A Comprehensive Guide to Distillation Columns and Energy Efficiency Opportunities
Distillation is one of the most energy-intensive operations in the petroleum refinery. It’s used to separate products from the CDU/VDU or from conversion processes. Heat is provided by process heaters and/or by steam. There are many energy efficiency opportunities available to optimize the distillation column. In this article, we will discuss optimization strategies and technologies to improve distillation column efficiency.
Optimization of the Reflux Ratio
Reflux ratio optimization is one of the most important strategies for improving the efficiency of distillation columns. It involves adjusting the reflux ratio to match the characteristics of the feed. If the characteristics of the feed have changed over time or compared to the design conditions, operational efficiency can be improved. Calculations to derive new optimal operational procedures should be done. The design reflux should be compared with the actual ratios controlled by each shift operator.
Check Product Purity
Many companies tend to excessively purify products, purifying to 98% when 95% is acceptable. To reduce reboiler duties, the reflux rate should be decreased in small increments until the desired purity is obtained.
Seasonal Operating Pressure Adjustments
In locations with winter climates, the operating pressure can be reduced according to a decrease in cooling water temperatures. This operational change will generally not require any investment.
Reducing Reboiler Duty
Reboilers consume a large part of total refinery energy use as part of the distillation process. By using chilled water, the reboiler duty can be lowered by reducing the overhead condenser temperature. A study of using chilled water in a 100,000 bbl/day CDU has led to an estimated fuel saving of 12.2 million Btu/hr for a 5% increase in cooling duty 2.5 million Btu/hr, assuming the use of chilled water with a temperature of 10°C (50°F).
Upgrading Column Internals
Damaged or worn internals can result in increased operation costs. Replacing the trays with new ones or adding a high performance packing can have the column operating like the day it was brought online. When replacing the trays, it may be worthwhile to consider new efficient tray designs, which can result in enhanced separation efficiency and decrease pressure drop.
Stripper Optimization
Steam is injected into the process stream in strippers. Steam strippers are used in various processes, and especially the crude distillation unit (CDU) is a large user. Optimization of these parameters can reduce energy use considerably. This optimization can be part of a process integration for the particular unit.
Conclusion
Optimizing the distillation column can result in significant energy savings. By considering the strategies and technologies discussed in this article, refineries can improve the efficiency of their distillation column and reduce energy consumption.