Frozen Monkfish,Frozen Monkfish Fillet,Frozen Monkfish Tail,Frozen Monkfish Skinless Zhejiang Zhoushan Jiaze Aquatic Co., Ltd. , https://www.tianjia-aquatics.com
Evaporation equipment is generally referred to as an evaporator, and its construction and variety are numerous, and its development history is long. From the operation mode, it can be divided into single-effect evaporation, multi-effect evaporation and direct contact evaporation; according to the fluid circulation mode, it can be divided into non-circulating evaporation, natural circulation evaporation, forced circulation evaporation, wiped film evaporation and centrifugal thin film evaporation. Different evaporators are used for different materials during design. The correct application can not only improve the quality of products, but also save energy, reduce production costs and improve economic efficiency. Among them, falling film evaporator is a common unit operation in modern evaporation technology. This paper will discuss the characteristics and related points of multi-effect falling film evaporator.
1 Falling Film Evaporator Overview 1.1 Falling Film Evaporator Introduction Working principle: The material is added from the top of the heating chamber and distributed downward through the liquid distributor. The tube is heated and vaporized, and the vaporized vapor is taken out from the lower end of the heating tube together with the liquid, and the concentrated liquid is obtained by gas-liquid separation.
In the operation of the falling film evaporator, since the residence time of the material is very short (about 5 to 10 s) and the heat transfer coefficient is high, it is widely used in heat sensitive materials, and can also be used for evaporation viscosity. Material, but not suitable for handling solutions that are easy to crystallize.
1.2 Comparison of the performance of falling film evaporator and rising film evaporator compared with falling film evaporator is shown in Table 1. 
2.1 The evaporator evaporator is a tubular heat exchanger, the tube passes through the liquid material, the shell passes through the heated steam, the liquid material enters from the top of the evaporator, passes through the distributor into the heating tube, and the liquid material flows down the heating tube, and It is heated and evaporated until the bottom of the heater. The concentrated liquid and the secondary steam generated by evaporation enter the separator for separation. The bottom of the heater is equipped with a liquid level switch for controlling the water distribution.
Function: heating and evaporating liquid materials.
2.2 Separator separator is a single-layer tank, the upper secondary steam interface is connected to the condenser, and the lower interface is connected to the evaporator.
Function: separating the secondary steam generated after heating from the concentrated liquid vapor.
2.3 Preheater The preheater is a horizontal tube-and-tube heat exchanger. The tube passes through the liquid material, and the shell passes through the secondary steam generated by evaporation.
Function: (1) preheating the liquid material entering the evaporator; (2) cooling the secondary steam to facilitate recycling.
2.4 The condenser condenser is a horizontal tube-and-tube heat exchanger, the tube is connected to the cooling water, and the shell side is connected to the shell side of the preheater.
Function: The secondary steam is condensed to facilitate recycling.
2.5 Condensate tank The condensate tank is a single-layer tank with a liquid level switch for controlling the liquid level.
Function: The condensate in the automatic discharge tank can be realized by connecting with the pump at the outlet.
Working principle and characteristics of 3 multi-effect falling film evaporator 3.1 Working principle of multi-effect falling film evaporator
Taking the three effects as an example, the flow of the multi-effect falling film evaporator is shown in Fig. 2.
Working principle: the dilute solution of the material enters the suction port of the third effect circulating pump through the raw material pump, is boosted by the pump, enters the feeding chamber at the top of the third effect evaporator through the preheater, and then enters the heating tube to evaporate and then enters the separation. The chamber, steam and liquid are separated here, and the solution flows into the pump suction port from the bottom, and is pumped to the preheater, the feed chamber, the heating tube, and the separation chamber for circulating flow and evaporation. The evaporated vapor enters the separator from the side of the separation chamber to further separate the droplets entrained by the vapor, and flows back to the separation chamber from the bottom of the separator, and the clean secondary vapor is discharged to the condenser and is completely condensed. The outlet of the circulation pump has a path to send the solution to the suction port of the second effect pump, and works in the same manner as the third effect, and the second effect secondary steam is sent to the third effect as the heating steam. Similarly, the second effect pump outlet has a path to feed the solution into the *effect pump suction port. The *effect operation is basically the same as the other two effects, and the secondary steam of the * effect is sent to the second effect as the heating steam. The *heated steam is supplied directly from the boiler and the condensate returns to the boiler room. In addition, the pump outlet has a road discharge concentrate that regulates the discharge to maintain the concentration of the discharge.
In the countercurrent operation, the concentrated solution outlet is in effect, and the temperature is higher than other effects, which can reduce the viscosity of the solution, which is beneficial to the concentration of the higher concentration solution, and can obtain 75% of the concentrated liquid.
Each effect evaporator is equipped with a liquid level controller, and the control valve of the inlet pipeline is used to keep the liquid level of each effect constant. The boiler steam supply line is equipped with a control valve, which controls the valve to achieve a constant heating steam pressure according to the *effect heating steam pressure sensor and the pressure controller. The condensed water discharged from each effect is collected into the condensate tank, and the liquid level controller is installed on the side of the tank, and the liquid level of the evaporator is controlled by the outlet pipe of the drain pump to a predetermined height.
3.2 Features of multi-effect falling film evaporator (1) Compact structure, reasonable layout, small floor space and convenient installation and operation;
(2) High production efficiency and large evaporation;
(3) The energy-saving effect is remarkable, and the energy consumption is only about 1/3 of that of the general falling film evaporator. QA/Q≤0.45, QB/Q≤8 (Q is the evaporation of clear water, QA is the steam consumption, QB is the cooling water consumption);
(4) The system can be controlled, the system adopts PLC programming, the process parameters of the equipment can be set and controlled, and the raw material liquid and cooling water can be automatically controlled. System control accuracy: temperature ± 1 ° C, pressure ± 0.01 MPa, liquid level height ± 10 mm.
4 Discussion on the related points of multi-effect falling film evaporator 4.1 The use of heated steam Evaporation is a process that consumes a large amount of heated steam to generate a large amount of secondary steam. From the point of view of energy saving, the multi-effect falling film evaporator fully utilizes the secondary steam generated by evaporation as the heat source of other effective heating systems, that is, the evaporation device can provide the secondary steam with higher temperature, which can reduce the steam generated by the boiler. The consumption can reduce the amount of secondary steam entering the condenser and improve the utilization of steam. Generally, the saturated steam used does not exceed 180 ° C. If it exceeds 180 ° C, the relative pressure is high, which increases the heat equipment and operating costs. The evaporation of a multi-effect falling film evaporator is designed to save heating steam.
If the first effect uses a higher pressure heating steam, the final effect can be atmospheric pressure evaporation or low vacuum evaporation. At this time, the secondary steam generated by the end effect has a higher temperature, and most of its heat energy is utilized.
4.2 Effect of the evaporator In the multi-effect evaporation, the former effect steam is used as the latter effect heating steam, so multi-effect evaporation can save the consumption of raw steam. But the more the better, the better, and its effectiveness is limited by technology and economy.
(1) The multi-effect evaporation increases with the effect, and when the total evaporation is the same, the amount of steam required is reduced, and the operating cost is reduced. However, the more the effect, the higher the equipment cost, and as the effectiveness increases, the amount of steam saved is less and less.
(2) In theory, the effect is too much, and the evaporation operation will be difficult to carry out. In general, the multi-effect evaporation of the *effect heating steam temperature and the operating temperature of the condenser are limited, and the multi-effect evaporation theoretical heat transfer total temperature difference (ie, the difference between the above two temperatures) is also limited. Under specific operating conditions, as the efficiency increases, the sum of the losses of the various effect temperature differences increases, and the effective total temperature difference decreases. When the effect is too much, the effective total temperature difference is small, and the effective total temperature difference assigned to each effect will be small enough to ensure normal boiling of each effect, and the evaporation operation is difficult to perform.
What is the effective number? It depends on the characteristics of the material being evaporated. Experience has taught people that the general electrolyte solution has a higher boiling point and can take 2 to 3 effects. Generally, the non-electrolyte solution has a slower boiling point and can take 4 to 6 effects.
4.3 Process of multi-effect falling film evaporator In the multi-effect falling film evaporator, the flow of the solution may be cocurrent, countercurrent, advection and cross flow. The comparison between them is shown in Table 2. The selection is mainly based on Material characteristics, mode of operation and economics are determined.
The three-effect falling film evaporator discussed in this paper is a countercurrent, and its solution is countercurrent to the vapor. In this example, the feed liquid is added by the final effect and is pumped into the previous effect. When the solution enters the previous effect from the latter effect, the temperature will be lower than the boiling point of the effect. In this process, the greater the concentration of the solution, the higher the evaporation temperature. Therefore, the viscosity of each effect solution does not differ too much, and thus the heat transfer coefficient is uniform.
5 Conclusions This paper starts with the overview of falling film evaporator, expounds the structure of multi-effect falling film evaporator, and discusses the working principle, process and related points of multi-effect falling film evaporator. The following conclusions can be drawn:
(1) Whether it is the falling film method or the rising film method, it should be selected according to the characteristics of the evaporated solution;
(2) From the perspective of energy saving, the falling film evaporator should be multi-effect. But the more the better, the better, should be considered from a technical and economic perspective.
(3) The confirmation of the multi-effect falling film evaporator process should also be based on the characteristics of the evaporated solution.
Working principle and application points of multi-effect falling film evaporator
Evaporation (or concentration) refers to a process in which a solution containing a non-volatile solute and a volatile solvent is concentrated by evaporation, and is mainly obtained by vaporizing a part of a solvent in a solution by heating. Evaporation process is widely used in pharmaceutical production. For example, in the production of traditional Chinese medicine, the extract is concentrated by evaporation to obtain a concentrate or a stream extract, and as in the production of antibiotics, it is used for fermentation filtrate, resin eluent and various Concentration of the extract.
Table 1 Comparison of performance of falling film evaporator and rising film evaporator
2 Multi-effect falling film evaporator The multi-effect falling film evaporator consists of evaporator, separator, preheater, condenser, condensate tank, circulation pump and other components. Its structure is shown in Figure 1. Table 2 Comparison of cocurrent, countercurrent, advection and crossflow
Parallel flow
countercurrent
advection
Cross flow
The solution is cocurrent with the vapor
The solution is countercurrent to the vapor
Add raw material solution for each effect
The solution and the vapor are in some effect, and in some cases, they are countercurrent.
No pump is required and the cost is low. However, it is not suitable for a solution whose viscosity increases rapidly with concentration.
Applicable to solutions with large viscosity changes with concentration, but heat sensitive solutions should have corresponding measures
Suitable for use in evaporation processes with crystallization
Operation is complicated, practically rarely applied