality of the compressed air delivered by the compressor is unsuitable for industrial use without treatment to improve its purity. Treating the compressed air generally involves filtering it, to remove dust, oil and water.

One method for separating out these different components uses adsorption, a process whereby specific molecules (the adsorbate) adhere to the surface of a highly porous solid (the adsorbent) by electrostatic and molecular forces. The adsorbent is normally made into granules or beads, which are used to form packed beds through which the adsorbate is passed and the process of adsorption can take place.

The new technology uses the same base adsorbent material but is extruded into nano-porous adsorbent hollow (tubular) fibres, which can be single or multi layered depending on the application. It is highly porous and provides a lower resistance for the transport of the adsorbate, and a much higher surface area to volume ratio (around 3-5 times more), allowing the adsorption process to be far more effective. The result of this is a much more efficient filter with subsequent lower energy losses.

Research shows that the adsorption performance of the multi layer hollow fibres is far better than that of an equivalent packed bed of spherical zeolite/carbon adsorbents with around one hundredth of the pressure drop – one of the main causes of energy use in air treatment systems. This allows the adsorption units to be installed in ductwork or in limited space without the need for additional gas compression.

The unique hollow fibre structure also overcomes some of the disadvantages commonly associated with granular or spherical adsorbent materials, such as the risk of settlement, attrition, channelling, by-pass, hot-spots and the deterioration of adsorption performance due to poor heat loss from the bed and the by-pass of the gas being processed.

A further advantage of the hollow fibre is that it enables faster regeneration times, which could reduce the length of the heating/cooling cycle from several hours to a matter of minutes. Another energy saving benefit to the new technology is that due to the compact nature of the new design, smaller compressor units are required – meaning less power is needed.

The new hollow fibre technology can be applied to the recovery and removal of many types of gases, liquids and particles and is suitable for high temperature applications and use in harsh environments. Its special layering structure also means that it can be configured according to the components that need separating and the specific application, claims NPSL.