A. H. Lundberg Associates, Inc. offers both air and molecular oxygen white liquor oxidation systems. White liquor is contacted with oxygen to oxidize the sodium sulfide to sodium thiosulfate. The oxidized liquor becomes a caustic source for a number of different mill systems including oxygen delignification of pulp and incinerator flue gas scrubbing.

The Lundberg Associates patented air oxidation system is a two-stage process within one tank, or if capacity is too large, in two tanks. The second stage of oxidation, which drives the residual sulfide to its exit concentration, is a plug flow arrangement.

In a single tank system feed white liquor enters the first (bulk oxidation) stage which is the center of the tank. The product from this zone enters an outer annulus and flows in a plug flow arrangement around the annulus. Ambient air is compressed and is sparged into the annular region. The air exits this zone through internal pipes and is sparged into the center bulk zone. The oxidized white liquor from the second stage should be directly used in process so that sulfide reversion does not occur. The air exiting the system passes through a mist eliminator for removal of caustic droplets.

The molecular oxygen oxidation process takes place under high pressure and temperature. Molecular oxygen is sparged into the feed white liquor. This mixture is passed through a series of serpentine pipes to induce mixing and give residence time for the reaction to occur. The progress of the reaction can be judged based upon the temperature rise of the white liquor through the reaction since the process is exothermic. The oxidized white liquor exists the reactor and the unreacted oxygen is separated in a phase separator. Oxidized white liquor is returned to the inlet of the reactor to insure a constant velocity and pressure drop through the reactor as well as some preheat of the incoming mixture. White liquor exiting the system can be mixed directly with the pulp in its hot state or cooled in a heat exchanger.

The molecular oxidation system can be supplied as a prepiped, skid mounted module including all instrumentation and valves ready to be mounted on the purchaser's foundation and connected to the service piping.