Sasol faced the challenge of improving process operations and reducing costs of its naphtha hydrotreater unit. The Synfuels facility operated a cascade loop between the inter-bed temperature transmitter and a hydrogen quench flow controller at its naphtha hydrotreater unit in manual as a result of the inability of standard PID control to handle the process dead time.
The company needed an effective method to maintain the temperature as it was a key parameter for the process to run close to the specification on final naphtha nitrogen and phenol content. Another challenge was that the installation of the software needed to be completed while the process was running - downtime was not an option available to consider.
Solution
Sasol opted for a trial version of Honeywell's Profit Loop technology to help optimise control of the naphtha hydrotreater unit temperature. The controller uses a simple model of the process to predict the effect of past, present and future control moves on the process variable. Because Profit Loop can anticipate future process behaviour, the controller knows exactly how much to move the process in order to meet the desired control objectives. The Profit Loop algorithm capabilities enable the easy replacement and online migration to this new technology. The controller configuration is similar to PID, but has a superior algorithm and is easier to tune and maintain than a conventional controller.
The software was installed and commissioned (while the plant was running) in less than 20 minutes. With migration to the new control technology, the system was now equipped to handle difficult process dynamics beyond the scope of a traditional PID controller.
The newly commissioned controller successfully kept the temperature within 1,5°C of set-point, yielding a performance better than any control previously attempted on this loop. Sasol was able to reduce the hydrogen consumption on the unit resulting in benefits that covered the cost of purchasing a site-wide licence for the software.
With Profit Loop, Sasol was able to:
* Improve loop operation and significantly reduce energy costs.
* Start using the tool without any training.
* Improve plant efficiency and product quality.
* Eliminate PID-related control tuning, software and services.
* Reduce maintenance costs.
* Use a more powerful algorithm without any CPU upgrade.
Profit Loop is Honeywell’s patented regulatory control algorithm that functions as a single input/single output (SISO) model predictive controller – specifically designed with the operating simplicity and computational efficiency of a standard PID controller. The technology is based on Honeywell’s patented robust multivariable predictive control technology (RMPCT).
Since Profit Loop can also be applied to virtually any regulatory control problem (temperatures, pressures, flows, discrete analysers, tank levels (loose and tight control), as well as complex dynamics and process delays), the need and expense of loop tuning packages and services is eliminated.
For more information contact Julie Brown, Honeywell Southern Africa, +27 (0)11 695 8000, [email protected]
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