Chemical Engineering and Processing: Process Intensification
Hydrodynamics of a cocurrent downflow of gas and foaming liquid through the packed bed. Part II. Liquid holdup and gas pressure drop
Introduction
The subject of the research in the present study is the hydrodynamics of the reactor in which the liquid and gas phases downflow cocurrently along the bed of catalyst particles.
Reactors of this type, called ‘trickle bed reactors’, form a very important group of apparatus used in quite a few branches of chemical industry, mainly in the processes of treating various fractions of crude oil with hydrogen.
In the present, part II of the study the results of experiments have been presented and analysed, in which the values of pressure drop and liquid holdup were determined. The experiments involved a specific group of systems studied i.e. systems which foamed in the high interaction regime.
The aim of the study was to create an experimental database which can be used to verify models describing the hydrodynamics of the system.
In the study much attention has been paid to model the pulsing flow since, as it was mentioned before, the systems investigated foam only in the high interaction regime.
A model which allows to calculate the values of both hydrodynamic parameters closest to the experimental data will be chosen as a result of the carried out verification.
Section snippets
Brief literature survey
Liquid holdup and gas pressure drop in the bed are the two key hydrodynamic parameters whose knowledge is necessary while designing and scaling up of the reactor. They are inseparable and appear together in the momentum balance equations of both fluids. The amount of the liquid held up in the packing is identified with the thickness of the film covering the packing particles. The increase in the thickness of this film limits the void volume of the bed, changes the space available for the gas
Experimental set-up and measurement technique
The diagram of the experimental installation has been presented in Part I of the study [15]. Its main part was a column 57-mm in diameter, filled with a 1.35-m high layer of glass spheres (0.003 m in diameter). Argon, nitrogen and helium were used as the gas phase, while the liquid phase formed water solutions of alcohols (methanol, ethanol and isopropanol) whose concentrations were chosen in such a way as to obtain foaming of the solutions in the high interaction regime. Physicochemical
The results of the experiments
The range of operating parameters used in the experiments has been presented on the flow map (Fig. 4).
Each of the systems tested foamed to a lower or higher degree in the pulse flow regime; however having exceeded the boundary of the regime change from pulsing to trickle flow foaming disappeared. This phenomenon occurred slightly earlier in weakly foaming systems. The appearance of foam in the system is demonstrated in diagram (Fig. 5), in which the measured values of liquid holdup and gas
Modelling of the pulse flow
The data-base, obtained as a result of experiments, comprising 245 points for the pulsing flow has been used to verify the models describing the hydrodynamics of the gas and liquid cocurrent flow through the bed.
The verification carried out will enable to point out the model which gives the values of εL and ΔP/H closest to those determined in the experiments.
Pulse flow regime appears in the reactor at relatively high flow rate of the liquid, thus the assumption that the packing particles are
Conclusions
The results of measurements of liquid holdup and gas pressure drop in the packing for the systems investigated which foamed in the pulse flow regime have been presented in this study. It has been concluded that such systems result in values of higher pressure drop and lower liquid holdup than non-foaming systems at the same velocities of both phases.
The influence of gas density on the parameters measured has been analysed. It has been found that at the same superficial velocity of both phases
Acknowledgements
This study was carried out as part of the research project sponsored by the Polish Committee for Scientific Research (Project No. PBZ/KBN/14/T09/99).
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2014, Chemical Engineering Research and DesignCitation Excerpt :The conductivity cells were calibrated by tracer injections and by the flow-stop methods. A detailed description of the way to determine liquid holdup by means of this method was presented in an earlier study (Bartelmus and Janecki, 2003). The research was carried out for SLOW and FAST-changing cycles.
Influence of the porosity profile and sets of Ergun constants on the main hydrodynamic parameters in the trickle-bed reactors
2014, Chemical Engineering JournalCitation Excerpt :A conductance cell, placed in the bed at the height 0.8 m from the top of the bed has been used to measure the conductivity of the solution. A detailed description of the experimental procedure has been presented elsewhere [42]. Gas pressure drop in the packing was measured by means of piezoelectric gauges (Cole–Palmer).
Pressure drop and its reduction of gas-non-Newtonian liquid flow in downflow trickle bed reactor (DTBR)
2014, Chemical Engineering Research and DesignCitation Excerpt :They evaluated the three model parameters: two accounting for the effect of reduction in cross sectional area available for each phase due to the presence of the other, the third accounting for the effect of bubble formation. Bartelmus and Janecki concluded that foaming systems result in values of higher pressure drop and lower liquid holdup than non-foaming systems at the same velocities of both phases (Bartelmus and Janecki, 2003). Guo and Al-Dahhan (2004) carried out experiment at room temperature and elevated pressure (0.8–2.2 MPa) with air–water system.
Trickle bed mechanistic model for (non-)Newtonian power-law foaming liquids
2009, Chemical Engineering ScienceCitation Excerpt :In contrast and in spite of their commonness in industry, the literature still remains very short about understanding and modeling the hydrodynamics of two-phase flow fixed-bed reactors implying (non-)Newtonian foaming fluids. Thus far, few experimental studies on flow regimes, liquid holdup and two-phase pressure drop for (non-)Newtonian foaming have been published (Larkins et al., 1961; Weekman and Myers, 1964; Charpentier and Favier, 1975; Midoux et al., 1976; Wild et al., 1991; Sai, 1997; Bartelmus and Janecki, 2003, 2004; Aydin and Larachi, 2008). These authors recognize that the values of liquid holdup for foaming systems are much lower than those prevailing with non-foaming systems of close physicochemical properties under identical flow rates of both phases.
Trickle bed hydrodynamics for (non-)Newtonian foaming liquids in non-ambient conditions
2008, Chemical Engineering JournalFast-mode alternating cyclic operation in trickle beds at elevated temperature for foaming systems
2007, Chemical Engineering ScienceCitation Excerpt :Most of these studies were concerned with ambient temperature and atmospheric pressure. Recently, Bartelmus and coworkers (Bartelmus and Janecki, 2003, 2004; Burghardt et al., 2003a, b; Janecki et al., 2005) investigated the trickle-bed hydrodynamics for weakly and strongly foaming systems and characterized the trickle-to-pulsing flow regime transition, the pressure drop and liquid holdup up to 2 MPa, and the pulse velocity and frequency at atmospheric pressure. At elevated pressure of up to 8.1 MPa, Larachi et al. (1991) reported some pressure drop and liquid holdup data using as a foaming system nitrogen–1% w/w ethanol/water.