Our scraped surface continuous crystallizer is actually a double-pipe heat exchanger, but quite an unusual one, because it generally performs as a cooling crystallizer. Heat transfer occurs across the inner pipe wall, with cold fluid outside, and process fluid inside.
Our scraped surface continuous crystallizer consists of multiple double pipe elements, generally with 6,8,10 or 12 inch nominal diameter inner pipes and larger diameter outer pipes. The annular space between the inner and outer pipe contains a circulating cooling fluid. The process fluid carrying inner pipe contains multiple rotating scraper blade elements.
As cooling occurs, crystals tend to form on the inner pipe wall. The rotating blades mix the process fluid, scrape the inner pipe wall and remove crystalline deposits which would inhibit heat transfer. The majority of the crystallization takes place in the bulk of the fluid, as opposed to the wall, thus allowing growth of easily separable crystals. A typical commercial sized installation will consist of several double pipe elements, each with a length of 20 to 40 feet, connected in series. This provides a flow path with a high length to diameter aspect ratio which results in a close approach to plug flow that is important in many crystallizations.
When compared to other methods of crystallization, scraped surface continuous crystallizers offer:
• Smaller equipment: less expensive installations, less floor space, less operator labor
• Better process control: fewer process upsets, lower peak utility demand
• Modular design for ease of expansion
• Simple, self-contained construction with minimal instrumentation and auxiliary equipment
• Extended run times between hot washings
• Higher process fluid to coolant temperature differences
• Extremely wide operating temperature range (-75C to +100C)
• Use with high solid percentages (as high as 65% solids as slurry)
• Can be used at high process fluid viscosity (10,000 cp or higher)
• Plug flow: easy conversion from batch operation, countless possible time-temperature patterns