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Fig. 7. Overall heat transfer coefficient as a function of system pressure; (a) F,=100 ml/h, (b) F,=60 ml/h, (c) F,=30 ml/h. Symbols: (@ ) Fe-=18 N L/h, (©) Fe=9 N L/h, ( Fo=3 NL/h.

Figure 7 Overall heat transfer coefficient as a function of system pressure; (a) F,=100 ml/h, (b) F,=60 ml/h, (c) F,=30 ml/h. Symbols: (@ ) Fe-=18 N L/h, (©) Fe=9 N L/h, ( Fo=3 NL/h.

Related Figures (9)

Fig. 1. Experimental set-up for feed temperature modulation: (1) feed, (2) HPL pump, (3) pulse dampener, (4) flow meter, (5) three-way valve (6) heater, (7) insulatio material, (8) reactor with flange, (9) temperature display, (10) sampling tube, (11) G-L separator and (12) gas flow meter. Prior to starting the experiments, the system was checked for leaks at ambient temperature and a total pressure of 25 bar; the column was then covered with the type and geometry of insulat- ing material selected for the experiment. Moreover, for minimiza- tion of axial heat conduction through the column walls and fitting connections, a system of two flanges with thermal insulation in between has been mounted at the column outlet. Tubing from the pre-heater outlet to the column inlet and from the column outlet to the gas-liquid separator was also insulated in particular to reduce heat loss in the inlet section of the column. After trickling through the packed bed retained by two metal grids, the exited gas-liquid flow was separated and the liquid fraction was stored in the 5 L gas-liquid separator. The residual gas flowing out of the
Fig. 1. Experimental set-up for feed temperature modulation: (1) feed, (2) HPL pump, (3) pulse dampener, (4) flow meter, (5) three-way valve (6) heater, (7) insulatio material, (8) reactor with flange, (9) temperature display, (10) sampling tube, (11) G-L separator and (12) gas flow meter. Prior to starting the experiments, the system was checked for leaks at ambient temperature and a total pressure of 25 bar; the column was then covered with the type and geometry of insulat- ing material selected for the experiment. Moreover, for minimiza- tion of axial heat conduction through the column walls and fitting connections, a system of two flanges with thermal insulation in between has been mounted at the column outlet. Tubing from the pre-heater outlet to the column inlet and from the column outlet to the gas-liquid separator was also insulated in particular to reduce heat loss in the inlet section of the column. After trickling through the packed bed retained by two metal grids, the exited gas-liquid flow was separated and the liquid fraction was stored in the 5 L gas-liquid separator. The residual gas flowing out of the
Experimental conditions employed.
Experimental conditions employed.
Fig. 2. Evolution of axial temperature during a standard experiment: P;y=15 bar, Fc=9 N L/h, (+) oven temperature, (@) axial temperature at z=1.5 cm, (C) axial temperature at z=10 cm, (A) axial temperature at z=20.5 cm.
Fig. 2. Evolution of axial temperature during a standard experiment: P;y=15 bar, Fc=9 N L/h, (+) oven temperature, (@) axial temperature at z=1.5 cm, (C) axial temperature at z=10 cm, (A) axial temperature at z=20.5 cm.
Fig. 3. Influence of different insulating materials and geometries on axial temperature profile in trickle bed column: P;=15 bar, F,=100 ml/h, Fo=18 N L/h; (A) without isolation, (4) ceramic fiber, (Ml) glass fiber, (©) rock wool foam, discontinuous lines represent model predictions. convex curving as the bed temperature gradient increases. A stronger gradient favors condensation of water vapor from the saturated gas phase and condensation effects may be at the origin of the observed trend.
Fig. 3. Influence of different insulating materials and geometries on axial temperature profile in trickle bed column: P;=15 bar, F,=100 ml/h, Fo=18 N L/h; (A) without isolation, (4) ceramic fiber, (Ml) glass fiber, (©) rock wool foam, discontinuous lines represent model predictions. convex curving as the bed temperature gradient increases. A stronger gradient favors condensation of water vapor from the saturated gas phase and condensation effects may be at the origin of the observed trend.
Fig. 4. Axial T profiles for different liquid flow rates and pressures; F¢=9 N L/h (carbon, rock wool foam); (a) Pr=9 bar, (b) Pr=15 bar, (c) Pr=25 bar; (@) F,=100r F_=60 ml/h, (4) F,=30 ml/h; lines represent model predictions. Fig. 4 evidences again that the predicted temperature profiles match well the experimental data and this holds for all other experimental conditions tested. A second observation to point out is the strong influence that has pressure on the shape of the temperature profiles. The flat and straight profiles that establish at 9 bar become more steep and curved for intermediate pressure of 15 bar and decreasing liquid flow rate. A further increase to 25 bar results in even steeper profiles, which however show no longer convex curving. The curving of the profiles with pressure may be related to condensation effects as already suggested in Section 4.1. At a total system pressure of 9 bar and 160°C, the saturated nitrogen phase flowing through the fixed bed contains actually a high fraction (ca. 70%) of water vapor. How- ever, the axial temperature gradients establishing at this pressure
Fig. 4. Axial T profiles for different liquid flow rates and pressures; F¢=9 N L/h (carbon, rock wool foam); (a) Pr=9 bar, (b) Pr=15 bar, (c) Pr=25 bar; (@) F,=100r F_=60 ml/h, (4) F,=30 ml/h; lines represent model predictions. Fig. 4 evidences again that the predicted temperature profiles match well the experimental data and this holds for all other experimental conditions tested. A second observation to point out is the strong influence that has pressure on the shape of the temperature profiles. The flat and straight profiles that establish at 9 bar become more steep and curved for intermediate pressure of 15 bar and decreasing liquid flow rate. A further increase to 25 bar results in even steeper profiles, which however show no longer convex curving. The curving of the profiles with pressure may be related to condensation effects as already suggested in Section 4.1. At a total system pressure of 9 bar and 160°C, the saturated nitrogen phase flowing through the fixed bed contains actually a high fraction (ca. 70%) of water vapor. How- ever, the axial temperature gradients establishing at this pressure
Fig. 5. Axial temperature gradient as function of system pressure for different liquid and gas flow rates; (a) Fe=3NL/h, (b) Fe-=9NL/h, (c) Fe=18NL/h Symbols: (@) F,=100 ml/h, (©) F,=60 ml/h, (4)F,;=30 ml/h.
Fig. 5. Axial temperature gradient as function of system pressure for different liquid and gas flow rates; (a) Fe=3NL/h, (b) Fe-=9NL/h, (c) Fe=18NL/h Symbols: (@) F,=100 ml/h, (©) F,=60 ml/h, (4)F,;=30 ml/h.
ig. 6. Overall heat transfer coefficient as a function of system pressure; (a) Fe-=3 N L/h, (b) Fe=9 N L/h, (c) Fe =18 N L/h. Symbols: ( @) F,=100 ml/h, (©) F,=60 ml/t ,=30 ml/h.
ig. 6. Overall heat transfer coefficient as a function of system pressure; (a) Fe-=3 N L/h, (b) Fe=9 N L/h, (c) Fe =18 N L/h. Symbols: ( @) F,=100 ml/h, (©) F,=60 ml/t ,=30 ml/h.
Fig. 8. Parity plot for experimentally determined hy and values calculated from the correlation proposed in Eq. (5).
Fig. 8. Parity plot for experimentally determined hy and values calculated from the correlation proposed in Eq. (5).
Fig. 9. Evolution of axial temperatures during operation with imposed feed temperature modulation: Pr=15 bar, Fe-=9 N L/h, period=1.8 h, split=5/6, (a) F,=100 ml/h, (b) F,=60 ml/h, (c) F,=30 ml/h, Rock wool foam. Symbols: (@) T (1.5 cm), (G1) T (10 cm), (A) T (20.5 cm); discontinuous lines represent model predictions. The results of experiments conducted with imposed tempera- ture feed modulation are illustrated in Fig. 9 for a total pressure of 15 bar a gas flow rate of 9 NL/h and three different liquid low rates. The cycle period and split for these experiments were set to respectively 108 min and 5/6, i.e. feed temperature was periodi- cally modulated between 25 °C during 18 min to 159 °C during 90 min. However, the arrangement of the tubing and inlet column connections originates a distortion of the ideal square wave for the feed temperature and generates a V-shaped temperature distribution at the column inlet similar to the measured profiles at z=1.5 cm (see Fig. 9). In all cases, the liquid flow rate is not high enough to cool the hot reactor inlet to ambient temperature within 18 min. A longer time interval with cold flow would be Steady state axial temperature profiles have been measured in 1 rock wool insulated packed bed column with co-current
Fig. 9. Evolution of axial temperatures during operation with imposed feed temperature modulation: Pr=15 bar, Fe-=9 N L/h, period=1.8 h, split=5/6, (a) F,=100 ml/h, (b) F,=60 ml/h, (c) F,=30 ml/h, Rock wool foam. Symbols: (@) T (1.5 cm), (G1) T (10 cm), (A) T (20.5 cm); discontinuous lines represent model predictions. The results of experiments conducted with imposed tempera- ture feed modulation are illustrated in Fig. 9 for a total pressure of 15 bar a gas flow rate of 9 NL/h and three different liquid low rates. The cycle period and split for these experiments were set to respectively 108 min and 5/6, i.e. feed temperature was periodi- cally modulated between 25 °C during 18 min to 159 °C during 90 min. However, the arrangement of the tubing and inlet column connections originates a distortion of the ideal square wave for the feed temperature and generates a V-shaped temperature distribution at the column inlet similar to the measured profiles at z=1.5 cm (see Fig. 9). In all cases, the liquid flow rate is not high enough to cool the hot reactor inlet to ambient temperature within 18 min. A longer time interval with cold flow would be Steady state axial temperature profiles have been measured in 1 rock wool insulated packed bed column with co-current
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Mechanical EngineeringChemical EngineeringChemistryDynamic ModelingChemical Engineering ScienceTrickle BedPacked BedCatalytic Wet air oxidation
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