A. H. LUNDBERG LIQUOR SEPARATOR


The concentration and proportion of the most desirable resin acids is highest in pine
species trees. During alkaline pulping these acids are neutralized (saponified) by a
portion of the caustic soda present in the cooking liquor. These soaps are of lower
density than black liquor and generally rise to the surface where they may be collected
from various tanks in the black liquor cycle. Most commonly, a tank especially designed
for this purpose is installed between effects of the black liquor evaporator.

The collected soap is then transferred together with varying amounts of black liquor to
storage. Storage is provided to accumulate soap for the tall oil acidulation plant; but more
importantly to provide time for the entrained black liquor to drain from the soap. The
amount of black liquor entrained in the soap varies with the point of collection as well as
with the equipment used. Entrainment of 10% to 25% liquor is not unusual. Even with
the best designed systems, the residual soap contains more than 5% black liquor.

In the recovery of tall oil soap, the first step is removal of soap from the black liquor. The
second, and equally important, step is the removal of black liquor from the soap.
Removal of liquor also increases the acid number of the tall oil recovered from the soap.
An independent study made at the Lakehead University in Thunder Bay, Ontario, with
soap from four different mills gave the following information:

% Black Liquor
    Mill Centrifuge Acid No.
Test
    A    1.9    153
    B    13.6    145
    C    5.1    145
    D    19.8    131


Note: Mill A, the only mill equipped with a Lundberg Liquor Separator, processes 40 tons
of soap per day through a 21 foot diameter tank.

The Lundberg Liquor Separator is designed to improve the drainage of liquor from soap.
The device is shown schematically on the attached drawing. The tank in which the
Lundberg Soap Separator is installed is always full to the overflow launderer and thus
does not provide usable soap storage. Since the separator provides full utilization of the
drainage tank it can be considerably smaller than tanks relying on gravity separation
alone.

It is an advantage to locate the drainage tank as close as possible to the storage tank
serving the tall oil acidulation plant or loading facilities as removal of liquor from the soap
results in a considerable increase in soap viscosity, about 10 to 15 times (i.e., viscosity
increases from 10,000 SSU to 250,000 SSU).

The Lundberg Liquor Separator provides a means for the gentle stirring of collected soap
in storage. This action leads to the release of liquor from the highly viscous soap while
the Lundberg Liquor Separator provides a path for liquor drainage. The Lundberg Liquor
Separator is usually installed in the first soap storage tank. When soap washing is
utilized, a second unit is recommended for the washed soap storage tank.

Black liquor solids in soap intended for the production of tall oil is undesirable from
several standpoints:
1.    It reduces the acid number (a measure of quality) of the product tall oil.

2.    It increases the amount of lignin "heel" (kraft lignin precipitates when the black
liquor is acidified). The lignin heel will contain about 30% tall oil plus a significant
amount of unreacted soap, thus the net yield of tall oil from a given amount of
soap is decreased by the amount lost with the heel. Studies have shown that the
acid number of the tall oil will decrease with setting times of over three hours
recovery.

3.    Additional process equipment is required to deal with the lignin heel.

4.    Acidulation of the reduced sulfur compounds in black liquor release H2S which increases
pollution control problems.

5.    If soap acidulation is done at the mill, the lignin heel requires additional expense
for chemical recovery.

6.    If the soap is processed by an outside processor, the black liquor content reduces
the value of the soap to the processor as well as increasing the transportation cost
and resulting in a loss to the mill of valuable chemicals.

Liquor-Soap Separator Tank
SS-1010-A