Continuous Drying and Curing System for Painting of Aluminum Tubes with VOC Controls
Project No 1087
The Challenge
And producer of Aluminum Tubes in China needed a continuous drying and curing system in order to dry Flux Paint on one stand of aluminum tube in a continuous process, quench to cool the aluminum tubing, dryer to dry the water from the tubing and thermal oxidizer for VOC destruction.
The aluminum tubing needed to be coated and cured during the process, with a single tubing strand passing through the oven at a time, with maximum pass through rate of 60 m/min (197 ft/min). The loading for the maximum pass through rate shall be 200 Kg/hr (440 lbs/hr) for single tubing strand.
The catenary style system needed to be able to remove 4 Kg/hr (8.8 lbs/hr)of solvent, with a uniform curing PMT of 120°C (248°F) PMT; and tube cooling Temperatures from 120C to 50°C (248°F to 122°F), dependent on line speed and water temperature.
The Solution
The Scope of the project included a curing oven, a quench, dryer, and thermal oxidizer.
In the oven system hot air is used to dry the paint (coating) on the aluminum tubing and to vaporize all residual process coming of the coating during the drying of the tubing. The VOC’s coming out of the painted metal are destroyed in an oxidizer, there is no emission of hazardous substances in the atmosphere. Air recirculation system is designed to produce uniform heating in the oven. The VOC’s are carried to the oxidizer for oxidation and heat release.
In the oven system the oxidizer serves as the pollution control device. Time, temperature and turbulence (known as three T’s) are the three necessary ingredients for successful oxidation. The design shall ensure that all of three are sufficiently present. Destruction Efficiency of 95% is achieved by using a residence time of 1 second at 1400ºF (1600ºF max.).
The curing oven exhaust was connected to a thermal oxidizer via ductwork as well as a push/pull type system with curing oven exhaust fan and oxidizer induced draft exhaust fan.
The Results
The VOC’s coming of the coated metal act as fuel to the oxidizer reducing primary fuel cost to absolute minimum.