Company: EEC International
Contact: Mr Emmitt W. Hall, III, Shared services, Project engineer
In Kaolin production, the kaolin is dried in so called spray dryers. Kaolin slurry is sprayed into a gas flame of 1050°F (566°C) where the kaolin is dried to powder that is falling down to the bottom of the spray dryer and transported away to a silo. The surface temperature of the spray dryer is 400°F (205°C) and the spray dryer is insulated both for reduction of heat loss and for worker protection. Normally the insulation consists of a 4 inch (100 mm) cementitious mineral wool insulation, reinforced with chicken wire and covered with a glass fabric wrapping.
A problem is, that due to the heat, the insulation cracks after some time. Therefore it is necessary to re-insulate the spray dryers at certain intervals.
To repair the spray dryer, it is necessary to remove all the insulation and afterwards to re-insulate it.
Maintenance work consequently means that the production has to be stopped for several weeks: The spray dryer must cool down before removal of old insulation and application of new one. Afterwards the new insulation needs time to harden.
The Kefa Heat Protection Solution
All old insulation is removed and the spray dryer is coated with Kefa Airless at a thickness of 80 Mill (2 mm). After one hour the operation of the spray dryer can be started again.
After a few weeks, Kefa Airless has sintered to a hard, mineral like substance.
Test dryer and result
A pilot spray dryer (Picture) was treated in March 1997. The Kefa Airless was applied at 50 mils (1,2 mm). The spray dryer is used for R&D and quality control work and is therefore running at longer and shorter periods. This means that the Kefa Airless insulation is frequently exposed to large temperature variations, i.e. a more extreme situation than a continuous production creates.
The test went on for 320 days. (Ended in Jan 1998)
At full operation of the spray dryer, the surface temperature of Kefa Airless measures 135-140°F (57-60°C), a reduction of 265°F (130°C) = 66%.
There is no discoloration and no visible deterioration of the coating.
No smoke or fumes from the coating have been observed during the test period
Full scale applications
After the successful results of the pilot plant, 5 full scale spray dryers have
been treated with Kefa Airless. These have all been applied with an 80 mill (2 mm) thick coat.
The surface temperature has decreased from 400°F (205°C) to 105°F (41°C).
The Kefa Airless coat replaces a cementitious mineral wool insulation of 4 in. (100 mm).
In 2003 there was a burn through in one of the Kefa Airless treated spray driers. With the old, conventional insulation it used to take several weeks before a burn through was discovered. This usually results in damages to the equipment and high repair costs. Under all circumstances the production has to be closed down and all insulation must be removed and replaced.
This time the burn through was detected in a few hours, due to discoloration of the Kefa Airless surface. The repair was easy. Loose paint was removed and the damaged area was recoated with Kefa Airless, a matter of a few hours.
Advantage
Kefa Airless is less expensive than conventional insulation – both material and labour cost are lower.
Maintenance and repairs of the spray dryer is simplified.
Repair can be done without removing the coating.
Damages to the Kefa Airless coating can be repaired without stopping production.
A productivity improvement has also been recorded – the dried kaolin contains 2% less water, indicating that there is a reduced heat loss in the production.
Consequently gas consumption is reduced.
