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Wet and Dry Scrubbing 227

Furthermore, the required reagent slurry flow will be dependent on, but not limited to,
gas temperature, pollutant concentrations, types of pollutant, type of reagent slurry, and
so forth.
3.4.3. Dry Scrubber Costs
When considering both dry and semidry scrubbers, the capital cost of a system is
approximated with the sizing exponent (n):
n = 0.73 (32)
Now, using the sizing equation

Ib = Ia (Cb/Ca) n (33)
where Ib is the cost of the system being sized, Cb is the size of system being considered,
Ia is the known cost of the existing system, and Ca is the size of the existing system.
Therefore, Eq. (33) uses a known system (a) of a given size and given cost as a reference
to estimate the cost of a differently sized system (b). Installed cost-to-purchase ratio is
estimated to be 2.17 (22).
As for all pollution control technologies, several solutions will normally present
themselves for a given pollution control challenge. As such, “average” cost estimation
of a dry scrubbing project is difficult at best. Also complicating the estimation is the fact
that OEM firms generally prefer to sell an entire scrubber system, not just one part. A
total system cost may be less if it is a “standard” package from a given supplier as opposed
to an individual design. However, the demands of the given pollution control project
may dictate the need for a custom design.
As of 1991 (28), a dry scrubber system treating 278,000 actual cubic feet per hour
(acfh) or 4633 acfm from an incineration source was reported to be $66/acfm of air
3
being treated or $38 per actual cubic meter of air per hour (am /h). This cost is below
that of a semidry system. However, a caveat to keep in mind is that a dry system will
most likely require more alkali and will return a lower removal efficiency of acid gases
than if the semidry scrubber option is chosen.
The installed cost of a SDA lime sprayer system (as of 1992) is $49/acfm or $28 per
3
am /h. Using the same gas flow figures just mentioned (278,000 acfh or 4633 acfm),
3
the installed capital cost of the SDA system is $59/acfm ($41 per am /h).
4. PRACTICAL EXAMPLES
Example 1
Absorption is the most widely used control process when dealing with inorganic vapor
emission control situations. A typical emission stream is presented in Table 11, which con-
tains inorganic vapors that are easily removed from the stream using absorption technology.
This example will demonstrate the operating data that an industrial installation must compile
to support an air emissions permit application.
Solution
From Table 11, the most important characteristics of the polluted emission stream are as
follows: