Static Mixers

Static mixers can be applied to a wide range of process operations, including dosing, dispersion, laminar flow heat exchange and emulsion formation. They offer many key benefits for combining liquids, gases and powders and they are tried, tested and trusted in many different industries. Mixing action is achieved by the continuous splitting, extension and transportation of the components. Motionless mixers use a series of precisely configured mixing elements to process the components. Differences in concentration, temperature and velocity are equalized over the flow cross-section. For further information go to principles of operation. Mixers are supplied as simple plain ended pipe sections, flanged with multiple injectors and sampling points, fitted in bends, or in square or rectangular section for ducts and open channels. They are manufactured in a wide range of materials, including carbon steel, stainless steel, exotic alloys, GRP, uPVC, cPVC, PTFE, etc.

The elements are made in various designs to suit different applications, and are available fitted into a range of housings, from high pressure to open-channel, making them ideal for all kind of industrial environments. The elements are fixed or removable and the necessary number of mixing elements for a specific application depends on the required homogeneity and on the volume flow ratio of the components.



Mixer elements

The homogeneity requirement differs according to the particular mixing task and should specified by the final user in terms of variation coefficient CoV. Usually a CoV between 0.01 and 0.05 is a reasonable target for most applications. The lower the value of CoV the better the mixture quality.

CoV is defined as:

where:

c : average measured concentration of the additive
cmean : theoretical mean concentration
ci : local concentration of the additive at the ith measurement position
N : number of position where the concentrate is measured

Benefits:
  • Static mixers deliver a high level of mixing efficiency, therefore the consumption of dosed chemicals and formation of byproducts can be dramatically reduced.

  • They eliminate the need for tanks, agitators, moving parts and direct motive power and they allows to gain highly efficient mixing with low energy consumption.

  • The energy required for mixing is efficiently extracted as pressure drop from the fluid flow through the elements. Mixers are invariably installed in existing systems without reducing the capacity of existing pumps.

  • The installation is very easy, no special skills are required other than normal engineering skills.

  • Mixers have no moving parts and are virtually maintenance free.

  • Static Mixers are available in all standard pipe sizes and, in the case of open channel designs, are available in any size with no upper limit.

  • Each Static Mixer is carefully designed to meet the specific requirements of each application.

Principles of operation

In case of two miscible liquids in laminar flow, the main mechanism in a static mixer is flow division. The elements are helical or pseudo-helical and are arranged in a series of alternating left and right hand 180 twists. The elements split the fluids entering in two streams and than rotate them through 180 degrees. The elements are in series in the mixer. As the number of streams or layers increases, the layer thickness decreases. Typically, 12 to 24 elements are required to provide a complete mix.

In case of two miscible liquids in a turbulent flow, the main mechanism is radial mixing: fluids are constantly moved from the pipe centre to the pipe walls and the fluid change direction with each succeeding element. To achieve a fully homogeneous mix in a turbulent flow 1.5 to 4 elements are sufficient.

In case of two immiscible liquids in a turbulent flow, the radial mixing mechanism reduces radial differences in velocity and in droplet sizes. This raises the surface area of contact between phases, improving the mixing. The disperser length necessary depends on the required contact time. For mass transfer processes in which equilibrium is quickly established, a length of 5 diameters is generally sufficient.

Drawing of Statiflo pipe mixer Series 100/150

Types and Applications

Static mixers are installed in thousand of process plants worldwide, providing the highest standard of mixing efficiency, reliability and economy.

Static mixers are grouped in the following categories:

Channel mixers: installed in new treatment works or retrofitted in existing installations, they rapidly achieve a high degree of mix with extremely low headloss on very short lengths. Channel mixers cover a wide range of flowrates and are ideal for efficient chemical dosing. They allow chemical savings with consequently economical and environmental savings.

Pipe Mixers: in stainless steel, PVC, PP, carbon steel, fixable or removable. Available with heating and cooling jackets, injectors, sample points and instrumentation bosses. Suitable for all industries. Wide range of diameters: from 10 to 300 cm.

Gas Dispersion systems: it uses two different mixers, one to form gas bubbles and the second to provide contact time and efficient mass transfer.



Statiflo Channel and pipe mixers

The main applications are in the following fields:

Water and wastewater treatment:

Oil, gas and petrochemical industries

  • Measurement of water content of crude oil in pipelines

  • Desalting crude oil with water

  • Diluting ployacrylamide for enhanced recovery

  • Mixing additives into gasoline or fuel oil

  • Adjusting the viscosity of heavy fuel oil with gas oil

Continuous process industry:

  • Plastics, fibres

  • PH control

  • Resins, adhesives, epoxies

  • Colours, hardeners

  • Detergents

Food and pharmaceutical

  • Mixing CO2 into fruit juices, wine or coffee extract

  • Mixing milk wit acids

  • Diluting molasses with water

  • Diluting concentrates and mixing flavourings

Pulp and paper:

  • Acid and caustic dilution

  • PH control

  • Blending

  • Low consistency bleaching

Lenntech can help you to design the mixer that best suits your application. Do not hesitate to contact us for a direct technical and commercial offer.

See also our web page on venturi principle and applications.

Source: www.statiflo.net







Lenntech BV

Rotterdamseweg 402 M
2629 HH Delft
The Netherlands

tel: +31 15 261 09 00

fax: +31 15 261 62 89

e-mail: info@lenntech.com











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