Previous situation

During an energy audit carried out at a paper company, combustion measurements were taken in the main natural gas steam boilers. The significant increase in free oxygen levels after the steam air preheater was immediately identified, increasing from values ​​below 2% in the combustion gases at the boiler outlet to almost 10% in the gases after passing through the air economizer. Given this situation, the exhaust gas temperature decreases due to the intake of false air, reaching ambient temperature since the air heater was out of service. Because less air enters the burners, the forced draft (FD) fans controlled by variable frequency drives must operate at a higher frequency to maintain the necessary airflow. 🌪️.

This generates a double energy expenditure: on the one hand, a higher consumption of natural gas in the boilers because the combustion air is not preheated and, on the other hand, a higher electricity consumption in the fan motor because it has to send more air than necessary.

The solution

These two inefficiencies were mitigated by completely replacing the deteriorated economizer tubes in one boiler and putting the steam air preheater into service. Thanks to this intervention, the thermal efficiency of the boiler was increased by 1.8% under high loads 🔥. For the same fuel consumption, it allowed for the generation of a greater quantity of steam available for the process. Regarding the fan motors, since they already had frequency converters, their consumption was reduced by half.