7
~ Pergamon Energy Convers. Mgmt Vol. 35, No. 7, pp. 597-603, 1994 Copyright © 1994 ElsevierScience Ltd 0196-8904(93)E0026-H Printed in Great Britain. All rights reserved 0196-8904/94 $7.00+ 0.00 EFFECT OF COAL PROPERTIES ON THE SPECIFIC COAL CONSUMPTION IN A TYPICAL THERMAL POWER STATION IN INDIA SHAIL, I M. S. SODHA,It RAM CHANDRA, t B. PITCHUMANI z and J. SHARMA 3 ICentre of Energy Studies and Research, Devi Ahilya Vishwavidyalaya, Indore (M.P.), 2Chemical Engineering Department, Indian Institute of Technology, Hauz Khas, New Delhi, and 3Chief Engineer, M.P. Urja Vikas Nigam, Bhopal (M.P.), India (Received 12 February 1993; received for publication 16 December 1993) Abstract--The effect of various coal properties like ash content, moisture content, fixed carbon and calorific value on specific coal consumption in a typical thermal power station in India is analysed. It is observed that the specific coal consumption is a strong function of moisture content, ash content and fixed carbon. For the Panipat Thermal Power Station (the one considered in the present analysis), it is observed that, for an increase in moisture content by 2%, the specific coal consumption increases by about 8%. If, however, the ash content is increased by 20, the specific coal consumption increases by about 5%. It is also observed that, for a 40 increase in fixed carbon, the specific coal consumption decreases by about 25%. INTRODUCTION Energy is essential for the economic growth of a country. The availability of a reliable source of energy in the most economical way is a basic prerequisite for the sustained development of a nation. In India, the need for increasing amounts of energy is now more than ever before. The power generating capacity, which is mainly owned and operated by utilities, has grown at the rate of over 9.7% per annum since 1950. The total installed capacity in the country, which was about 1340 MW in 1947, rose to about 70,000 MW in 1991-92; even then, there was an average power shortage of 7.8%. The peak power shortage was as much as 18.8%. The actual generation was about 200.63 billion units in the first three quarters of 1990-91. The thermal contribution was targeted to be about 73%; however, the actual thermal power generation was 134.58 billion units, i.e. 69%. In the last 20 years, the availability of energy in India has been growing at a compound annual rate of 4.9%. During the same period, the average compound annual growth rate of different sources of energy is given in Table i. In the year 1991-92, the total availability of all primary sources of commercial energy put together was equivalent to 200 million t. The consumption of various sources of energy in 1991-92 is also given in Table 1. It is clearly seen that coal is the major energy source. Out of 235.30 million t, 137 million t was used for power generation alone. Since our coal reserves are not going to last long, every effort should be made to use this source of energy as efficiently as possible. This requires a complete knowledge of coal properties and their effect on coal consumption. In the present paper, the effect of coal properties on the specific coal consumption in thermal power stations is analysed in detail. The three important properties of primary interest from a combustion standpoint are the fixed carbon, volatile matter and calorific value. Volatile matter consists of hydrocarbons and other gases (not including water vapour). FACTORS RESPONSIBLE FOR HIGH SPECIFIC COAL CONSUMPTION Gradual deterioration in the grade of coals, resulting in lowered calorific values from 500 kCal/kg to 3000 kCal/kg, lowered volatile contents from 24% to 17% and a staggering rise in the ash tNow at Lucknow University, Lucknow-226 007, India. 597

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Page 1: Effect of coal properties on the specific coal consumption in a typical thermal power station in India

~ Pergamon Energy Convers. Mgmt Vol. 35, No. 7, pp. 597-603, 1994

Copyright © 1994 Elsevier Science Ltd 0196-8904(93)E0026-H Printed in Great Britain. All rights reserved

0196-8904/94 $7.00 + 0.00

E F F E C T O F C O A L P R O P E R T I E S O N T H E S P E C I F I C C O A L

C O N S U M P T I O N I N A T Y P I C A L T H E R M A L P O W E R

S T A T I O N I N I N D I A

SHAIL, I M. S. SODHA,It RAM CHANDRA, t B. PITCHUMANI z and J. SHARMA 3

ICentre of Energy Studies and Research, Devi Ahilya Vishwavidyalaya, Indore (M.P.), 2Chemical Engineering Department, Indian Institute of Technology, Hauz Khas, New Delhi,

and 3Chief Engineer, M.P. Urja Vikas Nigam, Bhopal (M.P.), India

(Received 12 February 1993; received for publication 16 December 1993)

Abstract--The effect of various coal properties like ash content, moisture content, fixed carbon and calorific value on specific coal consumption in a typical thermal power station in India is analysed. It is observed that the specific coal consumption is a strong function of moisture content, ash content and fixed carbon. For the Panipat Thermal Power Station (the one considered in the present analysis), it is observed that, for an increase in moisture content by 2%, the specific coal consumption increases by about 8%. If, however, the ash content is increased by 20 , the specific coal consumption increases by about 5%. It is also observed that, for a 4 0 increase in fixed carbon, the specific coal consumption decreases by about 25%.

I N T R O D U C T I O N

Energy is essential for the economic growth of a country. The availability of a reliable source of energy in the most economical way is a basic prerequisite for the sustained development of a nation. In India, the need for increasing amounts of energy is now more than ever before.

The power generating capacity, which is mainly owned and operated by utilities, has grown at the rate of over 9.7% per annum since 1950. The total installed capacity in the country, which was about 1340 MW in 1947, rose to about 70,000 MW in 1991-92; even then, there was an average power shortage of 7.8%. The peak power shortage was as much as 18.8%.

The actual generation was about 200.63 billion units in the first three quarters of 1990-91. The thermal contribution was targeted to be about 73%; however, the actual thermal power generation was 134.58 billion units, i.e. 69%.

In the last 20 years, the availability of energy in India has been growing at a compound annual rate of 4.9%. During the same period, the average compound annual growth rate of different sources of energy is given in Table i. In the year 1991-92, the total availability of all primary sources of commercial energy put together was equivalent to 200 million t. The consumption of various sources of energy in 1991-92 is also given in Table 1. It is clearly seen that coal is the major energy source. Out of 235.30 million t, 137 million t was used for power generation alone. Since our coal reserves are not going to last long, every effort should be made to use this source of energy as efficiently as possible. This requires a complete knowledge of coal properties and their effect on coal consumption. In the present paper, the effect of coal properties on the specific coal consumption in thermal power stations is analysed in detail.

The three important properties of primary interest from a combustion standpoint are the fixed carbon, volatile matter and calorific value. Volatile matter consists of hydrocarbons and other gases (not including water vapour).

FACTORS RESPONSIBLE FOR HIGH SPECIFIC COAL CONSUMPTION

Gradual deterioration in the grade of coals, resulting in lowered calorific values from 500 kCal/kg to 3000 kCal/kg, lowered volatile contents from 24% to 17% and a staggering rise in the ash

tNow at Lucknow University, Lucknow-226 007, India.

597

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598 SHAIL et al.: COAL PROPERTIES AND COAL CONSUMPTION

Table I. Energy consumption in India in 1991-92 and compound annual growth rate

Energy source

Energy consumption Compound annual rate growth

Oil equivalent between 1970-71 Uni t s Quantity % share (Mt) and 1990-91

Coal Oil Natural gas Hydro

Nuclear

Lignite

Mt 235.30 57.9 115.50 5.6% Mt 54.50 27.3 54.50 5.5%

Million m 3 18400.00 7.9 15.80 13.4% Million 72557.00 3.0 6.20 5.4% kWh

Million 5585.00 0.2 0.50 4.9% kWh Mt 15.00 3.7 7.50 6.3%

Mt = Million tonnes. m 2 = Cubic metres. kWh = Kilowatt hour.

contents from 20 to 45% having a high percentage of alpha-quartz, is practically destroying the boiler plants and associated auxiliaries, resulting in increased downtime, low plant load factor (PLF) and an exponential rise in the cost of generation, maintenance, spares, inventories etc.

The combined ash and moisture of the present day coals which are received by the generating station far exceed the fixed carbon content, and this not only increases the per unit generation cost, but also brings down the plant's availability, security, stability and various other deleterious effects causing sliding of PLF(s).

There are many factors which are responsible for a high specific coal consumption and low outputs of the units. The major factor responsible for this is the supply of inferior and erratic quality of coal to the power stations. The inferior quality of coal directly affects boiler performance. Receipt of inferior grades of coal, compared to the declared and linked grade to which the boiler is designed, is being experienced in almost all the power stations. In addition to this consistent supply of inferior quality of coal, the extraneous substances, such as shale and stones in the form of boulders, are a common feature in many thermal power stations. This is creating numerous problems in unloading, handling and crushing in the power plants, resulting in increased wear and tear and frequent outages of coal handling system equipment. Hence, there is an urgent need to beneficiate the coal being supplied to thermal power stations.

C O L L E C T I O N OF E X P E R I M E N T A L DATA

The present study is based on data collected from the Panipat Thermal Power Station (PTPS) located on the Panipat-Safidoun road about 15 km from Panipat city in the state of Haryana (India). The total thermal power generating capacity of the plant is 650 MW, consisting of four units of 110 MW each and one unit of 210 MW which has been commissioned very recently. Coal to the power station is supplied from coal mines located in the Hazaribagh and Dhanbad districts of Bihar.

Table 2 gives the electricity generated per kW of installed capacity by the different 1 10 MW units at PTPS from 1984-85 to 1990-91. Similar results for the performance of all capacity units in the country are also given for comparison purposes.

Table 2. Units generated per kW of installed capacity (kWh/kW)

All capacity Year Unit 1 Unit 2 Unit 3 Unit 4 Station units in India

1984-85 2352 4608 -- -- 3480 3767 1985-86 3808 3011 -- 3455 3878 1986-87 1998 3102 1727 -- 2389 4109 1987 88 1435 3516 2631 5949 3383 4239 1988-89 1829 2816 6153 4271 3767 3976 1989-90 2430 3238 5000 4538 3802 NA 1990-91 2424 1687 3408 1312 2208 NA

Source: (i) Panipat Thermal Power Station. (ii) CEA Annual Report. NA = not available.

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SHAIL et al.: COAL PROPERTIES AND COAL CONSUMPTION

Table 3. Performance in terms of PLF (%)

599

110 MW All C units all units

Year Unit 1 Unit 2 Unit 3 Unit 4 Station India India

1984-85 27.0 52.7 - - - - 39.9 39.7 50. I 1985-86 43.9 34.4 2.4 - - 38.9 44.1 52.4 1986-87 22.8 35.4 19.7 18.0 26.0 44.8 53.2 1987-88 16.3 40.0 29.9 67.2 38.5 48.4 56.5 1988-89 20.9 32.1 70.2 48.7 43.0 48.4 55.0 1989 90 27.7 37.0 57.1 51.8 43.4 47.2 56.5 1990-91 27.8 19.3 38.9 15.0 30.3 NA NA

Source: (i) Panipat Thermal Power Station. (ii) CEA Annual Report~ NA = not available.

F rom Table 2, it is seen that the overall average energy generated from the four units at PTPS varied f rom 2208 to 3802 units per kW of installed capacity during the period from 1984-85 to 1990-9 i.

Table 3 gives unit-wise values o f plant load factor (PLF) and average P L F for the station. This is compared with the P L F of all the 110 M W units and also with all capacity units in India.

It is observed from Table 3 that the performance of units 1 and 2 has been consistently lower than the average P L F of all 110 M W units in the country. The performance of units 3 and 4 was not very good from 1984-85 to 1986-87, though it improved in 1988-89 and 1989-90 and again declined significantly in 1990-91.

Table 4 shows auxiliary power consumpt ion at the Panipat Thermal Power Station which is compared with all 110 M W units in the count ry and also with all capacity units. It is seen that auxiliary power consumpt ion at PTPS is always higher than the national average for similar units. In 1990-91, the auxiliary power consumpt ion was 12%, which is on the high side; ordinarily, the auxiliary power consumpt ion should be between 10-12%.

Table 5 gives the unit-wise specific coal consumpt ion for the four units and average consumpt ion for the station. It has also been compared with the specific coal consumpt ion of all capacity units in India. It can be easily seen that the all India average o f specific coal consumpt ion varies f rom 0.70 to 0.72 kg per unit o f electricity generated, whereas the specific coal consumpt ion at PTPS lies between 0.715 and 0 .92kg/kWh, which is exceptionally high. According to a recent study, a reduction o f just 0.02 kg /kWh in specific coal consumpt ion would be equivalent to almost 24 million t on an all-India basis. On monetary terms, it implies a saving of over 1200 crore rupees, an amoun t which cannot be neglected.

Table 6 gives an account o f the coal quality o f PTPS for coal received and utilized from 1987-88 to 1990-91. It is seen that the ash content varied from 36-40% and the average calorific value of the coal being used varied from 17,094-18,774 kJ/kg.

D A T A A N A L Y S I S

The informat ion regarding coal consumpt ion (in Mt) and generation (in million units) on a monthly basis was obtained f rom the coal handling plant personnel who maintain a cont inuous record of the amoun t o f coal used. These data are then used to calculate the specific coal consumption. The coal analysis reports were obtained from the laboratory of the Panipat Thermal

Table 4. Auxiliary power consumption (%)

110 MW units All capacity units Year PTPS all India average all India average

1984-85 13.5 12.6 10.6 1985 86 13.8 I 1.7 11.2 1986--87 16.7 11.6 10.0 1987 88 12.0 11.6 9.9 1988-89 12.0 10.0 9.87 1989-90 12.0 (E) NA 9.85 (E) 1990-91 12.0 (E) NA NA

Source: (i) Panipat Thermal Power Station. NA = not available; E = estimated.

Page 4: Effect of coal properties on the specific coal consumption in a typical thermal power station in India

600 SHAIL et al.: COAL PROPERTIES AND COAL CONSUMPTION

Table 5. Specific coal consumption (kg/kWh)

Year Unit 1 Unit 2 Unit 3 Unit 4 Station All India

1984-85 0.780 0.724 - - - - 0.742 - - 1985-86 0.887 0.887 - - - - 0.887 - - 1986-87 0.890 0.851 0.888 - - 0.871 0.70 1987-88 0.795 0.785 0.755 0.776 0.776 0.71 1988-89 0.715 0.724 0.715 0.725 0.721 0.71 198940 0.840 0.820 0.840 0.820 0.827 0.72 1990-91 0.910 0.91 0.910 0.920 0.915 0.72

Source: (i) Panipat Thermal Power Station. (ii) CEA Annual Report.

Power Station. Coal is periodically analysed in the laboratory and a record of the various coal properties is kept. This data is given in Table 7.

YEXP is the actual specific coal consumption for the various coal properties X1, X2, X3, X4. The relationship between specific coal consumption and coal properties is the polynomial with interacting variables (various coal properties). Therefore, for an arbitrary data set (as in the present case) wherein the total specific coal consumption is given and, along with it, coal properties are stated, one can easily study the combined effect of different coal properties on the specific coal consumption. The polynomial obtained for the data given in Table 7 is given by

Y C A L = - 10.57 + 0.16XI - 5.21 x 10-3X12 + 0.14X2

+6.84 x 10 -3 X22 + 4.7 x 10 3X1X2 + 0.29X3

+ 1.28 × 10 3X32_ 6.97 × 1 0 - 3 X I X 3 - 2 . 6 6 × 10-ZX2X3

+ 1 . 1 2 x 10 4 X 4 - 3 . 2 4 + I 0 - S X 4 Z + 2 . 6 1 x 10 - sXIX4

+3.93 × 10 5X2X4 x 1.09 × 10 6X3X4. (1)

Using the polynomial given by equation (1), the calculated values of specific coal consumption, YCAL, corresponding to different values of ash content, moisture content, fixed carbon content and gross calorific value are obtained. The values of YCAL are also given in Table 7. It is found that the average error between the two values is of the order of 1.22. Since the average error between YEXP and YCAL is very small, therefore, one can use equation (1) for studying the variation of specific coal consumption with various coal properties.

R E S U L T S AND D I S C U S S I O N

The variation in YCAL values is analysed for different X values. Figure 1 shows the variation of specific coal consumption with ash content, keeping the moisture content, fixed carbon and gross calorific value constant. The three curves correspond to three different values of moisture content, keeping the other properties constant.

It is clearly seen that, for a particular moisture content, the specific coal consumption tends to increase with an increase in the ash content of the coal. Simultaneously, if the moisture content also increases, then it adds to the already increased specific coal consumption.

Since ash is the non-combustible part of coal, therefore, if the ash content increases, the overall combustible portion of the coal is decreased. This results in an increased requirement of coal to generate the same units of electricity. Moreover, if the moisture content in the coal increases, the coal cannot be pulverized to the required size. This coal, which is in the form of lumps, does not burn completely, resulting in unburnt carbon loss in the bot tom ash, which further increases the

Table 6. Coal analysis

Ash V.M. Mois. F.C. G.C.V. Year (%) (%) (%) (%) (kJ/kg)

1987-88 35.61 19.14 1.51 43.74 19,782.0 1988-89 35.57 18.67 7,12 38.64 18,396.0 1989-90 36.01 18.71 7,07 38.21 18,177.6 1990-91 37.21 18.68 7.86 36.25 17,938.2

Source: PTPS.

Page 5: Effect of coal properties on the specific coal consumption in a typical thermal power station in India

SHAIL et al.: COAL PROPERTIES AND COAL CONSUMPTION 601

Table 7. Specific coal consumption and coal analysis data for the period 1988-91

YEXP X1 X2 X3 X4 YCAL

0.720 36.45 7.02 37.48 17957.28 0.765 0.744 34.91 8.33 37.06 18053.42 0.799 0.731 35.03 7.50 39.39 18316.76 0.726 0.723 35.44 6.71 38.95 18621.90 0.790 0.726 35.53 7.69 37.79 18120.30 0.774 0.719 36.53 7.05 38.14 17915.48 0.738 0.728 36.77 6.80 38.07 17957.28 0.748 0.726 33.81 6.67 40.88 18918.68 0.734 0.731 36.41 6.85 37.96 18103.58 0.771 0.739 37.28 7.36 3 5 . 3 1 17430.60 0.780 0.783 34.95 7.95 38.17 18262.42 0.763 0.816 35.99 6.71 37.86 18341.84 0.795 0.844 36.05 6.96 37.90 17806.80 0.717 0.859 34.93 6.83 39.03 18793.28 0.783 0.877 36.56 7.68 37.24 18379.46 0.879 0.833 36.44 5.87 37.75 18684.60 0.827 0.946 36.82 9.18 35.75 17714.84 0.964 0.960 35.76 9.18 36.53 17898.76 0.898 0.878 34.75 9.27 37.44 18463.06 0.891 0.913 37.11 8.87 35.88 17677.22 0.921 0.906 38.13 7.98 3 4 . 9 1 17388.80 0.859 0.945 38.08 9.18 33.54 16895.56 0.966 0.951 36.94 8.19 35.66 17802.62 0.907

Source: TERI (1991). Y = Specific coal consumption (kg/kWh); X I = ash content

(%); X2 = moisture content (%); X3 = fixed carbon (%); X4 = gross calorific value (kJ/kg).

specific coal consumption. An increase in the moisture content also implies that more heat is required to evaporate this excess amount of water. As a consequence, more coal has to be burnt to obtain the same output of electricity.

In order to reduce the specific coal consumption, it is suggested to use coal having a moisture content as low as possible. The ash content should also be low. For a typical Indian coal, the moisture content is anywhere between 7-20% and the ash content lies in the range 30-50% both of which are significantly high.

It is not possible to reduce the ash content because the ash is so intimately interspersed into the coal that, even by repeated washing, the ash content cannot be reduced to customary levels. However, the moisture can be reduced to a certain extent by utilizing the heat of flue gases.

It has been observed that an increase in the ash content by 2% increases specific coal consumption by almost 5% (for this particular thermal station). This is equivalent to about 0.17 × 106t of coal annually. Also, as the moisture content is increased by 2%, the specific coal consumption experiences an increase of 8% which is highly uneconomical since it amounts to 0.31 x 106t of coal.

.- 0.75

E

0 .70

0.65

0.60 33.8 34.3 34.8 35.3 35.8 36.3 36.8 37.3

Ash (%)

Fig. 1. Effect of ash on specific coal consumption. Where: ( - - . ) , moisture = 6.5*/,; ( ure = 7.5%, ( - - ) , mositure = 8.5%.

. . . . Moisture = 6.5%

- - ~ Moisture = 7.5%

. . . . . . Moisture = 8.5% ~ s ~ ~

Fixed carbon = 37% , Gross cal. value = 17.500 kJ/kg

I I I I I I L L 37.8

) , m o i s t -

Page 6: Effect of coal properties on the specific coal consumption in a typical thermal power station in India

6 0 2 S H A I L et al.: C O A L P R O P E R T I E S A N D C O A L C O N S U M P T I O N

e~

0 . 9 m

0 .8

0 . 7

0 . 6

0 . 5 3 3 . 8

. . . . Fixed carbon = 3 5 %

~ F i x e d carbon = 3 7 %

- - - . . . . . Fixed carbon = 3 9 %

Moisture = 7 . 5 %

Gross cal. value = 1 7 , 5 0 0 kJ/kg

f I J I J I I I 3 4 . 3 3 4 . 8 3 5 . 3 3 5 . 8 3 6 . 3 3 6 . 8 3 7 . 3 3 7 . 8

A s h ( % )

F i g . 2 . Effect o f ash on specific coal consumption, where: ( . . . . ) , fixed carbon = 3 5 % ; (

carbon = 3 7 % ; ( - - - ) , fixed carbon = 3 9 % .

), fixed

Figure 2 shows the variation of specific coal consumption with ash content, keeping the fixed-carbon content constant; the three curves correspond to three different values of fixed carbon content. The other constant parameters are moisture and gross calorific-value. It is observed that an increase in the fixed carbon content decreases the specific coal consumption. The fixed carbon content is a measure of the amount of carbon in the coal. Therefore, the higher is the fixed-carbon value, the higher will be the carbon content and, hence, the lower would be the coal consumption. It is also seen that, for the same percentage of ash content, the specific coal consumption decreases with an increase in the fixed carbon content.

As the fixed carbon content increases from 35 to 37% for an ash content of 36.8%, the specific coal consumption decreases from 0.816 to 0.614kg/kWh. This implies a decrease of almost 0.2 kg/kWh which is equivalent to 1.14 × 106 t of coal annually for the thermal power station under consideration.

From Fig. 3, one can see that, for an ash content of 33.8%, the specific coal consumption is 0.70 kg/kWh, whereas for an ash content of 37.8%, the value of specific coal consumption is 0.84 kg/kWh. The gross calorific value has been kept constant at 18,000 kJ/kg. One might say that increase in specific coal consumption is just 0.14 kg/kWh which is not very significant; but this is an additional 0 .14kg of coal for generating one unit of electricity. Therefore, for generating 650 MW, i.e. 5.7 × 10 9 units of electricity, an additional 0.80 × l 0 6 t of coal would be required annually.

It is seen that, with an increase in the ash content, the specific coal consumption also increases. This can be attributed to the fact that an increase in ash implies a decrease in the combustible portion of the coal. Here, by combustible, we mean basically the volatile matter and fixed carbon.

The presence of ash in coal is highly objectionable and uneconomical. It is, hence, suggested that a thorough washing of coal should be done to remove as much ash as is possible before using it for combustion. Also, instead of the generally employed water-tube boilers, fluidized bed combustion boilers should be used. These boilers are most suitable for high ash content coal.

Figure 4 shows the effect of moisture on specific coal consumption when the fixed carbon content is kept constant. The two curves correspond to two different values of fixed carbon content. It is seen that, for a low moisture content, the effect of fixed carbon content is not significant. For a

o

r.~

].0 --

0 . 9 - -

0 .8 - -

0 . 7

0 . 6 3 3 . 8

Moisture = 7 . 5 %

Fixed carbon = 3 7 %

Gross cal. value = 18,000 kJ/kg

I I I I I 1 I 3 4 . 3 3 4 . 8 3 5 . 3 3 5 . 8 3 6 . 3 3 6 . 8 3 7 , 3

A s h ( % )

F i g . 3. Effect o f ash on specific coal consumption.

3 7 . 8

Page 7: Effect of coal properties on the specific coal consumption in a typical thermal power station in India

S H A I L et al.: C O A L P R O P E R T I E S A N D C O A L C O N S U M P T I O N 603

e~

E

ca

W.

| . 0 --

0.9 -

0.8 -

0 . 7 ~ _ ~ -

0 . 6 - -

0 .5 5 . 9

Fixed carbon = 35%

- - Fixed carbon = 37% .---- . t -

A s h = 36~,~

G r o s s cal v a l u e = 1 7 , 5 0 0 k J / k g

I I I I ~ I 6 . 4 6 . 9 7 . 4 7 .9 8 .4 8 .9

M o i s t u r e (%)

Fig. 4. Effect o f mois ture on specific coal consumpt ion , where: ( • t, fixed carbon = 35%: ( - - - ) , fixed carbon = 37%.

moisture content of 5.9%, the specific coal consumption is almost the same for different fixed carbon contents. But, as the moisture content increases, the effect of fixed carbon also becomes pronounced. It is found that the specific coal consumption increases with a rise in moisture content, but as the fixed carbon increases, the coal consumption goes down. For a given moisture content, say 8.9%, the specific coal consumption for a fixed carbon content of 35% is 0.92 kg/kWh, and for a fixed carbon content of 37%, it is 0.75 kg/kWh.

It is, therefore, suggested that, before any coal is burnt, it should be thoroughly dried so that the coal consumption rate is reduced significantly. This can be easily done by resorting to heat recovery mechanisms which include utilization of the heat of the outgoing flue gases to evaporate the excess moisture content of the coal. A decrease in moisture content by 3% leads to a decrease in the specific coal consumption by almost I1% which is equivalent to a saving of 0.43 x 106t of coal annually.

For a fixed carbon content of 33.6%, the specific coal consumption for 34% ash is 0.76 kg/kWh, but if the fixed carbon increases to 39.1%, then for the same amount of ash, the specific coal consumption decreases to 0.58 kg/kWh. This implies a net 0.22 kg/kWh reduction in specific coal consumption, which amounts to an annual saving of about 1.25 x 1 0 6 t of coal.

Alternatively, if the fixed carbon content decreases from 39.1 to 33.6%, then 1.25 x l06 t of coal have to be burnt annually, which otherwise could have been saved. If the whole problem is viewed from the ash point of view, then keeping the fixed carbon constant at 33.6%, an increase in ash content from 34 to 36% increases the specific coal consumption by 0.11 kg/kWh, which is nothing less than 0.63 x 106t of coal, again annually.

Therefore, one can easily infer that even a slight increase in the ash content of a slight decrease in the fixed carbon content is highly uneconomical, especially in this era of energy crises.

R E F E R E N C E S

1. Power Engineers Tra in ing Society's W o r k s h o p on Energy Conservat ion . Thermal Power Station Personnel Training Institute, Badarpur, N e w Delhi .

2. Roy K. K., Qual i ty o f coal and its effect on thermal power generation, Proc. All India Seminar on Coal Technology. Vol. 1. B H E L , Tr ichy (1988).

3. Study o f Coal and Oil C o n s u m p t i o n in Panipat Thermal Power Station. TER1 Report (1991).