Calorific Value

What is Calorific Value?

Calorific Value is the parameter necessary for defining the energetic content of the materials; it is referred to as the gross calorific value (GCV) or high heating value. Also represented as the absolute value of the specific energy of combustion for a unit mass of a substance (generally, solid biofuel or food). The unit of calorific value is KJ/kg (kilojoule per kilogram).

The efficiency of fuel of food is dependent on the calorific value; higher the value, higher the efficiency, and similarly lower the calorific value, lower is the efficiency. Therefore, it can be said that the calorific value of a substance is directly related to or proportional to its efficiency. Also, water vapor that is generated in the combustion process contains heat and if it is recovered through different techniques, the substance will have higher calorific value (GCV) and vice versa when it results in lower or Net calorific value (NCV). NCV is the result when the products of combustion are allowed to escape. 

Which Fuel Has the Highest Calorific Value?

A good fuel is considered to have higher calorific value. For example, LPG, Petrol, Kerosene, and Biogas are considered to be suitable fuels having higher to lower calorific value in descending order with LPG having the highest calorific value. It is also fundamental for defining the commercial value of the substance and is the most important characteristic to establish the price of the solid biomass. 

Calorific Value Definition

“Calorific value can be defined as the amount of heat produced as a result of the complete combustion of a unit volume of the substance.” 

How to Calculate Calorific Value 

With the above understanding of calorific value, we can write the calorific value formula as follows-

Calorific Value Formula

Net calorific value (NCV) = Gross calorific value (GCV) - Latent heat of water vapors

OR

Gross calorific value = Net calorific value + Latent heat of water vapors

Calorific Value of Food

A food calorific value is calculated in terms of kilocalorie which is defined as the amount of energy required to raise the temperature of one litre of water by 1 degree. The energy value of food represents the value as a fuel to the body. This may be less than the heat value obtained with the help of experiments where food is burnt outside the body with the help of a bomb calorimeter. It is so because some of the food’s energy may be 'lost' during digestion and metabolism inside the body. As food also contains fiber components, it is usually subtracted from the total carbohydrate, fat, protein, or alcohol. It is found out that by burning all these energy-containing nutrients, the average values for-

Protein is 4 Kcal/gram

Carbohydrate is 4 Kcal/gram

Fat is 9 Kcal/gm

Alcohol is 7 Kcal/gm

It is mentioned below in the form of a chart where the calorific value of food is numbered in KJ/gm as well as Kcal/gm. Fat is the most energy-rich macronutrient, which is then followed by alcohol, protein, and carbohydrate.

Macronutrient

Kilojoules Per Gram

Kilocalories Per Gram

Fat

37

9

Alcohol

29

7

Protein

17

4

Carbohydrate

16

4

What is the Calorific Value of Fuel?

When we burn coal, petroleum, diesel, kerosene, or any flammable gas, it is capable of generating electricity in the thermal power generating plants. So, the best fuel to generate electricity depends on its quality which is determined by the calorific value of a fuel. So, the question is- ‘what is the calorific value of a fuel’? The calorific value of fuel can be defined as the amount of heat produced by the complete combustion of one unit of any fuel. The unit depends upon the type of fuel, for example, coal is a solid fuel so it is measured in weight units whereas we use volume units for any gaseous or liquid fuel. Therefore, the calorific value for them will be measured in Kilocalorie per Kilogram and Kilocalorie per Litre, respectively.

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In the chart above, the calorific value of different fuels have been drawn where Petrol, Diesel and Heavy Oil have their calorific values in a similar range, i.e. 11,000 Kcal per Kg. However, studies have shown that Petrol is having the maximum one. Anthracite coal and coal gas have 8500 kcal per kg and 76000 Kcal per cubic meters respectively. Bituminous coal has 7600 Kcal per kg whereas Lignite has 5000 Kcal per kg. Natural gas has 560 Kcal per cubic meters.

Significance of Calorific Value 

Since fuels and foods are parts and parcels of our lives that we use at every hour and seconds of time, it is essential to keep a track of the amount of energy we consume or transport. Having a knowledge of the calorific value of fuels and food, it helps us to undertake easy calculations that the gas suppliers and shippers will need to bill gas consumers. Also, it helps in determining the transportation charges; on the other hand, calorific value calculation of food will help in guiding people about a balanced calorie or food consumption to remain healthy. Food with too little or too high calorific value may lead to health problems, so it should be kept in mind that the body will be able to carry out daily activities and will remain fit if calories are consumed in a specific range. 

FAQ (Frequently Asked Questions)

1.  What is Calorific Value and Why is It Important?

Calorific value is the energy or amount of heat produced as a result of the complete combustion of a unit volume of the substance. It is important as it gives the value of fuel or food in numbers which can be calculated with a formula. As fuels and food are daily consumed by humans, it is important to track their usage and also is significant in financial and health terms. 

2. How to Calculate Calorific Value of Fuel?

There are standard conditions under which the calorific value of the fuel is calculated. Gross calorific value (GCV) and net calorific value (NCV) are the terms used in the formula to calculate calorific value of fuel. Latent heat escaped (in form of water vapor) is subtracted from the Gross calorific value to get the Net calorific value.