Rotary valve aids food production pilot

Seeking improved performance and reliability from its pilot plant in Fermoy, Co Cork, Moorepark Technology chose Rota Val to supply a custom-designed rotary valve for its spray drier.

Seeking improved performance and reliability from its pilot plant in Fermoy, Co Cork, Moorepark Technology chose Rota Val to supply a custom-designed rotary valve for its spray drier.

Moorepark is a subsidiary of Teagasc, the Irish Agriculture and Food Development Authority, and jointly-owned with a consortium of Irish food manufacturers.

This combination of private and public ownership provides financial support and research resources to maintain the pilot plant to test production processes for the international food industry.

The plant is large enough to simulate accurately commercial food processing.

It is for research, development and pre-commercial scale manufacturing in areas such as dairy products, cultured milk products, dried food ingredients, confectionery, beverages, sauces, dressing and dips, yellow fat spreads and margarines and bioprocessing including protein separation, fermentation and enzymatic conversion.

The plant consists of six self-contained, but interlinked, operating units - the cheesemaking unit, separation technology facility, wet process unit, fat technology unit, evaporation and drying, and food technology applications unit.

Around 120 manufacturers worldwide use the plant.

One area that needed upgrading was the evaporation and spray drying complex.

Sean Tuohy, General Manager, said: "We became concerned that the performance of a component of our spray drying plant was deteriorating and reaching a point where it would no longer operate to an acceptable standard".

"A rotary valve installed in the lean phase conveying system had been subjected to unusual and extreme conditions, and was beginning to cause problems".

The valve controlled material flow from the recovery cyclone into a 50mm pneumatic conveying pipe and had become unreliable with leakage and frequent pipe blockages.

Rotary valves are normally specified according to the type of material to be handled, their abrasive characteristics, thoughput and conveying density.

In this application, Moorepark had no definitive data because the material to be conveyed could be anything from fine, dry powder to sticky, fatty materials and the particle size could vary considerably.

"Our need was for a valve that could handle an unusually wide range of materials," said Tuohy.

In a normal production environment, the valve would be handling a consistent range of materials with well-defined characteristics.

It would be cleaned down at regular, but not necessarily frequent, intervals, and would be subject to standard maintenance procedures.

"In our case, none of this applied," he said.

"The need to supply a reliable service, to provide a wide range of pilot plant facilities, and to meet modern commercial pressures imposed a regime of frequent product changes, consequent clean-in-place procedures, and full strip down and clean out-of-place activities at frequent intervals".

"When considering the need to replace the original rotary valve, we looked at the problems we had with the existing installation".

"These included excessive product escape through worn seals, and a build up of material and blockages in a diverter valve about 3m downline from the rotary valve".

Rota Val Managing Director, Ian Blackmore, said: "When we examined the system, we discovered that the throughput required was very small, consequently the system had been designed around a conveying line of only 5cm diameter whereas the outlet of the cyclone and therefore the inlet of the rotary valve needed to be 250mm diameter to prevent bridging when handling the more difficult products".

"Originally it was expected that, as the throughput was to be controlled by the feed into the cyclone, the only function of the rotary valve was to act as an airlock".

"Consequently, a standard blowing seal valve had been incorporated: this had a discharge port size of 100mm requiring a taper adaptor to reduce down to the 50mm conveying line".

"The blowing seal configuration was out of balance for the needs of the system as a whole; principally the large rotor (300mm diameter) and 100mm entrainment trough presented such a large cross sectional area that the 50mm conveying line velocity was well below that needed to ensure good and consistent product entrainment".

"There was a tendency for high-fat products to stick within the rotor and not be swept clear by the conveying air until such time as the air velocity had increased to a point where pick-up occurred, when the product tended to break away in lumps giving rise to the blockages experienced".

Discussions between Rota Val and Moorepark established that a customised valve would give the best results.

So Rota Val developed a hybrid valve incorporating features of the established fast-clean valve design with some of the features of the Hypergienic range normally supplied to the pharmaceutical industry.

The result was a wholly fabricated stainless steel assembly incorporating a reduced capacity 250mm rotor with scalloped pockets; the overall design reducing the entrainment cross sectional area by some 75%.

The valve included 50mm pipe connections providing direct purging of the rotor pockets.

These ensured that the pick-up velocity is always sufficient and directed to provide reliable and uniform entrainment with even product distribution in the valve and pipe system.

Now installed and working for two years, the valve has shown it can cope with continuous operation, frequent strip-downs and conveying an unusually wide range of products.

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