The refining industry is currently undergoing many changes. The existing refineries are being modernized to stay competitive. These “Brownfield” projects are being designed to upgrade refineries to improve their energy efficiency, maximize throughput and improve product quality. Improvement of energy efficiency, and reduction of operating and maintenance costs are important considerations. Refinery safety and meeting stricter environmental regulations are also key challenges in such upgrade projects. New “Greenfield” refinery projects also face similar complex challenges but in addition must minimize capital expenditures. The operating refineries are continuously trying to reduce manpower but the equipment and operating requirements are becoming increasingly complex. To take advantage of cheaper high sulfur or heavy crude(s), refinery automation must be upgraded to deliver on-spec products. For reliable refinery operation, level measurement and level control is necessary in all refinery units. An average 100,000 barrels per day refinery may have more than 1000 level measurement points. Traditionally, displacers and floats have been used in about 80% of the level applications. Accuracy of these types of level instruments is affected by varying density and temperature which is caused by varying process conditions resulting from different crude types. Such density and temperature variations are present throughout the refinery. Such changes can cause inaccurate level measurements and affect control, which can negatively impact refinery production rates and quality. When considering the upgrade of level instrumentation, refiners are changing from floats, bubblers, capacitance and displacer technologies to lower maintenance and higher accuracy devices. Thus, using technologies that are immune to density changes hold additional value to the refiner and are a key step towards improving measurement accuracy and performance. Finally, refinery safety is of utmost importance. Just as there must be guards against overfilling vessels, the basic level measurement must be reliable, robust and accurate. To accomplish this, instrumentation upgrades are planned with an eye towards higher performance, lower maintenance and higher reliability. No one level technology will work in all applications. Decisions must be made with respect to the required performance, the characteristics of the application, the installation constraints, and the capabilities of the level product. This refinery handbook has been developed to provide the information necessary to understand the available level equipment, where to apply them, and the best practices for their implementation in a refinery.
EMERSON (2009) Level User Guide for the Instrument and Project Engineer in the Refining Industry