Application of Mixers in Water Treatment and Desalination Plants
One of the most vital equipment in municipal water treatment plants and industrial desalination units are mixers. These mixers are designed and supplied for various volumes and the following applications:
Flash Mixers & Flocculators
Separation of insoluble salts from water is a crucial and unavoidable process in water treatment and desalination. Initially, coagulating agents such as ferric chloride (FeCl3) or polyaluminum chloride (PAC) are added to the water and homogenized by high-power mixers. Then, in the flocculation tank, a flocculant substance like anionic or cationic polyacrylamide (PAM) is added, and gentle mixers or paddle flocculators aid in the formation of flocs and settling of solid salts.
pH Control
In industrial desalination units, it is preferable for water to be slightly acidic (pH<7) before entering the desalination membranes to prevent salt deposition on the membrane surface.
Two methods are used for this purpose:
- An acidic substance is added to a tank and homogenized into a solution using dynamic mixers.
- The desired acid is injected into the injection line before the static mixer, and after passing through the static mixer, water with the required pH is produced.
Production and Use of Lime Slurry
Lime slurry, also known as lime milk or lime suspension, is used in water treatment industry for the following purposes:
- pH adjustment and neutralization of acidic water.
- Assistance in better flocculation and removal of impurities.
- Removal of water hardness.
The use of lime requires the use of mixers in two different sections, which are as follows:
- Lime is produced as a solid powder and needs to be converted into a 10 to 15% concentration solution before use. In this section, the lime powder is introduced into a tank equipped with a dynamic mixer to produce a solution with a specific concentration known as lime slurry.
- The prepared lime slurry is injected into the water treatment tank or transfer lines and can be homogenized into a uniform solution using either a dynamic industrial mixer or a static mixer.
Chlorination
The final stage of water treatment, whether it is municipal or industrial, involves adding a certain type of biocide to the treated water to eliminate any microorganisms present or that may be introduced during the transfer process.
One of the most common biocides used is chlorine. Due to its high electronegativity, chlorine oxidizes microorganisms and eliminates them.
Chlorine is available in the market in three forms:
- Sodium hypochlorite solution or bleach with a maximum concentration of 11%, known in Iran under the brand name “Whitex.”
- Solid calcium hypochlorite with an approximate concentration of 70%.
- Chlorine gas with a concentration of 99%, which is used in municipal water treatment plants.
Static mixers are considered the ideal type of mixer for mixing chlorine and water. More precisely, chlorine should be injected into the nearest location to the static mixer to ensure the production of a homogeneous solution as it passes through it.
