Page 200 - Industrial Ventilation Design Guidebook

1 62 CHAPTER 4 PHYSICAL FUNDAMENTALS

References
TM.13, Minimising the Risk of Legionnaire's Disease (CIBSE).
Approved Code of Practice on the Prevention or Control of Legionellosis
(Health and Safety Commission, UK).
The Control of Legionellosis Including Legionnaires' Disease (Health and
Safety Executive, UK).
4.4.4.2 Separation Techniques
Up to now, only the water treatment aspects relating to the efficient run-
ning of a plant have been covered. It is necessary to consider the discharge of
the water from any cleaning process into the waterways or drainage systems,
in order to ensure that statutory regulations are not violated. The following
techniques are briefly considered:

• Separation of a liquid from a solid.
• Separation of a solid from a liquid.

The selection of the method used depends on many complex factors, which
are not covered in this paper. The basics of each of the two methods are briefly
covered. Only a few of these techniques would be used in the water treatment
procedure encountered in the industrial ventilation field; however, for the sake
of completeness others are also covered.

Separation of a Liquid from a Solid
The removal of the various solid particulates from a gas stream may
be achieved by washing either with chemicals or with water. Once this
process has been carried out, the problem is to remove the solids from the
liquid in order to

• Reuse the liquid
• Collect any valuable particulate matter for recycling
» Ensure that the drainage system is not contaminated

Numerous techniques may be used, each with disadvantages and advan-
tages. The methods used are

• Gravitational force
• Centrifugal force
• Application of a vacuum
• Application of mechanical force
• Action of a solvent
• Displacement
• Vaporization
In considering each of these techniques, the properties and principles on which
they depend are related to the liquid only.
The solid in the liquid mixture must be considered as

• Nonvolatile
« Insoluble