Coal is a versatile and important resource that has many uses, from power generation to steel making. Every year, billions of tonnes of coal are bought and sold in local and international markets. The price of coal reflects not only the amount of coal available but also the quality of the coal itself. In commercial operations, buyers often consider properties such as combustion energy or ash content when determining if a particular type of coal is suitable for their needs.
Coal's properties that affect combustion and environmental performance are often what sales contracts center around. These include a coal sample's calorific value, volatile matter, moisture, sulfur, chlorine, and ash (elemental composition) content. Payment for the coal is contingent on these analytical results. Furthermore, it is crucial to know a coal's quality for whatever application it will be used.
Coal sampling is done to evaluate the coal. The protocols for coal sampling must provide material that, when analyzed, will give results that are representative of the lot sampled. To make sure a representative sample is collected, follow correct sampling procedures and adhere to specific rules. Modifications from the standard procedures may significantly change the precision of the final results which often causes arguments between the seller and customer.
Sampling:
Sampling and analyses normally required for coal evaluation include the sample information with the Sample history, sampling date, sample type, and sample origin (mine, location) all required.
The Sampling protocols require assurance that the sample represents the gross consignment.
Chemical properties:
A proximate analysis determines the ‘proximate’ overall composition of the coal including moisture, volatile matter, ash, and fixed carbon content.
An ultimate analysis is the absolute measurement of the elemental composition such as carbon, hydrogen, sulfur, nitrogen, and oxygen content.
The analysis of the Sulfur forms to determine the Chemically bonded sulfur: organic, sulfide, or sulfate.
Ash properties:
Elemental analysis determines the major and minor elements.
Mineralogical analysis records the mineral content.
Trace elements analysis shows the analysis of trace elements; some enrichment in ash.
Ash fusibility is the qualitative observation of the temperature at which ash passes through defined stages of fusing and flow.
Coal evaluation (Speight, 2005)
ISO Standards
The ISO Standards for procedures related to coal sampling, preparation and bias test, coal characterization, and coal analysis are ICS 73.040: Coals (including lignites) and ICS 75.160.10: Solid fuels respectively.
The full list of coal-related ISO Standards can be found on the ISO’s website:
• ICS 73.040: Coals athttps://www.iso.org/ics/73.040/x/
• ICS 75.160.10: Solid fuels at https://www.iso.org/ics/75.160.10/x/
Various ISO standards have been modified and accepted in many countries as national standard methods. Notably, ISO Standards are broadly recognized and applied in international markets for the coal trade.
Other standards include
ASTM International:
http://www.astm.org/Standards/coal-‐and-‐gas-‐standards.htm
British standards:
http://shop.bsigroup.com/
Standardization Administration of China (SAC):
( http://www.sac.gov.cn/
Indian standards:
Bureau of Indian Standards (BIS) (Member of ISO and most standards based on ISO)
South African national standards:
https://store.sabs.co.za/catalogsearch/result/?q=mining+coal+p+7
Australian standards:
http://www.saiglobal.com/
When these standards are followed, the inspection and report done professionally the margin of error in the value of the coal can be reduced. The reports should provide all the details to negotiate a fair price for the coal in question.
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