Civil Engineering Reference
In-Depth Information
100
80
Monochloramine
60
40
Dichloramine
20
Nitrogen
Trichloride
3
5
6
7
8
pH
Fig. 19-5.
Distribution diagram for chloramine species with pH (
Source:
Reference 8)
at a pressure of 15 psi. The storage tank pressure is first reduced to approximately 40
psi using a pressure reducing valve, and then to 15 psi by another pressure-reducing
valve in the direct feed ammoniator. Typical low-pressure application points are open
channels and clearwell facilities. Figure 19-6 is a schematic of a direct anhydrous
ammonia feed system.
The solution feed method is used where the maximum ammonia feed rate is greater
than 1,000 lb / day or where the application point pressure is higher than 10 psi. The
solution feed method is similar to a chlorine vacuum feed system. A water supplied
eductor is used to withdraw ammonia from the ammoniator. The ammonia is dissolved
into the eductor water stream and applied to the process stream under pressure. So-
lution feed ammoniators are available up to 4,000 lb / day capacities and operate at
application point pressures up to 100 psi. Softened water with a hardness less than 29
mg / L as CaCO
3
is required for the carrier stream to reduce scaling. One concern of
TABLE 19-7. Time to 99 Percent Conversion of Chlorine
to Monochloramine
pH
Time (seconds)
2
421
4
147
7
0.2
8.3
0.069
12
33.2
Source:
Reference 4.
