Pushing more through major equipment is one of the keys to successful unit revamps. After years of dormancy, distillation trays have become major areas of success in applying new techniques to increase tower capacities. However, along with the successes have been failures in applying the equipment. Why is this? As equipment is pushed up against the ultimate capacity set by shell diameter tolerance for errors, short cuts, and incomplete knowledge decreases. To successfully maximize capacity requires that we know the process, its characteristics, behavior, and requirements. We must also fully understand the equipment being used, its principles of operation, limits, and capabilities. With proper knowledge, high capacity trays are effective for unit revamps. Without sufficient knowledge, guesswork results in ineffective operation, poor reliability, and unplanned shutdowns.
High capacity trays have been a great advance in moderate to high pressure distillation (above 100 psig). Until now, distillation at higher pressures has been limited to conventional trays or random packing. This has limited through-put for a fixed column to relatively lower rates than that in low pressure distillation where structured packing could be successfully used. Depending on the conditions, high capacity trays can increase unit throughput by 10% to 25% over a good standard tray design. Process including propane-propylene separation, refinery gas plants, and NGL plants have all benefited from this.
Changing from normal to high capacity trays feels, to the process plant, like shifting from a station wagon to a roadster feels to an average driver. The performance (capacity) change is exhilarating, so too are the crashes at 150 mph versus 50 mph. Not everybody needs a sports car to solve their transport problem. The same way, high capacity trays are not for all distillation problems.
What we cover is an introduction to the right way to use the new high capacity trays to improve your plant. This includes some of the major types available, how and why they work, general limitations, and cautionary discussion of what can go wrong.
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