The rotating drums are heated with steam at prescribed pressure and condensate drainage is ensured. The feed from feed vessel is admitted in the gap between the drums. The layer of the feed formed over the surface of the drum is scraped out as dry material by the scraper blade. The dry material falls into the discharge bins and may be collected periodically. The vapours exiting out of enclosure are condensed in the condenser and the vapour condensate is collected in the receiver. The entire process is carried out under vacuum.