.m i p p l i e r
Update
Virginia milluses “progressivepigging”to remove pitch
deposits from pipeline
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The bleach plant a t WestvacoS bleach
board mill in Covington, Va. had a problem: its pipes were clogged.
In an effort to reduce lost production
due to pitch in the hardwood stock line
from thescreen room to the bleach plant.
various steps were taken including adding talc and liquid dispersant on different
occasions in the brown stock area. Addition of these materials, however, did not
adequately address the problem, On the
other hand, it was found that quarterly
cleaning of this stock line alleviated the
difficulty.
Adding talc proved to be costly while
providing little or no benefit, therefore
more conventional liquid-type dispersants were evaluated. These provecl to be
effective in lowering the amount of pitch
as shown by a pitch paddle. But dispersant usealsocreated anotherdifficulty in
that the existing pitch deposits began to
break away and escalated the initial
problem.
The next step evaluated-and which
has now become routine practice at the
Covington mill-was t h e q u a r t e r l y
cleaning of the 2700-ft. 20-in. stainless
steel line linking the screening operation to the bleach room. Flowmore Services, Houston, %x., was contracted to
clean the line ofpitch, which had built up
to about 1in. thick. By keeping the line
clean, pitch deposits were no longer
shaken loose during s t a r t - u p s a f t e r
maintenance downtimes. T h i s has
proven to be t h e most cost-effective
means for handling this mill’s pitch problem.
Tb clean the line, a method known as
“progressive pigging” is utilized; pigs,
bullet-shaped foam rubber cleaning
swabs, of increasing densities are used.
Three types of cleaning pigs are used: a
swab type used to prove the pipeline and
remove debris; a b a r e t y p e used to
remove hard deposits; and a coated type
used t o remove t h e h a r d e s t pitch
deposits. Wo to three pigs of each type
are run through the pipeline during each
cleaning. A radio transmitting device is
Mvch 1989 Tappl Journd
Pig (left)waits to be launched into the hardwood stock line at Westvacos Covington, Va. bleach
board mill
contained in each pig to locate it if it ever
becomes stuck in the line.
‘Ib launch the pigs into the pipeline, a
24-in. to W i n . reducer with a hinged closure on the large end and a knife gate
valve on the reduced end is“Y’tl” into the
line to be cleaned just ahead of the line
pump discharge valve. The pig is closed
into the launcher and a 80-90 psi pressure is applied behind it using water
from a pumper truck. The valve on the
launcher is opened at the same time with
the pressure forcing the pig into the line.
The 250-hp chest pump is then started,
sending the pig through the 2700 ft of
line, pushing out the pitch in front of it.
The line C ~ be
R c!exnerl ir. 4 hours TUXning 8 pigs.
To verify that the pipeline has been
cleaned satisfactorily, several measurements are taken: difference in pressure
drop at the launcher or the pump, velocity increase during successive pig runs,
condition of the pigs esiting the pipeline,
observation of the effluent, and visual
inspection of the pipeline. Once satisfied, the line is restored to service.
Compliments....
Flowmore Services Corp.
19515 FM 149, B-150
Houston. TX 77070
Tel: 1-800-356-9667
F2x: (713)255-2385
Technical Assistance
Service
Pig Sales