CTMP and NSSC LIQUOR PREPARATION

General Description

The A. H. Lundberg, Inc. Liquor Making Plant is designed to supply SO2 gas as required
for Na2SO3 cooking liquor preparation.

The sulfur burner can be started up and shut-down with ease. Major changes in burning
rates can be rapidly made with only a slight interruption. Minor changes can be made
without interruption.

The SO2 concentration is adjusted independently of the sulfur burning rate and can be
held within 1/2 to 1% during steady operation. Concentrations between 16% and 18%
are easily obtained.

The burner consists of a hollow steel tube lined with refractory brick. Air and liquid sulfur
in the proper proportions are admitted at one end, burnt, and leave by the other end of
the burner. Air is admitted around the nozzle and burning takes place in the jet issuing
from the nozzle.

The hot gases pass from the burner to the Primary Cooler where they are quenched by
a water spray, the gas temperature being lowered from about 2000-2200 degrees F. to 180
degrees F.
This temperature drop is accomplished mainly by evaporation of the water spray. Due
to the extremely corrosive nature of the gases during this transition period, and in order
to protect subsequent equipment, it is extremely desirable to know that saturation is
completed in the primary cooker. Besides lowering the gas temperature very rapidly to
minimize the formation of SO3, the primary cooler acts as a scrubber to remove other
impurities which may be present in the gas stream.

The SO2 gas passes directly into the Na2SO3 absorption tower, where cooking liquor is
prepared by absorption of the SO2 in caustic soda or sodium carbonate solutions.

The hot water underflow from the cooler goes to the weir box. The relatively small flow
of contaminated effluent from the primary cooler is sewered. As the water temperature
is high, the SO2 loss is very low.

The continuous overflow from the weir box is valuable in preventing undue sulfur loss.
By observing the clarity of the water flow, the operator is warned that an operating
problem exists. Cloudy water indicates formation of sublimed or unburned sulfur.

The operator, being warned by the cloudy overflow, should immediately change draft
conditions and/or reduce the sulfur burning rate.

Following the Na2SO3 absorption tower the gases are scrubbed and vented to the
atmosphere through a fan. A draft control is used to adjust the amount of air brought into
the system and thus regulates the concentration of SO2 in the burner gases.

The Na2SO3 solution from the bottom of the absorption tower passes to the circulation
tank for recirculation through the absorption tower. A portion of this solution is bled from
the system to storage. The pH of the Na2SO3 liquor is automatically adjusted to the
value desired by the mill operation. Changes in pH level are easily made with a simple
adjustment to the Lundberg density column that controls the chemical feed to the
absorption tower.