Fossil-Fueled Power Plants - Energy and the Environment - page 103

Shaker

Clean
air
exhaust

Filter
bags

Particle-
laden
air in Plenum

and
hopper

Bottom plate

Trapdoor

Figure 5.9 Baghouse with mechanical shakers, schematic.

diameter. It is necessary to distribute the incoming flue gas equally to all tubes, which is done in
the plenum . The tubes provide a large surface area per unit of gas volumetric flow rate. The inverse
is called the air-to-cloth or filtering ratio, which is equal to the superficial gas velocity; it typically
ranges between 0.5 and 4 cm s − 1 .
The collected particles can be removed by mechanical shaking of the tubes or by the reverse
jet method. Mechanical shaking is induced by a cam-driven moving rack on which the tubes hang.
In the reverse jet method, a strong air flow is blown from the outside of the tubes toward the inside,
dislocating the particle cake that has built up. The removal of particles is not always complete,
because particles cling to the fabric and are lodged in the pores. This causes frequent break downs
and requires replacement of the fabric tubes about once a year. Ironically, the more clogged the
tubes, the better the removal efficiency, but at the expense of pumping power that has to be supplied
in order to maintain the superficial gas velocity. The removed particles fall into the bottom hopper
from whence they are carted away by trucks.
The flue gas at the entrance to the baghouse has a relatively high temperature of 300-350 ◦ C.
Also, the flue gas may contain corrosive gases and moisture. These conditions require a heat
and corrosion resistant fabric. Usually, fiberglass is chosen for coal-fired power plants, whereas
other fabrics, natural or synthetic, are applicable for other facilities, like cement kilns, ferrous and
nonferrous smelters, and paper and saw mills.