Design method for dense phase pneumatic conveying lines
Scale-up calculation from pilot tests
Types of pneumatic transport
Dilute Phase transport
Dense Phase transport
Airlock Rotary Valve
Product inlet / Injector
Conveying speed / velocity
Air volumetric and mass flowrate
Pipe Equivalent Length
Solids velocity in pipe
Pipe Diameter or Bore
Selecting dilute or dense phase
1. Method and limitations
There are few existing methods published to calculate dense phase pneumatic conveying systems but most of the knowledge here stays with specialized suppliers. Anyway, if dilute phase pneumatic conveying lines can be sized pretty confidently thanks to models, it is less true for dense phase conveying, thus pilot plant tests are almost every time conducted in order to design a new installation and to control / adjust model results. The calculations below are showing how to scale up - or scale down in some cases - the pilot plant results in order to design an industrial line, it focuses especially on the parameters to be kept constant.
In order to have meaningful test results, the following must be ensured :
- The test line has a similar length, but most importantly a similar number of bends as the industrial line
- The solids load ratio is similar to what is planned for the industrial line
- The pick-up speed and end of line speed are determined and kept equal for both test line and industrial line
From there, the pressure observed during the tests should be the same industrially and the industrial actual line actual need in conveying air and actual throughput can be calculated thanks to the following formula :
A trial is organized to design an industrial dense phase pneumatic conveying line for a material that is sensitive to breakage. The industrial line must be able to convey 8 t/h, the pipe layout is 50 m including 15 m vertical and has 5 bends.
The design needs to know the following :
A pilot plant test is carried out on a line featuring a diameter 60 mm. The layout is 50 m, with only 5 m elevation but 5 bends. The tests confirm the possibility to convey dense phase the materials. The tests results are given below :
The following calculation can then be performed :
- Qair = 67*1/2.2 = 30.5 m3/h
- Upickup = 30.5/(π*0.062/4) / 3600 = 3 m/s
- mair = 67*1.2 = 80 kg/h
- τ = 2000/80 = 25
The material flow and air relative to the pipe section are conserved through scale up.
For the example D = (8000/2000*0.06^2)^0.5 = 0.12 m
The air conveying velocity is conserved in between the pilot test and the industrial installation, thus the air flow can be calculated :
Qair = Upickup * Sindus = 3 * π * D^2 /4 = 122 m3/h at 1.2 bar g
This gives 267 Nm3/h
Note that the industrial line having a higher elevation than the test plant, the designer should consider an additional pressure generated by the column of product to lift and adjust the calculation - not detailed here.
can access the calculation Excel sheet here
As mentionned above, dense phase conveying is always a delicate conveying process and a design should always be done with a recognized company, the procedure above being only for awareness and not detail design,
This scale-up procedure can also be used in dilute phase.
|Do you want to
know more ?
www.powderprocess.net is covering all aspects of solids and powder processing and handling
The pages below will probably interest you !
Answers ALL your questions on solids and powder mixing
of MIX / MEASURING DEGREE OF MIXING
All you need to know about measuring the degree of mixing (Coefficient of Variation) of a dry mix
OF POWDERS / DEMIXING
All on the physical phenomena causing segregation of particles and how to avoid them
All on main size reduction processes, key equipement, design consideration..etc..
All on powder key physical characteristics, among others : flowability, density...etc..
All equipment found in bulk solids handling industries, explained, with design tips...
|You can find much more through the menus at the top of the page !|