The reasons to refurbish or upgrade an existing centrifuge are as many and varied as the processes on which they operate. To obtain the best possible result from any refurbishment or upgrade project, it is of vital importance that the centrifuge refurbishing company has a complete and accurate understanding of the user's process and operating requirement.
With regular maintenance, a centrifuge is capable of many years reliable and trouble-free service. Only after long periods of long arduous duty do vital components such as resilient mountings, oil seals, bearings and other moving parts need serious attention or replacement.
In many instances the casing and main structure of the machine remain in reasonable condition, and at the end of its life-cycle, can often be refurbished and retrofitted with ‘state-of-the art' ancillaries – even after 10 to 15 years of continuous operation.
Depending on the condition of the original machine, user expectations and financial constraints, centrifuge reconditioning can provide an extremely cost-effective option, offering a wide choice of variables – from basic overhaul/refurbishment to an advanced upgrade more appropriate to current user requirements.
As part of this refurbishment process, existing machines can be retrofitted with many of the latest features, including PLC based controls, improved feed and discharge arrangements and other recent refinements which often provide cost-effective benefits such as extended throughput, improved operational efficiency and increased production.
Certain upgrade requirements may also involve compliance with industry related legislation covering intrinsic safety in hazardous areas – Atmosphere Explosible (ATEX) category 2 Directive 94/EC – or the Good Manufacturing Practice (GMP) requirements resulting from the necessary ultra clean conditions of the pharmaceutical industry – and also conforming with the latest Good Automated Manufacturing Practice – level or version 4 (GAMP 4) Regulations.
In some instances, operators may require machines to be modified and upgraded to comply with the strict guidelines, recommendations and inspection procedures of the Food and Drugs Administration (FDA) that maintain high levels of control through the utilisation of ultra-clean processing facilities.
These machines can be refurbished as validateable centrifuges with ‘clean-in-place' systems which ensure there is no cross-contamination between batches and that total cleanliness is maintained during product change-over.
Modifications to the control systems of existing machines, including those operating in ATEX category 2 areas can include the supply of purpose-built Programmable Logic Control-based (PLC) systems with Variable Frequency Drives (VFD), local operator push button panels or Human-Machine Interface (HMI) to suit a particular process. It is possible to modify the control philosophy to suit a variety of process applications and maintain compliance with Functional Design Specification (FDS), Factory Acceptance Test (FAT), and Site Acceptance Test (SAT) protocols.
New machines for old
Standard centrifuge refurbishment work is highly competitive and cost-effective when compared with the purchase of new machinery. Even in situations where spare parts are unobtainable, these can be produced on a bespoke basis, from a variety of specified materials, including super duplex, monel and other special alloys. Replacement internal baskets can be manufactured to user requirements from materials such as stainless steel, Hastelloy and Titanium.
One of the most common concerns of companies using older centrifuges, centres around the need to refurbish machines in compliance with the ATEX Directive 94/9/EC. Older machines, operating in the old zone 1 hazardous (now ATEX category 2) areas, now need to be modified to include safer drive systems, internal atmosphere control, satisfactory electrical earthing of rotating parts and control of other sources of heat, including the monitoring of bearing temperature.
Where changing production requirements involves the processing of hazardous materials such as solvents, machines can usually be retrofitted with nitrogen-purging systems installed to remove the build-up of potentially explosive vapour and keep the atmosphere within the centrifuge at a safe level of oxygen during normal operation and discharge. Operating as an integral part of the centrifuge, the purging system is controlled by the centrifuge control system and incorporates a separate screen on the operator interface that allows the user to monitor and control the purge.
Conversion from hydraulic to electric drives
Many centrifuges, currently in service, are fitted with high maintenance hydraulic drives and plough discharge mechanisms that are fast becoming outdated. The hydraulic power packs installed on these machines are prone to leakages and use expensive filtration systems which require regular oil changes. Over time, many operators invariably find it difficult to maintain 100% leak-free oil seals.
Hydraulic powered centrifuges can be retrofitted with electric drives and plough units that are totally clean and completely eliminate potential contamination from leaking oil. This type of conversion can provide substantial cost-savings as the machine only uses power when the electric motor is operating – there is no need to purchase oil and no requirement for a continuous supply of cooling water.