Drying Desk: Mechanical dewatering -- the other predrying operation
When we speak of predrying, we usually think of a thermal processing operation involving moisture evaporation to make the feedstock more suitable for handling in the downstream dryer. For example, flash drying is often used to remove surface moisture stickiness from block copolymers prior to their entry into a fluid-bed dryer. However, another predrying operation -- mechanical dewatering -- can also have substantial impact on drying efficiency.
Consider a slurry feedstock that contains 75 percent moisture. This would amount to 3 pounds of water per 1 pound of solids or 300 percent moisture content dry basis (percentage of water per dry solids only). If you mechanically dewater this slurry to produce a cake with 33 percent moisture (50 percent dry basis), the evaporation load on the subsequent dryer would be reduced by as much as 83 percent (from 300 percent down to 50 percent). This 5-fold reduction in moisture content would reduce not only operating costs but the dryer size and, thus, your capital investment.