Q. I would like to set up a citric acid passivation line as follows: heated citric, drag-out tank, three cascading unheated rinse tanks and possibly a heated rinse to help in drying. Am I missing any tanks and or accessories that you would recommend? M.K.
A. Based on your description, you have all the major steps of the process identified. The rinse tanks should be counter-flow, cascade-rinse tanks. That would mean the cleanest water will enter the final rinse tank, cascade to rinse tank 2 and then to rinse tank 1. It is important to design the rinse tanks with a baffle or other means to ensure that contaminants in the tank are diluted with the water and simply don’t just skim over the surface to the overflow weir and into the next tank.
There is some additional equipment you may want to consider, depending on your product mix and manufacturing environment. Ventilation and exhaust of the heated tanks would be helpful to minimize the steam in the work area. Additionally, while the citric acid is relatively benign, you should check with an industrial hygiene expert to ensure you do not require ventilation over the citric acid tank.
Another process control improvement you may want to invest in is a conductivity-controlled solenoid valve to optimize the water usage in the line. It works by sensing the conductivity in the final rinse tank. As parts are processed through it, the conductivity will rise. When it reaches a pre-set value, the system will open the solenoid valve, allowing rinse water into that tank and cascading through the previous two rinse tanks. This will maximize water savings while minimizing water usage.