Overview of Evaporation in Ethylene Production in Evaporation Equipment

Evaporation equipment

Evaporation in the production of traditional Chinese medicine refers to the process in which some of the solvent in the liquid medicine is separated from the non-volatile components in the boiling state, and the liquid is concentrated. Therefore, evaporation is often referred to as concentration. If the active ingredient in the extract is mostly a volatile component, the volatile component should be separated at the time of extraction. Evaporation and concentration of Chinese herbal extracts is an important unit operation in the production of traditional Chinese medicine. The equipment used for evaporation is called an evaporator.

When choosing Chinese medicine concentrating equipment, it should be noted that many of the active ingredients of traditional Chinese medicine are heat sensitive substances, which are easy to coke and foam, and have the characteristics of high concentration, small batch size and variety. Try to use low boiling point, short heating time, good heat transfer and easy cleaning. Process and equipment.

First, the principle of evaporation

Evaporation is to provide heat to the extract by direct fire heating, electric heating, solar heating, and indirect steam heating to evaporate the solvent. At present, traditional Chinese medicine pharmaceutical production often uses water vapor as a heat source, and most of the evaporated liquid is a Chinese medicine aqueous extract, as long as the water vapor evaporated from the liquid is called secondary steam. The heated steam passes through the heat conduction of the metal partition wall, and releases the condensed latent heat to heat the liquid medicine on the other side of the partition wall to boil and vaporize itself to be condensed.

• Evaporation process

In the traditional Chinese medicine pharmaceutical industry, the evaporation operation consumes more energy, and the secondary steam can be reused to achieve energy conservation and cost reduction. In the past 10 years, the multi-effect evaporation of secondary steam has been widely used in the production of traditional Chinese medicine.

(1) Single effect evaporation

In the evaporation operation, the secondary steam generated by the chemical liquid is no longer used, which is called single-effect evaporation. The various types of evaporators used are called single-effect evaporators, and the liquid medicine is heated and vaporized by the metal partition wall, and the vapor-liquid separation is performed. After the second steam is directly discharged, it is discharged to the atmosphere.

• Multi-effect evaporation

According to the calorie balance, the latent heat value of the heated steam consumed in the evaporation operation is similar to that of the distilled secondary steam. It is obvious that the secondary steam also contains more heat, which is uneconomical if not used, in order to improve heating. The economic degree of steam, that is, the number of kilograms of water that can be evaporated per kilogram of heated steam, can be multi-effect evaporation operation. The evaporator that passes the heated steam is called a one-effect evaporator, and the secondary steam generated by the one-effect evaporator is used as an evaporator for heating steam, which is called a two-effect evaporator, and the secondary steam generated by the second effect is used as the heating steam. The evaporator is called a three-effect evaporator, and the rest is analogous. According to the difference of the relative flow direction of steam and chemical liquid, multi-effect evaporation has the following methods: downstream, countercurrent and advection.

1, downstream method

The three-effect evaporation process, because the flow direction of the chemical liquid and the steam is the same, sequentially from one effect to three effects, is called the downstream method. The operating pressure and temperature of each effect are lower than the previous effect, so the liquid medicine can use the pressure difference to carry out the automatic transportation between the various effects, and when the liquid medicine enters the first effect, a part of the secondary steam can be evaporated. The disadvantage is that the latter effect temperature is lower than the previous one effect, and the viscosity of the liquid medicine is higher than the previous one, so the heat transfer coefficient is lower than the previous one, thereby reducing the total heat transfer coefficient of the evaporator and affecting the heat transfer rate of the evaporator.

2. Countercurrent method

The flow of steam is opposite to the flow of the liquid, and the liquid enters from the third effect, and the pump is used to enter the previous effect. The solution needs to be pumped, and the feed liquid is sent from the aftereffect to the pre-effect, and it needs to be heated to the boiling point by consuming a certain amount of heat. The advantage is that the chemical solution increases from the aftereffect into the pre-effect concentration, and the temperature also increases, so the viscosity of the liquid solution has little difference between the effects, and the total heat transfer coefficient can be improved. The disadvantage is that the liquid is transferred by the pump between the various effects and consumes a certain amount of energy. This method is suitable for the concentrated Chinese medicine liquid whose viscosity is increased with the increase of the concentration, but it is not suitable for the concentration of the liquid containing more heat sensitive ingredients.

3. Advection method

Each effect is separately added to the liquid medicine and the concentrated liquid is discharged, and the advection method is suitable for evaporation of the crystal material which is easily precipitated during concentration.

The multi-effect evaporation has a temperature difference loss, and the effective temperature difference is lower than the effective temperature difference of the single effect. According to experience, the kilograms of water that can be distilled per kilogram of heated steam: single effect is 0.91; double effect is 1.76; three effects are 2.50; four effects are 3.33; five effects are 3.71. Therefore, the effectiveness of multi-effect evaporation should be comprehensively analyzed from the increase in steam economy and the increase in equipment investment costs. Generally 2-4 effect is suitable.

Three-effect energy-saving evaporation concentration process of traditional Chinese medicine extract. The three-effect external heating vacuum concentrator has good performance and the evaporation rate is 1.85 times higher than that of the single effect. Energy consumption is reduced by 75%. The first-effect evaporation temperature is 87 ° C, the second-effect evaporation temperature is 70 ° C, the three-effect evaporation temperature is 57 ° C, the evaporation temperature is 13-43 ° C lower than the conventional method, and the evaporation heating time is shortened to 1/3. The equipment investment fee can be recovered from the energy saving fee in one year.