Research Papers: Petroleum Wells-Drilling/Production/Construction

Performance Analysis of a Novel Compact Flotation Unit

[+] Author and Article Information
A. Hayatdavoudi

 University of Louisiana at Lafayette, P.O. Box 44446, Lafayette, LA 70504

M. Howdeshell

 Siemens Water Technologies Corporation, 301 W. Military Rd., Rothschild, WI 54474

E. Godeaux

 Siemens Water Technologies Corporation, 411 Commercial Parkway, Broussard, LA 70518

N. Pednekar

200 Oakcrest Dr., Apt C-135, Lafayette, LA 70503

V. Dhumal

200 Oakcrest Dr., Apt C-135, Lafayette, LA 70503

J. Energy Resour. Technol 133(1), 013101 (Mar 15, 2011) (9 pages) doi:10.1115/1.4003497 History: Received March 31, 2009; Revised December 23, 2010; Published March 15, 2011; Online March 15, 2011

The oil and gas industry produces large quantities of water as a by-product of petroleum production. Discharge specification of produced water requires efficient management and sophisticated technology. Conventional technologies such as those based on gravity separation, cyclonic separation method, filtration techniques, flotation technique, and natural gas/air sparge tube systems are used for treating produced water. However, most, if not all, of these technologies require a large footprint. This problem has created a challenge for the produced water industry, as well as for operators managing the offshore production facilities. Responding to the challenge at hand, Siemens Water Technologies Corporation has developed a novel compact flotation unit (CFU) equipped with a dissolved gas flotation (DGF) pump for treating produced water. The CFU has a small foot print and shorter residence time. The DGF pump is equipped with a unique, dual-sided impeller, which pulls the blanket gas on one side and the produced water on the other. Under applied backpressure, the gas entering the DGF pump dissolves in a portion of a recycled, cleaned water stream. The dissolved gas generates bubbles due to the pressure drop when the mixture of produced water and gas passes through a special valve before entering the CFU. The ratio of the inlet produced water flow rate to the DGF pump output rate plays an important role in optimum separation of oil droplets from the produced water. Besides the above-mentioned ratio, generation of an adequate number and size of bubbles provides another critical key factor in efficient operation of the CFU system. To validate our theoretical approach regarding the controlled forced vortex of the multiphase flow, we performed various tests in the shop facility of Siemens Water Technologies Corporation, as well as on a platform facility offshore Louisiana. We used a response surface methodology technique to analyze the CFU performance data and to generate an optimum surface response for free oil and grease removal efficiency. For optimizing the size of the piping and CFU dimensions, we used the rigorous yet simple principles of the constrained similitude. The free oil removal efficiency results in the shop and field tests, for CFU without the use of packing material, were satisfactory. Additionally, we found that CFU system tests resulted in the removal efficiency of water soluble oil (WSO). We did not expect this additional outcome as the CFU system was not designed to affect the removal of WSO.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Different sections of the CFU such as VGZ and the outer vessel (20)

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Figure 2

Testing the validity of forced vortex with and without the head of water. (a) Vortex generating zone test setup, (b) forced vortex bowl with circular streamlines inside the vortex bowl and velocimeter placed at the center, and (c) forced vortex bowl under a head of water (20).

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Figure 3

(a) A large number of small bubbles bringing oil droplets to the surface of the VGZ, (b) onset of forced vortex, (c) IGF bubbles, (d) DGF bubbles, and (e) the optimal (sweet) operating window of the DGF 1.25DA1 pump (20-21)

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Figure 4

1 cycle sequence of oil removal in shop test beginning with oily water (a) and ending with (f) clean water (20-21)

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Figure 5

(a) Sample of 3D velocity components recorded at the center of forced vortex field, VGZ water-only-tests at 150 GPM inlet water flow rate, and (b) transformed (denoised) signals of the single-phase flow (20)

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Figure 6

(a) The onset of multiphase forced vortex with very low flow rate at the top of the VGZ. (b) The appearance of a small forced vortex ring in the x-y plane to the right of the ruler. (c) The development of forced vortex under higher multiphase flow rates. (d) The oil droplets coalescing and concentrating under the influence of vortex rings in the forced vortex bowl. (e) The intensified forced vortex flow. (f) Further proof of the forced vortex theory. Note that the transformed (denoised) signals in multiphase flow conditions are not as smooth as in the case of single-phase flow of Fig. 5(20).

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Figure 7

(a) CFU system shop test loop, (b) 2D map of the optimal surface, (c) 3D RSM model showing the interaction effect of two flow rates on optimal oil removal efficiency, and (d) validation of the RSM best fit model (21,28,30)

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Figure 8

Water soluble oil removal efficiency and validation of the RSM model (21,29-30)

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Figure 9

Comparative removal efficiency plot of available field test data without packing material and oil lift mechanism (20)

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Figure 10

Field data showing free oil removal efficiency plot. Note the “golden window of the golden ratio: 0.6 to 1.33 (21).”



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