The Rototherm-E is Artisan’s most common evaporator design and belongs to the Thin-Film or Wiped-Film class of Evaporators. Artisan Industries has been designing and manufacturing these evaporators since the 1960’s. They installed more than 500 units worldwide.
The Rototherm-E is designed for applications where both the product feed entering the evaporator and the concentrated product exiting the evaporator are pumpable fluids (either liquids, pastes or sludges).
The Rototherm-E has many advantages over other kinds of finishers (as e.g. falling film finishers):
Short product residence time
The exposure of the product to a heated surface is very short (typically 1-5 minutes). Hence there is a reduced chance of product quality degradation.
Low Production Losses
The horizontal design assures that no dry spots will be created. As a result no fouling will occur on the heated surfaces. Consequently production losses are close to zero.
Low down-time
The residence time of the product inside the evaporator is very short. As a result the start-up (and the shut-down) of an operation is very quick.
High Turn-Down Ratio
The evaporation process is virtually independent of gravity. Consequently the feed-flow has little impact on the operation.
Highly Viscous Products
The design of the Rototherm-E allows handling of highly viscous materials (up to 4 million cP ). As such very high product concentration can be obtained.
High Heat Flux
The evaporation principle uses a large temperature difference over the heated surface. As such, a Rototherm requires only a relative small heat transfer area.
Easy Maintenance
The Rototherm®-E is easy to maintain. It has few moving parts installed. The bearings are on the outside the product flow area.
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Some Applications for the Rototherm-E
Problem
To carry out an equilibrium reaction, while simultaneously concentrating the product and discharging a solid or a slurry, all in a single step. Equilibrium reactions, such as saponification and esterification are typically carried out in batch reactors, taking 24 to 30 hours to reach the desired conversion. Furthermore, it has been demonstrated that rapid removal of reaction by-products, such as water in esterification reactions, significantly reduces reaction time. However, both heat and mass transfer rates are limited in batch reactors. Consequently, as the reaction proceeds toward completion, the water removal rate drops dramatically, inhibiting the reaction rate and wasting valuable reactor time.
Solution
Use an Artisan two-zone Rototherm-E to carry out continuous equilibrium reactions. A co-current design, along with a two-zone process section, permits reaction, concentration, and a heavy slurry or solid discharge in a single step. This mechanically-agitated thin-film processor provides a unique combination of efficient heat and mass transfer capability, short residence time, and mechanical integrity to perform continuous reactions of highly viscous, foaming, fouling and solids-containing products. The rapid evaporation of reaction by-product(s) enables near complete conversion of most saponification and esterification reactions in minutes, yielding superior products, while minimizing energy consumption.
Example
While concentrating a soap product all of the following are done in a single step:
- Single stage saponification of isostearic acid with sodium hydroxide, forming a stoichiometric soap.
- Steam stripping the “un-saps” from the soap.
- Discharging a paste-purified soap with an acid value of 195, and an un-sap value < 1.
Problem
Conventional evaporation technologies cannot accomplish the process of concentrating carbohydrates and other similar heat-sensitive products. The extreme sensitivity of these materials to time and temperature exposure, further compounded by foaming and fouling tendencies, make them particularly challenging to process without product degradation and fouling of the heat transfer surfaces.
Solution
The Artisan Rototherm-E is the ideal evaporator for this type of application. The mechanically-agitated evaporator provides extremely short residence time (measured in seconds), narrow residence time distribution, rapid surface renewal, and high heat transfer rates. The Rototherm can evaporate up to 99% of the feed solution in a single pass, while simultaneously achieving turn down ratios of 10 and higher, without product burn-on.
Example
Continuous vacuum evaporation and concentration of an artificial sweetener (sucralose) from16% solids to 73% solids by evaporating 93% of the solvent (consisting of dimethyl formamide, acetic acid, and cyclohexane) produces a highly concentrated carbohydrate product.
Problem
Recovering glycerin and other heat sensitive, solids-containing valuable food additives cannot be accomplished effectively using conventional evaporation techniques.
Solution
Use an Artisan Rototherm-E mechanically-agitated thin film processor, to continuously evaporate and distil heat sensitive solids-containing products, without colour formation, and achieve greater than 96% yield. Minimized product degradation and maximized purity and yield are due to the Rototherm’s extremely short residence time (measured in seconds), its rapid surface renewal, its narrow residence time distribution, and its high heat transfer rates.
Example
Recovering glycerin from vegetable oil (containing 20% glycerin and 2% sodium salts). Through continuous vacuum evaporation/distillation, highly purified glycerin is recovered overhead while a concentrated oil/salt residue is discharged as waste.
Problem
A high Free Fatty Acids (FFA) content crude feed-stock has a lower market value compared to low FFA feed-stocks.
Solution
The high Free Fatty Acids (FFA) content crude feed-stock flows through a feed/bottoms economizer and a trim heater to preheat the feed, while cooling the stripped product oil (bottoms) to its desired temperature. The preheated feed enters a vapor/liquid separator, operating under vacuum where a portion of the FFA as well as any moisture present is flashed off. The remaining liquid falls by gravity into the Rototherm®-E mechanically aided thin film evaporator where the centrifugal force generated by the spinning rotor maintains a thin film of material on the heated wall, evaporating essentially all the remaining FFA. The product discharges by gravity from the Rototherm®-E into an insulated bottoms accumulator, from which it flows through the feed/bottoms economizer before entering the biodiesel process.
The Rototherm®-E is designed with a counter–current liquid/vapor flow configuration to maximize mass transfer and minimize entrainment.
Turbulence created by the rotor blades constantly renews the film, aiding in both heat and mass transfer, enabling nearly complete removal of the FFA, while preserving the quality of the stripped oil.
Thermal Oil provides heat to the Rototherm-E. Nitrogen at very low rates is continuously sparged into the evaporator to aid in stripping. The FFA vapor from the Rototherm®-E combines with the pre–flashed vapor, passes through a mesh entrainment separator in the vapor/liquid separator and enters the condensing system.
Advantages of Artisan’s FFA process
- Handles up to 30% FFA in the feed and reduces it to less than 1% in a single pass.
- Green water-less process, reducing the generation of waste-water common in conventional deodorization processes.
- No chemical additives or treatments required, reducing hazardous chemicals and wastes from your plant site.
- Normally an ROI of less than 6 months based on only a 5 cent difference in low-cost vs. rendered feed stock prices.
- No degradation in quality of the oil product.
- Low energy usage due to high recuperation potential.
Example
Most biodiesel processes require less than 1% free fatty acid (FFA) in the feedstock. The price of these feed materials, generally vegetable oils, has skyrocketed with increasing demand.
Using the Rototherm®-E technology, Artisan developed an economical one–step process that yields a material with only 1% FFA from inexpensive low–grade feed-stocks containing up to 25% FFA with no need for chemicals. The process also produces high quality fatty acids that can be sold or further esterified to produce biodiesel.