Guide to efficient tank cleaning

Previous: Part 1- The cleaning mix

Part 2 - Efficiency Gains

Absolute efficiency gain

Whilst overall efficiency can be gained by reconfiguring the contributions from each element it is clearly beneficial to strive for efficiencies in each element. If, for example, a cheaper method of heating can be found then this element in its own right becomes more efficient, and thus the whole process is more cost effective. This would be an absolute efficiency gain as the same cleaning power is delivered using less overall resource.

An absolute gain in one element, however, might be better utilised by reducing the contribution from another more costly element. For example, if a more efficient heating method were found then either heat could be maintained at the current level for a lower cost OR heat could be increased for the same cost. If heat is increased then perhaps time could be reduced whilst keeping overall cleaning power at the same level. If the opportunity cost saved by reducing cleaning cycle time is greater than the savings made by improved heating efficiencies then this configuration is optimum. In other words a gain in efficiency in one element is not always best deployed in that element.

Water efficiency

“Water” is not one of the 4 elements of the mix but water usage clearly is an important factor. The amount of water used in any cleaning mix depends mostly on the role of the chemical element and the time element. Water is known as the universal solvent as it dissolves more substances than any other liquid. As such it often makes up all or the majority of the chemical component of the cleaning mix. It should also be obvious how a reduction in the time component of the cleaning mix will reduce water consumption. The shorter the cleaning cycle is the less water will be used.

Reducing water usage is a key driver for many businesses because it is an easy way to measure efficiency. Estimating the true cost benefit of improved time or reductions in chemical action or heat can be hard. The benefits are sometimes hard to measure and quantify. Water usage, however, is easy to measure. As we know that water consumption does equate to the “time” and “chemical” element we can use it as proximate measure of tank cleaning efficiency in many cases. As water usage is such a useful measure of efficiency it is worth modifying the Sinner Circle diagrams to include a measure of water consumption for each tank cleaning situation. Examples of these modified Sinner diagrams are shown below.

Water is money

The true cost of water is often under appreciated.

• Raw utility bill cost per m3 of water
• Cost of filtering and sanitising if recycling wash off
• Cost of caustics or other cleaning fluids

On top of this if we reduce the water needed to clean we can

• Lower pump running costs (electricity)
• Lower maintenance costs
• Longer lifetime for the pump
• Potentially use a smaller pump (reduced capex)

As the cost of energy and water are both increasing, and likely to continue to increase, reductions in water usage have significant financial benefits to any organisation. Further more the green environmental benefits are seen as a moral imperative by many organisations. Future green legislation is only likely to increase the need for more efficient water usage.

Time efficiency

Time is money. It may be a cliché but it’s still true. The time spent cleaning between production runs, whilst necessary, still represents downtime. This is time that the vessel can not be used for production. The opportunity cost associated with this downtime will vary greatly depending on the application, but in almost all cases a reduction on cleaning cycle time will have a direct financial benefit. Reducing cleaning time could allow for another batch to be produced per week or per month so the cost of having a longer cleaning cycle is equivalent to the value of the “lost” product. 

Chemical efficiency

As discussed above the biggest savings in the chemical element come from reducing water consumption. But, in addition to water reduction, lowering the use of caustics and other cleaning chemicals can be a key driver for many businesses. Cleaning chemicals are expensive to buy and also can incur considerable disposal costs as well. Typically a reduction in the chemical element of the cleaning mix will be compensated for by improved mechanical action and / or heat.

Heat efficiency

Heat improves the chemical action element of the cleaning mix. Heated water and caustics will act more quickly to dissolve and break up residues. As such the amount of each can be reduced and still contribute the same amount of cleaning power. Of course such savings are not absolute gains because they need to be offset against the energy cost of heating the fluids.

Next: Part 3 - The quick win of improved mechanical action