Optimising CIP to keep a clean sheet

How does cleaning in place work and where should you use it? Burkert explains how integral this should be to hygiene critical industries such as food and beverage processing

Cleaning in place (CIP) is commonly used in hygiene critical industries such as food and beverage to clean a wide range of plant. A mix of chemicals, heat and water to clean machinery, vessels or pipework without dismantling plant, the process can be one shot where everything goes to drain or recovery which recycles most of the liquid. Overall, it can be a very efficient way of cleaning and increasing health and safety legislation is set to make it more common.

CIP is principally concerned with soil removal: anything that should not be present in a clean vessel. Soil can cause tainting and often smell; it can be visible (scale, foreign bodies) or invisible in the form of bacteria such as E Coli or yeast spores. The time needed to remove soil is at least 15 minutes using a suitable chemical (strength dependent on supplier and product) at temperatures above 50C but no greater than 75C.

Cleaning agents

Commonly used chemicals for soil removal include caustic soda, phosphoric and nitric acids, sodium hypochlorite (hypo) and peracetic acid (PAA). An alkali typically used at 0.5-2% volume, caustic soda reacts with the fats in the soil and softens it for removal. However, it is not effective for removing scaling. Sequestriants are often added to keep soiling in solution. Phosphoric and nitric acids are used in detergent formulations for scale removal, often at lower temperatures than caustic.

These must be used with care as they can attack valve and pump seals. They are often used in dairies for one week in every six to remove milk scale and can be used after commissioning to remove installation debris. Sodium hypochlorite (hypo) is a low cost solution used primarily for disinfection because its ability for soil removal is poor; its active ingredient is chlorine (bleach). This can corrode stainless steel in high concentrations and will attack seals and personnel.

It will also taint if not rinsed out and if mixed with acid forms chlorine gas which is poisonous. PAA is an equilibrium mixture of acetic acid and hydrogen peroxide. A powerful oxidising agent with an oxidation capacity higher than sodium hypochlorite and chlorine dioxide, it is comparable to the oxidative capacity of ozone. PAA at 75 mg/L is reported to successfully kill 100% of a 10(7) cell/ml yeast or bacterial population in 30 seconds.

CIP line and vessel cleaning

When cleaning lines in process equipment using CIP the correct fluid velocity must be achieved: between 1.5-2.1 m/sec. In the cleaning of vessels two main methods are generally employed: high pressure cleaning heads to remove soil by mechanical action, the vessel surface being contacted in a series of passes or low pressure cleaning heads that rely purely on chemical action to remove the soiling.

CIP return

The majority of problems with CIP can be attributed to poor return. This causes excessive CIP times and use of detergent and heat with high effluent discharge. To overcome these problems the system must quickly and efficiently return the cleaning solutions back to the CIP Set. Critical in this respect is the choice of scavenge pump. Poor scavenge allows back-up of cleaning solution and poor cleaning of the lower part of the vessel. Effective scavenge allows fresh cleaning solutions to contact the vessel walls and carry away soil effectively.

CIP optimisation

Most CIP sequences are never altered from post installation settings; these are usually a set of 'defaults' which are set on commissioning. However CIP operators can optimise their systems by monitoring several key parameters:

• What temperature and concentration (conductivity) are the caustic tanks set to (often too high with no benefit)?

• Consider the pre-rinse: does it run clear and then keep going?

• Caustic fill: how high are the return conductivity and temperature transmitters set?

• Intermediate rinse: is it removing caustic solution and temperature prior to sterilisation?

• What strength is the sterilising agent and how long is the contact time?

All changes resulting from the CIP monitoring process should be documented and validated to meet any statutory regulations and/or specific client requirements.

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