Vertical tube evaporator or Short tube evaporator and Forced Circulation Evaporators

What is Evaporation and why do we need evaporators?

       Evaporation involves removing the solvent as vapor from a specified solution, it could also be a slurry or suspension of any solid in a liquid. The purpose is to concentrate a non-volatile solute, such as organic compounds, inorganic salts, acids or bases from the solvent. Most common solutes are different forms of sugar, caustic soda, caustic potash, sodium sulfate, sodium chloride, phosphoric acid, and urea. Water is the most common solvent in most of the evaporation systems.

Evaporation is different from the other mass transfer operations such as distillation and drying. In distillation, the components of a solution are separated depending upon their distribution between vapor and liquid phases based on the difference of relative volatility of the substances. Removal of moisture from a substance in presence of a hot gas stream to carry away the moisture leaving a solid residue as the product is generally called drying. Evaporation should normally stop before the solute starts to precipitate in the operation of an evaporator.

The evaporators in which the movement of the fluid takes puts thus of convection current set up by the warming procedure are called vertical tube evaporator or short tube evaporator.


Short-Tube Vertical Evaporators 

Short-tube vertical evaporators are the oldest but still widely used in sugar industry in evaporation of cane-sugar juice. These are also known as calandria or Robert evaporators. This evaporator was first built by Robert. It became so common in process industry that this evaporator is sometimes known as standard evaporator. Short-tube vertical evaporators consist of a short tube bundle (about 4 to 10 ft in length) enclosed in a cylindrical shell. This is called calandria. The feed is introduced above the upper tube sheet and steam is introduced to the shell or steam chest of the calandria. The solution is heated and partly vaporized in the tubes. The central tube in a calandria is of longer diameter. Typically it’s downcomer area is taken as 40 to 70% of the total cross sectional area of tubes. The circulation rate through the downcomer/downtake is many times the feed rate. The flow area of the downtake is normally approximately equal to the total tubular flow area.

DESCRIPTION, CONSTRUCTION, PRINCIPLE, WORKING, APPLICATIONS 

DESCRIPTION

Vertical tube evaporator or short tube evaporator goes under the order of the characteristic flow evaporators.

It comprises of various tubes. Around 1000 tubes are fitted in a vessel. The tubes are fitted with fluids and encompassed by steam. The level of the fluids is kept up somewhat over the top if the tubes so that the space which is left in the evaporators can be utilized with the end goal of partition of vapor from the bubbling fluids.

The fluid in the tube is warmed by steam and it starts to bubble. The blend of the fluid and vapor will leave the tube sets up a dissemination with bubbling fluid ascending in the littler tubes of calandria and returning down the substantial focal down take.

PRINCIPLE

In standard vertical tube evaporator or short tube evaporator fluid went through the vertical tubes and the steam is provided from the outside the tubes.
Warm exchange happens through the tubes and the fluid in side the tubes gets warmed. The solvents dissipates and the vapor escapes from the top. The concentrated fluid is gathered from the base.

CONSTRUCTION

The development of a standard Vertical tube evaporator or short tube evaporator comprises of a huge barrel shaped body made up the cast press with vault formed top and base.

In side the body calandria is fitted at the base. Calandria comprises of various vertical tubes whose breadth ranges from the 0.05 to 0.075 m and length of 1-2 m.

Around 100 such tubes are fitted in a body measuring 2.5 m or more measurement. Deltas are accommodated the steam and nourished.

Out lets are accommodated vapor concentrated items, non consolidated gasses and condensate.

WORKING 

Steam is presented outside the tubes. The condensate is gone through the comparing out let and non dense gasses escape through the vent.

The bolster is presented so as to keep up the fluids level somewhat over the highest point of the tubes. The fluids in side the tubes is warmed by the steam and starts to bubbles.

As the fluid bubbles it gushes up through the tubes and returns through the focal down take. It set up a dissemination of hot fluid which upgrades the rate of warmth exchange.

The vapor escapes through the top outlets. Steam is provided until required grouping of the items is acquired. At long last the items can be pulled back from the scrape the bottom let.

APPLICATIONS 

Vertical tube evaporator or short tube evaporator is utilized as a part of the produce of the cascara remove.

Vertical tube evaporator or short tube evaporator is utilized as a part of the produce of salts and scathing pop.

Vertical tube evaporator or short tube evaporator is utilized as a part of the make of salts.

Advantages

In Vertical tube evaporator or short tube evaporator tubes expands the warming surface about 10 to 15 times when contrasted and steam jacketed pot.

Fiery flow improves the rate of warmth exchange.

It can be associated with a condenser and beneficiary, which additionally expands rate of evaporation. Such connection is additionally appropriate for the unstable solvents.

Various units can be joined to got more proficient impact.

Disadvantages

The fluid is kept up over the level of the calandria. Consequently the upper layers of the fluid need quite a while for getting warmed. This issue can be minimized by evacuating accumulated fluid gradually at the base.

The vertical tube evaporator or short tube evaporator is convoluted consequently establishment cost increments.

Cleaning and support is troublesome when contrasted and steam jacketed pot.

Amid operation the weight in side the evaporator increments. In extensive evaporators where the fluid profundity might be the request of 2 m the weight increments to 25 kp, prompting to height of the breaking point by 5 or 6 @c. this lessens the compelling temperature slopes and may influences warm delicate materials.

Variations 

Forced Circulation Evaporators

Forced circulation evaporators are usually more costly than natural circulation evaporators. However the natural circulation evaporators are not suitable under some situations such as: - highly viscous solutions due to low heat transfer coefficient - solution containing suspended particles - for heat sensitive materials All these problems may be overcome when the liquid is circulated at high velocity through the heat exchanger tubes to enhance the heat transfer rate and inhibit particle deposition. Any evaporator that uses pump to ensure higher circulation velocity is called a forced circulation evaporator. The main components of a forced circulation evaporator are a tubular shell and tube heat exchanger (either horizontal or vertical), a flash chamber (separator) mounted above the heat exchanger and a circulating pump (Figure 3.4). The solution is heated in the heat exchanger without boiling and the superheated solution flashes off (partially evaporated) at a lower pressure are reduced in the flash chamber. The pump pumps feed and liquor from the flash chamber and forces it through the heat exchanger tubes back to the flash chamber.

Vertical tube evaporator or short tube evaporator with propeller

In short vertical tube evaporator or short tube evaporator course depends totally on bubbling . steam is provided into the calandria to prompted bubbling. At the point when steam supply is ceased naturally bubbling stops. Subsequently the particles settle down. These particles goes about as cores which develop as precious stones.

Subsequently this evaporators is here and there utilized as a taking shape evaporators. On the off chance that the crystallization is un alluring, the issue can be maintained a strategic distance from by introducing a propeller in the focal bit near the base. By expanding the rotating per min of the propeller the limit of the evaporator can be multiplied.

Uses

Since mellow steel or cast iron is utilized, the evaporators suits well for clear fluids and solidifying arrangements. Non destructive fluids and gentle scaling arrangements can be taken care of.

Advantages

Warm exchange coefficients are high because of high temperature slopes values. It requires low head room. Cleaning and upkeep is simple. It is generally in costly.

Disadvantages

Warm exchange coefficients are low because of low temperature angles. It requires high floor space and is more in weight. Generally more fluid is held. Rate of warmth exchange additionally diminishes because of high consistency fluids. Since body is extensive mellow steel or cast iron are utilized forits development to make it less costly.

Basket type evaporator

The wicker bin sort vertical tube evaporator or short tube evaporator has a funnel shaped base and once in a while a level base. In this sort bubbling is very brutal. Thus the gushing of the fluids prompts to entrainment.

This issue can be stayed away from by setting a redirectors over the tubes. For this situation the down take is annular in stead of being focal. The benefits of this sort is that whole warming components is a solitary unit. The entire unit can be expelled for repairs. Likewise the diverters counteracts entrainment misfortunes totally.