Single-effect falling film type concentrating equipment
(1) Structure of single-effect falling film type concentrating equipment
Falling film concentrating equipment, like the rising film concentrating equipment, is a natural mode liquid mode concentrating equipment. In order to distribute the liquid evenly in each pipe, it flows down the inner wall of the pipe, and a falling film distributor is installed on the top or the pipe of the pipe, and the structure is in the form of a sawtooth type, a baffle type, a hydrocyclone type and the like. Like the rising film evaporator, it has the characteristics of high heat transfer efficiency and short heating time, and is suitable for the production of juice and dairy products. However, it is difficult to uniformly distribute the liquid in the tube.
Its structure is roughly the same as that of the rising film evaporator, except that the feed liquid is added from the top of the evaporator, and a liquid distributor is arranged at the top to evenly distribute the liquid in each heating tube. The secondary steam and the concentrated liquid generally flow in parallel, and the liquid liquid is formed into a film by the action of the secondary steam when flowing down the inner wall of the pipe. Since the temperature difference between the heated steam and the feed liquid is large, the heat transfer effect is good. The vapor-liquid enters the evaporation chamber and is separated, the secondary steam is discharged from the top, and the concentrated liquid is taken out from the bottom.
In order to make the falling film evaporator high efficiency and low operation, the key problem of Zui is to make the liquid evenly distributed in the heating pipes without causing drift. The working principle of the material liquid distributor can be divided into three categories: one is to use the diversion tube (plate) to evenly distribute the liquid; the other is to use the sieve plate or the nozzle to evenly distribute the liquid.
The liquid distributor generally used in industrial devices has (1) a sieve plate type, a sieve plate generally adopts two layers, and (2) a spray type distributor, and the material liquid is pressurized by a pump and then sprayed into a uniform droplet through a nozzle; (3) is a draft tube with a serrated edge, surrounded by 3 to 4 radial legs, placed on each heating nozzle; (4) is a diversion with 2 to 3 spiral grooves The tube is surrounded by a ring bracket, the annular bracket surface covers the nozzle, and the liquid is uniformly distributed on the inner wall of the tube along the spiral groove; (5) is a typical draft tube, and the edge of the enlarged section of the lower part of the draft tube The diameter of the mouth is equal to the inner diameter of the heating pipe, and is processed into a zigzag shape along the mouth, and the liquid is uniformly distributed in the pipe wall through the tooth gap; (6) is a combination of the mesh plate and the deflector; (7) is a liquid The feed liquid is pressurized by the pump and then enters the swirling type distributor, and the liquid is uniformly distributed around the tube by centrifugal force.
The falling film evaporator is generally of a single flow type, that is, the liquid reaches the required concentration at the same time by the evaporation of the heating pipe, so the pipe must have sufficient length to ensure the heat transfer effect, and the aspect ratio is generally 100~250. If you use a pump, you can also become a circulating evaporator. In the food industry, falling film evaporators mostly constitute double-effect, multi-effect and heat pump type evaporation equipment.
(2) Typical equipment production process
Figure 6-12 shows the flow chart of a single-effect falling film vacuum concentrating device introduced by WIEGAND in Germany.
The utility model is composed of a heating chamber, a separation chamber, a heat pump (steam ejector), a material pump, a condensate pump, a water ring vacuum pump, a screw pump and a storage cylinder. Suitable for cow's milk concentration. During operation, the fresh milk enters the separator 10 from the storage tank 9 through the flow meter, and indirectly heats and vaporizes part of the moisture by the secondary steam; then, the material pump 4 sends it to the top of the heater* part of the tube, and the emulsion is evenly flowed through the distributor. The tube is heated to flow downward in a film form and simultaneously evaporated by heat; the emulsion evaporated by the * part of the tube is sent to the second part of the tube by the material pump 5 for further heating and evaporation, and is sent by the screw pump 6 after reaching the concentration requirement. After the secondary steam enters the separation chamber, a part of it is pressurized by the hot press pump and sent to the heating chamber as a heat source. The condenser is installed in the evaporator casing jacket, part of the secondary steam is condensed in the condenser, and is combined with the condensed water sucked from the heater, and discharged by the condensate pump 7.
The main technical parameters of this concentrating equipment:
Water evaporation: 800kg/h
Feeding amount: 1210kg/h (the total solid content of the feed is 25.65%)
Productivity: 410kg / h (outlet total milk solids content 74%)
Steam consumption: 465kg / h (steam gauge pressure 800kpa)
Water consumption: water pressure 0.3Mpa (gauge pressure) 22 ° C, 15m3 / h
Total motor power: about 10.4kW
The device is characterized by low energy consumption, stable operation and convenient cleaning.
(3) Characteristics of single-effect falling film type concentrating equipment
(1) It is a single-programming concentrating device. Although it has a material circulation, it can evaporate a material with a high viscosity due to the use of liquid film gravity as a falling film. The heating time of the material is only about 2 minutes, so it is suitable for the concentration of heat sensitive materials;
(2) The material forms a film on the surface of the heating pipe, the heat transfer coefficient is high, and the formation of foam can be avoided, and the heat is evenly distributed;
(3) The heat pump is adopted, the heat energy is economical, the cooling water consumption is reduced, but the stable pressure of the raw steam needs to be higher;
(4) At the inlet of the upper end of each heating pipe, although a distributor is installed in order to obtain a film of uniform thickness, the change of the liquid level affects the formation and thickness of the film, and even the surface of the heating pipe is exposed and coking;
(5) Using secondary steam as a heat source, due to the entrainment of a small amount of liquid droplets, the outer surface of the heating tube is prone to generate dirt and affect heat transfer;
(6) The length of the heating tube is long, and it is extremely difficult to clean after coking, which is not suitable for concentration of high concentration or viscous materials;
(7) During the production process, production cannot be interrupted at will, otherwise it is easy to scale or coke.
(d) operation
The operation method is similar to that of the single-effect film-lifting device. The specific operation procedure is as follows:
- Turn on the vacuum pump and condensate drain pump, and input cooling water;
- The feed pump is turned on, so that the liquid is added from the top of the heater, and when the cleavage of the party separator is discharged, the heating steam can be turned on, and if necessary, the gas is compressed;
- When the evaporation starts or after normal operation, the hot press pump is turned on, and after the concentration reaches the requirement, the discharge can be started;
- Adjust the discharge amount, so as to achieve the balance, and adjust the flow rate of raw steam, the flow rate and temperature of the cooling water, so that the parameters meet the process requirements.
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