Transcript High Concentration Fill Technology – A New Area on Ash Utilization

HIGH CONCENTRATION FILL
TECHNOLOGY – A NEW AREA
ON ASH UTILIZATION
By
Dr. C. N. Ghosh, Chief Scientist
Central institute of mining & fuel research
(Council of Scientific and Industrial Research)
Dhanbad
Email : [email protected]
INTRODUCTION
About 100 Thermal Power Stations in India consume about 400
Mt. of coal(35-50% ash) and generate about 150 Million Ton of
Coal Ash per annum.
About 3000 Million Ton of coal is locked up in pillars in different
coalfields in India and could not be extracted due to nonavailability of filling material.
Increased demand of coal production means increased depth of
working by faster mechanized extraction techniques and
decreased % extraction (about 30%) as coal pillars are left for
strata control
INTRODUCTION
Conventional hydraulic stowing demands classified material
(coarser size) for improved stowing performance
Reduced Cut – off – grade and increased ash production (80%
F.A+20% B.A) results in generation of finer waste
Paste fill technology facilitate high filling rate suitable for
mechanized operations and provides an avenue for utilization of
total tailings, Ash etc.
Share of mine filling in ash utilization is a meager 5-10%, the
use of ash in mines can produce a quantum jump in ash
utilisation and would help to achieve the aim of 100% ash
utilisation
DEFINATION OF PASTE
Paste flow
Slump Test: a) Small Slump
b)
Large
Slump
First used at the Grund Mine in Germany during the 1980’s, The term “Paste” refers
to a class of backfill that has an appearance akin to “toothpaste” and have low
water content such that the mixture has a consistency as measured by ASTM
slump cone test from slightly greater than zero up to nearly 305mm (12 inches),
high densities( > 75% Cw) low permeability, generally consisting about 15%
minus 20 micron meter (625 mesh) fines content.
OR
According to Golder Associates “A Paste can be defined as a mixture of solid and
water that has little or no bleed of water when Idle”
Paste Fill vis-à-vis Conventional fill
PASTE TECHNOLOGY OFFERS:
Low permeability with little or no water bleed, hence binder and leachate washout is
reduced.
Reduce mine dewatering costs.
Enhanced filling rate, hence mining cycle time is reduced.
Higher Strength with lesser binder as in-place segregation and dilution of constituent
particles is less
Much lighter/simple barricading arrangement
Hurdles :
High initial capital investment
Strict control (PLC) and greater level of engineering design
Relatively new technology and many technical aspect are not fully understood.
PASTE FILL MIX CONSTITUENT
Water
Expected
Slump
> 75%
(by weight)
Paste Fill
Binder
(OPC, blast furnace
slag etc.)
Pond Ash
(80% Fly Ash + 20%
Bottom Ash)
DESIGN OF PASTE FILL SYSTEM
void
PASTE BACKFILL PREPERATION
Paste Fill Plant has Three Essential Functional
Components
De-Watering
Mixing
Pumping, transportation and deposition
De Watering
Thickeners and Filters
High Density Thickeners
Cyclones
Centrifuges
Tank Dewatering
Tailspiner - special centrifugal case
Fluidization
PASTE BACKFILL PREPERATION
Mixer
Continual Mixing plant
ASH FROM
PLANT
Continual paste production plant
PASTE BACKFILL PREPERATION
Batch Mixing Plant
ASH FROM
PLANT
Batch paste production plant
PUMPING,TRANSPORTATION & DEPOSITION
Transportation of high concentration ash slurry via
pipeline distribution network to underground void is
facilitated by means of gravity or piston pumps.
Different Configuration of
Transportation
Gravity System
Gravity & Pumping System
Pumping & Gravity System
PUMPING,TRANSPORTATION & DEPOSITION
The pumpability of paste fill depends mainly on its
rheological properties (viscosity, yield stress) and type of
pump used.
High concentration low settling paste fail to obey Newton’s
law of viscosity and exhibit Non-Newtonian behavior.
The rheological behavior of Non-Newtonian fluid is
obtained by testing with viscometer
PUMPING,TRANSPORTATION & DEPOSITION
General Rheological Model Equation
= y
Where
+ k

n
 = Shear Stress (Pa)
y = Yield Stress (Pa)
( )
 = Shear Rate
k = Consistency Index
n = Flow behavior Index
(sec-1)
( y)
()
• The Bingham plastic and Power Law Model are most popular because of their
simplicity and the wide range of fluids they can describe
PUMPING,TRANSPORTATION & DEPOSITION
A Full scale pumping loop test on paste of desired
consistency is necessary to determine the pressure
gradient, head loss for various combination of pipe
diameter, flow rate and throughput.
Results of loop test will determine operating pressure,
choice of pipe diameter and flow rate.
In general pipe diameter of paste lies between 100 –
200mm, flow velocity varies between 0.1 – 1 m/sec
PUMPING,TRANSPORTATION & DEPOSITION
Pumping of high concentration slurry is
done by means of positive displacement
pumps
It discharges fixed quantity of fluid with
each revolution of pump roter, hence its
capacity remains unaffected by changes
in pressure it must develop
Envirotech Pump systems (Geho),
Putzmeister, Schwing, Abel are some of
the companies manufacturing high
pressure (165 bar) , high discharge rate
(80-100 m3/hr) piston pumps
LABORATORY STUDIES
For the first time in India high concentration ash stowing was
proposed to be undertaken at the underground mines of Madhuband
Colliery, Barora Area, BCCL using ash of Chandrapura Thermal
Power Station (DVC).
Laboratory study to determine the suitability CTPS ash, barricade
design, optimum concentration, compressibility etc was carried out
at CIMFR, Dhanbad
Physical characteristics:
Specific gravity
Bulk density
Percentage Void
:
:
:
2.15
0.83 t/m3
61.40%
LABORATORY STUDIES
Grain Size Distribution
Size ( microns)
+2360
+1180
+ 600
+ 300
+ 150
+ 106
+ 53
+ 25
- 25
% Retained
0.07
0.21
0.69
5.00
18.18
19.17
37.57
1.17
18
Auto – oxidation Characteristics
Proximate Analysis
Moisture percentage
:
Ash percentage
:
Volatile Mater percentage :
Unburnt Carbon percentage :
0.2021
92.7000
1.6340
5.4639
Crossing Point & Ignition Point Temperature
CPT & IPT : Not Reached till 2000 C
LABORATORY STUDIES
Gallery Model study was carried out to optimize slurry concentration,
barricade design, drainage rate and quantity etc.
Slurry of different concentrations (50%, 55%, 57%, 58% & 59% by
weight) was prepared and poured in to the model, following was
observed:
Cw < 55%
: behaved as dilute slurry
55% <= Cw <= 58%
: behaved as a paste/ semi paste
Cw > 58%
: found to be un-pourable
Drainage rate with optimized barricade configuration of single layer
bamboo matting and single layer hessian cloth was found to be good
LABORATORY STUDIES
Compressibility Characteristics
L/D
Comparative Compressibility of Pond Ash & Sand
= 0.8
Loading Rate
= 5 tonne
Material
= Air Dried Ash
Sample (CTPS)
At 100 kg/cm2 ( ~ 400m depth)
Compressibility:
Pond Ash = 11.07 %
Sand
= 7.5 %
Compressibility (%)
0
10
20
30
40
50
60
0
1
2
3
4
5
6
7
8
9
10
11
12
Sand
Pond Ash
Pressure (Kg/cm2)
70
80
90
100
CONCLUSIONS & RECOMMENDATIONS
To determine the suitability of any material to be used as paste fill
following investigations are recommended






Determination of particle size
Particle shape, mineralogy
Relation between slump vs. water content vs. pressure drop
Material Sp. Gr., Porosity, Permeability, strength test (UCS)
De-watering test (Thickening or filteration)
Generate frictional data from pump loop test
State- of–the –art PLC control is essential as slight change in moisture
content may lead to wide variation in viscosity and pressure drop.
Study of rheological properties of the mix is imperative
CONCLUSIONS & RECOMMENDATIONS




Laboratory study on CTPS Ash indicates its suitability for use in
underground coal mines.
Model test indicated that ash slurry up to a concentration of 58%
(by weight) can be used for stowing
Compressibility of pond ash was found to be slightly more than that
the desired value at 100 kg/cm2
Coordinated endeavor by both Power Plant and Mining officials are
required to implement this technology in India. Effort should be
directed not only to install new paste fill plant but also to modify
the existing stowing plant to meet the same end
THANK
YOU