CPRI
04-02-2015
EFFECT OF SURFACE MOISTURE IN COAL ON UNIT
HEAT RATE AND OPERATING COSTS FOR INDIAN
THERMAL POWER PLANTS
CPRI
The installed capacity of the country is ~250 GW out
of which ~140 GW is the share of coal based power
generation (~ 57 %).
04-02-2015
INTRODUCTION
Coal is contributing to ~ 1.5 % of the GDP as it is the
main energy source for power generation.
Nearly 60 % of the coal is transferred from the mine
to the power plant through Indian railways, 25 %
through trucks and the balance through dedicated
transfer systems such as merry-go-round-systems,
etc.
Indian coal
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being of drift origin are of high ash (25-50 %)
Gross Calorific Values (GCV) in the range of 2300-4500
kcal/kg.
Sulphur (< 0.6 %) is not a problem except in very few
specific mines.
04-02-2015
INTRODUCTION
Coal utilization efficiency (before it is used in the
boilers ,i.e., from mills till bunkers) is in the range of
80-98 %.
The main non chemically reactive ingredients in coal
which result in the drop in GCV are ash and moisture.
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Due to the open cast mining process, besides the inherent ash
the extraneous mineral matter (clay, sand, and stones
generally referred as mud) also gets mixed up with the coal is
called as extraneous ash.
It is not ash, techno commercially it is called as extraneous
ash because it is an incombustible component.
Extraneous mineral matter can be removed through washing
processes typically the run of mine jig wet washing process.
Inherent ash cannot be removed except by complex and cost
chemical methods in small sample sizes at the laboratory
scale
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COAL QUALITY
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Moisture in coal consists of inherent moisture (IM) and
surface moisture (SM). Then total moisture (TM) is a sum
of IM and SM.
Equilibrated Moisture means the moisture content, as
determined after equilibrating at 60% relative humidity
(RH) and 40 C as per the relevant provisions (relating to
determination of equilibrated moisture at 60% RH and 40
degree Celsius) of BIS 1350 of 1959).
Surface moisture is the difference between total moisture
and inherent moisture and is also called as excess moisture
(EM).
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COAL QUALITY
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IM or equilibrated moisture is a non controllable
parameter.
SM is an added quantity and can vary in any range.
Hence TM is affected by the criticality of SM. This
brings down the GCV of coal (thermal content of
coal) which reduces the output it delivers, reduced
boiler efficiency and unit overall efficiency.
Wet coal is difficult to handle
movement in conveyors, chutes, hoppers, bunkers
and pipes
Grinding, milling and flowability
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COAL QUALITY
GRADE OF
COAL
MIN
G1
7000
G2
6700
G3
MAX
MEAN
RUN OF
MINE COAL
PRICE,
Rs./t
COST OF
HEAT (FOB),
Rs./GCal
7000
3542
506
7000
6850
3393
495.33
6400
6700
6550
3244
495.27
G4
6100
6400
6250
3032
485.12
G5
5800
6100
5950
2886
485.04
G6
5500
5800
5650
2360
417.70
G7
5200
5500
5350
1840
343.93
G8
4900
5200
5050
1700
336.63
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GROSS CALORIFIC VALUE,
kCal/kg
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COST OF COAL (Rs./GCal) AS PER COAL INDIA
PRICES
MIN
MAX
MEAN
G9
4600
4900
4750
1500
315.79
G10
4300
4600
4450
1400
314.61
G11
4000
4300
4150
1130
272.29
G12
3700
4000
3850
910
236.36
G13
3400
3700
3550
690
194.37
G14
3100
3400
3250
610
187.69
G15
2800
3100
2950
510
172.88
G16
2500
2800
2650
474
178.87
G17
2200
2500
2350
420
178.72
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GRADE OF
COAL
COST OF
HEAT
(FOB),
Rs./GCal
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GROSS CALORIFIC VALUE, kCal/kg
RUN OF
MINE
COAL
PRICE,
Rs./t
120
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100
80
60
40
20
0
1975 1980 1985 1990 1995 2000 2005 2010 2015 2020
Year
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FOB cost of imported thermal coal, $/t
GRADUAL RISE IN COST [FOB (FREIGHT ON
BOARD)] OF IMPORTED COAL OVER THE YEAR
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60
y = 0.01x + 6.1
55
50
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Drop in GCV (kcal/kg) for 1 % moisture
DROP IN GCV OF COAL FOR 1 % MOISTURE
INCREASE
45
40
35
30
3000
3500
4000
Calorific value (kcal/kg)
4500
5000
10
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IM - affects the coal combustion process,
SM - gives rise to difficulties in handling (transfer and
flow ability) of coal with severe capacity reduction of all
equipment in the coal plant ranging from crushers to
conveyors.
Units tripping on mill choke up, load hunting due to
insufficient flow from bunkers, raw coal feeder jam, etc.,
are quite common during this period.
Even though the bunker level may be full, only 30 % of
the bunker capacity can be utilized due to bonding of
coal at the bunker periphery and flow is only through rat
hole in the bunker centre.
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EFFECT ON COAL MOVEMENT AND
HANDLING IN THE COAL YARD
11
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Rainy season restricts the plant load ability due to the
movement of sticky coal which contains clayey mineral
matter.
When the surface moisture of coal exceeds 6 %, it
becomes sticky in addition to the stickiness created by
the clay content of the mineral matter leading to severe
capacity restriction in the tipplers, conveyors, crushers,
bunkers and mills.
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EFFECT ON COAL MOVEMENT AND
HANDLING IN THE COAL YARD
12
13
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Stocking of sufficient coals of sandy background
which do not have serious sticky properties as
compared to coals of clayey background.
Use of washed coals of sandy background.
Blending of raw coal (GCV=14.5 GJ/kg) with
washed coals (GCV=17.5 GJ/kg) or imported
coals (GCV=21 GJ/kg).
Optimal (partial) filling of bunker levels.
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DEMANDS OF THE RAINY SEASON
THROUGH SEVERAL MEASURES
14
SOME OF THE SOLUTIONS FOR WET COAL HANDLING
MANAGEMENT OF CHUTES
AND BUNKERS
Increased
conveyor angles
Deflector plates of Stainless
steel (SS 304) to chutes
Tarpaulins to cover wagons
Multi bladed
cleaners
Vibratory
feeders/thumpers/rappers
in place of static feeders
Air blasters
Providing slopes for drainage Reduction in belt
of water
speeds
Concreting of storage yards Skirt board seals,
and providing retaining walls baffle plates and
centering plates
at loading points
Rain water channeling,
Self cleaning
Chute modification to
screening system increase angle
dredging and cleaning of
flow passages
Compacting by special
Well designed
compactors instead of bull
wash down
dozers.
drainage system
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Rain guards for conveyors
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MANAGEMENT OF COAL YARD MANAGEMENT OF
CONVEYORS
15
Storage pile design improvement
through compacting. Pyramidal
shapes with drains on either side
lead to low water absorption.
Further the piles must not have
surface depressions or pits.
Used oil may be sprayed on coal
yard instead of reselling.
Alternatively it can be blended
with fuel oil.
Dome for storage of coal
Provision for ground level
tippling (non-pit type) of wagons
MANAGEMENT OF
CONVEYORS
Management of
carry over return
MANAGEMENT OF
CHUTES AND
BUNKERS
Widening of
passages
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MANAGEMENT OF COAL YARD
04-02-2015
SOME OF THE SOLUTIONS FOR WET COAL HANDLING
Conveyor belt
sealing between
chute and pan of
vibratory feeder to
prevent spillage
Water jet cleaning
16
17
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04-02-2015
CORRELATION BETWEEN SURFACE MOISTURE
AND EQUILIBRATED MOISTURE IN MINED COAL
y = -0.827x + 11.927
12
10
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Surface Moisture (%)
14
8
6
4
2
0
5
5.5
6.5
7
7.5
8
8.5
Equilibriated Moisture (%)
9.5
10
18
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CORRELATION BETWEEN TOTAL MOISTURE AND
EQUILIBRATED MOISTURE IN MINED COAL
18
16
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Total Moisture (%)
20
14
12
10
y = 0.173x + 11.927
8
5
5.5
6.5
7
7.5
8
8.5
Equilibriated Moisture (%)
9.5
10
19
CPRI
In the case of indigenous coals - the heating value
for commercial purposes is based on equilibrated
moisture
Total moisture does not get reflected in the
commercial heating value.
Surface moisture does not get accounted in the
costing.
TPS must insist for coal costing considering TM at
mining point.
SM addition enroute to TPS and in coal yard must
be borne by user.
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BASIS FOR SALE OF COAL
20
y = -85.406x + 7223.4
R = 0.9057
7,000
6,000
5,000
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GCV of imported raw coal (kcal/kg)
8,000
04-02-2015
IMPORTED COAL
4,000
3,000
2,000
1,000
0
0
10
20
30
40
Total moisture in raw coal (%)
50
60
21
CPRI
There are three cost effects of moisture in coal:
Increase in operation costs due to decreased boiler
efficiency and decreased overall unit efficiency
(increase in heat rate)
Increase in operation and maintenance costs
attributed to handling of wet coal.
Decrease purchase cost of coal due to higher moisture
and hence lower GCV.
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EFFECTS OF MOISTURE IN COAL ON POWER
STATION PERFORMANCE
22
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EFFECTS OF MOISTURE IN COAL ON
POWER STATION PERFORMANCE
83.5
82.5
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Boiler efficiency, %
83.0
82.0
81.5
y = -0.0202x2 + 0.3588x + 81.879
R = 0.9812
81.0
80.5
10
12
14
16
18
Moisture content, %
20
22
23
2660
y = 0.6319x2 - 11.562x + 2628.6
R = 0.9277
2650
2640
2630
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Unit Heat Rate. kcal/kWh
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INCREASE IN UNIT HEAT RATE DUE TO
INCREASED MOISTURE
2620
2610
2600
2590
2580
2570
10
12
14
16
18
Moisture content, %
20
22
24
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Indian coal
The fuel supply agreements for Indian coals do not have
any provision for accounting the effect of total moisture.
Only equilibrated moisture (IM) gets factored in the pricing.
SM > 7% during the months from October to May and > 9%
during the months from June to September, the coal
quantities shall be calculated in percentage by which the
surface moisture exceeds the foregoing limits.
This corresponds to a TM of approximately 12 % in summer
and 14 % in rainy season which rarely happens.
On this account Indian coal costs do not show sensitivity to
total moisture as indicated in the following figures.
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COST SENSITIVITY OF MOISTURE IN COAL
25
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COST SENSITIVITY OF MOISTURE IN
INDIGENOUS COAL
y = 4.7112x + 844.65
R = 0.031
1400
1200
1000
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Indigenous coal price, Rs./Gcal
1600
800
600
400
200
0
0
10
Total Moisture, %
15
20
26
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SENSITIVITY OF INDIAN COAL PRICE (Rs./t)
TO TOTAL MOISTURE
4900
y = -16.121x + 4442
R = 0.0929
4500
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Indian coal price, Rs./t
4700
4300
4100
3900
3700
3500
0
10
Total Moisture, %
15
20
27
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SENSITIVITY OF INDIAN COAL PRICE (Rs./t) TO TOTAL
MOISTURE IF THE MOISTURE EFFECT IS CONSIDERED
4400
4350
4250
4200
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Coal cost, Rs./t
4300
4150
y = -43.38x + 4556.2
4100
4050
4000
3950
3900
0
6
8
10
Total Moisture, %
12
14
16
28
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880
870
860
850
840
830
820
810
800
790
780
770
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Coal cost, Rs./Gcal
SENSITIVITY OF INDIAN COAL PRICE (RS./GCal) TO
TOTAL MOISTURE IF MOISTURE EFFECT IS CONSIDERED
y = -9.7836x + 921.21
6
8
10
Total Moisture, %
12
14
16
29
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COST SENSITIVITY OF IMPORTED COALS TO
MOISTURE
5000
4500
4000
y = -90.488x + 5702.7
R = 0.8939
3500
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Imported coal price, Rs./MT
5500
3000
2500
2000
1500
1000
0
10
20
30
40
Total moisture, %
50
60
30
y = -0.2174x2 + 3.5573x + 730.98
R = 0.6839
800
700
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Imported coal price, Rs./GCal
900
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COST SENSITIVITY OF IMPORTED COALS TO
MOISTURE
600
500
400
300
0
10
20
30
40
Total moisture, %
50
60
31
Particular
Boiler efficiency
Design/
operating
Design
02
Boiler efficiency
Operating
03
Unit heat rate
Design
04
Unit heat rate
Operating
05
Impact on cost of energy
generated due to decreased
performance of boiler
Impact on cost of energy
generated due to decreased
performance of boiler
Impact on cost of energy
generation due to lower
purchase
price
of
high
moisture coal
Impact on cost of energy
generation due to lower
purchase
price
of
high
moisture coal
Design
% per 1 % -0.123
increase
in
-0.270
moisture
kcal/kWh per 1 % 3.1
increase
in
8.2
moisture
Rs./kWh
0.010
Operating
Rs./kWh
0.015
Design
Rs./kWh
0.36
Operating
Rs./kWh
0.38
06
07
08
Units
Value
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Sl.
No.
01
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COST SENSITIVITY OF COALS TO
GENERATION COST AND FUEL COST
32
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Imported coal
It is clearly seen that the cost impact due to actual
decrease in energy efficiency is very small (Rs. 0.01 to
0.015/kWh) as compared to reduced fuel purchase
cost component of generation cost (Rs. 0.36/kWh)
because as the TM increases the price of coals
decrease.
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COST SENSITIVITY OF MOISTURE IN COAL
33
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Moisture in coal has a negative impact on the energy
performance and all efforts are required from the mine
till the coal is fired into the boilers, to ensure that
moisture does not get added to the coal and its heating
value is preserved.
If the boilers are designed for operating on high moisture
coals, the high moisture
imported coals can be
successfully fired in an economical fashion as the open
market price of coals with higher moisture will be lower
than coals with lower moisture.
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CONCLUSIONS
34
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The overall cost of generation will be lower for coals with
higher moisture contents.
The increased generation cost due to lower boiler efficiency
and unit overall efficiency (Rs. 0.015/kWh) will be completely
offset by the component due to decreased purchase price of
higher moisture coals (Rs. 0.38/kWh).
Therefore, for imported coals the economics is in favour of
operating on higher moisture coals based on the coal pricing.
In the case of indigenous coals, the heating value for
commercial purposes is based on equilibrated moisture
which is equivalent to inherent moisture and the total
moisture does not get reflected in the commercial heating
value.
04-02-2015
CONCLUSIONS
35
CPRI
In other words, surface moisture does not get accounted in the
costing.
However, in the case of both imported coals and indigenous
coals, addition of surface moisture or moisture
addition/deterioration in heating value in the coal yard of the
power plant is to the account of the user and must be
minimized.
Besides just the heating value the difficulties in flow ability,
crushing, pulverizing and injection of coal into the furnace of
the boiler present operational problems which affect
loadability.
The impact of 1% moisture on unite heat rate is 8-9 kcal/kWh.
04-02-2015
CONCLUSIONS
36
CPRI
THANK YOU
37
04-02-2015
