Lime from kiln
and fresh makeup
White liquor slurry
Aux fuel Liquor
Lime mud slurry
Rotary lime kiln
Lime to storage for slaker
green liquor mixture flows to two or
three causticizers in a series to complete
the reaction. The liquor is separated from
the lime mud and becomes white liquor.
The calcium carbonate precipitate is
burned in the lime kiln to form calcium
oxide for use in the causticizing area.
Once the process has passed through
the third effect on the evaporators,
metal-seated valves are normally used
because the black liquor is becoming
heavier and more abrasive. If the
process has over half black liquor or the
material is going into the concentrator,
metal-seated ball valves are required.
When the fiber leaves the brown
stock washer, it either goes to the paper
machine or to the bleach plant, where
the stock will be whitened. Many different processes are used to whiten the
fibers—chlorine dioxide bleaching,
ozone bleaching, oxygen bleaching, peroxide bleaching, etc. Many of these
processes require higher alloy valves or
valves with liners.
In regards to these higher alloy
valves, a trend in the last few years is
that many mills that use 316 stainless
steel are complaining that steel isn’t
lasting as long as the 316 stainless
steel they bought years ago. This is
because environmental regulations
have forced many mills to close up
their systems. At one time, the paper
processing systems were open, and
many chemicals could go downstream.
Now, those processes are closed, which
means that chlorides and other chemi-
cals are building up. It also means
chemical concentrations are becoming
higher and higher, which is what is
causing accelerated corrosion.
The pulp and paper industry has hit the
doldrums, but they still require valves to
keep the mills operational. With the
state of the industry, mills will be looking to purchase high-quality valves from
people with an idea where the valves are
used and how to apply them properly.
With quality products, the mills can run
longer between shutdowns and repair
what they have purchased instead of
buying new ones every year. VM
HARLAN DUNK has been in the valve industry for 34
years.Th e last 10 have been with Velan (www.
velan.com), Montreal, QC, where he is the manager of several product lines. Reach him at