Evaporators handle pharmaceuticals, pulp, paper, food, drinks, polymers, resins, chemicals, salts, acids, bases, and diverse materials. Product qualities and intended outcomes dictate the optimal shape and size among various evaporator technologies.
Evaporation concentrates a solution by vaporizing the solvent, creating a concentrated liquid, slurry, or thick viscous product, differentiating from drying.
A heat exchanger or heated bath, valves, manifolds, controls, pumps, and a condenser are all components of an evaporator. The most commonly used designs include jacketed tanks, tubular heat exchangers, plate-and-frame heat exchangers, and agitated thin-film evaporators. At least, a well-designed evaporator must:
- Designing it to efficiently transmit heat at a high rate with a small surface area is essential for achieving cost-effectiveness in installation, operations, and maintenance.
- Separate the vapour from the liquid concentrate with ease
- Meet the requirements of the product being processed
- Produce a product that satisfies the quality requirements
- Make optimal use of steam via multiple-effect evaporation or vapour recompression where possible to save energy
- Fouling on heat transfer surfaces should be kept to a minimum
- Be made of corrosion-resistant materials
Product Characteristics and Critical Operations of Evaporators:
The critical operational and product parameters significantly influence the determination of the most suitable evaporator type for the job.
Heat Sensitivity:
Sensitive products require controlled conditions: low pressure, minimized volume, and reduced temperature differences between bulk boiling and heating medium for optimal evaporation.
Fouling:
Heat exchangers suffer efficiency loss and increased maintenance due to fouling from feed solids, concentrate precipitates, and product degradation.
Foaming:
During the vaporisation of a product, it is normal for it to foam. It can range from a tiny amount of readily broken unstable foam to a very stable foam that tends to fill the entire void of the evaporator system. Specific designs for the feed inlet (separation of feed from vapour stream) and the vapour/liquid separation area (special disengaging design) can typically reduce foaming. Reduce the boiling intensity of the liquid on the heat transfer surface (by operating at a lower temperature or at higher pressure) and the vapour velocity in the tubes to reduce foaming. Antifoam may solve or considerably decrease the problem if the product purity criteria allow it.
Solids:
To reduce foaming, lower the boiling intensity of the liquid on the heat transfer surface (by operating at a lower temperature or higher pressure) and the vapour velocity in the tubes. If the product purity criteria allow it, antifoam may solve or significantly reduce the problem.
Viscosity:
The overall heat-exchanger coefficient decreases as the viscosity of the concentration increases.
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Heat-exchanger coefficient Evaporators:
Distillate-to-concentrate Ratio-
In general, enough liquid must move through the evaporator to wet the heated walls. Due to a lack of wall wetting and fluid velocity, particles on heat transfer surfaces may foul and salt, resulting in reduced heat transfer and possibly product quality degradation due to hot spots on the heating surface. Recycling of portion of the concentrate may be necessary for operations that need high distillate-to-concentrate ratios.
Distillate vapour velocity Evaporators (pressure drop and entrainment)-
Consider the vapor velocity in the evaporator tubes and heating jackets. Maintain sufficient velocities to prevent exceeding pressure drop, erosion, or entrainment limits for adequate heat exchanger coefficients. Carefully consider the vapour/liquid separator’s specifications for separation efficiency and pressure drop to achieve optimal performance.
Heat transfer Medium Evaporators-
The heat transfer medium could influence the choice of evaporator type. Evaporators heated by liquid have lower overall heat exchanger coefficients and necessitate a larger heat transfer surface.If the product is temperature-stable, hot oil heating can help overcome the reduced heat-transfer coefficient. In some circumstances, a smaller evaporator could use this.
Evaporators construction-
When choosing an evaporator, one must consider the crucial factor of the required materials for construction. And, The choice of heat-exchanger surface material becomes critical as it not only influences the overall material cost but also governs the thermal conductivity of the material, thereby impacting the overall heat-exchanger coefficient and the required surface area.
Specify the needs, standards, and value of a marketable product before appraising the process and equipment. Then, identify the specific process requirements required to produce a commercial product. The method should result in a high-quality product with low waste.
Materials required for Evaporators construction-
It can be simple or difficult to select the best evaporator. High viscosities or heavy solids are examples of product qualities that provide some guidance. For many simple applications, however, any or a combination of the different categories will suffice. Hence, capacity a small batch production, previous plant expertise, available space, operator requirements, utility requirements, required maintenance, and/or cost may all play a role in making this decision.
Batch or stirred-batch evaporators are typically the most cost-effective option for low-volume or multi-product batch production. So, it’s easy to use, low-cost, and capable of handling a wide range of products with varying features and operating conditions. Although it may take longer to clean, it is usually a low-maintenance system. When a large capacity is required, industries typically employ continuous processes. When tubular evaporators are available, they should be used initially.
The throughput, viscosity, solids content, fouling propensity, and foaming tendency will determine the best-suited type, along with whether the design requires circulation. Higher heat-exchanger coefficients in certain cases allow smaller, cost-effective forced-circulation evaporators despite their general expense compared to natural-circulation evaporators.
When handling products with great temperature sensitivity, high viscosity, heavy particles, or a high tendency to foul, one may require technology such as the plate-and-frame or agitated thin-film evaporator. ALAQUA stands out as the best option in such cases.evaporators supplier in USA along with other processing equipment available. For more information contact us today!!!
