External circulation evaporator is also called external heat evaporator, its heater is directly placed on the outside of the evaporator, and the long diameter of the heating tube is relatively large, so the material liquid circulation flow rate is high.
The external circulation evaporator is mainly applicable to the evaporation of the material liquid with large concentration, large viscosity and easy to be scaled and coked. This kind of evaporator in chemical industry, medicine, food and other industries have application. Due to the material liquid in the tube liquid column is higher, improve the lower part of the liquid
The boiling point of the body, so the heating error is required to be larger, limiting the use of multi-effect. This evaporator raw steam (primary steam) heating temperature are higher.
1, feed: the liquid to be treated feed into the evaporator.
2, evaporation: in the external circulation evaporator, to be treated liquid from the feed pipe into a heater, and then be heated, so that part of it into a vapor state.
3.Condensation: The vapor passes through the
Condenser inside the evaporator, which is usually a tube bundle or heat exchanger, in which the cooling medium is transferred to condense the vapor into liquid.
4.Separation: Inside the evaporator, liquid and vapor are separated by a separation device. Commonly used separation devices include gravity separators, centrifuges and cartridges.
5.Recirculation: The separated liquid is recirculated inside the evaporator. Usually, part of the liquid will flow back to the bottom of the evaporator through a return tube to maintain the stable work of the evaporator.
6.Vapor discharge: The vapor that is not condensed is discharged from the evaporator through an exhaust port to enter the subsequent treatment or recycling.
Throughout the process, the external circulation evaporator through the heater to heat the liquid to its boiling point above, so that part of it into steam, and then through the condenser and separation device to separate the steam and liquid, and finally the remaining steam discharge. This method can realize the separation and concentration of the liquid, and at the same time achieve the purpose of energy recycling and environmental protection.
The characteristics of external circulation evaporator are as follows:
1.Heating unit is placed outside the evaporator, which is convenient for maintenance and cleaning.
2.The common specifications of heating tube diameter are ϕ19mm×2mm, ϕ25mm×2mm and ϕ32mm×2mm.
3.Heating tube length-to-diameter ratio can be 50~100, easy to get a high liquid circulation flow rate.
4.The circulating flow rate of material liquid can reach 1.5~2.0m/s, which is convenient to get high heat transfer coefficient.
5, the heat transfer coefficient is usually between 1200 ~ 3500W / (m2 - ℃).
6, the completion of the liquid and secondary steam separation of the vast majority of the separation chamber is realized in the separation chamber, the separation chamber volume is large, the inlet is tangential design, and need to be set up to capture the foam device.
7, the separation chamber of the secondary steam discharge pipe to be inserted into the separation chamber, usually 150 ~ 250mm, which can play the role of cyclone, conducive to further separation of steam and liquid.
8, out of the separation chamber of the secondary steam can be baffled or cyclone type foam trapping device to further separate the entrainment of liquid droplets, and then into the condenser.
9.Outside circulation evaporator can be set into multi-effect form.
Source:Reprint
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