Page 202 - Industrial Ventilation Design Guidebook

! 64 CHAPTER 4 PHYSICAL FUNDAMENTALS

Vaporization Methods. The above methods may be unacceptable on
certain counts, and if complete removal of the liquid from the solid is re-
quired, vaporization methods are used. A nonvolatile solid can be removed
from a volatile liquid by the application of heat, a vacuum, or both.
The various techniques can be classified as

* Heat applied at atmospheric pressure
* Heat applied at reduced pressure
* Vapor distillation
The dryers make use of warm air, flue gases, and direct radiant heat to the
liquid-particle mixture. This method allows complete extraction of the solid
through removal of the liquid by vaporization. Due to the energy input re-
quired with this method, it is the most costly.

Separation of a Solid from a Liquid
A solid in a liquid medium may be in either of the conditions:
1. The solid may be dissolved into the liquid medium.
2. It may be insoluble and remain suspended in the liquid.
The liquid is assumed to be saturated if undissolved material is present, with
solids both in suspension and in solution in the liquid phase.
The efficiency of separation will obviously affect the purity of the liquid,
and it may be necessary to provide a series of separate stages to meet the stan-
dard required by the specification.
The most important consideration is the actual condition of the solid
in the liquid. Is it in solution, or is it in suspension? Other consider-
ations are

1. The relationship of the solid to the liquid
(a) Solids in solution in the liquid
•The solid concentration in the solution
•Degree of solubility
•The relationship between temperature and solubility
•The viscosity of the liquid

(b) Solid in suspension in the liquid
•The relative amounts of solids in suspension
•The size of solid particulate matter
•The density of the particulate matter
•The compacting properties of the solid
•The viscosity of the liquid medium
•The nature of the solid— spongelike, gritty, etc.

2. The degree of separation required
3. The heat-sensitive properties of the solid or liquid
4. Corrosive nature of solids and liquids
5. The degree of separation required for both the liquid and the solid