Definitions and meanings

Moisture is the humidity value, in term of coal, it is divided into 2 types, namely:- Free moisture is the humidity clinging on the surface of coal, being the part that shows such a coal is damp, The damp coal will always cling to vessels or containers or tools, causing the flow initiated by its weight is not moving well.

  Inherent Moisture is the humidity existing in the texture or porous pores of coal,
    we may use inherent moisture as a way to identify the ranks of coal.
  Total Moisture is the total combination of Inherent Moisture and Free Moisture. In
    general, there will be an indication showing the Total Moisture of coals for delivery. The Total Moisture is the humidity influencing the heating value of coal itself.

                   Humidity              --------->              Low heating value 
                   Low humidity       --------->              High heating value



VOLATILE MATTER means volatile substance (gas and tar) existing in a coal, is a medium that will, at first, causes a coal to catch fire before burning carbon existing in that coal. The coal, which contains high volatile substance content, will catch fire easily and burn rapidly, but the coal, containing low volatile substance content, will be difficult to catch fire and it burns slowly.

Gasification exposes coal to temperatures that would normally cause the coal to combust but by carefully regulating the amount of oxygen in the gasifier and adding steam, the coal does not burn but rather separates into syngas. Syngas is a mixture of carbon monoxide (CO) and hydrogen (H2). The syngas can then be ‘shifted’ with the addition of more steam to produce more hydrogen and to convert the carbon monoxide into carbon dioxide (CO2).

Is mineral residue left over from burning coals. Good quality coals will produce less quantity of ash after burning.

Is an element containing in coals, which causes coals to be burnt and to produce heat
SULFUR or sulphur is a chemical element mixed in coals. This element, after combustion and combining with oxygen (oxidizing) will become sulfur dioxide gas (SO2), which is a toxic gas. Sulfuric content existing in coals will be much or less, depending on the type of coals. Coals bearing high quality, such as ANTRACITE and BITUMINOUS will contain very low sulfur. For SUB – BITUMINOUS, it will contain medium to low sulfuric content. However, all of 3 types of coals will contain lower sulfuric content than the bunker oil. This will cause it to be friendly to environment. As for LIGNITE and PEAT, they contain high sulfuric content.


CALORIFIC VALUE or HEATING VALUE is a heat quantity obtained from complete burning of coal per one weight unit, the heating value units, generally used are Kcal / Kg, KJ/Kg, Btu / lb, and others.
Analysis of coal characteristics
There are 2 ways of coal analysis, namely: Proximate Analysis and Ultimate Analysis.
PROXIMATE ANALYSIS is an analysis conducted for determining contents of
following substances: -
  Fixed Carbon
  Volatile Matter
Such analysis may be used for presenting a report based on following aspects.
As Received” is a heating value obtained from the real usage of coals,
    in which the total humidity is the “Total Moisture”.
  Air – Dried “is a heating value obtained after removal of Free Moisture from coals,
    the remaining value is Inherent Moisture value.
  Dry Basis or Moisture– Free “ is a heating value obtained after deduction
    of Free Moisture and Inherent Moisture values.
Heating value reporting can be done with 3 conditions, such as
  As Received (AR) is a burning or combustion of coals to cause heat to generate during the presence of Total Moisture, it
therefore causes the derived heating value to be minimal. Hence, it is the heating value generated in the real usage.
Calculation for determining the heating value (AR) = Heating value (AD) x (100 - %Total Moisture)  
(100 – %Inherent Moisture)
  Air Dry (AD) is a coal burning to cause heat to generate after drying in oven, in order to remove Free Moisture from coals.
    This will cause heating value to be generated higher than in the condition of “As Received”. However, this heating value will only be obtained in the laboratory.
  Dry Basis (DB) is a coal burning to cause heat to generate after passing coals through the drying in oven, in order
    to remove the entire Free Moisture and Inherent Moisture from coals, this coal combustion, therefore, causes the obtainable heating value to be very high. This heating value will only be derived from laboratory.

Is an analysis conducted for determining chemical composing parts of matters existing in coals, which can be burnt. And the report will be presented in the form of element contents, such as carbon, hydrogen, nitrogen, oxygen and details of compounds existing in ash. Calculation will be made in term of percentage of dried coals, and there will be neither ash nor sulfur left in coals.

          Analysis of this type is not the one regularly conducted, but it is the useful analysis for grouping the types of coal, and useful for calculating the burning or combustion of coals, that is the calculation in determining the air content required for burning, etc.


Coal gasification is also the first half of the indirect coal liquefaction process.

Currently there are 117 modern gasification plants operational worldwide, using 385 gasifiers of various designs – 49% of the total capacity is coal-fed. An additional ten coal-based plants are expected to come on-line in the near future, in North America, Europe and China.
Selection of quality coals for burning effectiveness

Unique Mining Services Public Company Limited has imported the good quality of BITUMINOUS type, having suitable heating value for burning the boilers currently being used, enabling the production of steam to be at low costs, together with low sulfuric content generated, which will result in being friendly to environment.
Coal bearing medium heating value, with ash content 4-6% and its size 20-50 mm., is suitable for using as fuel for the Underfeed Stroker Boiler system

  Coal having medium-high heating value, with ash content 8-10% and its size 19-20 mm. is suitable for being fuel to be used
    for the Travelling Grate Stroker Boiler and Chain – Grate Stroker systems.
  Coal having low-high heating value, with ash content 4-6%, and its size 5-10 mm., is suitable for being fuel to be used with
    the Fluidized Bed Boiler system.
  Coal having medium-high heating value, with ash content 8 – 10 %, and its size 0- 50 mm, is suitable for being fuel to be used
    for the Travelling - Grate Spreader Stroker Boiler system.