The ExStream way to remove solvents

With increasingly restrictive legislation on solvent emissions to atmosphere, industry must limit or remove the pollutants they release. A new cryogenic condensation technology may help do just that. Beverly La Ferla reports.

Organic solvents are a class of chemicals commonly used in a large number of industrial processes. They are fundamental to the production of pharmaceuticals by providing the medium in which reactions take place. They also separate desired chemical products from unwanted ones, maximising drug purity. In the paint and coatings industry, their function is to facilitate the application of a film of paint, ink or adhesive onto a surface or to clean surfaces prior to coating to remove grease or soil. They can also be used in food applications to extract oils and in wood treatment processes.

The EU Solvent Emissions Directive (1999/13/EC) came into force in 1999 and was translated into national legislation in March last year. It aims to reduce the emissions of volatile organic compounds (VOCs) within certain processes and industrial installations. VOCs have been targeted because of the role they play in the production of ground level ozone and other photochemical oxidants which are harmful to human health and the environment. In addition, some VOCs are inherently hazardous. The overall objective of the Directive is to reduce VOC emissions from Member States by 57 per cent of the 1990 emissions figures.

Due to the volatility of VOCs, they are mainly emitted directly or indirectly into air, generally in the form of organic compounds having undergone physical or chemical transformation. The Directive states that 'all installations must comply with and demonstrate compliance to emission limit values in waste gases, fugitive emissions values and total emissions limit values'. With both European and national laws breathing down manufacturers' necks, industry must find a way to comply on all counts or have their production operations suspended pending compliance.

Cryogenic condensation

One way to remove solvents is to cool the process gas using liquid nitrogen. This causes the solvents in the gas stream to condense out so in effect the gases are stripped of solvents.

Air Products, an international supplier of industrial gases as well as technology and services, has been involved in this area from the beginning. Diana Raine, business manager for cryogenic applications, explains, "Cryogenic condensation to recover solvents has been used for many years but has recently become a big topic with the enforcement of the Solvent Emissions Directive. At Air Products we are always looking for ways that we can use technology to help users find solutions to solve problems like this.

"With the legislation becoming more and more stringent, there has been a greater need for industry to reduce emissions still further and ensure that they continue to do so in the future."

With this in mind, experts in cryogenic technology at Air Products started to develop a new process that would meet and exceed any emissions targets and remove almost any solvent or solvent mixture, including 'difficult' solvents such as benzene, xylene and acetonitrile, at a lower cost than conventional technologies. "Through consultations with industry, we learnt that there was a requirement for low cost cryogenic abatement technology to deal with low process gas flows," says Diana, "It works on the same principle of cryogenic condensation that our established offering, CryoCondap, does but it is the next step in recovering solvents and does not require as much capital outlay."

CryoCondap ExStream shares the same principle of cooling the gas stream to condense out the solvents with other technologies but it is different in that with ExStream the liquid nitrogen comes into direct contact with the process gases. The solvents form ice crystals and freeze onto filter elements which are periodically cleaned to remove them.

"One of the major advantages of using ExStream is that the solvents can be extracted and then recycled," says Diana, "It can also be used for almost any solvent or solvent mixture including 'difficult solvents' which behave differently to other solvents."

Emissions limits

Another benefit is the inherent flexibility built into the system. ExStream can be used as a stand alone system or retrofitted onto an existing system which no longer meets legislative demands. Currently, TA-Luft emissions limits (which are followed as a guideline by most countries) are 20mg/m3 for VOCs in Class 1 and 100mg/m3 for VOCs in Class 2, but these limits could be lowered still further in the coming years.

"The ExStream meets and beats all existing emissions legislation," says Diana, "and will continue to do so even when tougher legislation comes into force. Many of our customers are global players. They are looking for solutions that will help them meet emissions requirements today with a view to the future."

The ExStream technology has been in development for the last three years and will be launched this month in the UK. "Primarily, we're looking at solvent users in the chemical and pharmaceutical industries but the system is so flexible that it can be used for almost any solvent in any type of industry," says Diana, "We want customers to understand that Air Products doesn't just supply the gases - we supply the technology, expertise and equipment too."



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