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Pads and vanes can also be damaged by freezing liquids in cold climates. In natural gas production and pipelining, hydrate formation is known to destroy mesh pads and vanes.
To cope with any of these scenarios, as shown in Figure 12, any or all of the following remedies can be applied to mist eliminator elements:
1. Reinforce with heavy-duty material.
2. Fasten with bolts instead of traditional tie wires, or provide an upper support ring in addition to the lower one.
3. Provide a pressure relief door in the case of mesh.
Figure 12. Protecting mesh pads from pressure damage
 Compressor knockout drum cases
Ethylene plant debottleneck
A large ethylene producer needed to debottleneck its six-stage compressor train to increase throughout. This project needed to be accomplished with minimal cost and down time.
Using conventional mist eliminators —horizontal mesh pads or vanes — the knockout drum before each compressor stage would have to be enlarged. For instance, the drum at the inlet to the first stage, eight feet in diameter, would be replaced by a 14-foot vessel.
Amistco thoroughly reviewed the process conditions and internal geometry of each knockout drum. We then customized each existing drum with double-pocket vanes and mesh agglomerators arranged as in Figure 8, using one, two, or four banks as required. To ensure proper gas distribution, we added inlet diffusers as in Figure 11 and flow distribution plates on the downstream side of the vane units. The result was 35% increased capacity while achieving an efficiency of 99.9% of 1 micron and larger mist droplets.
Fertilizer plant capacity boost & amine loss cut
A 4-train fertilizer plant needed more ammonia gas processing capacity in one of the trains to increase production capacity. The bottleneck was the overhead knockout drum in two of four carbon dioxide absorber towers in that train. Those vessels also served as suction drums for the compressors that followed. In addition, it was desired to reduce excessive loss of valuable amine in the form of mist escaping the knockout drums.
Amistco reviewed the absorber process conditions and the available space in the knockout drums. Although the space in one of the drums was very tight, we were able to solve this problem by retrofitting both drums with a double-bank system as in Figure 8. In each bank, a mesh agglomerator is followed by an Amistco Double-Pocket Vane unit. The result was a 30% capacity increase. In addition, the rate of amine loss fell to 0.05 gallon per million standard cubic feet, which corresponds to savings on the order of $75,000 per year. Another benefit was elimination of a cause of pitting corrosion in the compressors.
Gas production & condensate recovery increase
A large oil and gas company wanted to revamp several dozen of their 30-year-old two-phase field separators (sizes 2 to 5 feet OD). The purpose was to increase capacity and improve recovery of condensate. As in the preceding case, the separators were also suction drums for compressors.
Joining with a local fabrication shop, Amistco brought the separators from the field, removed the old internals, enlarged the inlet and outlet nozzles, and retrofitted the vessels with Amistco Double-Pocket Vane units. The separators were ASME-code recertified, painted, and reinstalled in the field with new instrumentation. This rejuvenation saved the company thousands of dollars per unit as compared to purchasing new separators. Gas capacity increased by up to 50%, and condensate recovery went up by many thousands of barrels per year.
THESE CASES are typical of many applications where Amistco’s separation technology made a big difference. Similar results can be achieved for a wide variety of compressor knockout drums in refineries, gas plants, oil and gas exploration and production, and petrochemical plants.
For information and consultation, call the author, Technical Director Bernhard Kalis, or any other Amistco separation specialist, at 281-331-5956 or amistco@amistco.com
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