PuK - Process Technology & Components 2024

Pumps and Systems
Screw pumps
Advancing fluid conveyance
beyond conventional boundaries
Peter Volkert
In the realm of chemical applications,
precision, safety, and efficiency
reign supreme. When it comes
to handling viscous fluids, positive
displacement pumps play a pivotal
role. Among these pumps, screw
pumps stand out as they offer distinct
advantages over their rotating
counterparts. They excel in
characteristics such as zero pulsation,
exceptional suction capacity,
low noise emissions, a broad flow
rate range achievable with a single
pump, and gentle fluid handling, all
while maintaining exceptional efficiency
and high performance.
Screw pumps fall into two major categories,
distinguished by the placement
of their bearings: outer bearing
and internal bearing pumps.
Fig. 1: Diagram of the volumetric efficiency of the L2MG at 1,500 rpm
Outer bearing pumps
These pumps shine when it comes
to handling liquids with higher solid
contents or extremely high gas fractions,
allowing for the conveyance of
substantial flow rates. However, due
to the necessity of four sealings and
complex supply systems, they can
become a costly solution.
Internal bearing pumps
In contrast, internal bearing pumps
offer a host of advantages. They require
only one mechanical seal, in
contrast to the four needed in their
external bearing counterparts, and
can also be equipped with a magnetic
coupling.
Screw pumps with magnetic coupling
represent a cutting-edge innovation
that has revolutionized fluid
handling across various industries,
particularly in chemical applications.
Leistritz, a revered name in the pump
technology sector, has been at the
forefront of this transformative development.
Fig. 2: L2MG twin screw pump rendering
A prime example
Handling isocyanates exemplifies the
prowess of this pump application,
and Leistritz has amassed a wealth
of experience in this regard with its
magnetic-coupled internal bearing
pumps.
Regrettably, the use of this pump
type has been limited in the handling
of low-viscosity solvents like hexane or
toluene, as the hydrodynamic bearing
systems necessitate higher viscosity.
Consequently, this highly secure and
cost-efficient solution remained inapplicable
for processes that required
solvent flushing, such as polymerization
loop processes. This limitation is
rooted in a fundamental fact.
This limitation has propelled conventional
screw pumps with external
bearings into a multifaceted role, excelling
in handling low-viscosity products
at the expense of higher costs.
For the Leistritz engineers, rejuvenating
screw pumps has become
an exciting challenge – and they conquered
it!
40 PROCESS TECHNOLOGY & COMPONENTS 2024