Wednesday, 11 August 2010

Storage and Mixing Vessel

This vessel can be used for several different liquids, one at a time.
It can also be used to blend different liquids.
The Vessel Receives liquid from an upstream source, which may be a tanker delivery or an upstream vessel
If then Delivers liquid downstream
It can stores the liquid at a controlled temperature, This may be above or below ambient depending on the liquid
The liquid is stirred, but the rate of stirring should ensure that energy is not wasted, by stopping the agitator or varying the speed.

Receiving can take place at the same time as delivering downstream, but this is not normally the case.
It is an Operator decision whether to all this.

The downstream process takes the material in batches, and there may be several downstream demands. These together may exceed the capacity of the discharge pump, so an arbitration system is required.

The vessel must be flushed with solvent to prevent cross contamination of different liquids.


  1. Francis -
    The very fact that this assemblage of equipment can receive and deliver material on command, it is a unit that contains, however fleetingly, a batch defined by the procedure that adds material for the batch and delivers it. The fact that it can modify that material (batch) simply makes that definition easier. The fact that it must be able to receive and deliver simultaneously makes the ISA-88 definitions a little outside the normal (we have to make up the rules the standard left out).

    Phases needed (parameters in parenthesis): - Add material (material ID, how much, agitation, temperature, etc); Deliver material (how much, agitation, temperature), Drain (how much, agitation); If more than one material needs to be added at the same time, we also need a phase for that to keep the possible mix-up as clean as possible.

    We also need a rather special control module that can be set to monitor the contents of the tank in lieu of procedure to let us know if the level changes without command or the temperature or agitation changes without procedural or manual command. This animal is sort of like a "monitoring phase" except it can't be a phase since it doesn't have a procedure as such. I suppose it has to do nothing but give a hoot and a holler if something bad happens. If it has to do more than that it is probably not a simple control module any more and requires some innovative invention the standard didn't try to address - like firing off emergency phases or procedures independent of a recipe or recipe procedure.

    I hope this is what you asked about :).

  2. Lynn
    A very good comment thanks.