Per-Åke Ohlson

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 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:  					

media and motor-driven indexed rotary jet heads.

Cleaning is preferably automated whenever possible and serves to									

fulfil legal and regulatory requirements.

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

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 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 (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.

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. 

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. 

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.  

Articles

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