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Fig. 24. A combined gas stripping and absorption process system for simultaneous ammonia
removal and recovery. (From US EPA.)

The cost for operating the chemical scrubber can be divided into chemical cost and
energy cost. Energy will always contribute most to the total cost of operation. For the
two-stage scrubber (see Fig. 22), the energy cost will be approximately two-thirds of
the total operational cost. Although some simpler types are available, chemical scrub-
bers are generally applicable only at large treatment plants, where biological methods
of control are not feasible.

Example 30

A combined gas stripping and scrubbing (absorption) process system was introduced and
discussed previously in Example 22. Example 30 introduces another new type of com-
bined gas stripping and scrubbing (absorption) process system for ammonia removal and
recovery. The new process system, shown in Fig. 24, has been developed by
CH2M/HILL Consulting Engineers, and is highly recommended by the US EPA (64,67).
Please review the theory, principles, and applications of stripping and scrubbing
(absorption) and examine the process system shown in Fig. 24 carefully. Please then dis-
cuss the following:
1. This new process system shown in Fig. 24, including its applications, technology status,
historical background, operation, and possible process modifications.