A second law analysis to determine the environmental impact of boilers supplied by different fuels

A novel procedure to determine the environmental quality of boilers based on the combustion entropy degradation, the pollutants emission and the device efficiency is proposed. The entropy generation due to the chemical reaction was determined and then the irreversibilities on the external environment were first quantified. Successively, the entropy generation numbers of the combustion reactions were combined with the heat transfer process entropy generation of the boilers to consider the actual functioning conditions, in order to quantify the environmental damages by introducing an Environment Quality Index (EQI). A parametric study varying the heat exchanger efficiency, fluid flow rates and temperatures, for different fuel typologies, was performed to assess the environmental impact. Solar hydrogen was considered for its importance as future renewable energy carrier. The results showed that the highest EQI was produced by the natural gas, but if heat exchanger parameters are defined opportunely, the score gap with other fluids can be recovered. For hydrogen and coal decreasing the flue gases temperature or by increasing the flue gases mass flow rate can strongly improve the EQI index, whereas the gap recovery for Diesel is rather difficult.