Highest In-Service Efficiency
We have developed a new definition of "IN-SERVICE EFFICIENCY" to describe these savings. The Definition is: The resulting efficiency of a boiler when the total operation cycles are taken into account such as day, night, weekends, high loads, low loads, standby loads. It is a comprehensive efficiency which is based upon an operating model and is the "bottom line" efficiency, which should be used in any boiler comparison. It reflects how well a particular boiler design handles a particular operating model.
The basic difference between Boiler Efficiency versus In-Service Efficiency is that the Boiler Efficiency is measured at a fixed fire-rate and includes radiation and convection losses; In-Service Efficiency measures how well a particular boiler design responds from bank firing (idling) to full fire under a projected operating schedule. For example a 100% fire rate - which includes convection and radiation losses (Boiler Efficiency) - the efficiency of a typical fire tube boiler for natural gas at an operating steam pressure of 8 kg/cm2G is about 81%. Drop the fire rate (due to convection + radiation losses) to 25% for the same boiler and the efficiency becomes about 78.5%. Likewise an In-Service Efficiency of a boiler at 100% load, (meaning full fire 24 hours per day, 365 days per year) will be equal to Boiler Efficiency. However,
drop the steam load to 25%, (i.e. full fire for six hours and idling for 18 hours) and the In-Service Efficiency will be much lower than 78.5% efficiency. Idle the boiler to keep it warm and ready to deliver steam upon demand and the In-Service Efficiency becomes zero. In-Service Efficiency is the most conservative approach to efficiency and should be considered in order to project what the bottom line fuel consumption of a boiler should be.
The combustion rate of our Once Through Boiler is set lowest at 30% for the K-L Series and 20% for the K-SE Series. This setting allows continuous operation of the boiler even when there is a low steam requirement. These modes of boiler operation would lead to less purge loss due to the start-stop operation and thereby increase In-Service Efficiency.
If we want to know true fuel savings, it should be based on the In-service efficiency because the above losses should be subtracted from the Boiler Efficiency.