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Pumping peracetic acid

Chemical

Peracetic acid is a colourless fluid with a strong vinegary odour. The acid is highly corrosive and can be cause respiratory and skin damage. The acid is available in 5-15% concentration. The fluid will decompose to hydrogen peroxide and acetic acid and may become flammable when it degrades further to water, carbon dioxide and oxygen.

Applications

  • Peracetic acid is primarily used as an anti-microbial biocide. As a biocide it may be used as a disinfectant in processing lines found in brewing and wineries, agricultural sites and food processing, particularly cheese and dairy production. Peracetic acid is highly suited to clean-in-place style systems as it naturally decomposes to carbon dioxide, oxygen and hydrogen. It is deemed safe enough to be returned to the water course, such as in the dosing of cooling tower water in power stations. The acid is sometimes used as a flush chemical following a prior treatment of caustic solution as it does not leave residue and will not oxidize stainless steel pipework.
  • The anti-microbial properties are also used to prevent the build up of bio-film. This is a sludge-like layer which forms in areas of moisture and warmth as an environment for microbes/bacteria to thrive. Examples may include paper pulp mixes and membrane filters in filtration processes.
  • As the acid is corrosive, it is sometimes used in dilute concentration to provide an aged or vintage effect to building and furniture materials known as ‘patina’.

Pumping considerations

The key pumping considerations for handling peracetic acid are chemical compatibility and containment of the fluid.

As the acid is corrosive and may cause damage to human tissue, the containment is important. To guarantee the fluid being contained, peracetic acid can be handled using a mag drive pump. This pump type is hermetically sealed with no wearable mechanical seals subject to frictional, abrasive wear on rotating drive components, creating an inherent risk of failure. Instead the unit is sealed with an o-ring seal type between the pump end and casing pieces. With no abrasive forces affecting the integrity of the seal it will contain the fluid providing the pump is run as stated when specifying the duties.

Verdermag mag drive pumps are available in both metallic and non-metallic materials. Peracetic acid can be used with SS316L, PTFE, ETFE and Polypropylene, all of which are commonly used in mag drive pumps.

It is recommended to avoid using carbon steel, bronze, copper, iron or galvanised metal due to these metals being vulnerable to oxidation. For higher concentrations and an elevated temperature, ETFE or PTFE is recommended as peracetic acid is exponentially more corrosive as the temperature rises to 40 degrees and above. Mag drive pumps will be exceptionally good where a large quantity of fluid requires transferring, where there is good flooded suction and the fluid is of a low viscosity and virtually no solids.

If the process involves different duty conditions then a mag drive pump may not be suitable as the pump may suffer cavitation from not having sufficient flooded suction in proportion to the discharge, the pump’s efficiency will drop drastically, the fluid may be too viscous to lubricate the bearings or the bearings may be damaged by abrasive particles.

An example of this may be a peracetic acid circulation application for pickling materials. In this instance, an air-operated double diaphragm pump may be more suitable. The aodd positive displacement principle is perfect for handling abrasive particles as there are no mechanical seals and the flow path allows small solids to pass. AODD pumps typically have a large selection of materials for chemical and abrasion-resistant properties. As they are powered by compressed air, they are suitable for installation in ATEX-rated zones. Where the pump is transferring from a barrel or IBC, the Verderair AODD pump can run dry and self-prime so is a more robust pump should there be problems with the suction line.

Where peracetic acid is dosed into a batch or process line, a peristaltic pump may be more suitable due to the accurate flow rate. A Verderflex peristaltic pump with EPDM chemically resistant hose can provide an accurate delivery of fluid, even those that are viscous and contain abrasive solids. A peristaltic pump can be connected to an inverter and analytical probe so that the pump can respond to a change in pH, turbidity or the parameter that is critical to the process. It is recommended for SS316L or non-metallic port flanges. A peristaltic pump may also run dry as there are no wearable parts requiring lubrication from the media itself. It can also provide excellent suction lift and be reversed in the event of the blockage.

Small component models are available for OEM applications such as etching units and CIP systems.