【Daily Question】12.11 True or False: For the same fuel, its high calorific value is lower than its low calorific value

Incorrect: The water content in products with a high calorific value is calculated based on condensation, while the water content in products with a low calorific value is calculated based on water vapor. For combustion purposes, the low calorific value is more relevant.

Incorrect, because the high calorific value includes the heat released from the condensation of water vapor produced during combustion, whereas the low calorific value does not include this amount of heat; therefore, the high calorific value is higher than the low calorific value

The heat released when a unit weight or volume of fuel burns completely is known as the calorific value of the fuel, with units of J/kg or J/Nm3. Liquid fuels are usually expressed in terms of their weight calorific value, while gas fuels are typically expressed in terms of their volume calorific value. Depending on the state of moisture in the fuel products, the calorific value is divided into high calorific value and low calorific value. The high calorific value refers to the sum of the heat of combustion of the fuel and the latent heat of condensation of water vapor in the combustion products; whereas the low calorific value represents only the heat of combustion of the fuel, without including the latent heat of condensation of water vapor. Obviously, for the same fuel, its high calorific value is greater than its low calorific value. In the calculation of heating furnace combustion and fuel consumption, since the moisture in the combustion products is usually released into the atmosphere in gaseous form, a low calorific value should be used as the basis for calculation. In the estimation of fuel oil consumption for heating furnaces, 10,000 kcal/kg of fuel (41.9*103 J/kg of fuel) is often used as the low calorific value of the fuel.

Both the high and low calorific values represent the heat released upon the combustion of a fuel. The difference between them lies in whether the combustion products are calculated based on water or water vapor; since water vapor releases additional heat when it turns into water, the high calorific value is calculated based on the formation of water, while the low calorific value is calculated based on the formation of water vapor. Generally, the low calorific value is used, as water vapor is produced directly rather than water, and the heat generated during the conversion of water vapor to water is hardly utilized. The high calorific value therefore has little practical significance

For the same fuel, its high calorific value is lower than its low calorific value

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