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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Open Archive Toulouse Archive Ouverte Open Archive TOULOUSE Archive Ouverte ( OATAO ) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16521 To link to this article : DOI : 10.1016/S0009-2509(02)00193-8 URL : http://dx.doi.org/10.1016/S0009-2509(02)00193-8 To cite this version : Boyer, Cristophe and Billet, Anne-Marie and Wild, Gabriel Measuring techniques in gas–liquid and gas–liquid– solid reactors. (2002) Chemical Engineering Science, vol. 57 (n° 16). pp. 3185-3215. ISSN 0009-2509 Any correspondence concerning this service should be sent to the repository administrator: [email protected] Measuring techniques in gas–liquid and gas–liquid–solid reactors Christophe Boyera;∗, Anne-Marie Duquenneb, Gabriel Wildc aCentre d’etudes et de developpement industriels (CEDI) “Rene Navarre” BP no 3, F 69390, Vernaison France bLaboratoire de Genie Chimique, ENSIACET—CNRS (UMR no 5503) 18 chemin de la Loge, F 31078 Toulouse cedex 04, France cLaboratoire des Sciences du Genie Chimique, CNRS (UPR no 6811)—ENSIC, B.P. 451, F 54001 Nancy, France Abstract This article o ers an overview of the instrumentation techniques developed for multiphase ow analysis either in gas/liquid or in gas/liquid/solid reactors. To characterise properly such reactors, experimental data have to be acquired at di erent space scale or time frequency. The existing multiphase ow metering techniques described give information concerning reactor hydrodynamics such as pressure, phases holdups, phases velocities, ow regime, size and shape of dispersed inclusions, axial di usion coecients. The measuring techniques are presented in two groups: the non-intrusive techniques that deliver global, cross-section-averaged or local data, and the intrusive probes that are dedicated to local measurements. Eventually some examples of multiphase instrumentation development are reported (trickle-bed and slurry bubble column at semi-industrial scale) in the re nery or petrochemical area. ? 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction time resolution of the technique used and the purpose of the study. The description and design of gas–liquid and gas–liquid– Measurement techniques can be classi ed according dif- solid reactors still relies to a large extent on empirical rules ferent ways. A rst classi cation distinguishes between and correlations, which in turn are based on measurements time-averaged and transient measurements and between made under conditions as relevant as possible to industrial local and global measurements. According to this classi - practice. This is true for the classical chemical engineering cation, the following types of values or characteristics are approach, where such quantities as liquid holdup or pressure measured: drop are predicted via empirical correlations based on data as numerous and precise as possible. Nevertheless, more mod- • Global steady-state characteristics of the reactor (gas or ern approaches such as computational uid dynamic (CFD) liquid holdup, pressure drop, ow regime, minimum u- are used to help in the design of multiphase reactors. Even idisation velocity, etc.) in this case, the physical models used require information • “Local” time-averaged characteristics on local and transient ow characteristics (e.g. turbulence • One-dimensional space: cross-section-averaged values at characteristics, wake coecients, etc.), since ab initio cal- a given level of a reactor culations are up to now impossible. • Two-dimensional space: local averaged values over a re- Reliable measuring techniques are therefore needed as actor cross-section (tomographic techniques) well in academia as in industry for the rational description • Three-dimensional space and the design of multiphase reactors. Depending on the aim • Local and transient characteristics of the ow eld. of the analysis, di erent types of measurements are required and it is important to maintain an adequacy of space and The local and/or transient character of the measurement can vary widely, depending on the time and the length ∗ scale. Corresponding author. As an example, in case of the design of a trickle bed re- E-mail addresses: [email protected] (C. Boyer), [email protected] (A.-M. Duquenne), actor, liquid distribution is of the utmost importance, but in [email protected] (G. Wild). most cases the ow is fairly steady state. In this case, for local time averaged, at least 2D measuring techniques of membrane of the sensor. The interpretation of the pressure the liquid velocity or liquid holdup are needed. In case of drop in terms of static pressure drop and friction pressure a slurry bubble column, global characteristics are required drop is not always easy: e.g. in case of trickle beds, the pres- (minimum settling velocity) but also local ones, like the lo- sure drop measured may be the friction pressure drop or the cal liquid velocity and gas and solid holdup. These mea- total pressure drop, depending on the measuring procedure. surement needs will be illustrated at the end of this paper by The large scatter observed in pressure drop data in trickle presenting some examples of instrumentation development beds is partly due to the fact that, quite often, the values re- in the oil industry. ported are “somewhere in-between” the friction and the to- Since the classi cation between local and global measure- tal pressure drop. In bubble columns, slurry bubble columns ment is not always possible another classi cation has been and three-phase uidised beds the friction pressure drop is preferred in this article. This classi cation relies more on usually negligible compared with the static pressure drop. the physical basis of the measurement and nally one can P P distinguish between invasive and non-invasive measuring = g(LL + S S + GG) + f: Z Z techniques. In the present work, a review of a number of non-invasive (b) Uses of the mean pressure drop. The main use of pres- and invasive measuring techniques is presented. In both sure measurements in such pieces of equipment is to deter- cases (non-invasive and invasive) the techniques are mine gas, liquid and/or solid holdup (Joshi, Patil, Ranade, & grouped according to the physical principle of the measure- Shah, 1990; Wild & Poncin, 1996) in such reactors. In case ment. In the meantime, the characteristics of the techniques of three-phase reactors, the pressure drop measurement has according to the rst classi cation (global or local, time to be combined with another technique to get all the phase averaged or transient) are indicated as well as orders of holdups. magnitude of the length and time resolution to be expected. In multiphase reactors, an exact description of the ow Finally, some examples of the use of measuring techniques behaviour by CFD is usually still impossible and the design with industrial constraint in the petrochemical and re nery of these reactors usually relies on empirical correlations of a industry are presented. number of characteristics of hydrodynamics, heat and mass transfer. Usually such correlations are valid at the best for a given ow regime; de ning ways to determine which is 2. Non-invasive techniques the ow regime is therefore an important task. According to Zahradnk et al. (1997), three main ow regimes can be There are numerous non-invasive techniques (Table 1) distinguished in bubble columns: homogeneous ow, tran- available to investigate hydrodynamics of gas–liquid and sition ow and established heterogeneous ow; in case of gas–liquid–solid reactors. First, techniques yielding char- small diameter columns, plug ow must be added. In gas– acteristics of the whole reactor or of a part of the reactor liquid–solid uidisation, usually homogeneous ow and het- (global techniques) will be examined, the characteristics be- erogeneous ow regime are considered. In trickle beds it ing e.g. the pressure drop, the gas and/or liquid holdup, the is usual to distinguish trickling ow regime (low interac- ow regime, the bubble size distribution, the mixing char- tion) and di erent forms of high-interaction ow regimes acteristics of the gas, the liquid or the solid phase. In some, (pulsing ow, bubble ow, spray ow, foamy ow, etc.) long-term averages are measured, in others uctuations are (Saroha & Nigam, 1996). Time-averaged values of the pres- analysed. Next, determination techniques of local character- sure drop or the phase holdups can be used to determine ow istics will be presented (gas and liquid velocity, bubble or regime transitions but give very uncertain results. This tech- particle size and position). Often, one single technique can nique has however been used in trickle beds (Purwasasmita, yield more than one characteristic. 1985). The classic drift ux analysis of Wallis (1969) (bub- ble columns) and of Zuber and Findlay (1965) (airlift re- 2.1. Global techniques actors) are relatively easy to use and give fair precision for both ow regime transitions in these reactors (see e.g. Vial 2.1.1. Time-averaged pressure drop et al., 2000). The pressure drop between two levels of a reactor is a very important variable to know, either because the pressure drop 2.1.2. Measurement and analysis of signal uctuations is important per se (design of the pumps and compressors), Analysing the uctuations of a signal depending on the or because it gives information on the holdup of the di erent hydrodynamics is a relatively direct way of determining the phases or on the ow regime. ow regime in a multiphase reactor. This signal may be a (a) Measuring technique. It is recommended to measure wall pressure (Matsui, 1984; Glasgow, Erickson, Lee, & the pressure with sensors ush to the wall; the price of piezo- Patel, 1984; Drahos & Cermak, 1989; Drahos, Zahradnk, electric pressure sensors decreased in the last 10 years and Puncochar, Fialova, & Bradka, 1991; Drahos, Bradka, & such equipment is now quite standard.

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