The W6 Chemical pilot plant is used to provide ... - GEA Messo PT

Niro CrystallizationHighly Efficient Product Crystal SeparationSuspension CrystallizationThe suspension-based crystallization process operateswith an extremely large number of crystals providing amassive growth surface. Since the total surface absorbsthe under-cooling of the solution, the resulting overallgrowth rate is very slow. This near ideal growth rateallows the formation of pure crystals in a single step.Product Crystal SeparationComplete separation of the pure crystal from the impuremother liquor is required. This is accomplished within theunique Niro Purifier - our proprietary wash columntechnology.Highly Efficient Product Crystal SeparationThe massive surface needed to create near ideal growthconditions requires an efficient washing process toremove the impure liquid from the crystal surface.High purity is possible with the Niro Purifier because: the crystal is already pure the counter-current wash uses pure melt the crystal bed is more than 50 cm height.The unwashed crystal mass is roughly 70-80% crystallineproduct with the remainder being the impure liquidmother liquor. As the pure wash liquid (product melt) isforced through the porous crystal bed it will effectivelywash away any impurities in the unwashed part of thebed and recrystallize as new crystal product uponcontacting the relatively cold crystals.This configuration provides highly efficient contactbetween crystal and wash liquid and allows sufficienttime to recrystallize the wash liquid within the packed bedthereby essentially eliminating product losses.The heat released by this crystallization warms thesurrounding crystal mass. This is a self controllingprocess where the recrystallizing wash liquid will releaseenough heat so that the crystals will reach the equilibriumtemperature of the pure product.This recrystallization zone, generally called the washfront, is a relatively narrow portion of the column. Thiswash front marks steep gradients in temperature,concentration and porosity.No wash liquid is lost to the filtrateAfter completing its task as wash liquid, the new crystalproduct is transported together with the now warmercrystals back towards the pure wash circuit.A reciprocating piston/filter draws acharge of crystal slurry into TheNiro Purifier and compresses thischarge into a compact bed ofcrystals while allowing the motherliquor to leave through the filter. Thescraper starts and the piston/filtercontinues to force the existingcrystal bed through the column asthe scraper disintegrates the bed atthe opposite end of the column.The pure melted product is forcedcounter-current to the crystal bedflow. The porous bed provides aunique environment where the puremelt contacts the significantly coldercrystals mass and results incomplete recrystallization of thewash liquid. This counter-currentwash flow effectively removes theimpurities remaining around thecrystals and returns the wash liquidas pure product crystals.The washed crystal bed isdisintegrated by a rotating scraper.The crystals are then reslurried withcirculating pure melt and melted in aheat exchanger. The final product isremoved through a control valve.Restricting this discharge will resultin an increase in the pressure of thecirculation loop which drives thewashing action in the crystal bed.Crystallization provides the heat required to warm upcrystals from T c to T wWash liquid supplyTS09.082008GEA Niro PT B.V.