CAPITULO IV RESULTADOS
4.2. Discusión de resultados
erosion damage in blades and corrosion in other downstream
equipment. ... The sizing of each of the
components of a knockout drum is
not trivial, and advanced simulation
tools must be used to ensure that the
device operates as designed.
Gas Processing | JANUARY/FEBRUARY 201627
PLANT DESIGN
These changes alone may not be sufficient to provide a uni-form velocity profile to each of the four sides. A third mitigat-ing effort is to adjust the open area of the downstream distri-bution baffle. Each perforated plate may be split horizontally, into as many as four sections, as shown in FIG. 17D. By using less net-free-area (NFA) baffles at the top (thereby restricting flow and higher velocities to the upper segment) and gradu-ally increasing the NFA toward the bottom, a more uniform flow distribution may be obtained at each face. This may even reduce the reversed flow, which is highly detrimental to a liq-uids separation system.
The most effective method is to perform iterative CFD by using various combinations of pressure drop vs. superficial velocity, using the Ergun equation4 or Smith and Van Winkle equation.5 Intermediate normal velocity contours may be plot-ted to check for optimally uniform intake flow fields. The cal-culated NFA are used to fabricate the perforated plate sections.
Exit nozzle considerations. The diameter of the outlet may be sized so that the overall pressure drop does not exceed the process design parameters, and the velocity of the gas flow does not exceed the inlet pipe velocity as it exits the system. A suggestion is to use a diameter that is at least three-fourths the size of the inlet diameter.
The liquid outlet at the bottom head of the drum should be sized so that the exiting liquid velocity does not exceed 2 m/s, to prevent vibration and surge-related issues. Sometimes, a filter basket with grating, a bucket, and a weir and panel are used if solids and heavy liquids are expected to be removed.
Takeaway. A number of guidelines and considerations are available to meet design challenges encountered during the design of liquid/gas separators. The key criteria are to ensure uniform distribution at the mist eliminator entry and to maxi-mize liquid removal efficiency.
Advanced simulation tools and empirical equations are used to ensure that the device is sized appropriately and oper-ates as designed. GP
LITERATURE CITED
1Hinze, J. O., “Fundamentals of the hydrodynamic mechanism of splitting in the dispersion process,” AIChE Journal, Vol. 1, No. 3, September 1955.
2Kouba, G. E., “Mechanistic models for droplet formation and breakup,” Proceedings of the ASME/JSME 4th Joint Fluids Summer Engineering Conference, Honolulu, Hawaii, July 6–10, 2003.
3Wallis, G. B., “The onset of droplet entrainment in annular gas-liquid flow,”
Report No. 62GL127, General Electric Co., Schenectady, New York, 1962.
4 Ergun, S. and A. A. Orning, “Fluid flow through randomly packed columns and fluidized beds,” Ind. Eng. Chem., June 1949.
5 Smith, P. L. and M. Van Winkle, “Discharge coefficients through perforated plates at Reynolds numbers of 400 to 3,000,” AIChE Journal, Vol. 4, No. 3, 1958.
JALEEL VALAPPIL is a principal process engineer and team lead for the advanced simulation group of Bechtel Oil, Gas and Chemicals in Houston, Texas. His areas of expertise include process engineering, simulation, control and optimization. He is responsible for developing and deploying advanced technical solutions during design, commissioning and operation of various Bechtel projects, including LNG terminals. Dr. Valappil holds a bachelor’s degree from the Indian Institute of Technology in Kharagpur and a PhD in chemical engineering from Lehigh University in Bethlehem, Pennsylvania.
PHILIP DIWAKAR is a senior engineering specialist at Bechtel with 23 years of experience in CFD, FEA and acoustic- and flow-induced vibrations. He is a lead specialist in Houston, Texas, responsible for providing solutions for warranty-, environment- and risk-related issues covering several of Bechtel’s business units. To his name, Mr. Diwakar has more than 25 publications, six outstanding technical paper awards, three journal publications and an innovation award for fluid-structure interaction. He has also received technical grants for the design of buildings to withstand explosions in LNG plants, thermal fatigue in dehydrators, fume gas treatment and acoustically induced vibration.
FIG. 17. Four-bank housing (a); side-to-side flow field (north to south) (b); crossflow field (east to west) (c) and variable-area perforated plates (d).
FIG. 18. Normal velocity contours at entry to each face of the mist eliminator in four-bank housing.
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Gas Processing | JANUARY/FEBRUARY 201629