Inductive Conductivity - CIP-Concentration Control In The Makeup System

By Mettler-Toledo AG, Process Analytical, Inc.

The food & beverage industry has stringent requirements regarding the cleanliness of all equipment in contact with food products. Technically these requirements are fulfilled by means of a CIP-system. CIP stands for Clean-In-Place. That means that the reactors, pipes, and so on are cleaned in place, and are not disassembled and cleaned elsewhere. The latter might be necessary for some equipment, such as filters for example. CIP is preferable whenever it is possible, because it allows a much higher degree of automation.

The actual cleaning is then done primarily by the use of liquids that are pumped through the system. Water to rinse, chemical, detergents, to clean, disinfectants to kill germs, etc.. Higher temperatures help the chemical cleaning effect; flow creates a mechanical cleaning effect. Sometimes the cleaning is supported by "pigs" send through the line, although that is limited to few cases where the actual layout allows the use of such things.

The chemicals used in CIP, NaOH for example is commonly found on the menu, are delivered and stored in high concentrations to save transportation cost and valuable storage space. Typically that would be a concentration of around 45 %. The concentration used in the CIP-cycle would be something like 2 to 5 %. This caustic solution would be made up in the quantity needed in the make-up system, and then kept there until it is used.

The concentration needs to be determined with sufficient accuracy, and, it has to be an on-line measurement to make efficient process control possible. The answer is conductivity measurement. In solutions of one chemical substance, NaOH in our example, and water, conductivity is directly related to concentration; in that sense it is used as a concentration measurement. Conductivity is also easy to install and maintain, and offers on-line readouts of the concentration.