Glass Tube Fluidized Bed Pilot Plant - Research Paper Example

UO 01 FLUIDISED BED Table of contents Table of contents 2 Abstract 3 1.0 Introduction 4 1.1 Aims 4 1.3 Theory 5 1.3.1 Voidage 5 1.3.2 Fixed and fluidized beds 5 1.3.3 Pressure drop across a fluidised bed. 6 1.4 Operating procedure 8 2.0 Results and discussion: 9 2.1 Data Collection and Validation 9 2.1.1 Error analysis. 1 9 2.1.2 Error analysis 2.:Precision in measurement of voidage 11 2.1.3 Sample calculations 11 2.2 Theoretical Validation 12 2.2.1 Relationship between sedimentation velocity and superficial velocity 12 2.2.2 Relationship between change in pressure and superficial velocity 13 2.2.3 Relationship between voidage and superficial velocity 13 3.0 Discussions 16 4.0 Conclusion and recommendation 19 References 20 Abstract This experiment involved a 100mm 1D glass tube fluidized bed pilot plant. The experiment involved use of antifreeze diluted with water as the fluid while the particles were pyrex glass beads with diameter of 3.45mm and density of 2.5kg/l. One of the aims of the experiment was to visually study the behaviours of the fixed fluidized bed. In the analysis of errors the error associated with superficial velocity was 1.4% while the error in calculation of sedimentation velocity was found to be much higher at 22.9%. The graph between sedimentation velocity and superficial was approximately linear but the points were seen to be scattered about the general trend line, this being attributed to the big error in calculation of sedimentation velocity. From the experiment it was found that increasing the superficial velocity was accompanied by an increase in change in velocity up a certain point when change in pressure remain constant. When voidage was plotted against superficial velocity a non linear graph was obtained. By plotting  versus  a straight line graph was obtained and the values of the constants were established as =2.19 and . It was concluded that the values which were obtained from calculation were reliable, the relationship between variables conformed to theoretical expectation. It was recommended that a similar experiment should be undertaken with a few variations including change in density of particles, and size of particles; using higher volume particles and also using a tube of different dimension. 1.0 Introduction This experiment involve using glass tube with 100mm internal diameter, and the fluidized bed where the fluid used is of antifreeze that is diluted with water and the particles are pyrex glass beads with 3.45mm diameter with density of 2.5kg/l. There is recirculation of pumped fluid at varied flow rates. Theory: Fluidisation. Chemical Engineering Volume 2 Coulson & Richardson. 1.1 Aims 1. To visually study the behaviour of a fixed and fluidised bed (varied feed flowrates). 2. Studying the behaviour exhibited by a liquid fluidised bed through determination of (a) The relationship between velocities of fluidisation and sedimentation (b) The relation between pressure drop and liquid velocity (c) The Reynolds number at incipient fluidisation (d) The relation between voidage and fluidisation velocity 3 Studying the behaviour of a fixed bed determination of (a) The relationship between pressure drop and velocity of liquid (b) The voidage of a fixed bed of spherical particles. In the experiment fluidization velocity is the variable. It is also important for the density to be determined because it is likely to change in a span of a week. 1.3 Theory 1.3.1 Voidage The voidage  in fixed (packed) or fluidized bed is the value obtained by dividing of interstitial space between particles (fully filled by fluid) and the volume of bed which is the volume of the particles together with the spaces that are fluid filled. This means that voidage will always be less than unity. Spherical particles and other irregular but equiaxed particles including salt, sugar, and coal will be packed in away that result to having 0.4% voidage. The value of voidage will show variation depending on the extent of consolidation as well as the shape of particles. Finding the voidage is thus one of the aims of this experiment. 1.3.2 Fixed and fluidized beds In order for fluid to be driven through the particles there is to be some pressure drop in both fixed and fluidized beds , just as in the case of flow of water in pipes where there is pressure drop to overcome friction between pipe walls and fluid as well as friction between fluid layers. We have a situation where there is flow for the bulk the fluid but apportion of the fluid that is in contact with the solid surface of the particles remain stationary. This brings about shear force that brings about friction drag which is a resistance to flow, and it is necessary to have a drop in pressure along the bed so as to have a steady flow being maintained. In case of packed bed, an increase in the superficial velocity of flow will result to an increase in rate of shear and drag force which will then translate to a pressure drop. But if it reaches a point where the upward flow velocity has reached a point the upward drag force is going beyond the net weight downward force (buoyancy-corrected) of the particles, then this will result to the particles being dragged upward and thus becoming fluidized. This will lead to expansion of the bed with the voidage being increased as a result of the distance between particles being increased. This brings about a reduction in the level of shear rate, bringing down the resistance to flow (drag force is reduced) and this brings about a situation where we have a balance between the drag force and net weight of particles. The amount of bed expansion that is required to have the balance maintained will increase with increasing flow velocity in the fluidized bed. The shear and drag force rate is to be unchanged irrespective of flow velocity owing to the fact that we have the net weight of the fluidized particles remaining constant. It is due to this scenario that we have the pressure drop increasing with the increasing superficial velocity of flow when dealing with a fixed bed whereas in the case of fluidized bed we have pressure drop remaining constant. There is also additional pressure drop contribution from pipe friction and this brings about a slight increase with increasing velocity of flow even when dealing with a fluidized bed. 1.3.3 Pressure drop across a fluidised bed. In dealing with a fluidized the upward drag force on the bed attributable to pressure drop can be equated to the net weight (buoyancy –corrected ) of bed This gives us : In the expression where A is area of the cross-section of the tube, and  represent the densities of the solid particles and liquid respectively , while  gives pressure difference resulting from fluid friction in the height h of bed. It is worth noting that the equation is only applicable to cases involving fluidized states. It is also important to note that the right side of the equation represents net weight of bed which is fixed , does not depend on fluid velocity, meaning that increase in h is to be compensated by a decrease in  and that  would remain constant. In this equation the small contribution of pressure drop resulting pipe friction is neglected. The superficial velocity uc for fluid flow in either fixed or fluidized bed is obtained by dividing fluid flow rate by the cross-section area of tube while interstitial velocity is obtained by dividing flow rate by cross-sectional area of tube that is available for fluid flow via the spaces between the particles. This means that the interstitial velocity will always be greater that superficial velocity with a value of  Critical look at fluidization and sedimentation will reveal that there is similarity between the two since in both cases we have fluid and assembly of particles moving relative to each other. In the case of sedimentation we have the fluid being stationary while the particles move downwards. For the case of fluidization we have the fluid moving upwards at the interstitial velocity with the particles remaining stationary in relation to the tube. In both cases we have a downward movement of particles considering the fluid to be the reference point. This means that the relative velocities between the particles and fluid should have similarity if the particle concentration is similar. This is to say, since we are dealing with relative velocities which are interstitial velocities in both cases, then it will be expected that  in the case of fluidization will approximately be equal to (sedimentation velocity in sedimentation process). It is thus expected that  and  which are the superficial fluidization velocity and superficial sedimentation velocity will exhibit similarity in the case where we have similar concentration level of particles. 1.4 Operating procedure It was ensured that the level in T1 was standing at 90% full. The next step involved opening valve V202 then starting pump P2 followed by slow opening of valve V204. Valve V201 is opened to sample feed. 2.0 Results and discussion: 2.1 Data Collection and Validation 2.1.1 Error analysis 1 2.1.1.(A) Precision in measurement of superficial velocity calculation Superficial velocity is given by  The measuring Q at 2000l/hr error is 50 This translates Thus at 2000l/hr  This shows a precision of 0.001 As a percentage =  2.1.1(B)Precision in measurement of sedimentation velocity Sedimentation velocity is given by  With   h=0.0583 t=1.91  This translates to a precision As a percentage = 2.1.2 Error analysis 2.:Precision in measurement of voidage Voidage is given obtained from expression Where  is given as height of water The measured quantities that bring about propagation of error are  and With  h=0.504  =0.31  As a percentage = 2.1.3 Sample calculations For first experiment h1=30.35cm =0.3035m Area of tube  1L/h =2.78x10-7 m3/s From experiment at 2000lll/s Sedimentation velocity at Q=2000 2.2 Theoretical Validation 2.2.1 Relationship between sedimentation velocity and superficial velocity Figure 4.1 shows the relationship between sedimentation velocity and  and superficial velocity. From the figure it can be seen that the two variables have a close to linear relationship. Figure 4.1 2.2.2 Relationship between change in pressure and superficial velocity The relationship between change in pressure  and superficial velocity is as shown in figure 4.2. From the figure it can be seen that initially there is a linear relationship between change in pressure and superficial velocity. But it reached a point when an increase in velocity does not result in and increase in change in pressure. Figure 4.2 2.2.3 Relationship between voidage and superficial velocity The relationship between voidage and superficial velocity is as shown in figure 4.3 .from the figure it can be seen that the graph tends to flatten as the superficial velocity is increased. Figure 4.3 2.2.4 Relationship between   In figure 4.3 it was observed that the relationship between superficial velocity and voidage does not exhibit a linear relationship. In order to obtain further information about the variables it was necessary to have a logarithm plot for the two variables as can be seen in figure 4.4. Figure 4.4 According to Richardson and Zaki's empirical equation,  Which can be written in logarithmic form as: This is what has been used to plot the graph figure 4.4 From the graph  Therefore =2.19 n is the gradient of graph =  Replacing the values of n and  in  We have Which can be written as 3.0 Discussions In this experiment a number of quantities required to be obtained through calculation. Some of the quantities used in the calculation were obtained by measurement using measuring instrument. With the calculations involving a number of quantities which had errors it means that the errors are propagated through the calculation and this means that there is need to know the extent of error propagation and hence the authenticity of the obtained answers. In the measurement of superficial velocity the quantity which was measured from experiment was the discharge Q and from the calculation it was found that there was a very small error in the calculated value where the percentage error was found to be 1.4%. In the calculation of sedimentation velocity the percentage error was found to be quite high standing at 22.1%. In this calculation two quantities obtained from experiment were used in calculation and there were no constants such as gravitational force of density which were used. The fact that we had two measured quantities being used in calculation means that the error in obtained is likely to be higher as opposed to the case where only one quantity is being obtained experimentally. The other issue was the precision of the measured quantities relative to the size of the measured quantity. It is found that the size of the two quantities ie time that was measured and the height h were relatively low relative to the level of precision. But there was caution taken to ensure that the margin of error was reduced by having 3 runs of the measured quantities so that the average value was used. With this precaution in place the sedimentation velocity calculated can be said to be within experimental error and acceptable. The calculation of voidage involved two measured quantities both of which were measured in heights and had the same level of precision. Even though this calculation involved other parameters such as densities and gravitational force this were regarded as constants and did not result to errors. The percentage error was obtained as 3.7% which is relatively low and this indicating that the obtained value highly accurate. In using the average values the variation in the values obtained maybe used to obtain the margin of error as opposed to the precision of the instrument. This may be especially useful when it comes to recording time. While the stop watch may be having very high level of precision the error in the time recorded may depend on the person using the stop watch where the watch may be stopped early or there may be delay in stopping the watch. In the experiment a graph of sedimentation velocity versus superficial velocity was plotted. From the graph it was seen that the general trend was that the two variables had a linear relation which is expected theoretically. But the points which were on the graph exhibited high level of scattering with very few lying on the general trend line. This can be attributed to the fact that the sedimentation velocity had very high errors as seen previously in the error analysis. In the plot of change in pressure  versus superficial velocity the graph conformed to what was expected. At the initial stage we had change in pressure increasing with an increase in superficial velocity but beyond a certain velocity change in pressure remained constant. When voidage was plotted against superficial velocity a non-linear graph was obtained a clear indication that the two variable were not related linearly. This was in support of Richardson and Zaki's empirical equation which shows a polynomial relationship between the variables. By using by plotting  versus  a straight line graph was obtained and the constants were successfully obtained from the graph. With the value of n and  being found to be 0.39 and 2.19 respectively, the precision of the values could be said to be 0.01. 4.0 Conclusion and recommendation From the experiment it the issue of precision of calculated values has been brought out very clearly. It can be safely be concluded that the values which were calculated were reliable looking at the percentage error even though in calculation of sedimentation velocity it was clearly that the values were more of approximation. From the graphs which were plotted and the calculations which were undertaken, the experiment conformed to what was expected. It is recommended that a similar experiment be done with different concentration of solids the same solids. Also there can be use of difference density solids and dimension of the tube to be changed. References V. C. Kelessidis, “Terminal Velocity of Solid Spheres Falling in Newtonian and non Newtonian Liquids,” Tech. Chron. Sci. J. TCG, vol. V, no. 1-2, pp. 43-54, 2003. ]15[ Y. S. Chong, D. A. Ratkowsky, and N. Epstein, “Effect of particle shape on hindered settling in creeping flow,” Powder Technology, vol. 23, no. 1, pp. 55-66, 1979/6//, 1979. A. Cuthbertson, P. Dong, S. King, and P. Davies, “Hindered settling velocity of cohesive/non-cohesive sediment mixtures,” Coastal Engineering, vol. 55, pp . .2008 ,1208-1197 R. A. Alrawi, N. N. N. A. Rahman, A. Ahmad, N. Ismail, and A. K. M. Omar, “Characterization of Oily and Non-Oily Natural Sedimentsin Palm Oil Mill Effluent,” Journal of Chemistry, vol. 2013, pp. 11, 2013. Y. Kousada, and Y. Endo, "Particle Density," Powder Technology :Fundamentals of Particles, Powder Beds, and particle Generation, H. Masuda, K. Higashitani and H. Yoshida, eds., pp. 49- 52: CRC Press, Taylor & Francis Group, 2007. R. Davies, "Size Measurment," Powder Technology: Fundamentals of Particles, Powder ,Beds, and Particle Generation H. Masuda, K. Higashitani and H. Yoshida, eds., pp. 13-32: CRC Press, 2007. Read More

1.3.3 Pressure drop across a fluidised bed. In dealing with a fluidized the upward drag force on the bed attributable to pressure drop can be equated to the net weight (buoyancy –corrected ) of bed This gives us : In the expression where A is area of the cross-section of the tube, and  represent the densities of the solid particles and liquid respectively , while  gives pressure difference resulting from fluid friction in the height h of bed. It is worth noting that the equation is only applicable to cases involving fluidized states.

It is also important to note that the right side of the equation represents net weight of bed which is fixed , does not depend on fluid velocity, meaning that increase in h is to be compensated by a decrease in  and that  would remain constant. In this equation the small contribution of pressure drop resulting pipe friction is neglected. The superficial velocity uc for fluid flow in either fixed or fluidized bed is obtained by dividing fluid flow rate by the cross-section area of tube while interstitial velocity is obtained by dividing flow rate by cross-sectional area of tube that is available for fluid flow via the spaces between the particles.

This means that the interstitial velocity will always be greater that superficial velocity with a value of  Critical look at fluidization and sedimentation will reveal that there is similarity between the two since in both cases we have fluid and assembly of particles moving relative to each other. In the case of sedimentation we have the fluid being stationary while the particles move downwards. For the case of fluidization we have the fluid moving upwards at the interstitial velocity with the particles remaining stationary in relation to the tube.

In both cases we have a downward movement of particles considering the fluid to be the reference point. This means that the relative velocities between the particles and fluid should have similarity if the particle concentration is similar. This is to say, since we are dealing with relative velocities which are interstitial velocities in both cases, then it will be expected that  in the case of fluidization will approximately be equal to (sedimentation velocity in sedimentation process). It is thus expected that  and  which are the superficial fluidization velocity and superficial sedimentation velocity will exhibit similarity in the case where we have similar concentration level of particles. 1.4 Operating procedure It was ensured that the level in T1 was standing at 90% full.

The next step involved opening valve V202 then starting pump P2 followed by slow opening of valve V204. Valve V201 is opened to sample feed. 2.0 Results and discussion: 2.1 Data Collection and Validation 2.1.1 Error analysis 1 2.1.1.(A) Precision in measurement of superficial velocity calculation Superficial velocity is given by  The measuring Q at 2000l/hr error is 50 This translates Thus at 2000l/hr  This shows a precision of 0.001 As a percentage =  2.1.1(B)Precision in measurement of sedimentation velocity Sedimentation velocity is given by  With   h=0.0583 t=1.91  This translates to a precision As a percentage = 2.1.2 Error analysis 2.

:Precision in measurement of voidage Voidage is given obtained from expression Where  is given as height of water The measured quantities that bring about propagation of error are  and With  h=0.504  =0.31  As a percentage = 2.1.3 Sample calculations For first experiment h1=30.35cm =0.3035m Area of tube  1L/h =2.78x10-7 m3/s From experiment at 2000lll/s Sedimentation velocity at Q=2000 2.2 Theoretical Validation 2.2.1 Relationship between sedimentation velocity and superficial velocity Figure 4.

1 shows the relationship between sedimentation velocity and  and superficial velocity. From the figure it can be seen that the two variables have a close to linear relationship. Figure 4.1 2.2.

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