Contact drying in the food industry

Three years ago, All­gaier Process Tech­nol­o­gy pre­sent­ed the disc dry­er with a revised design, which had already proven its worth in the chem­i­cal indus­try for sev­er­al decades. Fol­lowed by the mar­ket launch of a new dry­er mod­el for the food indus­try this year. The CDry is a steam-heat­ed disc dry­er oper­at­ing on the prin­ci­ple of con­tact dry­ing. Due to the large heat trans­fer sur­face in a small space and the robust mode of oper­a­tion, it has proven itself in recent years for dry­ing solids-laden liq­uids in the fine chem­i­cals, pig­ment, ceram­ics and fer­til­iz­er indus­tries and even in waste­water technology.
With­in this devel­op­ment project, the CDry was raised to the cur­rent stan­dard of the Machin­ery Direc­tive for food pro­cess­ing machines. For this pur­pose, the design of the rel­e­vant sys­tem com­po­nents was imple­ment­ed in a hygien­ic man­ner, con­sid­er­ing the guide­lines of the Euro­pean Hygien­ic Engi­neer­ing and Design Group (EHEDG). The All­gaier disc dry­er thus meets the demand­ing hygiene require­ments of the food industry.
Hygien­ic design
The CDry food looks very much like the chem­i­cal ver­sion of the dry­er. While the dis­tinc­tive and strik­ing appear­ance has been large­ly retained, the CDry food impress­es in detail with the hygien­ic design of all parts that come into con­tact with the prod­uct. The discs have a diam­e­ter of 900 mm, cre­at­ing a dry­ing area of around one square meter per disc. The discs are heat­ed with sat­u­rat­ed steam so that a max­i­mum tem­per­a­ture of 140 to 145 degrees pre­vails on the disc sur­face. To ensure that the prod­uct to be dried is not dam­aged, the dwell time on the sur­face can be con­trolled by the speed of rota­tion of the discs. Depend­ing on the prod­uct and resid­ual mois­ture con­tent, out­puts of 30 to 40 kilo­gram per square meter of sur­face area per hour can be achieved. The discs can be treat­ed accord­ing­ly in terms of their cor­ro­sion and abra­sion resistance.
Func­tion­al­i­ty
The sus­pen­sion to be dried is applied in excess to each side of each disc in the process cham­ber of the dry­er. After about one disc rev­o­lu­tion, knives scrape off the dried prod­uct. This falls out of the dry­er hous­ing via the prod­uct dropout chute and can either be col­lect­ed in a col­lec­tion con­tain­er or trans­port­ed away by oth­er equip­ment. The vapors are dis­charged from the dry­ing cham­ber. When chang­ing prod­ucts, the inte­ri­or of the dry­er can be com­plete­ly cleaned by the inte­grat­ed CIP sys­tem. The com­pact dry­er is designed for con­tin­u­ous oper­a­tion and, unlike roller or spray dry­ers, has a small foot­print. The knives for scrap­ing off the dry sub­stance can be eas­i­ly replaced via a quick-change device. Typ­i­cal­ly, they have a ser­vice life of 1–2 months, but can be resharp­ened sev­er­al times. The dry­er can be adapt­ed indi­vid­u­al­ly to all pos­si­ble prod­ucts. Dry­ing equip­ment for test­ing is avail­able at the head office in Uhingen.