Vacuum concentration: under the guidance of secondary steam and the suction of high vacuum of separator, the concentrated materials and secondary steam enter the separator along the tangent direction at a faster speed. Vacuum technology preserved the nutrition and aroma of raw materials.
Vacuum concentration, also known as decompression concentration, is the evaporation of water or other solvents by using the principle of boiling point reduction of water under low vacuum. It is widely used in industrial production and health food production.
Vacuum concentration has many advantages. In the boiling state, the solvent evaporates rapidly, and its boiling point changes with the pressure. The pressure increases, the boiling point increases, the pressure is small, and the boiling point decreases. For example, the boiling point of milk is 100 ℃ at 101kpa, while at 82.7-90.6kpa, the boiling point is only 45-55 ℃. Because of evaporation at lower temperature, a lot of energy can be saved. At the same time, because the material is not affected by high temperature, the destruction and loss of thermal unstable components are avoided, and the nutritional components and aroma of raw materials are better preserved.
The water ring vacuum pump produced by our company is widely used in vacuum concentration, especially in the sugar industry. The specific application of the sugar industry is analyzed as follows:
For every 1000 kg of sugar beet processed by sugar factories, about 125 kg of sugar juice can be obtained, and the sugar content is generally more than 10%. The syrup is then heated in an evaporation tank and condensed into a syrup containing 35% water. Because there is still a lot of water content, sugar can not be crystallized. At this time, syrup should be placed in a vacuum tank, and then concentrated into a cream containing 7-8% water, so sugar gradually crystallizes from the cream of saturated solution.
Because the concentration of syrup is very high, the boiling point is increased by 20 ℃, so the boiling point of syrup is 100 + 20 = 120 ℃. Boiling sugar (the process of concentration is boiling sugar) at such a high temperature will cause the coking of sugar and increase the loss. If sugar is boiled in a certain vacuum, boiling point will be greatly reduced. Therefore, syrup concentrate into enamel, to be carried out in a certain vacuum.
At first, the syrup was far from saturated due to the large amount of water, so the water should be evaporated under the maximum vacuum, the required vacuum is – 620 ~ – 640 mm Hg, and its boiling point is 68-70 ℃. If the concentration of the solution increases, the boiling point will increase. With the continuous concentration of syrup, the temperature of syrup will gradually rise to 74-77 ℃ under the same vacuum. The second stage of vacuum sugar boiling can be carried out under low vacuum, which requires a vacuum of – 420 ~ – 460 mm Hg and a boiling point of 93-94 ℃.