Membrane dryers in the spotlight
25 January 2013
The benefits of desiccant dryers and refrigeration dryers are well publicised. There is a third solution, however, that Steve Riley, general manager of Beko Technologies in the UK and Ireland, believes is often ignored or
When a plant engineer has to buy a compressed air dryer his first consideration will be what dewpoint is required and this will depend on the application; specifications of machinery using compressed air will guide the engineer as will codes of practice such as BRC/BCAS for the food industry. If a negative dewpoint is required then a desiccant dryer will be selected. The genre is likely to be well known to the engineer and will attract a significant capital and running cost particularly if a lower capital cost, heatless dryer is selected.
An alternative scenario is for positive dewpoint at typically 2Â° C and, again, an engineer will know that a refrigeration type dryer will handle this application with relatively low capital and running cost but that he must take care not to have pipework going below the dewpoint temperature.
A third solution is the membrane type dryer. Beko Technologies offers its Drypoint M range of membrane dryers alongside its Everdry and Drypoint RA, desiccant and fridge dryers.
I was amazed at how many Drypoint M's were being sold when I joined the company. A little research told me that 20,000 units had been sold since launch, in the UK alone. I guessed that many purchasers were original equipment manufacturers because the main benefit I had in my mind was the very small footprint. I knew also that some compressor manufacturers had a packaged unit which included a membrane dryer but I couldn't for the life of me guess the diversity of applications.
Research also revealed overall cost as a reason for selecting Drypoint M. This needs some explanation as what tends to put most engineers off is waste and it is a fact that membrane dryers lose a quantity of compressed air in purge loss. However this is not fixed and Beko's sales people have software which enables the choice of a low capital cost, higher purge loss unit or a higher capital cost and lower purge loss unit. I wanted to understand what maintenance revenue I would get from all these units. It was an unbelievable number - zero, and it is not such a short-lived product that if a problem should occur it would be more economical to throw it away. It is possible to destroy the membrane by having too much liquid ingress but Beko's design team has produced a dryer with close coupled separator and drain to protect against this eventuality. In fact there are no wearing or replaceable parts.
I have used the table below to show why I believe that it is a mistake, certainly on smaller flows, to disregard the option of a membrane dryer.