Page 105 - Membranes for Industrial Wastewater Recovery and Re-Use

Industrial waters 85

20,000 1 I
J
5
’ 15,000

B 10,000 ,
b
e,
5,000
0
0
Jun-Ol Aug-01 Oct-01 Dec-01
Date

Figure 3.8 Comparison of chloride andsodium levelsin estuarine water (data from Tampa Bay, Florida)

2,500
~ 500 4
a Sulfate ””-- ---. ... P
E 2,000 400 ”
ai
P 5 ._
1,500 300 g
b - 3 ---’ - I
0
M&g;&um..- .-.--\ _*__.- 200
.,____--
.- 5- l,ooo - 0
u) E
g 500 100 .;
CJ) -
m
0
0- 0

3.7.6 Optimisation of water use in recirculating cooling systems
Optimisation of water use in recirculating cooling towers is based on the quality
of water entering and leaving the system. As water evaporates, dissolved
constituents and salts become more concentrated in the liquid stream. The water
quality of the recirculating stream must be controlled to prevent operational
problems such as development of deposits on heat exchanger surfaces (scaling),
corrosion, or biological fouling. To control the quality of the recirculating
stream, water is removed as blowdown water, and to compensate for loss of
water through blowdown, evaporation and drift water is added to the
recirculating stream as make-up water (Table 3.3). Drift occurs when the water
droplets become entrained in the discharge air stream: evaporation is from air
passing through the cooling water and absorbing heat and mass: blowdown is
the imposed bleed-off of water to reduce the concentration of contaminants.
Continuous blowdown is the continuous removal of water, whereas intermittent
blowdown is initiated manually or by feedback based on water quality. These
same concepts apply to management of water quality for boiler systems (Asano et
al., 1988, Burger, 1979: Kemmer, 1988: Puckorius andHess, 1991).