CIP process efficiency: real-time monitoring and control — Part 1

Automated cleaning-in-place systems reduce the need to dismantle and clean food processing equipment to maintain food safety. The implementation of accurate process measurement in the CIP process enables food and beverage organisations to reduce waste and save energy while minimising the production downtime needed for cleaning.

In the food and beverage industry, the cleaning of process equipment is critical to ensure the health and safety of the consumer, as well as maintain the quality of the product. Proper cleaning is essential for the production of high-quality food products, especially those with extended shelf life.

Cleaning-in-place (CIP) systems are commonly found in many dairy plants, processed food plants, beverage plants and breweries — replacing manual strip down and cleaning of process equipment. The primary commercial advantage is a substantial reduction in the time that the plant is out of production and the ability to utilise more aggressive cleaning chemicals in a contained environment, which cannot be safely handled with manual cleaning. CIP has been defined¹ as:

“The cleaning of complete items of plant or pipeline circuits without dismantling or opening of the equipment, and with little or no manual involvement on the part of the operator. The process involves the jetting or spraying of surfaces or circulation of cleaning solutions through the plant under conditions of increased turbulence and flow velocity.”

A CIP system typically consists of vessels for preparation and storage of cleaning chemicals, pumps and valves for circulation of the CIP chemicals throughout the plant, instrumentation to monitor the cleaning process, and vessels to recover the chemicals.

It should be made clear that CIP is a methodology for removing product residues from a process plant and is not a means of eliminating microorganisms from the system (sanitisation or sterilisation).

Fouling of process plant

A side effect of processing of any food product is the build-up of debris (soiling) on surfaces and in pipes, resulting in fouling of the process equipment — especially those elements of equipment in which the product is heated.

When designing a CIP system, knowledge about the type and amount of soil, as well as its condition, is necessary. The main soil types are fats, proteins, carbohydrates (including various types of sugars) and mineral salts. Many of these types of soils are not water-soluble and therefore require the use of a cleaning solution.

Table 1: Solubility of food debris.

Soils resulting from food processing can be complex mixtures, depending on the food being processed, and heat treatment can make them more difficult to remove. How long a plant should wait between cleaning cycles depends on the plant and experience, but generally waiting too long between cleans can mean having to dismantle the plant.

A good example of soil complexity is the type of soils found in a dairy plant: milk remaining in a pipeline; air-dried films of milk; heat-precipitated milk constituents (protein and milk-stone); fat; and hard water salts. In the case of UHT milk production, protein will be the predominant soil at temperatures of up to 115°C while mineral deposits are common at higher temperatures. Each type of soil will need a specific regime for removal.

CIP challenges for food and beverage processors

The challenge for an organisation producing food and beverage products is in finding the balance between maintaining clean equipment for food safety and product quality, and not losing excessive production time by overcleaning. Then, when cleaning occurs, the process needs to be optimised to minimise the use of energy and resources (water and chemicals). It is therefore necessary to monitor the CIP process in real time — an inability to do so leads to overcaution and results in wastage, not only in cleaning resources but also in production time.

Another aspect of the CIP process is the elimination of waste and the recycling of chemicals and water. Smaller plants often use a single-use system, in which chemicals and soil residue are disposed of, but in larger plants, such waste can be very costly. Larger multi-use CIP systems recycle and filter the waste to return at least some of the water and chemical back to the CIP storage for re-use.

It is also now common for large processing plants to process their own wastewater in order to meet environmental regulations, so efficient CIP processes and recycling are also important to reduce the cost of waste processing.

The CIP cleaning process

Adhesive forces that hold the soil on a surface need to be broken to make the impurities leave the surface. To achieve this, there are four parameters involved in the cleaning process:

• Mechanical force
• Thermal force
• Chemical force
• Contact time

These processes all require energy (thermal, kinetic and chemical) applied over sufficient time in order to achieve the removal of the soil and carry it away. They are not independent, and changing any one parameter can affect the other three. For example, lowering the cleaning temperature may increase the contact time required — and therefore also the quantity of water and chemicals — and result in greater energy consumption overall.

Mechanical action

The shear forces created by the water or cleaning solution flow are the mechanical forces that help remove the soil. Nozzles increase the effective pressure and shear forces by concentrating the flow and effectively impacting the surface to be cleaned ‘harder’. Making effective use of spray nozzles means setting the flow rate such that the nozzles work most effectively.

In cleaning pipes, turbulent flow is necessary to create shear forces inside the pipe. Typically a flow velocity of greater than 1.5 m/s is necessary to cause turbulent flow. The use of a high velocity and turbulence also improves cleaning efficiency in small dead legs, eg, at instrumentation points or sample valves.

Research has also shown that flow velocities that are too high (greater than 2.1 m/s) are not beneficial, so pumping the solution to a higher pressure simply wastes energy for no greater effect.

The volume flow rate necessary to achieve a flow velocity between 1.5 and 2.1 m/s will depend on plant design — in particular, pipe diameters and choice of nozzles.

Table 2: Typical flow and volume for different pipe diameters at turbulent flow.²

Instruments for monitoring flow rate

Accurately measuring flow rate with a flow meter makes it possible to ensure that optimal pressure is maintained at spray nozzles, and that turbulent flow in pipes is sustained, without overpumping and wasting energy. For this reason, and depending on the design of the CIP system, flow meters may be required at multiple points in the system.

Measuring process liquid flow can be accomplished by any number of flow measurement technologies. In a CIP application, flow measurement should ideally be achieved by an instrument that is minimally intrusive in the CIP flow, is not affected by cleaning chemicals and does not lose accuracy when there is turbulent flow.

The requirements of flow measurement in the CIP system (sanitary, accurate over a wide range of flow rates, unobtrusive and robust) can all be fulfilled with the use of a magnetic flow meter. Flow rates of cleaning chemicals are generally twice the velocity of the product, so a sensor with a full bore design will ensure that no added pressure drop occurs in the system, meaning that energy costs associated with increasing flows and pressures are kept to a minimum.

The accuracy of a typical magnetic flow instrument used for CIP is unaffected by large flow variations and the accuracy of the instrument should be guaranteed over a turndown of 1000 (0.01 to 10 m/s). Since the magnetic measurement principle is virtually independent of pressure, density, viscosity and temperature, it is ideal for monitoring in the extreme conditions found in CIP (cold, low-viscosity water up to high-temperature chemicals and high-density/viscosity products).

Figure 1: Magnetic flow meters designed for sanitary applications.

Magnetic flow meters are readily available that meet all guidelines for sanitary applications, such as 3-A and EHEDG.

Temperature

Molecules move faster at an elevated temperature and therefore the effectiveness of a cleaning process is increased with increased temperature, due to higher molecular energy. As a general rule, a plant should be cleaned at the same temperature as it has been processing the food. Contrary to what might seem intuitive, however, ever higher temperatures are not necessarily effective. If a higher cleaning temperature is used, then reactions in the soil layers — such as denaturation of proteins — may occur, making the soil harder to remove. Table 3 shows cleaning temperature ranges for some dairy processing equipment.

Table 3: Cleaning temperatures for dairy processing equipment.³

Rinsing will also occur at different temperatures, with an initial flush being in the 40–60°C range, the post-alkaline rinse being a hot rinse and the final rinse being cold.

Instruments for monitoring temperature

Temperature sensing should occur at two places in the CIP system: at the initial water heating point, to manage feedback for the water heating process, and in the CIP return to confirm the temperature of the wash and rinse are correct.

The real-time temperature of the wash solutions will also be necessary to compensate for correct calculation of chemical concentration from conductivity data.

Temperature sensors that come in contact with CIP cleaning solutions should be of a hygienic compatible design: 3-A or EHEDG to ensure cleanability is met. They are generally constructed with 316L stainless steel wetted parts. A compact thermometer that utilises a Pt100 (Class A) sensor element for measurement is the most appropriate. Additionally, a device with a Pt100 4-wire connection eliminates errors caused by the resistance of the sensor feed cables. A built-in transmitter in the device converts the Pt100 input signal into the 4–20 mA signal.

Figure 2: A typical temperature sensor used in CIP processes.

Modern temperature sensors use a new kind of thin-film sensor element that is soldered directly into the sensor tip. The thin-film design improves upon previous generation sensors, as its performance is not affected by vibration that is commonly found on CIP systems. Soldering the thin-film sensor directly onto the tip also results in extremely fast temperature response as it ensures ideal heat transfer from the process to the sensor element.

A side benefit of fast temperature response is that it can be used to compensate for the change in conductivity based on temperature by taking the 4–20 mA value directly into the conductivity transmitter. This ensures fast determination of the conductivity and concentration values derived from the conductivity instrument, saving both time and money.

In Part 2

In Part 2 of this article, we will examine in detail the monitoring of cleaning solution concentration using conductivity sensors and other important CIP parameters.

References

1. Romney A (ed) 1990, CIP: cleaning in place, Society of Dairy Technology, Cambridge.
2. Tetra Pak, Cleaning in place: A guide to cleaning technology in the food industry.
3. op cit.