ENVIRONMENTAL MANAGEMENT IN THE BEE- HIVE COKE OVEN PLANTS IN ASSAM AND MEGHALAYA: AN OVERVIEW OF ISSUES AND MANAGEMENT PRACTICES

CENTRAL POLLUTION CONTROL BOARD (MINISTRY OF ENVIRONMENT & FORESTS)

1.0 Introduction

Coke is a solid carbonaceous material produced by destructive distillation of low-ash

and preferably low-sulfur bituminous coal. Coal is baked or distilled in ovens at

controlled temperature of about 12000C and coke is produced as a combustible residue

consisting of residual ash and fixed carbon and in the process, the impurities present in

coal, such as volatile matters (tars, oil and grease, etc), are driven off. It is considered

that levels of 26-29 % of volatile matter (VM) in the coal are good for coking purposes.

The process of distillation or baking at controlled temperature does not allow burning of

Carbon present in coal.

Coke derived from coal is generally grey, hard and porous. Coke, also known as Low

Ash Metallurgical Coke (LAMC), is used in Blast Furnace for steel manufacturing

industries. Coke acts both as reducing agent as well as a source of fuel to melt the iron

ores. Coke is also used in the ferro alloy, graphite and carbon black industries.

The caking behavior of coal is critical to coke making. Caking behavior is a unique

property of coal and is an essential property for coal used for coking. As a caking coal is

heated, it passes through a region where it becomes very plastic, softens, swells and

then re solidifies. The re-solidified residue is a cellular coke mass. Non caking coals, on

baking or distillation, do not form any cake but simply form a non coherent or weakly

coherent char.

Bituminous coals of high grade (low ash content and high caking index) are produced in

the coalfields of Assam (Makum Coalfield) and Meghalaya (Coalfields in Jaintia, Garo

and Khasi Hills). As there is good demand of the LAMC in India, in the past few years,

a large number of bee-hive coke oven plants have been set up in the states of Assam

and Meghalaya.

This study has been carried out to assess the status of environmental management in

the bee- hive coke oven plants in Assam and Meghalaya. The study overviews the

environmental issues of bee-hive coke oven plants and also recommend various

measures for better environmental management in the beehive coke oven plants.

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2.0 Industry description

In the coke-making process, bituminous coal is fed into a series of ovens, which are

sealed and subsequently burnt at high temperature of about 12000C in an Oxygen (O2)

deficit atmosphere, typically in a cycle lasting for 24 to 36 hours. There are primarily

two (2) types of coke oven plants, viz., recovery type coke oven plants and bee-hive

coke oven plants (non recovery type). The characteristics of both the types of coke oven

plants are briefly discussed in the following sections.

2.1 Recovery type coke oven plants

In recovery type coke oven plants, low ash metallurgical coke (LAMC) as well as coke

oven gas is produced from suitable grades of coal by involving the pyrolysis process

(heating in absence of air). Coke breeze is also produced as a by-product in a coke

oven plant.

Coke oven gases, which are produced during the coking process, contain various

volatile compounds and these gases are further processed to recover combustible

gases and other bye-products like tar, ammonium sulfate, phenol, naphthalene, light oil,

sulfur, etc., and the gas is subsequently reused as fuel for heating the ovens.

Cooling of flue gases from coke oven plants is required to derive the bye-products.

Cooling of coke oven gases results in the formation of flushing liquor, which contains

tar. This flushing liquor and liquor from primary coolers are sent to a tar decanter.

Generally, with an electrostatic precipitator or suitable gas liquid separators, tar is

removed from coke oven gas. Ammonia liquor is also separated from the tar decanter

and sent to wastewater treatment after ammonia recovery.

Coke oven gas, after removal of tar, is further cooled in a final cooler and Naphthalene

is removed in the separator on the final cooler. Light oil is then removed from the coke

oven gas and is fractionated to recover Benzene, Toluene, and Xylene. A tar distillation

unit is generally installed in a non recovery type coke oven plant. The Claus process is

normally used to recover sulfur from coke oven gas.

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During the coke quenching, handling, and screening operation, coke breeze is

produced. It is either reused on site (e.g., in the sinter plant) or sold off site as a by-

product.

2.2 Non-recovery type bee-hive coke oven plants

In non-recovery type coke oven plants, there is no provision for recovery of various

valuable products from the coke oven gases. All the coke oven gases are emitted as

flue gas. Low ash metallurgical coke (LAMC) is the main target product for this type of

non recovery coke oven plants. Coke breeze is the only bye-product in the non-recovery

type plant. Majority of coke oven plants operating in India are of non recovery type. All

the coke oven plants operating in Assam and Meghalaya are of non recovery type coke

oven plants. These plats are also known as bee-hive coke oven plants, owing to the

bee-hive structure of the ovens in a coke battery.

2.2.1 Manufacturing process in bee-hive Coke Oven Plants

A beehive coke oven plant consists of a number of coke ovens placed in series

(Photograph 1 & 2). Each oven has the capacity to feed 5-10 MT of bituminous coal

depending on the size of the oven. Coal is fed from the top of each oven with the help

of trolleys, which are mounted on rails placed all along the top of the oven-mouths.

Various processes involved in production of coke in beehive coke oven plant is

summarized in Table 1.

3.0 Characteristics of Coal of North Eastern India

The Coke oven plants in Assam and Meghalaya use coal available in Meghalaya and

Assam as raw material. While Carbon, a tetravalent element, is the main composition of

coal, other elements like Hydrogen, Oxygen, Sulphur and Nitrogen are also

predominantly available in coal in an appreciable quantity (Bhattacharya, 1996). As the

emission load from the coke oven plants are dependent on the quality of coal being

used for coking, the characteristics of the coal produced in the North Eastern Region

are briefly described in the following section.

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Photo 1: Inside view of a Coke Oven

Photo 2: A beehive coke oven plant with number of ovens in series forming a coke battery.

The tertiary coal deposits of northeastern region of India range in age from Paleocene

to Oligocene. Coals found in Meghalaya, are of Eocene Age while coals available in

Assam, Nagaland and Arunachal Pradesh are of Oligocene Age. The Oligocene coal

deposits of northeastern India occur along a narrow and linear belt of over-thrust known

as ‘belt of Schuppen’, which is more than 300 km long and extends over the states of

Nagaland through Assam to Arunachal Pradesh (Misra and Ghosh, 1996). The

chemical characteristics of Eocene and Oligocene coals available in the North Eastern

India can be broadly summarized in Table 2.

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Table 1: Brief description of various processes employed in a Beehive Coke Oven Plant.

Sl No Process Brief description 1 Washing of coal Coal received from various coal mining

areas is washed to remove impurities or foreign material.

2 Crushing The washed coal/unwashed coal is crushed in crushing mill, generally known as hammer mill. Coal is crushed to a size of about 6 mm.

3 Feeding and charging Trolleys, mounted on rails, are used to feed coal into the coke ovens. Each Trolley can support up to a weight of 9.0 to 10.0 MT. After opening the hopper of the Trolley, coal is fed into each oven from the top.

4 Carbonization Coal is carbonized through destructive distillation at about 1200-15000C. During this process, all the volatile matters that are present in the coal escape into the air.

5 Discharge and quenching

After carbonization of coal, hot cake of coke is formed in the oven bed (Photograph 3). The entire hot coke is then dragged out of the oven by mechanical pulling followed by immediate quenching by spraying water on the top mass of the hot cake to obtain Low Ash Metallurgical Coke.

6 Coke Crushing and sizing

Coke Lumps formed during the process of quenching are fed into a Jaw crusher, where coke is crushed and then screened into different sizes.

7 Coke Breeze The smallest coke particles that formed during handling and crushing of coke are segregated and packed as Coke Breeze, which is a valuable by-product.

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Photograph 3: Formation of hot cake of inside an oven

3.0 Characteristics of Coal of North Eastern India

Coal available in Assam and Meghalaya are used as raw material in the Coke oven

plants in Assam and Meghalaya use coal available in Meghalaya and Assam as raw

material. While Carbon, a tetravalent element, is the main composition of coal, other

elements like Hydrogen, Oxygen, Sulphur and Nitrogen are also predominantly

available in coal in an appreciable quantity (Bhattacharya, 1996). As the emission load

from the coke oven plants are dependent on the quality of coal being used for coking,

the characteristics of the coal produced in the North Eastern Region are briefly

described in the following section.

The tertiary coal deposits of northeastern region of India range in age from Paleocene to

Oligocene. Coals found in Meghalaya, are of Eocene Age while coals available in Assam,

Nagaland and Arunachal Pradesh are of Oligocene Age. The Oligocene coal deposits of

northeastern India occur along a narrow and linear belt of over-thrust known as ‘belt of

Schuppen’, which is more than 300 km long and extends over the states of Nagaland through

Assam to Arunachal Pradesh (Misra and Ghosh, 1996). The chemical characteristics of

Eocene and Oligocene coals available in the North Eastern India can be broadly summarized

in Table 2. There are a number of small coalfields in the North Eastern States, especially in

Meghalaya, Assam and Arunachal Pradesh. A few detail studies on chemical characteristics of

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coal found in north eastern India had been done in nineties (CMPDIL 1991; Mishra and Gosh,

1996). Data available from these studies for the major coalfields of the North Eastern India are

shown in Table 3.

Table 2: Chemical Characteristics of Eocene and Oligocene Coals of NE India

Parameters Eocene Coals

Oligocene Coals

Air-Dried Basis Moisture (%) 1-12 1-6 Ash (%) 3-34 2-29 Total Sulphur (%) 2-7 1-10

Dry, mineral-matter free basis Volatile matter (%) 38-57 41-52 Carbon (%) 68-83 74-85 Hydrogen (%) 4-9 5-7 Calorific Value (kcal/kg)

6500-8500 6255-8650

(Source: CMPDI 1991; Mishra and Gosh , 1996)

Table 3: Chemical Characteristics of Eocene and Oligocene Coals of NE India

Name of Coalfield Moisture (%)

Ash (%)

Volatile Matters

(%)

Total Sulphur

(%)

C (%)

H (%)

Eocene Coals of Meghalaya (Garo Hills) Karaibari 11.5 6.6 46.7 3.0 67.5-70.2 4.0-4.9 Rongrenggiri 10.1 17.4 43.6 4.7 75.4 6.7 Siju 6.8 5.4 37.9 3.5 77.7-79.6 6.2-8.8 Darranggiri 8.4 2.7 41.3 2.3 72.6-79.5 5.6-7.3 Balphakram 3.5-4.5 3.8-18.3 41.9-47.6 4.2-4.4 79.4-80.6 6.3-6.7 Eocene Coals of Meghalaya (Khasi Hills) Langrin 6.5-6.9 3.3-3.8 40.1-44.8 2.3 78.0-81.2 6.0-6.6 Shella 1.9 1.9 9.2-20.9 3.9-4.7 76.0-81.7 5.2-6.3 Laitryngew 1.0-1.5 7.7-31.3 30.3-43.7 4.0-4.2 78.7-83.2 5.8-6.5 Eocene Coals of Meghalaya (Jaintia Hills) Jarain-Tkentalang 1.7-3.1 7.2-14.2 40.5-46.9 5.5-6.7 80.0 5.7 Bapung 2.9-5.4 6.0-23.4 37.7-43.1 3.7-6.0 79.9-83.1 5.6-6.4 Khliehriat 0.9 8.7 44.6 6.9 Sutnga 1.1-1.7 7.5-34.1 29.7-39.2 4.8-5.9 75.9-82.3 5.2-6.0 Mawla-Musiang Lumare

1.0-1.5 6.7-15.6 35.6-37.3 4.6-4.7 77.3 4.8

Lumshnong 1.1-1.5 24.7-28.1 28.2-29.9 3.9-4.2 80.8-84.2 5.1-5.8 Olegocene Coals of Assam Makum Coalfield 1.0-2.3 1.7-27.2 32.4-43.7 1.9-6.5 79.1-85.3 5.3-6.6 Dilli-Jeypore 4.8 1.9 44.7 1.3-9.8 73.7-79.9 5.4-6.7

Oligocene Coals of Arunachal Pradesh Namchik-Namphuk 2.2-4.1 1.8-8.8 40.3-44.1 1.8-4.9 79.5-82.8 5.8-6.6

(Source: CMPDI 1991, Mishra and Gosh, 1996)

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It is observed that the sulphur contents of coal available in the NE States are

comparatively very high in contrast to the coal deposits available in the other parts of

the country. The average characteristics of coal available in major coalfields in North

Eastern India and major coalfields in other parts of India (Singareni, Kushmanda,

Singrauli, Jharia, Neyvelli, etc) are summarized in Table 4 and Table 5 respectively.

Due to high Sulphur concentration in the NE coal, which is the only raw material for the

Beehive Coke Oven Plants in Assam and Meghalaya, the emission from these plants in

terms of Oxides of Sulphur (SOX) are obviously very high and is, therefore, detrimental

to the surrounding environment.

3.1 Coal washery plant for coal beneficiation

A coal washery plant helps in improving the quality of raw coal by removing impurities

like ash content, which in turn helps in reducing air pollutants like particulate matters

(PM). Thus a coal washery should be an essential unit in a coke oven plant for

reducing the ash content in the raw coal and thereby controlling the size and quality of

the feed.

A few bee-hive coke oven units in Assam, namely M/s K.D. Coke, M/s S.M. Coke and

M/s Pride Coke have installed their captive coal washeries. However, most of the coke

oven plants of Assam and Meghalaya are not having any coal washery and as such

coal available in the region are used for coking without any beneficiation of the mineral.

Quality of the raw coal improves after washing in terms of reduction in ash content and

increase in carbon content. A general qualitative characteristic of raw coal and washed

coal is shown in Table 6.

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Table 4: Total Sulphur and Sulphur Forms of Coals in the NE Region (in %)

Name of Coalfield

Total Sulphur Pyritic Sulphur

Sulphate Sulphur

Organic Sulphur

Eocene Coals of Meghalaya (Garo Hills)

Karaibari 1.36-6.01 0.07-1.90 0.15-1.68 0.61-2.42

Rongrenggiri 3.19-5.57 0.30-2.06 0.13-1.03 2.39-3.61

Siju 0.80-7.58 0.21-5.53 0.02-0.96 0.66-7.16

Darranggiri 1.21-3.68 Nil-0.96 0.01-0.51 1.07-2.33

Balphakram 4.24 1.73 0.21 2.30

Eocene Coals of Meghalaya (Khasi Hills)

Langrin 2.3 0.08 0.06-0.08 2.10-2.19

Shella 1.3-4.0 Nil-0.88 0.05-0.18 1.28-3.40

Laitryngew 2.31-4.27 0.64-3.60 0.08-0.25 1.57-2.63

Eocene Coals of Meghalaya (Jaintia Hills)

Jarain-Tkentalang

5.9 2.21 0.07 3.66

Bapung 4.8-6.9 2.11-5.05 0.10-0.25 1.79-3.11

Sutnga 4.8-4.9 2.63-3.76 0.05-0.11 1.01-2.12

Mawla-Musiang Lumare

4.6 1.01 0.15 3.39

Lumshnong 3.9 1.63 0.14 2.14

Olegocene Coals of Assam

Makum Coalfield 1.9-5.90 0.16-1.42 0.05-0.43 1.25-4.73

Dilli-Jeypore 1.3-9.8 0.05-4.30 0.02-1.47 0.51-3.78

Oligocene Coals of Arunachal Pradesh

Namchik-Namphuk

1.8-4.9 0.17-3.24 0.07-1.35 1.0-2.7

(Source: Mishra and Gosh, 1996)

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Table 5: Characteristics (Proximate Analysis) of Coal Available in major coalfields in India

Coal Mines Singareni

Kushmanda Singrauli Jharia Neyvelli Total average

value

Moisture (%) 9.6 10.0 12.0 13.0 42.52 17.42 Volatile Matters (%) 23.3 23.0 20.1 17.51 24.5 21.68 Fixed Carbon (%) 32.9 25.0 27.9 28.22 19.5 26.70

Ash (%) 34.0 40.5 40.0 36.08 07.5 31.61 Sulphur (%) 0.363 0.28 0.31 0.41 0.63 0.39 Cal. Value (K.cal/kg)

4133.3 5590.0 3641.6 3300.0 2850.0 3902.98

Characteristics

Table 6: Quality of pre-washed (Raw Coal) and washed Coal

Method of analysis Coal Elements (in %)

Raw Coal Washed Coal

Ultimate Analysis (Air Dried Basis)

Carbon (C) 58.99 71.78 Hydrogen (H) 4.52 5.12 Nitrogen (N) 0.64 0.71 Sulphur (S) 5.60 4.70

Proximate Analysis ( Air Dried basis)

Moisture 1.7 1.7

Ash 17.4 8.1 Volatile Matter (VM) 36.0 41.0

(Source: Report of Central Fuel Research Institute for M/s K.D. Cokes, Assam as analysed for coal from

Bapung coalfield, Meghalaya)

4.0 Waste characteristics from bee-hive coke oven plants The coking process emits various air pollutants like particulate matters (PM); volatile

organic compounds (VOCs); poly-nuclear aromatic hydrocarbons (PAHs); methane,

carbon monoxide, hydrogen sulfide, ammonia, etc., besides oxides of sulphur (SOx)

and nitrogen (NOx). In non-recovery types of coke oven plants like the bee-hive coke oven plants in Assam and Meghalaya, all the above mentioned pollutants are released

into the environment directly. These coke oven plants are considered to be major air

polluting industries. Both stack and fugitive emissions from coke oven plants contribute

significantly towards air pollution.

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A World Bank study revealed that the non recovery type coke oven plants emit various

pollutants like methane, ammonia, carbon monoxide, hydrogen sulphide, SOX, NOX,

particulate matters, VOC at very high levels as shown in the Table 6 below. Table 6: Pollutants released from non-recovery type coke oven plants

Name of the Pollutants Release of pollutants per MT of Coke produced

Methane 0.1 kg

Ammonia 0.050–0.080 kg

Carbon Monoxide 0.050–0.080 kg

Hydrogen Sulphide 0.050–0.080 kg

SOX 2.9 kg *

NOX 1.4 kg

Particulate Matters 0.7-7.4 kg

VOC 3.0 kg ** * Release about 30% of sulfur in the feed ** Includes about 2 kg of benzene

(Source: Pollution Prevention and Abatement Handbook, World Bank Group, 1998)

4.1 Emissions from bee-hive coke oven pants in Assam and Meghalaya

4.1.1 Stack Emission

There are about forty (40) beehive coke oven plants in Assam while two (2) similar coke

oven plants are being operated in Meghalaya. During the present study, detail emission

monitoring was carried out in 16 coke oven plants, including 2 such units in Meghalaya.

Plants operating in full capacities were selected for the study. The salient features of all

the coke oven plants selected for this Study are shown in Table 7.

The findings of the study in terms of emission characteristics of major pollutants

released from the coke oven plants in Assam and Meghalaya are shown in the Table

8.0.

Pollution Loads in terms of particulate matters (PM), carbon monoxide (CO), oxides of

sulphur (SOX) and oxides of nitrogen (NOX) released per day by the Coke Oven Plants

have been assessed and shown in Table 9.0. The ranges of emission of PM, CO, SOX

and NOX have been found to be 9.351-246.80 kg/day, 0.03-100.95 kg/day, 0.15-13.19

kg/day and 8.13-455.90 kg/day respectively.

Table 7: Salient features of the coke oven plants monitored for the study

Sl No Name of the Industry State Year of

Commissioning

No of Ovens Stack Height

(m)

Coal

Consumption

(MT/Day)

Coke (LAMC)

Production

MT/day

APC Devices

Installed to

control Stack

Emission 1 Balaji Coke Assam 2005 38 33.5 328.00 176.66 None 2 G L Coke Assam 2003 24 36.0 165.00 90.00 Wet Scrubber 3 Global Coke Assam 2005 18 44.0 216.67 120.00 None4 GM Coke Assam 2005 32 32.0 220.00 120.00 None5 J.D.B. Coke Assam 2004 40 36.5 340 187.00 None6 K.D. Coke Assam 2005 68 38.0 345.00 190.00 None7 Kamrup Coke Industries Assam 2003 40 33.0 250.00 125.44 None8 Mortex Coke Industry Assam 2005 36 35.0 185.00 100.00 None9 Pride Coke Assam 2004 44 39.0 350.00 175.00 None

10 R.P. Associates Assam 2005 36 38.0 290.5 154.00 None11 RPG Coke Assam 2004 32 30.0 135.00 70.00 None12 S.K. J. Coke Industries Assam 2003 60 33.0 290.00 160.00 None13 Shyam Carbon Company Assam 2005 16 35.42 150 86.66 None14 SM Coke Assam 2001 20 41.1 233.33 128.00 None15 Abhi Coke Industry Meghalaya 2007 18 30.0 98.50 54.17 Wet Scrubber 16 Jaintia Coke Industry Meghalaya 2007 32 30.0 93.66 42.85 Wet Scrubber

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Table 8: Flue Gas Characteristics in the Coke Oven Plants in Assam and Meghalaya

Name of the Industry

Flue Gas

Quantity

(Nm3/sec)

Flue Gas

Temperature

( 0 C)

PM

Concentration

(mg/Nm3)

Corrected to 6

% CO2

O2 (%) CO2 (%) CO

(mg/ Nm3)

NOx

(mg/Nm3)

SO2

(mg/ Nm3)

Balaji Coke 2.463 747.3 NA 12.8 5.8 31.84 14.90 790.34

G L Coke, Changsari 5.886 407.3 96.03 16.7 2.9 1.75 20.58 541.98

Global Coke 2.977 528 93.29 13.4 4.9 267.49 20.09 804.34

GM Coke 3.512 730 NA 13.4 4.9 21.69 16.64 942.43

J.D.B. Coke 11.068 711 NA 17.7 2.7 4.85 8.78 609.02

K.D. Coke 9.114 688 NA 17 4.3 6.20 16.75 510.72

Kamrup Coke

Industries

2.217 552 523.84 18.9 1.5 0.36 8.31 424.42

Mortex Coke Industry 0.269 835.3 NA 19.5 1.3 1.08 4.57 180.69

Pride Coke 19.794 666 NA 14.8 4.1 59.03 NA 87.27

R.P. Associates 11.403 447 250.537 18.9 1.6 7.86 7.86 462.73

RPG Coke 1.797 544 NA 15.8 3.2 296.91 14.23 254.59

S.K. J. Coke Industries 1.919 791.4 NA NA 4.6 6.72 11.76 513.18

Shyam Carbon

Company

0.402 468.9 NA 20 1.2 31.33 4.42 234.17

SM Coke 4.570 387 237.69 16.3 3.4 117.85 19.42 810.92

Abhi Coke Industry 1.938 280.6 89 18.2 NA 397.80 13.46 494.15

Jaintia Coke Industry 0.790 433.7 136.91 17.3 2.2 370.66 3.80 315.84

NA: Could not be analyzed due to very high temperature of Flue Gas

Table 9: Pollution Load from the coke oven plants in Assam and Meghalaya

Name of the Industry PM

(kg/day) CO

(kg/day) NOX

(kg/day) SOX

(kg/day) Balaji Coke NA 6.77 3.17 168.19 G L Coke 56.641 55.27 10.84 80.88 Global Coke 23.997 23.11 5.17 206.90 GM Coke NA 6.58 5.05 285.98 J.D.B. Coke NA 4.63 8.40 582.39 K.D. Coke NA 0.54 13.19 402.18 Kamrup Coke Industries

100.334 0.03 1.59 81.29

Pride Coke NA 100.95 NA 149.25 R.P. Associates 246.840 0.68 7.75 455.90 RPG Coke NA 46.10 2.21 39.53 S.K. J. Coke Industries

NA 0.58 1.67 85.07

Shyam Carbon Company

NA 1.09 0.15 8.13

SM Coke 93.861 10.18 7.67 320.22 Abhi Coke Industry 14.906 34.37 1.16 82.76 Jaintia Coke Industry 9.351 32.02 0.26 21.57

NA: Data Could not be generated due to very high temperature of flue gas

Emission of particulate matters (PM), carbon monoxide (CO), oxides of sulphur (SOX)

and oxides of nitrogen (NOX) per MT of coke production in the coke oven plants under

the study have been calculated and shown in the Table 10. The ranges of emission of

PM, CO, SOX and NOX have been found to be 0.20-1.60 kg/MT, 0.001-1.230 kg/MT,

0.002-0.120 kg/MT and 0.094-3.173 kg/MT respectively.

It has been observed that most of the coke oven plants are being operated without any

air pollution control (APC) devices. Only four (4) Units, viz., M/s Maa Kamakhya Coke

Industry (Assam), M/s G.L. Coke (Assam), M/s Jaintia Coke (Meghalaya) and M/s Abhi

Coke Pvt Ltd (Meghalaya) have installed wet scrubber to treat the flue gases before

releasing into the environment through stacks of adequate heights. Wet scrubber

installed by M/s Jaintia Coke in Meghalaya is shown in the Photograph No 4.

Table 10: Emission of Pollutants in the Coke Oven Plants per MT of coke production

Name of the Industry PM (kg/MT)

CO (kg/MT)

NOx (kg/MT)

SOX (kg/MT)

Balaji Coke NA 0.038 0.018 0.952 G L Coke 0.629 0.014 0.120 0.899 Global Coke 0.20 0.573 0.043 1.724 GM Coke NA 0.055 0.042 2.383 J.D.B. Coke NA 0.025 0.045 3.114 K.D. Coke NA 0.026 0.069 2.117 Kamrup Coke Industries

0.799 0.001 0.013 0.648

Pride Coke NA 0.577 * 0.853 R.P. Associates 1.602 0.050 0.050 2.960

RPG Coke NA 0.659 0.032 0.565 S.K. J. Coke Industries

NA 0.007 0.012 0.532

Shyam Carbon Company

NA 0.013 0.002 0.094

SM Coke 0.733 0.364 0.060 2.502 Abhi Coke Industry 0.275 1.230 0.042 1.528 Jaintia Coke Industry 0.218 0.591 0.006 0.503

NA: Data Could not be analyzed due to very high temperature of Flue Gas * Data Could not be analyzed due to Sensor error during monitoring

The wet scrubbing of flue gases is showing satisfactory result, in terms of reduction in

the gaseous pollutants, as shown in Table 11 (a) and Table 11 (b).

Photograph 4: Wet Scrubbing system of M/s Jaintia Coke, Meghalaya

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Table 11 (a): Flue Gas characteristics of a coke oven plant with scrubber as well as scrubber bypassed condition (M/s Jaintia Coke Industry)

Operating Condition

Parameters Monitored (M/s Jaintia Coke Industry, Meghalaya) Flue Gas

Temp (0C)

SOX (mg/Nm3)

NOX (mg/Nm3)

CO (mg/Nm3)

CO2 (%) O2 (%) PM (mg/ Nm3)

With Scrubber

431.9 317.45 3.81 372.55 2.2 17.2 136.91

With scrubber bypassed

479.4 679.84 7.51 510.57 2.1 16.8 NA

Table 11 (b): Flue Gas characteristics of a coke oven plant with scrubber as well as scrubber

bypassed condition (M/s G.L. Coke, Assam)

Operating Condition

Parameters Monitored Flue Gas

Temp (0C)

SOX (mg/Nm3)

NOX (mg/Nm3)

CO2 (%) O2 (%) PM (mg/ Nm3)

With Scrubber

294.4 126.05 * 1.7 17.60 88.27

With scrubber bypassed

407.7 541.98 * 2.8 16.70 96.03

* Could not be analyzed due to Sensor Error in Flue Gas Analyzer, NA: Not Analyzed

4.1.2 Fugitive emissions from coke oven plants

Though stack emissions (Photograph 5) are considered to be the major sources of air

pollution from the coke oven plants, fugitive emissions from various processes involved

in coke manufacturing contribute significantly towards environmental pollution. Coal

handling operations like coal crushing, coal charging and coke handling operations like

coke pushing, quenching and crushing are the major sources of fugitive emissions in

coke oven plants. Fugitive emissions, in large scale, were seen in most of the coke

oven plant during the study. Large scale fugitive emissions occur during charging of

coal into the oven and also during coal pushing and quenching operations (Photograph

6 and 7). Moreover, high level of fugitive emission are released from the ‘secondary

holes’ provided in both sides at the bottom of the main flue tunnel in the coke oven

plants (Photograph 7) during the initial hours of charging of coal.

16

Photograph 5: Stack Emissions from Coke Oven Pants

Photograph 6: Fugitive Emissions in coke oven pants during charging of coal

Photograph 7: Fugitive emissions occur during pushing and quenching of coke

Photograph 8: Fugitive emissions from ‘Secondary Holes’ provided in ‘flue tunnel’ during initial hours of charging of coal

17

In M/s S.M. Coke, Byrnihat, provisions have been made to collect fugitive emission,

generated during charging of coal into the ovens, from the top of the ovens through a

common duct (Photograph 9). Long duct and ID fan have been installed for the purpose

to collect the fugitive emission and pass the same into a water chamber for retaining

and recovering the dust.

Photograph 9: Ducts with openings provided over the ovens to control fugitive emissions (SM Coke, Byrnihat)

4.1.2.1 Assessment of fugitive emissions from coke oven plants

To assess the level of fugitive emission inside coke oven plants, concentration of

various pollutants, viz., PM, SOx and NOx was measured near the source of fugitive

emission using low volume sampler (Make: Envirotech, Model: Handy sampler APM

881). Fugitive mission monitoring was carried out at two industries (M/s Pride Coke and

M/s K.D. Coke industry) after selecting suitable locations considering the source of

emission during coal feeding, quenching and coke crushing operations. The result of

monitoring is shown in the Table 12.

From fugitive emission monitoring, level of suspended particulate matter (SPM) is

observed in the range of 666 – 14666 (µg/m3) near the coke ovens and coke crushing

areas. The levels of SOx and NOx are observed in the range of 0.25-216.88 µg/m3 and

22.65-36.88 µg/m3 respectively and these concentrations are alarmingly high looking

into the ambient air quality standards in India

18

Table 12: Level of fugitive emission in Coke Oven Plants Name of the Unit Source of Sampling Concentration of pollutants

SPM (µg/m3)

SO2 (µg/m3)

NOX (µg/m3)

Pride Coke (Date of monitoring : 20.07.2010)

Oven floor level (during quenching operations in an oven) 14666 0.55 22.65

Oven mouth level ( during Coal charging) 666 216.88 23.85

K D Coke (Date of monitoring : 06.08.2010)

Coke crushing yard (during crushing ) 5556 4.58 36.88

Near ovens floor level (during quenching operations in an oven) 13333 0.25 36

4.1.3 Ambient Air Quality in Coke Oven Plants

The ambient air quality inside the premises of a few coke oven plants, as monitored by

recognized laboratories, is shown in Table 12.

Table 12: Ambient air quality in the premises of coke oven plants

Name of the Unit Source of Sampling Concentration of pollutants

Jal Coke Company RSPM (µg/m3)

SPM (µg/m3)

SO2 (µg/m3)

NOX (µg/m3)

Between office and Coke Crusher unit

85.80 293.72 27.00 32.32

Between office and Coke Crusher unit

265.49 699.96 30.50 17.94

Main Gate 71.88 341.83 34.50 24.90

Global Coke Products Coal Yard near ovens (Sample 1)

96.28 364.87 35.67 23.48

Coal Yard near ovens (Sample 2)

285.29 775.39 35.00 20.58

Main Gate 88.71 256.22 28.17 21.54

S.M Cokes Ltd Between Coke Crusher and Coke Ovens-I

106.21 322.18 40.17 20.58

Between Coke Crusher and Coke Ovens-II

315.76 575.72 49.33 21.80

Source: Jal Coke Company, Global Coke Products, S.M Cokes Ltd as analyzed by Eco Care, Asansol, Dist. Burdwan, West Bengal

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4.2 Existing emission standards available for beehive hard coke oven,

effluent standards recovery type coke oven plants and coal washeries in India

4.2.1 Environmental standard for beehive hard coke oven

Pollutant Emission Limit New Unit Particulate Matter

(corrected to 6 % CO2) 150 mg/Nm3

Existing Unit Particulate Matter (corrected to 6 % CO2)

350 mg/Nm3

Note: For control of emissions and proper dispersion of pollutants, the following

guidelines shall be followed

• Units set up after April 2, 1996 shall be treated as new units

• A minimum stack height of 20 m shall be provided by each unit.

• Emission from coke ovens shall be channelised through a tunnel and finally

emitted through a stack. Dumper adjustment techniques shall be used to have

optimum heat utilization and also to control the emission of un-burnt carbon

particles and combustible flue gases.

• Wet scrubbing system or waste heat utilization for power generation or byproduct

recovery system should be installed properly to achieve the prescribed standards.

• After April 01, 2000, all the existing coke units shall comply with the standards

prescribed for the new units.

Source: EPA Notification [ GSR 176 (E) April 2, 1996]

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4.2.2 Coke ovens : Wastewater discharge standards

Parameters Concentration in the effluent when discharged into inland surface water not to exceed, mg/l (except for pH)

pH 5.5 to 9.0 Biochemical oxygen demand (270C, 3 days) 30

Suspended solids 100 Phenolic compounds (As C6H5OH) 5 Cyanides (As CN) 0.2 Oil & grease 10 Ammonical nitrogen (As N) 50

Source : EPA Notification [S.O. 64(E), dt. 18th Jan., 1988]

4.2.3 Environmental standards for coal washeries A. Fugitive emission standards The difference in the value of suspended particulate matter, delta (Δ), measured

between 25 to 30 metre from the enclosure of coal crushing plant in the downward and

leeward wind direction shall not exceed 150 microgram per cubic meter. Method of

measurement shall be High Volume Sampling and Average flow rate, not less than 1.1

m3 per minute, using upwind downwind method of measurement.

B. Effluent discharge standards

The coal washeries shall maintain the close circuit operation with zero effluent

discharge.

If in case due to some genuine problems like periodic cleaning of the system, heavy

rainfall etc. it become necessary to discharge the effluent to sewer/land/stream then the

effluent shall conform to the following standards at the final outlet of the coal washery.

21

Sr. No. Parameter Limits 1 pH 5.5-9.0 2 Total suspended solids 100 mg/l 3 Oil & Grease 10 mg/l 4 B.O.D. (3 days 27 deg C) 30 mg/l 5 COD 250 mg/l 6 Phenolics 1.0 mg/l

C. Noise level standards Operational/Working zone — not to exceed 85 dB (A) Leq for 8 hours exposure.

The ambient air quality standards in respect of noise as notified under Environmental

(Protection) Rules, 1986 shall be followed at the boundary line of the coal washery.

D. Code of practice for Coal Washery.

Water or Water mixed chemical shall be sprayed at all strategic coal transfer points

such as conveyors, loading/unloading points etc. As far as practically possible

conveyors, transfer points etc. shall be provided with enclosures.

• The crushers/pulverizers for the coal washeries shall be provided with enclosures,

fitted with suitable air pollution control measures and finally emitted through a stack

of minimum height of 30 m, conforming particulate matter emission standard of 150

mg/Nm3 or provided with adequate water sprinkling arrangement.

• Water sprinkling by using fine atomizer nozzles arrangement shall be provided on

the coal heaps and on land around the crushers/pulveriser.

• Area, in and around the coal washery shall be pucca either asphalted or concreted.

• Water consumption in the coal washery shall not exceed 1.5 cubic meter per MT of

coal.

• The efficiency of the setting ponds of the wastewater treatment system of the coal

washery shall not be less than 90%.

22

• Green belt shall be developed along the road side, coal handling plants, residential

complex, office building an all around the boundary line of the coal washery.

• Storage bunkers, hoppers, rubber decks in chutes and centrifugal chutes shall be

provided with proper rubber linings.

• Vehicles movement in the coal washery area shall be regulated effectively to avoid

traffic congestion. High pressure horn shall be prohibited. Smoke emission from

heavy duty vehicle operating in the coal washeries should conform the standards

prescribed under Motor Vehicle Rules 1989.

(Source: G.S.R. 7 dated 22nd December, 1998)

4.3 Emission factor for hazardous air pollutants (HAPs)

In non recovery type bee-hive coke oven plants, by-products are not recovered and as

such the hazardous air pollutants like benzene, toluene, isomers of xylene, cyanide

compounds, naphthalene, phenol, and polycyclic organic matter are contained in the

coke oven gas and are emitted to the atmosphere through stack emission as well as

fugitive emission.

There are no emission standards for these HAPs. Moreover, no quantitative emission

data suitable for use in development of air pollutant parameters in respect of benzene,

toluene, isomers of xylene, cyanide compounds, naphthalene, phenol, and polycyclic

organic matter are available for any of these HAPs. However, an emission factor for the

HAPs may be calculated as described in the following section.

4.3.1. A sample calculation for emission factor

HAPs like benzene and other class of compounds termed as Polycyclic Organic Matter

(POM) are the known carcinogens and therefore, are of serious health concern. POM

condense as fine particulate at ambient temperature. There are thousands of POM

reported as Benzene Soluble Organics (BSO) or Benzene (a) Pyrene. The emission

factor for the BSOs can be calculated as shown in the following example.

23

Let, a particular bee-hive coke oven has 40 ovens with 20 percent of doors leaking at an

average rate of 200 gm of BSO per hour per leaking door (1 door in each oven). Let,

each oven is charged with 5 Ton of coal in 24 hours cycle in a day and the coke oven is

operated 300 days per year. i) Number of leaking doors = 40 ovens x 1 door/oven x 0 .2 (fraction leaking)

= 8 doors

ii) Benzene soluble organics

(BSO) emitted per year

= 8 doors x 0.2 kg hour/door x 7200 hr/yr

= 8 x 1440 kg/year

= 11520 kg/year

iii) Total coal uses in the Coke

oven plant per year (for 5

MT of coal per oven and

24 hr cyclic time, 300 days

in a year),

=

=

5 tons of coal/oven x 40 ovens/24 hr x 7200 hr/yr

60000 Tons/year

iv) Emission factor for BSO = ( 11520 kg/ year)/ 60000 MT/year

= 0.192 kg of BSO /Ton of coal usage

= 192 gm of BSO /Ton of coal usage

5.0 Power generation from waste heat of Flue Gases in bee-hive coke oven plants.

M/s Patkai Coal Products, Samukjan Village, Margherita, Assam has put a

commendable effort to generate electrical energy from the flue gases emitted from the

coke ovens. The unit has installed a plant to generate 500 KW of electric power from

the flue gases.

In M/s Patkai Coal Products Limited, there are 36 beehive coke ovens with an installed

hard coke production capacity of 15000 MT/year. However the workable capacity has

been reported as about 12,000 MT/year. The unit has estimated that about 1.2 lakh m3/hr of flue gases shall be available from the plant. The unit is also of the opinion that

about 1.5 MW of electrical energy may be generated from the quantum of the flue gases

24

available. However, as a first attempt, the unit is targeting to generate about 500 KW of

electricity.

5.1 Various units installed for the power plant The unit has already installed a Gas Collection Chamber (Capacity: 12.68 cu m) to

collect the flue gases from the flue duct (Photograph 10). Earlier the flue duct was

directly connected with a chimney of about 30 m. Now that tunnel is blocked by a

damper and the flue gas is routed through the gas collection chamber. The gas

collection chamber is then connected with a steam boiler (Photograph 11), which has

steam generation capacity of 18 MT/hr, followed by a steam super-heater and turbine

generator (500 KW capacity).

Flue gas To Boiler

Gas Collection Chamber

Photograph 10 : Gas Collection Chamber

25

Boiler

Photograph 11 : Steam boiler (capacity 18 MT/hr)

The installation of the power plant is almost complete. Trial run has already been made

by the unit. Though sincere efforts have been put by the unit, the power plant is not

fully successful so far.

5.2 Difficulties faced by the unit in running the power plant.

M/s Patkai Coal Products has invested about ` 1 crore in installation of the power plant,

as has been reported. However, following difficulties have been faced by the power

plant for continuous running the power plant for generation of electricity.

i) Due to high water table in the plant site, there occur water seepage in the flue

tunnel and subsequently the flue gases get cooled and as such there is not

sufficient d temperature in the flue gas to run the boiler.

ii) There is drop in steam pressure frequently and as such there is difficulty in

running the boiler smoothly.

To overcome the problem of low heat of the flue gas, the unit has planned to use natural

gas as auxiliary fuel and also plans to generate about 1.0 MW electricity in near future.

26

6.0 General observations

• Exit flue gas temperature was found to be more than 5000c in most of the coke

oven plants and as such particulate matters in flue gas could not be measured in

many coke oven plants because the glass fibre thimbles used for emission

monitoring can withstand a temperature of about 5000 C only.

• Almost all the units have installed bag houses to reduce fugitive emissions from

the coke crushing operations. However, uncontrolled fugitive emissions were

observed in many coke crushing units due to poor maintenance of the bag

houses.

• Crushing of coke in moist condition was seen practiced by a few units, where

lesser fugitive emission was observed.

• All the units have a settling tank to store and recycle water required for coke

quenching. When water is sprayed over the hot coke for quenching, significant

amount of water is spilled over into the drains surrounding the coke –ovens. In

most of the coke oven plants, the drain surrounding the coke ovens, is seen

connected to a settling tank, where the coke fines are settled and water is further

recycled for coke quenching. The arrangement of settling tank thus allows

settling of coke fines in one hand, while serves as a measure of water

conservation on the other hand.

• CO2 percentages (0.6 – 5.8 %) in the Flue Gases are found to be very low and

when corrected to 6 % CO2 conditions, very few units could achieve the

Standards.

• Coal washery is useful in reducing ash content by 9.0-10.0 %.

• Anthracite is the highest rank of coal and is characterized by low volatile matter

(always less than 10 %) and high carbon content. It is capable of burning without

smoke.

• Though coking is done in oxygen starved condition, a portion of oven above the

coal charge in non recovery ovens (since by products are not recovered) is

27

subjected to an oxidizing atmosphere. This is because secondary air is

introduced into the oven chamber for combustion through several ports located

above the charge level in both pusher and coke side doors of the oven. This

oxidizing atmosphere in the oven assumes special significance as guiding factor

for the selection of refractors. Refractory bricks work in the non recovery type

ovens are likely to be subjected to thermal shocks and hence alumina refractory

bricks are ideally suitable as alumina bricks provide better resistance to thermal

shocks. Higher alumina bricks (with alumina 61 %) are superior to silica bricks

with respect to compressive strength, bending strength, coefficient of thermal

expansion and modulus of elasticity

• The coke ovens plants, which have installed either the scrubber system or the

fugitive emission control system or both, do not run the air pollution control

devices regularly as those are power consuming equipments and also, it is

possible to run the plant bypassing the APC devices.

7.0 Suggestive measures for controlling stack emission and fugitive emission

• The industry should prevent fugitive emission from all active operations by installing

suitable pollution control devices. Fugitive emission generated during the Coal

charging processes should be collected through common ducts connected with ID

Fan as has been done by M/s S/M. Coke, Assam. Fugitive Emissions, thus

collected, should be passed through Air Pollution Control (APC) Devices like

scrubber before releasing through the Stack of Suitable Height.

• Airborne dust should be extracted to the maximum extent from various locations like

unloading of raw materials, coal and coke crusher discharge, and other material

transfer points by providing suction & duct arrangement equipped with cyclone &

bag filters.

• Dry extraction cum bag filter with adequate extraction volume should be installed in

the coke crushing house to control airborne dust generated during coke-crushing

operations.

28

• Emission from coke ovens shall be channelized through a tunnel and finally emitted

through a stack. Dumper adjustments shall be used to have optimum heat utilization

and also to control the emission of un-burnt carbon particles and combustible flue

gases.

• The vibratory screen for sizing the coke should be provided with a dust extraction

arrangement equipped with bag filter to prevent fugitive emission from that section.

• Controlled automated system for introduction of tertiary air in the common flue duct

shall be installed to ensure proper combustion of combustible particulate matters

(PM) in the flue gas.

• The natural draft shall be produced by the chimneys alone. It is caused by the

difference in weights between the column of hot gases inside the chimney and the

column of outside air of the same height and cross section. Being much lighter than

outside air, chimney flue gas tends to rise and the heavier air outside air flows in

through the ash pit to take its place. It is usually controlled by hand operated dumper

in the chimney. Here no fans or blowers are required to be used.

• The hot flue gases containing a number of pollutants, including HAPs, shall be

discharged through chimney at such a height that it will not be a nuisance to the

surrounding community in case of a non recovery coke oven plant. All hydrocarbons

shall be incinerated due to high operating temperature in the oven and also the flue

gas passage.

• A very high coking temperature of 1200oC-1500oC shall be achieved to burn and

break combustible compounds of hydrocarbons in the coke oven gas.

• Wet scrubbing shall be installed with the installation of high pressure nozzles

(minimum 7.5 kg/cm2) for control of SO2 emission.

• NOx levels should be minimized by control in oven temperature.

• Charging and pushing emissions shall be minimized by coal cake compaction and

precision on oven door openings.

• Higher alumina bricks (with alumina 61 %) are superior to silica bricks with respect

to compressive strength, bending strength, coefficient of thermal expansion and

29

modulus of elasticity and such alumina bricks shall be used for construction of coke

oven walls.

• Coal washery should be made mandatory more new bee hive coke oven plants.

Coal washery is useful in reducing ash content by 9.0-10.0 %.

• Anthracite is the highest rank of coal and is characterized by low volatile matter

(always less than 10 %) and high carbon content. It is further capable of burning

without smoke. Such coals shall be used by the coke oven plants, if available.

• Water used for quenching and spillage thereof should be properly channeled into a

sedimentation tank, from where water should be recycled for the quenching

operations and other purposes, as a measure of water conservation..

• Water should be periodically sprayed on the stockpiles/coal yard so as to retain

some moisture in the top layer and thus to avoid wind blowing of fines. The

frequency and quantity of watering may vary from season to season and the area to

be covered, which should be decided and recorded, based on average evaporation

rate in the region. Coal should be sufficiently moistened to suppress fines by

spraying minimum quantity of water.

• Adequate ventilation for the coke crushing and packing hall should be provided for

venting out suspended particulates thereby ensuring dust free work environment.

• Storm water around the coal yard should be isolated. sedimentation tank and

neutralization tank in series to be provided in the storm drain to avoid discharge of

coal dust laden water (wastewater with high suspended solids) into the environment

• Water should be periodically sprayed on the stockpiles/coal yard so as to retain

some moisture in the top layer and thus to avoid wind blowing of fines. The

frequency and quantity of watering may vary from season to season and the area to

be covered, which should be decided and recorded, based on average evaporation

rate in the region. Coal should be sufficiently moistened to suppress fines by

spraying minimum quantity of water.

30

8.0 Recommended guidelines for better environmental management in coke oven plants

• Some of the coke oven plants are having the flue tunnel at the top of the coke

oven battery ( Upward draft ) and the chimney is placed in the middle of the coke

ovens. In some other coke oven plants, flue gases are routed through an

underground tunnel ( Downward draft) before releasing the gases through a

chimney. In this former case, the travel path of flue gases is very less as

compared to the later. Moreover, the flue gas temperature at the chimney is very

high (upto 750-8000C) in the former while in the later case, it is under 5000C.

As the flue gases have to travel more in the underground channel, the

particulates get time for burning and settling and it is therefore observed that the

particulate matter concentration in the flue gas in less in bee hive coke oven

plant, in which the flue gases are passed through an underground tunnel before

releasing through a chimney. Therefore upward draft coke oven units should be

converted to downdraft provided with well designed underground Tunnel of

adequate length for reducing the emission levels of particulate matter.

• Airborne dust should be extracted to the maximum extent from various locations

like unloading of raw materials, coal and coke crusher discharge, and other

material transfer points by providing suction & duct arrangement equipped with

cyclone & bag filters.

• Controlled automated system for introduction of tertiary air in the common flue

duct shall be installed to ensure proper combustion of combustible particulate

matters (PM) in the flue gas and thereby reducing the level of particulate matter

in the flue gas.

• Wet scrubbing system should be made installed in coke oven plants as

significant reduction of gaseous pollutants were observed with wet scrubbing of

flue gases. Wet Scrubbing of gases have been found to be adequate to reduce

the Flue gas temperature less than 500 0C and also to reduce the concentration

31

of gaseous pollutants, especially SOx and CO, to about 50 %. Scrubbing of flue

gases are thus essential for two basic purposes:

a) To lower the concentration of particulate matters and also to reduce the

volume of toxic gases

b) To lower the temperature of emission.

• Wastewater generated from the scrubber should be treated with lime to

neutralize pH. The sludge should be properly dumped after it is removed from the

water recirculation tank.

• Fugitive emissions are of major environmental concern in coke oven plants.

Fugitive emissions from the oven mouths during coal charging is found to be the

maximum and, therefore, should be collected through common ducts placed over

the ovens and should be passed through water chambers before letting out with

the help of ID Fans to the chimneys.

• Utilization of waste heat for electric power generation shall be the best possible

option for reducing the gaseous pollution and also in recovering the heat from the

flue gases. This may be made mandatory for the new bee hive coke oven units.

• All the Coke oven plants should have similar air pollution control (APC) devices.

As of now, there are only a few plants which have APC devices and are not

operated regularly. State Pollution Control Board should ensure that all the

Beehive Coke Oven plants install APC devices should ensure action against the

defaulting units.

9.0 Scope for future studies

Status of ambient air quality in the Byrnihat area, where cluster of coke oven plants

are being operated, should be studied in detail. Such study should incorporate

determination of heavy metals (HM), Poly-nuclear Aromatic Hydrocarbons (PAH) in

ambient air of Jorabat and Byrnihat, located in the Assam –Meghalaya Border.

--------------------------

32

33

References:

CMPDIL, 1991, Compendium on coal occurrences of the North Eastern region, Vol. II A-

Makum Coalfield, Assam. Central Mine Planning and Design Institute Limited, 188 pp.

Coal Chemicals, CFRI Golden Jubilee Monograph, edited by R.N. Bhattacharya,

Central Fuel Research Institute, Dhanbad, 1996

Dasgupta, A. B. and Biswas, A. K., 2000, Geology of Assam. Geological Society of

India, 169 pp.

Mishra, H. K. and Ghosh, R. K, 1996, Geology, Petrology and Utilization Potential of

some Tertiary coals of the Northeastern Region of India. International Journal of Coal

Geology, 30: 65 -100.

Pollution Prevention and Abatement Handbook, World Bank Group July 1998

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