Why It Pays To Be Clean

Process industries are faced with increasing demands for product safety, improved quality, efficiency and profitability. The chemical, pharma and cosmetic industries are no exception.

Flexible and efficient production allowing rapid and smooth changeover between different products with minimum waste is an essential requirement in modern production. Increased attention must also be paid to protecting the environment, for example, by recycling and reusing materials whenever possible.

Equipment cleaning is an important parameter in achieving some of these objectives and, because of this, more attention is paid to optimizing clean-in-place (CIP) systems.

In most cases, applying rotary spray heads or rotary jet heads offers an effective method for the fast and automated cleaning of tanks, reactors and other process equipment, thus optimizing the use of the cleaning solution and minimizing downtime between batches, and thereby optimizing production, efficiency and capital utilization.

The cleaning process

The various methods of cleaning process equipment depend on the process equipment to be cleaned and the product that is produced in the equipment. Another important aspect is to also consider the consistency between cleaning cycles and how this can be controlled. One way of improving the consistency is by increasing the level of automation and the sophistication of in-line control methods. Tank cleaning can be categorized and performed by manual cleaning methods:

• hand and brush

• high-pressure spray lances

• fill-boil-dump.

Automated cleaning methods:

• static spray balls

• reaction-driven rotary spray heads

• media and motor-driven indexed rotary jet heads.

Cleaning is preferably automated whenever possible and serves to

• prevent cross-contamination

• remove sludge and sediments

• control microbiological activity

• improve/maintain heat transfer

• protect the equipment against corrosion

• prepare a tank for human entry

• prevent explosive atmospheres

• fulfil legal and regulatory requirements.

This article will discuss a number of efficient and next generation cleaning units.

Static spray balls

Today, process vessels are typically cleaned with static spray balls. The traditional static spray ball was introduced in the early 1900s and is still the most widely used, permanently installed cleaning device. Available in various shapes, sizes and capacities it provides a simple method of distributing cleaning fluid onto tank and vessel walls.

Rinsing by a static spray ball, at best, washes the tank walls. The small jets of liquid from each hole in the perforated ball continually hit the same place on the wall. Because of the size of the jets, the impact force on the wall is very low where the fluid actually hits; and where it does not hit, the force is zero. Therefore, there is a reliance on large volumes of cleaning liquid or high chemical concentrations. Other factors that may have the desired cleaning effect include elevated temperatures and/or extended time.

The static spray ball also strains particles circulated in the cleaning liquid, which can cause inactivation of a spray ball part. This will cause inefficient cleaning and is frequently only detected after a certain period of time.

Recent observations show that bacteria and microorganisms have a strong tendency to stick to smooth surfaces such as stainless steel. To ensure that such microorganisms are effectively removed, it is necessary to rely on high mechanical impact. However, more and more rotary spray heads are being installed.

Rotary spray heads

Rotary spray heads are, in most cases, a superior substitute for conventional static spray balls. Because of the rotating fan generated by the rotary spray heads, a wall will be hit in a uniform and vibrating pattern. This combination of pattern and physical impact removes any deposits quickly — using less water and chemicals compared with static spray balls.

Rotary spray heads can be used in the same tanks and vessels as static spray balls. The static spray balls and rotary spray heads are mounted either with a threaded connection or by a pin/clip-on connection, with the latter used in installations where it is required by regulatory standards.

Rotary jet heads

Rotary jet heads (Figure 1) clean by means of a number of jets being rotated in such a way that the entire interior surface of the tank is hit in a successively denser pattern.

The principle of rotary cleaning equipment was extended to early forms of rotary jet heads, where nozzles were incorporated into mini-sparge arms. Control of the rotational speed was linked to the operating pressure, and was such that the cleaning action provided could be regarded as a sophisticated development of the garden sprinkler.

Figure 1. A jet head designed specifically for the biotech and pharmaceutical industries.

Some of these early versions experienced considerable difficulty in maintaining a stable rotation and a good cleaning effect. This lead to the development of nozzles with larger diameters of 2.5–5.5 mm, which can provide sufficient throw length.

The modern design of rotary jet heads uses the cleaning media to drive the turbine to make the cleaning nozzles perform a geared rotation around the vertical and horizontal axes. In the first cycle, the nozzle lays out a course pattern on the tank surface. Subsequent cycles ensure the pattern becomes gradually denser until a full pattern is reached after 8 cycles.

The choice of nozzle diameters optimizes jet impact length and flow rate at a desired pressure, and an electronic rotation sensor validates a full coverage of the tank surface.

Key points

The combination of horizontal and vertical rotation together with the high speed jet which splashes at the tank wall and then reflect a spray back from the wall again will facilitate a high impact on even the most difficult to reach spots. The benefit of this can be seen in more complicated tanks and vessels equipped with agitators, baffles and various internal fittings, where typically multiple stationary spray balls are required, but where a single rotary jet head will often be sufficient to clean the entire tank.

The nozzle size of the rotary jet head and the media pressure to the rotary jet head determine the flow rate, throw length and nozzle revolution, and the corresponding cleaning time. Normal operating pressure of the rotary jet head is approximately 3–10 bar.

A new generation

The new generation of rotary jet heads are created for sanitary applications and comply with the stringent requirements on hygienic design, material and documentation required for pharmaceutical manufacturing. These rotary jet heads are fitted with an external drive to minimize product contacted surfaces and are self-cleaned both on the inside as well as on the outside. Normally, the cleaning media drive the machine, but it can also be supplied with either an electrical or air driven motor with a magnetic clutch. The motor driven version is used mainly when an even higher impact on the tank wall is needed for specifically sticky product because on this version it is possible to increase the pressure without increasing the revolution speed of the rotary jet head.

The nominal temperature range of the rotary jet head is 0–90°C, and it is also possible to use steam sterilization at a maximum temperature of 140°C. The pressure range is 3–13 bar, although recommended operating pressure is 3–8 bar.

Jet heads have been designed to provide self-cleaning on both internal and external surfaces. The design incorporates cleaning of the down pipe, which means that the machine can remain mounted in the tank during production, even if it is mounted below the level of product in the tank during production. This is particularly beneficial for cleaning tanks and process plants where, for instance, heating or cooling of the product takes place during production, and where high cleaning standards are required to conform to standards.

Cleaning patterns

Tanks can be cleaned according to a number of patterns depending on the choice of equipment. One is the 'golden section' cleaning pattern, where the movement starts very coarse and refines itself in a sequential way by laying out the subsequent cleaning tracks approximately in the middle of the two most distant tracks that have already been made. In this way, the jets will quickly make a gross removal of products on the tank wall followed by a denser pattern until the tank surfaces is completely cleaned, and thereby remove as much deposit as possible in the shortest possible time.

When a complete cleaning pattern is not required, it is possible to achieve cleaning within a shorter time using a smaller amount of cleaning fluid compared with a traditional step-wise cleaning pattern that is requiring a complete pattern to get uniform cleaning. Furthermore, because of the uniform cleaning pattern, the cleaning can be stopped at any time, whereas with traditional non uniform cleaning patterns this would not be possible.

Design

Cleaning simulation software (Figure 2) can be used to recreate how a rotary jet head would perform in a specific tank. The simulation provides information on wetting intensity, pattern mesh width and cleaning jet velocity. Using this knowledge, it is possible to determine the best location for the tank cleaning unit and the correct combination of flow, time and pressure. Thus, it is possible to set up the most effective operating parameters and optimize the cleaning operation at an initial design stage.

Figure 2. Software can simulate the performance of a rotary cleaning machine in a tank before installation.

Qualification/validation

Today, cleaning qualification is performed in various ways. Riboflavin or other similar coverage tests are widely used to ensure that the tank or vessel is properly cleaned to avoid microbial and cross-contamination. Typically during the cleaning validation three consecutive applications of the cleaning procedure should be performed to confirm the effectiveness of the cleaning procedure.

However, to ensure consistent tank cleaning after a cleaning validation has been performed and approved, an in-line monitoring system monitoring that the cleaning device is operating consistently is needed. No matter what type of cleaning device that is used there is always a risk that sludge or sediments could block the hole or jet for the cleaning solution or that the device is malfunctioning because of other reasons. For the rotary jet heads there is a system available that detects the pressure impact from the jet stream and will detect every time the jet stream is hitting the monitor. With the 'golden section' cleaning pattern it is possible to predetermine the time between every hit of the monitoring sensor and thereby the intervals of jet stream detection for a system that is operating consistent. If the monitoring sensor will not be hit within the predetermined interval a signal will be generated. This signal can be audible, visual or integrated into the process control specification.

A rotary jet head in tank cleaning action.

Benefits of rotary jet heads

Effective optimization of the cleaning cycles is often difficult. However, the use of rotary jet heads offers a range of benefits to the pharmaceutical industry, including

• Proprietary dimensioning and selection software to ensure optimum location/position.

• Effective and optimal cleaning.

• Efficient cleaning of tanks with agitators, baffles and difficult to reach areas.

• Reduced cleaning time, water consumption and cleaning agents.

• Reduced energy consumption.

• Reduced manpower.

• Increased time available for production and reduced product losses.

• Consistent cleaning and continuous monitoring of the cleaning process.

Some of these benefits can be seen directly; however, the benefits of a monitored cleaning consistency together with the effects of reduced cleaning time and more production time must be considered when justifying an investment in more advanced cleaning equipment.

Cost comparison

Frequently, manufacturers are not fully aware of the actual cleaning cost or cleaning various process equipment, and neither of the potential cost reductions available for optimized cleaning procedures.

Naturally, there will always be some reluctance to investing in more expensive cleaning devices, but all implications, including future operating costs, and the costs for the CIP skid must be considered. For example, the size of CIP bulk unit tanks, pipe work and valves, is significantly affected by the choice of the cleaning nozzle used and the actual vessel to be cleaned. Static spray balls will generally demand bulk unit tanks that are 50–100% larger compared with using rotary jet heads.

When making the cost/benefit analysis it is important to include benefits such as increased production, increased sales, the value of improved product quality and the reduced environmental impact. Even though difficult to calculate, the cost or cost reduction of a monitored cleaning consistency and thereby a decrease in the risks for cross contamination and the effect of this should also be considered when a cleaning device is selected.

Conclusion

A new generation of rotary jet heads has been developed for applications in a wide range of industries, including biotechnology and pharmaceuticals. Hygienic design and self-cleaning ability together with monitoring possibilities for consistent operations/cleaning make the new generation of tank cleaners perfectly suited to applications where product cross-contamination must be avoided.

Their design makes them particularly suitable for tanks with surfaces that are difficult to reach and clean as well as for products that are highly viscous, foaming and/or thixotropic. It should not be assumed that rotary jet heads will always be the correct choice of cleaning nozzle for a particular tank, but it is important to evaluate the factors discussed in this article when deciding on the actual design of the CIP system.

Today, based on actual tank drawings, tank-cleaning suppliers can engineer cost-effective systems, give advice on the optimal choice of tank cleaning machine and make the relevant cost/benefit analysis. The modern sanitary design of rotary spray heads and jet heads offers opportunities to optimize cleaning systems and provides a wide range of benefits to manufacturers.

Bo Knudsen is portfolio manager for tank equipment at Alfa Laval Sanitary Equipment, Denmark Per-Åke Ohlson is application manager at Alfa Laval Sanitary Equipment, Sweden.