Understanding Coal Analysis
by Michael Hutagalung on 02/06/08 at 1:30 am | 31 Comments | Print article | Email article
“How to understand a coal sample analysis? What is the difference between proximate and ultimate analysis? What is AR (as-received) basis? Is is the same with DAF (dry, ash free) basis? How about AD (air-dried) basis? And what coal ash analysis is all about?”
Well, it is indeed a long list of questions to answer but the explanation is actually not as twisted as it seems. The main purpose of coal sample analysis is to determine the rank of the coal along with its intrinsic characteristics. Furthermore, these data will be used as the fundamental consideration for future concerns, for instance: coal trading and its utilizations.
Coal Properties
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.
- 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 analyzed. 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.
- 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. - 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. - 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.
Coal Proximate Analysis
The objective of coal ultimate 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.
| 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 |
A table is shown above containing an example of proximate analysis data of coal. Conversion from one basis to another can be performed using mass balance equations. The standard practice for proximate analysis of coal may be referred to ASTM D3172-07a or ISO 17246:2005.
Coal Ultimate Analysis
Similar to coal proximate analysis, the objective of coal ultimate analysis is to determine the constituent of coal, but rather in a form of its basic chemical elements. The ultimate analysis determines the amount of carbon (C), hydrogen (H), oxygen (O), sulfur (S), and other elements within the coal sample. These variables are also measured in weight percent (wt. %) and are calculated in the bases explained above.
| 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 |
A table is shown above containing an example of coal ultimate analysis data and showing significant elements only. Conversion from one basis to another can be performed using mass balance equations. The standard practice for ultimate analysis of coal may be referred to ASTM D3176-89(2002) or ISO 17247:2005.
Ash Analysis
| Oxides | wt.% of ash (Calculated) |
Elements | wt.% of ash (Measured) |
|---|---|---|---|
| Na2O | 0.35 | Na | 0.26 |
| MgO | 0.48 | Mg | 0.29 |
| Al2O3 | 20.0 | Al | 10.6 |
| SiO | 74.1 | Si | 34.6 |
| P2O5 | 0.05 | P | 0.05 |
| K2O | 1.1 | K | 0.92 |
| CaO | 0.68 | Ca | 0.49 |
| TiO2 | 0.80 | Ti | 0.48 |
| Mn3O4 | 0.06 | Mn | 0.05 |
| Fe2O3 | 3.25 | Fe | 2.28 |
An analysis of coal ash may also be carried out to determine not only the composition of coal ash, but also to determine the levels at which trace elements occur in ash. These data are useful for environmental impact modelling, and may be obtained by spectroscopic methods such as ICP-OES or AAS. An example of coal ash composition is shown on the right.
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.
You might be interested to read an article of coal characterization equipments here, illustrated with photos, including coal proximate analysis, ultimate analysis, and ash fusion point analysis equipments.
Reference: CSIRO Energy Technology, ISO, ASTM, Wikipedia
31 Comments
selly cipta
Jun 11th, 2008
have comment an method to reduce sulpur?
agung
Jun 16th, 2008
i just wanna give sugestion, how if you give us about coal fix bed combustion. please send that explain to my mail. thanks
Cecilia Davis
Jul 1st, 2008
This info is quiet educational. but my problem is how do I make the conversion of the Gross calorific value of the fuel from ar to DAF analysis. I understood how to get the DAF analysis for the components from AR analysis but how do I get the calorific value?
Will appreciate if u explain
Tejasvini
Aug 19th, 2008
Hi.
I want to understand the nature of Indonesian coal. Want to know about the coal characteristics like moisture content, ash, sulfur, etc.
Would appreciate any help in this regard.
Adeel
Oct 30th, 2008
Can any body send me a procedure to determine the Sulfur contents in coal ash by wet analysis.
Haseeb
Nov 22nd, 2008
Hi,
Can any body send me a procedure to determine the Coal Consumption when 4 different Coals of different GCV’s is being utilised.
JIm Shirazi
Dec 9th, 2008
I am looking at a coal analysis for Lignite. The heating values were reported as BTU /Lb include various conditions:
As received, Dry, DAF, and MMMFree. While I know the first TWO, I am not too sure about DAF and MMMFree. Could you explain these terms for me. Thank you.
johnzactruba
Dec 20th, 2008
reply for selly – Sulphur in coal cannot be reduced . But the sulphur dioxide formed during combustion caan be captured or reduced in Flue Gas desulphurising units or using limestone as a sorbent.
reply for Jim-
DAF means dry , ash free basis. The % is calculated based on 0 % moisture and 0 % Ash.
MMMF means Moisture and Mineral Matter free basis. Sometimes for high ash coals apart from ash there some mineral matter also is reported in the ultimate analysis. Mineral matter free basis is considering 0 % of ash and mineral matter.
johnzactruba
Dec 20th, 2008
reply to Haseeb :
Consider a large coal fired power plant has an efficiency of 33 % .
This means the plant heat rate is
3600/ 33% = 10909 kJ/kwhr (kiloJoules/Kilowatthour)
If the calorific value of Coal A is 20,000 kj/kg
then the coal required is = 10909 /20000 = 0.545 kg / kwhr.
If the calorific value of Coal B is 15,000 kj/kg
then the coal required is = 10909 /15000 = 0.727 kg / kwhr.
Of course ther will be a small change in th power plant efficiency because of the coal. But for quick calculations you can consider efficiency to be constant.
sam
Dec 30th, 2008
The website provides quite good information but basic. I will request for application of the coal characteristics particularly for coal ranking.
shahrom
Jan 11th, 2009
I’m looking for all 4 types of coal analysis.
1. lignite or brown coal
2. bituminous coal or black coal
3. anthracite
4. graphite
Sachin Trivedy
Jan 21st, 2009
Sir,
I am looking for formula to derive ultimate analysis of Caol from proximate analysis & GCV of Coal.
Can you guide me so thatt we are able to get more precise efficiency of our plant.
A line of confirmation shall be highly appriciated.
john zachariah
Jan 22nd, 2009
for ST,
Following is a formula collected by me long time back. I dont remeber the reference.
Applicable for bituminous coal.
FC – Fixed Carbon % by weight on Moisture and Ash Free basis
VM- Volatile Matter % by Weight on Moisture and Ash Free Basis
Hydrogen % ( Moisture and Ash free basis )= VM *[ 7.35/(VM+10) - 0.013 ]
Nitrogen % ( Moisture and Ash free basis ) = 2.1 – 0.012 * VM)
Carbon % ( Moisture and Ash free basis) ={ [FC + 0.9*( VM-14)] – Sulphur %}
Sulphur % has to be assumed based on some prevoius analysis.
Convert all the above to Air dired basis or As recieved basis, as per the
Ash % and Moisture % in the proximate sample.
Then Subtract from 100 to get Oxygen %.
Another method is to use regression analysis form a large no of samples of both Ultimate and Proximate analysis to derive a quadratic equation. I did this long time back for Indian coals. Maybe in a few days time i can search and post it here thanks.
ashok sanap
Feb 14th, 2009
i have coal sample on recevied basis .i want to convert on dry basis please give me formula for ash moisture volatile matter fixed carbon & GCV
Ramsen
Feb 20th, 2009
Hi
Can I get the average composition of coal (A’cite,L’nite,B’nus) to find the theoritical O2 required for combustion & Is there any thumb value for coal/MW Power.
Expecting your appreciable reply
aiman nasim
Mar 10th, 2009
hi
i want to know about the type of coal found in pakistan and how can we improve it?
vinothkumar
Mar 15th, 2009
did we convert coal into diamond or not?
P.K.Ghosh
Mar 24th, 2009
hi,
I wish to know educational. how do I make the conversion of the Gross calorific value of the fuel from ar to DAF analysis. I understood how to get the DAF analysis for the components from AR analysis but how do I get the calorific value?
Secondly If anybody quoted on ADB basis of IM and GCV then I make convert in GAR Basis of GCV How I will calculate.
Please clear me.
Arun Prasad
Mar 25th, 2009
http://majarimagazine.com/2008/06/understanding-coal-sample-analysis/
In above web site , typing mistake is observed . Under heading – Proximate analysis ,
wrong Statement :
The objective of coal ultimate analysis is to determine the amount of fixed carbon (FC), volatile matters (VM), moisture, and ash within the coal sample
Correct Statement:
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
magdik
Mar 27th, 2009
i would like to do a university project on basic coal analysis however i got no clue what to as a project,actually what to test for project purpose not like day to day analysis.
saman abbasi
Apr 9th, 2009
I need to know on how many basis does coal is classified and what are they and i also want the classification.
What are the tests required basically in proximate and ultimate analysis(list of the tests) and are float and Sink, hard groove grindability Index included in ultimate analyses.Thanks!
saman abbasi
Apr 9th, 2009
Sir, one more thing want to know
1) formula to determine total sulphur on as received basis, when pyretic sulphur, sulphate sulphur and organic sulphur is given.or do total sulphur has any relation to these sulphures during calculations
Thanks,for your time!
saman abbasi
Apr 20th, 2009
may i know the answers of my previous questions.
Granny Kanyeto
May 7th, 2009
its my first time to visit your site. please send me the procedure on determining ultimate analysis using AAS
Granny Kanyeto
May 7th, 2009
would you please give me the procedure on ultimate analysis using AAS
adam
May 7th, 2009
hi, thank alot about this info.
can you described how the method coal analysis?
selcuk
May 13th, 2009
Sir,
Beside above tests, there are some physical tests carried out for coal, such as Hard Grove Grindability Index and Abrasion Index
What are the requirements for these tests for a coal fired power plant with a CFB boiler
Thanks
brahma
May 19th, 2009
thanks for above comments it helped me lot……………
kami
May 22nd, 2009
i want to understand the chemical analysis of
Pakistan coal located at Lakhra
PRADEEP TAMBE
Jun 4th, 2009
I am attending one coal fire . Before fire coal ash was 24%. After fire extinguished by water,
samples were drawn and tested.Found that TM 5%, ash 38%. My understanding is that even if partly burnt coal is fully burnt in laboratory coal ash should remain same as 24%.
why there is increase ?
Please reply
Tambe
Suneet
Jun 18th, 2009
Any Questions related to Coal Analysis are welcome on my email ID
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