The unit of solid or liquid calorific value is kilocalories/kg (kcal/kg), kilojoules/kg (KJ/kg) or megacalories/kg (Mcal/kg), megajoules per kilogram (MJ/kg); gas The calorific value of the fuel is kcal/standard cubic meter (kcal/Nm3), kilojoules/standard cubic meter (KJ/Nm3) or megacard/standard cubic meter (Mcal/Nm3), megajoules/standard cubic meter ( MJ/Nm3). The fuel calorific value has two types of high calorific value and low calorific value.
The high calorific value refers to the total amount of heat released by the fuel when it is completely burned, that is, the calorific value when the water vapor in the combustion product condenses into water, which is also called hair heat.
Low calorific value
The low calorific value refers to the calorific value of the fuel when the fuel is completely combusted, and the water vapor in the combustion product is in the gaseous state, which is also called net heat.
The difference between the high calorific value and the low calorific value is whether the water in the fuel combustion product is liquid or gaseous, the water in the liquid state is the high calorific value, and the water in the gaseous state is the low calorific value. The low calorific value is equal to the condensation heat from which the water vapor is deducted from the high calorific value.
Most of the fuel is used for combustion. The exhaust temperature of various kiln exceeds the condensation temperature of water vapor, and it is impossible to release the condensation heat of water vapor. Therefore, in the energy utilization, the low heat generation of the fuel is generally used as the calculation. basis. Different countries have different choices. Japan and North America are accustomed to using high calorific value, while China, the former Soviet Union, Germany, and the Organization for Economic Co-operation and Development are converted to low calorific value, and some countries use both calorific values.
The high and low calorific values of coal and oil differ by about 5%, and natural gas and gas are about 10%.