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Use of Helical Coil Pipes for Depressurization in a Supercritical Water Oxidation (SCWO) Pilot Plant: Experimental Results & Simulation

Authors:
José Manuel Benjumea Trigueros at Universidad de Cádiz
José Manuel Benjumea Trigueros
J. Sánchez-Oneto at Universidad de Cádiz
J. Sánchez-Oneto
J.R. Portela at Universidad de Cádiz
J.R. Portela
Enrique J. Martinez de la Ossa at Universidad de Cádiz
Enrique J. Martinez de la Ossa
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Abstract

The use of backpressure regulator valves in SCWO at laboratory scale is highly extended, but the use of that valve is not suitable when applying this technology with high flow rates at industrial scale. The aim of this work is to present the use of helical coil pipes to achieve the depressurization step based on the pressure drop of a fluid that circulates for a pipe of great length and small diameter. To design it, several correlations of friction factors were studied and simulated with Engineering Equation Solver (EES) Software. Finally, the depressurization system installed in the SCWO pilot plant located at University of Cádiz, is composed of three series legs of helical coil pipes. In order to compare simulated and experimental data, a set of experiments were carried out at pilot plant with air and water mixture feeds. The working pressure is approximately 250 bar and the flow rates were 10 l/h for water stream and 80 g/min for air stream. Experimental results obtained are compared with the simulation carried out with friction factor correlations appearing in the literature. The best fit is achieved adding a new parameter proposed in this work that takes into account interaction between gas and liquid phases.
11.- Depressurization SCWOx-
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... The use of coiled pipes provides a different way to achieve a gradual pressure change along the pipe length [7,8]. Thus, it is possible to redistribute the mechanical stress along the length of a coiled pipe rather than producing an abrupt pressure change in a single valve. ...
Depressurization System by Coiled Pipes Applied to a High Pressure Process: Experimental Results and Modeling
Article
Full-text available
  • Jul 2017
  • Open Chem Eng J
Background The use of backpressure regulator valves is widespread in high-pressure processes both at laboratory and pilot plant scales, but being a single step for effluent depressurization, such valves may have some limitations at industrial scale. In an effort to improve the depressurization step, this work studies a system based on the pressure drop of a fluid that circulates through coiled pipes. Method The equipment, based on three series of variable length coiled pipes, was installed to achieve depressurization of 240 bars in a SCWO pilot plant. Results The experimental results were compared with those obtained by the modeling carried out using different friction factor correlations from the literature. Conclusion Among all the correlations tested, the Lockhart–Martinelli correlation showed the best agreement with experimental data. However, it was necessary to obtain an appropriate C parameter to achieve a good agreement with experimental data.
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... HCT is used across a broad range of industries (e.g., energy, chemistry, food and refrigeration engineering) because of its high heat transfer efficiency, effective compactness, excellent structure robustness and flow stability [1][2][3][4][5]. Because of centrifugal force, two phase flow in HCT is more complicated than that in straight tubes (e.g., asymmetry phase distribution, secondary flow and annular flow reversion). ...
Bubbly-intermittent flow transition in helically coiled tubes
Article
  • Apr 2017
  • CHEM ENG J
This paper experimentally investigated the bubbly-intermittent flow (BI) transition in helically coiled tubes (HCT) with coil diameter of 20, 40 and 80 cm. A double sensor conductivity probe and a high-speed camera were used to obtain local phase distribution parameters and flow imagery. Because of the centrifugal force, buoyancy was redirected and enhanced, leading to a highly asymmetry and concentrated bubble distribution. As a result, BI transitions occurred at much lower gas flow rates in HCTs. Observation of the BI transition revealed two mechanisms: bubble accumulation in flow direction due to bubble velocity difference (liquid superficial velocity lower than 1.5 m/s), and bubble accumulation in radial and peripheral direction due to strong buoyancy (liquid superficial velocity higher than 1.5 m/s). The critical void fraction at which BI transition occurred (e.g., 0.065 for coil diameter of 40 cm) increased as the coil diameter increased, and was much lower than that of straight tubes ( 0.25-0.51). A correlation predicting BI transition was established, covering both straight inclined tubes and HCTs; which met the experimental results well when the coil diameter was larger than 0.2 m.
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Simulation of Supercritical Water Oxidation with Air at Pilot Plant Scale
Article
Full-text available
  • Mar 2010
  • INT J CHEM REACT ENG
Supercritical Water Oxidation (SCWO) processes have been studied by numerous researchers. The effectiveness of this approach to treat a wide variety of wastes has been proved and the kinetics involved in some cases have been described. Phenol is commonly present in industrial wastewaters and it is extremely toxic. Hence, phenol is a model pollutant that has been the subject of numerous studies by SCWO on a laboratory scale. In this work, a pilot-scale SCWO system has been used to compare experimental and predicted conversions in the SCWO of phenol, using the reaction kinetic equations obtained at the laboratory scale. In this context, "PROSIM PLUS" software was employed to develop a simulator for the pilot plant facility, with the reaction kinetic parameters adjusted to represent the experimental data. In this study it was necessary to determine the thermal losses between the experimental reactor and its surroundings. These thermal losses were obtained from tests with pure water and oxidant streams in the absence of chemical reaction. An equation that predicted the effect of flow rate and temperature on the thermal losses was used. Experimental oxidation tests were conducted with initial temperature in the range 380 to 425-° C, at 250 bar and phenol concentrations ranging from 1 to 12 g/l. Good agreement in the simulation was obtained by adjusting the kinetic parameters within their confidence range. This simulator was used to optimize the SCWO of phenol solutions in the pilot plant facility.
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Pressure drop and friction factor in helical heat exchangers under nonisothermal and turbulent flow conditions
Article
Full-text available
  • Jan 2007
  • J FOOD PROCESS ENG
This study involved the determination of pressure drop and friction factor (f) in helical heat exchangers under turbulent flow conditions. the experiments were conducted in helical heat exchangers, with coils of two different curvatures ratios (d/D = 0.114 and 0.078) at various flow rates (9.46 × 10−5 - 6.31 × 10−4 m3/s) and end-point temperatures (20, 93.3, 121, 149C). the computed friction factor (f) in the helical heat exchanger was compared to published correlations, and it was found that the experimental data was in good agreement with them. In addition, correlations to determine pressure drop based on the Reynolds number, curvature ratio, and temperature were developed.
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Friction Factors for Turbulent Flow in Curved Pipes
Article
  • Jun 1959
The object of this paper is to furnish the engineer with reliable data on the friction factors to be used in computing the pressure losses for turbulent flow in smooth curved pipes. The empirical formulas proposed, backed by theoretical considerations, appear to define the influence of curvature upon the law of resistance with satisfactory accuracy.
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Heat transfer and pressure drop in helically coiled tubes
Article
  • Jan 1986
Centrifugal forces in a fluid flowing through a curved pipe cause secondary flows increasing the heat transfer and the pressure drop. The effects of the curvature of the tube can be described by the characteristic parameter (d/D). In the case of an elliptical cross section of the pipe the aspect ratio gamma equals (a/b) additionally influences the velocity profile. Based on experimental data from the literature, equations are presented to calculate pressure drop and heat transfer. The friction factors result from equations for the circular pipe enlarged by factors containing the Dean-number for laminar flow or (d/D) for turbulent flow. In case of an elliptical cross section the Dean number is modified and the hydraulic diameter is used. The critical Reynolds number can be calculated for both cross-sections from the same equation. In laminar flow the heat transfer coefficient depends strongly on (d/D). With fully developed turbulent flow the heat transfer coefficients can be correlated by the same equation as for the straight tube, when the friction factor of the coil instead of that of the tube is inserted. For the transition region an interpolating equation is given.
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Pressure Drop Correlations for Flow Through Regular Helical Coils
Article
  • Apr 2001
  • FLUID DYN RES
An attempt has been made to arrive at a better characterizing dimensionless group for steady isothermal flow of Newtonian fluids in helically coiled circular tubes. Pressure drop versus flow rate data has been experimentally obtained for helical coils made from thick-walled polyethylene tubing. Generalized pressure drop correlations have been developed in terms of Euler number, Eu, Reynolds number, Re, and the obtained geometrical group, Grhc=(d0.85Deq0.15/Lc), where d is the inside diameter of the tube, Deq is the equivalent diameter which accounts for the torsion effect, and Lc is the length of the coil. The Fanning friction factor for helical coil tube is found to depend on Reynolds number and a geometrical number, d/Deq, separately both, and not by a dimensionless number obtained by any combination of Reynolds number and some geometrical number as is the case of Dean number, , where D is the diameter of the coil. There exist four regimes of flow for the flow through helical-coiled circular tubes. The obtained pressure drop correlations are simple to use.
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Note on the Motion of Fluid in Curved Pipe
Article
  • Jun 1959
In the stream-line motion of fluid in a curved pipe the primary motion along the line of the pipe is accompanied by a secondary motion in the plane of the cross-section. The secondary motion decreases the rate of flow produced by a given pressure gradient and causes an outward movement of the region where the primary motion is greatest. It is difficult to deduce these consequences from the exact equations of motion, but it is easy to do so if it is assumed that the actual secondary motion is replaced by a uniform stream; conditions in the central part of the section mainly determines the motion and here the secondary motion is approximately a uniform stream. The appropriate velocity of the stream can be determined from the relation that has been found experimentally between the rate of flow in a curved pipe and the pressure gradient.(Received April 17 1959)
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An experimental investigation of the frictional pressure drop of steam–water two-phase flow in helical coils
Article
  • Jul 2001
  • INT J HEAT MASS TRAN
Fractional pressure drops of single-phase water and steam–water two-phase flows were studied in a pressure range of 3.0–3.5 Mpa. Two helical coiled tubes were employed as test sections and their four different helix axial inclinations were examined. It is found that helix axial angles have little influence on the single-phase frictional pressure drop, while variation of the steam–water two-phase flow frictional pressure drop is enlarged to 70%. For single-phase flow, some previous correlations were quite accurate in predicting the frictional pressure drop for lower Reynolds number conditions, and a modified correlation was obtained from an enlarged Reynolds number range of the present test. For boiling two-phase flow, great deviation was found among the published few empirical equations and their capability of practical utilization is rather poor on account of their complication in structure. A new easily stipulated correlation is deducted from our present data.
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