Beginner’s guide to cleaning in place

Cleaning in place (CIP) is used to clean primary (and some ancillary) plant lines without dismantling the plant. A mix of chemicals, heat and water is used to clean machinery, vessels and pipe work in a one-shot process, where everything goes to drain, or in a recovery system, which recycles most of the liquid.

CIP has has been around for about 50 years. It can be a very efficient way of cleaning in hygiene critical industries, such as food, beverage, biotechnology and pharmaceutical.

CIP should be used in any industry and plant where hygiene is critical; the process is usually an integral part of established automation systems. However, expanded health and safety/food security compliance is set to make CIP more stringent - which is good given that a shiny surface on the outside of plant is no guarantee of cleanliness on the inside!

CIP is principally concerned with soil removal; however, soil refers to anything that should not be present in a clean vessel and is therefore ‘soiling’ the vessel. Soil can cause tainting and can often be smelled. It may be visible (scale, foreign bodies) or invisible in the form of bacteria, such as E. coli, or yeast spores. A CIP process of at least 15 minutes of a suitable chemical (strength dependent on chemical supplier and product) is required to remove vessel soiling. The CIP process should optimally run between 50 and 75°C, as there is no cleaning advantage to heating beyond 75°C.

Cleaning agents

Commonly used chemicals for soil removal include caustic soda (sodium hydroxide NaOH), phosphoric acid (H₃PO₄) and nitric acid (HNO₃) acids, sodium hypochlorite (NaOCl) and peracetic acid (CH₃CO₃H).

Caustic soda is an alkali typically used at 0.5 to 2% volume. It reacts with fats in the soil to soften them for removal. One downside is that caustic soda is not effective for removing scaling. In addition, sequestrants 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. Phosphoric and nitric acids are frequently used after commissioning, to remove installation debris.

Sodium hypochlorite, usually called ‘hypo’, is very inexpensive, which offers a strong advantage. However, it is primarily used for disinfecting because its ability for soil removal is poor. The active ingredient of hypo is chlorine (bleach). When concentrated, this can corrode stainless steel and will attack seals and personnel. It will also taint the process if not carefully rinsed out and is dangerous if mixed with acid as it will form poisonous chlorine gas.

Peracetic acid (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 75 mg/L is reported to successfully kill 100% of a 10⁷ cell/mL yeast or bacterial population in 30 seconds.

CIP systems and solutions vary.

CIP line and vessel cleaning

When cleaning lines in process equipment using CIP, the correct fluid velocity must be achieved to obtain good cleaning. Laminar flow below velocity 1.5 m/s does not give good cleaning characteristics; quite turbulent flow is instead required, at velocities between 1.5 and 2.1 m/s. There is no gain at velocities above 2.1 m/s.

In vessel cleaning, two main methods are generally employed:

• High-pressure cleaning to remove soil by force, with the vessel surface being sprayed in a series of passes.
• 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 CIP return. This causes excessive CIP times, excessive use of detergent and heat, and high effluent discharge.

To overcome these problems, the system for return must quickly and efficiently return the cleaning solutions back to the CIP set. Critical in this is the choice of scavenge pump. Poor scavenge causes back-up of cleaning solution as well as poor cleaning of the lower part of the vessel. In contrast, effective scavenge allows fresh cleaning solutions to contact all vessel walls and carry away soil effectively.

CIP optimisation

Most CIP sequences are never altered following installation; they are usually set to ‘defaults’ which are set during commissioning. However, CIP operators can optimise their systems by monitoring a number of key parameters.

• At what temperature and concentration (conductivity) are the caustic tanks set? These are often set too high, increasing costs and offering no additional benefits.
• Consider the pre-rinse - does it run clear and then keep going? Is the pre-rinse eliminating sufficient residue? Could it operate more efficiently?
• Caustic fill - are the return conductivity and temperature transmitters’ settings optimised? Keep these parameters as near as possible to the limiting effective temperature and pressure as higher parameters offer no benefits but cost in resource inputs.
• Intermediate rinse - is it removing caustic solution and temperature prior to sterilisation? Optimise volume, velocity and time of rinse.
• Sterilisation - what strength is the sterilising agent and how long is the contact time? Avoid wasted resources by ensuring strength and contact are idealised.

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