EP0669852B1 - Process and device for dissolving a quantity of gas in a flowing liquid quantity - Google Patents

Abstract

The invention relates to a process for dissolving a quantity of gas in a flowing liquid quantity, especially for dissolving carbon dioxide in beer, in which streams of liquid and gas are brought together and the gas is dispersed in the liquid, mixed therewith and part of it is dissolved therein. The invention is intended to increase the actual quantity of gas soluble in a liquid in given conditions as against prior art processes. In addition, the device for implementing the process is to be of simple construction, cleanable in place (CIP) and its adaptation to certain practical requirements and its regulation is to be facilitated to the utmost. Technically this is achieved in that there is a separation into a bubble-free stream of liquid (L1*) and a gas/liquid stream (G*/L2) taking the form of a two-phase flow, the gas/liquid stream (G*/L2) is fed back and together with the supplied unaerated or aerated flow of liquid (L1 or L1/G) and the gas bubbles are redispersed therein. The device for implementing the process is characterised in that a return line (7) is connected to the head of the separator (6), the return line opens on the other side at a second introduction point (9) into a section (1a) of a pipe (1), there is a second conveying device (8) in the return line (7) and the introduction point (4) in the return line (7) is arranged behind the second conveying device (8) or in the pipe section (1a), i.e. in front of or behind or at the second introduction point (9).

Description

The invention relates to a method for dissolving an amount of gas in a flowing amount of liquid according to the preamble of claim 1 and an arrangement for performing the method.

A method of the type identified in the introduction and an arrangement for carrying out the method are known from WO-A-8802276. The separating device used in the known arrangement has a partition which is permeable to the bubble-free liquid and which retains the gas bubbles in the circulating liquid.

Another arrangement that documents the state of the art for solving a quantity of gas in a flowing quantity of liquid is, for example, from the company publication "Haffmans CO2 measuring and control system", type AGM-05, from Haffmans BV, RD Venlo, the Netherlands , Pages 2 to 5, known. In the arrangement for carrying out the method described in this publication, CO2 gas and beer are combined in a so-called carbonating device. A CO2 line ends in the middle of a beer line, and the distribution of the CO2 gas takes place via static mixing elements. In a solution section downstream of the carbonation device, further static mixing elements ensure that the bubble distribution is maintained, which is a necessary prerequisite for the desired mass transfer (absorption of gas in liquid).

The procedural and fluid-mechanical requirements for the gas / liquid mass transfer are well known. The gas must be supplied to the liquid, dispersed in it and distributed homogeneously over the cross-section through which the liquid flows. The so-called equilibrium curve, the solution equilibrium between gas and liquid, provides the maximum amount of gas that is soluble in the liquid at a given line pressure and temperature. The amount of gas resulting from the solution equilibrium, if it is offered to the liquid in exactly this amount, theoretically, they can only be dissolved in the liquid over an infinitely long period of time. Therefore, in practice, the solution equilibrium is generally not achieved and the choice of the changeable operating parameters ensures that there is a sufficient concentration gradient between the equilibrium concentration (also saturation concentration) and the desired and ultimately occurring actual concentration. It is also well known that absorption is made difficult by low pressure, high temperature, high setpoint concentration of the gas to be dissolved and, as a rule, low flow rate. The pressure loss in the static mixer and in the subsequent solution section leads, at least gradually, to a steadily decreasing static pressure over the flow path, which in turn determines the local equilibrium concentration. A reduction in the latter in turn leads to a reduction in the effective concentration gradient that crucially determines the mass transfer.

Since the known arrangements aim to dissolve a predetermined amount of gas in a certain flowing amount of liquid with well-known means, these arrangements do not achieve any procedural or apparatus advantages that go beyond the prior art in this field.

In the search for methods and arrangements for intensifying the mass transfer, with which the mass transfer that can be achieved in the aforementioned carbonation device in connection with the downstream solution section can be improved, the person skilled in the art comes across in the journal Chem.-Ing.-Tech. 64 (1992) No. 8, page 762, on an article on the topic "Modeling a loop reactor fumigated from above and measuring hydrodynamic parameters". There is carried out among other things:
"For the gassing of low viscosity liquids in in the chemical industry and in biological wastewater treatment, jet-driven loop reactors are increasingly used. The gas and the liquid are fed to a compact reactor via a two-component nozzle which is arranged at the top of the reactor. This nozzle can be operated both in ejector mode and in injector mode. The mixture of gas and liquid supplied via the two-substance nozzle flows downward together with the two-phase mixture which is drawn in from the annular space. Part of the liquid is drawn off at the lower end of the reactor. The other part of the liquid flows upwards together with the gas in the annulus. At the top of the reactor, part of the gas degasses, while the other part together with the liquid again participates in the circulation in the reactor. "

Loop reactors are to be understood to mean apparatuses in which at least one defined circulation of a fluid or fluidized system, which comprises the total flow, takes place. In this case, a continuous flow can be superimposed on the circulating flow, as a result of which the flow pattern of a “loop” is created. There are loop reactors with internal and external circulation.

A transfer of the loop reactor principle briefly outlined above to a method of the type identified in the introduction is not readily possible. On the one hand, outgassing a part of the supplied gas at the upper end of the reactor, which cannot be completely eliminated, would be undesirable and disadvantageous; rather, the aim is that the quantity of gas supplied is actually dissolved, which makes the material balance extremely simple. On the other hand, the fixed geometric relationships of the loop reactor only allow the process to be conditionally adapted to changing ones Operating conditions. In addition, regardless of whether it works with an internal or external circulation, a loop reactor, on the one hand, is not particularly easy to clean or clean, particularly when used in the food and beverage industry, where it is extremely important that all areas of the reactor are cleaned biologically CIP-compliant arrangement (CIP: abbreviation for "cleaning in place", which means "cleanable on the spot in the flow"), and on the other hand it may have to be classified as a pressure vessel that has to meet certain safety requirements, which means that it can be subject to approval or monitoring, which makes it technically complex and expensive from the outset.

DE 39 20 472 A1 discloses a method for the defined loading of a liquid with a gas, in which the loading process at a specific point in the flow path of the liquid is essentially ended by coalescence of the undissolved gas bubbles. Undissolved, coalesced gas bubbles are either redispersed and mixed again in the course of the flow path of the liquid to be loaded in the latter, or they are separated from the liquid. For this purpose, the known device for carrying out the aforementioned method provides a separating device at the end of the loading section, in which a separation of undissolved gas bubbles from the liquid is achieved by centrifugal forces in the rotating liquid. This separating device is a container in which the rotating liquid forms a paraboloid of revolution, over the free surface of which the undissolved gas bubbles are separated (column 4, lines 37 to 51). Because of these conditions, the separated material flow is a pure gas flow, and no further statements are made regarding its further use.

The object of the present invention is to increase the amount of gas which is actually soluble in a liquid under given conditions compared to known methods. In addition, the arrangement for carrying out the method in the structure should be simple, flow-cleanable (CIP-capable), and its adaptation to certain practical requirements and its regulation should be as simple as possible.

The procedural problem is solved by applying the features of the characterizing part of claim 1. Advantageous refinements of the proposed method are the subject of claims 2 to 4. An arrangement for carrying out the method is implemented by using the characterizing features of the dependent claim 5, while advantageous refinements of the proposed arrangement are the subject of the further subclaims.

The separation of the total flow by subjecting it to flow guidance on curved paths into a bubble-free liquid flow and a gas / liquid flow designed as a two-phase flow ensures, on the one hand, that no uncontrollable after-gassing takes place in the liquid continued from the separation point. On the other hand, the separation is the prerequisite for the return of a partial flow. The recirculated gas / liquid stream is superimposed as a recycle stream on the supplied non-gassed or fumigated liquid stream, which forms the continuous flow. The recycling offers the possibility of redispersing the undissolved gas bubbles contained in the circulating stream and distributing them homogeneously in the overall stream. In addition, the concentration gradient is increased at the point where the throughflow and circulation flow are brought together, and the superimposition of both flows also results in increased turbulence there.

In contrast to known ventilation and gassing processes (representative of this is the briefly outlined Haffmans arrangement), which all strive for the gas solution in a single pass and are therefore content with a lower achievable actual concentration of the gas to be dissolved, or which are a relatively long and therefore highly pressure-lossy mixing and solution section require, the principle of action "separation of the undissolved gas portion from the liquid and repetitive recirculation" has been consistently implemented in the subject of the application, such that the undissolved gas portion in the form of a two-phase flow (gas / liquid flow) from the bubble-free liquid flow via a particularly effective Separation mechanism is separated.

It has been found to be advantageous both in terms of process technology and apparatus, as is provided by an embodiment of the method according to the invention, when the gas flow is introduced into the returning gas / liquid flow. On the one hand, this results in the freshly supplied gas flow being dispersed in the two-phase flow, on the other hand, the outlay on equipment can be reduced compared to an arrangement in which the gas flow is introduced directly into the pipeline, since the return line receiving the returning gas / liquid flow is always smaller in the nominal cross section as the pipeline section guiding the non-degassed liquid flow.

According to a further advantageous embodiment of the proposed method, the gas in the returning gas / liquid stream is at least partially redispersed in its carrier liquid before being combined with the supplied non-gassed or fumigated liquid stream (continuous flow). This measure contributes to a further improvement of the mass transfer.

In order to intensify and force the separation into a bubble-free liquid flow and a gas / liquid flow, another embodiment of the proposed method according to the invention provides that the combined gas / liquid mixture is subjected to flow guidance on curved paths and the rotational energy required for this is obtained from the energy of the flowing gas / liquid mixture is disputed, which results in a relatively simple apparatus implementation of this process step.

Since the arrangement for carrying out the method can be designed in the form of simple pipelines in the area of the flow, the total as well as the circulation flow, this results in extremely easy-to-clean and thus CIP-compliant flow and system areas which do not contain pressure vessels in the sense of contain relevant regulations. The centerpiece of the arrangement according to the invention is a separating device in which a separation of undissolved gas bubbles from the liquid is achieved by centrifugal forces in the rotating liquid, the mixing device or the solution section opening into an inlet of the separating device and, on the one hand, to an outlet of the separating device Continued pipeline section of the pipeline for the bubble-free liquid flow and, on the other hand, the return line for the remaining gas / liquid flow is connected to a head region of the separating device. With the second conveying device arranged in the return line, the gas in the gas / liquid stream to be recycled, in the sense of the procedural measures already proposed above, can be at least partially and effectively effective in its carrier liquid before being combined with the supplied non-degassed or fumigated liquid stream redispersed and homogeneously distributed over the return line cross section, which serves to further improve the mass transfer. The proposed arrangement can be regulated in a very simple manner by the second conveying device in the return line, so that it can be adapted very easily to changed operating conditions.

By designing the separating device as a centrifugal separator, specifically in a first embodiment as a hydrocyclone, as is provided by another embodiment of the proposed arrangement, it is particularly easy to separate the total flow into a bubble-free flow and a circulation flow designed as a two-phase flow (gas / liquid flow) , but still extremely effective. The return line is connected to the dip tube of the hydrocyclone.

When the separating device is designed as a hydrocyclone, under certain operating conditions, so-called "trombone formation" can occur, as a result of which the gas concentrating in the vortex core is partially entrained in the outlet arranged coaxially in the separating device. Special design precautions are then required in the sequence so that the gas can be retained in the separating device, at least up to a certain degree of loading of the liquid with gas, and can be discharged solely via the dip tube used to discharge the two-phase flow (gas / liquid flow).

The separation performance, even under the conditions of extremely high gas-laden liquids, improves compared to the design of the separating device as a hydrocyclone if, as is provided by a further advantageous arrangement according to the invention, it is designed as a container into which the inlet is tangential Drain, in continuation of the direction of flow, open tangentially, and a dip tube engages a bit in the interior of the container via the discharge-side end face of a dip tube in the direction of the axis and concentrically to the lateral surface of the container, the dip tube on the other hand is connected to the return line. In this embodiment, the outlet, like the inlet, is also arranged in the jacket region of the container, as a result of which the degassed liquid rotating in this region can preferably be removed. The liquid rotating in the center, in the area of the container axis, and highly loaded with gas now only has the option of leaving the separating device in the form of the two-phase flow (gas / liquid flow) via the dip tube. It is essential that the immersion tube is arranged in the outlet-side area of the separating device so that the dwell time necessary for separating the gas bubbles from the jacket area into the axial area of the container is available for the gas / liquid mixture flowing through the container.

.A very simple and efficient separating device is obtained if the container is designed as a slim cylinder, its cylinder jacket having a height H that is appreciably greater than its diameter D, preferably a ratio $\text{H / D = 3 to 6}$

.

It has proven to be particularly effective with regard to redispersion and homogeneous distribution of the as yet undissolved gas bubbles in the gas / liquid stream to be recirculated if, as a further embodiment of the proposed arrangement provides, the second delivery device is designed as a self-priming centrifugal pump, preferably as a side channel pump is. Self-priming centrifugal pumps are relatively simple in construction; they can convey both a two-phase mixture and pure gas, they are self-cleaning, they have no abrasion and therefore require little maintenance.

According to a further advantageous embodiment of the proposed arrangement, by introducing the gas flow into the return line behind the second conveying device, its properties which have a favorable effect on the redispersion of the gas bubbles are also made usable for the freshly supplied gas flow. In addition, in this embodiment, as already explained above, the outlay on equipment is reduced compared to an embodiment of the arrangement in which the gas flow is introduced directly into the pipeline.

Exemplary embodiments of the arrangement for carrying out the proposed method are described below using the Figures of the drawing shown and briefly explained.

Figur 1

in schematischer Darstellung ein erstes Ausführungsbeispiel der Anordnung zur Durchführung des Verfahrens gemäß der Erfindung mit einer als Hydrozyklon ausgebildeten Trenneinrichtung;

Figur 2

ein zweites Ausführungsbeispiel der Anordnung zur Durchführung des Verfahrens gemäß der Erfindung, wobei die Trenneinrichtung nach einer besonders vorteilhaften Ausführungsform gemäß der Erfindung ausgebildet ist und

Figur 2a

eine Draufsicht auf die Trenneinrichtung gemäß Figur 2 mit den Anschlüssen für Zulauf, Ablauf und Tauchrohr.

Show it

Figure 1

a schematic representation of a first embodiment of the arrangement for performing the method according to the invention with a separation device designed as a hydrocyclone;

Figure 2

a second embodiment of the arrangement for performing the method according to the invention, wherein the separating device is designed according to a particularly advantageous embodiment according to the invention and

Figure 2a

a plan view of the separation device according to Figure 2 with the connections for inlet, outlet and dip tube.

The arrangement (Figure 1) consists of a pipe 1, which consists of the pipe sections 1a and 1b. The pipe section 1a opens into a static mixing device 5, which is optionally followed by a solution section 5a. The entire mixing and solution device can also consist of only one solution section 5a. The static mixing device 5 can be constructed from a single static mixer or a mixing element or from a plurality of static mixers connected in series; it is referred to below as "static mixer 5". The static mixer 5 or the solution section 5a are connected to an inlet 6a of a separating device 6, in which, according to the invention, the gas / liquid mixture is separated into a gas / liquid and a bubble-free liquid flow. The pipeline 1 is continued behind the separating device 6 in the pipeline section 1b via an outlet 6b arranged in the foot region thereof. A return line 7 is at the head region of the separating device 6 connected, which engages in the interior of the separating device 6 via an immersion tube 6c and which, on the other hand, opens into the pipeline section 1a at a second introduction point 9.

In a first, particularly advantageous embodiment of the invention which is particularly simple in terms of apparatus, a gas line 3 serving the gas supply G, which is led via a metering device 10, leads via an introduction point 4 into the return line 7 behind a second conveying device 8 arranged therein. In relation to the direction of flow within the pipeline 1, the introduction point 4, as provided by further configurations of the arrangement according to the invention, can also be arranged in front of or behind or at the second introduction point 9 (dash-dotted representation of the part of the gas line 3 opening at the introduction point 4). .

A separating device 6 designed as a cylindrical container (FIG. 2) has an inlet 6a arranged tangentially and an outlet 6b opening out tangentially from the container in continuation of the flow direction. This becomes clear in the top view of the separating device 6 (FIG. 2a). For the mode of operation of the separating device 6, it is irrelevant which wrap angle (seen in a container cross-sectional plane) the inlet and outlet 6a and 6b to each other. The only decisive factor is that the rotational flow in the container can flow smoothly and thus inevitably into the outlet 6b in the direction of flow. It is also irrelevant to the mode of operation of the separating device 6 whether it is arranged vertically, horizontally or in any inclined position in space with respect to its container axis. It is essential, however, that the immersion tube 6c over the outlet-side end face of the container of the separating device 6, in the direction of Axis and concentrically to the lateral surface of the container, a piece engages in the container interior, wherein it is connected to the return line 7 on the other hand. Inlet and outlet 6a and 6b of the separation device 6 are integrated into the overall arrangement in the same way as is the case with the arrangement according to FIG. 1 and has already been described there.

in der Rückführleitung 7 zusammengeführt; beide Ströme treten dann in ihrem weiteren Verlauf durch den statischen Mischer 5 und ggf. durch die sich anschließende Lösungsstrecke 5a in den gewünschten Stoffaustausch miteinander.An ungased amount of liquid L1 (liquid phase) is supplied via the pipe section 1a (see FIGS. 1, 2 and 2a), which is conveyed through the arrangement by means of the first conveying device 2, which can be a centrifugal pump, the amount of liquid L1 being the so-called continuous flow forms. A gas quantity G (gas phase) is supplied via the gas line 3. The gas flow G can be set by means of the metering device 10, which is generally designed as a throttle and control valve. At the point of introduction 4 of the gas line 3 into the return line 7, the gas / liquid flow G * / L2 formed as a two-phase flow is combined with the gas flow G, the entire gas fraction G + G * in the further course through the return line 7 being at least partially already in it Carrier liquid L2 can be redispersed. At the second introduction point 9, the non-degassed liquid flow L1 in the pipeline section 1a with the gas / liquid flow $\text{(G + G *) / L2}$

merged in the return line 7; in their further course both streams then pass through the static mixer 5 and possibly through the subsequent solution section 5a into the desired mass exchange with one another.

In addition to the liquid flow L1 (continuous flow), the static mixer 5 and the solution section 5a, if provided, are acted upon by the flow which is established in the return line 7. Due to the design of the separation device 6 according to the invention in the return line 7 the gas / liquid flow G * / L2 formed as a two-phase flow. The latter forms the so-called circulation flow, which is superimposed on the flow current L1 within the pipeline 1 between the second introduction point 9 and the separation device 6. A bubble-free liquid flow L1 * (liquid phase) is discharged via the outlet 6b of the separating device 6, which is connected to the pipe section 1b. Since the second delivery device 8 has to deliver both bubble-free liquid L2 and pure gas G * in addition to the two-phase flow G * / L2 under certain operating conditions, it is expediently designed as a self-priming centrifugal pump, preferably as a side channel pump. It goes without saying that the second conveying device 8 can also be substituted by another pump, such as, for example, a rotating displacement pump, in particular an impeller pump or jet pump, provided that it has the required conveying properties.

The arrangements shown in FIGS. 1 to 2a for carrying out the proposed method are particularly suitable for the so-called carbonization of beer. Carbonation of beer refers to the enrichment of beer with CO2 gas, whereby brewery technology today demands a complete solution of a given amount of CO2 in a certain amount of beer. Design criteria for such a carbonation plant are therefore firstly to ensure a certain CO2 concentration in the beer and secondly its complete and therefore bubble-free solution.

Similar carbonation tasks arise in other areas of the food and beverage industry, where liquids with a specific content of CO2 gas have to be enriched (including lemonades, soft drinks).

The mechanisms of action on which the proposed method is based, to which the increase in the amount of gas which can actually be released without bubbles to a decisive extent is to be attributed, have already been explained in the introduction.

Claims (11)

1. Process for dissolving a quantity of gas in a flowing liquid quantity, especially for dissolving carbon dioxide in beer, in which streams of liquid (L1) and gas (G) are supplied and brought together and the gas is dispersed in the liquid, mixed therewith and part of it is dissolved therein, and subsequently a bubble-free stream of liquid (L1*) is separated from a gas/liquid mixture, and a remaining gas/liquid stream (G*/L2) is fed back and together with the supplied unaerated or aerated flow of liquid (L1 or L1/G) and the gas bubbles are redispersed in the gas/liquid mixture, characterized in that the gas/liquid mixture is subject to a flow guidance on curved tracks, causing the separation into the bubble-free stream of liquid (L1*) and the gas/liquid stream (G*/L2) to be returned.
2. Process according to Claim 1, characterized in that the stream of gas (G) is supplied to the returning gas/liquid stream (G*/L2).
3. Process according to Claim 1 or 2, characterized in that the gas (G*, G+G*) in the returning gas/liquid stream (G*/L2 or $\text{(G+G*)/L2}$

   

   ) is at least partly redispersed in its support liquid (L2) before being brought together with the supplied unaerated or aerated stream of liquid (L1, L1/G).
4. Process according to one of Claims 1 to 3, characterized in that the rotational energy necessary for the flow guidance on curved tracks is generated from the energy of the flowing gas/liquid mixture.
5. Device for implementing the process according to one of Claims 1 to 4 with an introduction point (4) for the gas (G) into the liquid (L1) flowing in a pipe (1), with a first conveying device (2) in a section (1a) of a pipe (1) and with a subsequent mixing device (5), preferably a statical one, and/or a dissolving area (5a) possibly adjacent to the latter, with a return line (7) branching off from the pipe (1) behind the mixing device (5) or the dissolving area (5a) that on the other hand flows into a pipe section (1a) at a second introduction point (9) and in which a second conveying device (8) is provided, characterized in that a separator (6) is provided in which a separation of unsolved gas bubbles from the liquid is achieved by centrifugal forces in the rotating liquid, with the mixing device (5) or the dissolving area (5a) discharging into a supply (6a) of the separator (6), and on one hand an extended section (1b) of the pipe (1) is connected to a drain (6b) of the separator (6) for the bubble-free stream of liquid (L1*) and on the other hand the return pipe (7) for the remaining gas/liquid stream (G*/L2) is connected to a top area of the separator (6).
6. Device according to Claim 5, characterized in that the separator (6) is designed as a hydrocylone and that the return line (7) is connected to its immersion pipe (6c).
7. Device according to Claim 5, characterized in that the separator (6) is designed as a container into which the supply (6a) discharges tangentially and from which the drain (6b) discharges tangentially in continuation of the flowing direction, through its area of contact at the drain and front side an immersion pipe (6c) being engaged partly into the interior of the container in direction of the axle and concentrically to the shell surface of the container with the immersion pipe (6c) being connected on the other hand to the return pipe (7).
8. Device according to Claim 7, characterized in that the container is designed cylindrically, with the cylinder shell providing a height (H) substantially larger than its cross-section (D), preferably $\text{H/D = 3 to 6}$

   

   .
9. Device according to one of Claims 5 to 8, characterized in that the second conveying device (8) is designed as a self-priming centrifugal pump, preferably as a lateral channel pump.
10. Device according to one of Claims 5 to 8, characterized in that the second conveying device (8) is designed as a rotary pump, preferably as an impeller pump.
11. Device according to one of Claims 5 to 10, characterized in that the introduction point (4) is arranged in the return pipe (7) behind the second conveying device (8) or in the pipe section (1a) in front of or behind or at the second introduction point (9).

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