Case Histories
1. Chemical fiber plant reduces cleaning cycle
A Midwestern fiber production plant had to shut down two identical vertical gas-liquid separators four times a year to replace the horizontal mesh pads due to fouling with fibers. Each shutdown lasted two days because of the time required for ventilating the vessel and building a scaffold inside to reach the mesh pad. The plant was operating near maximum capacity, so any down time directly affected the company’s bottom line.
The separators were 36 inches in diameter and 84 inches high. The incoming stream consisted of an off-gas with a density of 0.25 lb/ft3 and a throughput of 3,600 actual cubic feet per minute. The feed contained less than 0.1% water with droplets greater than 10 microns in size, and also traces of fibers. The gas outlet nozzle had an inside diameter of 12 inches.
Based on the process conditions, Amistco designed a 12-inch MistFix unit with a length of 30 inches for each separator, using 316 SS mesh. As of this writing in the summer of 2004, these devices have been operating very successfully for several years. The plant keeps spare MistFix units in inventory and can easily change a fouled MistFix in a few hours.
2. Refinery capacity increase and downtime reduction
A medium-size Midwestern refinery needed to increase the capacity of three knockout drums by 10%. At the same time, management was looking for ways to reduce the periodic down time of the vessels for replacing the horizontal mesh pads. The drums had an outside diameter of 60 inches and a height of 108 inches. For each vessel, the gas flow rate was 8,000 ACFM. The gas was fuel gas with a density of 0.15 lb/ft3. The mist consisted of oil with a density of 50 lb/ft3, the liquid load being less than 0.1%. The exit nozzles were 16 inches in diameter.
One of the knockout drums was chosen for retrofit with a MistFix unit on a trial basis. Amistco’s design was for a diameter of 16 inches, a length of 48 inches, Monel for the mesh, and 316 SS for the frame. The device has been operating successfully for 16 months. Because of this positive experience, the refinery is considering MistFix units for the other two separators as well as additional applications in the plant.
3. Specialty chemicals plant with lined vessels
A specialty chemicals plant had increased its capacity over the years and was operating without mist eliminator pads in any of its vessels. Now frequent liquid carryover in several places required corrective action. Unfortunately, most of the vessels involved were lined for corrosion resistance. Adding a mesh pad would require welding a support ring to the vessel wall, entailing considerable expense to restore the lining.
Amistco designed a MistFix unit 36 inches long for one vapor-liquid separator with 42-inch outside diameter and 108-inch height. The diameter of the gas outlet nozzle was 10 inches. The gas flow rate was 3,000 ACFM, and the gas density was 0.007 lb/ft3. To resist corrosion, the mesh was made of Ni-200 and Teflon. Using a MistFix unit in the gas outlet avoided damaging the vessel lining. As a result of success in that retrofit, the plant has ordered additional MistFix units for other lined vessels.
For information and consultation, call Bernhard Kalis, Technical Director, or any other separation specialist at Amistco’s headquarters in Alvin, Texas: 800-839-6374 or 281-331-5956, fax 281-585-1780, e-mail Amistco@amistco.com.
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