·Wiped Film Evaporator

· Summary
Thin film evaporator is a new-type high-effective evaporator with high-speed flowing, high-effective heating transfer, and short stick-time (around 10~50 quadrics), in which the liquid film is formed compulsively by rolling film scraper, and processing down-flow film evaporated under vacuum conditions.

It consists of one or more cylinders heated with jackets and film-scraper that rolling inside. The film-scraper continuously scrapes the charging material to even liquid film at the heating surface and move down, during the process, components with low boiling points is evaporated and the hangover is expelled from the bottom of the evaporator.

· Functional characteristics
> Small vacuum pressure drop
There is a certain differential pressure that exits when the boil-off gas sent to an exoteric condenser from the heating surface. The differential pressure in a normal evaporator is relatively high, sometimes too high to be accepted. However, in a scraping thin film evaporator, there are quite large amount of gas going through the space and the pressure inside the evaporator can be considered as the same as that in the condenser, so the pressure drop is tiny, and the vacuity can attain 5mmHg.

> Low operation temperature
Because of the characters mentioned above, the process of evaporator can be operated under a relative high vacuum condition. Because of the increasing of vacuity, the corresponding material boiling point falls down sharply. Consequently, the operation can be carried out in a lower temperature, which will decrease the heat decomposing of the product.

> Short being heated time
Because of the particular structure of scraping thin film evaporator, film-scraper is provided with pump sending function, which allows the stick-time of the material in evaporator is short. In addition, in the heated evaporator, the product will not stay at the surface of the evaporator because of the high-speed on-flow of the thin film. Therefore, scraping thin film evaporator is especially applicable for the evaporation of heat sensitivity material.

· High efficiency of evaporation
The drop of boiling increases temperature difference of heated medium; the membrane wiper thins the liquid membrane, which is onflow, so that it reduces the thermo-resistance. Meanwhile, materials are restrained to be wall or scale on the heated surface accompanied with good heat exchange. Therefore, the coefficient of total heat transfer in WFE is improved.

· High flexibility in process
To WFE, the particular performance makes it suit to process those materials, which are thermo-sensitive, viscous and need to be evaporated smoothly, and whose viscosity are rapidly increasing with its consistence in smooth evaporating period.

It can be successfully applied in evaporation and distillation for materials containing solid granule, crystallation, polymerization and scale, etc.

· Application field
WFE is widely applied in heat exchange engineering. Especially to thermo-sensitive materials in short heat-exchanging time, WFE makes for heat exchanging and distilling to complex products by different designs.

WFE has been used in the following field by evaporating for concentration, solvent doffing, vapor extraction, reaction, off-gas and deodorization, etc. which achieves good effect:

Medicines: antibiotics, sugar solution, tripterygium, radix astragali and other Chinese herbs; methylimidazole, mono-nitrilamine and other intermediates.

Light and food industry: fruit juice, meat liquor, pigment, essence, spice, enzymatic products, lactic acid, xylose, cotn sweetener and potassium sorbate, etc.

Lipid and daily chemicals: lecithin, VE, fish liver oil, oleic acid, glycerol, fatty acid, waste lubricant, alkyl-amylose glycoside and ether-alcohol sulphate, etc.

Composed resin: polyamide resins, epoxies resins, polyoxymethylene (POM), PPS, PBT, propylene formic acid ester.

Composed fiber: PTA, DMT, carbon fiber, poly-tetrahydrofuran and polyether of polyhydric alcohols, etc.

Petrochemicals: TDI, MDI, trimethyl-hydroquinone, trioxylmethyl propane and sodium hydroxide, etc.

Pesticide: herbicides such as acetochlor, proprochlor, chlorpyrifos, furan powder, and cartentrazone etc. insecticides, weedicides and acaricides.

Wastewater: wastewater contains abio-salts.

· Process theory
Material feeds into evaporator from the top of heater and distributes to its surface by a wiper. The screwing wiper continually scrapes material to an even liquid membrane, which is overfall in high speed on the surface of heater. The liquid membrane is protected to be adjusting and scale on the heater so as to improve the coefficient of total heat transfer in WFE. Light compounds are evaporated into vapor which rising to an external condenser that connects directly to the evaporator by a separator. The heavy compounds exhaust from the bottom of WFE.

A particular wiper not only distributes material equably to the surface of heater and avoids material spattering into vapor flow in the evaporator but also protects fresh material flash-steaming at once. It can eliminate bubbles and make material to be steamed along the surface of heater.

A centrifugal separator designed according to the characters of materials is installed on the top of evaporator, which returns the liquid condensed from the rising vapor to distributor.

· Specification and model