A solution for biomass abrasion

Sept. 2, 2011, Quebec City – Over the past
10 years, the landscape of the North American pulp and paper industry has seen a dramatic change. The addition of
biomass boilers has been a popular choice for energy cost reduction. The forest
industry now meets more than half its energy needs with self-generated biomass
wastes. Although typically defined as wood residues such as bark or hog fuel,
biomass also includes the plant effluent, de-inked mud, and other residues.

The White Birch
Paper plant in Quebec City is not unlike many other newspaper paper mills in
North America. To survive, it took the necessary steps of modernizing the
plant. With the same energy concerns, it installed a high-efficiency biomass
boiler in 2006 to decrease energy costs. One of the keys to high-efficiency
boilers is to pre-dry the biomass before feeding into the boiler. This is
accomplished at White Birch Paper using a rotary dryer followed by ducting up
to two 50 foot tall (15 m) cyclones that sit 130 feet (40 m) off the ground.
The larger particles fall out of the rotary dryer onto a conveyor, which then
feeds into the boiler. The hot air and fines from the outlet are sucked up into
the cyclones where the fines are separated and sent to the boiler while the hot
air is sent back to the feed end of the rotary
dryer to pre-dry the biomass.

The
biomass comprises 40% plant effluent and 50% de-inked mud. The two cyclones are
made of 3/16 inch thick SS304 to deal with the slightly corrosive (SO₂)
plant effluent. The cyclones operate under negative pressure (air pulled
through and not pushed) because of the high flammability of the dried effluent
and are equipped with an extinguishing system of water nozzles. Only one fire
has occurred since commissioning, and
this was due to leaky seals on the rotary valves and flange connections. Normal
operating temperature at the top of the inlet is
95°C and 65°C at the cone outlets.

Signs
of wear

After 18
months of operation, the cyclones started showing signs of wear, requiring the
replacement of several sections. Replaceable liners made of AR400 steel plates
were installed for the inlet and upper barrel section. The lower 10 foot
diameter (3 m) cone was also replaced and fabricated using AR400 plate.

Over the
following year, wear continued to occur in both cyclones, requiring several
maintenance interventions. Due to all the patching and uneven surfaces, the
wear rate continued to increase, becoming a cause for concern.

The
steam plant maintenance superintendent at the time had heard about a
cyclone-lining project completed a year earlier at a nearby cement plant using
Kalcret, a cement bonded wear compound. He inquired about the possibility of
doing the same with White Birch Paper’s cyclones. Initial discussions about
lining the inside of the cyclones with Kalcret were held in June of 2009, but
due to short outage periods, the decision was taken to install AR liners during
the September outage.

An
inspection in January 2010 showed severe wear on all the AR liners, and the
concern was that the original steel would be too thin to receive any more
liners.

A solution

After
several more discussions and meetings, it was concluded that lining the
cyclones with Kalcret offered two major advantages: the cyclones would not need
replacing, representing a significant cost savings, and the logistics were
simpler.

The
contract was awarded to Abresist Kalenborn Inc. of Pointe-Claire, Quebec, to
line the bifurcated inlet section and both cyclones, an area totaling
approximately 3,000 square-feet. The turnkey project was handled entirely by
the Canada Kalprotect installation team, including the mobilization of cranes,
scaffolding, and installation of all materials.

It was
determined that Kalcret-BTS sprayable material would be used for each entire
cyclone, with the exception of the bifurcated inlet area and lower cones. For
safe and proper installation of the scaffolding, the first three sections of
cones were removed and lowered to ground level. These lower cones would be
completely replaced with new steel lined with Kalcret-BTX trowellable compound.

A wire
mesh anchoring system was installed on all surfaces receiving the Kalcret wear
compound. The inlet area and cyclone roofs were lined with the BTX trowellable
Kalcret, and the bull nose was protected using an engineered Kalocer ceramic
tile.

Using
the spraying equipment, quick work was made of the remaining 2000 square-feet,
where Kalcret-BTS was applied. The new lower cones, now lined with Kalcret-BTX,
were then positioned back into place and reassembled. Final touch-ups and one
final site cleanup were followed by demobilization on schedule.

According
to Louis Senechal, project manager, “The benefits of the Kalcret lining were
noticed immediately after startup, as the operators were able to control the
temperature and airflow much more effectively, which will allow for a more
precise and efficient operation of the boiler.”

Increases
in equipment wear life, as well as an improved operating efficiency, were just
two of the benefits of the Kalcret abrasion resistant wear compound.

Lining
the remaining 1000 square-feet of duct leading into the cyclones is already
being discussed for the next outage.