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NETZSCH: Tank farms get greater efficiency โ€“ screw pumps strip out even highly viscous media

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Hydrocarbon Engineering,


As containers and temporary storage, tanks to entire tank farms are the backbone of many industries, in particular in the oil and fuel sector. But the stored media are often highly viscous, making it difficult to empty or ‘strip’ all the medium out of the tanks. Residual product is normally left behind, significantly reducing the useful volume of the tank.

More and more companies in these sectors are using NOTOS® screw pumps from NETZSCH Pumps & Systems to maximise the profitability of their tanks. Excellent intake at low NPSHr values means that these pumps can completely empty tanks – even of crude oil and bitumen. They can be used flexibly for different viscosities with an almost constant flow rate, which can be regulated over a broad range by adjusting the pump speed. This optimises the profit margin of raw material and processing plants, which is a particularly important consideration when it comes to non-renewables.

Tanks are ideal for storing media that is volatile, potentially hazardous or has to be protected against contamination. They are therefore commonly used for mineral oils and oil products from diesel and petrol to polyols, as well for plant-based products such as palm oil.


Storage tanks are standardly used to store many different types of liquid and gaseous materials. How-ever, it can be difficult to empty or ‘strip’ highly viscous media from tanks without leaving behind valua-ble product..


More and more companies in the oil industry are using screw pumps, such as NOTOS® pumps from NETZSCH, to increase efficiency when emptying tanks of mineral and vegetable oils and to ensure that medium is pumped smoothly.

Pumping hot bitumen efficiently

The multi screw pumps from NETZSCH have been tried and tested for more than 35 years on numerous occasions. Depending on application and parameters, they are available as two-spindle single-flow, three-spindle single-flow or two-spindle double-flow models (2NS, 3NS or 4NS). One of the world’s largest companies handling petroleum products wanted its 4NS pumps at a terminal in England to be fitted with an additional heating jacket to keep the bitumen hot in the pumps. The heating jackets maintains media temperatures between 130 and 200 °C, so that the product can be kept at a comparatively low viscosity of 500 cSt. The performance of the pumps is unaffected by the heat, as the robust units are designed for temperatures up to 300 °C.

Besides the separation that is required for structural reasons between bearing and pumped medium, this is possible thanks to a range of materials from grey cast iron and chrome-nickel steel to Hastelloy alloys that are used for the pumps. The choice of materials also contributes to pump performance, as spindles made with these materials also have almost no deflection, which allows for fine production tolerances between the dynamic and static parts, thereby reducing backflow. In combination with a pump chamber with a geometry designed for optimum flow and to minimise turbulences, it is possible to achieve high rates of efficiency while still gently pumping the medium.


NOTOS® pumps operate on the displacement principle, which ensures that even highly viscous materials can be sucked in reliably at low NPSHr values.One shipping agent uses the pumps for bitumen at 200 °C.


All pumps are adapted to each specific application and a wide range of optional accessories is also available. One palm oil producer, for example, had its ship-loading pump fitted with a storage temperature monitoring system.

High efficiency regardless of viscosity

What is particularly important in the oil sector however – even more important than efficiency – is the flexibility that screw pumps provide when it comes to the viscosity of the medium. Whilst centrifugal pumps have fixed operating points and their efficiency drops rapidly as viscosity increases, NOTOS® screw pumps run with excellent rates of efficiency across the entire range of viscosity up to 50 000 cSt, as they operate on the principle of displacement. This pumping process relies on the interaction between the spindles and the housing to form chambers, which continuously convey the medium at stable pressure from the suction to the discharge side, almost entirely regardless of the consistency or viscosity. The flow rate is determined by the rotational speed, the screw diameter and the thread pitch. So it is directly proportional to rotation and can be set over a continuous range by adjusting the speed.

Even better – the pump speed and the viscosity of the medium affect the NPSHr value, which determines the intake behaviour. As NOTOS® pumps can be regulated flexibly, they can keep NPSHr values appropriately low to match conditions so that the medium is sucked in uninterruptedly and the tank can be completely stripped, even of the highly viscous derivatives of crude oil.

A further advantage of low NPSHr values is that all NOTOS® screw pumps can normally be operated right next to the tank. But whatever the design of the pipe work, which may cover several hundred metres, the pumps reliably suck in the medium. For particularly deep tanks or highly viscous media that can only be accessed from above, the pumps can also be submerged to guarantee high flow rates even when tank fill levels are low.

Custom adaptations for exceptional robustness and reliability

For best possible performance once the model has been chosen, the pumps can also be adapted to the specific application, in particular in terms of size, but also with accessories. Pressure relief vales, storage monitoring systems with temperature/vibration sensors and alternative seal systems are just some of the options available.

NOTOS® pumps have special design features that provide hydraulic compensation too. While the spindle package normally experiences axial thrust from the pressure difference, which places increased load on the bearing, the 2NS and 3NS models have a fine channel that links the suction and discharge sides. This cancels out the forces that occur and the net axial force is close to zero. Special bearing bushings are also used to absorb the loads. The 4NS is also designed so that there are no axial loads on the bearings. The two spindles are placed contact-free, so that even non-lubricating media can be pumped easily. The synchronised gear of the two shafts of the 4NS is also physically separated from the pumping chamber and filled with lubricant oil. In 2018 the IBExU Institute for Sicherheitstechnik also confirmed that NOTOS® multi screw pumps meet the requirements of explosion groups IIB and IIC (and therefore also ex-plosion groups IIA, IIB and IIA) for ATEX certification. In addition, suitability for use in explosive atmospheres at ambient temperatures between -20° and +40° was confirmed.


The screw spindles in combination with the geometrically adapted housing form chambers, which transport the medium at stable pressure and without significant pulsation. The flow rate can be regulated easily via the speed.


The 4NS 2-spindle double-flow screw pump is the most frequently used model, as it combines high flow rates with excellent intake be-haviour. The pump also has a very robust design – from hard materials to the zero-contact arrangement of the spindles and the physically separated synchronised gear.


The 2NS and 3NS models have a channel linking the suction and dis-charge sides to achieve maximum durability. It cancels out the forces that occur and the net axial force is close to zero.

For more than 60 years, NETZSCH Pumps & Systems has served markets worldwide with NEMO® progressing cavity pumps, TORNADO® rotary lobe pumps, NOTOS® screw pumps, grinding machines, barrel emptying systems, dosing systems and accessories, providing customised, sophisticated solutions for applications in every type of industry. With a workforce of over 2000 and a turnover of more than €281 million (2018 financial year), NETZSCH Pumps & Systems is the largest business unit with the highest turnover in the NETZSCH Group, alongside NETZSCH Analysing & Testing and NETZSCH Grinding & Dispersing.

Contact:
NETZSCH Pumpen & Systeme GmbH
Geretsrieder Strasse 1
84478 Waldkraiburg
Germany
Phone: +49 8638 63-0
Fax: +49 8638 67981
pr.nps@netzsch.com
https://www.netzsch.com


For more than 60 years, NETZSCH Pumps & Systems has served markets worldwide with NEMO® progressing cavity pumps, TORNADO® rotary lobe pumps, NOTOS® screw pumps, grinding machines, barrel emptying systems, dosing systems and accessories, providing customised, sophisticated solutions for applications in every type of industry. With a workforce of over 2000 and a turnover of more than €281 million (2018 financial year), NETZSCH Pumps & Systems is the largest business unit with the highest turnover in the NETZSCH Group, alongside NETZSCH Analysing & Testing and NETZSCH Grinding & Dispersing.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/10062019/netzsch-tank-farms-get-greater-efficiency--screw-pumps-strip-out-even-highly-viscous-media/

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