SCRUBBER ABSORBER
NEWSLETTER
March 2001
No. 321
Smelter Uses Combined System
At the St. Lawrence Reduction Plant in Massena, NY, alumina
is smelted into primary aluminum. Emissions from the process include sulfur
dioxide, fluoride and polycyclic organic material (POM). To handle these
emissions, the largest fume treatment center in North America was installed.
It also combines wet and dry scrubbing. The dry process uses Pleno IV
technology from Danieli Corus, where a vertical radial injector (VRI) injects
alumina into the gas stream. Effective dispersion by the VRI ensures a high
degree of contact between the alumina and the gases for efficient scrubbing.
The baghouse consists of 24 modules, each 20x20 ft in
cross-section and housing 964 22-ft-long bags. Continuous cleaning of the bags
is accomplished by a 12-psi rotary pulsing system.
The wet scrubber system has two vertical stainless steel
absorber towers, 51 ft in diameter and 150 ft high. In the towers, a sodium
sulfate/sodium carbonate solution is sprayed countercurrent to the gas flow.
After the gas has contacted the solution, it passes through a mist eliminator
to remove any fine mist and liquor droplets remaining in the gas stream. The
system uses soda ash as the neutralizing reagent.
Twelve main exhaust fans provide the system with capacity to
handle the total gas volume of 2,016,000 SCFM.
Danieli Corus’ scope of engineering included the design,
supply, erection, training, commissioning and operating assistance for the dry
and wet scrubber systems, including the alumina-handling system, pump houses,
electrical system, and fully integrated control system.
Some 4600 tons of structural steel and platework were
fabricated by several large fabricators in Canada and the U.S., and were
transported by road, rail and barge to the jobsite. Collector ductwork from
the potrooms ranged from 12 in. to 16 ft in diameter and totaled more than
40,000 ft in length.
The system was designed to emit less than 0.8 mg/Nm3
fluoride, 5 mg/Nm3 particulate and 1 mg/Nm3 POM, and
remove 90 percent of the SO2.