Page 198 - Industrial Ventilation Design Guidebook

I 60 CHAPTER 4 PHYSICAL FUNDAMENTALS

control fall in the pressure range of 35-90 bar PO 4 between 10 and 20
1
1
mg kg" and in the range 67-125 bar between 7 and 15 nig" .
=
3. 725 Conductivity of boiler water from a neutralized sample at 25 °C.
Although the table is outside the scope of most industrial ventilating engi-
neering requirements, it does indicate the many problems to be considered in
the measurement techniques.
To finish this section, a typical flow diagram has been included (Fig. 4.42 }.
Biological Factors
It is essential that the engineer not lose sight of the numerous potential
problems related to microbiological concentration. These include
• Microbiological fouling in heat exchanger pipelines, cooling towers, etc.
• Microbiological corrosion in pipe work
« The effects of contaminated water on human health
In the case of a closed water system, once the correct water treatment
is provided, the incidence of microbiological fouling or corrosion is virtu-
ally eliminated, provided that the addition of fresh water is not a frequent
occurrence. It is, however, essential to have water tests carried out at regu-
lar intervals by a water laboratory.
In the case of an open water system, the problem is compounded due to the ad-
dition of microorganisms from the atmosphere. Water temperature control is critical
to stop the water from becoming a breeding soup culture for the microorganisms.
The aerosols formed in an open system, if inhaled, can cause various
forms of Legionella. No one biocide is adequate to control these, as there are
some 30 known groups, the most virulent being Legionella pneumophila.
It is essential to practice good design of all open systems by adhering to
set guidelines. A well-planned and effective maintenance program is of prime
importance.
The use of ozone for water treatment is now well established and has the
following advantages:
• An efficient biocide
• Low owning and operating costs compared with other methods
• No chemical handling, storage, or discharge problems
• Simple methods of automatic control
Ozone is more effective than chlorine in deactivating poliovirus, Cryptospo-
ridium parvum, Giardia lamblia, and other protozoa. It also improves the
color, taste, and odor of water dramatically. However, since no residual
amount remains, it is always necessary to add a small amount of a more stable
disinfectant as well (sodium hypochlorite, chlorine dioxide, etc.).
The disadvantages are
• High or medium initial cost. The energy cost for ozone synthesis is
l
about 12-15 kW h (kg O 3)~ consumed (1999), while 10-15 years ago
1
it was in the 25-30 kW h (kg C^)" range.
• Limitations on water temperature and quality.