100825 pneumatic transport 10 intro theory

8/22/2019 100825 Pneumatic Transport 10 Intro Theory

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CEMENT

Pneumatic Conveying System,

Introduction, TheoryPneumatic Conveying Systems (PCS)

Training


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100825_Pneumatic Transport_10_Intro_Theory.ppt 2

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)



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)



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



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



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



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



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




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).




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




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



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,)



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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100825 Pneumatic Transport 10 Intro Theory ppt 19

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

100825 pneumatic transport 10 intro theory

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