Plasma technology provides cleaner, greener air

The market forecasts for standard air filtering technologies are predicted to reach US$7bn (€4.4bn) by 20101 and there is increasing global demand for more efficient and innovative air purification systems. With a technology portfolio enabling reduced capital and running cost solutions across a wide range of applications, Plasma Clean aims to be at the forefront of this clean, green air revolution.

The company provides technology-based air purification systems that use non-thermal plasmas. Think of non-thermal plasma as a “sea of energy” through which polluted air passes. It is this energy that converts harmful airborne contaminants into harmless by-products.

The energy demands, are surprisingly low and, unlike other air purification technologies on the market, the energy efficiency actually increases as the pollutant concentration decreases. This is particularly important for applications requiring ultrapure air where tolerances are in the sub-ppm to ppb range.

The technology was conceived and patented at the University of Manchester and commercialised by the university’s intellectual property company UMIP. Since 2005, Plasma Clean has tested prototypes across a range of industrial, commercial and domestic environments. With a major UK distribution deal in place, the company is approaching partners for potential germicidal, VOC and odour abatement applications.

At the core of the technology is a simple cassette and power supply (see above), which can be incorporated into Plasma Clean’s partner companies’ existing or new product lines. With a simple but robust construction, the cassettes can be applied to a range of air cleaning and filtration needs across a variety of sectors – including semiconductor processing, industrial, medical, aircraft, military, environmental and domestic.

Plasma is created by subjecting a gas to an electrical field, created by a high voltage current or discharge (see figure 1). The electrons from the gas atoms or molecules are removed and gain energy. These energetic electrons collide with the atoms and molecules of the gas creating further excited states and ions, causing molecules to break apart, forming free radicals and reactive fragments. When this system is used in air, ozone is produced – a strong oxidising agent that reacts with the pollutant molecules, further enhancing plasma destruction efficiency.

No build-up

Plasma contains a “soup” of highly reactive radicals, electrons, atoms, molecules and ions created by a discharge. When a pollutant gas is passed through plasma, it is pulled apart and broken down into less harmful substances such as carbon dioxide and water. There is no build-up of contaminants as are normally seen in activated carbon systems. Destruction efficiency is maintained, and as the cassettes convert pollutants at source they do not create costly and regular landfill disposal problems, reducing environmental impact. And, unlike thermal oxidisers, plasma technology becomes more energy efficient at lower pollutant concentrations.

Non-thermal atmospheric pressure plasma can be used to destroy pollutants in waste gas streams and volatile organic compounds (VOCs) from processing plants or odorous molecules from landfill sites, food processing plants and animal houses. It can do this at lower capital cost, as well as lower maintenance and running costs.

Rather than competing with existing air purification technologies, there is a great degree of synergy because Plasma Clean systems operate best in the space where activated carbon and thermal oxidisers are simply inefficient (figure 2). This simple fact is driving the strategy of partnering through licensing or joint venture with organisations that have the ability and drive to bring Plasma Clean’s technology to the chosen market, whether VOC and odour abatement, or germ control in industrial, commercial or domestic applications. This is the best option to maximise the potential of this system.

The company’s first product, Xtract, is aimed at odour and infection control in commercial and healthcare premises, that require a deep clean of the room or ductwork.

The company has recently signed the first of a series of distribution agreements with AAC Eurovent, a Midlands-based manufacturer and supplier of VOC and odour control equipment. With AAC Eurovent, Plasma Clean is targeting commercial kitchens and in this application the Xtract odour neutraliser releases charged ions and activated oxygen into the kitchen extraction system, where it reacts to reduce odours, smoke and grease build-up. The system has been successfully trialled and is now being introduced into restaurants and food outlets throughout the UK, including some well-known high street food chains.

The benefit of the Xtract odour neutraliser compared with UV systems is that the unit sits outside the air stream so contributes no back pressure; in addition, the plasma components do not get coated with grease and smoke particles so the unit maintains its efficiency over time. This means significantly reduced maintenance, and has the added benefit of significantly reduced power consumption.

Emission control

Plasma Clean has also created a hybrid Plasma Catalyst VOC oxidiser system to control VOC emissions from light industrial applications such as electronics assembly and printing applications. This has been successfully trialled in a printed circuit board assembly plant to reduce emissions of isopropyl alcohol from individual soldering stations.

This product application was developed for a customer who was falling foul of the Integrated Pollution Prevention and Control (IPPC) regulations but because of its flexible production approach, each individual station required a separate VOC abatement system. This ruled out a thermal oxidiser approach due to the high capital cost.

Activated carbon was also considered by the customer, but the high carbon usage would mean a complete changeover every 10 days; the associated landfill disposal costs would also add to the cost burden. By incorporating a plasma catalyst hybrid system, the emissions were brought within the permitted limits and, as a result, Plasma Clean will be installing several more systems into the plant over the next few months.

Tests carried out on the destruction of toluene2 illustrate the VOC removal efficiency at low energy consumption. In this example (see Figure 3), simply by adjusting the energy applied to the plasma cells, or ‘deposited energy density’, the amount of VOC removed by the system can be controlled. Figure 3 shows that the energy required to remove 25ppm toluene is less than that required to remove 70ppm toluene, so by extrapolating this data it is easy to see the efficiency of these systems in the sub-ppm to ppb levels of VOCs.

Plasma performance increases as the concentration of the airborne pollutant decreases because the proportion of ions and free radicals in the plasma cassette increases relative to the pollutant; put more simply, there is more energy per molecule of pollutant.

Figure 3 also illustrates that the system is switchable, so that there is instantaneous VOC and odour control – in contrast to thermal oxidisers, which require high energy inputs over a period of time before reaching their operating temperature. Plasma Clean systems don’t have such a lag phase because they don’t need to get to temperature to operate, being truly non-thermal in nature.

Plasma Clean technology for air purification provides an effective abatement solution. But it goes one step further by minimising disposal costs and environmental impacts associated with standard air purification and conditioning technologies.

All Plasma Clean products include the following features:

• High efficiency removal of target pollutants
• Low capital cost and running costs
• No build up of hazardous wastes
• Negligible maintenance
• A small green footprint
• Absence of NOx, which is generally common in plasmas

Arguably the most efficient air purification technology on the market, plasma offers technical as well as customer benefits. Plasma systems are easy to install, scaleable according to customers’ needs, and require very low maintenance.

Plasma Clean systems avoid the need for regular maintenance and cartridge refills. And in a world increasingly aware of environmental responsibilities, plasma-based air purification systems do not create costly disposal and landfill obligations.