Causes of coking of falling film evaporation equipment and prevention methods

Causes and prevention methods of coking in falling film evaporation

Causes of coking of hair equipment and methods of prevention

Falling film evaporation equipment has been successfully applied in dairy, pharmaceutical, chemical and starch sugar industries which have been produced from corn in recent years. With the continuous expansion of its application fields, coking occurs in the production process. It also happens from time to time. Coke refers to coke feed pipe phenomenon is occurring in the liquid flowing downwards along the wall of the tube falling film evaporation process. When the focus is generally tube material has undergone deterioration, fouling often affect product quality First, the other will also affect the heat transfer coefficient and even reduce equipment, heat-sensitive materials such as milk, eggs, juice and corn steep liquor, etc. are Absolutely not allowed.
The reason for the design is reasonable. Causes are many coking, wherein the design liquid feed rate is too small wetted perimeter is one of the main coke generation rate is outside the wetting liquid material flows down along the wall of the tube falling film in the unit time Quantity . If the amount of liquid is too small, when the flow is downward, there will be a break or dry wall to cause the focus tube . Coking generally occurs at the bottom of the final effect (except for the focus tube caused by thermal imbalance).
If the peripheral wetting rate is less than its critical value, consideration should be given to increasing the peripheral wetting rate. Better wetting of the periphery of the current method is to increase the tube length increases the falling film tube or partition using the process in the form of points.
The design of the material distributor is unreasonable. At present, there are mainly two types of distributors used in falling film evaporators, one is plate type and the other is three stage disc type distributor. The main role of the distributor is to feed liquid feed solution can be uniformly distributed to each tube, falling film, falling film along the feed liquid and the tube wall at the action of gravity feed liquid and its vapor stream to the secondary to a film Flowing down. The uneven distribution of the liquid is mainly due to the incorrect distribution of the pores of the distribution plate, and the distribution holes are too large or too small to cause severe deformation of the distribution plate. The correct distribution of the small holes in the distribution plate should be on the lower distribution plate, and the arrangement of the small holes facing the falling film tube and the falling film tube are the same or similar. The upper and lower distribution plate apertures are staggered. If the small hole in the distribution plate is too large, the liquid can not completely cover the surface of the disk, causing the local small holes to be free of material or material. If the small distribution hole is too small, the local small holes are easy to block, and the individual falling film tube liquid distribution is too small. Or cut off, zui eventually leads to coking.
The other one is the coking caused by severe deformation at the bottom of the distribution disc. The deformation is generally that the bottom of the disc protrudes inward or outward. Both kinds of deformation will make the distribution of local small hole liquid on the distribution disc too little or no material distribution. For the falling film tube , the distribution plate is generally made by spinning and forming, and then the small holes on the disk are small in deformation, and it is easy to be corrected after deformation. It is not easy to use the material to be cut into a circular sheet and then welded into a disk shape, which is easy to deform, and the deformation is not easy to correct. It is necessary to take corresponding anti-deformation measures to complete.
The pump configuration is not reasonable. Main evaporation plant design is reasonable, if the pump configuration can also cause inappropriate coke, which is mainly manifested in the flow rate of the pump and lift small selection caused by materials in the production process generally take several preheating stage before entering the evaporator , greater resistance, each evaporation effect evaporation plant is generally greater than the theoretical value, if the flow amount of the pump head and does not leave a certain margin, in the production process is likely to cause coking. This example is also often occur in practical applications, so the choice of the pump to leave a certain amount of margin so as to feed a wide range of adjustment.
Operational reasons The equipment must be adjusted according to the operating parameters on the equipment instruction manual during use. It should not be too far from the operating parameter range. The heating temperature is too high, the feed amount is too small, the condenser cooling water temperature is too high, a small amount of water and the body shell efficiency level is too high will cause equipment fouling, etc., followed by deterioration of the material easy to coke, such as higher acidity value Milk is easy to coke during production, which must be brought to the attention of the user.
Cleaning. In addition to the appropriate control of equipment parameters, the equipment must be cleaned on time. The example of coking caused by cleaning is not common. This must be taken seriously by the use unit. For example, the concentration of full-fat milk in the dairy industry is easier to hang . Milk is a heat-sensitive material, which is characterized by improper control of parameters such as heating temperature and easy to produce protein denaturation. Therefore, it is necessary to carry out regular cleaning according to the nature of the material. The cleaning time for the concentrated equipment for producing full-fat formula powder is 5 to 7 hours. The long interval between cleanings not only causes the equipment to coke but also reduces the production capacity of the equipment. More common in the sugar industry.
Blanking. Production process in addition to a very special case is absolutely not allowed to artificially control the feed amount is too small, i.e., the feed amount of not less than the discharge amount and the amounts of evaporation or completely blanking-off material must immediately stop the steam supply, and then in accordance with The length of the stop time determines whether or not to clean the device.