TRANSPORTATION OF DRY FLYASH: ISSUES FOR
CONSIDERATION
By
V.K.Agarwal
Indian Institute of Technology, Delhi
Figure 9 Sketch of Particulate Flow in Dilute Phase Conveying
Mode of Conveying
Dilute Phase - Suspension Flow:
Requirements None
Pick-Up Velocity 12 m/s fine powders (minimum)
16 m/s fine granules
for horizontal conveying
Figure 11 Sketch of Particulate Flow in Moving Bed Flow
Mode of ConveyingDilute Phase - Suspension Flow
Requirements NonePick-Up Velocity 12 m/s fine powders (minimum) 16 m/s fine granules
Dense Phase - Non-Suspension FlowSliding Bed Flow:
Requirements Good Air Retention
Pick-Up Velocity 3 m/s (minimum)
Figure 14 Sketch of Particulate Flow in Plug Type Flow
Mode of ConveyingDilute Phase - Suspension Flow
Requirements NonePick-Up Velocity 12 m/s fine powders (minimum) 16 m/s fine granules
Dense Phase - Non-Suspension FlowSliding Bed Flow:
Requirements Good Air Retention
Pick-Up Velocity 3 m/s (minimum)
Plug Flow:
Requirements Good PermeabilityPick-Up Velocity 3 m/s
Solids Loading Ratio
a
p
m
m
63
where ϕ = solids loading ratio
= mass flow rate of material - tonne/h
and = mass flow rate of air used - kg/s
pm
am
(dimensionless) - - (3)
Diagram to Illustrate the Wide Range of Conveying Systems Available for Conventional Systems Operating With a Single Air Source
Sketch of Typical Negative Pressure Conveying System
Ash Accumulation Points and Typical Ash Distribution of a Dry Bottom Furnace
Typical Arrangement of Electrostatic Precipitator Ash Collection Hoppers
Pneumatic Ash Removal Systems with Conveying Parameters Indicated
Typical Dry Fly Ash Handling Arrangement at a Power Station
CONVEYING CAPABILITY
In Terms of• Material Flow Rate• Conveying Distance• Minimum Conveying Air Velocity• Power Requirements
Depends Upon:• Pipeline Bore
• Pipeline Length
• Pressure Drop Available
• Material Properties
Parameters Relating Compressor Rating with Material Flow Rate
Influence of Solids Loading Ratio on Conveying Air Velocity for Fine and
Coarse Grades of Flyash
Sketch of Test Facility Pipeline at the IIT
Pipeline Details:
Bore - 63 mm Length - 133 m
Bends - 10
Conveying Characteristics for Fine Grade of Fly Ash with Conveying Line Inlet Air Velocity Data
Superimposed
Conveying Characteristics for Coarse Grade of Fly Ash with Conveying Line Inlet Air Velocity Data
Superimposed
Air Mass Flow Rate - kg/s
Fly
Ash
Flo
w R
a te
- t o
nne/
h
24
20
16
12
8
4
0
Conveying line pressure
drop - bar
Solids loading ratio
Conveying limit
0 0·04 0·08 0·12 0·16
Conveying line inlet air
velocity - m/s
152·0
14161820
0·40·8
1·2
1·6 10
5
NO
GO
AREA
Air Mass Flow Rate - kg/s
24
20
16
12
8
4
0
Conveying line pressure drop
- bar
Solids loading ratio
Conveying limit
0 0·04 0·08 0·12
Conveying line inlet air velocity - m/s
NO
GO
AREA
20
10
30
40
506080
160 120 4 6 8 10
12
1∙4
0·40·8
1·2
1·6
2·0
100
Fly
Ash
Flo
w R
a te
- t o
nne/
h
a) Coarse fly ash b) Fine fly ash
Figure 5 Comparison of Conveying Characteristics for Fine and Coarse Grades of Fly Ash in IIT Pipeline
1·8
14
Conveying Parameters for Design Cases Considered in Relation to 63 mm Bore Line
Reference Point
Pressure Drop(bar)
Air Flow Rate (kg/s)
Inlet Air
Velocity (m/s)
Solids Loading Ratio
Fly Ash Flow Rate (tonne/h)
Test Loop
Plant Test Loop
Plant
1 1.8 0.038 3.7 150 103 20.5 14.1
2 1.3 0.060 7.2 55 40 11.8 8.64
3 1.0 0.090 12.3 20 16 6.6 5.22
4 0.8 0.087 13.2 14 11 4.5 3.59
Fly Ashy Flow Rate in Plant Pipeline of Various Bores for Range of Conveying Line
Pressure Drops Considered
Pipeline Bore(mm)
Fly Ash Flow Rate – (tonne/h)
Conveying Line Pressure Drop – (bar)
1.8 1.3 1.0 0.8
150 80 51 33 23
200 144 91 60 41
250 226 144 95 65
300 325 209 138 94
Sketch of a Typical Vacuum Conveying System Incorporating a Stepped Pipeline for
Conveying Different Grades of Fly Ash
Conveying air Velocity Profiles for the Conveying of both Coarse and Fine Ash in a
Common Negative Pressure Conveying System
RECOMMENDED OPTIONS FOR COAL ASH HANDLING AND SAFE DISPOSAL