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Evaporator Presntation

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INTRODUCTION TO EVAPORATORS

PRESENTATION

Submitted by:M.Shabbir Iqbal Najeeb-ullah M Usman M.Umar Shaheen Zubair Talha 2007-bpe-18 2007-bpe-34 2007-bpe-35 2007-bpe-10 2007-bpe-13

Dated: 08-02-2010

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Table Of Contents:Evaporation. 5 What an Evaporator Does?.............................................6 Working principle6 Elements of evaporator...7 Evaporator Accessories...7 Basis of classification of evaporators.8 Types of evaporators..8 a) Natural/forced circulation evaporator8 b) Falling film evaporator..11 c) Rising film (Long Tube Vertical) evaporator13 d) Plate evaporator.15 e) Multiple-effect evaporators..16 8. Troubleshooting18 9. References. 1. 2. 3. 4. 5. 6. 7.

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Evaporation:Evaporation is the removal of solvent as vapor from a solution or slurry. For the overwhelming majority of evaporation systems the solvent is water. The objective is usually to concentrate a solution; hence, the vapor is not the desired product and may or may not be recovered depending on its value. Therefore, evaporation usually is achieved by vaporizing a portion of the solvent producing a concentrated solution, thick liquor, or slurry. Evaporation often encroaches upon the operations known as distillation, drying, and crystallization. In evaporation, no attempt is made to separate components of the vapor. This distinguishes evaporation from distillation. Evaporation is distinguished from drying in that the residue is always a liquid. The desired product may be a solid, but the heat must be transferred in the evaporator to a solution or a suspension of the solid in a liquid. The liquid may be highly viscous or a slurry. Evaporation differs from crystallization in that evaporation is concerned with concentrating a solution rather than producing or building crystals.

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What an Evaporator Does?As stated above, the object of evaporation may be to concentrate a solution containing the desired product or to recover the solvent. Sometimes both may be accomplished. Evaporator design consists of three principal elements: heat transfer, vaporliquid separation, and efficient utilization of energy. In most cases the solvent is water, heat is supplied by condensing steam, and the heat is transferred by indirect heat transfer across metallic surfaces. For evaporators to be efficient, the equipment selected and used must be able to accomplish several things: Transfer large amounts of heat to the solution with a minimum amount of metallic surface area. This requirement, more than all other factors, determines the type, size, and cost of the evaporator system. Achieve the specified separation of liquid and vapor and do it with the simplest devices available. Make efficient use of the available energy. This may take several forms. Evaporator performance often is rated on the basis of steam economyPounds of solvent evaporated per pound of steam used. Meet the conditions imposed by the liquid being evaporated or by the

solution being concentrated. Factors that must be considered include product quality, salting and scaling, corrosion, foaming, product degradation, holdup, and the need for special types of construction.

Working principle:The solution containing the desired product is fed into the evaporator and passes a heat source. The applied heat converts the water in the solution into vapor. The vapor is removed from the rest of the solution and is condensed while the now concentrated solution is either fed into a second evaporator or is removed.

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Elements of evaporator:Three principal elements are of concern in evaporator design: Heat transfer Vapor-liquid separation Efficient energy consumption. The units in which heat transfer takes place are called heating units or calandrias. The vapor-liquid separators are called bodies, vapor heads, or flash chambers. The term body is also employed to label the basic building module of an evaporator, comprising one heating element and one flash chamber. An effect is one or more bodies boiling at the same pressure. A multiple-effect evaporator is an evaporator system in which the vapor from one effect is used as the heating medium for a subsequent effect boiling at a lower pressure. Effects can be staged when concentrations of the liquids in the effects permits; staging is two or more sections operating at different concentrations in a single effect. The term evaporator denotes the entire system of effects, not necessarily one body or one effect.

Evaporator AccessoriesVarious types of equipment, both major and minor, must be supplied for every evaporator in addition to the evaporator body itself. These include: (1) Condensers (2) Vacuum producing equipment (3) Condensate removal devices (4) Process pumps (5) Process piping (6) Instrumentation (7) Safety relief equipment (8) Thermal insulation (9) Equipment and pipeline tracing (10) Valves, manual and control (11) Process vessels (12) Electric motors and turbines (13) Refrigeration.Evaporators Page 7

Basis of classification of evaporators.1. Heating medium separated from evaporating liquid by tubular heating surfaces. 2. Heating medium confined by coils, jackets, double walls, flat plates etc. 3. Heating medium brought into direct contact with evaporating liquid. 4. Heating with solar radiation.

Types of evaporators1. Natural/forced circulation evaporator. 2. Falling film evaporator. 3. Rising film (Long Tube Vertical) evaporator. 4. Plate evaporator. 5. Multiple-effect evaporators.

1.Natural/forced circulation evaporator:This type of evaporator is generally made of long tubes (4-8 meters in length) which are surrounded by steam jackets. The uniform distribution of the solution is important when using this type of evaporator. The solution enters and gains velocity as it flows downward. This gain in velocity is attributed to the vapor being evolved against the heating medium, which flows downward as well. This evaporator is usually applied to highly viscous solutions so it is frequently used in the chemical, food, and fermentation industry.

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Forced circulation evaporator with external horizontal heating elementEvaporators Page 9

Forced circulation evaporator with internal vertical heating element

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2.Falling film evaporator.In this type of evaporator, boiling takes place inside the tubes, due to heating made (usually by steam) outside the same. Submergence is therefore not desired; the creation of water vapor bubbles inside the tube creates an accessional flow enhancing the heat transfer coefficient. This type of evaporator is therefore quite efficient, the disadvantage being to be prone to quick scaling of the internal surface of the tubes. This design is then usually applied to clear, non-salting solutions. Tubes are usually quite long (4+ meters); sometimes a small recycle is provided. Sizing this type of evaporator is usually a delicate task, since it requires a precise evaluation of the actual level of the process liquor inside the tubes. Recent applications tend to favor the falling film pattern rather than this one.

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LTV Falling-Film EvaporatorEvaporators Page 12

3. Rising film (Long Tube Vertical) evaporator.In this type of evaporator, boiling takes place inside the tubes, due to heating made (usually by steam) outside the same. Submergence is therefore not desired; the creation of water vapor bubbles inside the tube creates an accessional flow enhancing the heat transfer coefficient. This type of evaporator is therefore quite efficient, the disadvantage being to be prone to quick scaling of the internal surface of the tubes. This design is then usually applied to clear, non-salting solutions. Tubes are usually quite long (4+ meters); sometimes a small recycle is provided. Sizing this type of evaporator is usually a delicate task, since it requires a precise evaluation of the actual level of the process liquor inside the tubes. Recent applications tend to favor the falling film pattern rather than this one.

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LTV Rising-Film Evaporator with Vertical-Tube Surface Condenser

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4. Plate evaporator.Plate evaporators have a relatively large surface area. The plates are usually corrugated and are supported by frame. During evaporation, steam flows through the channels formed by the free spaces between the plates. The steam alternately climbs and falls parallel to the concentrated liquid. The steam follows a co-current, counter-current path in relation to the liquid. The concentrate and the vapor are both fed into the separation stage where the vapor is sent to a condenser. Plate evaporators are frequently applied in the dairy and fermentation industries since they have spatial flexibility. A negative point of this type of evaporator is that it is limited in its ability to treat viscous or solid-containing products.

Spiral tube and bank assembly evaporators

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5. Multiple-effect evaporators.Unlike single-stage evaporators, these evaporators can be made of up to seven evaporator stages or effects. The energy consumption for single-effect evaporators is very high and makes up most of the cost for an evaporation system. Putting together evaporators saves heat and thus requires less energy. Adding one evaporator to the original decreases the energy consumption to 50% of the original amount. Adding another effect reduces it to 33% and so on. A heat saving % equation can be used to estimate how much one will save by adding a certain amount of effects. The number of effects in a multiple-effect evaporator is usually re