Page 71 - Air Pollution Control Engineering

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Air Quality and Pollution Control 51

disposal problems. As a result, it may be necessary to provide auxiliary facilities to
dewater or even completely dry the slurries, deodorize wastes, and cover dry discharges
to prevent the escape of fugitive dust. Incorporation of air pollution control systems
is often a convenient method of “closing the loop” in a process, and recycling the by-
product of the control system should be examined.
Economic considerations are linked closely to the end use of the byproduct. When
considering recycling of the byproduct, one needs to examine the potential market. It has
been shown that fly ash, for example, can be used in construction material (lightweight
strong building blocks, concrete, and asphalt) and the demand in some markets has
exceeded the supply.
The economical analysis of control system must include both capital and operational
costs. Significant factors in this economical analysis include the cost of money (inter-
est rate), the age of the existing process facilities, and/or the expected life of the pro-
cessing system with pollution controls. Additionally, both the capital and operational
costs must be examined. The operating cost for a control system is often related to the
cost of purchase and installations of the control equipment. Often, control equipment
with a high-cost capital has a low operational cost. Conversely, it is also true that con-
trol equipment with a lower capital cost has a high operational cost. The gas pumping
system (blowers, etc.) is the single largest energy-related operating expense for a con-
trol system. Therefore, a control system that requires a high-pressure gas pumping sys-
tem will have high energy demands that result in high operating expenses.
Another economical consideration is the actual operation and maintenance proce-
dures, which can influence the operating costs significantly. Control equipment requires
frequent and periodical preventive maintenance care and inspection to ensure the use-
ful life of control equipment. This work will be performed by either the operator or the
maintenance personnel. For example, blowers, pumps, and other parts in a control unit
require routine lubrication, adjustment of belts and seals, and inspection. Periodically, a
control unit requires complete inspection of the entire unit. Additionally, some control
units may also require a complete shutdown in order to purge the system so that it can
be entered for inspection.
To maintain performance and assist in the maintenance of the equipment, provisions
should be made for obtaining sample measurements, including the building in of sample
and velocity ports and pressure taps into equipment. Routine measurement of pressure
drop across the control unit, pressure in the system, and gas and liquid flow rates are
minimal requirements for ensuring proper operation of control equipment. It is impor-
tant during the startup of the control that baseline information on the control equipment
be taken and recorded. This information should include measuring and recording the
outlet and inlet static pressures at the blower and current draw from the blower motor.
These startup measurements are compared to the regularly made pressure drops and
current draws to help in troubleshooting.
To handle the maximum process emission rate without inducing adverse pressure
(negative or positive) on the process, the control system must be sized properly.
Important considerations in sizing control equipment are temperature fluctuations and
humidity changes. Changes in the temperature and humidity of the emission can sig-
nificantly affect the volume of gas required for treatment by a control unit. Section 6