The document provides details on the analysis of coal and coke, including: - Types, composition, preparation of samples, and proximate and ultimate analysis methods. - Coal is a combustible sedimentary rock formed from decomposed vegetation. Its composition varies by type and includes carbon, hydrogen, oxygen, nitrogen, sulfur and trace elements. - Accuracy, precision and bias are defined in relation to analytical testing methods. Sampling protocols aim to obtain representative samples given coal's heterogeneous nature.

1. Analysis of coal and coke
Analysis of coal and coke-Types, composition, preparation of sample, proximate and
ultimate anlaysis calorific value by bomb Calorimetry.
Coal is an organic sedimentary rock that contains varying amounts of carbon, hydrogen,
nitrogen, oxygen, and sulphur as well as trace amounts of other elements, including mineral
matter.Coal is a solid, brittle, combustible, carbonaceous rock formed by the decomposition
and alteration of vegetation by compaction, temperature, and pressure. It varies in colour
from brown to black and is usually stratified. The source of the vegetation is often moss and
other low plant forms, but some coals contain significant amounts of materials that originated
from woody precursors.
Type and composition
Accuracy, Precision and Bias:
Accuracy is used to indicate the reliability of a measurement or an observation, but it is,
more specifically, a measure of the closeness of agreement between an experimental result
and the true value. Thus, the accuracy of a test method is the degree of agreement of
individual test results with an accepted reference value.
Precision is a measure of the degree to which replicate data and/or measurements conform to
each other, the degree of agreement among individual test results obtained under prescribed
similar conditions. Hence, it is possible that data can be very precise without necessarily
being correct or accurate.
Bias: Systematic error which leads to the average value of a series of results being
persistently higher or lower than those which are obtained using a reference sampling method
which is intrinsically unbiased.

2. Sampling:
For homogeneous materials, sampling protocols are relatively simple and straight-forward.
On the other hand, the heterogeneous nature of coal complicates the sampling procedures. In
fact, apart from variations in rank of coal is often visibly heterogeneous. Thus, the variable
composition of coal offers many challenges to analysts who need to ensure that a sample
under investigation is representative of the coal. Indeed, the substantial variation in coal
quality and composition from the top to the bottom of the seam, from side to side, and from
one end to the other, within an unmined bed offers challenges that are perhaps unprecedented
in other fields of analytical chemistry. Transportation (by belt, rail, or truck) can initiate (due
to movement of the coal) processes that result in size and density segregation. Thus,
variations from one side of a conveyor belt to the other, from side-to-side, end-to-end, and
top-to-bottom locations in individual cars or trucks, and between one location and another in
a coal pile, must be anticipated.
The basic purpose of collecting and preparing a sample of coal is to provide a test sample
which when analysed will provide the test results representative of the lot sampled. In order
that the sample represents the coal from which it is taken, it is collected by taking a definite
number of increments distributed throughout the whole volume of coal.
General procedure for establishing a sampling scheme:
• Decide for what purpose the samples are taken e.g. plant performance
evaluation, process control, commercial transactions etc.
• Identify the quality parameters to be determined, i.e. general analysis, total
moisture, size analysis, washability, etc.
• Define the lot and precision required
• Determine the number of sub-lots and the number of increments per sub lot
to achieve the required precision
• Determine the minimum mass per increment and the minimum mass of the
total sample
• Decide on the method of combining the different increments to produce the
gross sample
• Decide on drawing common or separate samples, for general analysis and
moisture
Stream sampling and Sampling at rest:
Stream sampling and flow sampling: usually reserved for the collection of sample
increments from a free-falling stream of coal as opposed to the collection of increments from
a motionless (stopped) conveyor belt. Coal that passes from one belt to another at an angle
tends to become segregated because of the momentum caused by density and particle size
differences, with a pre- dominance of coarse particles on one side and a predominance of fine
particles on the other side.
Sampling at rest: consists of acquiring a coal sample when there is no motion. In such
instances, it may be coal is loaded into hopper cars. In addition, heavy rainfall can cause the
moisture content of the coal to be much higher at the top and sides of a railcar than at the
bottom. Similarly, the onset of freezing conditions can also cause segregation of the moisture

3. content. Difficult, if not impossible, to ensure that the sample is truly representative of the
gross consignment.
Sampling error:The difference that occurs when the property of the representative sample is
compared to the true, unknown value of the gross lot.
A gross sample of coal is a sample that represents a quantity, or lot, of coal and is composed
of a number of increments on which neither reduction nor division has been performed.
Manual Sampling
There are two considerations involved with the principle of manual sampling (that every
particle in the entire mass to be sampled have an equal opportunity to be included in the
sample):
(1) The dimensions of the sampling device (opening of the sampling device must be two to
three times the top size of the coal to meet sampling method), and
(2) Proper use of the sampling device.
Sampling tools
Standard practice for manual sampling of stationary coal from railroad cars, barges, trucks, or
stockpiles. The gross samples are to be crushed, divided, and further prepared for analysis.
Mechanical Sampling
A wide variety of mechanical devices are now in use and include flow-through cutters,
bucket cutters, reciprocating hoppers, augers, slotted belts, fixed-position pipes, and rotating
spoons. These systems typically collect the primary increments and perform at least part of
the sample preparation by crushing and dividing it down to the 4- or 8-mesh stage of
reduction specified.
A major advantage of these systems is that they sample coal from a moving stream, and most
of them satisfy the principle that every particle in the entire mass has an equal opportunity to
be included in the primary increments.
A pipe sampler is an off-the-belt sampler that collects increments from within the stream
cross section by means of one or two pipes. A spoon sampler consists of one or more pipes,
arranged like the spokes of a wheel. Openings located at the tips collect the sample as the
device is rotated through coal on a moving belt. An auger drill is also used as a sampling
device for penetrating a stationary mass of coal and withdrawing material from its interior.
SAMPLE PREPARATION

4. Once a gross sample has been taken, it is reduced in both particle size and quantity to yield a
laboratory sample. This aspect is known as coal preparation. Sample preparation includes
drying (in air), as well as crushing, dividing, and mixing a gross sample to obtain a sample
that is ready for analysis. Sample preparation is not just simply a matter of dividing a gross
sample into manageable or usable increments. The task must also be accomplished in a
manner that produces an unbiased sample ready for analysis.
Two processes of sample division and reduction are covered:
(1) Procedure in which manual riffles are used for division of the sample and mechanical
crushing equipment for reduction of the sample, and
(2) Procedure in which mechanical sample dividers are used for division of the sample and
mechanical crushing equipment for reduction of the sample. A third process that is, in reality,
a combination of procedures 1 and 2 may be used at any stage.
Many issues, including (1) loss or gain of moisture, (2) improper mixing of constituents, (3)
improper crushing and grinding, and (4) oxidation of coal, may arise during the sampling and
sample preparation processes.
The distribution of mineral matter in coal presents problems for crushing, grinding, and
uniform mixing at each step of the sampling procedure. The densities of the various coal
constituents cause segregation, especially if there is a wide particle size distribution. Thus,
crushing and/or grinding coal from a large particle to a very small particle should involve a
reasonable number of steps that are based on the starting particle size and nature of the coal.
Coal washing is a process by which mineral matter is removed from coal by the use of any
one of several washing processes to leave the coal as near mineral-free. Mineral matter
occurs in coal as in two clearly defined forms, intrinsic mineral matter(in intimate association
and originates from inorganic material essential to the growth of the vegetable matter) and
extrinsic mineral matter(purely adventitious, is derived from the roof and floor of the coal
seam and from any noncoal or inorganic material that may be associated with the seam itself).
The coal is generally of lower density than the mineral matter.
Analysis of Coal
To ascertain the commercial value of coal certain tests regarding its burning properties are
performed before it is commercially marketed. Two commonly usedtests are : Proximate
analysis and Ultimate analysis of coal. Calorific value of coalis defined as the quantity of heat
given out by burning one unit weight of coal in acalorimeter.
Proximate Analysis of Coal
This analysis of coal gives good indication about heating and burning properties of coal. The
test gives the composition of coal in respect of moisture, volatile matter, ash and fixed
carbon. The moisture test is performed by heating 1 gm of coal sample at 104o
C to 110o
C for
1 hour in an oven and finding the loss in weight. The volatile matter is determined by heating
1 gm of coal sample in a covered crucible at 950o
C for 7 minutes and determining loss in
weight, from which the moisture content as found from moisture test, is deducted. Ash
content is found by completely burning the sample of coal in a muffled furnace at 700oC to
750o
C and weighing the residue. The percentage of fixed carbon is determined by difference
when moisture, volatile matter and ash have been accounted for(Fixed carbon is the
difference of these three values summed and subtracted from 100).

5. The results of proximate analysis of most coals indicate the following broad ranges of various
constituents by weight:
The importance of volatile matter in coal is due to the fact that it largely governs the
combustion which in turn governs the design of grate and combustions space used. High
volatile matter is desirable in gas making, while low volatile matter for manufacturing of
metallurgical coke. The term volatile matter content (of coal) is actually a misnomer, insofar
as the majority of the volatile matter is the volatile product of the thermal decomposition of
coal through the application of high temperatures The extent to which the more volatile
smaller molecules of add to this is dependent on the coal and should be determined by non-
destructive methods such as extraction by solvent(s).
MOISTURE CONTENT
There are several sources of the water found in coal. The vegetation from which coal was
formed had a high percentage of water that was both physically and chemically bound. Water
is present in most mines and circulates through most coal seams. After mining, many coals
are washed with water during preparation for market and are then subject to rain and snow
during transportation and storage.
The total moisture in coal is the determination of the moisture (in all forms except water of
crystallization of the mineral matter) that resides within the coal matrix.
Methods for determination of the total moisture in coal have been placed into the following
categories: (1) thermal methods that often include distillation methods; (2) a desiccator
method; (3) distillation methods, which often include extraction and/or solution methods; (5)
chemical methods; and (6) electrical methods.
The various forms of moisture in coal are described according to the manner in which they
are measured by some prescribed standard method. These forms are (1) inherent moisture, (2)
surface or free moisture, (3) total moisture, (4) air-dry loss moisture, (5) residual moisture,
(6) as-received moisture, (7) decomposition moisture, and (8) water of hydration of mineral
matter. Inherent moisture (bed moisture, equilibrium moisture,
ASH
Ash is the residue remaining after the combustion of coal under specified conditions and is
composed primarily of oxides and sulphates. It should not be confused with mineral matter,
which is composed of the unaltered inorganic minerals in coal. Thus, ash is formed as the
result of chemical changes that take place in the mineral matter during the ashing process.

6. The quantity of ash can be more than, equal to, or less than the quantity of mineral matter in
coal, depending on the nature of the mineral matter and the chemical changes that take place
in ashing.
The various changes that occur include (1) loss of water from silicate minerals, (2) loss of
carbon dioxide from carbonate minerals, (3) oxidation of iron pyrite to iron oxide, and (4)
fixation of oxides of sulfur by bases such as calcium and magnesium.
The determination of mineral ash in coal is usually by heating (burning) an accurately
weighed sample of the coal in an adequately ventilated muffle furnace at temperatures in the
range 700 to 750◦
C for 4 hours.
VOLATILE MATTER
Volatile matter, as determined by the standard test methods is the percentage of volatile
products, exclusive of moisture vapour, released during the heating of coal or coke under
rigidly controlled conditions. The rate of heating of the sample influences volatile matter
values.
heating a weighed sample of coal (usually about 1 g) in a covered crucible to a predetermined
temperature; the loss in weight (excluding losses due to water) is the volatile matter content
(expressed as a weight percent).
FIXED CARBON
Fixed carbon is the material remaining after the determination of moisture, volatile matter,
and ash. It is, in fact, a measure of the solid combustible material in coal after the expulsion
of volatile matter. It is a measure of the solid combustible material that remains after the
volatile matter in coal has been removed. For this reason, it is also used as an indication of
the yield of coke in a coking process. Fixed carbon plus ash essentially represents the yield of
coke.
Ultimate Analysis
The ultimate analysis of coal involves determination of the weight percent carbon as well as
sulfur, nitrogen, and oxygen (usually estimated by difference). Trace elements that occur in
coal are often included as a part of the ultimate analysis.
The carbon determination includes carbon present as organic carbon occurring in the coal
substance and any carbon present as mineral carbonate. The hydrogen determination includes
hydrogen present in the organic materials as well as hydrogen in all of the water associated
with the coal In the absence of evidence to the contrary, all of the nitrogen is assumed to
occur within the organic matrix of coal. On the other hand, sulfur occurs in three forms in
coal: (1) as organic sulfur compounds; (2) as inorganic sulfides that are, for the most part,
primarily the iron sulfides pyrite and marcasite (FeS2); and (3) as inorganic sulfates (e.g.,
Na2SO4, CaSO4). The sulfur value presented for ultimate analysis may include, depending
on the coal and any prior methods of coal cleaning, inorganic sulfur and organic sulfur.
The broad range in which the constituents of coal vary by weight as determined by ultimate
analysis are given below :

7. The standard method for the ultimate analysis of coal and includes the determination of
elemental carbon, hydrogen, sulfur, and nitrogen, together with the ash in the material as a
whole. Oxygen is usually calculated by difference.
CARBON AND HYDROGEN
Carbon and hydrogen, which, respectively, account for 70 to 95% and 2 to 6% by weight
(dry, ash-free) of the organic substance of coal, are thought by some to be the most important
constituents of coal. Almost all of the carbon and hydrogen in coal occurs in combined form
in the complex organic compounds that make up coal. But carbon also occurs in the mineral
carbonates, with calcite being the principal component, and hydrogen is also present in the
various forms of moisture found in coal.
Elemental carbon and hydrogen is determined by combustion in a closed system (combustion
train), and the products of combustion are collected in an absorption train. The percentages
by weight of carbon and hydrogen are calculated from the gain in weight of the relevant
segments of the absorption train. This method gives the total percentages of carbon and
hydrogen in the coal, including any carbon in the carbonates and any hydrogen in free
moisture and in water of hydration of silicates.
In the analytical procedure, a weighed amount of coal is placed in either a boat (glazed
porcelain, fused silica, or platinum) and inserted into the combustion tube under the first
furnace, where the sample is burned in oxygen. The combustion products are allowed to flow
over the heated copper oxide and lead chromate or silver and into the absorption train. The
copper oxide ensures complete combustion of the carbon and hydrogen in the coal, whereas
the lead chromate absorbs the oxides of sulfur. If silver gauze is used, both the sulfur oxides
and chlorine will be absorbed. The preweighed absorbers in the absorption train absorb water
and carbon dioxide, and the percent of carbon and hydrogen in the sample is calculated from
the gain in weight of absorbers.
NITROGEN
Nitrogen occurs almost exclusively in the organic matter of coal. Very little information is
available concerning the nitrogen-containing compounds present in coal, but they do appear
to be stable and are thought to be primarily heterocyclic. The original source of nitrogen in
coal may have been both plant and animal protein. Plant alkaloids, chlorophyll, and other
porphyrins contain nitrogen in cyclic structures stable enough to have withstood changes
during the coalification process and thus to have contributed to the nitrogen content of coal.
The standard procedure of nitrogen determination by many laboratories is Kjeldahl–Gunning
macro method. By this method, any nitrogen present in the sample is converted into
ammonium salts by the destructive digestion of the sample by a hot mixture of concentrated
sulfuric acid and potassium sulfate. After the digestion mixture has been made alkaline with
sodium or potassium hydroxide,ammonia is expelled by distillation, condensed, and absorbed
into a sulfuric acidsolution and the excess acid is titrated with sodium hydroxide solution.
The alternative method is similar except that after the complete digestion, the ammonia is

8. distilled into a boric acid solution and titrated with a standard acid solution. A catalyst is used
in the Kjeldahl–Gunning method to increase the rate of digestion of the coal .For most
bituminous and low-rank coals, the digestion period is on the order of 3 to 6 hours, even with
the aid of a catalyst, and anthracite may require as much as 12 to 16 hours.A variety of
catalysts can be used, including mercuric sulfate (HgSO4) and sele-nium, mercuric selenite
(HgSeO3), or cupric selenite dihydrate (CuSeO4 ・ 2H2O).
SULFUR
Sulfur is an important consideration in coal utilizatio., The emission of sulfur oxides leads to
the corrosion of equipment and slagging of combustion or boiler equipment, as well as
contributing to atmospheric pollution and environmental damage. Sulfur data are therefore
necessary for the evaluation of coals to be used for combustion purposes. Most coal
conversion and cleaning processes require two sets of sulfur values: the sulfur content of the
coal before it is used and the sulfur content of the products formed.
Sulfur is present in coal in three forms, either as (1) organically bound sulfur, (2) inorganic
sulphur (pyrite or marcasite, FeS2), or (3) inorganic sulphates.
The three most widely used test methods for sulfur determination are (1) the Eschka method,
(2) the bomb washing method, and (3) the high-temperature combustion method, and all are
based on the combustion of the sulfur-containing material to produce sulfate, which can be
measured either gravimetrically or volumetrically.
In the Eschka method, 1 g of the analysis sample is thoroughly mixed with 3 g of Eschka
mixture, which is a combination of two parts by weight of light calcined magnesium oxide
with one part of anhydrous sodium carbonate. The combination of sample and Eschka
mixture is placed in a porcelain crucible (30 mL) and covered with another gram of Eschka
mixture. The crucible is placed in a muffle furnace, heated to a temperature of 800 plus minu
25◦
C ,and held at this temperature until oxidation of thesample is complete. The sulfur
compounds evolved during combustion react with the magnesium oxide (MgO) and sodium
carbonate (Na2CO3) and under oxidiz- ing conditions are retained as magnesium sulfate
(MgSO4) and sodium sulphate (Na2SO4). The sulfate in the residue is extracted and
determined gravimetrically.
OXYGEN
Oxygen occurs in both the organic and inorganic portions of coal. In the organic portion,
oxygen is present in hydroxyl (–OH), usually phenol groups, carboxyl groups (CO2H),
methoxyl groups (–OCH3), and carbonyl groups (=C=O).
% oxygen = 100 − (%C + %H + %N + %S organic)
The resulting figure for oxygen is therefore burdened with the accumulation of all the
experimental errors involved in the determinations of the other constituents that form part of
the equation. Consequently, the oxygen content was, and still is, of a low order of accuracy.
For this reason, oxygen determined by difference should not be designated percent oxygen
but percent oxygen by difference. These errors may be partially compensating, or they may be
additive.
CALORIFIC VALUE (http://www.youtube.com/watch?v=9suiA6EWQ18)

9. The calorific value is the heat produced by the combustion of a unit quantity of coal in a
bomb calorimeter with oxygen and under a specified set of conditions. For the analysis of
coal, the calorific value is determined in a bomb calorimeter either by a static (isothermal)
method or by an adiabatic method The calorific value is a direct indication of the heat content
(energy value) of the and represents the combined heats of combustion of the carbon,
hydrogen, nitrogen, and sulfur in the organic matter and of the sulfur in pyrite and is the gross
calorific value with a correction applied if the net calorific value is of interest.
The heat energy measured in a bomb calorimeter may be expressed either as calories (cal),
British thermal units (Btu) or Joules (J), with the International Steam Table calorie as the
basic unit in this system. One calorie equals 4.1868 absolute Joules, and is roughly
equivalent to the heat energy required to raise the temperature of one gram of water one
degree Celsius at 15°C.The British thermal unit equals 251.996 calories and is roughly
equivalent to the heat energy required to raise one pound of water one degree Fahrenheit at
60°F. These and other energy relationships are shown in the table below.
Calorific Values
1 cal = 4.1868 Joules 1 Btu/lb = 2.326 Joules/gram
1 Btu = 1055.06 Joules 1.8 Btu/lb = 1.0 cal/gram
1 Btu = 251.996 calories
The calorific value is neither part of the proximate analysis nor part of the ultimate analysis;
it is, in fact, one of the many physical properties of coal.
The bomb calorimeter provides the most suitable and accurate apparatus for determination of
the calorific values of solid and liquid fuels. Since the combustion takes place in a closed
system, heat transfer from the calorimeter to the water is complete.
A weighed sample is burned in an oxygen bomb covered with water in a container
surrounded by a jacket. In the isothermal calorimeter system, the temperature rise of the
calorimeter water is corrected for the heat lost to or gained from the surrounding jacket
during the burning of the sample.