Crude olive oil, which still contains fragments of crushed olive stones, is a very abrasive medium to pump. Spanish producers are discovering that lobe pumps may be the optimal solution for this application. Steve Minett and Feld Kenwick report.
The Spanish olive oil industry is centred on Jaen, 300km south of Madrid, in Andalucia, which is the largest olive oil producing region in the country. Andalucians are rightly proud of their product which they claim is the finest in the world. The region produces about 350000 tonnes per year, depending on the weather, selling for around 300000 ptas per ton. This gives an annual total of about US$544.25million.
To serve this industry, the engineering company Transmission y Rodajes SL established itself in Jaen in the early 1970s, and specialised in service, maintenance and parts supply for olive oil processing equipment. In 1991 a sister company, Centrifugacion Alemana (CA), was set up to sell olive oil processing equipment manufactured by the German company, Hiller. CA has between 500 and 600 customers, mainly in Spain but also in Morocco, Portugal and Tunisia, served by its eight-strong work force.
Oil production
Fresh, ripe black olives picked from the trees give the best quality olive oil. (Green olives are less mature and are consumed as whole fruit but they are not used for oil production.) The growing season varies somewhat according to the weather but in Spain the fruit generally starts appearing in April. Harvesting mature trees starts around Christmas but the smaller trees are picked later, from January to March.
The whole olives are dropped into a grinder with an Archimedean screw, which produces a paste of the raw fruit. The paste is transferred to a blender consisting of two long channels, one above the other, fitted with rotating paddles. As the paste flows along the top channel and back along the lower one, it is blended and its temperature is raised by thermostatically controlled heaters to 40oC.
In the blender, the moisture content is adjusted to that of fresh-picked olives, which is 60percent. Olives which have been allowed to lie in the sun may have dehydrated and may need additional water. On leaving the blender, the crude oil passes through a wire strainer with a mesh less than 5mm, and is then pumped to a decanter which separates the nearly pure virgin oil from contaminants such as fragmented stones and skins.
Final processing
The particle paste, which is separated out in the decanter, goes through another process to extract the non-virgin residual oil which is sold for lower grade applications. What is left of the particle paste is sold as a biofuel to local industries, for example a ceramics factory, and as a domestic fuel.
The virgin oil is treated in a centrifuge which rids it of any final traces of particles and water before packaging and sale.
Extracting oil from olives involves crushing the fruit, including the stones, to produce a highly abrasive paste. Even after straining the crude oil contains fragments of stones which can seriously damage seals and the internal surfaces of pumps. Careful choice of pump types and materials, however, has reduced downtime from pump failure to a minimum.
Pump selection
Centrifugacion Alemana sells olive oil processing equipment manufactured by the German company, Hiller, and originally offered its 500600 customers a screw pump for use in olive oil plant. Technical sales manager Antonio Trujillo Anguita says that it was the best available at the time but performance was poor.
"The main problem with screw pumps is that they can be damaged very quickly if they are allowed to run dry,“ he says. "This can happen quite easily if the operator fails to keep a careful check on the level of fluid at the pump inlet. After about ten minutes of dry running, the stators can be completely destroyed. At that stage in the refining process, the crude olive oil contains stone fragments and other contaminants and is an abrasive medium to pump,“ he continues. "Even with a continued good supply of the pumping medium, therefore, the stators had to be replaced after pumping between one and five million kilograms. After some years, therefore, we started to switch to lobe pumps for this application.“
Lobe pumps
The family of twin rotor displacement machines, to which rotary lobe pumps belong, came under intensive development in the middle of the 19th century. They operate on a different principle to screw pumps.
Two interacting, contra-rotating rotors, typically having three lobes each, are externally geared together so that they maintain a design clearance between themselves and between the pump housing.
Lobe pumps produce a gentle pumping action without shear and without damaging the pumping medium. They are ideal for moving fluids with solid pieces in the stream since the pump head components are not easily worn. They are available in sizes to suit a wide range of flows and with different design factors to suit the huge number of media needing to be pumped.
Design factors include rotor clearance, which influences the volumetric efficiency of the unit since it determines how much of the pumped medium slips back from the outlet side to the inlet side. The length and profile of the rotors determine the pressures that the pumps can attain and of course the size and speed influence the volume flow.
One of their greatest advantages is their inherent simplicity and the fact that they can be dismantled easily without disturbing the pipework or pump mounting. This makes them very useful for food processing applications where the plant must be cleaned regularly.
Competing designs
The first lobe pump that Centrifugacion Alemana offered its customers was a Spanish-built machine. Antonio remembers that this was an improvement on the screw pumps originally supplied by the company since it gave a stator life of between 56 millionkg. However, there were problems with the internal dynamics of the units and a number of them suffered housing failure. This was a serious fault since replacement involved dismantling the pipework which was a time-consuming job.
"During 2000 we began testing an ITT Jabsco Hy-line pump,“ says Antonio. "We ran comparative trials against the Spanish equipment for a period and then dismantled them both. We made careful measurements and found that the Jabsco machine was the much harder wearing unit of the two. We also preferred the design since it had a removable back plate. This exploited the simplicity of the lobe pump principle and enabled our customers to clean the machine in situ without uncoupling the pipework.“
Says José A. Rodriguez from Tecnica de Fluidos, who is the sales contact for Centrifugacion Alemana. (Tecnica de Fluidos are ITT Jabsco's distributor in Spain): "The Hy-line's seals are positioned for easy inspection and replacement. They are fitted from the front which also makes them more accessible to product flow and for CIP liquids. As the seals are further forward than in many other pumps, they are mounted in the flow of the liquid, exposing the sealing faces and the seal joints to the liquid, preventing the oil from partial drying out and becoming sticky. The full exposure also means complete circulation of the product is guaranteed, which avoids stagnant areas where bacteria can multiply“.
The seals are also balanced, giving controlled pressure between the faces for longer face life. The static face is energised instead of the rotating face, which eliminates wobble and the resultant shaft wear, to provide effective sealing, even at low pressures. Long life at high pressures is another advantage.
The Hy-line design includes a flat crevice-free front cover, flush rotor securing screws, sealed drive splines and absence of recesses where the oil could stagnate and compromise maintenance or hygiene.
The pumps have scimitar type rotors and, because they do not require accurate synchronisation, they are easier to bring into service and more tolerant of abuse. No shimming or other timing adjustments are required. The rotors are suited to pumping abrasive fluids since they do not touch each other or the rotor case when in operation.
The bearing arrangement utilises a simple preloading mechanism which can be adjusted without the shims and is easy to service. The rotor case is completely removable for easy replacement and provides a wide separation between product and gearbox. These features reduce dismantling and reassembly time during cleaning procedures, a factor well received at the production plant.
Customer feedback
"Customer reaction to the Jabsco pumps was favourable,“ recalls Antonio. "They commented on the superior quality and they especially liked the removable back plate which gives easier maintenance. It means that work can be done on the pump without taking the whole unit out of the system. This minimises production downtime.“
Antonio acknowledges that it is more expensive than other pumps but for large-scale users the reliability and ease of maintenance, which give increased uptime, are very popular with users. They are very happy if a pump can give two or three years service without major attention, he says.
"We are keeping accurate records of the pumps in service,“ says Antonio. "In a few more years we shall have first hand experience of service life and we will be able to calculate accurate figures for total cost of ownership. That takes in initial costs, routine running costs and service. We expect this to be substantially below other equipment on the market.“
Steve Minett is a freelance writer and Feld Kenwick is with ITT Jabsco. For more information, visit www.jabsco.com
