Wiped Film Evaporator: The Ultimate Guide
What Are Wiped Film Evaporators?
Wiped film evaporators (or WFE) have emerged as solutions for separation processes in various industries. These devices excel in distilling, desolventizing, purifying, and stripping high-value products, utilizing the efficient wiped film evaporation process to achieve desired concentrations and purity levels.
Key Features
- Feed – The feed supply is composed of the prepared and purified crude oil to be distilled within the evaporator. Most machines have a pumping mechanism between the feed supply and the still body to provide a consistent flow rate.
- Still – This is the main body of a WFE where distillation occurs. The “still” body is one of the system’s most complex sections, including a motorized wiper mechanism, a feed connection, an inner or external condenser, and two discharge/vessels for distillate and residue. The still also has an outer jacket that is heated or cooled to create conditions for distillation.
- Distillate & Residue – The WFE produces these two end products. The distillate is the targeted, purified compound that was selectively collected at boiling point, while the residue is any feed constituent that did not evaporate during distillation. It is considered a waste product or saved for another material application.
- Vacuum system & cold trap – The vacuum system allows distillation to occur at a lower temperature. It comprises one or more vacuum pumps and a secondary cold trap after the still. The cold trap traps any light vapor that doesn’t condense in the internal or external condenser, helping increase vacuum longevity.
Wiped Film Distillation: A Powerful Separation Technique
How Does a Wiped Film Evaporator Work
A WFE uses a specialized internal mechanism to efficiently separate components with different boiling points. The process begins when the feed material is introduced onto a heated vertical cylinder. Internal wipers spread the material into a thin film across the hot surface, stimulating rapid evaporation of the more volatile components. The vapors produced ascend to a cooler condenser, where they revert to liquid and are collected. The less volatile substances, unable to evaporate at these temperatures, are also collected.
An In-Depth Guide to The Process
The first step in wiped film distillation involves introducing the feed liquid into the WFE. This feed liquid could be a mixture that needs separation or purification, such as essential oils or pharmaceutical compounds. Once inside the evaporator, a rotating heated wiper blade spreads the liquid into a thin, even layer across the surface.
- Vaporization: When the thin layer of feed liquid touches the evaporator’s heated surface, it quickly vaporizes due to the efficient heat transfer. This rapid vaporization results in faster processing compared to traditional methods like simple batch distillation.
- Separation: As the liquid vaporizes, the different components in the mixture separate based on their boiling points. Substances with lower boiling points vaporize faster than those with higher boiling points. This allows for precise control over which substances are collected at different stages of the wiped film evaporation process.
- Condensation: Once the components have been separated through selective vaporization, the vapors move toward an external condenser. Here, they cool down and condense into liquid form, now separated based on their unique boiling points.
- Collection: The condensed liquids, now separated into distinct components, are collected in a separate container. Meanwhile, the leftover residue, or “waste,” remains on the evaporator surface. This waste can either be disposed of or further processed if needed.
Thin Film Evaporator vs. Wiped Film Evaporator
At their core, a thin film evaporator and a WFE are essentially the same, but understanding the small differences between them starts with recognizing the distinct structural elements and operational mechanics that set them apart. Both systems operate on the same basic principle of evaporation and condensation, yet they diverge significantly in execution and performance.
The Differences
A thin film evaporator employs rotating blades that spread the feed into a thin film across the inner surface of a heated cylindrical jacket, compared to a WFE, which utilizes wipers or rollers to spread the liquid into a film. This distinct feature affects the material’s exposure to heat, separation efficiency, and the final product’s quality. The wiped film evaporator excels in handling viscous and sensitive materials that require short residence times due to the enhanced agitation provided by the mechanical wipers.
Advantages of the Wiped Film Evaporator
When observing the advantages that the WFE has over the thin film evaporator, several stand out. Chiefly, the capability to process feeds with higher viscosities and produce a more uniform film contributes to better heat transfer and mass transfer rates. Consequently, these evaporators are more effective at evaporation and distillation of heat-sensitive materials, as the brief exposure to high temperatures reduces degradation. Additionally, the wiped film evaporator often exhibit lower pressure drops, leading to more efficient operations and the ability to reach deeper vacuum levels, an essential condition for distilling high-boiling or temperature-sensitive components.
Choosing the Right Wiped Film Evaporator
Choosing the right WFE takes analyzing several features. The selection criteria influence operation efficiency and determine the scale of operation and the quality of the end product.
Features to Consider When Selecting a WFE
Material Construction: Stainless steel or glass components offer distinctive benefits, with the steel providing robustness and the glass ensuring visibility of the process.
Surface Area: A larger surface area facilitates increased distillation rates, impacting productivity.
Feed Rate: The equipment’s capacity to process material continuously must align with operational demands.
Vacuum System: A high-performance vacuum system enables lower distillation temperatures, beneficial for heat-sensitive materials.
Wiper System: The design and material of wipers affect film distribution and residue, impacting separation efficiency.
Condenser Design: The size and type of condenser influence the rate at which vapors condense, affecting throughput.
Operational Pressure: Equipment must maintain consistent pressure settings to ensure repeatable distillation results.
Temperature Control: Precise control systems regulate the heating temperature, which is essential for achieving the desired product purity.
Explore this Technology For Yourself
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