|David W. Spitzer|
This is the final article in a series based on the troubleshooting of a mysterious unit shutdown due to flowmeter performance problems.
RELATED: Read Part IX in the “Troubleshooting Operational Isssues” Series
If you’ve followed this column for most of 2014, you know that what should have been a liquid ammonia stream to the feed plant became problematic due to the occurrence of bubbles of ammonia gas. These bubbles caused an ultrasonic flowmeter in a unit to indicate zero flow and caused the reactor to scram (shut down) under warm operating conditions. The source of the bubbles was traced back to the pressure drop associated with a control valve located at the exit of the liquid ammonia tank farm.
This issue was resolved by identifying the problem and fixing it at its source. This was a pragmatic approach at the time (early 1980s) given the operation of the cooling system in the unit and the limited selection of applicable flowmeter technologies.
By the early 1990s, changes were implemented that eliminated all process cooling requirements—except for the small jacketed cooler upstream of the liquid ammonia flowmeter. In other words, after these changes, the entire cooling system would be operated and maintained to cool a few meters of one small ammonia pipe. Coincidently, at about the same time, Coriolis mass flowmeters became more mature and could reasonably measure the mass flow of liquid streams with homogeneous low levels of vapor.
The convergence of these two events resulted in another approach to the problem that was not available in the early 1980s—i.e., install a Coriolis flowmeter that could operate in the presence of bubbles. The purchase and installation of a Coriolis mass flowmeter was given high priority given its impact on unit operation, economics and safety (by eliminating the “midget-maker” (see March 2014, page 14)).
Plant requirements and the technology that can meet plant needs keep changing. An excellent solution today can become outdated in just a few years. However, there are few substitutes for understanding fundamentals when addressing a problem. In other words, there can be more than one way to skin a cat.
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC offering 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.