Online Monitoring Highlights Deterioration in Desalter Performance & Direct Linkage to Upset Overhead Conditions
Effectively managing desalters and overhead corrosion control programmes can be a challenge; the combination of frequent crude changes with significant batch to batch variation make good control difficult. Coupled with process variability and the typical low frequency of measurements, the reality is that good control is difficult to achieve and there is total ignorance about what is happening in the intervening periods between measurements.
90% of Overhead Corrosion can happen in as little as 10% of the time.
A Gulf Coast Refiner installed the Nalco Water Online Salt Analyzer (OSA) at the desalted crude outlet of a crude unit, complimenting the 3D TRASARTM Technology for Crude Overhead Systems (3DTCOS) that was already installed on the unit. Both inorganic and organic chlorine were detected by the OSA, providing real-time chlorine measurements, ensuring that upsets can be detected quickly and mitigating actions taken whilst enabling ongoing desalter performance to meet critical KPI’s.
The refiner operated in total ignorance between measurements and was often unaware of the impact even the smallest upset can cause. Shortly after commissioning the OSA, the refinery experienced an issue with one of the two fired heaters and as a consequence, had to reduce feed rates. Upon reducing feed rate, the OSA began to show a sharp increase in salt exiting the desalter with the 3DTCOS showing an increase in overhead chlorides.
The online analyzers alerted Operations to the increases, and it was quickly determined that the reduction in feed rate resulted in a reduction in the mix valve dP that impacted desalting efficiency. Once this was recognized, the mix valve dP was increase and the salt in crude and overhead chlorides reduced almost immediately, returning to typical levels.
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