1.0 1. 0
ABSTRACT/SUMMARY
A tubular tubular reactor reactor is a vessel through through which which flow is continuou continuous, s, usually at steady state, and config configure uress so that that conver conversio sion n of the chemic chemicals als and other other depend dependent ent variab variables les are functions of position within the reactor rather than of time. The objectives of this experiment are to examine the effect of pulse input and step change input in a tubular flow reactor . Furthermore, the purpose is to construct a residence time distribution (RT! function for the tubular flow reactor . First of all, the general set up is run before the experiment begin. After that, the flowrate "##m$%min is set up. After the the conductivity for inlet and outlet collected are reaching to three times constant value, the experiment is stopped. For the first experiment which is pulse input, the conductivity for inlet and outlet after & minutes are #.#m'%cm and #.#m'%cm while the second experiment is .)m'%cm and *.* +s%cm respectively. The outlet conductivity, ( t ! then is calculated and the value is--...for the first experiment and--for the second experimen experiment. t. Then, the distribution distribution of exit time, (t ! are able to determine. The (t ! is calculated for each *# seconds. For the first experiment, the sum of ( t ! is --while the second second experim experiment ent is----w is----whic hich h is the residen residence ce time time distrib distributi ution. on. The The mean mean residence time, tm for the first experiment is ---. minute and ---minute for second experiment. The variance, / and the s0ewness, s0ewness, s * are also then calculated. The value get for / is --- and for the s * is --... in the first experiment while while the value / in the second experiment is---. and s * is----- 1raphs for outlet conductivity, ( t ! against time and distribution of exit time, ( t ! against time is plotted. The graphs get from this experiment are just the same with the graphs in the theory. theory. The value of ( t ! is depends on the value of (t !. !.
2.0
INTRODUCTION
2.1 The Flow Concept of Tuul!" Re!cto"
2n the tubular reactor, the reactants are continually consumed as they flow down the length of the reactor. Flow in tubular reactor can be laminar, as with viscous fluids in small3 diameter tubes, and greatly deviate from ideal plug3flow behaviour, or turbulent, as with gases. Turbulent flow generally is preferred to laminar flow, because mixing and heat transfer are improved. For slow reactions and especially in small laboratory and pilot3plant reactors, establishing turbulent flow can result in conveniently long reactors or may re4uire unacceptable high feed rates. 5owever, many tubular reactors that are used to carry out a reaction do not fully conform to this ideali6ed flow concept. 2n an ideal plug flow reactor, a pulse of tracer injected at the inlet would not undergo any dispersion as it passed through the reactor and would appear as a pulse at the outlet. The degree of dispersion that occurs in a real reactor can be assessed by following the concentration of tracer versus time at the exit. This procedure is called the stimulus3response techni4ue. The nature of the tracer pea0 gives an indication of the non3ideal that would be characteristic of the reactor. For most chemical reactions, it is impossible for the reaction to proceed to 7##8 completion. The rate of reaction decreases as the percent completion increases until the point where the system reaches dynamic e4uilibrium (no net reaction, or change in chemical species occurs!. The e4uilibrium point for most systems is less than 7##8 complete. For this reason a separation process, such as distillation, often follows a chemical reactor in order to separate any remaining reagents or by products from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in the 5aber process.
2.2
The Appl#c!t#on of Tuul!" Flow Re!cto"
Tubular flow reactors are usually used for this application which are large scale reactions,fast reactions, homogeneous or heterogeneous reactions, continuous production and high temperature reactions.
Residence Time istribution (RT! analysis is a very efficient diagnosis tool that can be used to inspect the malfunction of chemical reactors. 2t can also be very useful in modelling reactor behaviour and in the estimation of effluent properties. This techni4ue is, thus, also extremely important in teaching reaction engineering, in particular when the non3ideal reactors become the issue. The wor0 involves determining RTs, both by impulse and step tracer injection techni4ues, and applying them to the modelling of the reactor flow and to the estimation of the behaviour of a nonlinear chemical transformation. The RT techni4ue has also been used for the experimental characteri6ation of flow pattern of a pac0ed bed and a tubular reactor that exhibit, respectively, axially dispersed plug flow and laminar flow patterns (F9:!. The concept of using a ;tracer< species to measure the mixing characteristics is not limited to chemical reactors. 2n the area of pharmaco0inetics, the time course of renal excretion of species originating from intravenous injections in many ways resembles the input of a pulse of tracer into a chemical reactor. =ormally, a radioactive labelled ( 5, 7>, *:, etc.! version of a drug is used to follow the pharmaco0inetics of the drug in animals and human. Another important field of RT applications lies in the prediction of the real reactor performance, since the 0nown project e4uations for ideal reactor are no longer valid. =ow the concepts of macro and micro mixing are fundamental. For each macro mixing level, expressed in the form of a specific RT, there is a given micro mixing level, which lies between two limiting cases, complete segregation and perfect micro mixing.
$.0
OB%&CTI'&S/AIMS
For the experiment one, the purpose of the experiment is to examine the effect of a pulse input in a tubular flow reactor and to construct a residence time distribution (RT! function for the tubular flow reactor. 2n experiment two, the objective is to examine the effect of a step change input in a tubular flow reactor and to construct a residence time distribution (RT! function for the tubular flow reactor.
(.0
T)&ORY
2n a tubular flow reactor, the feed enters at one end of a cylindrical tube and the product stream leaves at the other end. The long tube and the lac0 of provision for stirring prevent complete mixing of the fluid in the tube. 5ence the properties of the flowing stream will vary from one point to another, namely in both radial and axial directions. 2t is often not necessary to 0now details of the entire flow fluid but rather only how long fluid elements reside in the reactor (i.e. the distribution of residence times!. This information can be used as a diagnostic tool to ascertain flow characteristics of a particular reactor. Tubular reactors
resemble batch reactors in providing initially high driving forces, which diminish as the reactions progress down the tubes. Tubular reactor are often used when continuous operation is required but without back-mixing of products and reactants. Flow in tubular reactors can be laminar, as with viscous uids in small-diameter tubes, and greatly deviate from ideal plug-ow behavior, or turbulent, as with gases. Turbulent ow generally is preferred to laminar ow, because mixing and heat transfer are improved. For slow reactions and especially in small laboratory and pilot-plant reactors, establishing turbulent ow can result in inconveniently long reactors or may require unacceptably high feed rates.
Tubular reactor is specially designed to allow detailed study of important process. The tubular reactor is one of three reactor types which are interchangeable on the reactor service unit. the reactions are monitored by conductivity probe as the conductivity of the solution changes with conversion of the reactant to product. This means that the inaccurate and inconvenient process of titration, which was formally used to monitor the reaction progress, is no longer necessary. The ;age< of a fluid element is defined as the time it has resided within the reactor. The concept of a fluid element being a small volume relative to the si6e of the reactor yet sufficiently large to exhibit continuous properties such as density and concentration was first put forth by anc0werts in 7)&*. 2n order to analy6e the residence time distribution of the fluid in a reactor the following relationships have been developed. Fluid elements may re4uire differing lengths of time to travel through the reactor. The distribution of the exit times, defined as the ( t ! curve, is the RT of the fluid. The outlet conductivity of a tracer species ( t ! can be used to define ( t !. That is? t
E ( t ) ≈
C out ( t ) ∞
∫ C
t out
( t ) dt
0
@ased on the data collected, a graph of conductivity versus time could be draw to obtain the (t! curve and data of the integral (t! could be calculate. ∞
∫ C ( t ) dt =∑ C i ∆ t = Area 0
Figure 4.1? Theory of graph with its formula area under the graph
ther things that are needs to be determined in this experiment are? +ean Residence Time
B
t (t !.dt
BC tii(t !
'econd moment Dariance, / B
(t 3 tm! (t !.dt BC (t 3 tm! (t !
Third +oment '0ewness, s* B
(t 3 tm!* (t !.dt BC (t 3 tm!* (t !
2f the RT function, ( t !, is very broad, however, it may be difficult to inject an amount of tracer that is sufficiently large so as to 0eep the outlet concentration sufficiently high to be measured accurately.
Figure 4.2? xample of graph when distribution exit time is very abroad
*.0
A++ARATUS AND MAT&RIA,
App!"!tu- !n !te"#!l SO,T& Tuul!" Flow Re!cto" Cloc w!tch
1. 0.1M of So#u )"o3#e 2. 0.1M of So#u Acet!te $. 0.1M of De#on#-e w!te"
+u"po-e The main instrument to read the conductivity, open and close the valve and the pump and etc. To record every ! second for reading of conductivity until it constant about three times and then stop. The materials used to prepare the standard solution before the experiment run.
Figure 5.1 ? 'oltec Tubular Flow Reactor instrument
4.0
&5+&RIM&NTA, +ROC&DUR&S 4.1
6ene"!l St!"t7up +"oceu"e
For the general start3up procedure, initially all the valves are closed except valve ". Then, #$iters of salt solution is prepared. =ext, the feed tan0 @ is filled with the sodium chloride solution. After that, the power button is turn on. The water e3ioni6er is connected to the laboratory water supply. Dalve D* is opened and the feed tan0 @7 is allowed to feed with the water. Dalve D* is closed as the water level reached the tan0 mar0. Dalve D and D7# then is opened and pump :7 is switched on. From observing the flow meter F73#7 value, The :7 pump is adjusted by controlling the flow controller to obtain a flow rate of approximately "##m$%min. =ext, valve DE and D7 are opened and pump : is switched on. From observing the flow meter F73# value, The : pump is adjusted by
controlling the flow controller to obtain a flow rate of approximately "##m$%min. Then the valve D7 is closed and pump : is turn off. The experiment can now be carried out.
4.2 &3pe"#ent One 8 +ul-e #nput #n ! Tuul!" Flow Re!cto". For the experiment one, the valve D) initailly is opened and pump :7 is switched on. The :7 pump is adjusted by controlling the flow controller to obtain a flow rate of approximately "##m$%min of de3ioni6ed water into the reactor R7. Then, the de3ioni6ed water is allowed to continue flowing through the reactor until the inlet (73#7! and outlet (73#! conductivity values are stable at low levels. @oth conductivity values is recorded. After that, the valve D) is closed and pump :7 is switched off. Dalve D77 is opened and pump : is switched on. The timer is simultaneously started. :ump : flow controller is adjusted to give a constant flow rate of salt solution into the reactor R7 at "##m$%min at F73 #. The salt solution is allowed to flow for 7minute, the timer is reset and restarted. This will start the time at the average pulse input. Dalve D77 is closed and pump : is switched off. Dalve D) is 4uic0ly opened and pump :7 is switch on.
@y adjusting pump :7 flow
controller, the de3ioni6ed water flow rate is always maintained at "##m$%min. The inlet (73 #7! and outlet (73#! conductivity values are recorded at regular interval of *# seconds. The conductivity values are recorded until all readings are almost constant and approach stable low level values.
4.$ &3pe"#ent Two8 Step Ch!n9e Input #n ! Tuul!" Flow Re!cto"
For the second experiment on step change input, the general start3up procedure was performed again as in E.7. Dalve D) was opened and pump :7 was switched on. :ump :7 flow controller was adjusted to give a constant flow rate of deioni6ed water into the reactor R7 at approximately "## m$%min at F23#7. The deioni6ed water was allowed to flow through the reactor until the inlet (23#7! and outlet (23#! conductivity values are stable at low levels. @oth conductivity values were recorded. Then, valve D) was closed and pump :7 was switched off. Dalve D77 was opened and pump : was switched on. The timer was set simultaneously. @oth the inlet (23#7! and outlet (23#! conductivity values were recorded
at regular intervals of *# seconds.
The conductivity values were ta0en down until all
readings are almost constant.
4.(
6ene"!l Shut7Down +"oceu"e
For the general shut3 down procedure, both pumps :7 and : were switched off. After that, the valves D and DE were closed. The heaters were switched off. ooling water was 0ept to circulate through the reactor while the stirrer motor is switched on to allow the water jac0et to cool down to room temperature.
Finally, the power for the control panel was
switched off.
:.0
R&SU,TS
:.1 &3pe"#ent One8 +ul-e #nput #n Tuul!" Flow Re!cto"
Flow rate " #!!m$%min &nput type " 'ulse input
T#e ;#n< 0.0 0.* 1.0 1.* 2.0 2.*
Conuct#=#t ;S/c< Inlet Outlet !.! !.( !. ).) !.( ). !.( ).* !.! ).* !.! !.+
$.0 $.* (.0 (.* *.0
!.! !.! !.! !.! !.!
!. !.( !.! !.! !.!
Table 7.1 : Table conductivity of pulse input
&3pe"#ent Two8 Step Ch!n9e Input #n ! Tu"ul!" Flow Re!cto" Flow rate
#!! m$%min
&nput type " tep change T#e ;#n< 0.0 0.* 1.0 1.* 2.0 2.* $.0 $.* (.0 (.* *.0 *.* 4.0 4.* :.0 :.* >.0
Conuct#=#t ;S/c< Inlet outlet !.! !.! ).# !.! ).+ !.! ).+ !.! ).+ !.! ).# (. ).# (. ). (. ). (. ).+ ).0 )./ ). )./ ).# )./ )./ )./ .( )./ . )./ . )./ .
