Post on 04-Feb-2018
Physical and chemical properties
of coal and its products
Lecture no.L-02-1
Dr hab. inż. Marek Ściążko
Prof. nadzw.
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Chemical properties of coal
• Coal comes in four main types or ranks:
lignite or brown coal, bituminous coal or
black coal, anthracite and graphite. Each
type of coal has a certain set of physical
parameters which are mostly controlled by
moisture, volatile content (in terms of
aliphatic or aromatic hydrocarbons) and
carbon content.
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Proximate analysis
• The objective of coal proximate analysis is to determine the amount of fixed carbon (FC), volatile matters (VM), moisture, and ash within the coal sample.
• The variables are measured in weight percent (wt. %) and are calculated in several different bases. AR (as-received) basis is the most widely used basis in industrial applications. AR basis puts all variables into consideration and uses the total weight as the basis of measurement.
• AD (air-dried) basis neglect the presence of moistures other than inherent moisture while DB (dry-basis) leaves out all moistures, including surface moisture, inherent moisture, and other moistures. DAF (dry, ash free) basis neglect all moisture and ash constituent in coal while DMMF (dry, mineral-matter-free) basis leaves out the presence of moisture and mineral matters in coal, for example: quartz, pyrite, calcite, etc. Mineral matter is not directly measured but may be obtained by one of a number of empirical formula based on the ultimate and proximate analysis.
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Moisture
• Moisture is an important property of coal, as all coals are mined wet. Groundwater and other extraneous moisture is known as adventitious moisture and is readily evaporated. Moisture held within the coal itself is known as inherent moisture and is analysed quantitatively. Moisture may occur in four possible forms within coal:
– Surface moisture: water held on the surface of coal particles or macerals
– Hydroscopic moisture: water held by capillary action within the microfractures of the coal
– Decomposition moisture: water held within the coal's decomposed organic compounds
– Mineral moisture: water which comprises part of the crystal structure of hydrous silicates such as clays
• Total moisture is analysed by loss of mass between an untreated sample and the sample once analysed. This is achieved by any of the following methods;
– Heating the coal with toluene
– Drying in a minimum free-space oven at within a nitrogen atmosphere
– Drying in air at 100 to 105 °C (212 to 221 °F) and relative loss of mass determined
Source: http://en.wikipedia.org/wiki/Coal_assay#Chemical_properties_of_coal Copyright-MS-2013 4
Volatile matter
• Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbons and some sulfur. The volatile matter of coal is determined under rigidly controlled standards. In Australian and British laboratories this involves heating the coal sample to 900 ± 5 °C (1650 ±10 °F) for 7 minutes in a cylindrical silica crucible in a muffle furnace. American Standard procedures involve heating to 950 ± 25 °C (1740 ± 45 °F) in a vertical platinum crucible.
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Ash
• Ash content of coal is the non-combustible
residue left after coal is burnt. It represents
the bulk mineral matter after carbon,
oxygen, sulfur and water (including from
clays) has been driven off during
combustion. Analysis is fairly
straightforward, with the coal thoroughly
burnt and the ash material expressed as a
percentage of the original weight.
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Detailed ash analysis
• An analysis of coal ash may also be carried out to determine not only the content of coal ash, but also to determine the levels at which trace elements occur in ash. These data are useful for environmental impact modeling.
• Beside composition of coal ash, ash fusion point is also one significant parameter in ash analysis. The optimum operating temperature of coal processing will depend on the gas temperature and also the ash fusion point. Melting of the ashes may cause them to stick to the walls of the reactor and result in a build-up.
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Fixed carbon
• The fixed carbon content of the coal is the carbon found in the material which is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample.
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Conversion of the data basis
Proximate Analysis unit (ar) (ad) (db) (daf)
Moisture (wt. %) 3.3 2.7
Ash (wt. %) 22.1 22.2 22.8
Volatile Matter (wt. %) 27.3 27.5 28.3 36.6
Fixed Carbon (wt. %) 47.3 47.6 48.9 63.4
Gross Calorific Value (MJ/kg) 24.73 24.88 25.57 33.13
(ar) – as received
(ad) – air dried
(db) – dry basis
(daf) – dry ash free
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Ultimate analysis
• Ultimate analysis is the determination of
the percentage composition in terms of
carbon, hydrogen, sulfur, nitrogen, and
ash, and the calculation of the oxygen
content the difference.
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Conversion of the data basis
Ultimate Analysis unit (ar) (ad) (db) (daf)
Carbon (C) (wt. %) 61.1 61.5 63.2 81.9
Hydrogen (H) (wt. %) 3.00 3.02 3.10 4.02
Nitrogen (N) (wt. %) 1.35 1.36 1.40 1.81
Total Sulfur (S) (wt. %) 0.4 0.39 0.39
Oxygen (O) (wt. %) 8.8 8.8 9.1
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Conversion table
Desired
Basis >
Given Basis
As Received Air Dried Dry Dry, ash
free
Dry, mineral
matter free
As Received 100-Mad
100-Mar
100
100-
Mar
100
100-
(Mar+Aar)
100
100-
(Mar+MMar)
Air Dried 100-Mar
100-Mad
100
100-
Mad
100
100-
(Mad+Aad)
100
100-
(Mad+MMad)
Dry 100-Mar
100
100-Mad
100
100
100-Ad
100
100-MMd
Dry, ash
free
100-
(Mar+Aar)
100
100-
(Mad+Aad)
100
100-
Ad
100
100-Ad
100-MMd
Dry,
mineral
matter free
100-
(Mar+MMar)
100
100-
(Mad+MMad)
100
100-
MMd
100
100-MMd
100-Ad
Definition of Variables
M = moisture (%)
A = ash (%)
MM = mineral matter (%)
Definition of Subscripts
ar = as received basis
ad = air dried basis
d = dry basis
Specific Energy Conversions
For conversions between units:
1 Btu/lb = 0.002326 MJ/kg
1 kcal/kg = 0.0041868 MJ/kg
1 Metric Ton (tonne) = 1.10231
short tons
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Chemical constitution of coal
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Atomic composition of different fossil fuels
(kmol at. in 100 kg of org. substance)
0
1
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7Type of fuel
Nu
mb
er
of
ato
ms
1 Peat
2 Lignite3 Flame coal, type 314 Gas coal, type 33
5 Ortho-coking coal, type 356 Semi-coking coal, type 377 Anthracite
No. Type of fuelHydrogen Oxygen Carbon
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Atomic ratio of (C/O)at, (C/H)at, (H/O)at in different
fossil fuels
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7
Typ paliwa
Sto
su
nk
i a
tom
ow
e
C/O C/H*10 H/O
The critical change
is observed in oxygen
content
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• On the average in a bituminous coal hydrogen content equals to ca. 5% w/w daf., and carbon content ca. 84%. It means, that statistically every 7 atoms of carbon meets 5 atoms of hydrogen.
• The next substantial element is oxygen, that can be found in a coal at the average concentration 10% w/w. It means that for every 7 atoms of carbon acounts for only 0.5 atoms of oxygen, however what will be shown its content substantially effects the coal properties.
• The remaining elements like sulfur - S and nitrogen - N can be found in coal on the average in amount of 0.5 i 1% and due to its concentration does not influence the coal gross properties very much.
Atomic structure of coal
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Atomic composition of different fossil fuels
(kmol at. in 100 kg of org. substance)
0
1
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7Type of fuel
Nu
mb
er
of
ato
ms
1 Peat
2 Lignite3 Flame coal, type 314 Gas coal, type 33
5 Ortho-coking coal, type 356 Semi-coking coal, type 377 Anthracite
No. Type of fuelHydrogen Oxygen Carbon
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Atomic ratio of (C/O)at, (C/H)at, (H/O)at in different
fossil fuels
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7
Typ paliwa
Sto
su
nk
i a
tom
ow
e
C/O C/H*10 H/O
The critical change
is observed in oxygen
content
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• On the average in a bituminous coal hydrogen content equals to ca. 5% w/w daf., and carbon content ca. 84%. It means, that statistically every 7 atoms of carbon meets 5 atoms of hydrogen.
• The next substantial element is oxygen, that can be found in a coal at the average concentration 10% w/w. It means that for every 7 atoms of carbon acounts for only 0.5 atoms of oxygen, however what will be shown its content substantially effects the coal properties.
• The remaining elements like sulfur - S and nitrogen - N can be found in coal on the average in amount of 0.5 i 1% and due to its concentration does not influence the coal gross properties very much.
Atomic structure of coal
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High heating value vs. carbon
content in a fuel (daf)
0
5000
10000
15000
20000
25000
30000
35000
40000
60 65 70 75 80 85 90 95 100 105
Zawartość pierwiastka C [%]
Cie
pło
sp
ala
nia
[kJ/k
g]
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Coal heating - devolatilization
Heating rate, K/min
Source: Journal of Analytical and Applied Pyrolysis
58–59 (2001) 685–701 Copyright-MS-2013 21
5,860,171,173,9369,5730,216,82,5
OdaS
caNaHaCaVaAaWa
OxygenSulphurNitrogenHydrogenCarbonVolatileAshMoisture
Content, % mas.
5,860,171,173,9369,5730,216,82,5
OdaS
caNaHaCaVaAaWa
OxygenSulphurNitrogenHydrogenCarbonVolatileAshMoisture
Content, % mas.
Heating valueEnthalpy
of formation
Activation
energy
Frequency
index
Qsdaf, MJ/kg
fHo
, kJ/kg E, kJ/kmol ln (k8
)
34,7 -463,2 11181,2 -5,97
0
0,1
0,2
0,3
0,4
500 700 900 1100 1300
Temperature, K
Yie
ldo
f p
rod
uc
ts,
kg
/kg
H2 CO
CH4 CO2
C2H6 H2O
V Tar
0
0,1
0,2
0,3
0,4
500 700 900 1100 1300
Temperature, K
Yie
ldo
f p
rod
uc
ts,
kg
/kg
H2 CO
CH4 CO2
C2H6 H2O
V Tar
0
0,1
0,2
0,3
0,4
0,5
0,6
500 700 900 1100 1300
Temperature, K
Ga
s c
om
po
sit
ion
, km
ol/k
mo
l
0
0,1
0,2
0,3
0,4
0,5
0,6
500 700 900 1100 1300
Temperature, K
Ga
s c
om
po
sit
ion
, km
ol/k
mo
l
Biuminous coal
- Wieczorek -
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Coke
• Coke is the solid carbonaceous material
derived from destructive distillation of low-
ash, low-sulfur bituminous coal. Cokes
from coal are grey, hard, and porous.
• Coke is used as a fuel and as a reducing
agent in smelting iron ore in a blast
furnace. It is there to reduce the iron oxide
(haematite) in order to collect iron.
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Coal tar
• Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons.
• Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas.
• Coal tars are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds, about 200 substances in all.
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Coke gas
• Coal gas (also town gas and illumination gas) is a flammable gaseous fuel made by the destructive distillation of coal containing a variety of calorific gases including hydrogen, carbon monoxide, methane and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen.
• It was the primary source of gaseous fuel both the United States and Great Britain until the widespread adoption of natural gas during the 1940s and 1950s. It was used for lighting, cooking and heating and was often supplied to households via a municipally-owned piped distribution system.
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