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CEMENT
Pneumatic Conveying System,
Introduction, TheoryPneumatic Conveying Systems (PCS)
Training
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Introduction Section contents
1. Presentation of the team and 3-day program (annex)
2. Safety
Safety during training, local information
Safety during the visit on site (day 3) - Organization
Safety relating to PCS included in the relevant sub-sections
3. Pneumatic Conveying definition, technologies detailed in training
4. DVD (general presentation)
Theory
Material, Pressure Drops, Terminology and key points, Pipeline
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General
What is a pneumatic conveying? Where can pneumatic transportbe found?
The pneumatic conveying consists in handling solid bulk materialsuspended in or forced by a gas stream through a dust proofpiping
We will find pneumatic transport systems where there is dry andsolid bulk material
Raw mix (mill to silo, kiln feed)
Pulverised coal (hopper to burner with dosing, burner)
Cement (conveying to silo)
Some additives: Ash, Dust, Gypsum
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Technology developed during training
Refer to the training course program:
Screw-pump systems:
Mainly based on FK pumps (H, Z-flap, M type)
Overview of other technologies
Pressure vessel systems
Single or twin vessel systems
Airlift system
Miscellaneous
Aero-slides
Rotary valves + ejectors
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Theory - Contents
DVD presentation (20 min)
The material (characteristics to be considered)
Pressure drop overview, Conveying classification (phase types,pressure)
Terminology & key points
Conveying pipeline tips
Power estimation
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Material Hardness MOHS scale
1 = Talc
2 = Gypsum
3 = Calcite Cement industry: raw material 3 to 4
4 = Fluorine
5 = Apatite
6 = Feldspar Cement industry: cement = 6 to 7
7 = Quartz
8 = Corundum
9 = Diamond
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Material Hardness MOHS scale
Abrasion f (speed 3.5)
Pressure f(speed 2)
Abrasion f(speed 3.5)
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Material characteristics to be considered
Moisture content (hot, dry material better for pneumatic transport)
(H2O weight / Dry material weight) %
Inherent moisture + air high in moisture (dry air required) => build-up
Particle size distribution and Specific Size Area
diagram of cumulated rejects at x m, BLAINE
Bulk density kg/m3
theoretical, & actual bulk density at inlet (aerated product?)
Temperature
Abrasion (see MOHS)
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Material characteristics to be considered
Angle of repose
Compressibility
Ratio btw bulk material / packed tight material density
Cohesion Fine powder = high cohesion
Fluidisation aptitude of the product
Aptitude to get the same behaviour as a fluid when mixed with gas
Note: in a two-phase mix (gas + solid), experience is crucial for a
proper understanding of behaviour, loss of pressure, friction
All these criteria will impact the conveying system design: choice ofmaterial to air ratio, air-flow, conveying velocity
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Pressure Drop, Loading Ratio (material to air ratio)
Biphasic flow (air + solids) higher P drop than air alone seenext slide
Q (loading ratio) = kg material / kg air [or kg mat. / m3 air] = basicdata
Lean phase Dense phase
Pressure drop =
f (loading ratio) in arange 0-10 kg/kg
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Pressure Drop = f (gas velocity) for biphasic
A curve =P due to the air only (# proportional to v2)
W curve = Wedging of the material
F curve = sliding friction of the material (slow down, re-acceleration)
C = TotalP = f (m/sec)
C = at higher mat./air ratio
Phase types & characteristics:
lean phase (pure suspension)
dense phase, continuous
dense , waves-motion
solid phase (plugs, low speed) F
W
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Conveying system possible classification
PRESSURE PHASE TECHNOLOGY CONCENTRATION
Qualified as: Material to air ratio(kg/kg - approximate)
Qualified
HP < 6 bar Dense (continuous orWave motion)
Compressor + VesselSystem
> 40 High
HP < 3 bar Dense (continuous or
Wave motion)
Compressor + Vessel
System
15 to 40
HP < 2 bar Dense (continuous) Compressor + ScrewPump
15 to 30
MP 0.5-1 bar Lean or semi-dense Roots Blower + Airlift # 13 MediumMP Lean or semi-dense Roots + Rotary
Feeder / MLLER P.8 to 15
MP Lean Roots + airlock /ejector 4 Low
LP 0.3 bar Lean Multi-stages blower < 3LP < 0.15 b Lean Fan + airlock /ejector < 1Special: Fluidized aero-slide Blower or Fan
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Terminology and key points in conveying systems
Concentration (loading ratio) = material to air ratio Material (kg/h) /Air (m3/h) - or kg/kg
Air flow QV = volume at ambient, site conditions (air compressorintake)
Air (mass) flow = QV x 1.293
Loading ratio is inherent to the pipeline length and to the choice(capacity) of the conveying system technology
Refer to the previous table usually between 15 and 40 for commonsystems in cement industry
Next, required airflow to be calculated from this ratio & expectedoutput
Then, from a first pipeline sizing (refer to next slide), pressure Dropcalculations, and finally optimization
Iterative calculation needed to optimize both conveying velocity &P
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Terminology and key points in conveying systems
Gas Velocity = actual air flow (at P bar, TC) / pipe cross-sectional area Basic characteristics to ensure transportation of the particles and minimize wear
Pick-up Velocity (at the conveying pipeline inlet)
For common products in cement industry, usually recommended 10 m/sec,
Take care to calculate the actual airflow at P bar (P1
V1
at compressor intake, P2
V2 at the pick-up point, P1 V1 = P2 V2 ) & at the estimated temperature
Exit Velocity (at the discharge point)
Exit velocity usually recommended 30 m/sec, usually at ambient pressurecondition and at conveying temperature)
Gas expansion along the pipeline (speed mastering = stepped pipeline) The air will expand as it moves down the pipeline. In a pipeline with fixed
diameter, this can result in a high velocity at the end of the circuit. The pipediameter can be increased by step to keep the velocity within a proper range(next slide).
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Terminology and key points in conveying systems
Stepped Pipeline: from the graph (principle), it is useful in a longdistance system (>150m?) to keep the gas velocity in an envelope
Most economical system = minimizing both air flow (wasted energyfor the air, wear) and pressure drop. Length and of each section tobe carefully designed, f( material and rate)
Lower limit required10m/sec pick-up &conveying velocity
Upper limit required toprevent wear
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Terminology and key points in conveying systems
Conveying Pipeline equivalent length E.L. (m) formula used tocarry out pressure drop estimations - example:
E.L. = LH + 2^LV + 5^NB= (220 m)
LH = actual horizontal pipe length (150 m)
LV = actual vertical pipe length (25 m)
NB = number of bends (4)
singular P drop
Diverters, feeder
TOTAL required P
ID 183mmL1 = 25m
ID 183mmL2 = 100m
ID 183mmL1 = 25m
ID 207mmL1 = 25m
ID 207mm
L1 = 0m
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Conveying Pipeline
Many types of bends can be
used:
Long radius bends
Recommended radius = 6 x pipe to avoid excessive P drop. With or
without wear-back (thick wall)
DENSIT wear-cast 2000 typeinside (corundum aggregate)
Spherical fabricated bends
(permanent settling insideprotecting the bend)
No problem in horizontal planes
Other types (tees,)
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Conveying Pipeline
Do not forget expansion joints wherever itis required (air intake or conveying pipe)
Ex: DILATOFLEX type, allowed pressure 1.5 to 12 bars
depending on the
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Power Estimation
Rough figures, kWh/t and per m. of pipeE.L.- From 0.01-0.02 (vessels, screw pumps) 0.02-0.03 (airlifts,
MLLER pumps, rotary valves) 0.03-0.04 (rotary valve +ejector)
Simplified formulae
PKWpump =1,3 x Q material x p
P
PKW compressor=QV
60x 1,72 x
p
Patm
0,78
p = bar
Q material = kg/h
P= 900kg/m3
raw materialP= 600kg/m3 dust
P = 1100kg/m3 for cement