How to select the right tank cleaning machine

By selecting the most appropriate tank washer, other parameters of the process can be optimised along with the complete CIP cycle. Turnaround times can be shortened and productivity increased, which ultimately improves profit and competitive advantage.

Selecting a tank washer isn’t difficult, but the information needed is varied and not always to hand. There are five areas to consider:

1. The result the cleaning needs to achieve
2. The product being cleaned and its characteristics
3. The cleaning fluid
4. The vessel dimensions and design
5. The CIP system set-up and resources available

Step 1: Cleaning requirement

Start with what you want to achieve, how quickly, and the health and safety of staff. In most cases this means a total clean of the vessel, as quickly and safely as possible. But there are other factors: product recovery, passive flushing between batches, cleaning part of a vessel such as the nozzles, decontamination, sterilisation and how much cleaning media to use.

Example 1

You make the same blue paint in the same vessel, batch after batch, with little time in between. You may not need to fully clean between batches, as a little residue won’t affect the next one, so a rinse may do and turnaround time is more critical. But if colours change every batch, a 100% clean in between becomes vital.

Example 2

A high-value pharmaceutical or chemical product becomes explosive once it dries out but is stable while damp. Here product recovery matters, and after production the cleaning device may need to use very low volumes of liquid to keep residues damp without diluting the recovered product. The tank washer can then do more than clean: it can recover product, or even sterilise in place after the CIP cycle.

Step 2: Product characteristics

The product’s characteristics show how much cleaning power you’ll need. You don’t always need to name the product, which helps with confidentiality. Consider:

• Is it easily soluble?
• How sticky and how viscous is it?
• How toxic or corrosive (acid or alkali)?
• Is it explosive?
• How valuable is it?
• Does it change properties when wet or dry?
• How quickly must it be removed?

An easily soluble product might suit a passive washer, while a sticky, viscous one needs a jetting machine. Speed of removal can be critical too: a coating such as resin can be impossible to remove once it dries hard.

Step 3: Cleaning fluid

A solvent could create an explosive atmosphere in the vessel, which calls for an ATEX-certified machine. High-viscosity fluids affect flow and pressure. A fluid that removes soiling on contact needs only a low-power unit, while one that needs mechanical help suits a jetting unit. High temperatures, changes of fluid during the cycle and the effect of chemicals on seals, bearings and other materials all matter too. A highly acidic atmosphere, for example, can attack stainless steel, so Hastelloy may be more appropriate.

Step 4: Vessel design and attributes

The two main dimensions are tank diameter and height. The diameter shows how far the machine must throw the cleaning fluid with enough energy to clean the walls. Height affects the angle and distance to the wall, so two tanks with the same diameter but different heights may need completely different machines. Tank shape matters as well.

Internal fittings such as baffles, mixers, dip pipes, stirrers, scrapers and ladders affect the type and number of machines, because cleaning fluid can’t pass through a solid surface. Always ask: “how are we going to clean that?”

Example 1

With a central agitator, fit at least two machines either side of it so the shaft doesn’t cause blind spots. Retracting units may be needed to clean the underside of the agitator.

Example 2

Baffles can deflect liquid and cause blind spots, especially if the machine isn’t centrally mounted. Where baffles are fitted, multiple machines give better angles of attack.

Check the number, size and location of inlets too. If the only access is a CIP inlet with a 90 mm maximum opening, a larger machine simply won’t fit. Ideally, the inlet size and position should be chosen to suit the best machine.

Step 5: CIP system set-up

In an ideal world, the flow and pressure the best machine needs would be made available. In reality they are often limited by the plant’s existing CIP set. If so, measure the flow and pressure at the cleaning head rather than relying on the pump rating or theory. If you can’t, provide the pump output and pipe lengths and diameters as a guide.

If there isn’t enough flow and pressure, options include changing the delivery pump, adding a buffer tank, or using a different machine or multiple units. Remember that changing inlet flow affects outgoing flow: a scavenge pump must be set to match, or liquid will pool and reduce cleaning. Check the planned CIP cycle for changes in chemicals and any recirculation, which needs adequate filtration, ideally 500 to 1000 micron, sized so it doesn’t restrict the machine.

Summary checklist

1. What type of result is required?
2. What product is being cleaned?
3. How quickly must the vessel be cleaned?
4. Which cleaning fluid or fluids will be used?
5. What are the vessel dimensions?
6. Are there internal attributes?
7. What inlets are available?
8. What flow is available at the tank washer?
9. What pressure is available at the tank washer?
10. What is the intended CIP cycle?
11. Are there recirculation stages?
12. Is there adequate filtration?
13. Are there drawings of the tank?

Dasic will work with you at every stage to find the most practical solution, and can supply pumps and complete CIP systems if needed.