Working principle of vertical closed-circuit dryer

Nitrogen filling and oxygen removal process

Close the corresponding pipeline control valve, the system is in a completely closed state, open the air exhaust pump, and pump out the air in the system, so that the system reaches a micro-negative pressure state, when the system pressure gauge shows a certain value, close the corresponding emptying valve, and at the same time Turn off the exhaust air pump. At this time, the nitrogen filling control valve is opened, and nitrogen is filled into the system. When the online oxygen detection device detects that the residual oxygen in the system is less than the required value, the system is in a slightly positive pressure state. At this time, the nitrogen filling control valve is closed and the next step is entered. process.

Drying process

Turn on the circulating fan to make the material in a good boiling state; turn on the radiator to heat the temperature in the system to the required temperature, and the heat will take away the moisture and organic solvent in the material through nitrogen transfer, and take away a small amount of fine powder; in the system, the fine powder is passed through the dust collector. (filtered to 2~μm) and collected, the hot and humid gas condenses the solvent and organic solvent into a liquid state by the condenser and is collected by the liquid storage tank; the dry nitrogen after condensation and dehumidification is circulated in the system through the action of the fan.

System nitrogen protection

Nitrogen protection is mainly controlled by an online oxygen detector. When the oxygen content exceeds the required value, the nitrogen filling device is automatically opened and nitrogen is filled into the system. When the oxygen content in the system meets the requirements, the nitrogen filling device is automatically closed.

System overvoltage protection

When the pressure in the system exceeds the set value, the pressure detection device will act to automatically drain and release the pressure; when the system pressure meets the requirements, the automatic drain valve will be closed and the system will operate normally.

Practical application analysis

1) The laboratory vertical closed-circuit Dryer (model FGBX-5) has been rectified according to the structure in Figure 2 and can be put into use.

2) Prepare 5 kg of starch material containing about 30% ethanol for use.

3) After the equipment is completely sealed, start the air exhaust pump to pump out the air in the system. After the system reaches a certain negative pressure value, turn off the air exhaust pump, open the filling nitrogen valve at the same time, and input nitrogen into the system. When the pressure is positive and the oxygen content in the system reaches a certain requirement, close the valve for filling nitrogen; during this process, if the system is in a state of slight positive pressure, but the oxygen content has not yet reached the standard, nitrogen should continue to be filled into the system. When the positive pressure in the system exceeds the safe set pressure of the automatic pressure relief valve on the equipment, the automatic pressure relief valve will open to release the pressure. When the pressure is released, the mixed gas of nitrogen and air in the system will be discharged, and the oxygen content in the system will continue. When the pressure in the system reaches the safe set value, the automatic pressure relief valve will automatically close, and this cycle will continue until the oxygen content in the system reaches the set value.

4) Start the condensation recovery device, and inject the chilled water of about 3° into the chilled water inlet of the condenser. Then start the closed induced draft fan and set the fan frequency to about 20 Hz.

5) Using the material level difference and the principle of double butterfly valve, the material is put into the system which is mainly nitrogen circulation.

6) Start the steam heater and control the inlet air temperature at about 60°.

7) The material is in a boiling state during the nitrogen circulation movement. The organic solvent ethanol and a small amount of water in the material are taken out by nitrogen and condensed into a liquid state by the condenser and flow into the recovery box. The dust removal bag is shaken up and down under the action of the shaking bag cylinder, and the material attached to the bag is shaken into the silo to continue drying. Without any other gas entering the system, the micro-positive pressure state in the system will not be very fast. Increase and open the automatic pressure relief device, the mixed gas of nitrogen and organic solvent will not be discharged from the system frequently, so that the nitrogen content in the system is stable, nitrogen will not be replenished into the system frequently, and the organic solvent will not be discharged.

It pollutes the environment and is conducive to the recovery of organic solvents in good condition. If the process shown in Figure 1 is used, due to the pulse backflushing method used in the dust removal system of the upper cylinder during the drying process, a certain pressure of nitrogen must be used for each backflushing, so that the pressure in the system will increase rapidly and the pressure will be automatically released. The valve will be opened frequently to release pressure, which will take away a large amount of nitrogen and organic solvents, which will not only pollute the environment, consume a large amount of nitrogen, but also have a very low recovery rate of organic solvents. At the same time, in the drying process, since the system only needs a slight positive pressure during operation, the required air volume is small, which can not only reduce the boiling height of the material, but also make it difficult for the material dust to come into contact with the dust removal bag of the upper cylinder, which will reduce the cloth

The bag resistance will also improve the yield of materials, and the frequency of the induced draft fan can also be reduced, saving energy consumption and reducing noise.

8) After the material is dried for 10 minutes, take samples through the sampler to confirm that the product has met the requirements.

9) The weighing result of the product after drying shows that the starch material is 3.45 kg, and the ethanol in the recovery box of the condensation recovery device is 1.4 kg. meet the experimental requirements.