Improving accuracy of separators

22 October 2008

SEITAL is using Emerson Process Management’s Micro Motion Coriolis meters to provide accurate density readings on their range of high performance centrifugal separators, delivering what is says is unsurpassed performance for customers.

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SEITAL Separatori Italia srl is an expert in centrifugal separation and produces vertical disc centrifuges for chemical, pharmaceutical, dairy, beverage, vegetable oils, fuels, biofuels and mineral oils purification. Established in 1983 as a producer and supplier of machines for the dairy sector, SEITAL initially manufactured classic milk skimmers, before satisfying the growing needs of the dairy industry for reliable centrifugal separators. The company now boasts a work force of fifty employees, a turnover of €7 million and has developed equipment for other applications such as oenology, fruit juices and beer, and non-food applications such as biotechnologies and bio-fuel.

SEITAL only produces centrifugal disc separators, 70% of which are exported to a market consisting mainly of OEMs. Disc centrifuges perform process engineering tasks such as the clarification of liquids, separation of liquids with different densities, and the recovery of valuable solids like catalysts. Competition in the centrifugal separators market centres on the quality of the machines, their reliability over time (these are machines that have to last at least thirty years), and their efficiency.

Efficiency in the dairy sector corresponds to the ability to achieve the minimum possible residue of fat in the skimmed product, within the machine’s nominal range. Any fat that isn’t separated and remains in the milk can constitute a clear financial loss. Based on an annual production of 6-8 hours a day, a machine that recovers a few hundredths of a percent by lowering the fat concentration from 0.06% to 0.03%, pays for itself in little more than a year.

In this sector, a production phase called standardisation is required to obtain the correct levels of fat concentration in different milk products such as full fat, skimmed and semi-skimmed. The objective is to reduce losses due to incorrect mixes, and improve the quality and consistency of finished products. This means that precision in measuring product density is essential.

In the preparation of milk used in the production of yoghurt, milk arrives by tanker and is stored in silos that feed into a pasteuriser. SEITAL was asked to provide a centrifugal separator for installation in line with the pasteuriser, which would provide automatic standardisation of the fat content of both milk and cream.

Untreated whole milk with an average fat content of 3.8% is fed into the separator. The separator has two output lines: one for skimmed milk with a fat content no higher than 0.03%, and the other for cream, which, depending on the client’s requirements, contains either 36% or 40% fat with a requested precision of ± 0.2%. The milk used for the production of whole yoghurt must have a fat content of 3.5%, with a precision of two or three hundredths. This means that the milk has to have a fat concentration of 3.5% ± 0.02% or 3.5% ± 0.03%.

The standardisation system controls the separator’s operating parameters to ensure perfect skimming and then remixes the cream with the skimmed milk in order to achieve the required fat concentration. The accuracy of standardisation is a critically important factor in dairy plants. Therefore it is essential to have the most accurate meters available to measure the fat concentration in milk.

“We considered a number of manufacturers and compared the performance of their products because we wanted to provide the customer with the most accurate equipment possible. If we want to produce a successful machine, we have to use the best equipment on the market, and that’s why we turned to Emerson, and in particular to their Micro Motion products. In the areas of mass flow and density measurement, these instruments have the highest accuracy on the market,” said Giancarlo Sopelsa, sole Director of SEITAL srl.

SEITAL selected Emerson’s Micro Motion ELITE® CMF100 Coriolis mass flow and density meter to determine the cream concentration by measuring the density and temperature of the milk. Emerson also helped SEITAL to understand the relationship between the parameters measured and the fat concentration, which enabled them to meet the accuracy levels set by their customers.

“Emerson immediately put us in contact with an expert who works in this specific sector and was able to give us the right, highly detailed information.”

In addition to the Micro Motion meter with enhanced electronics, SEITAL also specified a Rosemount® PT100 temperature sensor to achieve the maximum possible levels of accuracy. Even though the density meter already measures the temperature of the measuring tube, SEITAL wanted a more precise measurement of the product itself. The temperature measurement made by the PT100 is transmitted using the HART® protocol to the Micro Motion transmitter, which makes the final calculation of fat concentration.

“We had a very good response from Emerson, who shared the problem of finding the fat concentration based on the density value, which was slowing down the development of the machine.” said Sopelsa. “After just a few tests with the instrumentation we were able to implement a formula to generate these values. Emerson acted like a true partner, giving SEITAL the confidence it felt it needed.

The standardisation machine heads up a new line from SEITAL and so far it has been very successful.