Cryogenics for cleaner air
11 May 2005
Recent technological developments in the use of cryogenic technology mean that this form of emissions control has become more viable for a wider range of processes, providing a highly efficient means of solvent emissions recovery.
Cryogenic technology has been at the forefront of developments in emissions control since the first cryogenic condensation system in the late 1980s. Today, these are flexible, high performance solvent recovery solutions, capable of meeting the requirements of ever-tightening environmental legislation.
With a successful track record in solvent emissions control, cryogenic technology has continued to evolve to meet the needs of solvent-using process industries, in particular the pharmaceutical and fine chemicals industries. The efficiency of new generation cryogenic condensation systems and their ability to recover even the most difficult volatile organic compounds from process gas streams is helping to secure their industrial popularity.
Among the main developments in cryogenic condensation systems have been enhancements which have enabled them to operate as continuous single unit systems, with just one heat exchanger, significantly reducing their size. In addition, these single unit systems can be controlled easily on-site, allowing process operators to adjust the system to meet variables such as flow rates, temperature, solvent types and loading concentrations. Moreover, the compact, single unit cryogenic condensation systems are now capable of recovering even the most complex VOCs at low gas flow rates, which means they are suitable for a much wider range of processes.
All of these advances have been made possible by the experience and expertise of technology innovators from knowledge gained about VOCs — their freezing temperatures and how they behave.
Single-unit condensation systems can be controlled easily on site, with adaptations for flow-rates, temperatures and solvent concentrations to suit the individual processes
Tightening environmental legislation is the main driver of these technological advances. The EC Solvents Directive (1999/12/EC) was the first major piece of legislation to put pressure on industry to reduce air pollution. The directive established a goal for the reduction of solvent emissions in
Adding to the legislative pressure, the ongoing roll-out of the Integrated Pollution Prevention and Control (IPPC) regime in the
Just meeting the new requirements has proved challenging enough for most solvent-using plants and changes to guidance notes introduced last year mean that some could find they are required to comply earlier than expected. The changes state that ‘substantial change’ to the installation, leading to a significant increase in capacity, or any change resulting in a 10% increase in solvent emissions could trigger regulatory requirements under either the Solvent Emissions Directive (1999/12/EC) or IPPC or both. All solvent-using processes will be required to comply fully with the Solvent Emissions Directive by 31 October 2007.
Adding to this legislative pressure, a new EU-wide pollution inventory, called the European Pollutant Emission Register, was published last year in response to the EU IPPC Directive. The inventory lists a number of specific emissions including chlorinated solvents, a high proportion of which are produced by industries in
And the legislative changes are unlikely to stop here. The EU has forewarned industry of proposals to impose harmonised emissions limits in order to ensure emissions reduction targets are met. These centrally imposed limits would apply across all EU member states and would bring an end to the current self-regulation of emissions limits.
Choosing a coolant
The latest guidance for solvent-using industries, as set out by Envirowise, reminds managers that they should consider various factors when selecting an appropriate emissions control solution. For example, they should consider the nature of the air stream, the properties of the solvent concerned and the specific application. In particular, the advice states that condensation methods of solvent recovery using coolants or refrigerants are highly suitable for organic solvents with reasonably high boiling points. Cryogenic condensation systems using liquid nitrogen are ideal for solvents with lower boiling points, particularly where liquid nitrogen is used elsewhere on site.
This advice points to a potential benefit of the new generation cryogenic condensation systems, which has not yet been fully realised.
In the wake of tightening legislation, many pharmaceutical and chemicals manufacturers are seeking new ways to enhance the overall sustainability of the plant and in particular, to reduce their solvent consumption. High performance cryogenic condensation systems are capable of recovering solvents from process gas streams in a pure form which can potentially be re-used on site. Even where this is not possible, plants could sell it back to suppliers or to other manufacturers.
With so much already achieved since their introduction, where will cryogenic solvent recovery systems take us next? Significant developments have been made in the last twenty years to enhance the efficiency and flexibility of this technology and it will be important for this development work to continue.
In particular, solvent-using process industries must continue to drive efficiency in order to remain competitive and in order to take products to market as quickly as possible. In doing so, they will need to explore and utilise the technological benefits of cryogenic systems to the full.
The pressures of global competition and the need to demonstrate environmental best practice will undoubtedly force further developments in cryogenic solvent recovery technology in the future. The industry will need to work closely with technological and environmental partners in order to profit from more efficient and sustainable solutions in the future. PE
Luc Rijnbeek is Air Products’ global Commercial Manager Environmental Cryogenics.