DK170824B1 - Process and appliance for continuously culturing micro- organisms in association with a high rate of use of gaseous substrates - Google Patents

Description

in DK 170824 B1

METHOD AND APPARATUS FOR CONTINUOUS CULTIVATION OF MICRO-ORGANISMS AT HIGH USE OF GAS SUBSTRATES

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for the continuous cultivation of microorganisms by high utilization of gaseous substrates in which one or more gases are introduced and mixed into a fermentation liquid which is introduced into a loop reactor having a top portion, a substantially vertical downstream portion and also a substantially vertical upstream portion, which three parts form part of a fermentation liquid circuit which is circulated in the loop reactor by a pump together with gases introduced and mixed into the fermentation liquid through several injection sites, at least one of which injection site is located in the upper portion of the downstream portion close to the top portion.

The process of the invention serves to ferment gaseous substrates for biomass, particularly for the continuous cultivation of microorganisms to produce protein from methane or natural gas and oxygen.

The invention also relates to an apparatus for use in the process according to the present invention and in the form of a loop reactor having a top part, a substantially vertical downstream part and a substantially vertical upstream part, which three parts are included in a circuit for the fermentation liquid. which, together with the gases, are circulated in the loop reactor of a pump, and means for introducing fermentation liquid and gas injection sites for introducing one or more gases into the fermentation liquid, at least one of which is located in the upper part of the downstream portion close to the top part .

In conventional tank reactors or tank fermenters, the mixing and absorption of gaseous substrates in the fermentation liquid is effected by agitators which atomize the gas into small bubbles, thereby obtaining a large gas / liquid contact area per unit volume. volume unit of fermentation liquid. Although a good homogenization of the gas-liquid mixture can be obtained in this type of fermenters, traditional fermenters are not suitable for large-scale production when a high utilization rate of the gas is desired. Namely, the gas passes through the fermentation liquid in a matter of seconds during its ascent from a normal nozzle located at the bottom of the fermenter to the surface of the liquid. Thereby, the gas does not achieve a sufficiently long residence time in the fermentation liquid for an approximately complete utilization of the gas to occur. In addition, the pumps, which are usually of the propeller type and which serve to stir or circulate the fermentation liquid in the fermentor, have a large power consumption expressed in kWatts of 15 power per unit. mass unit of gas absorbed into the liquid.

The movement of the gas / liquid mixture that takes place in a normal stirred tank fermentor by means of agitators mounted on one or more shafts in the container can also take place in an annular reactor structure - a so-called loop reactor - where a forced circulation of the fermentation liquid is provided. The gas is usually blown into the bottom of a long vertical pipe forming one branch of the loop reactor. At the top of this branch, which is referred to as the headspace of the loop reactor 25, the gas is separated from the fermentation liquid, which then runs back toward the bottom of the second branch of the loop reactor, which is also arranged vertically. Fluid circulation is most often effected by means of a pump arranged in a short connecting tube between the lower ends of the two vertical branches of the loop reactor. Some natural liquid circulation occurs due to the difference in density between the gas / liquid mixture in the ascending branch and the gas-free fermentation liquid in the descending branch of the loop reactor.

35

The gas can be blown in through nozzles or ejectors located in the bottom of the ascending branch. A good mass transition between gas and fermentation liquid is achieved in the vicinity of the nozzles or ejectors, but the gas bubbles quickly assume one of the physical properties of the fermentation liquid, which is much larger than that obtained close to the nozzles or ejectors. As a result, the mass transition in the total volume of the loop reactor will usually be very low.

EP Patent Application No. 90610050.8, published as EP Publication Publication No. 0 418 187 A1 and having priority from DK Patent Application No. 3867/89 of August 7, 1989, discloses a method of applying a series of static mixers in both the ascending and descending branch of a loop reactor, a repeated dispersion of the gas in the fermentation liquid achieves a significantly higher total mass transition in the given fermentation volume than previously known.

In the same patent application it is also shown how, in relation to a normal loop reactor, a significantly longer residence time for the gas can be obtained by introducing the gas close to the top of the descending branch of the loop reactor rather than at the bottom of the ascending branch. Through the invention disclosed in the EP patent application, a good gas / liquid contact is obtained in each volume of the fermentation volume as well as a long residence time for the gas in the fermentation liquid. The increased power requirements due to the static mixers are met by using a larger pump than is normally required in a loop reactor.

30

Nevertheless, the utilization of the gas in the fermentation liquid is not optimal in the known process, and the power requirement seems unnecessarily large, and it is therefore the object of the present invention to provide such an embodiment of the process that the gas is utilized to an even greater extent than it has previously been. possible with a loop reactor and using less power.

Also provided as part of the invention is an apparatus in the form of a loop reactor for use in the practice of the method.

This object is achieved by a method of the type mentioned in the preamble, which method is peculiar in that a substantial part of the mass transport from 10 gas to liquid phase and the associated fermentation process takes place in an oval or otherwise shaped pipe piece which runs substantially horizontal to the side from the plane formed by the downstream portion and the upstream portion between the lower ends of the downstream portion and the upstream portion, respectively, and that the fermentation liquid is circulated by at least one pump disposed in the horizontally extending pipe portion.

Hereby, due to the pressure from the above liquid column in the vertical pipes, it is possible to transfer a particularly large amount of substance from gas phase to liquid phase per minute. unit of time, since the solubility of gas in the liquid - and thus the mass transport - increases proportionally to the absolute pressure.

It is advantageous hereby that the substantially horizontally extending piece of pipe is constituted by a lower horizontal connecting pipe, with one end connected to the lower end of the vertical downstream part and with its other end connected to the end of an upper horizontal connection. supply pipe, which at its opposite end is connected to the lower end of the vertical upstream portion, and that the pump is constituted by several propellers, preferably located in the lower horizontal connecting pipe.

35 A substantial part of the mass transport from gas phase to liquid phase and the associated fermentation process will thereby take place in the lower horizontal connecting pipe.

It is further advantageous that the two horizontal connecting pipes are parallel, with the construction cost 5 for establishing the pipe piece and its support thereby being smaller than if the pipe piece ran as a circular arc or in an oval between the lower ends of the vertical pipes in the loop reactor. .

It is also advantageous for spacers to be disposed at intervals in the longitudinal direction of the substantially horizontal portion in order to avoid the presence of gas bubbles above a predetermined size.

The invention also relates, as stated above, to an apparatus, such as a loop reactor, for use in carrying out the method according to the invention, which apparatus is peculiar in that the apparatus has an oval or otherwise shaped pipe piece which extends substantially horizontally. to the side 20 from the plane formed by the downstream portion and the upstream portion between the lower ends of the downstream portion and the upstream portion, respectively, and that the at least one pump is disposed in the horizontally extending pipe piece.

The method and apparatus according to the invention will be explained in more detail below with reference to the drawing, in which:

FIG. 1 is a perspective view of one embodiment of an apparatus according to the invention; and FIG. 2 schematically shows a vertical section along the axis of a horizontally arranged tube in the embodiment of FIG. 1.

35 In FIG. 1 represents 1 an embodiment of an apparatus according to the invention. The apparatus is provided as a loop reactor having a downstream portion 2 and an upstream portion 3, two portions 2, 3 extending substantially vertically in the operating position of the loop reactor 1. Downstream portion 2 is provided at the top with a top 5 portion, usually called headspace.

The top portion 4 of the loop reactor 1 is formed as a cylinder 5 having a substantially larger diameter than the downstream portion 2, which cylinder 5 is connected to the downstream portion 2 by means of a tapered transition piece 6. The upstream portion 3 is tangentially inserted into a pipe bend 7. side of cylinder 5. This construction contributes to a good separation of fermentation liquid and gas bubbles during the operation of the loop reactor 1, with centrifugal forces acting in the tube bend 7, and in the cylindrical part 5 a strong circulation of the fermentation liquid occurs. with associated centrifugal forces. Thus, the separation of gas bubbles from the fermentation liquid is solved in a very advantageous way.

In known loop reactors, the lower ends of the downstream portion and the upstream portion are connected to each other by the thickness of a short horizontal tube to produce a closed circuit in which fermentation liquid can be circulated by means of a pump or similar means.

25

In the loop reactor 1 according to the invention, the lower end 8 of the downstream part 2 is connected via a 90 ° pipe bend 10 to a first connecting pipe 11 which extends substantially horizontally to a side away from that of the downstream part 2 and the upstream portion 3 formed plane. At the opposite end of the first connecting pipe 11, this is connected through a second pipe bend 12, which is 180 °, to a second connecting pipe 13, which also extends substantially horizontally parallel to the first connecting pipe 11. Finally, the end of the pipe the second connecting tube 13 connected to the lower end 9 of the upstream tube 3 by means of a DK 170824 B1 pipe bend 14 of approx. 90 °. The reference numeral 16 in the drawing indicates a pipe loop fairy formed by the first connecting pipe 11, the pipe bending 12 and the second connecting pipe 13.

5

By means of at least one pump not shown in the drawing, a fermentation liquid is caused to flow in the loop reactor 1 in the flow direction indicated by an arrow 15.

Said pipe loop 16 could in itself also be formed as part of a circular arc, an oval or an ellipse.

Preferably, the lower ends 8, 9 of the downstream portion 2 and 15 of the upstream portion 3 are further truncated in such a way that the lower end 8 of the downstream portion 2 is at a lower level than the lower end 9 of the upstream portion 3, and it can be understood. that the first connecting pipe 11 will therefore be at a lower level than the second connecting pipe 13.

The tubes constituting the downstream portion 2, the upstream portion 3 and the upper horizontal connecting tube 13 may be formed with the same diameter as the lower horizontal connecting tube 25 11, but the diameters of the tubes 2, 3, 11 and 13 may also be different. Thus, the vertical upstream portion 3 and the upper horizontal connecting pipe 13 can be formed with smaller diameter than the lower horizontal connecting pipe 11, whereby a greater part of the total residence time in the loop actuator 1 is spent in the more productive lower horizontal connecting pipe 11.

In order to avoid the gas and liquid phases being separated radially by horizontal flow in longer free tubes due to density differences, so-called spreaders 17 are arranged at periodic intervals in the lower horizontal connecting pipe 11. A spreader 17 is in this context defined as a structure characterized by two properties: 5 (a) It splits and distributes gas bubbles 18 over the entire pipe cross section; (b) on the output side, the spreader 17 creates swirls the size of which is comparable to the hydraulic diameter of the element or the pipe diameter.

For example, the spreader 17 may consist of a type of disperser that satisfies property (a), followed by guide vanes which change the local direction of flow so that property (b) is attributed. However, several static mixers combining the two properties in one and the same geometry are commercially available.

The actual distribution of gas bubbles 18 after 20 of a spreader 17 having properties (a) and (b) is shown schematically in FIG. 2, showing a vertical section along the axis of one of the horizontal connecting pipes 11, 13 in the loop reactor 1 according to the invention.

25 In FIG. 2, Lm denotes the length of a spreader 17 along said axis, while L0 denotes the stretch of spreader 17 within which gas bubbles 18 produced in the spreader are approximately evenly distributed within the pipe cross section. After the stretch L0, the gas bubbles 18 will eventually gather along the inside 19 of the upper side of the connecting pipe 11, 13, the bubble front inclined forwardly and upwardly at an angle a. The pipe cross-section is determined by the pipe diameter D.

At a moderate volumetric gas fraction (less than 0.15), the distance L0, preferably depends on the flow rate and viscosity of the fermentation liquid 9 and the vortex-creating geometry of the spreader 17 (the vortex size according to characteristic (b)). The slope of the bubble front, a, is approximately given by the ratio of the mean rise velocity of the gas bubbles 18 to the horizontal flow rate of the liquid, where the mean rise rate depends on the viscosity and surface tension of the liquid. L0 and α can either be estimated from theoretical considerations and model calculations or be found experimentally for given fluid-mechanical conditions, such as holdup, viscosity, surface tension and flow rate of liquid, and for a given spreader geometry.

Spacers 17 must be spaced apart through the horizontally extending pipe loop 16 of the loop reactor 1, which distance must be adjusted so that the gas bubbles 18 after a spreader 17 are still distributed over the predominant portion of the pipe diameter, D, measured in vertical direction if the tube cross section is oval. This spacing between successive spreaders 17 must be less than or equal to a maximum distance, Lmax, given by L0 and a.

In the case of static mixers of the kind mentioned previously as spreader 17, the minimum length is

Lm min, of a mixer given that the mixer for the given 25 distribution of the gas bubbles 18 on the input side must satisfy the property (a) on the output side.

Since the specific mass transport is typically 5-10 times higher in a static mixer than in a corresponding length of free pipe piece, the average mass transport per reactor volume could be increased by increasing the length Lm of the individual mixer in addition to Lm Bin and / or by placing the mixers at a smaller distance than Lmax. However, this also increases the energy consumption in the form of the required pump power, since the pressure drop 35 over a mixer is much larger than over a corresponding length of free pipe.

10 DK 170824 B1

Static mixers may also be placed at appropriate intervals in the vertical pipes, downstream portion 2 and upstream portion 3, to avoid the occurrence of gas bubbles 18 above a certain predetermined maximum size and to increase the total mass of transport. In the case of the vertical tubes 2, 3 there is no upper limit on the distance between two consecutive mixers from a special radially asymmetric phase separation consideration.

10

The gas introduction may be effected through nozzles, ejectors or porous filters not shown in the drawing located in the lower horizontal connecting tube 11, and there may be one or more injection sites. There may also be one or more gas inlets in the vertical downstream portion 2, one of which will be located in the upper portion of the downstream portion 2 just below the tapered transition piece 6.

At each injection site, such a gas quantity of 20 time unit that a particular desired residence time is obtained in the fermentation medium around the insertion site.

The choice of number and location of injection sites is determined from the following guidelines: 25 (1) Gas introductions are made at sufficiently short intervals along the fermentor tube so that the actual local residence time in downstream portion 2 and lower horizontal connecting tube 11 does not decrease significantly relative to the desired optimum value, and (2) a sufficient length relative to the fluid flow rate of the last portion of the lower horizontal connecting tube 11 is kept free of injection sites so that a desired gas utilization is achieved upon the gas bubbles' arrival at the top portion 4 of 11 DK 170824 B1 loop reactors 1.

In addition to increasing the hydrostatic pressure in the lower horizontal connecting tube 11, the vertical tubes, the downstream portion 2 and the upstream portion 3, have an important function in the separation of CO 2 formed by fermentation with microorganisms. The longer the vertical upstream portion 3 and possibly also the upper horizontal connecting tube 13, the lower average content of 10 dissolved CO 2 will be in the fermentation liquid during a fermentation with the same total mass transport. Therefore, when fermenting certain microorganisms which are inappropriately inhibited by high concentration of dissolved CO 2, the ratio of the lengths of the lower horizontal connecting pipe 11 to 15 the vertical upstream part 3 can be used as an important design parameter.

In the present embodiment of the top part 4 as a cyclone, the centrifugal forces are used to expel gas bubbles 20 from the fermentation liquid.

Insertion of microorganisms and fermentation medium can take place through tubes located at random locations along the loop reactor 1.

25

Continuous harvesting of biomass can be effected by bottling at any location along the loop reactor 1, but this bottling is most conveniently effected from the outside of one of the lower pipe bends 10, 14, where centrifugal forces cause the liquid stream content of gas bubbles 18 to be least possible.

The loop reactor 1 according to the invention is designed specifically for continuous fermentation, but can also be used for batch fermentation.

12 DK 170824 B1

In particular, the advantages of the method and apparatus or loop reactor 1 according to the invention are to be seen in that - by means of a large volume and horizontally located volume relative to the total volume of the loop reactor 1, an arbitrary large total residence time of the gas bubbles 18 can be obtained. a fermentation liquid and thus a high gas utilization per liter. circulation in the loop reactor 1 that mass transport in the horizontally located pipe loop 16 is particularly high due to the hydrostatic pressure exerted by the vertical parts of the loop reactor 1, the downstream part 2 and the upstream part 3, and the construction costs for the horizontal part 16 of the loop - the reactor 1 will be considerably less than the cost of constructing a similarly vertical fermentor volume with the necessary supporting and supporting structures, - that by periodically placing sprinklers 17 in the lower horizontal connecting tube 11, 20 is a mixture of gas and fermentation liquid for each spreader, thereby utilizing this portion of the loop reactor 1 to avoid separation of gas bubbles 18 and fermentation liquid, and - by following the stated guidelines for designing the spreader 17 and number and location of gas nozzles can adapt the characteristics of the loop reactor 1, such as high / low gas utilization, energy consumption / mass transfer rt, to the desired fermentation within very wide limits.

Claims (8)

13 DK 170824 B1 A process for the continuous cultivation of microorganisms by high utilization of gaseous substrates, by which method one or more gases are introduced and mixed into a fermentation liquid introduced into a loop reactor (1) having a top portion ( 4), a substantially vertical downstream portion (2) and also a substantially vertical upstream portion (3), which three portions (2, 3, 4) form part of a fermentation liquid circuit which is circulated in the loop reactor by a pump along with gases introduced and mixed into the fermentation liquid via several injection sites, at least one injection site located in the upper portion of the downstream portion (2) near the top portion (4), characterized by a substantial part of the mass transport from gas to liquid phase and the associated fermentation process takes place in an oval or otherwise shaped piece of pipe (11, 12, 13, 16) which extends mainly horizontally outward from that of the downstream part (2) and the upstream portion (3) formed between the lower ends (8, 9. of the downstream portion (2) and upstream portion (3), respectively), and that the fermentation liquid is circulated by at least one pump disposed in the horizontally extending pipe portion (11). , 12, 13, 16). 25 Method according to claim 1, characterized in that the substantially horizontally extending pipe piece (11, 12, 13, 16) is constituted by a lower horizontal connecting pipe (11), with one end thereof connected to the lower end 30 (8). of the vertical downstream portion (2) and with its other end connected to the end of an upper horizontal connecting pipe (13) connected to its lower end to the lower end (9) of the vertical upstream portion (3) and is comprised of several propellers which are preferably arranged in the lower horizontal connecting pipe (11). 14 DK 170824 B1 Method according to claim 1 or 2, characterized in that the two horizontal connecting pipes (11, 13) are arranged parallel to each other. Method according to any one of claims 1-3, characterized in that in the substantially horizontal extending piece of pipe (11, 12, 13, 16) spacers (17) are arranged at intervals of the pipe piece (11, 12, 13). 16) longitudinal direction. 10 Apparatus for use in carrying out the method of claim 1 and in the form of a loop reactor (1) having a top portion (4), a substantially vertical downstream portion (2) and a substantially vertical upstream portion (2). 3) which three parts (2, 3, 4) are included in a fermentation liquid circuit which is circulated with the gases in the loop reactor (I) of a pump, as well as means for introducing fermentation liquid and gas injection sites for introducing a or more gases in the fermentation liquid, of which at least one injection site is located in the upper part of the downstream part (2) close to the top part (4), characterized in that the loop reactor (1) has an oval or otherwise formed pipe piece (11, 12, 13, 16) extending substantially horizontally outwardly from the plane formed by the downstream portion (2) and the upstream portion (3) between the lower ends (8, 9 of the downstream portion (2) and the upstream portion, respectively) (3) and that at least one pump is disposed in the horizontally extending pipe piece (11, 12, 13, 16). Apparatus according to claim 5, characterized in that the substantially horizontally extending pipe piece (11, 12, 13, 16) is formed of a lower horizontal connecting pipe (II), with one end thereof connected to the lower end (8). of the vertical downstream portion (2) and with its other end 35 is connected to the end of an upper horizontal connecting tube (13) which is connected to its opposite end to the lower end (9) of the vertical upstream portion (3). ), and that the pump is comprised of several propellers, preferably located in the lower horizontal connecting pipe (11). Apparatus according to claims 5-6, characterized in that the two horizontally extending connecting pipes (11, 13) extend in parallel. Apparatus according to any one of claims 5-7, 10, characterized in that spacers (17) are arranged in the substantially horizontally extending pipe piece (11, 12, 13, 16) at intervals in the pipe piece (11, 12, 13). 16) longitudinal direction to avoid the occurrence of gas bubbles (18) above a predetermined size. 15