Inlet Devices, Gas Demisting Devices Are Keys to Improving Scrubber Performance
The SPE Separations Technology Technical Section continued its series of webinars on scrubber design and internal technologies with a presentation on the devices being tested and implemented by operating companies to improve inline separation and scrubber performance.
In his presentation, titled “Scrubbers: Advances in High Capacity Scrubber Internals and Performance Boosting With Inline Pre-Separation,” Danny Thierens looked at recent developments in inlet device and gas demisting technology. Thierens, a global key account manager of upstream at Sulzer, also explained how to enhance separation efficiency by using an inline cyclonic separator as a pre-separator upstream of the scrubber.
Thierens highlighted recent improvements in inlet device technology, primarily those that have improved inlet distribution to the gas demisting device and minimized the amount of liquid entrained in the feed stream pre-separation.
He said improper inlet distribution may lead to the formation of localized high-velocity spots in the demister and the re-entrainment of liquids to the downstream separation process, while a decrease in pre-separation liquid would lighten the workload of the gas demisting internals and allow for optimization of the scrubber.
Feed conditions are among the primary parameters that factor into the design of current inlet devices. Thierens defined these properties as the flow rate and density at the operating pressure and temperature of the gas and liquid phase, and the viscosity and surface tension of the liquid. He said the size and geometry of the upstream piping and scrubber inlet nozzle were also important factors.
“There are certain guidelines given for minimizing the number of bends upstream of the inlet nozzle and having piping of a sufficient size. So, you should not use an expansion section ahead of the inlet nozzle, but rather have an entire section of upstream piping of the same size to allow for some flow profile stabilization,” Thierens said.
An example of the new technology is Shell’s Schoepentoeter Plus, an inlet vane device with catching rims designed to capture additional liquid and minimize re-entrainment.
Current gas demisting technologies have improved the processing capacity of the demisters and reduce scrubber size, which allows more flow through a smaller area. A higher process capacity allows for the design of more compact scrubbers, and operators may lower the weight and cost of new units by reducing the scrubber size.
Thierens said the more advanced technologies accomplished this objective without impairing the efficiency of the separator.
“We should try to maintain the overall separation efficiency,” he said. “Even if we try to increase the capacity, we should not forfeit separation efficiency.”
Thierens discussed two examples of technological advancements in this area. Sulzer’s MKS Multi Cassette mist eliminator consists of cassettes equipped with a structured wire mesh demisting packing that allows the feed stream to enter through the bottom of the device. The company’s KnitMesh V-Mister is used as a mist eliminator and agglomerator upstream of secondary demisting devices.
The industry should look for ways to boost the performance of inline separators pre-separation so that it may eventually design compact inline separators strong enough to replace scrubbers in the field, Thierens said.
The key to accomplishing this task is understanding the core principles of inline gas/liquid separation. The cyclone-based inline separation takes place in the process pipe instead of the pressure vessel, separation efficiency should be high with an optimal range between 90% and 99%, and the process is a function of the feed conditions.
Companies looking to optimize their separation systems should have a good understanding of the separation efficiency needed to ensure an optimized fit-for-purpose design, Thierens said.
They must also have an in-depth knowledge of full process systems, separation internals, and compact inline designs. For an accurate performance mapping, extensive testing and qualification is needed at the appropriate operating pressure with full hydrocarbon systems that are similar to field applications.
The webinar is available at https://webevents.spe.org/products/scrubbers-advances-in-high-capacity-scrubber-internals-and-performance-boosting-with-inline-pre-separation
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