GEA Process Engineering Inc.
Evaporator (Falling Film / Rising Film)
Product Description
Falling Film Evaporators:
In falling film evaporators the liquid product (A) usually enters the evaporator at the head (1) of the evaporator. In the head the product is evenly distributed into the heating tubes. A thin film enters the heating tube are it flows downwards at boiling temperature and is partially evaporated. In most cases steam (D) is used for heating the evaporator. The product and the vapor both flow downwards in a parallel flow. This gravity-induced downward movement is increasingly augmented by the co-current vapor flow. The separation of the concentrated product (C) form its vapor (B) is undergoing in the lower part of the heat exchanger (3) and the separator (5).
Falling film evaporators can be operated with very low temperature differences between the heating media and the boiling liquid, and they also have very short product contact times, typically just a few seconds per pass. These characteristics make the falling film evaporator particularly suitable for heat-sensitive products, and it is today the most frequently used type of evaporator.
However, falling film evaporators must be designed very carefully for each operating condition; sufficient wetting (product film thickness) of the heating surface by liquid is extremely important for trouble-free operation of the plant. If the heating surfaces are not wetted sufficiently, dry patches and incrustations will occur; at worst, the heating tubes will be completely clogged. In critical cases the wetting rate can be increased by extending or dividing the evaporator effects, keeping the advantages of single pass (no recirculation of product) operation.
The proper design of the product distribution system in the head of the evaporator is critical to achieve full and even product wetting of the tubes.
Because of the low liquid holding volume in this type of unit, the falling film evaporator can be started up quickly and changed to cleaning mode or another product easily.
Falling film evaporators are highly responsive to alterations of parameters such as energy supply, vacuum, feed rate, concentrations, etc. When equipped with a well designed automatic control system they can produce a very consistent concentrated product.
The fact that falling film evaporators can be operated with small temperature differences makes it possible to use them in multiple effect configurations or with mechanical vapor compression systems in modern plants with very low energy consumption. More information on energy consumption and energy savings are available in Energy Management / Energy Optimization section.
Rising Film Evaporators:
These operate on a "thermo-siphon" principle. Feed product (A) enters the bottom of the heating tubes and as it heats, steam begins to form. The ascending force of this steam produced during the boiling causes liquid and vapors to flow upwards in parallel flow. At the same time the production of vapor increases and the product is pressed as a thin film on the walls of the tubes, and the liquid rises upwards. This co-current upward movement against gravity has the beneficial effect of creating a high degree of turbulence in the liquid. This is advantageous during evaporation of highly viscous products and products that have a tendency to foul the heating surfaces.
Usually there must be a rather high temperature difference between the heating and boiling sides of this type of evaporator. Otherwise the energy of the vapor flow is not sufficient to convey the liquid and to produce the rising film. The length of the boiling tubes will typically not exceed 23 ft (7m).
This type of evaporator is often used with product recirculation, where some of the formed concentrate is reintroduced back to the feed inlet in order to produce sufficient liquid loading inside the heating tubes. A number of different designs have been developed using this basic principle. A good example is the Roberts evaporator, which is the oldest type of circulation evaporator. This type of evaporator has a wide circulation tube in the center of the heating tube bundle through which concentrate flows back to the bottom of the tube bundle. The Roberts evaporator is still widely used in the sugar industry.
GEA Process Engineering Inc — Liquid & Powder Processing Systems:
The GEA Process Engineering segment of the GEA Group offers a wide range of process equipment, process technology and know-how for the dairy, food, chemicals, pharma, and beverage industries as well as for environmental protection. Most of the companies of GEA Process Engineering are world-wide leaders in their processing technologies and have many decades of international experience and the most widely accepted technologies. The GEA Process Engineering Segment is able to offer solutions and complete process lines tailored to each customer`s needs and requirement.
GEA Process Engineering Inc. (formerly known as Niro Inc.) - Process Equipment, Systems and Solutions:
GEA Process Engineering Inc. is a full-service company offering engineering, systems, and solutions for powder and liquid processing. Established in 1974, the company is known for innovative processing systems for drying, granulation, agglomeration, coating, evaporation, distillation,crystallization, filtration, liquid processing, filling and aseptic filling, bottling, bottle and PET conveying systems, powder handling and packaging, tableting, mixing, containment, cleaning (CIP) andfermentation. GEA Process Engineering is a member of the GEA Group, a global technology group specializing in process systems and solutions. GEA Process Engineering Inc. offers products and services through these strategic business units/groups:
