Why is the thermal efficiency of the boiler greater than 100%?

First, let's take a look at the two calorific values ​​of fuel: high calorific value and low calorific value.

High calorific value refers to all the heat released when the fuel is completely burned, which includes the latent heat of vaporization released when the water vapor in the flue gas condenses into water. It's like when fuel burns, it not only releases the heat of the flame, but also hides the energy when water vapor condenses.

The low-level calorific value is the caloric value obtained by subtracting the latent heat of vaporization of water vapor in the flue gas from the high-level calorific value. This can be understood as we exclude the heat released when water vapor condenses and only calculate the heat generated by the combustion of the fuel itself.

The relationship between the high-level calorific value and the low-level calorific value can be expressed by a simple equation: the high-level calorific value is equal to the low-level calorific value plus the latent heat of vaporization of water vapor.

In practical applications, the low-level calorific value is closer to the real calorific value of industrial boilers during combustion, so it is often used in design calculations. In other words, the efficiency calculation of the original boiler does not take into account the latent heat of gasification that accounts for about 11% of the exhaust smoke. Usually, the thermal efficiency of a boiler is between 90 and 92%.

Therefore, when using low calorific value to calculate boiler efficiency, if condensation technology is introduced to recover the latent heat of vaporization and part of the sensible heat in the exhaust gas, the efficiency of the boiler may indeed exceed 100%. This is because condensation technology can effectively convert otherwise wasted heat into usable energy, thus improving the energy efficiency of the entire system. But it is worth noting that "efficiency greater than 100%" here does not mean that it violates the law of conservation of energy, but because when calculating efficiency, we use low-level heat generation as the benchmark, and the heat recovered by condensation technology is not included in this benchmark. Therefore, from a practical application perspective, improving boiler efficiency through condensation technology is a feasible and effective energy-saving measure.