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.
The Electronic Descaling 2000 unit was installed on the water feed pipe to the recovery boiler.
Case 2:Shell-and-Tube Heat Exchanger
A hot water boiler was used to provide
domestic hot water from waste steam in a semiconductor plant in a
hard water area in Pennsylvania. Due to health-related concerns, the
plant decided not to use any scale-inhibiting chemicals even though
they had a very hard water of 350 ppm CaCO3 equivalent. After one
month operation without ED2000 unit, a new tube bundle was completely
coated with thick scales. Subsequently, the overall heat transfer
coefficient was dropped by 70% from the maximum value.
The Electronic Descaling 2000 unit was installed on the water inlet to the steam water heater. After one month operation, the new tube bundle was removed and found clean.