Gas dispersion is not to be underestimated; many applications like waste and water treatment require it. It involves a mixer agitator and the injection of gasses to achieve a process or chemical reaction. This could sound like the simpler side of mixing, but there is a delicate balancing act behind gas dispersion; the volume and rate of gas introduced are critical for the efficiency of the system. The following key points should be considered when it comes to successful operation and design:
Avoid Flooding by Paying Attention to the Gassing Systems
Gas dispersion is one of the few mixing applications where agitator tanks can go from operating successfully to not operating at all without any changes to liquids or solids in the tank. The gas forces the change, and if gassing systems are incorrect, or if there is too much gas beneath the impeller, the impeller can run the risk of ‘flooding’, also known as operating in a big bubble of gas. When this happens, solids will not suspend and gas will not disperse, often resulting in immediate failure of the process.
Sepro’s design programs can accurately predict what the level of gassing needs to be in the tank and how it will impact the mixing system. For example, the Canamix CHG4 high solidity, gassing impeller was specifically designed to accommodate high gas dispersion requirements. Typically used in bioleaching, hydrogenation, fermentation, cyanide destruction and other gassing processes, this impeller has a high solidity ratio, meaning the gas ‘sees’ a rotating disc, minimizing the amount of gas passing through the agitator impeller.
The impeller’s high pumping capacity provides effective gas retention, meaning the interfacial contact between gas and solids is extended.
Systems Need to Meet Your Specific Requirements and be Mechanically Reliable
For a successful operation, it is important that agitator impellers and sparging systems are designed to cater to the type of gas being used and to work together as an integrated system. With bigger gas dispersion systems, sufficient power must be installed to overcome any potential risk of flooding. The amount of power needed also determines the size of the agitator impellers. Typically, they are larger than impellers used in other mixing applications; this means higher horsepower, larger gearboxes, and larger shaft diameter. More exotic materials may also need to be considered, for example, high chromium stainless steel, or austenitic stainless steel.
Don’t forget the Sparging Systems
There are also things to pay attention to with sparging systems. For example, if a ring-sparger becomes partially blocked and air is coming out on only one side, the agitator shaft will end up pushed over to one side as well. This will put very high unequal loading on the gearbox and the bearings. This is not what you want; however, we use proven safety factors in our designs to prevent a mechanical failure if this situation does arise.
Learn More about Agitators
Efficiency in design and operation is what motivates Sepro to spend a significant amount of time designing gas dispersion systems compared to other mixing applications. If you are looking for the best mixing and pumping system for your project and want to learn more, contact the agitator experts at Sepro today.