If you’re unfamiliar with the phrase “heat rate” used in the electrical power generation industry, it means the amount of heat energy in BTUs as input to the turbine generators divided by the amount of electricity generated in kilowatts. Accurate level measurement in the boiler drums and feedwater heaters is critical to optimize efficiency and run the turbines reliably over time.In a Processing magazine article, Overcoming Level Gauging Challenges in Boilers, Emerson’s Matthew Brummer provides an excellent overview of large boiler operations and how to improve operations. If you’re new to this type of process or have curiosity about it, the article is well worth your time to read.
When steam comes out of the exhaust vent of a turbine, it goes into a condenser where it is sufficiently cooled to condense back into water… This creates a negative pressure on the back side of the turbine as well as a larger pressure differential from the inlet, which helps prepare the water to be sent back to the boiler and used again.
Boiler efficiency is increased when the water from condensed steam is heated in the feedwater heater. For maximum heat transfer and efficiency:
…the steam should condense fully within the heater, so there should be some water accumulation inside. Any steam blown out represents unrecovered heat, and the water accumulation helps protect against tube leaks, so some condensate within a specific level range is desirable.
Too much condensation reduces efficiency, and if too excessive:
…it also can cause condensate to back up all the way to the turbine, blasting water into the blades along with steam. This can damage the blades and reduce turbine life, potentially causing catastrophic failure of the turbine.
Accurate level control is critical. The traditional approach of differential pressure (DP) level measurement has its accuracy affected by changes in density.
Guided wave radar (GWR) technology, such as the Rosemount Model 5300 GWR, has several advantages in this application:
- Level measurement independent of density changes
- Able to withstand the high temperatures and pressures characteristic of the application
- No moving parts
- No need for ongoing calibrations or zeroing
- Largely unaffected by changes within the vapor space
Matt described a plant that switched to GWR technology: The plant:
…recognized a 2ºF increase across the single heater in the train. The plant upgraded the other two heaters in the same way to gain a 6ºF improvement across the train. For this plant, a 6ºF increase reduced the heat rate by 13.4 Btu/kWh, or about 0.12 percent. This might not sound like much, but for a 500-MW unit, it translated into cost savings in excess of $70,000 per year, resulting in a pay-back time of eight months. Extrapolating the solution to the whole plant would result in approximately $200,000 in savings each year.
Read the article for more on the second application he described in maintaining boiler drum stability to reduce unplanned downtime and increase overall efficiency.
You can connect and interact with other level measurement experts in the Level group in the Emerson Exchange 365 community.