Cours project by discipline «basic technological processes and devices» content

6. Basic device statement
Such devices are used for evaporating crystallization and foaming solutions. Such an evaporating device is divided into two parts: a heating chamber and a separator. A vapor-liquid mixture is formed in the heater tubes and passes to the separator. The secondary steam is separated in the separator, and the liquid returns to the heater pipes through the circulation pipe. The length of the heater pipe is up to 7 meters. With the increase in the length of the pipes, the intensity of the circulation also increases, because the difference between the vapor-liquid mixture formed in the pipes and the density of the liquid inside the circulation pipe increases. The separate location of the heater from the separator makes it convenient to clean and repair the pipes. Forced circulation devices have been used in the chemical and food industry in recent years to increase the circulation intensity and heat transfer coefficient. In vaporizers with a separate heater, the circulation speed of solutions is equal to 1.5 m/s. Such vaporizers are widely used due to their high heat transfer coefficient and ease of use. Some split-heater evaporators do not have a circulation tube. In such an evaporator, the solution to be evaporated is vaporized as soon as it passes through the heater tubes, and the process is similar to that of direct-flow evaporators. .
Crystallizing solutions cannot be evaporated in these rectilinear evaporators. In vaporizers with a separate heater, the heaters are installed vertically, horizontally and horizontally. To increase the intensity of the evaporation process, devices with a separate boiling zone and a circulation pipe are used. In natural circulation evaporation devices, the solution moves at a speed of 0.25 ... 1.5 m/s and the heat exchange surface is filled with solid particles. as a result of planing, its productivity decreases. It is stopped periodically to clean the device. In order to reduce the layer of impurities formed on the heat exchange surface during evaporation of crystallizing solutions, the circulation speed of the solutions is increased and the boiling zone is removed outside the heating chamber. In such vaporizers, the solution to be vaporized moves upward from the bottom of the heater tubes. The height of the heating pipes is 4-7 m, and because of the high hydrostatic pressure in the pipes, the solution does not boil. The solution coming out of the heating pipes passes into the expanded part of the heating chamber located at the bottom of the separator and begins to boil due to low hydrostatic pressure. Thus, the evaporation process takes place outside the surface of the heating chambers. The circulating solution falls into the heated tube outside and is fed back into the tubes of the heating chamber. The evaporated solution is separated from the lower part of the separator. The secondary steam hits the barrier installed in the boiling zone and escapes through the drip tray at the top of the apparatus. The water droplets separated from the secondary steam fall back into the circulation tube. In such devices, the vaporizing solution can be supplied to the bottom of the heating chamber from below or above the circulation pipe. Due to the fact that the solution does not boil in the pipes, layers of contamination are less formed inside them. Since the temperature difference between steam and solution is greater (up to 30°C) and the pressure loss in the boiling zone is small, the circulation speed of solutions in such devices is 1.8 m/s. As a result of the increase in the circulation speed, the efficiency of the device and the intensity of heat exchange become effective. Such vaporizers are used for vaporization of medium viscosity and crystallizing solutions.