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Is the water in your Sub Zero heat transfer fluid system costing you money?

Water causes extensive plant reliability problems and is a major cause of plant failure and production loss. Synthetic fluids are used as a heat transfer medium at temperatures down to –100°C and up to 400°C and water causes problems through the whole range. Sub Zero systems are particularly susceptible to problems.

In order to reduce system water content, we have designed a range of mobile and fixed drying units based on ‘nitrogen stripping’ and ‘distillation’ principles.

The units can dry fluid down to below 10 parts per million while in continuous production at Sub Zero temperature or in stand alone batch processing.

The Problem

The water saturation point of heat transfer fluids varies with the fluid type and the operational temperature.

Free water, above the saturation point, will circulate as ice particles which will deposit themselves on heat exchanger surfaces, in chiller heat exchangers and in expansion tanks.

It should be noted that the surface temperature on heat exchangers will be far lower than the circulating fluid and that the refrigerant temperature should be taken into consideration. Allow at least 10°C lower than the fluid requirement.

As systems are closed loop, eliminating water is not easy. Cycling chillers and allowing individual reactors jackets to warm to release water still leaves the problem of removal or the water that will simply deposit itself elsewhere in the system.

How does water get in?

  • New systems:
    New systems, extensions and alterations not being sufficiently dried at commissioning

  • New fluid:
    Fluid suppliers do not necessarily guarantee a low moisture content on barrelled fluid. We have tested new fluids at 60—80ppm:- not much help if you are running at –30°C!

  • Poor housekeeping:
    External filling points unprotected from the weather. Barrels stood upright and not properly dried before use. Barrels that are partially full being stored upright wit loose caps. The use of non dedicated filling pumps and hoses

  • Plant failure:
    Water heat exchangers, reactor jackets failing:- the nightmare scenario

  • Services:
    Saturated nitrogen used for blanketing. We have experienced systems where 30% water was found after a heat exchanger failure, with a complete plant closure. Similarly we have seen systems where around 20ppm is causing maintenance headaches, particularly where Plate Heat Exchangers are used

What can be done?

Our units, available for hire or purchase, are connected to the system as a side stream, taking a proportion of the flow through a heat exchanger to a temperature below the boiling point of the HTfluid and above 100°C.

The fluid is passed through a ‘flash chamber’, over a series of micromeshes, cooled and returned to the system. Nitrogen is passed through the ‘flash chamber’ to pick up the released vapours and passed through a condenser.

The condensate can be collected for safe disposal or further reconditioning.

A recent example

Reduction in water content in a 20,000 litre system of Dowtherm Syltherm 800

TFS water cooling graph
   Starting content: 2520ppm
   Finishing content: 36ppm
   System content: 20,000 litres
   Rig operated: 24 hours per day

   System content: 20,000 litres of
   Syltherm 800
   Drying cycle: 42 hours
   Water removed: 68 litres
   Water content: 2520 ppm dried
   to 36 ppm