WET SCRUBBER WATER TREATMENT IN THE IRON AND
STEEL INDUSTRY USING LAMELLA GRAVITY SETTLERS™
Mark C. Fischer, Process Engineer
Parkson Corporation
Fort Lauderdale, Florida 33334
INTRODUCTION
In recent years, efforts to reduce pollution from steelmaking operations have given
rise to widespread use of wet scrubber systems.   These systems are generally associated
with high flowrates of the scrubber water, which contains variable amounts of suspended particulate matter.
Wet scrubbers are commonly involved with closed loop water systems.   For this
reason efficient removal of the suspended matter is of primary importance to the performance of the scrubber.   Generally, scrubber feed should contain less than 100 mg/l
suspended solids.
Typically the loop will be processed by a physical/chemical treatment step to remove
suspended matter.   This step requires pH control, addition of a flocculating aid, and
gravity sedimentation.
Through laboratory testing, pilot studies, and full scale operations, Parkson Corporation has developed and refined methods of treatment for scrubber water systems.   In
the Iron and Steel Industry, Parkson's scrubber experience includes:   Q-BOP and BOF
operations, blast furnace systems, sinter plants, foundries, coke ovens, and open hearth
works.
This paper will briefly examine the use of Lamella Gravity Settlers in the clarification step of these systems.   Although some require similar treatment methods each
operation presents different operational conditions.
THE LAMELLA PRINCIPLE
Simply stated, the Lamella Gravity Settler (Figure 1) is an inclined plate liquid-
solids separator designed to reduce space, energy, and capital requirements.   The
inclined plates (45    or 55°) allow clarification space to be stacked such that only one
tenth the land area is needed for equivalent clarifier capacity.   The differentiation between angle of inclination is chosen based on the type of solids to be settled and on
the characteristics of the solids transport, by gravity, down the plate.   Parkson has
found that for solids having a specific gravity less than or equal to 1.1 (such as metal
hydroxides) a 55° angle settling system is warranted; for denser materials (such as
scrubber particulates) the 45° slope is normally utilized.   The plates are fed from the
side allowing separation to take place without disruptive upflow feed currents.   Flow
distribution to each plate is controlled by throttling orifices on the top of the plate
pack.   This factor forces an equalized hydraulic load on each plate resolving the short
circuiting problem found with most clarifiers.
The solids drop off the plates into the four-sided hopper section.   Parkson mechanically works the slurry by use of a low amplitude vibrator.   The vibrator primarily
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