Neutralizing Water pH Without Reliance on Expensive CO2
Chemical dosing · Cost reduction
Paying for CO₂ the plant shouldn’t have needed.
An industrial plant was using a combination of boiler stack gas and expensive carbon dioxide (CO₂) to lower the pH of its recycled water, which needed to be neutral prior to use. Stack gas was added at several points in the treatment train using simple coarse-bubble diffusers in a clarifier center well and a subsequent pH adjustment tank.
Because the stack gas could not reach neutral pH in the last reaction tank, the company also purchased and injected CO₂ into the clear well near the water supply pumps that fed the manufacturing process.
At times that purchased CO₂ foamed downstream — the pumps drew in the gas and pushed out a supersaturated gas/water mixture that interfered with production and forced operation curtailments. The client was making the neutral water they needed, but knew there had to be a better, more cost-effective way.
A better mixing pattern, built from spare pipe.
Mr. McKinnon observed that the individual stack gas diffusers were ineffective at mixing gas through the water column. Much of the gas escaped undissolved — losing its pH-adjustment potential — and most of the water never contacted the stack gas as it passed through the tank’s uneven distribution.
He proposed that plant staff build an alternative diffuser array from commonly available pipe and the existing stack gas connection points, arranged to create a spiral roll mixing pattern. The pattern traps gas bubbles in the turbulent flow path and mixes them through the entire water column.
No purchased CO₂ since installation.
After a successful test run of the trial array, the team installed a permanent pipe diffuser. It has performed so well that the client has not purchased CO₂ since — saving at least $13,000 a year.
Better mixing also lets operators throttle the gas flow, hitting the target pH at lower flows. The result is tighter pH control with less variability, improving overall water quality for the facility.