RU2848026C1 - Method for forming vortex flows to intensify mass transfer in a bioreactor - Google Patents

Abstract

FIELD: biotechnology.

SUBSTANCE: method is proposed for forming vortex flows to intensify mass transfer in a bioreactor, according to which a cylindrical reactor is filled with liquid, and with the reactor walls moving, the rotation of the reactor cover generates a vortex motion in the upper layer of the liquid until the vortex motion spreads to the lower layers. The temperature of the liquid is controlled with an accuracy of 0.05°C, and the vibration level of the bioreactor walls is controlled by vibration sensors. The reactor lid is driven by a stepper motor, while a digital laser phototachometer installed at a distance of half the radius of the reactor bottom from the side wall of the reactor controls the angular velocity of the adaptively rotating side wall. A computer transmits a signal to the stepper motor that drives the reactor lid to adjust the angular velocity of the reactor lid, taking into account changes in the vibration level of the bioreactor walls.

EFFECT: increased efficiency of biological and chemical processes in vortex bioreactors.

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Description

Field of technology

The invention relates to methods for generating vortex flows to enhance mass transfer in a bioreactor, particularly in the cultivation of tissue cells, microorganisms, and algae. The invention may find application in biotechnology, pharmaceuticals, the chemical and food industries, and agriculture. Vortex mixing is a common method for intensifying processes in chemical and bioreactors. Known in the art are methods for conducting biochemical processes by organizing vortex motion of liquid media, carried out in gas-liquid vortex reactors. In known technical solutions, the culture medium is mixed using a concentrated air vortex generated by an activator installed under the bioreactor lid above the surface of the culture medium. Mixing of the medium is achieved by creating a three-dimensional motion within it, similar to a "rotating vortex ring"—a quasi-stationary flow with axial countercurrent generated by an aerating gas vortex due to the pressure difference above the surface and the frictional force of the air flow on the surface of the liquid. The absence of a mechanical mixing element in the liquid ensures energy-efficient, 0.06–0.1 W/l, compared to 1–4 W/l for bioreactors with a mechanical mixing device and airlift bioreactors, gentle and effective mixing of liquids, including viscous ones, without the formation of foam and cavitation, water hammer, highly turbulent and stagnant zones, as well as microzones with high temperatures.

State of the art

Gas-vortex bioreactors for carrying out biochemical processes are known [RU 2538170, 15.08.2011, C12N 1/00, C12M 1/04, C12M 1/06; RU 2299903, 12.05.2004, C12M 1/04, C12M 3/00, C13K 1/06]. The inventions are aimed at increasing the efficiency of mixing and accelerating biochemical processes in liquid media. Biochemical processes in the known vortex bioreactors are carried out as follows. The bioreactor is filled with a nutrient medium so that a cavity for the movement of the aerating gas remains above the surface of the medium in the upper part of the container, and an annular partition (washer) is located in the nutrient medium near its surface. The desired temperature is then set, the cell seeding dose is introduced, and the drive for the stirring device, which consists of a paddle wheel activator mounted horizontally on a vertical shaft at the top of the container under the lid, is turned on. Rotation of the paddle wheel above the cell suspension surface creates a vacuum in the axial zone of the container and an increased pressure at the periphery of the container. The pressure differential between the periphery and axial zone of the gas cavity above the cell suspension surface creates an intense swirling gas flow, which generates a rotational motion in the culture fluid with intensive mixing along the axis of the container. The gas vortex velocity is 3-6 m/s. The annular partition—a floating washer—rotates in the same direction and at the same angular velocity as the culture fluid and is held on a rod and used to stabilize the gas-liquid interface. In these technical solutions, air serves as the swirling device, which swirls the washer, which is located on the surface of the liquid. The densities of air and liquid differ by three orders of magnitude, in particular, air-to-water - by a factor of 1000. The transfer of rotation from air at a speed of about 100/1. Therefore, rotating the liquid with air is ineffective, and if rotated through a washer with sails, partial contact of the working fluid with the solid washer occurs - this can lead to damage to the cells of the culture medium. In addition, the presence of internal devices (an annular partition mounted on a rod - a telescopic tube) increases the power consumption by 10-20%. A gas-liquid vortex reactor for carrying out biochemical processes is known [I.V. Naumov, S.G. Skripkin, B.R. Sharifullin, V.N. Stern. STUDY OF VORTEX MOTION IN A GAS-LIQUID BIOREACTOR. Processes in Geoenvironments, No. 3 (29), 2021]. Biochemical processes in a well-known gas-liquid vortex bioreactor are carried out as follows. The reactor was filled with a 65% aqueous glycerol solution. A paddle wheel (activator) generates a high-speed, swirling, tornado-type gas flow above the surface of the liquid medium. The aerating gas interacts with the liquid only through the free surface, without mixing with it. The high velocity of the aerating gas intensifies interphase mass transfer and ensures uniform mixing of the suspension without the formation of stagnant zones. In this solution, the swirling device is an activator, swirling the air, and the swirling air flow swirls the liquid. The study demonstrates that the speed and mixing of the working medium depend on the rotational speed of the activator. The optimal operating range of the activator rotation, which eliminates interface fluctuations, is 150 - 1800 min–1. It is known that process intensification by increasing the rotational speed of the mixing device is usually accompanied by an increase in the power expended on mixing. Thus, the specified technical solution, based on the use of air as a device for swirling the liquid medium, is energy-consuming and not very effective.

Disclosure of the essence of the invention

The objective of the invention is to create a highly efficient technology for intensifying biological and chemical processes in vortex two-liquid reactors to produce a high-quality product.

The technical result is highly efficient intensification of biological and chemical processes and mass transfer in vortex bioreactors. In this case, efficiency is expressed in the following effects: low energy consumption for fluid spinning and rotation, achieved through the low angular velocities of the reactor lid required for fluid swirl, as well as the freely rotating sidewall.

A method for generating vortex flows to intensify mass transfer in a bioreactor involves filling a cylindrical reactor with water. With the reactor walls moving, rotating the reactor lid generates vortex motion in the upper liquid layer until the vortex propagates to the underlying layers. The liquid temperature is controlled with an accuracy of 0.05°C. The bioreactor wall vibration level is monitored using vibration sensors, and the reactor lid is driven by a stepper motor. A digital laser phototachometer installed at a distance of half the reactor bottom radius from the reactor sidewall monitors the angular velocity of the adaptively rotating sidewall. A computer transmits a signal to the stepper motor driving the reactor lid, adjusting the angular velocity of the reactor lid to account for changes in the bioreactor wall vibration level.

1. The adaptive rotation system operates autonomously, responding to changes in flow conditions and providing an optimal balance between energy consumption and process efficiency; 2. intensity and uniformity of mixing without foam and cavitation formation, water hammer, high-temperature microzones, highly turbulent and stagnant zones; 3. high intensity of mass transfer, which is also achieved by creating a flow structure that simultaneously implements vortex motion in the paraxial plane and circulation motion in the meridional plane of the liquid; 4. reduction in the duration of the process, which is a consequence of point 3, since the movement is more intense. 5. high quality of the resulting product, which is achieved: - for the culture medium - non-traumatic, uniform mixing without foam and cavitation formation, water hammer, highly turbulent and stagnant zones, high-temperature microzones; - for a chemical process - more thorough mixing at low speeds without foam formation, the absence of direct contact of the aggressive medium with the swirling device, which also results in its safety; 6. reduction in operating costs for reactor maintenance, which is due to the reactor design and the structure of the generated vortex flow, which eliminates the fouling of the reactor's internal walls with biological material or sediment as a result of a chemical reaction, as well as the absence of direct contact of the aggressive medium with the swirling device. 7. reduction in hydraulic resistance: due to the fact that the side wall rotates with the flow, friction between the liquid and the wall surface is reduced. This reduces hydraulic resistance and reduces the energy costs of maintaining the required level of circulation.

The method for generating vortex flows to intensify mass transfer in a bioreactor includes the following steps: 1. filling a cylindrical reactor with liquid; 2. then, with movable walls of the reactor, vortex motion is generated in the upper layer of liquid by rotating the reactor lid only until the vortex motion propagates to the underlying layers; 3. during the process, the process is controlled by an automated control system. The cylindrical reactor is mounted on a bearing. As the disk rotation speed increases, the cylindrical container begins to rotate under the action of the friction force of the liquid against the side wall. The process control includes the following steps: periodic measurement of the medium temperature by temperature sensors at one or more fixed control points inside the reactor chamber, installed on the reactor wall, in order to prevent them from disturbing the flow inside the reactor; transmission of measurement data to a computer equipped with the appropriate software and a database of experimentally obtained reference values of the medium temperature; calculation and comparison with a specified accuracy of the obtained values of the medium temperature with the reference values. During the biological and chemical process stages, the environment temperature is controlled with an accuracy of 0.05°C. The reactor lid is driven by a stepper motor. A digital laser phototachometer, installed halfway between the reactor bottom and the reactor sidewall, monitors the angular velocity of the adaptively rotating sidewall. A vibration sensor is mounted on the bioreactor walls, monitoring the vibration level of the bioreactor walls. Data from the vibration sensor is transmitted to a personal computer. If the vibration level exceeds the permissible level for the bioreactor design, a signal is transmitted from the personal computer to the stepper motor driving the reactor lid, adjusting the angular velocity of the reactor lid to account for changes in the vibration level of the bioreactor walls.

Implementation of the invention

The reactor consists of a vertically installed cylindrical container with a lid shaped like a rotating disk. The Reynolds number is determined by two parameters: the relative elongation h = H/R, where H is the height and R is the radius of the cylindrical container, and the Reynolds number Re = ω _d R ² /ν, where ω _d is the angular velocity of the lid rotation and ν is the kinematic viscosity of the liquid. The reactor is filled with liquid. The vortex motion of the liquids is generated by the reactor lid (disk), which rotates with an angular velocity ω _d , while the side wall begins to rotate independently at a frequency ω _cyl , due to internal friction. The rotation of the lid is created by a stepper motor. At the lid, centrifugal force pushes the adjacent liquid from the axis to the periphery, generating meridional circulation, i.e., the liquid descends near the side wall to the interface, where it spirals toward the axis, where it returns to the vicinity of the lid. Thus, the layer of upper liquid forms a "liquid rotating lid," which swirls the underlying liquid layers. The speed of the slowest rotation of the reactor lid (the minimum angular velocity achieved at 150 min ^–1 ) is selected so that the swirl rate of the medium is higher than the rate at which the reactor's inner walls become fouled with biological material or sediment as a result of a chemical reaction. It is known that the fouling rates of the reactor's inner walls range from 0.01 to 0.5 m/s. As the lid rotation increases, the flow structure changes: slip is observed, i.e., the radial velocity at the interface experiences a jump, changing not only its magnitude but also its direction. Unlike known slip mechanisms, such as those in a rarefied gas, on a rough surface, or created by surfactants, in this case slip is caused by centrifugal force. In a liquid, centrifugal circulation transfers angular momentum from the rotating lid down along the side wall and then to the axis at the bottom. In a liquid, converging motion causes an increase in angular velocity as it approaches the axis, forming a tornado-like swirling jet. The adaptively rotating sidewall of a bioreactor alters the boundary conditions at the fluid's periphery: when the wall is stationary, the velocity there is zero, causing excessive frictional losses between the viscous fluid and the wall, which in turn leads to excess heat generation at the stationary reactor wall. When the wall is adaptively moving, the boundary conditions are different: the velocity at the periphery is nonzero and equal to ω _cyl R, where ω _cyl is the angular velocity of the reactor wall and R is the reactor radius. Initially, flow swirling occurs due to forced rotation of the upper disk. The presence of this velocity (ω _cyl R) at the sidewall allows the flow swirling to penetrate deeper into the underlying layers of the liquid, compared to a stationary sidewall. The presence of adaptive rotation of the sidewall increases flow swirling compared to a stationary reactor sidewall. This effect intensifies mixing between adjacent layers of liquid, which allows for mixing of liquid layers in the reactor with lower initial energy costs.

Peripheral velocity profiles were measured in horizontal cross-sections at various Reynolds numbers and at different distances from the bottom. A strong influence of sidewall rotation on the flow is observed. Near the bottom, the maximum shift toward the axis is less than for a stationary wall. Also, near the bottom, the velocity is higher than at the center of the reactor, since the bottom also rotates. With a stationary wall, the velocity at the bottom is approximately half that at the disk, while in a rotating cylinder, the velocity drops by 25-33%. A reduction in hydraulic resistance is observed due to the adaptive rotation of the reactor sidewall. With a rotating wall, the flow velocity is 2-3 times higher than in a stationary cylinder, indicating increased flow swirl and, consequently, intensified mass transfer.

The proposed reactor configuration enables efficient control of vortex flows without additional energy or resource consumption, unlike the case of forced rotation of the reactor side walls at a fixed angular velocity. Thus, the resulting flow structure promotes highly uniform mixing of the medium, intensified mass transfer, reduced process time, and improved product quality (gentle, non-traumatic mixing). Low energy consumption for fluid spinning and rotation is achieved due to the low angular velocities of the reactor lid and, additionally, the adaptively rotating wall, while still being sufficient to generate swirling of the working medium. Experiments have shown that the following parameters influence the speed of spinning and rotation of the medium: the relative elongation of the reactor h = H/R, where H is the height and R is the radius of the cylindrical container. The greater h, the more energy is required to spin the fluids. With a higher kinematic viscosity of the fluid, more energy is required to spin the fluids. Flow swirl and, accordingly, the Reynolds number, are determined by the viscosity of the fluid adjacent to the rotating disk. Thus, in each specific case of chemical, pharmaceutical, biological or other processes, it is necessary to generate a vortex motion with specific properties, which is achieved by varying the parameters affecting the structure and degree of swirl. To ensure the specified physicochemical conditions for mass transfer processes in reactors, regardless of the reactor type, biological or chemical processes, the medium temperature and the vibration level of the apparatus require strict control. Monitoring the medium temperature and controlling the stepper motor are carried out by means of an automated control system (ACS), which includes: temperature sensors for measuring the liquid (medium) temperature; a controller for controlling the stepper motor; a computer with installed specialized software (SW) designed for: calculating the medium temperature, comparing the obtained values with the reference, calculating the optimal angular velocity of rotation of the reactor lid; generating and transmitting a control signal to the controller for controlling the stepper motor. Monitoring the temperature of the medium and controlling the stepper motor includes: 1. periodic measurement of the temperature of the medium by temperature sensors at one or more fixed control points inside the reactor chamber, installed on the reactor wall, in order to prevent disturbance of the flow inside the reactor; 2. transmission of measurement data to a computer equipped with the appropriate software and a database of experimentally obtained reference values of the temperature of the medium; 3. calculation and comparison of the obtained values of the temperature of the medium with the reference values; 4. transmission of the appropriate signal to the stepper motor driving the reactor lid in order to correct the angular velocity of rotation of the reactor lid taking into account the change in kinematic viscosity depending on the temperature of the liquid. In the event that the temperature turns out to be higher or lower than the reference value, the angular velocity of rotation of the reactor lid is changed so as to ensure, with a given accuracy, the necessary speed values for ensuring optimal mass transfer in the liquid, while maintaining the laminar flow regime of the medium. The reference values of the temperature of the medium are selected experimentally for different liquids and stored in the database of reference values. The temperature values are determined depending on the kinematic viscosity of a particular liquid. Vibration level monitoring and stepper motor control are performed by means of an automated control system (ACS), which includes: vibration sensors (vibration sensor) for measuring the vibration level; a controller for controlling the stepper motor; a computer with special software installed, designed for: calculating the vibration level of the bioreactor, comparing the obtained values with the permissible ones, calculating the maximum angular velocity of rotation of the reactor lid; generating and transmitting a control signal to the controller for controlling the stepper motor. Vibration level monitoring and stepper motor control includes: 1. periodic measurement of the vibration level by vibration sensors at one or more fixed control points on the walls of the reactor chamber, installed on the reactor wall, in order to prevent them from disturbing the flow inside the reactor; 2. transmitting measurement data to a computer equipped with the appropriate software and a database of the experimentally obtained permissible vibration values; 3. calculating and comparing the obtained vibration level values with the limit values. 4. Transmitting a corresponding signal to the stepper motor driving the reactor lid to adjust the angular velocity of the reactor lid's rotation, accounting for changes in the bioreactor wall vibration level and reducing it below the threshold. If the vibration level exceeds or falls below the threshold, the angular velocity of the reactor lid's rotation is adjusted to ensure, with a specified accuracy, the required speed values for optimal mass transfer in the liquid while maintaining laminar flow. Reference values for the apparatus wall vibration level are selected experimentally for different designs and stored in a reference value database. The temperature and vibration monitoring systems are integrated into a single circuit for self-consistent operation. Coordination of the systems is achieved in the computer software through the exchange of relevant information from the monitoring systems and comparative analysis, after which the developed algorithm issues a final command to change the reactor lid's rotation speed.

An experimental study of a closed vortex flow in a freely rotating cylinder with a rotating upper disk was conducted. Flow velocities were measured using anemometry based on particle images in rotating and stationary cylinder modes, and the effect of the rotating wall on the flow structure was investigated. The study was carried out at a liquid height equal to the bottom diameter of the cylindrical bioreactor and a disk rotation frequency of Fd = 9.5 Hz, 10.5 Hz and 11.5 Hz, the cylinder was filled with 80% glycerol solution (kinematic viscosity ν = 40 cSt, density ρ = 1.209 kg/l). The side wall rotation frequencies were 1.52 Hz, 2.11 Hz, 2.91 Hz, respectively. Circumferential velocity profiles were obtained in horizontal sections at different Reynolds numbers and at different distances from the bottom. A strong effect of the rotation of the side walls of the reactor on the flow is observed. Near the bottom, the maximum shift toward the axis is less than for a stationary wall. Also, near the bottom, the velocity is higher than at the center of the reactor, since the bottom is also rotating. For a stationary wall, the velocity at the bottom is approximately half that at the reactor head, while in a rotating cylinder, the velocity drops by 25-33%. A decrease in hydraulic resistance is observed due to the adaptive rotation of the reactor sidewall. With a rotating wall, the flow velocity is 2-3 times higher than in a stationary cylinder, indicating increased flow swirl and, consequently, intensified mass transfer. An analysis of the axial velocity component distributions along the axis was conducted, as well as flow visualization for a rotating cylinder wall in all measured modes. It was shown that bubble breakup is absent in this case. It was found that with increasing disk rotation frequency, the axial velocity decreases, and an inflection appears in the velocity profile, similar to a precursor to bubble breakup of a vortex. A comparison of the axial velocity component profiles for a stationary and rotating reactor sidewall was performed, along with flow visualization for a stationary cylinder in all measured modes. Based on the velocity profiles and visualization, it was found that vortex breakdown is observed in the measured modes for the stationary wall.

This allows for not only an optimal flow structure but also an optimal rotation speed, ensuring gentle and thorough mixing of ingredients without direct contact with the swirling device. The use of adaptive sidewall rotation in this method significantly improves the characteristics of exchange processes and mass transfer, while simultaneously reducing operating costs and increasing the reliability and environmental friendliness of the process.

Claims (1)

A method for generating vortex flows for intensifying mass transfer in a bioreactor, characterized by filling a cylindrical reactor with liquid, generating a vortex motion in the upper layer of liquid by rotating the reactor lid with movable walls until the vortex motion propagates into the underlying layers, controlling the temperature of the liquid with an accuracy of 0.05°C, monitoring the vibration level of the bioreactor walls using vibration sensors, setting the reactor lid in motion with a stepper motor, monitoring the angular velocity of the adaptively rotating side wall with a digital laser phototachometer installed at a distance of half the radius of the reactor bottom from the side wall of the reactor, and transmitting a signal to the stepper motor setting the reactor lid in motion using a computer to adjust the angular velocity of the reactor lid rotation taking into account changes in the vibration level of the bioreactor walls.