Cryogenics moves into the future

Diana Raine, business manager for cryogenics in Europe at Air Products discusses the role of cryogenic condensation technology in VOC recovery.

As legislation tightens and industries look for ever more efficient technologies to deal with emissions control, a wider range of installations than ever before are now discovering the benefits of cryogenic condensation technology as a flexible, highly efficient and cost-effective alternative to more traditional abatement techniques.

Cryogenic condensation technology has been around since the 1980s and was first used as part of chemicals and pharmaceutical industry processes in the late 1980s. The main benefits were its efficiency in recovering solvents although it was considered most suitable for high gas flow installations and in the early days was not necessarily considered the most flexible option.

Recent technological developments have changed all that and cryogenic condensation technology is now winning recognition among process industries as the only technology capable of recovering even the most difficult solvents, at low flow rates. It is also regarded as a highly flexible solution, which can be adapted to deal with different gas mixes easily on-site. Another important advantage of the system is its use of liquid nitrogen as the refrigerant agent for the condensation process. The low temperature of the liquid ensures easy compliance with recovery targets. In fact, the liquid nitrogen used to recover the solvents can itself be recovered into a separate vessel and reused elsewhere around the plant in order to maintain safe processing in an inert environment.

Technological advances

While solvent-using process industries have since come to appreciate the benefits of cryogenic condensation methods above other traditional abatement techniques such as activated carbon and liquid absorption systems, it is interesting that few have yet chosen to take advantage of the method as a means of recovering solvents for reuse. This could be for many reasons. For example, historically, processing industries have focused their attention on the recovery and disposal of pollutants and not necessarily regarded these substances as having any cost-reducing potential. Clearly, relatively recent developments in the efficiency of cryogenic condensation methods mean that the reuse of recovered solvents is now a viable option.

One of the main technological step forwards for the cryogenic condensation method came during the 1990s, at a time when tighter legislative requirements for solvent recovery were being introduced and new targets set. The dual freeze-thaw system was developed - a highly efficient system of solvent recovery - although it needed two separate condensation/freezing units, which meant it was fairly large and not cost-effective for low gas flow rate installations.

Today, cryogenic condensation systems have evolved to become a more flexible and cost-effective option for all solvent-using installations. The latest cryogenic technology now operates as a single unit continuous system, which is more compact and is capable of achieving the toughest zero emissions targets, even at low-gas flow rates. The simplicity of the new systems means that mixes and controls can be simply adjusted on site.

Tougher targets

While the main driver for the technological advances made in cryogenic condensation technology to date has been the need to provide a more efficient and cost-effective emissions control solution, it is impossible to ignore the impact of changing legislation.

The EC Solvents Directive (1999/12/EC) first put the spotlight on air pollution, setting out its goal for the reduction of solvent emissions in Europe by 67 per cent by 2007. Ever since take up of the directive in the UK, industry has been seeking new ways to reduce solvent use and minimise emissions, using more efficient recovery methods. Adding to this pressure, the roll out of the Integrated Pollution Prevention and Control (IPPC) regulations in the UK are encouraging industry to adopt best available technology (BAT) in order to reduce their impact on the environment.

Against this tightening legislative backdrop, it is interesting that, until now at least, emissions limits have been set by industry and emissions control has been effectively self-regulated. The question is how long can this last? At the moment, self-regulated emissions limits are 20mg/m3 for Class 1 solvents - a benchmark set by TA Luft, the German technical directive for air pollution abatement. In the near future however, it is likely that emissions limits could be set even lower, possibly as low as zero and solvent-users are already working towards this goal.

Recovery and reuse

While zero emissions limits and emissions recovery are the main focus for solvent-using industries, there is also a new area of opportunity opening up, which some installations are already considering as they aim to develop sustainable processes.

The latest, state-of-the-art cryogenic recovery systems are not only capable of recovering even the most difficult solvents to zero emissions limits, they are also capable of recovering these substances in such a way that they can be stored and reused.

In the future, industry and those involved in developing and implementing emissions control technologies must work even more closely together. By co-operating more closely at the start of any production project it will be possible to assess the total emissions control requirements of the process in order to optimise efficiency and create a sustainable solution.



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