Wikisheet Oscillating Baffle Reactors

Transcription

1 Wikisheet Oscillating Baffle Reactors Intensification by independent control of flow and mixing Objective Contribute to energy efficiency program Background, Wikisheets Process Intensification within the PIN-NL program 2016 project Parties Focal points Phone Author Henk van den Berg T h.vandenberg@utwente.nl M Second reading and comments Henk Akse, chairman PIN-NL T M henk.akse@traxxys.com Version, date 6 April 2017 Document: WikiOsillatingBaffleRXv1 Status Version 1 Comments: Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 1

2 1. Description A description of the essentials of OBR have been given by Xiong-Wei Ni (2006) as follows. Companies such as NiTech Solutions have developed a tubular reactor that can achieve plug flow under laminar flow conditions. Figure 1 shows the basic configuration of a NiTech continuous oscillatory baffled reactor (COBR). It consists of a tubular device with periodicallyspaced orifice baffles, superimposed with fluid oscillation. There are three key features for this type of system. Firstly, mixing is achieved by the generation and cessation of eddies. As each baffled cell acts as a CSTR, it is possible to have a very high number of tanks in series by simply arranging baffle cells as shown in Figure 1. Secondly, the mixing in the COBR is independent of net flow, so laminar flows can be operated, maintaining much longer residence times that cannot be achieved in turbulent flow system. Lastly, the reactor allows controlling mixing with a high degree of precision, providing a wide range of mixing conditions from 'soft' mixing with plug flow characteristics, to the most intense, approaching mixed flow conditions. Figure 2 shows the residence time distributions in a COBR, and the plug flow characteristics are clearly seen here. Figure 1 Schematic of a COBR continuous oscillatory baffled reactor Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 2

3 Figure 2 RTD profiles in a specific COBR, Re o = 4518 (x o = 6 mm, f = 3 Hz); Re n = 504 ( flow = 1.5 l/min); Probes 1, 2 and 3 were located 3.7, 7.9 and 10.1 m away from the tracer injection port respectively Note. Re o = oscillatory Re number, x o = oscillation amplitude. Correlations see below in 2. Process envelope. From Xiong-wei Ni in Wikipedia: The technology incorporates annular baffles to a tubular reactor framework to create eddies when liquid is pushed up through the tube. Likewise, when liquid is on a downstroke through the tube, eddies are created on the other side of the baffles. Eddy generation on both sides of the baffles creates very effective mixing while still maintaining plug flow. By using COBR, potentially higher yields of product can be made with greater control and reduced waste. And: A standard COBR consists of a mm ID tube with equally spaced baffles throughout. There are typically two pumps in a COBR; one pump is reciprocating to generate continuous oscillatory flow and a second pump creates net flow through the tube. This design offers a control over mixing intensity that conventional tubular reactors cannot achieve. Each baffled cell acts as a CSTR and because a secondary pump is creating a net laminar flow, much longer residence times can be achieved relative to turbulent flow systems. Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 3

4 Figure 3. Flow eddies in the NiTech COBR, from NiTech - Continuous Oscillatory Baffled Reactor, Case study 012/ Process envelope In 2003 Ni, Mackley, Harvey, Stonestreet, Baird and Rao published a review paper. We will take basics about COBR from this publication. The fluid mechanical conditions in an COBR are governed by two dimensionless groups, namely, the oscillatory Reynolds number (Re o ) and the Strouhal number (St), defined as: where D is the column diameter (m), ρ the fluid density (kg/m 3 ), μ the fluid viscosity (kg/m.s), x o the oscillation amplitude (m) and ƒ the oscillation frequency (Hz). The oscillatory Reynolds number describes the intensity of mixing applied to the column, while the Strouhal number is the ratio of column diameter to stroke length, measuring the effective eddy propagation. The product of 2πƒx o is the maximum oscillatory velocity (m/s). For continuous operation, the traditional net flow Reynolds number (Re n = ρdu/μ) is also relevant, where u is the net flow velocity (m/s). In the publication of Abbott et al. (2013) scale-up has been clearly explained. A promising aspect of OBR technology is the ability to scale-up processes by maintaining geometrical and dynamic similarity, allowing mixing and flow conditions produced at laboratory scale to be easily replicated for pilot and industrial-scale processes. St, Re o and Re n are assumed to fully define the fluid dynamic conditions for a particular OBR geometry. By keeping these parameters constant, an OBR with a diameter of, for example, 24 mm should behave the same as one with a diameter of 150 mm. Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 4

5 However, at higher diameters, the frequency of oscillation must be extremely low, which reduces the mixing intensity and the opportunity for improved mass transfer. To overcome this problem, a method of scale-up involving a bundle of relatively small diameter OBRs operated in parallel, thereby removing the need for extremely low frequencies, has been proposed. This solution produces two other problems: how to maintain an equal distribution of flow to each separate tube, and generating equal oscillating conditions. Table 1 Required conditions to maintain St and Re o at 1.0 and 500 respectively Meso-OBR is related to smaller size COBR systems. Publications reviewed by McDonough, Phan and Harvey (2015) cover systems for flows ml/min and tube diameters <15 mm, typically mm. Meso-OBR technology can conveniently be used for screening purposes and can be more efficient than batch tests. See the publications of Phan et al. (2010, 2011, 2012). The meso-obr also has a variety of different baffle configurations including: integral, central axial, helical and wire wool designs, see Figure 4 (from McDonough et al.). Figure 4 Mesoscale baffle configurations: (a) integral baffles, (b) central axial baffles, (c) roundedged helical baffles, (d) sharp-edged helical baffles, (e) sharp-edged helical baffles with a central insert, (f) wire wool baffles. The integral baffle design is particularly advantageous for shear-sensitive applications such as bio-processes because of the smooth constriction. They have also been used for gas liquid and solids suspension applications. The helical baffles with central insert and wire wool designs are beneficial for enhanced interphase dispersion between immiscible liquids. The central axial design has been used for homogeneous liquid reactions due to the higher shear compared with the integral design, while the helical baffles can provide a high degree of plug flow over a wide range of oscillation conditions. Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 5

6 3. Advantages and limitations An essential advantage of a COBR is that the flow and the mixing can be controlled independently. According to Ni, Mackley, Harvey, Stonestreet, Baird and Rao (2003): In a COBR can be realized: - Improved residence time distribution, independently of net flow conditions - Improved heat transfer compared to laminar flow in tubes - Good mixing and dispersion at uniform shear stress in combination with lower maximum shear stress than observed in stirred tank vessel From the review of Abbott et al. (2013) we extract the following overview: Table 2 Advantages provided by OBRs over conventional CSTRs and tubular reactors According to Ni, Mackley, Harvey, Stonestreet, Baird and Rao (2003): COBR could be ideal for use as plug flow reactors in chemical, pharmaceutical or biochemical unit operations, particularly for long residence time processes where the large length-to-diameter ratio of the reactor (necessary to achieve the high Re n required for plug flow) can make reactor operation extremely difficult, often rendering the reactor impractical. This illustrates one of the OBR s niche applications: the OBR allows the conversion of long residence time batch processes to continuous processing, an example of process intensification. From Xiong-wei Ni in Wikipedia: Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 6

7 The low shear rate and enhanced mass transfer provided by the COBR makes it an ideal reactor for various biological processes. For shear rate, it has been found that COBRs have an evenly distributed, five-fold reduction in shear rate relative to conventional tubular reactors; this is especially important for biological process given that high shear rates can damage microorganisms. For the case of mass transfer, COBR fluid mechanics allows for an increase in oxygen gas residence time. Furthermore, the vortexes created in the COBRs causes a gas bubble break-up and thus an increase in surface area for gas transfer. For aerobic biological processes, therefore, COBRs again present an advantage. An especially promising aspect of the COBR technology is its ability to scale-up processes while still retaining the advantages in shear rate and mass transfer. Though the prospect for COBR applications in fields like bioprocessing are very promising, there are a number of necessary improvements to be made before more global use. Clearly, there is additional complexity in the COBR design relative to other bioreactors, which can introduce complications in operation. Furthermore, for bioprocessing it is possible that fouling of baffles and internal surfaces becomes an issue. Perhaps the most significant needed advancement moving forward is further comprehensive studies that COBR technology can indeed be useful in industry. There are currently no COBRs in use at industrial bioprocessing plants and the evidence of its effectiveness, though very promising and theoretically an improvement relative to current reactors in industry, is limited to smaller laboratory-scale experiments. 4. Commercial status / TRL level The COBR technology was developed in the nineties of the previous century. Cambridge Reactor Design have been involved with Oscillatory Flow since its inception at Cambridge University in the 1990s. NiTech solutions founded by professor Xiong-wei Ni provides design service and sells equipment as well. A limited number of industrial applications have been published, research and development for new applications (e.g. bio systems) is ongoing. We consider COBR technology as having a high TRL, Examples of application Xiong-wei Ni (2006) gives the following example of application. In the production of a photographic chemical at James Robinson in the UK, two batch STRs of 3000 l and l respectively were used to perform a three-stage reaction and operated in a cascaded format, occupying a floor space of 12 m x 10 m x 10 m. The first two stages were done in the first STR at 7 C, the content of which is then discharged into the second STR for the thirdstage reaction at 80 C. Each batch operation takes about 18 h to complete. This batch production has been converted into a continuous process using one glass COBR system of two sections: section A consists of a number of 40 mm diameter tubes and section B of 80 mm diameter tubes. The first two stages take place in section A, the third in section B. The Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 7

8 total flow path is about 70 m long. Figure 3 shows the comparative layouts of the two operations with Table 1 comparing the performances. The COBR system reduces the footprint by a factor of more than 36 and provides a flexible and portable manufacturing facility. Figure 3 COBR and Batch STR at James Robinson Ltd Table 1 Comparison of operations Table 2 Comparison of overall reaction times On the website of NiTech solutions the following statement of Bayer Technology Solutions: BTS has purchased a DN15 continuous crystalliser and reactor from the UK s NiTech Solutions, having identified it as a potential key technology for the future. Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 8

9 6. Technology and developments Xiong-wei Ni and coworkers published several studies on crystallization, see References. In general they found that an OBR enables better control of the crystallization process and gives higher purities of the crystals. Components examined are e.g.: - Urea - Sodium chlorate - Adipic acid - Salicylic acid The purpose of the studies of Manninen et al. (2012) was to simulate highly viscous non- Newtonian flows in the oscillatory baffled reactor as such problems arise in polyaniline production processes. The main focus was to investigate how the axial dispersion coefficient is affected by the viscosity and operational parameters of the reactor. The performance of D s (dispersion coefficient) as a function of viscosity of both Newtonian and non-newtonian fluids established through the CFD work is important for reactor design and operation: it shows that increase of the intensity of oscillation can lead to either increased or decreased dispersion depending on viscosity. A compromise has to be found in order not to deviate too much from the plug flow, as well as to keep the level of mixing sufficient. Harvey and coworkers examined performances of small scale meso OBRs equipped with e.g. helical coils, see publications of Phan and Harvey et al. (2010, 2011, 2012). The review of McDonough, Phan and Harvey (2015) gives detailed information about different types of baffles, flow profiles, enhanced mass transfer, mixing of liquids and solids. Scaling rules need additional investigation. McDonough et al. (2015) also report studies for the successful determination of kinetics in meso- OBR systems. The studies of Ping Gao et al. (2003) demonstrated that the oscillatory flow is efficient for use in advanced photochemical oxidation of organic compounds. Using the present PBTPR (pulsed baffled tubular photochemical reactor), organics such as salicylic acid can be mineralized within 3 hr of UV irradiation, whereas a geometrically similar CSTR can only achieve up to 50% mineralization in a similar duration. 7. Potential for industrial branches - Chemical process industries (MJA3 + MEE) - (Animal) Food industry (MJA3) - Pharmaceutical industries (MJA3) - Margarine, Oil and Fat industry (MJA3) - Dairy industries (MJA3) - Fine chemistry, Special Chemistry (MJA3) - Nanoparticle manufacture (MJA3) Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 9

10 8. Self assessment for application Consider application of a (C)OBR for fluids and solids containing fluids reaction systems which are not too fast, require uniform residence times, good phase transfer or mixing at low and uniform shear rate and/or need good heat transfer as well. Crystallization in a OBR can lead to more uniform crystals of increased purity. COBR technology can be applied for bio conversion processes as well. 9. Tags Process intensification, new opportunities for reactor design by independent control of the flow and the mixing of fluids and solid containing fluids enabling transition of batchwise operation to continuously operation in smaller and more efficient configuration, for much longer residence times that cannot be achieved in turbulent flow system. 10. References Abbott MSR, Harvey AP, Valente Perez G, Theodorou MK. 2013, Biological processing in oscillatory baffled reactors: operation, advantages and potential. Interface Focus 3: C. J. Brown, Y. C. Lee, Z. K. Nagyc and X. Ni, Evaluation of crystallization kinetics of adipic acid in an oscillatory baffled crystallizer CrystEngComm, 2014, 16, 8008 DOI: /c4ce00192c Craig J. Callahan and Xiong-wei Ni, An investigation into the effect of mixing on the secondary nucleation of sodium chlorate in a stirred tank and an oscillatory baffled crystallizer, CrystEngComm, 2014, 16, 690 DOI: /c3ce41467a Hannah McLachlan & Xiong-wei Ni (2016), An Investigation into Parameters Affecting Crystal Purity of Urea in a Stirred Tank and an Oscillatory Baffled Crystallizer, Chemical Engineering Communications, 203:9, , DOI: / Hannah McLachlan, Xiong-wei Ni, On the effect of added impurity on crystal purity of urea in an oscillatory baffled crystallizer and a stirred tank crystallizer, Journal of Crystal Growth 442(2016)81 88 doi.org/ /j.jcrysgro J.R. McDonough, A.N. Phan, A.P. Harvey, Rapid process development using oscillatory baffled mesoreactors A state-of-the-art review, Chemical Engineering Journal 265 (2015) doi.org/ /j.cej Anh N. Phan, Adam Harvey, Development and evaluation of novel designs of continuous mesoscale oscillatory baffled reactors, Chemical Engineering Journal 159 (2010) doi: /j.cej Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 10

11 Anh N. Phan, Adam P. Harvey, Effect of geometrical parameters on fluid mixing in novel mesoscale oscillatory helical baffled designs, Chemical Engineering Journal 169 (2011) Anh N. Phan, Adam P. Harvey, Characterisation of mesoscale oscillatory helical baffled reactor Experimental Approach, Chemical Engineering Journal 180 (2012) doi: /j.cej Anh N. Phan, Adam Harvey, Joshua Lavender, Characterisation of fluid mixing in novel designs of mesoscale oscillatory baffled reactors operating at low flow rates ( ml/min), Chemical Engineering and Processing 50 (2011) doi: /j.cep Ping Gao, Wing Han Ching, Mark Herrmann, Chi Kwong Chan, Po Lock Yue, Photooxidation of a model pollutant in an oscillatory flow reactor with baffles, Chemical Engineering Science 58 (2003) Xiong-wei Ni, Unwrapping the myth about plug flow, Chemical Engineer (TCE) 779, May 2006, Xiong-wei Ni, Oscillatory baffled reactor and continuous oscillatory baffled reactor technologies, European Roadmap of Process Intensification, Technology report, Xiong-wei NI in Wikipedia visited 3/4/17 X. Ni; M.R. Mackley; A.P. Harvey; P. Stonestreet; M.H.I. Baird; N.V.R. Rao. Mixing through oscillations and pulsations - A guide to achieving process enhancements in the chemical and process industries. Chemical Engineering Research & Design 2003, 81(A3), Xiong-wei Ni et al. on crystallization: Cameron J. Brown, Juliet A. Adelakun, Xiong-wei Ni, Characterization and modelling of antisolvent crystallization of salicylic acid in a continuous oscillatory baffled crystallizer, Chemical Engineering and Processing 97 (2015) doi.org/ /j.cep C. J. Brown, Y. C. Lee, Z. K. Nagy and X. Ni, Evaluation of crystallization kinetics of adipic acid in an oscillatory baffled crystallizer, CrystEngComm, 2014, 16, 8008 DOI: /c4ce00192c Craig J. Callahan and Xiong-wei Ni, An investigation into the effect of mixing on the secondary nucleation of sodium chlorate in a stirred tank and an oscillatory baffled crystallizer, CrystEngComm, 2014, 16, 690 DOI: /c3ce41467a Hannah McLachlan & Xiong-wei Ni (2016), An Investigation into Parameters Affecting Crystal Purity of Urea in a Stirred Tank and an Oscillatory Baffled Crystallizer, Chemical Engineering Communications, 203:9, , DOI: / Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 11

12 Hannah McLachlan,Xiong-wei Ni, On the effect of added impurity on crystal purity of urea in an oscillatory baffled crystallizer and a stirred tank crystallizer, Journal of Crystal Growth 442(2016)81 88 doi.org/ /j.jcrysgro Companies, internet references NiTech solutions Cambridge Reactor Design Ltd Wikisheet Oscillating Baffle Reactor version 1, 6/4/17 12