Transcript HANDLING AND TRANSPORTATION OF DRY FLYASH: ISSUES …

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 Conveying
Dilute Phase - Suspension Flow
Requirements
Pick-Up Velocity
(minimum)
None
12 m/s
16 m/s
fine powders
fine granules
Dense Phase - Non-Suspension Flow
Sliding 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 Conveying
Dilute Phase - Suspension Flow
Requirements
Pick-Up Velocity
(minimum)
None
12 m/s
16 m/s
fine powders
fine granules
Dense Phase - Non-Suspension Flow
Sliding Bed Flow:
Requirements
Pick-Up Velocity
Good Air Retention
3 m/s (minimum)
Plug Flow:
Requirements
Pick-Up Velocity
Good Permeability
3 m/s
Solids Loading Ratio
 
m p
3 6 m a
(dimensionless)
-
-
(3)
where ϕ = solids loading ratio
m p = mass flow rate of material - tonne/h
and m a = mass flow rate of air used - kg/s
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
Solids
Conveying line inlet air
Conveying line
loading
ratio
velocity - m/s
pressure drop
4 6
- bar
Conveying limit
8 10
160 120
100 80 60 50
24
24
Conveying
2·0
NO
line inlet air
20
20
12
NO
Solids loading velocity - m/s
40
1·8
ratio
16
16
30
Conveying
1·6
GO
limit
12
GO
14
12
14
1∙4 20
Conveying
15
16
2·0
8 line pressure
8
18
1·2
1·6
10
drop - bar
20
10
1·2
4
4
AREA
5
0·8
AREA 0·8
0·4
0·4
0
0
0
0·04 0·08 0·12 0·16
0
0·04 0·08 0·12
Air Mass Flow Rate - kg/s
Air Mass Flow Rate - kg/s
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
Conveying Parameters for Design Cases
Considered in Relation to 63 mm Bore Line
Referenc
e Point
Pressur
e Drop
(bar)
Air
Flow
Rate
(kg/s)
Inlet
Air
Velocit
y (m/s)
Solids Loading
Ratio
Test
Loop
Fly Ash Flow Rate
(tonne/h)
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
Fly Ash Flow Rate – (tonne/h)
Pipeline Bore
(mm)
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