There probably isn’t a process engineer in the world who hasn’t received a request or order from management saying: “We need to increase throughput. Figure out how to do it without any major capital improvements.” When there is market demand that is going unfilled, such a request is understandable, and incremental production increases tend to be very profitable since most costs have already been covered. The question is how to fulfill such a request, because if our engineer is worth his or her salt, the plant is probably already running as close to maximum as practical.
Christiane Lederer examines this very situation in her article titled Safely Maximizing Production Capacity with Wireless Corrosion Sensors in the July 2019 issue of Flow Control. She explores what can happen, and what has happened, when companies try to get that extra bit from existing equipment.
Vessels, burners, pipes, pumps, valves and other process and control equipment are sized and selected to handle the types of feedstock and production volumes the plant operator originally envisioned. As a result, it is not easy to make major changes in output or accommodate feedstocks with different characteristics. Unfortunately, in the real world, plants are often called upon to make these kinds of changes. This often requires changing equipment configurations to relieve some of the tightest bottlenecks.
Simply opening valves and running pumps faster can probably get more product through the process, but as Christiane points out, it’s hard to make reactions act more quickly or increase the heat transfer of a boiler. Other tactics to increase profitability might include using cheaper feedstocks to lower costs, even if they have problematic side effects.
Opportunity crudes used as refinery feedstocks are usually inexpensive for a reason: They often contain contaminants in the form of sediment or acids that can increase equipment wear, corrosion and erosion rates. For example, the alloys selected for piping and vessels when the refinery was built will have reflected the feedstocks expected at the time. Light, sweet crudes can work well with inexpensive carbon steel piping, but high total acid number (TAN) crudes can cause far more rapid metal loss.
She goes on to cite a specific project where management called for more throughput and operators had no choice but to give it a try. The plant engineers tried to figure out what would happen and it looked like it might just work. The article goes into more detail, but eventually running hard caught up with the plant, with the first problem a header.
A problem revealed when the increased liquid velocity caused by the higher flow rate resulted in erosion in the complex header created to join the outlets of the air-cooled heat exchangers. At this point, the eight individual heat exchanger outlets had to be joined into one. One day, operators discovered a plume of liquid propane with high H2S content shooting out of a newly formed leak in the header, creating serious safety and environmental issues, not to mention product loss.
Obviously, once the leak was patched, the engineers had to determine if the header was about to break into pieces, or if this leak was the result of a poor-quality weld performed many years earlier. They had to figure out how to assess the header’s condition as quickly as possible.
To determine the existing header’s condition, the evaluation team installed five ultrasonic wall thickness sensors at strategic points where the liquid streams passed through different velocity stages. The total sensor installation project costs were approximately 25,000 €; however, given the production value of the unit at about 1 million € per day, it was regarded as a minor expense.
The sensors were from Emerson’s Corrosion & Erosion Monitoring solutions (formerly known as Permasense) which are designed to monitor pipes and vessel walls for metal loss due to corrosion or erosion from the inside. In this case, the engineers determined it was a combination of effects due to higher liquid velocities combined with higher H2S content. Nonetheless, the header proved to be in better condition than initially feared. Operators were able to begin fabrication of a stainless steel replacement without paying rush charges, and the plant was able to carry on until the next scheduled turnaround. Crisis averted.
Such sensors can be used in a wide variety of applications to provide very precise, real-time analysis of your equipment, whether it’s being pushed beyond limits or running exactly as intended. They are easy to install and communicate via WirelessHART, so there is no wiring needed.
You can find more information like this and meet with other people looking at the same kinds of situations at Emerson Exchange and in the Emerson Exchange 365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Oil & Gas and IIoT Groups, and other specialty areas for suggestions and answers.
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