Dilute And Dense Phase Pneumatic Conveying
Dear Teus,
I am sure you are familiar with the "classic" Zenz phase diagram. Mode of conveying to the right of the saltation line as shown in this diagram is dilute phase mode. Mode of conveying to the left of the saltation line is dense phase.
For some materials there can be a short region where these two modes exist near the saltation line. This region is "mixed" mode.
Regards,
Amrit Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: Dilute Or Dense Phase Conveying ?
Dear Mr Agarwal,
Thank you very mich for your prompt reply.
If you refer to the diagram with on the x-axis the air velocity or air flow and on the y-axis the pressure drop per meter of length, than I know that diagram.(The name is not familiar to me).
The region around the lowest point in that diagram gives the design with the lowest energy demand per conveyed ton.
On the right of that region, the pressure demand and the airflow increase and the energy demand, as a multiplication of the two, increases also.
This area has therefore to be avoided.
On the left side the pressure demand increases, but the air flow decreases.
Then it is not clear whether the energy demand increases or decreases.
Therefore I made a calculation Capacity=function(airvolume) and Energy=function(airvolume)
Table
pressure discharging
product cement
length of pipeline = 62 meters
number of bends = 7
diameter of pipeline = 0,243 m (10”)
discharge pressure = 2,5 bar(o)
Pump volume - capacity
m3/sec - tons/hr - kWh/ton
0,20 - 37,1 - 1,17 - sediment
0,25 - 62,4 - 0,87 - sediment
0,30 - 94,2 - 0,69 - sediment
0,55 - 133,3 - 0,57 - sediment
0,40 - 175,3 - 0,49 - sediment
0,45 - 211,4 - 0,46 - sediment
0,50 - 235,6 - 0,46 - sediment
0,55 - 247,3 - 0,48 - sediment
0,60 - 255,7 - 0,51 - sediment
0,65 - 263,8 - 0,54 - sediment
0,70 - 271,0 - 0,56 - no sediment
0,83 - 276,8 - 0,65 - no sediment
1,00 - 281,1 - 0,77 - no sediment
1,25 - 284,5 - 0,95 - no sediment
1,50 - 285,9 - 1,14 - no sediment
1,75 - 285,9 - 1,33 - no sediment
2,00 - 285,0 - 1,53 - no sediment
2,25 - 283,0 - 1,72 - no sediment
2,50 - 297,5 - 1,94 - no sediment
If you convert this table into a graph you will see the shape of the diagram you mentioned.
Conveying below 0,70 m3/sec would be considered dense phase ?
Am I getting it right ?
Best regards ■
Teus
Re: Dilute Or Dense Phase Conveying ?
Dear all interested,
Based on the definition of dense- or dilute phase, given by mr Agarwal, I calculated an existing cement conveying installation for a range of air volumes.
The result of this calculation explains the shape of the Zenz diagram and is presented here below.
The table can be put in a spreadsheet and a curve can be made (The Zenz curve)
Zenz diagram
The curve in the Zenz - diagram represents pneumatic conveying as the pressure drop per unit of length as a function of the air flow (or air velocity).
For this curve the solids flow rate and the pipeline are kept constant.
For an existing cement conveying pipe line, this curve is calculated.
The calculated curves are given below:
cement200 ton/hr
pipeline12"
length185 meter
pressure SLR
Pumpvolume pressure/ meterkWh/ton mu
m3/secmmWCmmWC
0,8-24745-134-0,86-55,68
0,9-20475-111-0,82-49,49
1,0-18577-100-0,83-44,54
1,1-17295-93-0,86-40,49
1,13-17048-92-0,87-39,53
1,2-16428-89-0,90-37,12
1,3-15794-85-0,95-34,26
1,4-15333-83-0,99-31,81
1,5-15040-81-1,05-29,69
1,6-14819-80-1,10-27,84
2,0-14612-79-1,37-22,27
2,1-14680-79-1,44-21,21
2,2-14750-80-1,51-20,25
2,3-14875-80-1,59-19,37
2,4-15013-81-1,67-18,56
2,5-15171-82-1,76-17,82
3,0-16175-87-2,22-14,85
3,5-17460-94-2,76-12,73
4,0-18844-102-3,37-11,14
4,5-20340-110-4,05-9,90
5,0-21900-118-4,81-8,91
5,5-23540-127-5,65-8,10
6,0-25260-137-6,57-7,42
From 0.8 m3/sec to 2.0 m3/sec, the pressure drop decreases.
This can be explained as the stronger influence of the decreasing loading ratio, opposed to the
weaker influence of the increasing velocity, which would increase the pressure drop per meter.
In addition, the residence time of the particles becomes shorter with increasing velocity and the required pressure drop for keeping the particles in suspension decreases.
From 2.0 m3/sec to 6.0 m3/sec, the pressure drop increases.
This can be explained as the weaker influence of the decreasing loading ratio and the decreasing pressure drop for keeping the particles in suspension, opposed to the
stronger influence of the increasing velocity, which increases the pressure drop per meter.
The lowest pressure drop per meter occurs at 2.0 m3/sec.
Left of this point of the lowest pressure drop per meter, the pneumatic conveying is considered: dense phase and on the right of this point, the pneumatic conveying
is considered: dilute phase.
As can be read from the calculation table, the loading ratio (mu) is higher on the left part of the curve than on the right part of the curve.
Regarding the energy consumption per ton conveyed, the lowest value
occurs at 0.9 m3/sec.
This can be explained as follows:
The energy consumption per ton is depending on the required power for the air flow.
( solids flow rate is kept constant)
This required power is determined as a function of (pressure * flow ).
It appears that the minimum in pressure drop does not coincide with the lowest power demand of the air flow.
As soon as the decreasing airflow (causing lower power demand) is compensated by the increasing pressure drop, the lowest energy consumption per conveyed ton is reached.
The calculation for an air flow of 0.8 m3/sec indicated the beginning of sedimentation in the pipeline, due to the velocities becoming too low.
From this calculation, it can be concluded that a pneumatic conveying design for the lowest possible energy demand, is also a design, using the lowest possible air flow (or velocity).
The lowest possible velocities are also favorable for particle degradation and component’s wear.
This exercise also shows that dense- or dilute phase conveying are 2 different regions by definition of the same pneumatic conveying technology.
Attachments
■
Teus
Dilute or dense phase conveying ?
dear members of this forum,
I have been communicating on this forum for abt. 4 weeks now.
I have myself (more or less) specialized in dilute pneumatic conveying of cement and some other powdery products.
In the literature I find different definitions of dilute phase conveying opposed to dense phase conveying.
Loading ratio is often given as the key to determine this difference, but also sometimes the
applied velocities.
Then I understand that plug conveying is also dense phase.
The knowledge I gained so far, resulted in a calculation program that calculates a complete pipeline in the time domain, works as long as the particles do not touch each other.
In other words the product conveys as long as the product is fluidized (or over fluidized) and
other conditions, s.a. air velocity, are met.
The question is : What is the definition of DILUTE phase conveying and what is the definition of DENSE phase conveying
Waiting with interest ■
Teus