What is wrong (or not) with the following actual boiler measurements?
- Feedwater conductivity setpoint › 2,500 microsiemens (µS)
- Feedwater conductivity > 2,550 µS
- Drum level setpoint > 50 percent
- Drum level > 47 percent
- Feedwater flow > 4,100 liters per minute
- Steam flow > 46 metric tons (MT)/hr
The feedwater conductivity and drum level are near their respective setpoints and are likely operating properly. Water chemistry and historical charts should be examined to confirm this presumption.
The density of cold water is approximately 1 gram per cubic centimeter (g/cc), so the operating density of hot feedwater would be lower (say 0.9 g/cc), and the feedwater flow would be approximately 0.9 x 100 x 60, or 5,400 kilograms per hour (5.4 MT/h).
By observation, the steam flow is higher than the feedwater flow. This cannot occur, so something is incorrect. Flowmeters that measure steam are typically less reliable than flowmeters that measure hot water, so (absent other information) the operation of the steam flowmeter should be investigated.
Additional complicating factors
Further investigation should be undertaken to determine the expected steam to feedwater flow ratio typical of the installed feedwater treatment system. Knowing the expected ratio will make it easier to know when the investigation reveals the problem.
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes LLC, which offers engineering, seminars, strategic, marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. He has more than 40 years of experience and has written more than 10 books and 350 articles about flow measurement, instrumentation and process control.
Spitzer may be reached at 845-623-1830 or via spitzerandboyes.com. Click on the "Products" tab to find his Consumer Guides to various flow and level measurement technologies.