Lesson 3 - Cleaning Systems and Control SAQ

**Compare and contrast options available for spray device selection for a new 20 x 3,000 hL vessel fermenting cellar.

Response:

There is a choice of three types of spray device available:

a) Static or stationary spray balls

b) Rotary spray heads

c) Rotary jet heads

Static or stationary spray balls

The static spray ball sprays detergent onto a fixed location on the tank surface through each perforated hole that is also from a fixed location. As the jets hit the tank surface, they create an area where the impact force and shear stress are active. After impact, the jets change to cascades of detergent, which run down the sides of the tank, creating a free-falling-film. This free-falling-film generates an uneven pattern of shear stress on the interior walls of the tank. The decisive factors that determine when the tank is clean are time, chemistry and heat.

The CIP pump pressure must match the design pressure and flow for the spray ball, which is typically between 1-2.5 bar.

This spray device has the cheapest capital cost but is the least effective at cleaning. The jets impinge on the same predefined areas on the tank wall. This results in longer cleaning time and higher water use.

Rotary spray heads

The rotary spray head, however, is a dynamic cleaning device. The flow of the cleaning media released from the spray head causes the head to rotate. This creates a swirling fan movement, which enables the detergent to hit the tank surface with an impact force that is higher than the one of the static spray ball.

The pulsating force, combined with the impact created, provides both shear stress and variable falling-film of cleaning fluid that covers all the internal surfaces of the tank. Compared to the static spray ball, the rotary spray head reduces the amount of cleaning time required to achieve the desired cleaning results.

The rotating spray heads are more expensive than the static spray balls, but this cost will be recovered with savings in time and water use, which can be 30% less.

Rotary jet heads

Rotary jets create the highest impact force and highest shear stress. The jet rotates at a predefined speed around two axes to provide a full 360º moving cleaning pattern over time. The impact force and wall shear stress from a rotary jet head footprint are significantly higher than the wall shear stress in the free-falling-film created by a static spray ball.

Rotary jets cannot be retrofitted to existing spray balls. The system operates at a much higher pressure, and the CIP delivery system needs to be upgraded. In addition, intrusive check sensors need to be fitted to each tank. The cost is significantly higher than spray balls and rotary spray heads, but as the cellar would be new and therefore containing a number of large fermenters, it would make rotary jets a serious consideration.

The rotary jets clean more effectively over a defined cycle time, saving both CIP time, detergent (as the chemical is replaced by mechanical force to remove soil) and overall water use.

The life cycle costs of this system are more expensive due to the complexity; however, savings of up to 70% over the costs of the spray ball CIP systems, are achievable.