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Appnote: Controlling pH with CO2 injection

Controlling pH with CO2 injection

A customer approached Alicat with a water treatment application in which carbon dioxide would be sparged into a body of water to control the pH of the water. The application required controlling mass flow over a wide flow range and reducing the time lag between CO2 injection and pH changes of the water.

One challenge the customer faced: the bodies of water they work with vary in volume and therefore require a wide range of CO2 flow rates to maintain the pH balance of the bodies of water.

Another challenge: larger volumes of water don’t react in step with the CO2 injection process, causing a time lag between the CO2 injection into the water and the subsequent pH change of the water.

An Alicat flow controller for pH control of a tank of water following a CO2 injection

pH control of a water tank following a CO2 injection.

Alicat’s Solution

Alicat application engineers determined that the Alicat MC-Series mass flow controller would solve both these challenges.

The 200:1 turndown ratio of the Alicat mass flow controllers allows the instrument to be used accurately down to 1/200th of the full-scale flow rate. This permits customers to use a single instrument to control a very wide flow range, reducing costs and increasing available space.

To resolve the time lag problem, the Alicat device needed to be able to interface with an automated digital control system, which would report the progress of the pH change and adjust the setpoint of the Alicat controller in real time.

Because every Alicat mass flow, liquid and pressure device is equipped with both analog and digital communications as a standard feature, the Alicat device integrated seamlessly into the customer’s system. Alicat’s 100 ms control time allowed for a significant reduction in phase lag between CO2 delivery and pH adjustment.