AcidRecovery.com

Aerospace Parts Manufacturer

Northeast United States

Acid Recovery System

Background:

In the manufacturing of high-precision aircraft components, imperfections are not allowable, including the final coating having to meet stringent specifications. If the final product does not meet these quality standards, aerospace manufacturers strip the imperfectly-coated components using hydrochloric acid (HCl) so that the metallic coating can be reapplied.

Problem:

While reapplying the coating ensures a quality product, the stripping process produces a contaminated acid solution that requires frequent changing. For one aerospace manufacturer, the spent acid solution had to be replaced every five days, resulting in the high costs of system shutdown, off-site disposal and acid replenishing.

Solution:

To reduce the costs associated with the handling and disposal of the spent acid and its replacement with fresh acid, it was decided that an Acid Recovery System should be installed. The Acid Recovery System provided by Mech-Chem Associates, Inc. utilizes a distillation column that recovers the spent hydrochloric acid solution and returns the clean distilled acid to the acid strip line at 10 gallons per hour (GPH).

The system operates continuously, 24 hours a day, 7 days a week recovering a 16% to 20% HCl acid solution. The recovered acid solution is returned at the same concentration as the feed solution (16% to 20%), as the goal of the system is to purify, not concentrate the acid.

Above: Examples of the controls and instrumentation found in the hydrochloric Acid Recovery Sytem, including the control panel (left) and a level transmitter (right).

Continuous operation of the system is possible by the use of advanced instrumentation and automation technology. Instruments such as the level and temperature controls are carefully chosen to sustain the aggressive chemical environment. These controls are integrated into a PLC which allows the system to run safely and continuously with a minimum amount of operator attention. The controls are mounted in a custom-designed control panel with graphical displays.

Technology/Treatment Used

The Acid Recovery System uses materials of construction based on compatibility with the hydrochloric acid. The system's boiler has a shell made of Teflon-lined steel and the bundle is constructed using tantalum. The distillation column is comprised of glass components which provides an additional benefit of being able to see the distillation process in action. The use of glass ensures compatibility with the hot acid, while lowering fabrication costs compared to a system constructed entirely of Teflon-lined steel.

To ensure the safety of the system, the components are surrounded by an epoxy-coated structural steel support module that supports the system, while protecting the instruments and components. The distillation system is on a single skid with the structural steel support module containing most of the equipment, components, piping, instrumentation and controls. Only the control panel and pumps are outside the steel support module.

Results:

With a greatly increased life for the processing bath, the aerospace manufacturer has eliminated the need to stop production each week in order to replenish the acid. The system now operates continuously without stopping, eliminating downtime and increasing production. With 90% of the HCl acid recovered, fresh acid purchases have been dramatically reduced. Additionally, transportation and off-site disposal of hazardous wastes has been reduced to less than 10% of previous levels.

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