Cleaning In Place ( CIP ) and the need for soft water

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Due to the fact that water usually falls as rain onto a land mass and then percolates through the layers of soil and rock, it gains hardness. This hardness is due to the fact that water is a very good solvent and part of the rock that the rain passed over is now dissolved in the water. As the rock strata vary in different parts of the country, water from different areas contain a wide variety of dissolved materials. Unlike matter that is suspended in the water these dissolved particles of rock can not be filtered out in the conventional way.

 

 

In CIP systems hard water can and will lead to the formation of "hard water scale" on the surfaces of plant being cleaned. This scale starts as an unsightly white "bloom" on plant that would otherwise be bright and shiny. As the scale builds layer upon layer it forms a creamy white blanket, that gradually becomes a hard brittle layer. Although a coating of hard water scale may seem fairly smooth and impervious at a microscopic level, it is as porous as a sponge and offers an excellent harborage for bacteria.

Scale bloom on the outside of a tank.

When a layer of hard water scale has formed within a plant it drastically reduces the efficiency of any CIP system. Bacteria can effectively "hide" from the effects of  temperature, detergent and chemical sterilants.

Hard water scale causes a number of other problems for the plant operator, both pump and valve seals will wear prematurely due to the abrasive nature of the scale particles. In systems that have high liquid velocities, items such as flow meters and conductivity probes will suffer initially with excessive wear, then will gradually become covered in a layer of scale that upsets their calibration and accuracy

When a layer of hard water scale forms on stainless steel plant, it prevents oxygen from reaching the surface of the metal. This lack of oxygen defeats stainless steels ability to defy rusting, and leads to corrosion "pits" forming beneath the scale


Detergent suppliers can, for a price, sell you their particular detergent specially formulated to cope with "hard water".

BEWARE, a detergent formulated to cope with hard water will fall into one of two categories:

1. Those that will contain far more of the "magic ingredients" than you need and will dramatically      increase your detergent costs.

2. Those with insufficient "magic ingredient" that will still let hard water scale form on your plant.

This isnít really the detergent manufactures fault, as the hardness of the water being used will vary enormously depending where it originally fell as rain. The detergent manufacturer has to make an estimate of the sort of water hardness his detergent is likely to have to cope with and weigh that against the cost of his particular " magic ingredient".

These magic ingredients are chemicals that are particularly good at holding things in suspension within the detergent solution, (usually some form of chelating agent). They work by suspending the hard water scale within the liquid and preventing it depositing onto the plant. Unfortunately most of the chelating agents have a tendency to form stable froth. Froth is not at all useful in a CIP system and actually hampers the cleaning process in vessels.

The use of an acid based detergent will prevent the scale problems completely, but at a price.

 

So what can be done ?

Removal of the hardness salts from the water prior to its use in the CIP system is the best long term solution.

The dissolved rocks, known as hardness salts fall broadly into two sorts, "temporary hardness" and "permanent hardness".

Removal of the "temporary hardness" is relatively easy, just raise the temperature of the water to near boiling and these hardness salts will come out of solution and coat the heating vessel (usually your kettle or hot water tank heater).

 

Removal of the "permanent hardness" salts is a more involved operation, usually involving alterations to the pH and ion balance within the water. This can be a major problem in CIP systems as caustic soda based detergents do this very effectively.


The most cost effective method of softening water on a large enough scale for CIP systems is by a process known as "ion exchange softening".

The hard water scale is caused by dissolved particles of rock that fall out of solution causing an insoluble scale. If the dissolved rock can be exchanged for some other chemicals that donít form a scale then the problem wouldnít exist. This is exactly what "ion exchange softening" does.

A normal "ion exchange softener" works by replacing the Calcium and Magnesium salts that form hard water scale with Sodium salts that are soluble and donít form scale. This process is normally carried out in an ion exchange column.

 

The column normally consists of a cylinder full of an "ion exchange resin" this resin is formed into millions of tiny beads. Each bead has the ability to "grab" Calcium or Magnesium ions and release Sodium ions.

The rest of the system is simply a set of valves that allow water to be pumped through the resin.

Obviously this process cannot go on indefinitely as the resin beads eventually become saturated with Calcium and Magnesium ions and can not "grab" any more.

Fortunately this grabbing process is reversible and if the resin is flushed with a solution that is highly concentrated with sodium ions then the resin will release the Calcium and Magnesium and grab Sodium ions. This process is often referred to as re-generation.


For Full Details Contact Neil at N.E.M Business Solutions

click here to E-mail    neil@nem.org.uk

Tel  / Fax 01823 680119

Mobile 07768 981196


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