SCRUBBER ABSORBER
NEWSLETTER
March 2001
No. 321
AirPol Venturi Scrubber Controls Particulate
AirPol Inc. (Parsippany, NJ) installed a venturi scrubber at
Domtar Papers, Cornwall, Ontario, Canada. The scrubber has reduced particulate
matter from the recovery boiler stack by 95 percent and eliminated the visible
phume, operating to specification with no maintenance since startup in April
1998.
A wet scrubber
installed with the boiler kept particulates within regulatory tolerance, but
emissions were visible and occasionally produced an objectionable odor.
After research and a pilot test, Domtar chose the AirPol
scrubber. Specifically developed for boiler service, the venturi is equipped
with a round throat and a dual-leaf adjustable damper. Designed like a
dentist's bowl, the gas-liquid contact system consists of a funnel through
which the raw gas and scrubbing liquid flow concurrently. As the gas enters
the large end of the funnel, liquid is injected tangentially against the walls
of the funnel. The water swirls down the sides and toward the bottom ―
the small end of the funnel ― covering the entire surface of the funnel
walls. As the liquid and gas flow into the converging section of the funnel,
the increasing gas velocity atomizes the liquid and particulates are entrapped
in the liquid droplets. The droplets are combined in larger droplets that can
be separated easily from the gas in a cyclone-type separator.
The gas/liquid mixture then enters a cyclone that separates
the particulate-laden liquid droplets from the gas. Clean gas exits the stack
and the scrubbing liquid drains to a recycle tank for recirculation in the
venturi. The solids concentration in the recycle liquid is controlled by bleed
from the recycle tank. The bleed stream, high in sodium sulfate, is returned
to the plant’s black liquor system and weak black liquor is used as makeup
in the recycle tank.
Jorgen Hedenhag, sales manager for AirPol, says the shape of
the AirPol scrubber’s throat creates efficiencies not found with venturis
with rectangular cross-section throats. “The round cross-section ensures
coverage of the throat walls with scrubbing liquid, eliminating the potential
for dry spots and the resultant abrasion damage,” Hedenhag says. “A round
throat also improves the particulate removal efficiency by maintaining a more
uniform gas velocity profile.”
The AirPol venturi has operated to specification without
maintenance requirements since its installation. Particulate discharge from
the recovery boiler stack has been reduced by 95 percent, maintaining
particulate emissions well below 0.08 grams per Dry Standard (DS) cubic meter
(g/DSm3). The venturi handles 130,000 DSm3/hr [97,231
actual cubic feet per minute] of gas and uses a recycle flow of 1500 gallons
per minute. In addition, a visible steam plume nearly has been eliminated.