By Matt Hale, International Sales & Marketing Director, HRS Heat Exchangers
Scraped surface heat exchangers (SSHEs) have been used for difficult heat transfer applications involving viscous fluids or where fouling is an issue, such as sludge evaporation.
The HRS Unicus Series is specifically designed to provide the improved heat transfer of a traditional SSHE but is suitable for a range of wastewater and sludge applications including digestate pasteurisation and sludge evaporation. Different scraper designs have been developed, meaning that every application can be handled in the most efficient yet gentle way possible.
The design uses a patented stainless-steel scraping mechanism which moved hydraulically back and forth within each interior tube. The movement performs two key functions: it minimises potential fouling by keeping the tube wall clean, and also creates turbulence within the material. Together, these actions increase the rate of heat transfer in the material, creating a highly efficient process which is ideal for viscous and high fouling materials.
Since they are controlled separately, the speed of the scrapers can be optimised for a particular product being processed providing high levels of heat transfer. The Unicus Series has proven useful in treating the digestate from anaerobic digestion processes where the texture and consistency are particularly challenging.
Each Unicus SSHE consists of three elements: a hydraulic cylinder and power pack (although in smaller units a pneumatic cylinder can be supplied instead), a separation chamber to ensure hygiene and preserve product separation from the motor, and the heat exchanger itself. The heat exchanger consists of a number of tubes, each of which contains a stainless-steel rod to which the appropriate scraping elements are fitted. Using a range of materials including Teflon and PEEK (polyether ether ketone), these provide different internal geometry setups according to the application, such as 120° scrapers for large particulates and 360° scrapers for viscous fluids without particulates.
One area where the Unicus Series excels is in evaporation applications, where the prevention of fouling is particularly important. HRS has a specific version of the Unicus for use in evaporation units where volume reduction of the material is essential and Unicus evaporators can be used in multi-effect setups or in combination with mechanical vapour recompression.