Application of evaporation and concentration equipment in fo
Update time 2021-03-08 00:44 Read
The purpose of hair concentration is to obtain a favorable vapor-liquid equilibrium condition by using the difference of volatility between solvent and solute. That is to say, when the volatility of solute in solution is small and the solvent has obvious volatility, heating method is commonly used in industry to vaporize the solvent to achieve the purpose of solute concentration, which is evaporation operation.
Most concentrated materials in food industry are aqueous solution. Evaporation refers to the evaporation of aqueous solution. According to the viewpoint of molecular kinematics, when the solution is heated, the solvent molecules obtain kinetic energy. When the energy of some solvent molecules is enough to overcome the attraction between molecules, the solvent molecules will escape from the liquid surface and enter the upper space, becoming steam molecules, which is called vaporization.
If we do not try to remove these vapor molecules, the chemical potential of water between the vapor phase and the liquid phase will gradually balance, and the vaporization process will gradually weaken and even stop.
Necessary conditions for evaporation: continuous supply of heat energy (saturated steam) and continuous elimination of generated steam.
The purpose of food concentration: 1. Remove a lot of moisture in food, reduce the cost of packaging, storage and transportation.
2. Increase the concentration of the product and the preservation of the product.
3. Concentration is often used as a pretreatment process for drying or more complete dehydration.
4. Concentration is used as a pretreatment process for some crystallization.
The characteristics of food material evaporation and concentration are as follows
1. Thermal sensitivity: heating temperature and heating time
2. Corrosivity: acid food
3. Viscosity: protein, sugar, pectin
4. Scaling: protein, sugar and pectin are overheated
5. foaming: formation of materials when boiling
6. Volatile components: aromatic components and flavor components
The effects of evaporation on food: 1. Flavor, loss of flavor substances and deterioration of flavor
The solutions include: A. mixing the concentrate with some fresh materials to improve the flavor; B. recycling the flavor substances
2. Color: Deepening
3. Loss of nutrients
Main equipment of evaporation and concentration: evaporator
The evaporator is mainly composed of heating chamber (heater) and separation chamber (separator). The function of the heating chamber is to use steam as the heat source to heat the concentrated liquid. The function of the evaporator separation chamber is to separate the entrained mist from the secondary steam.
Typical evaporators commonly used in food industry
1. Standard evaporator
2. Hanging basket evaporator
3. Evaporator with heating chamber outside
4. Long tube evaporator
5. Scraper film evaporator
6. Plate evaporator
1. Condenser: a large amount of secondary steam produced by the evaporator must be eliminated by leading it into the condenser for condensation. Generally, hybrid condenser is used
2. Steam trap: in order to use the steam of evaporator economically and keep good heat transfer. Like other steam heating equipment, it is necessary to install the equipment to remove the condensate, that is, the steam trap.
3. Vacuum pump: because the condenser can condense the gas is mainly water vapor. The vacuum of the system can not be maintained for a long time if the non condensable gases such as air are not removed. The purpose of using vacuum pump is to extract these non condensable gases.
4. Non condensable gas removal device: to maintain the heat transfer efficiency of the heating chamber. The method is that an air extraction pipe orifice is arranged on the side wall of the heater and connected with a pipe and an exhaust valve.
5. Foam Catcher: during the evaporation operation, try to avoid or reduce the entrainment of mist by secondary steam. In the process of concentration, entrainment has an effect on the yield and evaporation capacity. If it is multi effect evaporation, the next effect heating surface may form dirt or corrosion. Especially in the concentration of fruit and vegetable juice such as tomato juice, strong corrosive acid mist will bring serious consequences.