X

Calorific Value of Coal and Wood Calculations

What is Calorific Value or Heating Value?

  • The calorific value is used to find the amount of heat energy produced after the complete combustion of one kg of fuel.

Gross Calorific Values (GCV/HHV)

  • Gross calorific value (GCV)  is  also called as a higher Heating Value (HCV)
  • It measures the amount of heat released by the complete combustion of a unit of fuel. GCV considers that all water vapor (H2O) produced during the combustion process is fully condensed
  • The flue gas formed from combustion is condensed during waste heat recovery and water condensate is formed.
  • In such cases as coal-fired boilers, the GCV value is used to find out the firing capacity.

The formula for Higher Heating value or  GCV

Dulong’s formula  is used to calculate  the  GCV (Kcal/kg) of coal

        GCV  = 1/100* (8080*C + 34500* (H – O/8)+ 2240*S)   Kcal/kg

where C, H, O, and S are percentages of carbon, hydrogen, oxygen, and sulfur  in coal

Net Calorific Value (NCV)

  • It is called a lower heating value (LHV) or lower calorific value (LCV)
  • Its value is calculated by subtracting the latent heat of vaporization of the water vapor from the higher heating value (HHV)
  • It assumes water vapor leaves with the combustion products is the gas phase that it is not condensed
  • For furnaces firing with gaseous fuel, a lower heating value is used to find the firing capacity.
  • The flue gas formed from combustion is not further condensed.

Formula for LCV

     LCV =  GCV – 9/100*H*587  Kcal/kg

where H  is the percentage of carbon, hydrogen, oxygen, and sulfur  in coal

Note:

  • The higher heating value (HHV) of fuel is calculated when the product of water is in the liquid phase.
  • The Lower heating value (LHV) is calculated when the product of water is in the vapor (gas) phase
  • Refer to the basics of combustion for more details in the post

GCV and LCV Calculator

 

[stm-calc id=”3485″]

 

Calculation of Heating Value of Wood and Coal

  • The heating value of wood and coal can vary depending on factors such as species of wood, moisture content, and type of coal.
  • Heating value is typically measured in British Thermal Units (BTUs) per pound or kilogram.

Wood:

  • The heating value of wood can range widely depending on the type of wood and its moisture content.
  • Dry wood typically has a higher heating value than wet wood because the energy is not spent evaporating moisture.
  • Dry hardwoods generally have a higher heating value compared to softwoods.
  • On average, dry wood can have a heating value ranging from about 7,000 to 9,000 BTUs per pound (15,000 to 20,000 kJ/kg).
  • Softwoods tend to be on the lower end of this range, while hardwoods are generally on the higher end.
  • The heating value of wood can be calculated using the formula:

                    LHV

Where:

    • is the heating value of wood (in units of energy per unit mass or volume, such as BTU/lb or MJ/kg).
    • is the moisture content of the wood (expressed as a decimal).
    • is the higher heating value of the dry wood.
    • is the moisture content of the water (expressed as a decimal).
    • The higher heating value ) of dry wood is typically measured experimentally and can vary depending on the type of wood and other factors. It represents the total amount of heat released when the wood is completely combusted, assuming that the water vapor produced during combustion is condensed and the latent heat of vaporization is recovered.
    • The moisture content () of the wood is usually determined by weighing a sample of wood, drying it to remove all moisture, and then reweighing it. The difference in weight is used to calculate the moisture content as a percentage of the original weight.
    • The moisture content of the water () is the moisture content of the wood’s water, which is usually close to 1 (since water is typically 100% water).
  • Using this formula, you can calculate the heating value of wood given its moisture content and the higher heating value of the dry wood.

Here is a table showing the heating value of different types of biomass in megajoules (MJ):

Heating Value of Biomass Fuels

Biomass Type Lower Heating Value (LHV) (MJ/kg) Higher Heating Value (HHV) (MJ/kg)
Wood (Dry) 14 – 18 18 – 20
Wood Chips (50% Moisture) 7 – 10 10 – 12
Sawdust (Dry) 15 – 17 18 – 20
Bamboo 16 – 18 18 – 20
Rice Husk 12 – 15 15 – 18
Wheat Straw 13 – 16 15 – 18
Corn Stover 14 – 17 17 – 19
Sugarcane Bagasse (50% Moisture) 6 – 10 10 – 12
Coconut Shell 18 – 20 20 – 22
Palm Kernel Shell 17 – 19 19 – 22
Peanut Shell 15 – 18 18 – 20
Sunflower Husk 16 – 18 18 – 20
Cow Dung (Dry) 12 – 15 14 – 16
Biomass Pellets 16 – 19 18 – 21
Bamboo Pellets 17 – 19 19 – 21
Charcoal 28 – 32 30 – 35

Notes:

  • HHV (Higher Heating Value) includes the energy from water vapor condensation.
  • LHV (Lower Heating Value) excludes the latent heat of water vaporization.
  • Moisture content significantly affects the heating value of biomass.

Calorific value of Biomss: woods and coal in Kcal/kg

  • Here’s a table listing the approximate calorific values of various types of wood and coal. These values may vary slightly depending on moisture content and other factors.
Fuel Type Calorific Value (kcal/kg) Remarks
Wood (dry) 3,500–4,500 Dependent on species and dryness
Wood (wet) 2,000–3,000 Higher moisture reduces efficiency
Hardwood (e.g., Oak) 4,000–4,500 Dense woods, high energy content
Softwood (e.g., Pine) 3,000–4,000 Lower density than hardwood
Bamboo 4,000–4,500 Renewable and high calorific value
Coal Types
Anthracite 7,800–8,000 High carbon content, low moisture
Bituminous Coal 5,500–8,000 Versatile use, moderate impurities
Sub-Bituminous Coal 4,500–5,500 Lower sulfur, used for electricity
Lignite 2,500–3,500 Low energy, high moisture content
Peat 1,500–3,000 Early stage of coal formation

Calorific value of woods and coal in Btu /hr

  • Here’s a table listing the calorific values of various types of wood and coal in BTU per pound (Btu/lb).
  • To convert from kcal/kg to Btu/lb, multiply the kcal/kg value by 1.8 (approximate conversion factor).
Fuel Type Calorific Value (Btu/lb) Remarks
Wood (dry) 6,300–8,100 Dependent on species and dryness
Wood (wet) 3,600–5,400 Higher moisture reduces efficiency
Hardwood (e.g., Oak) 7,200–8,100 Dense woods, high energy content
Softwood (e.g., Pine) 5,400–7,200 Lower density than hardwood
Bamboo 7,200–8,100 Renewable and high calorific value
Coal Types
Anthracite 14,040–14,400 High carbon content, low moisture
Bituminous Coal 9,900–14,400 Versatile use, moderate impurities
Sub-Bituminous Coal 8,100–9,900 Lower sulfur, used for electricity
Lignite 4,500–6,300 Low energy, high moisture content
Peat 2,700–5,400 Early stage of coal formation

Notes:

  • 1 kcal/kg ≈ 1.8 Btu/lb.
  • Hardwood vs. Softwood: Hardwoods typically produce more heat and burn longer than softwoods.
  • Coal: As the rank increases from lignite to anthracite, the energy density (Btu/lb) also increases
  • Dry vs. Wet Wood: Moisture content significantly affects the calorific value of wood. Always consider using well-seasoned wood for better efficiency
  • Coal: Calorific value increases with coal rank, from lignite (lowest) to anthracite (highest)
  • Applications: Hardwood is preferred for domestic heating, while softwood is common for quick burning.

Coals Heating Value

  • Coal is classified into different types such as anthracite, bituminous, sub-bituminous, and lignite, each with varying heating values. Anthracite coal has the highest heating value among coals, followed by bituminous coal, sub-bituminous coal, and lignite, in that order.
  • Anthracite Coal:
    • The heating value of anthracite coal can range is given as below
    • Imperial Units:
      • 24 to 35 million BTUs per ton
      • 12,000 to 17,500 BTUs per pound
    • SI Units: 24,000 to 35,000 kJ/kg.
  • BituminSI Unious Coal:
    • Bituminous coal generally has a heating value ranging below
      • 20 to 28 million BTUs per ton
      • 10,000 to 14,000 BTUs per pound
    • SI Units: 20,000 to 28,000 kJ/kg.
  • Sub-bituminous Coal:
    • Sub-bituminous coal typically has a heating value range given below
    • Imperial units:
      • 17 to 24 million BTUs per ton
      • 8,500 to 12,000 BTUs per pound
    • SI Units: 17,000 to 24,000 kJ/kg.
  • Lignite Coal:
    • Lignite coal has the lowest heating value among coals, ranging as below
    • Imperial Units:
      • 8 to 17 million BTUs per ton
      • 4,000 to 8,500 BTUs per pound
    • SI Units: 8,000 to 17,000 kJ/kg.
  • Note these values are approximate and can vary depending on the specific composition and quality of the wood or coal.
  • It’s essential to consider the specific type and condition of the material when calculating its heating value for practical applications like combustion or energy generation.
  • For more information  of biomass pellet and applications, you can refer in the post

Application of of CFD for  biomass combustion Calculations

  • Refer Articles for Biomass like pellet and briquette used for domestic cooking. Various biomass stoves or furnace have been used in food and processing industries.
  • The scope of Computational Fluid Dynamics (CFD) for biomass combustion is vast and encompasses various applications in both industrial and research fields. Here’s an overview
  • Design and Optimization of Biomass Combustion Systems
    • CFD can model and optimize biomass combustion systems such as boilers, furnaces, and stoves.
    • It helps improve combustion efficiency, reduce pollutant emissions, and optimize fuel utilization.
    • CFD tools can simulate the airflow, temperature distribution, and combustion reactions.
  • CFD modeling and process design is required to evaluate the biomass fuels and stove parameters