1. Tank body
The tank body of a fermentation tank is welded from a cylinder and an elliptical or disc-shaped head, and the head and cylinder of a small fermentation tank are connected by flanges. The top of the tank is equipped with a sight glass and a light mirror for easy observation of the fermentation status inside the tank. The connections on the top of the fermentation tank include: feed pipe, feed pipe, exhaust pipe, inoculation pipe, and pressure gauge connection. The connections on the tank body include cooling water inlet and outlet pipes, air inlet pipes, sampling pipes, thermometer pipes, and measurement and control instrument interfaces.
2. Size ratio of tank body
The dimensions of each part of the tank have a certain proportion, and fermentation tanks are generally slender due to the special needs of fermentation, with a height to diameter ratio of about 1.7-2.5.
3. Blender
Fermentation tanks are usually equipped with two sets of agitators, with a spacing S of approximately three times the diameter of the agitators. For large fermentation tanks and those with high liquid depth HL, three or more sets of agitators can be installed. The bottom set of agitators is usually closer to the outlet of the air duct, and the distance C from the bottom of the tank is generally equal to the diameter Di of the agitator, but it should not be less than 0.8Di, otherwise it will affect the circulation of the liquid.
Axial agitator: blade type, propeller type
Radial (turbine) agitator (Disc turbine): straight blades, curved blades, arrow blades
4. Barrier board
The function of the baffle is to change the direction of the liquid flow from radial flow to axial flow, causing the liquid to vigorously flip and increasing dissolved oxygen.
Full baffle condition: it refers to adding accessories in the tank at a certain number of revolutions while the shaft power remains unchanged. To reach the full baffle condition, the following requirements must be met:
5. Defoamer
The defoamer is used to break foam. The commonly used forms of defoamers include serrated, comb shaped, and orifice plate. The aperture of the orifice plate is about 10-20 millimeters. The length of the defoamer is approximately 0.65 times the diameter of the tank.
6. Coupling
The mixing shaft of a large fermentation tank is relatively long and often divided into two to three sections. A coupling is used to firmly and rigidly connect the upper and lower mixing shafts. There are two commonly used types of couplings: drum shaped and clamp shell shaped. Small fermentation tanks can use flanges to connect the stirring shaft, and the shaft connection should be vertical with the centerline aligned.
7. Bearing
In order to reduce vibration, medium-sized fermentation tanks usually have bottom bearings inside the tank, while large fermentation tanks have middle bearings. The horizontal position of the bottom and middle bearings should be adjusted appropriately. Lubricating oil cannot be added to the bearings inside the tank, and liquid lubricated plastic bearings (such as polytetrafluoroethylene, etc.) should be used. The gap between the bearings and the shaft is often taken as 0.4-0.7% of the shaft diameter. To prevent journal wear, a shaft sleeve can be added to the shaft in contact with the bearing.
8. Variable speed device
The test tank adopts a continuously variable transmission device. The commonly used variable speed devices for fermentation tanks include V-belt transmission, cylindrical or spiral bevel gear reduction devices, among which V-belt variable speed transmission is more convenient.
9. Shaft seal
The function of the shaft seal is to seal the gap between the top or bottom of the tank and the shaft, preventing leakage and contamination of bacteria. The commonly used shaft seals include packing box and end face shaft seal, and mechanical seals are generally used.
① A stuffing box type shaft seal is composed of a stuffing box body, a stuffing bottom liner, a stuffing cover, and clamping bolts, etc., to achieve a sealing effect on the rotating shaft.
The advantage of a stuffing box shaft seal is its simple structure. The main disadvantages are: many blind spots, difficult sterilization, easy leakage and bacterial contamination; The wear of the shaft is severe; The friction power consumption is high after the packing is compressed; Short lifespan, frequent maintenance, and high labor consumption.
② End face type shaft seal, also known as mechanical shaft seal. The sealing effect is achieved by the pressure of elastic elements (springs, bellows, etc.) to tightly adhere the smooth surfaces of the moving and stationary rings perpendicular to the axis, and to rotate relative to each other to achieve sealing.
10. Heat exchange device for fermentation tank
① Jacketed heat exchange device
This device is commonly used in fermentation tanks with smaller volumes; The height of the jacket should be slightly higher than the height of the stationary liquid level. The advantages of this device are: simple structure; Easy to process, no cooling equipment inside the tank, few dead corners, easy to clean and sterilize, beneficial for fermentation. Its disadvantages are: thick heat transfer walls, low cooling water flow rate, and poor cooling effect during fermentation.
② Vertical snake tube heat exchange device
This device is installed in vertical snake tube groups inside fermentation tanks, with four, six, or eight groups depending on the diameter of the tubes. Fermentation tanks with a volume of 5 cubic meters or more are often equipped with this heat exchange device. The advantage of this device is that the flow rate of cooling water inside the pipe is high; High heat transfer coefficient. This cooling device is suitable for areas where the cooling water temperature is low and the amount of water used is relatively small. However, in areas with high temperatures, the cooling water temperature is relatively high, making it difficult to cool down during fermentation. The fermentation temperature often exceeds 40 ℃, which affects the fermentation yield. Therefore, frozen salt water or frozen water cooling should be used, which increases equipment investment and production costs. In addition, curved positions are more prone to erosion.
③ Vertical tube heat exchange device
This device is symmetrically grouped and installed in a fermentation tank in the form of tubes. Its advantages are: easy processing, suitable for areas with high temperatures and abundant water sources. The disadvantage of this device is that its heat transfer coefficient is lower than that of a serpentine tube, and it requires a larger amount of water.