Energy Efficiency Indicators
The energy efficiency indicators of the steam boiler are crucial for a power plant to make the best use of its capacity. They allow to identify abnormal operational deviations in order to implement corrective actions. However, they do not take into account the ON-OFF losses, heat radiation and convection losses and more, which are not reflected by the fuel-to-steam efficiencies. This is why the energy performance evaluation of the entire boiler system — and not just its thermal efficiency — is crucial to optimize energy usage.
The main energy efficiency indicators of the Energy Efficient Steam Boiler are its stack gas temperature, water-from-fuel loss and unburned carbon in the residue (fuel reactivity). These factors depend on the technology type and the combustion processes used in the boiler. The stack gas temperature is the key factor, since it influences the dry matter and water content of flue gases. In addition, it has a strong influence on the combustible fraction of the fuel (as a function of the combustion air volume) and the overall fuel utilization (as a function of the excess air percentage).
Water loss from the steam turbine is also important for determining boiler energy efficiency. A large portion of the energy is lost due to leakage through the steam turbine, piping and other equipment. It is also important to consider the steam turbine’s own energy requirements, which are a function of its own internal pressure and speed.
Energy Efficiency Indicators of the Steam Boiler
Another major source of energy loss is the heat transfer in the boiler, which can be caused by scale build up and corrosion. In addition, a considerable amount of energy is wasted in the blowdown process, which is needed to maintain the proper water levels of conductivity, TDS, alkalinity, silica and acidity. The use of waste heat from the blowdown system to preheat the boiler feed water can reduce this energy loss by about 1%.
On the other hand, energy consumption can be reduced by adjusting the blowdown rate to match the system’s load profile. This can lead to a savings of up to 3% of the gross steam production.
Finally, the emissions of noxious gases are another important aspect for determining boiler efficiency. These gases are the products of incomplete combustion and include nitrogen oxides, sulfur oxides and volatile organic compounds. The portion of these pollutants in the emission gases depends on the quality of the fuel, its purity and pollutant ingredients, the combustion process and the control systems.
These factors may seem complicated to calculate, but they can be simplified using a standard calculation method such as the DIN 1942 acceptance test. This calculation can be used to compare the performances of different steam generators and make wise purchasing decisions. It also helps with the implementation of technical-organizational measures in order to improve the steam boiler’s energy efficiency. This is in contrast to AFUE which evaluates the boiler’s performance under optimal conditions only and is not a good indicator of actual usage.