Energy-saving in tanks and vats

The main opportunities to save energy in tanks and vats relate to (a) stirring or agitation and (b) heating.

On mechanical agitation, things to look out for are:

  • Tanks agitated when they do not need to be (for example, overnight). If the contents are being agitated to prevent constituents settling out, a simple experiment will show whether it is safe to stop agitating outside working hours, and how long it takes to restore proper mixing.
  • If tanks are stirred to mix batches of ingredients, has anyone done a study to find out how best to determine the 'end point' of the process? If not, blending times will always have to be longer than necessary.
  • Are tanks agitated by compressed air? If so, is clean, dry, high-pressure air from a central compressor being used? The alternative is to use lower-specification air from a local blower. If agitation is required when there are no other uses for compressed air, this will also allow the central plant to run fewer hours.
  • Consider using a mechanical stirrer rather than compressed air.
  • Assess the design of mechanical stirrer paddles. Better hydrodynamic design could achieve the same mixing effect with less energy.
On the question of heated tanks, some things to look for are
  • Excessive preheat periods
  • Tanks heated while idle for long periods
  • Lack of insulation not just on the tanks but on associated pipes and fittings
  • Lack of lids on tanks. This can be a contentious issue because operators tend not to like them. One way to overcome their objections might be to involve them in the design of a lid system that does not interfere with their work unduly. Remember that effective lids or ball-blankets can reduce heat, humidity and condensation in the working area. Spirax Sarco's on-line learning centre includes a module on heating of tanks and vats which gives a very useful theoretical background.
  • Excessive extract air velocities over exposed liquid surfaces
  • Continuous uncontrolled top-up and overflow or run to waste.
  • Aqueous tank contents boiling when 95C would be effective.
  • Steam blowing through directly-heated tank contents
  • Local ventilation extract drawing air from general heated space. Consider whether a local fresh air supply can be ducted in to balance local extract.

V.V. 5 Feb 06 Close this window
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