COAL TRADING Compiled by Divyanshu Dayal. dayal1005@gmail.com Created on: 15th Sept’13. B.E. Mechanical, MBA, Procurement

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PART-1 COAL CLASSIFICATION Coal is a hydrocarbon. Coal is classified according to the

amount of heat it produces. Heat content of coal depends on

amount of fixed carbon (carbon in its free state and not combined with other elements) it contains.

Rank of coal is degree of progressive alteration in the transformation from lignite to anthracite.

There are four primary ranks of coal 1. Anthracite (Semi-anthracite, anthracite

and meta-anthracite) 2. Bituminous (high-volatile, medium

volatile and low-volatile) 3. Lignite (brown coal and lignite) 1.1 Anthracite Hard and very brittle. Dense, shiny black. Homogeneous with no marks or layers.

High percentage of fixed carbon. Low percentage of volatile matter

chiefly methane (CH4).

Used in heating home and production of natural gas.

Fig.1 Anthracite 1.2 Semi-anthracites Dense but softer than anthracite, shiny

gray. Somewhat granular in structure. Grains

have tendency to break off during handling and produce a coarse, sand-like slack.

1.3 Bituminous Soft coals and are in abundance. Grayish black and either distinctly

homogeneous with very faint indication of grains but show distinct layers or granular in structure depending on content of volatile matters from high, middle and low.

When granular the coal tends to crumble during handling and reduces to slack.

When heated they reduce to cohesive binding sticky mass.

Their carbon content is less than anthracite.

They have higher volatile matters as compared to anthracite.

Volatile matters are higher in calorific value.

They burn easily especially in pulverized form.

High volatile content makes them good for producing gas.

Their binding nature enables them to be used in coke.

Nitrogen in them is utilized in producing ammonia.

Bituminous coals are chiefly used to generate electricity.

They are also used to produce aluminum, cement, food, paper and textiles.

Bituminous 1.4 Sub-Bituminous Soft coal. Brownish black or black. Most are homogeneous and have

smooth surface with no indication of layers.

They appear dry, but have high moisture content.

When exposed to air they lose part of moisture and make an audible noise.

After long exposure to air they disintegrate.

They are non-coking coals.

Burn readily and can be used for household as well as for industrial plants.

Fig.2 Sub-bituminous 1.5 Lignite Brown and laminar structure. Comprise of remnants of woody fibers Lignite coals are tough and require

heavy impact with hammer to break up the large lumps.

When exposed to air they lose moisture rapidly and disintegrate.

Due to high moisture and low heating value, they are not economical to transport to long distances.

They are also known as “brown coals” are generally found close to the surface and readily recovered by stripping.

Fig.3 Lignite 2.0 Analysis of Coal 1. Ultimate Analysis 2. Proximate Analysis

2.1 Ultimate Analysis Determines all component elements solid or gaseous like carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and sulphur (S) 2.2 Proximate Analysis Determines percentage by weight of fixed carbon (FC), volatile matter (VM), moisture (M) and ash (A) content in coal- also sulphur (S) and calorific value (CV) can be expressed on any of the above basis. 3.0 Significance of Various Parameters 3.1 Fixed Carbon Fixed carbon acts as main heat generator during burning. 3.2 Volatile Matters Volatile matters are methane, hydrocarbons, hydrogen and carbon monoxide and incombustible gases like carbon dioxide and nitrogen found in coal. Volatile matters proportionately

increases flame length and helps in easier ignition of coal.

Set minimum limits of furnace height and volume.

Influences secondary air requirements and distribution aspects.

Influences secondary oil support. 3.3 Ash Content Reduces handling and burning capacity. Increases handling costs. Affects combustion efficiency and

boiling efficiency. Cause clinkering and slagging. 3.4 Moisture content Moisture replaces combustible matter

and decreases the heat content per kg of coal.

Increases heat loss due to evaporation and superheating of vapor.

Helps to a limit in binding fines. Aids radiation heat transfer. 3.5 Sulphur content Clinkering and slagging tendency. Corrodes chimney and other

equipments such as heaters and economizers.

Limits exit flue gas temperature

COAL TRADING Compiled by Divyanshu Dayal. dayal1005@gmail.com Created on: 15th Sept’13. B.E. Mechanical, MBA, Procurement

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Fig.4 Ranks of Coal. 4.0 Typical Parameters of Coal (% by weight unless the unit is specified in the cell) 4.1 Class of Coal Based on Volatile Matters Class VM

(% Weight) General Description

101 < 6.1 Anthracites

102 3.1-9.0 201 9.1-13.5 Dry steam coal

Low Volatile Steam Coal

202 13.6-15.0

203 15.1-17.0 Cooking steam coals

204 17.1-19.5

206 19.1-19.5 Heated altered low volatile steam coals

301 19.6-32.0 Prime cooking coals

Medium Volatile Steam Coal

305 19.6-32.0 Mainly heat altered coals 306 19.6-32.0

401 32.1-36.0 Very strong coking coals

High Volatile Steam Coal

402 > 36.0 501 32.1-36.0 Strongly coking

coal 502 > 36.0 601 32.1-36 Medium coking

coal 602 > 36.0 701 32.1-36.0 Weakly coking

coals 702 > 36.0 801 32.1-36.0 Very weakly

coking coal 802 > 36.0 901 32.1-36.0 Non-coking coal

902 > 36.0 Tbl.1 Class of coal based on volatile matter. 4.2 Other Parameters Anthracite Bituminous Lignite S 0.6-0.77 0.7-4.0 0.4 M 2.8-16.3 2.2-15.9 39 FC 80.5-85.7 44.9-78.2 31.4 Bulk Density

800-929 kg/m3

673-913 kg/m3

641-865 kg/m3

A 9.7-20.2 3.3-11.7 4.2 Tbl.2 Typical Parameters of Coal.

5.0 Coal Conversion Statistics 5.1 As Received Basis (ar): (Total Moisture (TM) =Free Moisture + Inherent Moisture (IM) ) + Ash + Volatile Matter + Fixed Carbon.

Fig.5 As Received Basis 5.2 Air Dried Basis (ad): Inherent Moisture (IM) + Ash + Volatile Matter + Fixed Carbon

Fig.6 Air Dried Basis. 5.3 Dried Basis (db): Excludes all Moistures.

Fig.7 Dried Basis 5.4 Dry Ash Free Basis (daf): Excludes all Moistures and Ash.

Fig.8 Dry Ash Free Basis

6.0 Conversions in Proximate Analysis Percentage of parameters like % of Ash, Volatile Matters, Fixed Carbon and Sulphur can be derived on ad, db, daf basis. 6.1 Air Dried Basis (ad) = ar x (100-IM%)/ (100-TM%) =db x (100-IM%)/ 100 6.2 Dried Basis (db) =ar x 100 / (100-TM%) =ad x 100/ (100-IM%) 6.3 As Received Basis (ar) = ad x (100-TM%) / (100-IM%) = db x (100-TM%) / 100 Example: (Pink cell indicates % by weight values derived during proximate analysis and without conversion. Other values are derived by using the formulae mentioned in the conversion section above) ar ad db daf TM 11.0 - - - IM 2.0 2.0 - - A 12.0 13.2 13.5 - VM 30.0 33.0 33.7 39.0 FC 47.0 51.8 52.8 61.0 S 1.0 1.1 1.12 - Tbl.3 Example of Conversions. 7.0 Mass Metric ton (t) = tonne = 1000 Kilograms

= 2204.6 lb Imperial or Long ton (lt) = 1016.05

Kilograms = 2240 lb Short (US) ton (st) = 907.19 Kilograms =

2000 lb 8.0 Calorific Values (CV) kCal/kg: Kilocalories per Kilogram MJ/kg- Megajoules per Kilogram Btu/lb- British Thermal Units per pound 8.1 Gross and Net Calorific Values Gross Calorific Value (GCV), Higher Calorific Value, Higher Heating Value (HHV) The water of the combustion is entirely

condensed and that the heat contained in the water vapor is recovered.

It is Calorific Value (CV) under laboratory conditions.

Net Calorific Values (NCV), Lower Calorific Value, Lower Heating Value (LHV) The products of combustion contain

water vapor and that the heat in the water vapor is not recovered.

Useful calorific value in the boiler plant. 8.2 Conversions- Gross/ Net (per ISO, for As Received (ar) figures) Kcal/kg

Net CV= Gross CV -50.6H-5.85M-0.191O MJ/kg

Net CV=Gross CV-0.212H-0.0245M-0.0008O

Btu/lb

Net CV= Gross CV-91.2H-10.5M-0.34O

COAL TRADING Compiled by Divyanshu Dayal. dayal1005@gmail.com Created on: 15th Sept’13. B.E. Mechanical, MBA, Procurement

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M is % Moisture, H is % Hydrogen, O is % Oxygen ( from ultimate analysis, also As Received) 9.0 Coal for Power Sector 9.1 Stoker Stoker is a type of coal firing in boiler. A stoker is a device consisting of a feed and a grate and is used for feeding coal into a furnace, distributing it over a grate, admitting air to the coal for combustion and providing a means for discharge of ash.

Fig.6 Stoker. Parameters 9.1.1 Total Moisture Limits: 8-15% If too low, fines can blow away from the bed without burning. 9.1.2 Ash Limits: 7-30% (ad) Minimum Ash contents are required to protect grate from reflected heat. 9.1.3 Volatile Matter Limits: 25-40% (daf) 9.1.4 Maximum Size: Limit: 30 mm 9.1.5 Size Consist: Limit: Max. 30% -3mm Min. 25% +6mm 9.1.6 Ash fusion temp: Limit: IDT (Initial Deformation Temperature) min 1200 oC If the temp is lower ash melts and forms clinkers 9.1.7 Crucible Swelling Number: Max.3 High swelling coals gives uneven combustion. 9.2 Pulverised Coal (PF- Pulverised Fuel) Firing is combustion of powdered coal suspended as a cloud of small particles in the combustion air. It eliminates supporting grates and thus equipment size restrictions. They are suitable for large boilers. More heat is released per unit volume than stoker firing. Parameters 9.2.1 Total Moisture Limit: 15% (ar) High moisture reduces CV, creates handling problems 9.2.2 Ash Limit: 20% (ad) High Ash reduces calorific value. 9.2.3 Volatile Matter Limits: Min 20-25% (daf)

9.2.4 Calorific Value Requires high calorific values 9.2.5 Sulphur Limit: Max. 1% (ad) Local emission regulations are critical. 9.2.6 Nitrogen Limit: Max 1.5% to 2% Subjected to regulations on nox emissions. 9.2.7 Maximum Size Limits: 40 -50 mm Depends on capacity of grinding equipment. 9.2.8 Fines Content Limit: Max -3mm High fines contents can increase moisture contents and create handling problems. 9.2.9 Ash fusion temp Limit: Dry bottom boiler IDT > 1200 oC Wet bottom boiler flow temp < 1300 oC 10.0 Coal for Steel Sector 10.1 Coking Coal Steel production requires Coke. Coke is

produced by heating coking coal in oven through a process called as Carbonization.

Crushed, mostly blended coal (approximately 80% less than 3 mm) is charged into the coke oven and heated until the centre of the charge has reached a temp of 1100 oC.

After completion of the carbonization, the incandescent coke is pushed from the oven and quenched with water or inert gas. This process is common due to energy savings resulting from heat recovery.

Parameters 10.1.1 Total Moisture Limit: Max. 10% (ar) High moisture creates difficulty in handling and lowers the amount of carbon. 10.1.2 Ash Limit: Max 10% (ad) High ash reduces efficiency of blast furnace. 10.1.3 Volatile Matter Limits: 16-36% (ad) High VM reduces coke yield. 10.1.4 Sulphur Limit: Max. 0.8% (ad) High sulphur reduces quality of steel. 9.1.5 Phosphorus Limit: Max. 0.1% (ad) High phosphorus makes carbon steel brittle. 10.2 Pulverised Coal Injection (PCI) The reduction process in the blast

furnace is carried out primarily by carbon monoxide and a maximum temperature in the furnace of 1650 oC is achieved.

Additional fuel is injected into the furnace with the blast air and helps to maintain furnace stability. This fuel can

take the form of heavy fuel oil or tar, or pulverized coal.

PCI allows replacement of coking coal by steaming coal.

PCI with injection rate of 100 kg/tonne can replace approximately 119 kg of coking coal or 85 kg of coke.

PCI parameters are similar to that of coking coal and requires low sulphur, phosphorus and alkalis. Ash should be below 8% preferably, however up to 12% is used.

11.0 Coal For Cement Sector Wet and dry processes are two basic process in cement production and are named in the manner in which the raw mix is introduced in the kiln. Wet process has slurry with 20-40% moisture. In dry process the mix is dry. Approximate Coal Consumption in Cement Plants Type of Plant Heat

Required Kcal/ kg of Clinker

Tonnes of Clinker produced per tone of coal with CV 6000 kCal/ kg (ar)

Tonnes Coal with CV 6000 kCal/ kg ( ar) per 106 tonnes of Clinker

Most Modern- Dry process, pre-heating

600 10 100,000

Less Modern- Dry Process- Semi Dry Process

1100 5.5 180,000

Least Modern- Wet Process

1700 3.5 280,000

Tbl.4 Approximate Coal Consumption in Cement Plants Parameters 11.1 Total Moisture Limit: Max 15% (ar) High moisture creates handling problem. 10.2 Ash Max 25% (ad) Limit: Max. 25%

COAL TRADING Compiled by Divyanshu Dayal. dayal1005@gmail.com Created on: 15th Sept’13. B.E. Mechanical, MBA, Procurement

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12 Gradation of Coal 12.1 Indian Coal based on Calorific Values Grade CV Range (kCal/kg) A Exceeding 6200 B 5600-6200 C 4940-5600 D 4200-4940 E 3360-4200 F 2400-3360 G 1300-2400 12.2 Indonesian Coal Benchmark (HPB Marker) Coal Brand GCV

(GAR) TM (% ar)

TS (% ar)

A

Gunung Bayan I

7,000 10 1.0 15.0

Prima Coal 6,700 12.0 0.6 5.0 Pinang 6150 6,200 14.5 0.6 5.5 Indominco 5,700 17.5 1.6 4.8 Melawan Coal

5,400 22.5 0.4 5.0

Envirocoal 5,000 26.0 0.1 1.2 Jorong J-1 4,400 32.0 0.3 4.2 Ecocoal 4,200 35.0 0.2 3.9 Tbl.5: Bench Mark for Indonesian Coal 12.3 Australian Grades of Coal

Parameter Type 1 Type 2 Type 3 Type 4 Type 5 Type 6

Gross Calorific Value (ADB)

6,500 kcal/kg

6,300 kcal/kg

6,000 kcal/kg

5,800 kcal/kg

5,500 kcal/kg

5,300 kcal/kg

Gross Calorific Value (ARB)

6,000 kal/kg

5,800 kcal/kg

5,500 kcal/kg

5,200 kcal/kg

4,500 kcal/kg

3,600 kcal/kg

Net Calorific Value (ARB)

5,700 kcal/kg

5,500 kcal/kg

5,200 kcal/kg

4,900 kcal/kg

4,300 kcal/kg

3,400 kcal/kg

Total Moisture (ARB)

9-12% 12-15% 15-20% 22-28% 32-38% 38-44%

Inherent Moisture (ADB)

7-9% 8-10% 10-12% 12-15% 15-18% 18-21%

Ash Content (ADB) 8-15% 12-17% 12-17% 10-14% 8-12% 8-12%

Volatile Matter (ADB)

38-43% 38-43% 37-42% 36-40% 36-40% 36-40%

Fixed Carbon (ADB) 43-48% 42-45% 40-43% 38-42% 37-40% 35-39%

Total Sulfur (ADB) 1.00%

0.8-1.0%

0.8-1.0%

0.6-1.0%

0.5-1.0%

0.4-1.0%

Hydrogen (Hd) (Dry Basis)

4.90% 4.90% 4.90% 4.90% 4.90% 4.90%

Handgrove

Grindability

Index (HGI)

38-43 38-43 39-45 45-50 48-52 50-55

Ash Fusion Temperature IDT (Initial Deformation Temperature)

1250C 1250C 1250C 1250C 1250C 1250C

Size 0-50mm

(95%)

0-50mm

(95%)

0-50mm

(95%)

0-50mm

(95%)

0-50mm

(95%)

0-50mm

(95%)

Tbl.6: Australian Grades of Coal