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Synthetic food grade lubricants in atomisers
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What are atomisers?
Atomisers are widely used throughout the food industry in the process of spray-drying. The process involves the conversion of a liquid, slurry or low viscosity paste to a dry powder solid. This is achieved by using a hot air stream to atomise the fluid and evaporate the water. Atomisers are used in the drying or dehydration of a number of food and dairy products including baby food, coffee, flavourings and soup mixes.
How do they work?
Depending on the mechanics of the atomiser, the liquid feed is atomised by either a single-fluid nozzle, a two-fluid nozzle or a rotary atomiser (a spinning wheel). Each device performs the same atomising function, but can be used to produce different particle sizes. The atomisers can also be used in different operations and can accommodate variations in the volume and consistency of the liquid feed.Nozzle spray-dryers atomise by producing high pressure hot air streams in the atomiser chamber. The single-fluid spray nozzle allows more versatility in terms of positioning the spray's direction. Two-fluid spray nozzles are often used for more viscous or abrasive feeds and are able to produce the necessary additional atomisation to form smaller particles. Nozzles are generally used to spray-dry liquid feeds that contain a high percentage of fats such as dairy products. The versatility of the nozzles allow the particles to be spray-dried with a lower fat content than if they were dried in a rotary atomiser.
The rotary atomiser can accommodate high volumes and production rates. lts spinning wheel can reach more than 300 foot per second and generates a centrifugal force which disperses and atomises the liquid feed. The speed of the wheel is used to control the particle size.
Nozzle and rotary atomisers operate using a number of moving parts which come into close contact with the liquid feed being atomised. The different types of atomisers both feature an oil pump system, a feed pipe, an air heater and a drying chamber. The rotary atomiser features a gearbox and electric motor, which drives the spinning wheel.
Spray-drying is a continuous operation and atomisers are used to dry loads ranging from five kilograms to 80 tons per hour. The exacting demands placed on the atomiser are often intensified by companies running the machines twenty four hours a day, seven days a week, in a bid to meet production demand. This continuous operation means that machines must be well maintained and lubricated to minimise downtime.
How are they lubricated?
Lubricants used in spray-drying are an important consideration for food companies as they play a key role in reducing the amount of friction and heat generated by the moving components. Whilst they are essential to the smooth running of the operation they also present a threat of accidental contamination. Food companies involved in the spray-drying process are faced with the difficult and risky task of lubricating moving components which operate in close proximity to where the liquid feed is spray-dried.Reducing lubricant contamination risk
Working closely with food Original Equipment Manufacturers (OEMs) such as Niro Denmark, Shell has developed lubricants which meet these demanding lubricant requirements while reducing the threat of contamination. Niro Denmark is part of the international GEA group which specialises in the development, design and engineering of liquid and powder-processing equipment and supplies the energy, environmental and process industries with spray dryers and coolers, fluid bed systems and membrane filtration systems.Demands on the lubricant
Niro had been using mineral food grade lubricants for approximately two years in its atomiser gearboxes but had experienced problems with machine wear and cleanliness. This was because mineral-based food grade lubricants lack oxidation and thermal stability to withstand the atomiser's high temperatures which can reach 80°C. As a result the lubricants were not able to meet the required 3,000 operating hour oil change intervals. This resulted in machine and component wear and lubricant deposits in the atomiser. In the long term this increases atomiser downtime and maintenance costs.Field trial Shell Cassida Fluid HF
In a bid to find a synthetic food grade lubricant which could provide the required performance properties, Niro decided to run a series of field trials designed to test the lubricity and durability of Shell's food grade lubricant range - Shell Cassida Fluid HF (hydraulic fluid).Shell Cassida Fluid HF has been formulated using synthetic high performance poly alpha olefins (PAO) base fluids and specially selected additives, which increase oil life and cleanliness. A tasteless, odourless and colourless lubricant, Cassida is harmless if it accidentally comes into contact with food below the Food and Drug Administration's (FDA) maximum level of ten parts per million.
This lubricant provides excellent oxidation and thermal stability, high anti-corrosion and optimal anti-wear properties. lts synthetic PAO base means that it can be used to lubricate non-ferrous metals, such as those found in the atomiser's worm gear system. Cassida Fluid HF has been developed in accordance with industry standards and practices and meets DIN 51524 parts 2 and 3, DIN 51517 part 3, hydraulic oils levels HLP and HLVP and gear oil level CLP.
Food grade lubricant is essential
The composition of the atomiser is such that it contains a number of lubrication contamination control points (LCCPs). The gearbox and lubricant system are located above the rotary wheel and near to where the liquid feed is spray-dried. This poses a potential threat of contamination from lubricant leakage or drips into the drying chamber from the gearbox. This can be seen in the diagram below.
Shell identified the LCCPs and advised how Cassida Fluid HF could be used to reduce the risk of contamination. A Shell team, together with Niro's service engineer, conducted two field trials of Shell Cassida Fluid HF. The tests were carried out on two different atomiser gearboxes and included oil-monitoring and maintenance inspections of the machinery. Internal inspections of the gearbox were also carried out after the operation.
Field trial results
Before switching from the mineral-based food grade lubricant to Shell's synthetic food grade lubricant, the atomisers underwent a complete overhaul. Inspections of the atomisers and oil analysis were then carried out every 1,000 operating hours. Atomiser one ran for more than 6,000 hours and atomiser two managed 7,132 hours. In both cases, the oil was still in a good condition, but the oil was changed due to scheduled maintenance of the atomisers.Shell Cassida Fluid HF exceeded the recommended oil change interval of 3,000 hours. After 7,000 hours there were no visual signs of wear on the gears or the oil pump system and the machine's internal components were as clean as when the trial had started. These performance properties ensured that maximum productivity was reached without compromise to food safety. Despite the superior performance of Cassida Fluid HF, Niro and Shell recommend that lubricants in the atomisers are still changed every 3,000 operation hours to ensure that they remain fit for purpose.
Following the field trials and the superior performance of Shell Cassida Fluid HF, Niro is reviewing its lubricant recommendations to customers and is reluctant to recommend the use of mineral-based lubricants or lubricants not supported by proven field or operational experience. Shell Cassida Fluid HF is now being placed at the top of Niro's food grade lubricant recommendation list and is used in Niro's atomisers around the world.
Food OEMs are continually working to develop and design machinery which can meet the industry's increasing operational demands. Part of this development includes working with experienced lubricant providers such as Shell, who can advise on lubricant applications and practices. This enables OEMs to improve machine lubrication and ensure increased levels of operational efficiency, food safety and quality.
Für nähere Auskünfte: FUCHS LUBRICANTS GmbH
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