Title of Invention

NON-FLOODING SELF-INDUCING IMPELLER APPARATUS

Abstract

The present invention discloses a non-flooding self-inducing impeller apparatus used in gas-liquid contactor. The apparatus in this invention involves self-inducing impeller rotating in a stator. The stator is connected to the contactor headspace by the standpipe. The reacting gas present in the contactor headspace is brought down into the non-flooding self-inducing impeller by suction and then dispersed into the contactor without any external apparatus. The facility of internal recirculation of gas eliminates external equipment for recirculation as well as energy necessary to operate the external equipment. The internal recirculation of gas is used for many gas-liquid and gas-liquid-solid reactions, where it is desirable to have complete utilization of gas like hydrogenation, chlorination, halogenationation, hydrohalogenation, alkylation, etc. These types of contactors can also be used for aeration purpose in fermentation and biological oxidation. The apparatus in this invention prevents sudden drop in mass transfer, mixing, heat transfer and suspension characteristics due to flooding. The apparatus in present invention is also optimized to improve the mass transfer characteristics at given power densities for the gas-liquid contacting.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 OF 1970) -PROVISIONAL/COMPLETE SPECIFICATION [section 10, Rule 13] 1. AN IMPROVED NON-FLOODING SELF-INDUCING COMPOUND STATOR ROTOR APPARATUS FOR MECHANICALLY AGITATED REACTORS 2. Patil Swapnil Shiridhar University Institute of Chemical Technology, University of Mumbai Chemical Engineering Division, Nathalal Parekh Marg, Matunga, Mumbai- 400 019, India Indian Joshi Jyeshtharaj Bhalachandra University Institute of Chemical Technology, University of Mumbai Chemical Engineering Division, Nathalal Parekh Marg, Matunga, Mumbai- 400 019, India Indian The following specification particularly describes the nature of the invention and the manner in which it is to be performed: Prior Art The prior art methods are for effecting mass transfer of gas into liquid, by liquid agitation. The internal recirculation of gas is used for many gas-liquid and gas-liquid-solid reactions, where it is desirable to have complete utilization of gas like hydrogenation, chlorination, halogenationation, hydrohalogenation, alkylation, etc. These types of reactors can also be used for aeration purpose in fermentation and biological oxidation. U.S. Pat. Nos. 2,274,658 and 2,294,827 (Booth) describe the use of an impeller to draw gas into a liquid medium and to disperse the gas as bubbles in the liquid medium for the purpose of removing dissolved gaseous materials and suspended impurities from the liquid medium, particularly a waste stream from rayon spinning, by agitation and aeration used by distribution of the gas bubbles by the impeller. U.S. Pat. No. 3,273,865 (White et al.) describes an aerator for sewage treatment. A high speed impeller in the form of a stack of flat discs forms a vortex in the liquid to draw air into the aqueous phase and circulate the aqueous phase. As in the case of the two Booth references, this prior art does not describe or suggest an impeller shroud combination for affecting the gas-liquid contact. U.S. Pat. No. 4,287,137 (sonoyama et al.) describes vane-type impeller for effective gas-liquid contact in chemical or fermentation process. U.S. Pat. Nos.5,500,135; 5,520,818 and 5,527,475(Smith et al.) describe use of gas-liquid contact apparatus with impeller- apertured shroud combination, for different applications. 2 U.S. Pat. No. 5009816 (Weise et al.) describes gas-liquid mixing process and apparatus employing two or more stacked impeller-draft tube assemblies for effective ingression into a recirculating body of liquid by vortex development. U.S. Pat. Nos. 5,451,348 (Kingsley and Jeffrey) describes a variable liquid level eductor/impeller gas-liquid mixing apparatus for dissolving gas in liquid. In all above patents the effect of impeller speed on the gas induction rate and on performance of the gas liquid contacting process is not discussed. Further, the hydrodynamic stability or flooding conditions in the apparatus is also not discussed. For optimum reactor performance, the mixing characteristics, the gas-liquid interfacial area and mass transfer coefficient should be improved at given power density. Concomitantly the hydrodynamic instability should be eliminated to prevent any sudden drop in the above characteristics. Object of Invention One objective of present invention is to eliminate an unstable behaviour in the gas dispersion, mixing and mass transfer characteristics which is especially observed at higher power consumption densities and/or lower depth of impeller from gas liquid surface into the reactor (impeller submergence). Another object of the invention is to provide an apparatus for effective gas induction and gas dispersion in liquid or liquid-solid mixtures. This effective gas dispersion will promote gas dissolution essentially in single stage cascade. Still another object of this invention is to provide such an apparatus for gas dispersion method which substantially lowers power consumption densities than heretofore achieved in such mixtures. Further objective of this invention is to provide inexpensive yet reliable equipment. With this compound impeller stator rotor apparatus, the gas dispersion in 3 the equipment is maintained at optimum conditions over entire range of power consumption densities. Still further objective of this invention is to provide an aeration apparatus for performing a method useful in aerobic digestion of wastewater, which promotes high degree of gas dissolution at relative low power densities. Summary of Invention The invention relates to improved version of an aerator in an extremely simple manner having gas induction, mixing and mass transfer characteristics without any instability. Moreover, at given power density, uniform aeration can be achieved. Mundale and Joshi (Mundale, V.D., and J.B. Joshi, "Optimization of Impeller Design for Gas Inducing Type of Agitated Contactor" Can. J. Chem. Eng., 73, 6-17, 1995) have investigated comprehensively the effect of impeller and stator design on the gas induction and found an unstable behaviour of optimum stator rotor combination. To understand the mechanism of gas induction and the causes of instability, authors of this invention investigated different parameters like impeller speed (N), dimensions of stator, dimensions of impeller, scale of reactor and impeller submergence. The gas induction process occurs due to the forced vortex formation. The nature of gas induction (QG, nL/s) with respect to impeller speed (N, 1/s) is as shown in line 1 in Figure 1. The mechanism of the gas induction process is shown in Figure 2. When the impeller is not rotating (N=N1=0, Figure 2), the liquid height in the standpipe 12 is equal to the height of liquid in the reactor 13 . When the impeller speed is increased from zero, the level of liquid drops progressively (N-N2, N3, Figure 2). This happens due to a decrease in pressure in the vicinity of the self inducing impeller. At a certain critical speed, the liquid level reaches fairly close to the impeller (N= N4, Figure 2). Under this condition, the impeller can generate eddies 4 at the gas-liquid interface and these eddies entrap bubbles. The liquid flow carries these bubbles through the stator into the bulk liquid. The phenomenon of bubble entrapment is similar to that in surface aeration. The speed at which the gas induction process begins is the critical impeller speed point 3 (N=N4, Figure 2) for the onset of induction. Before critical impeller speed only liquid flow 10 is discharged from self inducing impeller whereas after critical impeller speed gas-liquid flow 11 is discharged from self inducing impeller. With an increase in the impeller speed (N4 5 because of the hydrostatic head of liquid which pushes liquid from the bottom, and the part of the impeller always remains dipped into the liquid (Figure 2, N=N6). Under these conditions, the liquid level shows very wide fluctuations due to the opposing actions of the impeller motion and the static liquid head. As a result, the rate of induction also shows wide fluctuations. Hence, the fluctuations in the rate of gas induction are relatively much higher in state-2 (line 6-7) as compared to those in state-1 (line 3-4). This is clearly seen in Figure 1 as indicated by error bars. One more important observation is the existence of hysteresis behaviour between state-1 and state-2. For instance, a decrease in speed along the line 6-5 (state-2) results in a decrease in QG, even when N was lowered below N at point 4. At point 7, the rate of gas induction increases steeply. This speed is called the second transition speed (N at point 7). When the impeller speed is less than N at point 7, again the induction behaviour coincides with the state-1. Depending upon the ratio of impeller diameter to internal diameter of stator and the impeller location (with respect to the stator), the difference between first transition speed and the second transition speed 9 was found to be greater than or equal to zero. Thus, the state-2 operation (line 6-7) is unsuitable because of two reasons. Firstly, the rate of induction is approximately half of that in state-1. Secondly, the fluctuating behavior in state-2 also means wide fluctuations in the power drawn and apparatus becomes amenable to mechanical problems. The new compound impeller design claimed in this patent eliminates this instability and sub-optimal zone of impeller operation. The line 2 in Figure 1 has showed the performance of the compound impeller. While eliminating the instability, the performance of the impeller also enhances. 6 A self inducing impeller stator-rotor assembly Is shown In Figure 3. The impeller 18 (the impeller design showing instability, line 1 in Figure 1) is mounted on the shaft 17, which runs trough a standpipe 14. The stator 15 - impeller 18 assembly is provided at the bottom end of the standpipe 14. The upper end of the standpipe extends into the headspace of the reactor, where it may have opening 16 for gas suction. Alternatively, the upper portion of the standpipe may be connected to an outside space for aeration. The gas passage from the opening of the stand pipe 16 into the impeller 18 is through annular space between standpipe 14 and shaft 17. The shaft 17 is connected directly or through gear "box 21 to the motor 20. P or the reactors used for internal circulation with high-pressure operations, mechanical seal 19 is used. Whereas for aeration operations, the mechanical seal 19 need not "be used. The impeller 18 is a heart of the apparatus. The rate of gas induction, critical impeller speed for gas induction, power consumption density, stability of gas induction rate, etc. are strongly dependent on the impeller design. Entrapment of gas bubbles from the gas liquid interface of forced vortex and effective "bubble carriage are the main functions of the self inducing impeller. By balancing these two steps, the present invention effectively performs the gas induction as well as mixing operation and enhances the reactor performance. For optimum operation the stator design also match the compound self inducing impeller design. The stator protects the forced vortex form ingressing liquid and also reduces the shock losses of the outgoing liquid form the impeller into the reactor bulk. Brief Description of Figures Figure 1: Nature of gas induction of conventional self inducing impeller and compound self inducing impeller. Figure 2: Mechanism of gas induction of self inducing impeller Figure 3: Self inducing stator-rotor assembly 7 Figure 4: Top plan view of the stator of compound self inducing impeller, with stator being partly broken away to show interior details Figure 5: Sectional view along line I-I in Figure 4 Figure 6: Elevation of compound self inducing impeller apparatus Figure 7: Bottom plan view of compound self inducing impeller apparatus Figure 8: Mass transfer characteristics of conventional and non-flooding compound self inducing impeller Detailed Description The stator design in present invention is as shown in Figures 4 and 5. The recirculated gas from the reactor headspace enters into the stator through the top opening 28. The stator Is connected to the standpipe 14 by flange 22. The stator essentially consists of an impeller hood 23, stator vanes (or baffles) 24, a vane-shrouding ring 25 and a vane air ring 26. The main function of the impeller hood 23 is to prevent a gross ingress of liquid from above and protect the gas-liquid interface formed due to the forced vortex in the stator. The shape of the impeller hood 23 is conical. The angle of the conical surface to the base will be not higher than 7°. The linger angled conical surface gives higher turbulence and results into lowering the gas induction rate for the same power consumption. The impeller hood 23 along with the vane-shrouding ring 25 can be called as stator shroud. The stator shroud mechanically supports the stator vanes 24 and the stator airing 26. The stator vanes 24, the vane-shrouding ring 25 and the vane air ring 26 is collectively referred to as stator diffuser. The passage between the two adjacent stator vanes 24, which is welded between vane-shrouding ring 25 and stator air ring 26, is called as stator diffuser channel 27. The impeller rotation causes mainly tangential flow in the region between the impeller and the stator diffuser. This flow impinges on the stator vanes 24 and gets deflected. The overall flow pattern leaving the impeller through the stator diffuser channels 27 therefore becomes radial. In this manner the stator diffuser channels 27 guides the 8 flow out of the impeller zone and Improves the dispersion characteristics. During the flow through the stator diffuser channels 27, the gradual decrease in fluid velocity along with Increase In the pressure head reduces the shock losses. Therefore, the gas induction efficiency is lower when the stator diffuser section is not provided. The hydraulic losses during the fluid flow from impeller to the bulk through the stator diffuser channels are: 1. Head loss at the entrance of stator diffuser due to the thickness of stator vanes. 2. Head loss due to change in the velocity direction of the fluid at the entrance of the stator diffuser. This type of loss occurs due to the poor stator diffuser design and lowers the pumping capacity than the rated quantity. 3. Head loss due to friction in the stator diffuser channel. 4. Shock losses at the discharge of the stator diffuser. The extent of guiding depends on the number of stator vanes, the vane angle and the width of stator diffuser zone. If the number of stator vanes is low the head loss due to point (2) and point (4) increases. "Whereas, in the case of higher number of stator vanes, the pressure drop due to the point (1) and point (3) increases. The number of stator vanes should be in the rage of 3 to 24. For structural stability the number of stator vanes was not less than 3. The stator vane angle should be in the range of 20° to 60°. The width of stator diffuser should be in the range of 0.12 to 0.25 times the stator diameter. For efficient gas dispersion as well as to prevent instability, the two steps in the gas induction namely: bubble entrapment and bubble carriage, are balanced by compound impeller design. The impeller design is shown in Figures 6 and 7. There are two sets of blades (appears like two impellers are connected to each other and therefore called compound impeller). In both the sets, the number of blades can be 9 varied in the range of 3 to 12. The blade angle at the impeller hub to the horizontal plane, of upper set of blades 29 and lower set of blades 31, should in the range of 30° to 60°. The ratio of blade width to its respective diameter for upper set of blades 29 and lower set of blades 31 should be in range of 1/12 to 1/2. Width of the upper set of blades can be further optimised depending upon the operating range of power density. The width of lower set of blade can be further fine tuned by considering the operating range of impeller tip speed and hydrodynamic properties of reaction mixture like viscosity. The upper set of blades 29 of compound impeller are of pitched bladed down flow type. The function of upper set of blades 29 is of bubble entrapment and bubble carriage. For efficient gas entrapment the top set of blades are twisted along the doted line 32. The angle of twist is in the rage of 3° to 25°. The lower set of blades 31 are of pitched bladed up flow type. The lower set of blades 31 pumps liquid upwards and helps the upper set of blades for efficient bubble carriage. The lower set of blades 31 also helps in keeping an optimum size of forced vortex and the impeller always remains sufficiently dipped in the liquid and hence removes the cause of instability. The diameter of the lower set of the blades to the upper set of blades of compound impeller is in the range of 1/3 to 1. An increase in the diameter ratio above the limit increases the power consumption. At the same time the gas induction with respect to power consumption does not increase in that proportion. The extended part to the upper impeller blade at blade tip 30 prevents the instability further. It also prevents the extra power consumption without any increase in the rate of gas induction which happens due to higher diameter of lower set of blades. For special applications where vigorous mixing is required or solid loading is high (>10% of liquid mass), second impeller can be added below the inducing impeller 18 on the same shaft 17. For maintaining the rate of gas induction, the inlet liquid flow into the inducing impeller 18 should be maintained. The diameter of second impeller should be in the range of 0.8 to 1.2 times diameter of upper set of blades 29 of non-flooding self inducing compound impeller 10 We Claim :- 1. A compound non-flooding self inducing stator-rotor apparatus consists of self inducing impeller having two sets of blades, pitched blade downflow type upper set of blades 29 and pitched blade up flow type lower set of blades 31, rotating in a stator 15, is characterized by: a. The number of upper set and lower set of blades of a compound non-flooding self inducing stator-rotor apparatus is in the range of 3 to 12. b. The said upper set and lower set of blades of a compound non-flooding self inducing stator-rotor apparatus are of pitched type and the blade angle at the impeller hub is in the range of 30° to 60°. c. The blade width of the said upper set 29 and lower set 31 of the compound non-flooding self inducing stator-rotor apparatus is in the range of 1/12 to 1/2 times diameter of the respective set. d. The upper set of blades 29 of a compound non-flooding self inducing stator-rotor apparatus is twisted along the line 32 in the rage of 3° to 25°. The ratio of diameter of the said lower set of blades 31 to e. the said upper set of blades 29 of a compound non-flooding self inducing stator-rotor apparatus is in the range of 1/3 to 1. f. The ratio of the width of the extension 30 to blade width of the upper set of blades 29 is in the rage of 1/10 to 1/4. The total length of lower blade 31 and the extension 30 is equal to length of the upper blade 29 of the compound non-flooding self inducing stator-rotor apparatus. g. The impeller hood 23 of the said stator 15 of a compound non-flooding self inducing stator-rotor apparatus has conical shape having angle of the conical surface to the base not more than 7°. h. Number of stator vanes 24 of the said stator 15 of a compound non-flooding self inducing stator-rotor apparatus is in the range of 3 to 24. i. The angle of the stator vanes 24 to the radial direction along the rotational 11 direction of the impeller of a compound non-flooding self Inducing stator-rotor apparatus is in the range of 0° to 60 . j. The width of the vane-shrouding ring 25 and a vane air ring 26 of said stator 15 of a compound non-flooding self inducing stator-rotor apparatus is 0.12 to 025 times to the stator diameter. k. The height of the stator vanes 24 of a compound non-flooding self inducing stator-rotor apparatus Is In the range of 1 to 2 times of vertical projected Made width of the upper set of self inducing impeller blades 29. 1. The ratio of diameter of stator opening 28 to the outer diameter of statorl 5 of a compound non-flooding self inducing stator-rotor apparatus diameter is in the range of 1/8 to 1/2. The said compound non-flooding self-inducing apparatus in the claim 1 has upper set 29 and lower set 31 of Impeller "blades In the range of 3 to 6 for efficient gas induction as well as gas dispersion The width of the upper set of blades 29 Is In the rage of 1/10 to 1/3 times of its diameter. The blade angle of the upper set 29 at the hub is in range of 40° to 60°. The angle of twist of upper set of blades 29 along the line 32 is in range of 10° to 17°. The said compound non-flooding self-Inducing apparatus In the claim 1 has lower set of blades 31 have the blade angle in the range of 40° to 60° at impeller hub for eliminating flooding as well as for efficient operation. The blade width of lower set of impeller blades 31 is in the range of 1/5 to 1/3 times diameter of lower set of Impeller blades 31. The width of extension 30 is in the range of 1/10 to 1/8 times diameter of upper set of impeller blades. The said compound non-flooding self-inducing apparatus In the claim 1 has number of vanes 24 in the range of 6 to 12 for effective guiding the outgoing fluid. The vane angle to the radial direction along the rotational direction of the impeller is in the range of 35° to 50° the height of stator vanes 24 is in the rage of 1.05 to 1.2 times of vertical projected width of upper set of impeller 12 blades 29. 5. The said compound non-flooding self-inducing apparatus in the claim 1 shows at least 25% Increase in mass transfer characteristics (Figure 8) at given power density. 6. For special applications where "higher liquid mixing characteristics or good suspension characteristics is required, an additional second impeller is fitted below the compound impeller stator apparatus and on the same shaft 17. Dated this 5th .day of.. feb.....20S4. To The Controller of Patents The Patent Office, Mumbai 13 Abstract 23 AUG 2004 The present invention discloses a non-flooding self-inducing impeller apparatus used in gas-liquid contactor. The apparatus in this invention involves self-inducing impeller rotating in a stator. The stator is connected to the contactor headspace by the standpipe. The reacting gas present in the contactor headspace is brought down into the non-flooding self-inducing impeller by suction and then dispersed into the contactor without any external apparatus. The facility of internal recirculation of gas eliminates external equipment for recirculation as well as energy necessary to operate the external equipment. The internal recirculation of gas is used for many gas-liquid and gas-liquid-solid reactions, where it is desirable to have complete utilization of gas like hydrogenation, chlorination, halogenationation, hydrohalogenation, alkylation, etc. These types of contactors can also be used for aeration purpose in fermentation and biological oxidation. The apparatus in this invention prevents sudden drop in mass transfer, mixing, heat transfer and suspension characteristics due to flooding. The apparatus in present invention is also optimized to improve the mass transfer characteristics at given power densities for the gas-liquid contacting.

Documents:

131-mum-2004-abstract(23-8-2004).doc

131-mum-2004-abstract(23-8-2004).pdf

131-mum-2004-abstract.doc

131-mum-2004-abstract.pdf

131-mum-2004-cancelled pages(25-1-2005).pdf

131-mum-2004-claims(granted)-(25-1-2005).doc

131-mum-2004-claims(granted)-(25-1-2005).pdf

131-mum-2004-claims.doc

131-mum-2004-claims.pdf

131-mum-2004-correspondence(25-1-2005).pdf

131-mum-2004-correspondence(ipo)-(20-10-2004).pdf

131-mum-2004-descripiton (complete).pdf

131-mum-2004-drawing(25-1-2005).pdf

131-mum-2004-drawings.pdf

131-mum-2004-form 1(23-8-2004).pdf

131-mum-2004-form 13(23-8-2004).pdf

131-mum-2004-form 19(5-2-2004).pdf

131-mum-2004-form 2(granted)-(25-1-2005).doc

131-mum-2004-form 2(granted)-(25-1-2005).pdf

131-mum-2004-form 3(23-8-2004).pdf

131-mum-2004-form 3(5-2-2004).pdf

131-mum-2004-form-1.pdf

131-mum-2004-form-13.pdf

131-mum-2004-form-19.pdf

131-mum-2004-form-2.doc

131-mum-2004-form-2.pdf

131-mum-2004-form-3.pdf

131-mum-2004-granted.pdf

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