Glass fermenter is a typical representative of aerobic bioreactor. Its main components are shell, temperature control part, stirring part, ventilation part, material inlet and outlet, measurement system and auxiliary system, etc. The main body is made of stainless steel, usually a turbine The connection between the stirring shaft and the tank should be aseptically sealed. The bottom of the tank is provided with an air distributor or nozzle, and the sterile air passing through the air filter is blown into the culture solution from a porous tube with a diameter of several millimeters.
The glass fermenter is driven to rotate at a certain speed by a stirring motor placed on the top of the tank, and the swollen air is broken into small bubbles by the liquid vortex and shear force generated by the stirring turbine, which are evenly dispersed in the culture medium. In this way, the oxygen required for cell growth is provided, and the concentration of the culture solution is uniform at the same time. The charging coefficient of the reactor is generally 70-80%. device etc.
Glass fermenters are suitable for most biological engineering, and have the following advantages: easy to control pH value and temperature; more research on industrial scale-up methods; suitable for continuous culture. The disadvantages are: the power consumption of stirring is relatively large; the structure is relatively complicated, it is difficult to completely disassemble and clean, and it is easy to contaminate bacteria;
As one of the main features of the aerated stirred tank, the power provided by the glass fermentation tank is the basic guarantee for the mass transfer, heat transfer, mixing and uniform distribution of the suspended matter in the mechanical stirring tank. The design and selection of the stirring device must be comprehensively considered to meet the above requirements and Reduce cost and power consumption. The glass fermenter consists of a motor, a gearbox, a stirring shaft, a stirring paddle, a shaft seal and a baffle.
- Motor and gearbox
The motor and gearbox are placed outside the tank. For small glass fermenters, single-phase electric motors can be used, while large-scale reactors generally use three-phase motors. For large reactors, since the speed of the motor is generally much higher than the stirring speed, the speed must be reduced through the gearbox. The glass fermenter can be infinitely variable and does not require a gearbox. In batch culture, each stage of cell growth has different requirements for shear force and oxygen transfer. In order to reduce power consumption, it is best to use an adjustable speed motor.
- Stirring Shaft
The stirring shaft can extend into the tank from the top or from the bottom. The former is called upper stirring and the latter is called lower stirring. Generally speaking, the manufacturing and installation cost of the upper agitator is slightly higher than that of the lower agitator. However, when using lower stirring, the solid particles in the medium or the crystals formed by the soluble components after the water volatilizes will damage the shaft seal and increase the maintenance cost. Different sizes of ventilated stirring tanks have different layers of stirring paddles. Small ventilated stirring tanks generally have only one layer of stirring paddles, while large ventilated stirring tanks generally have 2 to 4 layers of stirring paddles to improve mixing and mass transfer.
- The main function of the shaft
Seal is to prevent microorganisms in the environment from invading the reactor and leakage of the culture solution. Mechanical transmission parts are often one of the main causes of bacterial contamination, so the key to shaft seal design is to avoid bacterial contamination and leakage, and aseptic sealing materials should be used as much as possible.
- In order to prevent large vortices on the liquid surface during stirring, and to promote the mixing of fluids in the tank in all directions, the baffle plate is also installed on the tank body corresponding to the stirring paddle .
The baffle is designed to satisfy the “full baffle condition”. The so-called full baffle condition means that when adding baffles or other accessories in the stirring tank, the stirring power will not increase, and the full baffle condition is the minimum condition to eliminate the liquid surface vortex.
- The stirring paddle glass fermenter can be divided into radial flow stirring paddles and axial flow stirring paddles according to the initial direction of the fluid movement generated by stirring. The baffle is then folded back up and down both sides to generate secondary flow, and the axial flow stirring paddle makes the fluid move in the axial direction at the beginning. Generally speaking, the reactor with axial flow impeller has a lower power factor, and the energy consumption required to achieve the same mixing effect is much lower than that of the radial flow impeller. The shear force caused by the radial flow impeller is greater than that of the axial flow impeller, which is beneficial to break up the air bubbles, thereby increasing the overall oxygen transfer rate constant, but can cause damage to some cells. Therefore, glass fermenters are used for the cultivation of aerobic bacteria and yeasts that are not sensitive to shear force, while axial flow impellers are mostly used for shear force sensitive biological reaction systems. For glass fermenters, a hybrid configuration of these two types of paddles can be used to take full advantage of each.