Pharmaceuticals, pulp and paper, foods and drinks, polymers and resins, chemicals, inorganic salts, acids and bases, and a variety of other materials are all processed using evaporators. Evaporators technology come in a variety of shapes and sizes, and the optimal one out of them is determined by the product’s qualities and intended outcomes.
Evaporation is a technique for concentrating a solution containing a nonvolatile solute and a volatile solvent, which is usually water. To create a concentrated solution, slurry, or thick, viscous liquid, a portion of the solvent is vaporised. The difference between evaporation and drying is that the residue is a liquid rather than a solid. Evaporation differs from distillation in that the vapours are not separated into their constituent parts. It’s possible that the desired product is the vapour, concentrate stream, or both. As a result, the evaporator should be constructed to separate the vapours from the condensate and feed in a clean and efficient manner.
A heat exchanger or heated bath, valves, manifolds, controls, pumps, and a condenser are all components of an evaporator. Jacketed tanks, tubular heat exchangers, plate-and-frame heat exchangers, and agitated thin-film evaporators are among the most commonly used designs. At least, a well-designed evaporator must:
- Be cost-effective for installation, operations, and maintenance, it must be designed to efficiently transmit heat at a high rate with a small surface area
- 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
The critical operational and product parameters of the solution to be evaporated play a big role in determining which evaporator type is best for the job.
- Heat Sensitivity: Many foods, pharmaceuticals, chemicals, and resins are heat or temperature-sensitive, necessitating modest heating temperatures, a short time exposed to the heat, or both. This can be accomplished by reducing the product’s bulk boiling temperature by operating the evaporator at lower pressures, as well as minimising the volume of product in the evaporator at any given time. Lowering the internal working pressure while maintaining an appropriate heat-exchanger driving power may also allow lower heating temperatures to be used (difference in temperature between the bulk product’s boiling point and the heating medium’s temperature).
- Fouling: Solids in the feed, precipitating solids in the concentrate, and product degradation are the most common causes of fouling of heat exchanger surfaces. The overall heat-exchanger coefficient will gradually decrease when a layer forms on the heat exchanger surfaces over time. This will eventually necessitate the process being shut down and the heat exchanger surfaces being cleaned, resulting in production downtime and more maintenance labour.
- 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 vapor/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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- 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 vapor velocity (pressure drop and entrainment): In the evaporator tubes and heating jackets, the vapour velocity must be considered. To achieve adequate heat-exchanger coefficients without exceeding pressure drop, erosion, or entrainment limits, sufficient velocities are required. The vapor/liquid separator’s specifications for separation efficiency and pressure drop must be carefully considered.
- Heat transfer Medium: The type of evaporator chosen could be influenced by the heat transfer medium. Evaporators that are heated by liquid have lower overall heat exchanger coefficients and require a larger heat transfer surface. If the product is temperature-stable, hot oil heating can help overcome the reduced heat-transfer coefficient. This could allow a smaller evaporator to be used in some circumstances.
- Materials required of construction: The required materials of construction may be a crucial factor to consider when choosing an evaporator. The heat-exchanger surface material is critical because it not only influences the overall material cost but also dictates the material’s thermal conductivity, which influences the overall heat-exchanger coefficient and necessary surface area.
The needs, standards, and value of a marketable product must all be specified before the process and equipment can be appraised. The general process requirements needed to make a commercial product must next be determined. The method should result in a high-quality product with low waste.
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. Capacity, 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. 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. Continuous processes are typically employed when a large capacity is required. When tubular evaporators are available, they should be used initially.
The best suited type will be determined by the throughput, viscosity, solids content, fouling propensity, and foaming tendency, as well as whether the design calls for circulation. Forced-circulation evaporators are generally more expensive than natural-circulation evaporators, although, in some situations, the higher heat-exchanger coefficients allow for a smaller evaporator to be employed, lowering capital expenditures.
Technology such as the plate-and-frame or agitated thin-film evaporator may be required when the product is difficult to handle due to great temperature sensitivity, high viscosity, heavy particles, or a high tendency to foul. ALAQUA is the best evaporators supplier in USA along with other processing equipment available. For more information contact us today!!!