Design and operation of micro-chemical plants—bridging the gap between nano, micro and macro technologies

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<ul><li><p>Computers and Chemical Engineering 29 (2004) 5764</p><p>Design and operation of micro-chemicalacr</p><p>Campus</p><p>July 200er 2004</p><p>Abstract</p><p>In the last s for rereported the ew micresearch, the sed frothe design p ms: ththe entire m ystemsbe solved by ics ofchemical pla the desthe possibility to act as a bridge between chemical engineering science and process systems engineering. 2004 Elsevier Ltd. All rights reserved.</p><p>Keywords: Micro chemical plant; CFD simulation; Numbering up; Optimal design</p><p>1. Introdu</p><p>Advanction of prothe processof strategytion of highof temperadifficult forEven thougfor the procup from labproblems,of the micr</p><p>The resfields. Thechemical lacombinato</p><p> Tel.: +81E-mail a</p><p>0098-1354/$doi:10.1016/jction</p><p>ed chemical industries always move in the direc-ducing high value-added products and reducingdevelopment period. The problem is what kind</p><p>can be taken to achieve these targets. The produc-value-added products requires the precise control</p><p>ture, flow pattern and residence time, etc., but it isconventional plants to satisfy these requirements.h computer-aided design systems have been usedess design, many steps are still needed for scalingoratory size to industrial size. To overcome these</p><p>many researchers have discussed the availabilityo-systems for production.earch on micro systems is classified into four</p><p>first is related to the efficient operation ofboratories. The research called lab-on a chip orrial chemistry belongs to this field. The second</p><p>75 383 2667; fax: +81 75 383 2657.ddress: hasebe@cheme.kyoto-u.ac.jp.</p><p>field is the development of the analytical devices using themicro technologiesusually called micro-TAS. The thirdinvolves the micro fabrication techniques. The techniquesdeveloped in the field of micro-electro-mechanical systems(MEMS) are widely used to develop micro devices. The lastis the research on the development of the production systemsconsisting of micro devices. This manuscript is limited tothe problems related to the last field. Micro-chemical plants(MCPs) consist of micro devices such as micro reactors,micro mixers, and micro heat exchangers. The developmentof these devices is indispensable to constructing MCPs. Inas-much as there are exhaustive reviews on the present statusof the development of these micro unit operations (Hessel&amp; Loewe, 2003a, 2003b, 2003c) and introductory booksof micro process engineering (Ehrfeld, Hessel, &amp; Loewe,2002b; Hessel, Hardt, &amp; Loewe, 2003), in this researchthe problems related to individual unit operation are notdiscussed.</p><p>Few micro-chemical plants (MCPs) have been used forreal production; therefore, engineers have neither the expe-rience in designing MCPs, nor any systematic tools for their</p><p> see front matter 2004 Elsevier Ltd. All rights reserved..compchemeng.2004.07.020between nano, micro and mShinji Hasebe</p><p>Department of Chemical Engineering, Kyoto University, KatsuraReceived 11 June 2004; received in revised form 27</p><p>Available online 11 Septemb</p><p>decade, much effort has been devoted to developing micro deviceadvantages of using such micro devices for production. However, fdesign and operation problems of micro chemical plants are discus</p><p>roblems of micro chemical plants are classified into two sub-probleicro plant. For each of the sub-problems the features of the micro s</p><p>process systems engineers are pointed out. Then, the characteristnts are summarized. Finally, it is pointed out that the research onplantsbridging the gapo technologies</p><p>, Nishikyo-ku, Kyoto 606-8501, Japan</p><p>4; accepted 28 July 2004</p><p>action, mixing and separation. Many researchers havero chemical plants are used for real production. In thism the viewpoint of process systems engineering. First,e design of the micro unit operations and the design ofare explained and the dominant problems which must</p><p>the instrumentation and control problems of the microign and control problem of micro chemical plants has</p></li><li><p>58 S. Hasebe / Computers and Chemical Engineering 29 (2004) 5764</p><p>design and control. One of the dominant characteristics of theMCPs is that the research results can be transferred into pro-duction much faster. Thus, it is very important to elucidate theproblems wpropose sothe emphasthe MCPs asolved; theexplained.</p><p>2. Possibil</p><p>When ason for usito say thattional planat the prodconventionwhich is drdecade, mamicro devifer a compsystems. Hisfy the aboengaged inresults from</p><p>One oflarge surfais decreasebecomes oThe increabeneficial ccomes efficcan be conalso be usethe efficiennumber bebecomes lathe residenare interestthese char2002; DECRinard, 20decreasedtimes smalone of theto the prodthe amount</p><p>Fig. 1 sthat the batdifferent prand/or prodare requireis operatedproduct is p</p><p>lly. WCP? Irate oamount of production with the batch plant is aroundcm3/h. This amount of production can be attained byuare channels each of which has a cross-sectional area0m 600m, if the average flow speed is 0.1 m/s (see2). However, it should be mentioned that the residenceis 1 s if the length of the device is 10 cm. From thisple, it becomes clear that the residence time, not the sizedevice, is the problem. In this case, much effort should</p><p>voted to increasing the reaction rate. One of the featuresicro devices is that the temperature can be controlledy. If the device can be operated at a higher temperatureing this characteristic, the reaction rate can be increased.example shows that if a sufficient reaction rate can beved in micro-devices, the MCPs can be used not onlye production of small volume specialty chemicals but</p><p>for the production of commodity chemicals of mediume.</p><p>esign problem of MCPs</p><p>e design problem of MCPs is classified into two sub-lems: the design of micro devices, and the design ofntire plant. Here, the dominant characteristics of theselems are explained.hich occur in the design and control of MCPs andlutions for those problems. From this viewpoint,is is placed on explaining the characteristics ofnd pointing out the future research subjects to beconcrete techniques to solve the problems are not</p><p>ity of MCPs</p><p>n MCP is developed for real production, the rea-ng micro devices must be clear. It is meaninglessa product which can be produced in a conven-</p><p>t can also be produced in an MCP. We must aimuction of materials that cannot be produced inal chemical plants, or the production efficiency ofastically improved by using an MCP. Over the lastny kinds of materials have been produced throughces. Hessel and Loewe (2003a, 2003b, 2003c) of-rehensive list of the materials produced by microowever, the number of products which really sat-ve conditions is not clear. Scientists and engineersthe research of MCPs must always evaluate theirthe viewpoint of real production.</p><p>the dominant characteristics of micro devices isce to volume ratio. When the diameter of a tubed to one hundredth, the surface to volume ratione hundred times larger than the original device.se in the surface to volume ratio exhibits manyharacteristics. Heat transfer through the wall be-ient, and as a result the temperature in the devicetrolled precisely. The surface of the channels cand efficiently. This results in the improvement ofcy of catalytic reaction. Because the Reynoldscomes very small, the flow inside the deviceminar flow, which is very helpful for controllingce time distribution precisely. Many researchersed in the development of micro systems that takeacteristics into account (Ehrfeld, 1999; Baselt,HEMA, 2003; Matlosz, Ehrfeld, &amp; Baselt, 2001;00). However, when the diameter of the tube isto one hundredth, the flow rate becomes 10,000ler than the original device. The production rate isdominant problems of an MCP when it is applieduction process. Thus, it is meaningful to discussof production of MCPs with an example.</p><p>hows a conventional batch plant. It is assumedch size is 1.0 m3 of product, and that ten kinds ofoducts are produced by changing the raw materialuction conditions. It is also assumed that 2 daysd for one batch of production, and the process320 days in a year. In this case, 16 m3 of eachroduced in a year when every product is produced</p><p>equaan Mflowsame</p><p>200016 sqof 60Fig.timeexam</p><p>of thebe deof measilby usThisachiefor thalsovolum</p><p>3. D</p><p>Thprobthe eprobFig. 1. Conventional batch plant.</p><p>Fig. 2. Micro chemical plant.</p><p>hat is the same amount of products is produced inf one train of MCP is assigned to one product, thef each production train which is enough for the</p></li><li><p>S. Hasebe / Computers and Chemical Engineering 29 (2004) 5764 59</p><p>Fig. 3. Effect of shape on flow distribution.</p><p>3.1. Design of micro unit operations</p><p>Many types of micro devices have been proposed for eachof the micro unit operations (MUO), but there is no standardshape for eaof the desigexplained i</p><p>3.1.1. FormIn a co</p><p>are modeleflow, steadywords, eachsystem. Rsimulationalgorithm.simulationso complicfrom the ptime distri</p><p>design problem of MUOs usually includes the constraints onthe temperature profile, residence time distribution and/orsize of segments to be mixed. To satisfy these requests, theshape of the device must be included in the design variables inaddition to the size of the device. As the flow inside the devicebecomes laminar flow, it is possible to execute precise CFDsimulation, and it can be embedded in the design algorithm.</p><p>In order to show how the shape of the device affects theflow pattern in the device, the design problem of a plate fintype micro device is used as an example (Commenge, Falk,Corriou, &amp; Matlosz, 2002; Ehrfeld et al., 2000a). The platefin type micro device is a typical micro reactor for catalyticreaction. When the catalytic reaction occurs in the channels,it is desirable to make the residence times at all channelsuniform. Fig. 3 shows the mass flow rate at each channelof the plate fin type micro devices (Tonomura et al., 2003).The black circle in the figure represents the flow rate at eachchannel of a Type B-1 device. The white circle shows theflow rate of a Type B-2 device. From the viewpoint of flowuniformity, Type B-2 is better than Type B-1. The differencebetween these two devices is the size of the outlet manifold</p><p>That iow die shait is araints</p><p>e conse deviully sn properatg all c</p><p>iven o</p><p>. Deshen cn march type of MUO. Thus, the general characteristicsn problems of micro unit operations (MUOs) aren this section.</p><p>ulation of design problemnventional design problem, the unit operationsd by using terms such as perfect mixing, pistonstate, and total heat transfer coefficient. In otherunit operation is modeled as a lumped parameter</p><p>ecently, computational fluid dynamics (CFD)has been gradually introduced in the designHowever, much effort is required to adjust theparameters, because the flow inside the vessels isated. The desirable characteristics of MUOs ariserecise controls of the temperature, the residencebution and/or the degree of mixing. Thus, the</p><p>area.</p><p>the flTh</p><p>thus,constof thof thcarefdesigunit oisfyinthe g</p><p>3.1.2W</p><p>desigFig. 4. Design algorithm of micro unit operations.</p><p>s, the magnification of outlet manifold area makesstribution uniform.pe of the device has a large degree of freedom;lmost impossible to derive the best shape if noare added to the shape. However, the introductiontraints to the shape interferes with the emergenceces designed by a completely new idea. We mustelect the constraints which are embedded in theblem. Fig. 4 shows a design algorithm of microions. In this algorithm, the shape of the device sat-onstraints is gradually improved so as to optimizebjective function.</p><p>ign marginhemical equipment is designed, some amount ofgin is added to each variable so as to compensate</p></li><li><p>60 S. Hasebe / Computers and Chemical Engineering 29 (2004) 5764</p><p>for unforesthe designproductiona device stdesign andIn this caspected. Incross-sectiobe the domvice. It is ois not satisIf the deviincreased,from this emodel andsign margifor by themargin.</p><p>Laminamicro-devisimulationreactions iThe advanpossibilitiesystem andmargin.</p><p>3.1.3. ReevThough</p><p>ventional cwith atomstablished inthe behavioterms whiccannot be nthe resultsexplained.</p><p>Plate-finof micro hplate-fin-ty(Tonomuraof plates ar</p><p>6. Schematic view of counter-flow plate-fin micro heat exchanger.</p><p>. Under the conditions shown in Fig. 6, CFD simulationsFluent code were performed to analyze the influence</p><p>ysical properties of materials on the heat transfer per-ance. Three types of materialscopper, stainless steel,lasswere examined. Their thermal conductivities are16.3, and 0.78 W m1 K1, respectively. Temperatureges of heat transfer fluids were used to evaluate the per-ance o</p><p>arizeicro hr thanhen thure pre longn in Fangerthe waefore,ved byh lead</p><p>1ransfer</p><p>ials</p><p>ress stee</p><p>0.78 64.8Fig. 5. Effects of design margin.</p><p>een variations. This method can be used whenmargin always shows a beneficial effect on theefficiency of the device. In MUOs, the size of</p><p>rongly affects its function, that is, the functionalphysical design cannot be executed separately.</p><p>e, the design margin may not work as well ex-the simple micro device shown in Fig. 5, thenal area and the residence time are assumed toinant factors which affect the function of the de-bvious that the function expected from the devicefied when the cross-sectional area is increased.ce is lengthened or the number of channels isthe residence time is also increased. It is clearxample that in the MCPs the uncertainties of theparameters may not be compensated by the de-</p><p>ns. Thus, the disturbance should be compensatedadjustment of the operation as well as the design</p><p>r flow characteristics are exhibited in a channel of ace. Recent advances of computer technology andalgorithms enable us to simulate the flows with</p><p>n the micro devices by using a CFD simulator.ce of the CFD simulation algorithm creates news for embedding the CFD simulator into the designdesigning devices which do not require any design</p><p>aluation of the neglected termsa micro device is fairly small compared with con-hemical equipment, it is still very large compared</p><p>Fig.</p><p>flowsusingof phformand g388,chanformsumm</p><p>of mhighe</p><p>Wperatin thshowexchsideTherachiewhic</p><p>TableHeat t</p><p>Mater</p><p>CoppeStainlGlassor molecules. In principle, the physical laws es-the conventional world can be used to describe</p><p>r in the device. However, it is probable that someh have been neglected in the conventional designeglected in the design of MUO. As an example,of an efficiency analysis of heat exchangers are</p><p>-type micro heat exchangers are representativeeat exchangers. Fig. 6 shows the counter-flowpe micro heat exchanger investigated in this work, Kano, Hasebe, &amp; Hashimoto, 2002). A numbere stacked, and on each plate a hot or cold stream Ff micro heat exchangers. The simulation resultsd in Table 1 show that the heat transfer efficiencyeat exchangers made of stainless steel or glass is</p><p>that of copper.e copper micro heat exchanger is used, the tem-ofile inside the wall (device itself) becomes flatitudinal direction due to high heat conduction asig. 7 (left). The stainless steel or glass micro heatgenerates an appropriate temperature gradient in-ll in this case study, as shown in Fig. 7 (right).higher...</p></li></ul>