Problem:
A waste heat recovery boiler manufactured by Missouri Boiler and Tank Co.
was used in the recovery of heat from process steam in an chemical
processing plant. In this recovery boiler, there are 166 tubes making two
passes inside the shell. The process steam enters the recovery boiler at 260°C
and leaves at 200°C as a condensate in the tubeside. In the shellside, a
subcooled water at 50°C enters the shell and leaves at 193°C as a
superheated steam.
The outside walls of the tubes regularly scaled up. This resulted in a
loss of heat transfer, leading to the reduction of condensate production.
This necessitated plant shut down for maintenance. This particular boiler
was located on the second floor of an exterior tower, hence a crane was
needed to remove the bundle. This procedure required eight men, three days
of scraping sand blasting and jet spraying to remove the scales from the
tube bundles.
On one occasion, the bundle became so encrusted with scale that it become
completely wedged in the boiler and was damaged when removed for cleaning.
This resulted in a two week shutdown and a new, $50,000 bundle.
