CIP Processes for Hygiene-Critical Applications
The principles of CIP can be applied to any industry and plant where hygiene is critical, and the process is usually an integral part of any automated plant. Increasing health and safety legislation is likely to make CIP more common, which, according to the company, is a positive thing because a shiny surface on the outside of plant is no guarantee of cleanliness on the inside. CIP is principally concerned with soil removal - soil being anything that should not be present in a clean vessel. Soil can cause tainting and can often be smelt; it can be visible (scale or 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 chemical supplier and product) at temperatures of more than +50C, but no greater than +75C because there is no advantage to be gained above this temperature. Commonly used chemicals for soil removal include caustic soda, phosphoric and nitric acids, sodium hypochlorite (hypo) and peracetic acid (PAA). Caustic soda is an alkali typically used at 0.5 to 2.0 per cent volume. It reacts with the fats in the soil and softens it for removal.
One downside is that caustic soda is not effective for removing scaling. In addition, 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 acids 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 weeks to remove milk scale and can be used after commissioning to remove installation debris. Sodium hypochlorite (hypo) offers the advantage of a very low cost.
It is used primarily for disinfection because its ability for soil removal is poor. The active ingredient of hypo 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 is dangerous if mixed with acid, forming chlorine gas, which is poisonous. PAA is an equilibrium mixture of acetic acid and hydrogen peroxide; it is a powerful oxidising agent with an oxidation capacity higher than sodium hypochlorite and chlorine dioxide and is comparable to the oxidative capacity of ozone.
PAA at 75mg/litre is reported to successfully kill 100 per cent of a 10(7) cells per millilitre of yeast or bacterial population in 30 seconds. When cleaning lines in process equipment using CIP, the correct fluid velocity must be achieved to ensure good cleaning. Laminar flow, from velocities below 1.5m/sec, does not result in good cleaning characteristics. What is required is turbulent flow at velocities between 1.5m/sec and 2.1m/sec; there is no gain at velocities of more than 2.1m/sec. In the cleaning of vessels, two main methods are generally employed.
The first uses high-pressure cleaning heads to remove soil by mechanical action - the vessel surface being contacted in a series of passes. The second method employs low-pressure cleaning heads that rely purely on chemical action to remove the soiling. The majority of problems with CIP can be attributed to poor CIP return; this causes excessive CIP times, the excessive 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. In this respect, the choice of scavenge pump is critical.
Poor scavenge enables the back-up of the cleaning solution and the poor cleaning of the lower part of the vessel. In contrast, effective scavenge allows fresh cleaning solutions to contact the vessel walls and carry away soil effectively. Most CIP sequences are never altered from post installation settings; these are usually a set of 'defaults' that are set on commissioning. However, CIP operators can optimise their systems by monitoring a number of key parameters. They should consider what temperature and concentration (conductivity) the caustic tanks are set to; they should ask if the pre-rinse runs clear and then keeps going; they should consider the caustic fill and ask how high the return conductivity and temperature transmitters are set; they should check if the intermediate rinse is removing caustic solution and temperature prior to sterilisation; and, finally, they should ask what strength the sterilising agent is and check the length of 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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