Single-effect Falling Film Evaporation Equipment
Falling film concentration equipment, like rising film concentration equipment, is a natural circulation liquid film concentration equipment. In order to make the feed liquid evenly distributed in each pipe and flow down along the inner wall of the pipe, a falling film distributor is installed on the top of the pipe or inside the pipe. 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 fruit juice and dairy products.
Similar to the structure of the rising film vacuum concentration equipment, the falling film evaporator is composed of a heater, an evaporation separation chamber, a partition condenser, a vacuum pump, a condensate pump, a sterilization balance tank, a heat pump and a thermal instrument. The main difference is that the feed liquid is added from the top instead of from the bottom. In order to make the feed liquid evenly distributed in each heating tube and flow down along its inner wall, a falling film distributor is installed on the top of the heating tube or inside the tube. To make the falling film concentrator operate efficiently, the most critical issue is to make the feed liquid evenly distributed in each heating tube without causing bias flow, so a falling film distributor is installed on the top of the tube or inside the tube. There are many types of distributors, which can be divided into three categories according to their working principles: 1. Use the guide tube (plate) to distribute the material and liquid evenly. 2. Use sieve plates or nozzles to distribute the liquid evenly. 3. Utilize a hydrocyclone.
The liquid distributors commonly used in industrial installations are as follows:
(1) Sieve plate type, the sieve plate generally adopts two layers, and some use one layer of sieve plate.
(2) Spray type distributor, the feed liquid is pressurized by the pump and then sprayed into uniform droplets through the nozzle.
(3) A diversion tube with a zigzag edge, surrounded by 3 to 4 radial feet, placed on each heating tube. Another method is to protrude the heating tube to a certain height outside the tube plate, and process the edge into a zigzag shape, and the feed liquid is evenly distributed on the inner wall of the heating tube through the tooth gap.
(4) A diversion tube with 2 to 3 spiral grooves, surrounded by a ring bracket, the surface of the ring bracket covers the nozzle, and the feed liquid is evenly distributed on the inner wall of the tube along the spiral grooves.
(5) The diversion tube is a cylinder with a spiral groove, and the lower part of the diversion tube is a cone, and the bottom of the cone is concave to prevent the liquid flowing down the surface of the cone from gathering in the center.
(6) Combination of sieve plate and deflector.
(7) Cycling type, the feed liquid is pressurized by the pump and enters the swirling flow distributor, and the feed liquid is evenly distributed around the tube by centrifugal force.
The feed liquid to be concentrated enters the heater from the top, and evenly enters the heating tube under the action of the feed liquid distributor. Affected by the rapid flow of the secondary steam and its own gravity, the material naturally flows downward in the form of a film along the inner wall of the tube, and is continuously evaporated and concentrated by heat. The concentrated feed liquid and secondary steam enter the separator for separation, the secondary steam is discharged from the top of the separator, and the concentrated liquid is discharged from the bottom. A key factor to the good operation of using a falling film thickener is to obtain a uniform dispersion of the material on the heated surface. In order to make the feed liquid evenly distributed in each heating tube and flow down along the inner wall of the tube, a falling film distributor is installed on the top of the tube or inside the tube.
The specific operation procedure is as follows:
(1) Turn on the vacuum pump and the condensed water discharge pump, and input cooling water;
(2) Turn on the feed pump to feed the feed liquid from the top of the heater. When the material is sprayed out from the tangent opening of the separator, the heating steam can be turned on, and compressed air is required if necessary;
(3) When the evaporation starts or after normal operation, turn on the heat pump, and start discharging after the concentration reaches the requirement;
(4) Adjust the discharge volume to achieve a balance, and adjust the flow rate of raw steam, cooling water flow and temperature, so that all parameters meet the process requirements.
The characteristics of single-effect falling film concentration equipment are as follows:
(1) It is a single-pass concentration equipment. Although there is material circulation, it can evaporate materials with high viscosity because the gravity of the liquid film is used as the falling film;
(2) The material forms a film on the surface of the heating tube, which has a high heat transfer coefficient, can avoid the formation of foam, and is heated evenly;
(3) Adopt heat pump, heat energy is economical, cooling water consumption is reduced, but the stable pressure of raw steam needs to be higher;
(4) Although there is a distributor at the entrance of the upper end of each heating tube, in order to obtain a film of uniform thickness, due to the change of the liquid level, the formation of the film and the change of thickness will be affected, and even the inner surface of the heating tube will be exposed and coked;
(5) Using the secondary steam as the heat source, because it entrains a small amount of liquid droplets, the outer surface of the heating tube is easy to generate dirt, which affects 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 the concentration of high-concentration or viscous materials;
(7) During the production process, the production