Coal technology development activities in India

0360-5442/86 $3.00 t0.00 Pergamon Journals Ltd

Energy Vol. 11, No. 11/12, pp. 1231-1237, 1986 Printed in Great Britain

COAL TECHNOLOGY

DEVELOPMENT INDIA

ACTIVITIES

IN

M. CHAKRABORTY Central

Fuel Research

Institute,

Post-F.R.I.,

Pin-828108,

Dhanbad,

India

Abstract-India is endowed with relatively large reserves of coal that are and are likely to remain the principal source of primary energy for many years to come. The typical Indian coals, however, have a high ash content (20-30%) and poor washability characteristics. These and other problems as well as the positive aspects of Indian coals are discussed. The coal technology development programs planned to respond to the peculiar characteristics of Indian coals and the requirements of the country are highlighted. The significance, concepts, and status of work done on some of the priority projects, such as beneficiation, direct and indirect liquefaction, solvent-refined coal for processing to metallurgical coke, coal-liquid mixture fuels, and organic coal fertilizers, are presented.

INTRODUCTION

India is endowed with relatively large reserves of coal, the country’s principal commercial source of primary energy. Although the production of petroleum crude in recent years has increased significantly, the reserves of mineral oil are limited and a substantial quantity of crude is still imported. In view of diminishing reserves of petroleum and an uncertain international situation, coal is likely to play a major role in industrial development and in the domestic fuel supply in India for many years to come. Most of the basic principles of coal technology were established prior to and during World War II. Liberal use of cheap and clean petroleum-based fuels and chemical feedstocks during the 1960s and early 1970s all over the world has, however, set new standards of operation efficiency, economy, and environmental acceptability. This has necessitated the reorientation and recasting of coal technologies so that coal can be used as a substitute for petroleum-based products with all their advantages. With this objective in view, the major effort in many countries has been in the field of new coal technologies. This paper highlights some of the activities being pursued in this area in India.

BACKGROUND

India has coal resources of about 112,000 million tonnes up to a depth of 1200m.’ This is roughly about 1% of the total global resources. Considering India’s future requirements, however, this is substantial, even if it is assumed that only 50% of the coal resources will be recoverable. In contrast, India’s resources of petroleum and the oil equivalent of gas are round 3400 million tonnes, of which about 900 million tonnes are believed to be extractable.2 Table 1 shows the reserves of Indian coal and petroleum crude, their expected demand and the expected durations of their availability. It can be seen that coal reserves are relatively immense and that thus, in the foreseeable future, coal will remain the major source of energy in India. As of today, among the various sources of primary energy, the share of coal is the highest-coal, 59.5%; oil, 27.0%; hydroelectric power, 12.5%; and nuclear, 1.0% (all expressed as coal equivalent in terms of energy content). Unless the reserve levels of oil and gas do not dramatically and spectacularly change for the better, it is almost certain that in India coal will have to increasingly bear the brunt of energy development and development of the metallurgical industries. This is reflected in the estimate of demand for coal by sector3 for the end of Sixth (1984-85), Seventh (1989-90), and Eight (1994-95) Five-Year Plans as presented in Table 2. 1231

1232

M. CHAKRABORTY

Table 1. Reserves of coal, petroleum, and gas (oil equivalent) in India, availability

Coal Prime coking Medium coking Semi- to weakly caking Non-coking Total” Additional reservesb Total coal Petroleum and oil equivalent of gas

their expected

demand,

and expected

durations

RWXXCW (million tonnes)

Recoverable ReSel-WS (million tonnes)

Expected demand (1989+90) (million tonnes)

Expected duration of availability (years)

4956 9340 3615 67,533 85,444 24,184 111,628

55,814

237

278

3400

900

60

15

of

“On the basis of seam thickness and depth up to 1.2 and 600 meters, respectively. bOn the basis of seam thickness and depth up to 0.5 and 1200 meters, respectively. ‘Assuming 50% extractable.

Table 2. Demand

for coal, by section, for the Sixth, Seventh, and Eighth Five-Year Final Year of Seventh Five-Year Plan (1984-85)

Sixth Five-Year Plan (1984-85) Sector

%

Steel industty Power industry Railways Cement industry Fertilizer industry Soft coke/low temperature Brick industry and others

carbonization

Colliery consumption Exports Total

“Figures in brackets

34.50 65.00 (3.50) 11.70 8.60 5.60 6.00 32.70 (1.50) 3.50 0.40 168.00 (5.00)

Plans (million

20.54 38.70 6.96 5.12 3.33 3.57 19.46 2.08 0.24 100.00

tonnes)

Eighth Five-Year Plan (1984-85) %

44.61 121.52 (7.59) 8.00 12.65 6.83 4.70 34.31

18.79 51.18

4.20 0.60 231.42 (7.59)

1.77 0.25 100.00

3.37 5.33 2.88 1.98 14.45

% 60.00 169.50 (11.50) 6.00 16.00 11.00 6.50 42.00

18.93 53.46

5.00 1.00 317.00 (11.50)

1.58 0.32 100.00

1.89 5.05 3.47 2.05 13.25

indicate middlings.

CHARACTERISTICS

OF

INDIAN

COALS

The organic components of a particular class of coal are generally the same everywhere.4 The main difference between coals of different countries lies in the content of ash, its nature, and the manner in which it is present. This is indicated in Table 3, an analysis of a few of the best coking and non-coking coals of the United Kingdom, the United States, and India. The ash content (a measure of mineral matter content) in Indian coals is generally high, most often between 20 and 35%, whereas the ash content of American and European coals rarely exceeds 10%. Moreover, the washability characteristics (as expressed by washability number5) of most Indian coals are remarkably poor. This is primarily because most of the mineral matter in these coals, in view of their drift origin, is intrinsic, being finely disseminated throughout their physical matrix, making liberation difficult. The mineral matter in most European and American coals, on the other hand, is adventitious in nature, thus making these coals very amenable to beneficiation by densimetric principles. Indian coals are also typically non-coking, with poor grindability (Hardgrove Grindability Index of 45-55). There are, however, some positive aspects of Indian coals. For example, sulfur content is usually low except in coals from the northeastern region. The coals are very reactive and their ash fusion temperature is relatively high (generally more than 1100 “C in a mild

technology

Coal Table 3. Analysis

and characteristics

development

of selected non-coking

activities

in India

and coking coals of the United India dmf basis

country origin

Type of Coal

of

United Kingdom North land Yorkshire Durham United States Indiana Kentucky (west) Pennsylvania West Virginia India Raniganj Raniganj Jhacia Jharia ‘Calorific

Moisture (“/)

Ash

1233 Kingdom,

(%)

(%)

Sulfur (%)

V

C

H

Q

H/C (atomic)

the United

States, and

Washability number (WNS’

Non-coking Non-coking Coking

9.6 2.8 0.9

2.9 2.1 2.5

0.9 1.3 0.7

31.4 39.8 21.2

81.8 84.1 89.4

5.3 5.5 5.1

14,360 14,970 15,680

0.78 0.79 0.68

Non-coking

12.8

6.9

2.6

46.0

82.3

5.5

14,690

0.80

Non-coking Coking

10.1 1.8

4.4 8.7

2.4 2.3

43.9 20.0

83.0 91.2

5.6 4.8

14,750 15,830

0.81 0.63

Coking

1.6

6.2

0.7

22.4

90.3

5.0

15,800

0.66

108

Non-coking Non-coking Coking Coking

7.1 2.6 1.1 0.8

16.5 18.0 21.1 26.1

0.4 0.5 0.6 0.7

40.1 41.0 27.3 23.8

80.5 84.0 89.7 90.1

5.2 5.6 5.0 4.8

14,400 15,000 15,640 15,700

0.79 0.80 0.67 0.64

19

157

value, Btu/lb.

bWashability

number (WN) =

Optimum

degree of washability Clean coal ash

x 10

reducing atmosphere). Also, although the locations of the coal reserves in India uniform, most of the coal seams are 30-40m thick and 200-300m deep, thus Indian coals easily mineable and extractable in many cases by open-cast mining. It should be mentioned that large deposits of low-rank, high-volatile coal (or have been found in a west province (state of Gujarat) at a depth of more than Since it would be difficult to extract these deposits by means of conventional methods, possibilities of underground gasification are being explored.6

RESEARCH

AND

DEVELOPMENT

are not making lignite) 1OOOm. mining

PRIORITIES

Considering the peculiar characteristics of India’s coal and the national requirements for its use, projects for developing relevant coal technologies have been taken up on different scales. The main objective, however, is to find appropriate ways and means to use the coals in the metallurgical industries and as substitutes for petroleum-based fuels and feedstocks. The areas of the major research and development activities identified and being pursued are: (1) beneficiation of high-ash coal; (2) substitution of coal for metallurgical coke and petroleum-based fuels and chemical feedstocks (through liquefaction, gasification, coal-liquid mixture fuels, etc); (3) combustion of high-ash coal; (4) slurry transport; (5) production of environmentally acceptable domestic fuel; (6) production of organic coal fertilizer; and (7) underground gasification. The main priorities for the next 5 yr are gasification and slurry transport of coal. During 1985-86 to 1989-90, $200 million will be used for coal research, out of which $160 million will be earmarked for the development of gasification and slurry transport technologies. To respond to the rapid increases in coal production and to achieve the objective of replacing fuel oil with coal as much as possible, transportation of coal to the demand centers away from the pitheads has become all the more important. Hydraulic transport of coal through pipelines is considered an economicaly viable method in India, with minimal environmenta impacL7 A major part of the activities involved in these R&D efforts is being conducted at the Central Fuel Research Institute (CFRI), one of the major energy research laboratories under the Council of Scientific and Industrial Research in India. The significance and status of some of the R&D activities being pursued at CFRI are briefly highlighted here.

1234

M. CHAKRABORTY

Benejiciation Although, in order to eliminate free silica and other abrasive inerts, deshaling of steam coal by simple washing techniques has been proposed, beneficiation is particularly important for preparing coal for metallurgical use. Beneficiation can be either physical or chemical. The comparative performance of physical beneficiation methodssP9 with typical Indian coals is shown in Table 4. Both the yields and the ash content in cleans are poor with the centrifugation of froth flotation methods. Oleo-flotation resulted in better performance, but the ash content in the feed coal was low with relatively higher washability characteristics. Oil-agglomeration is certainly an attractive method compared to more conventional routes. This process is now being tried at the pilot-plant level and attempts are being made to reduce the consumption of oil. Table 4. Performance

Particulars of coal”

Beneficiation Centrifugation (2700-4250G) Froth floatation Oleoflotation Oilagglomeration

Seams IX/X Seams V/v/VII - do seams IX Seams V/VI/VII - do Lodna middling

of selected physical beneficiation

processes with typical high-ash

Indian coals

Size consist (mm)

Ash content of feed coal (“/)

Oil used (% of coal)

13.0

36.0

0.00

25.531.0

16.018.0

34.1 41,2

0.15 0.053

30.6 30.6

0.01 0.01

31.5 78.1

20.9 21.8

43.6 89.6

0.5

19.4

1.53

84.8

14.8

90.2

0.1 0.1

36.5 36.0

11.5 19.2

61.9 65.0

21.2 21.9

86.9 82.7

0.1

41.6

15.5

60.0

21.5

84.5

‘All coals are from the Jharia coal field in India and are medium/prime do = ditto.

Cleans Yield Ash (“/) (%)

Recovery of combustible material (“/.)

coking coals.

Chemical demineralization of coal, which involves treatment with alkali at about 150 “C and atmospheric pressure, followed by acid and water leaching under specific conditions, has remarkable merits. The ash content in cleans can be largely controlled to the desired level with practically complete recovery of combustible material. No middlings are produced and fine grinding as in froth flotation and oil agglomeration is not required. Typical results of chemical demineralizationl” are presented in Table 5.

Table 5. Typical results of chemical demineralization

of coal’

Ash content of feed coal (“/)

Yield

Ash

Recovery of combustible material

of coal

Size consist (mm)

(“/)

(“/)

(“/)

Seam III, Jharia (East Bhowra) Ae Washed Dugda AoMiddlings (Patherdih) -do-doSeam XIV, Jharia (Bararee) Raniganj, non-coking (Samla)

3.0 3.0 3.0 0.2 3.0 1.0 0.2 3.0 0.2

32.3 32.3 21.5 21.5 41.6 41.6 41.6 15.4 12.8

80.7 70.8 85.3 79.5 70.7 61.5 65.0 89.1 86.5

18.3 8.0b 10.3 4.0 21.5 17.9 15.6 6.5 2.7

100.0 100.0 99.0 99.0 99.6 100.0 99.3 99.6 97.6

Particulars

Cleans

‘One of the advantages of the chemical method is that no fine grinding of coal is necessary as in the physical process. bThis was done under 30 atm pressure, which shows greater effectiveness of beneliciation under that condition despite coarser coal size. do = ditto.

Coal technology

development

activities

in India

1235

Chemical demineralization has been tried on a 150-kg-batch scale. The economics of the process depends largely on the recovery and reuse of the alkali and acid used and on the recovery of the by-products produced. Preliminary estimates show that the capital investment for a 5004onne/day plant is approximately $160 million and that the cost of demineralized coal is about $90/tonne. A 3-tonne/day continuous chemical demineralization pilot plant has been planned in order to optimize the process steps, collect scale-up data, and establish economic feasibility. Substitution for petroleum-based fuels and chemical feedstocks. In this area projects are being implemented to study direct liquefaction, Fischer-Tropsch (F.T.) synthesis, coalliquid mixture fuels, gasification, and modified F.T. synthesis. Liquefaction and Fischer-Tropsch synthesis. Liquefaction of coal, although not economically viable under prevailing conditions, would probably, in view of international strategies, be worthwhile for an oil-importing country like India. Because of these considerations, both direct and indirect liquefaction of coal are being pursued. The direct liquefaction process, along with upgrading of synthetic crude, is being studied in a OS-tonne/day pilot plant. A number of typical non-coking coals with lo-12% ash content have been used for direct liquefaction experiments. Problematic let-down valve erosion has been largely minimized. The total conversion of coal in the direct liquefaction process is around 80%. A program has been started to establish the material balance with various coals of different ranks and to up-scale the process. The indirect liquefaction process, known as Fischer-Tropsch (F.T.) synthesis, involves liquefaction of coal via gasification. The technology is proven, does not critically depend on the ash content of coal, and is being commercially exploited in South Africa. Although efficiency is relatively low, indirect liquefaction is flexible and has other merits, particularly when the coals used are of poor quality. Bench-scale studies on the F.T. process have been completed and include preparation of the catalyst and evaluation of its selectivity and activity. A process development unit with a fixed-bed reactor system with a capacity of 5 1. liquid fuel/day has been designed, installed, and will soon be commissioned. Coal-oil mixture (COM) fuel.” In India, coal has a significant price advantage over fuel oil. A coal-oil mixture using low-grade coal can find application in industrial oil-fired furnaces. A 50-50 coal-fuel-oil (No. 6) stabilized slurry has been developed, and its combustion characteristics have been found to be satisfactory. Prolonged tests to assess erosion problems are under way. The use of a stabilized coal-oil mixture in a utility boiler of a steel plant has been planned. Coal-water mixture (CWV)fuel.” A CWM project is being conducted under the support of the U.S. Agency for International Development (USAID). A CWM containing up to 65% coal with or without demineralization has been prepared. Attempts are being made to increase the coal loading while keeping the viscosity and stability within acceptable limits. The CWM is prepared on the principles of surface and colloid chemistry and of rheology. A number of surface-active agents prepared from coal are found to be effective. In addition to its use as a substitute for petroleum-based liquid fuel, CWM holds potential for use in fluidized-bed combustors and pressure gasifiers. The demineralization of coal for these applications is not essential. The coal washery slurry can also be utilized in the form of CWM fuel. Both the CFRI and Bharat Heavy Electricals, Ltd (BHEL) Tiruchirapalli, are working on this project under a grant from USAID. Substititution for metallurgical coke

At present about 1.5 million tonnes of coking coal is imported. The use of non-coking coal as a source of metallurgical-grade coke is of great relevance to India. In this sector, research and development work is being pursued in the following areas: (1) formed coke, (2) solvent-refined coal (SRC), and (3) treatment of coal prior to carbonization. The SRC process is of particular interest. In this process, coal, irrespective of its rank and nature, is chemically reconstituted to the level of highly coking coal and its mineral matter is eliminated.i3 In the United States SRC is used as a low-ash, low-sulfur, pollution-

M. CHAKRABORT~

1236

free fuel. While the use of SRC as a boiler fuel under the prevailing oil price is not economically attractive, the use of SRC as a blending agent to produce high-grade coke appears to have significant potential in India. It has been observedI that blending of SRC (up to lo-20%) with certain non-coking coals might yield cocarbonization coke that is suitable for steel-making. Since the requirement of SRC in the blend is small, its cost would not be a critical factor for this application. Japan is conducting large-scale pilot plant studies with similar objectives.’ 5 At CFRI in India, bench-scale experimental studies have been completed. It has been proposed to conduct the studies in a continuous process development unit in order to generate design data and to establish large-scale blending tests.

Production

of organic coal fertilized6

Controlled oxidation of coal with nitric acid under specific conditions yields a product that is useful as a multifunctional soil conditioner. The product is alkali soluble and designed as nitrohumic acid (NHA) that can be further oxidized to water-soluble polycarboxylic acids (PCAs). On neutralization with ammonia these coal acids act as a slow-release organic fertilizer. Coal acid, particularly nitrohumic acid, is relatively easy to prepare and, when used (lo-15%) in combination with conventional inorganic fertilizers like urea and ammonium sulfate, increases the productivity of the soil by about 30%. The chemical physical, and microbiological characteristics of the soil are significantly improved by the application of these coal-derived products. The water-holding capacity of the soil is increased and loss of nitrogen through leaching and nitrification is largely minimized when coal acids are used in combination with urea or ammonium sulfate, resulting in favorable residual effects. Consistent field trials of this fertilizer and soil conditioner are being conducted.

SUMMARY

AND

CONCLUSIONS

India’s technology and energy policies essentially stress self-reliance, efficient utilization of indigenous raw materials, and replacement of petroleum-based fuels and chemical feedstocks with coal wherever possible. India is endowed with large reserves of coal, the main source of commercial energy. Indian coals generally are high in ash content, are noncoking, and are difficult to beneficiate. Research and development activities are directed toward development of suitable technologies to produce clean coal, substitutes for metallurgical coke and petroleum-based fuels, fertilizers and chemical feedstocks. Relevant projects are being pursued on different scales. At CFRI, two projects to study coal cleaning by heavy-media cyclones and coal-water mixture fuel development are under the support of USAID. Acknowledgement-The author wishes to record his thanks and gratitude Development for the financial assistance to attend this conference.

to the U.S. Agency

for International

REFERENCES

1. Geological Survey of India, “Report on Total Reserves of Coal in India” (1978). 2. A. K. Malhotra, “Indian Energy Scenario-Energy and Oil”, Paper presented at the 12th Congress of World Energy Conference, New Delhi (1983). 3. Government of India, Department of Coal, “Draft Report of the Working Group for the Seventh Five-Year Plan on Coal and Lignite”, Ministry of Energy, New Delhi (1984). 4. B. K. Mazumdar, M. Charaborty and D. K. Mukherjee, “Problems and Prospects of Coal Utilization in India”, Paper presented at the 37th Annual Session of the Indian Institute of Chemical Engineers and the Joint Symposium with the American Institute of Chemical Engineers, New Delhi (1984). 5. G. G. Sarkar, H. P. Das and S. Ghose, World Coal 3, 10 (1977). 6. S. Ramanathan, UREA 16, 471 (1984). 7. N. N. Tiwary, J. Tiwary and S. K. Das, “Slurry Transport of Coal in India-A Review in Retrospect and its Prospect”, Paper presented at the Symposium on Hydraulic Transportation of Solids through Pipeline,

Coal technology

development

activities

in India

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Rnchi (1985). 8. G. G. Sarkar, B. B. Konar, S. Sakha and K. P. Das Chawdhury; and D. C. Mitra, D. P. Nag, R. Biswas, K. Raja and G. G. Sarkar, “Beneficiation Studies on High-coking Coals, Middlings and Slurries by Oilagglomeration Process” (in two parts), Paper presented at the Eighth International Coal Preparation Congress, Donetsk (1979). G. G. Sarkar. A. K. Chakravarti and A. Lahiri, “An Integrated Process for Simultaneous 9. J. Chattooadhvav. Upgrading and &watering of Small Coal”, Paper presented at .the Sixth -International Coal Preparation Congress, Paris (1973). “Status and Prospects of the Process of Chemical Demineralization 10. A. N. Sen Gupta and B. K. Mazumdar, of Coal”, In Coal Preparation and Use--A World Reoiew, S. R. R. Rao, ed., p. 205, IX International Coal Preparation Congress, New Delhi (1982). Patent Specification filed (1982). 11. R. N. Paul, B. K. Mall and M. Chakraborty, “Coal-Water Mixture Fuel and Preliminary Studies on its Rheological Charactetrstics”, 12. M. Chakraborty, Proceedings of the Second United States Agency for International Development/GO1 Workshop on Alternative Energy Resources and Development: Coal Conversion and Biomass Conversion, p. 84, New Delhi (1985). “Conversion of Non-coking Coals and Lignites 13. S. R. Dwivedi, S. Sarkar, R. R. Prasad and M. Chakraborty, to Coking Coals by the Technique of Hydroextraction”, Proceedings of the First Indian Carbon Conference, p. 239, New Delhi (1982). and S. R. Dwivedi, Fuel Sci. Technol. 3, 139 (1984). 14. D. C. Mitra, D. P. Nag, S. B. Chowdhury Jpn Indust. Technol. Bull. 10, 2 (1983). 15. Japan External Trade Organization, “Status and Prospects of Coal Fertilizer and Coal-Acids in Augmenting Food Production”, 16. B. K. Mazumdar, Proceedings of a Group Discussion on R&D in Fertilizer Industry/Research Centres, The Fertilizer Association of India, Bombay (1982).