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Multi-cassette designs provide a new option for mist elimination

In many industrial processes, the entrainment of liquid in gas streams can lead to damage to compressors or filler materials such as molecular sieves or, at the very least, reduction of throughput. The formation and the size of liquid droplets in the gas stream are determined mainly by the process application. With the wide variation of entrainment and processes, various technologies continue to develop to best meet those needs.

New Mist Elimination Technology
The Sulzer MKS Multi CassetteTM separator was designed to provide higher droplet removal efficiency and capacity with lower costs. The MKS consists of an axial inlet cyclone with a succession of separating cassettes mounted above it. The inlet cyclone swirls the gas, thereby causing some of the droplets to be separated initially. This liquid is collected in the bottom cassette and drained. Above the cyclone, the gas, still carrying the remaining entrained droplets, is distributed radially outward to the cassettes. Each cassette is equipped with several layers of wire mesh packing which efficiently separates the remaining droplets by both direct interception (barrier effect) and inertial interception. The liquid collected in each cassette is drained to the next lower cassette by a piping system. Finally, all the liquid is collected at the bottom cassette and then drained downwards out of the device through pipes.

Application in Gas Drying Column
The drying of natural gas in glycol (often TEG) dehydrators is a widely used and well established process. However, the use of modern, high-capacity packing such as Sulzer MellapakPlusTM in absorption columns has increased the demands on ancillary equipment as well. In these applications, the droplet size is in the range of 5–25μm. To minimize the carryover, a glycol mist eliminator is required at the top of the column in order to satisfy the stipulated standard of no more than 13.7 liters loss of glycol per million standard cubic meters of gas (0.1 USgal/ MMSCF). This loss expressly concerns only the glycol present in liquid form. As a result, a column equipped with high performance packing requires a suitably sized high capacity mist eliminator to meet design gas flow rates. The MKS Multi Cassette mist eliminator ideally combines with Sulzer Mellapak-Plus in glycol dehydrators to provide proven performance in natural gas drying columns.

Application in Separators
The separation of hydrocarbon liquids from natural gas under high process pressure is always a challenge for mist eliminators. In many cases, the cause of moisture formation is an upstream condensation process where the liquid surface tension is quite low, generating very small and unstable droplets. Until now, designs for high gas flow rates or minimum space and weight, required axial cyclone (Shell SwirltubeTM) or vane pack (Sulzer MellachevronTM) mist eliminators. However, vane pack mist eliminators are generally not recommended for high pressure applications containing hydrocarbon liquids and tend to have relatively low separation efficiency. Axial cyclones are often the first choice and are optimally designed for these tough conditions, but they also require a higher minimum available installation height in the separator. When converting separators to higher capacity, the available installation height is often limited. Also, modifications inside the column can be restricted because, in general, no additional attachments can be welded directly to the column wall. With the MKS Multi Cassette mist eliminator, Sulzer provides an optimal addition to the category of high-capacity mist eliminator internals. Its reliability and performance have already been demonstrated in numerous installations of natural gas dehydrators and separators.

Sponsor : Sulzer Chemtech

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