Original title: See enough at a time: 22 kinds of evaporation, crystallization equipment structure and working principle diagram! Source: Chemical 707 Forum 1 Central-circulation tubular evaporator The heating chamber of the central circulation tube evaporator is composed of a vertical heating tube bundle (boiling tube bundle). In the center of the tube bundle, there is a tube with a larger diameter, called the central circulation tube, whose cross-sectional area is generally 40-100% of the total cross-sectional area of the heating tube bundle. When the heating medium is introduced between the tubes for heating, since the heated area of the liquid per unit volume in the heating tube is larger than that in the central circulating tube, the relative density of the liquid in the heating tube is small, resulting in a density difference between the liquid in the heating pipe and that in the central circulating tube, which causes the solution to flow in a natural circulation of descending from the central circulation tube and then ascending from the heating pipe. The circulation speed of the solution depends on the density difference produced by the solution and the length of the tube. The greater the density difference, the longer the tube, and the greater the circulation speed of the solution. However, this type of evaporator is limited by the total height, so the length of the heating tube is short, generally 1 ~ 2 m, the diameter is 25 ~ 75 mm, and the length-diameter ratio is 20 ~ 40. Performance characteristics: The central circulation tube evaporator has the advantages of compact structure, convenient manufacture and reliable operation, so it is widely used in industry and is known as the so-called “standard evaporator”. But in fact, due to the limitation of structure, its circulation speed is relatively low (generally below 0.5m/s); and because the solution circulates continuously in the heating tube, its concentration is always close to the concentration of the finished solution, so the boiling point of the solution is high and the effective temperature difference is reduced. In addition, the cleaning and maintenance of the equipment is not convenient enough. 2 Externally heated evaporator The structural feature of the externally heated evaporator is that the heating chamber is separated from the separation chamber, which not only facilitates cleaning and replacement, but also reduces the total height of the evaporator. Because the heating pipe is long (the ratio of the pipe length to the pipe diameter is 50-100), and the solution in the circulating pipe is not heated, the circulating speed of the solution is high, which can reach 1.5m/s. 3 Rising film evaporator The heating chamber of the rising film evaporator is composed of one or several vertical long tubes. The diameter of the heating tube is usually 25 ~ 50mm, and the ratio of the tube length to the tube diameter is 100 ~ 150. After being preheated, the raw material liquid enters from the bottom of the evaporator, and the heated steam is condensed outside the tube. When the solution is heated and boiled, it vaporizes rapidly, and the generated secondary steam rises at a high speed in the tube, driving the liquid to flow upward along the inner wall of the tube in a film shape, and the rising liquid film continues to evaporate due to heating. Therefore, the solution is gradually concentrated in the process of rising from the bottom to the top of the evaporator, and the concentrated solution enters the separation chamber and is discharged from the bottom of the separator after being separated from the secondary steam. The secondary steam velocity at the outlet of the heating tube under normal pressure shall not be less than 10 m/s, generally 20 ~ 50 m/s, and sometimes 100 ~ 160 m/s or higher during decompression operation. Expand the full text Performance characteristics: The climbing film evaporator is suitable for the solution with large evaporation capacity (i.e. dilute solution), heat sensitivity and easy foaming, but not suitable for the solution with high viscosity, crystal precipitation or easy scaling. 4 Horizontal evaporator It is basically similar to the structure of the horizontal shell and tube condenser. According to the way of liquid supply,wiped film distillation, it can be divided into shell and tube evaporator and dry evaporator. Horizontal shell and tube evaporators are widely used in closed saline circulation systems. Performance characteristics: Compact structure, good contact between liquid and heat transfer surface, high heat transfer coefficient. However, it needs to be filled with a large amount of refrigerant, and the liquid column will have a certain impact on the evaporation temperature. And when the concentration of the saline is reduced or the brine pump is shut down for some reason, the saline may be frozen in the pipe. If the refrigerant is Freon, it is difficult for the lubricating oil dissolved in the Freon to return to the compressor. In addition, it is necessary to stop working during cleaning. 5 Vertical tube type cold water tank evaporator 6 Spiral tube evaporator The common point of vertical tube and spiral tube evaporators is that the refrigerant evaporates in the tubes, and the whole evaporator tube group is immersed in the box (or pool, tank) filled with secondary refrigerant. In order to ensure that the secondary refrigerant circulates in the box at a certain speed, a longitudinal partition is welded in the box and a spiral stirrer is installed. The coolant flow rate is generally 0.3 ~ 0.7 m/s to enhance heat transfer. Performance characteristics: Vertical tube and spiral tube evaporators can only be used in open cycle systems, so the secondary refrigerant must be non-volatile substances, such as saline and water. If saline is used, the evaporator tubes are easily oxidized, and the saline is easy to absorb moisture and reduce the concentration. These two evaporators can directly observe the flow of secondary refrigerant and are widely used in saline refrigeration system with ammonia as refrigerant. 7 Cooling tube bank A cooling calandria is an evaporator used to cool the air. It is widely used in low temperature cold storage. The refrigerant flows and evaporates in the cooling tube,wiped film evaporator, and the cooled air outside the tube as the heat transfer medium makes natural convection. Performance characteristics: The biggest advantage of the cooling calandria is that it is simple in structure, easy to make, and causes less dry loss to the non-packaged food stored in the warehouse. However, the heat transfer coefficient of the calandria is low, and the defrosting operation is difficult, which is not conducive to the realization of automation. For the ammonia direct cooling system, the seamless steel tube is welded, and the smooth tube or wound finned tube is used; for the Freon system, the wound or set finned copper tube is mostly used. 8 Coil type calandria Coil type jacking pipe gravity liquid supply or ammonia pump liquid supply can be used; single-row and double-row coil type wall calandria can be used for an ammonia pump liquid supply system and a gravity liquid supply system of a bottom-in and top-out type, and a single coil type calandria can also be used for an ammonia pump top in and bottom out liquid supply system and a thermal expansion valve liquid supply system. Performance characteristics: The coiled calandria has the advantages of simple structure, easy manufacture, small liquid storage and strong applicability. Its main disadvantage is that the steam produced in the lower section of the calandria can not be drawn out in time and can only be discharged after passing through the full length of the calandria, so the heat transfer coefficient is small and the vapor-liquid two-phase flow resistance is large. 9 Air cooler (air cooler) Air cooler is a complete set of equipment composed of axial flow fan and cooling calandria. It relies on the fan to force the air in the warehouse to flow through the cooling pipes in the box for heat exchange, so as to cool the air and achieve the purpose of reducing the temperature of the warehouse. The air cooler can be divided into dry type, wet type and dry-wet mixed type according to the way of cooling air. Among them, the refrigerant or secondary refrigerant flows in the calandria and passes through the tube wall to cool the air outside the tube, which is called dry air cooler; the sprayed secondary refrigerant liquid directly exchanges heat with the air, which is called wet air cooler; the mixed air cooler has a secondary refrigerant spraying device in addition to cooling the calandria. Dry air coolers commonly used in cold storage can be divided into ceiling type and floor type according to their installation positions. They are all composed of air cooling pipes, ventilators and defrosting devices, and the cooling pipes in the air cooler are all sheet-type. Large dry air coolers are often floor-mounted. 10 External circulation type evaporation equipment The evaporator is characterized in that the heating pipe is lengthened and the heating chamber is arranged outside the evaporator, so that the total length of the evaporator can be reduced, and meanwhile, the circulating pipe is not heated by steam, so that the natural circulation speed of the solution is higher. 11 Basket evaporator It is an improvement of the central circulation tube evaporator. The heating chamber is like a hanging basket, which is hung at the lower part of the evaporator shell and can be taken out from the top for easy cleaning and replacement. The heat medium enters that heat chamber through the central steam pipe, and there is an annular channel between the outer wall of the heating cham and the inner wall of the evaporator shell, which acts like a central circulating pipe. During operation, the solution descends along the annulus and ascends along the heating tube, forming a natural circulation. Generally, wiped film evaporator ,thin film distillation, the cross-sectional area of the annular gap is about 100-150% of the total area of the heating tube, so the solution circulation rate is relatively high (about 1-1.5m/s). Since the boiling liquid is in contact with the evaporator shell at a lower temperature, there is less heat loss. Performance characteristics: The basket-type evaporator is suitable for evaporating the solution which is easy to scale or has crystal precipitation. Its disadvantage is that the structure is complex and the amount of equipment materials required for unit heat gathering in the center. The liquid descends along the inner wall of the heating tube in a film shape through the tooth gap. Performance characteristics: ssing capming d(Disclaimer: This article only represents the views of the author,cbd centrifugal extractor, and does not represent the position of this public account. If there are intellectual property disputes, contributions and cooperation matters, please contact) Return to Sohu to see more Responsible Editor:. toptiontech.com
See enough at a time
