MUTLIPLE EFFECT EVAPORATORS. PROJECT REPORT DONE BY: KAVITA YADAV 2009305060 ABHISHEK SINGH2009305061 PRIYANKA RAVIKUMAR2009305062 SURIYASRI.S2009305063 SATYANARAYANAN20086242. INTRODUCTION:.
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MUTLIPLE EFFECT EVAPORATORS
PROJECT REPORT DONE BY:
KAVITA YADAV 2009305060
Temperature difference in between steam chest temperature and product temperature.
Volatile solvent is removed from the feed.
Solution (volatile solvent + non volatile solute)
Concentrate (Higher solute Conc.)
Vaccum for non condensable
Steam in (Saturated vapor)
Condensate out (Saturated Liquid)
Single effect evaporator
Double effect evaporator
Triple effect evaporator
Multiple effect evaporator
It may be possible to make use of this, to treat an evaporator as a low pressure boiler, and to make use of the steam thus produced for further heating in another following evaporator called another effect.
Consider two evaporators connected so that the vapour line from one is connected to the steam chest of the other as shown in making up a two effect evaporator
If liquid is to be evaporated in each effect, and if the boiling point of this liquid is unaffected by the solute concentration, then writing a heat balance for the first evaporator:
q1 = U1A1(Ts - T1)=U1A1DT1
where q1 is the rate of heat transfer, U1 is the overall heat transfer coefficient in evaporator 1, A1 is the heat-transfer area in evaporator 1, Ts is the temperature of condensing steam from the boiler, T1 is the boiling temperature of the liquid in evaporator 1 and DT1 is the temperature difference in evaporator 1, = (Ts - T1).
Similarly, in the second evaporator, remembering that the "steam" in the second is the vapour from the first evaporator and that this will condense at approximately the same temperature as it boiled, since pressure changes are small,
q2 = U2A2(T1 - T2) = U2A2 DT2
If the evaporators are working in balance, then all of the vapours from the first effect are condensing and in their turn evaporating vapours in the second effect. Also assuming that heat losses can be neglected, there is no appreciable boiling-point elevation of the more concentrated solution, and the feed is supplied at its boiling point,
q1 = q2
Further, if the evaporators are so constructed that A1 = A2, the foregoing equations can be combined.
U2/U1 = dT1 / dT2
The above equation states that the temperature differences are inversely proportional to the overall heat transfer coefficients in the two effects. This analysis may be extended to any number of effects operated in series, in the same way
recompression unit, (2) Steam for heating (3) Feed in (4) Calandria
(5) Feed out
(6) Vapour Separator (7) Pre-heater
(8) Condenser (9)Cooling water in, (10) Cooling water return
TVR = Thermal Vapour Recompression uses a sonic nozzle jet and high pressure steam to recompress a lower pressure steam/vapour. In the live steam nozzle (1) the pressure of the in-flowing steam is converted into velocity. A jet is created which draws in the low pressure vapour. In the diffuser (2) a fast flowing mixture of live steam and vapours is formed, the speed of which is converted into pressure (temperature increase) by deceleration.
A vapour-liquid separator is a vertical vessel used in several industrial applications to separate a vapour-liquid mixture. Gravity causes the liquid to settle to the bottom of the vessel, where it is withdrawn. The vapour travels upward at a design velocity which minimizes the entrainment of any liquid droplets in the vapour as it exits the top of the vessel.
Pre heater is a device for preliminary heating of a material, substance, or fluid that will undergo further use or treatment by heating. Preheating in stages increases efficiency and minimises thermal shock stress to components.
It is an apparatus in which vapour is condensed within tubes that are cooled by the evaporation of water flowing over the outside of the tubes.
Water heat exchanger
Overview of thermal recompressor
The pressure in the second effect must be reduced below that in the first. In some cases, the first effect may be at a pressure above atmospheric; or the first effect may be at atmospheric pressure and the second and subsequent effects have therefore to be under increasingly lower pressures. Often many of the later effects are under vacuum. Under these conditions, the liquid feed progress is simplest if it passes from effect one to effect two, to effect three, and so on, as in these circumstances the feed will flow without pumping. This is called forward feed
In the case of a forward feet operation, the raw feed is introduced in the first effect and is passed from effect to effect parallel to steam flow. The product is withdrawn from the last effect. This procedure is highly advantageous if the feed is hot. The method is also used if the concentrated product may be damaged or may deposit scale at high temperature
Alternatively, feed may pass in the reverse direction, starting in the last effect and proceeding to the first, but in this case the liquid has to be pumped from one effect to the next against the pressure drops. This is called backward feed and because the concentrated viscous liquids can be handled at the highest temperatures in the first effects it usually offers larger evaporation capacity than forward feed systems, but it may be disadvantageous from the viewpoint of product quality.
In the backward operation, the raw feed enters the last (coldest) effect and the discharge from this effect becomes a feed for the next to last effect. This technique of evaporations is advantageous, in case the feed is cold, as much less liquid must be heated to the higher temperature existing in the early effects. The procedure is also used if the product is viscous and high temperatures are required to keep the viscosity low enough to produce good heat transfer coefficients.
Typical materials of construction for a number of evaporator applications are shown below:
STEAM CONSUMPTION AND RUNNING
COSTS OF EVAPORATORS
Energy reduction schemes for multiple effect evaporator systems
Shabina Khanam1, Bikash Mohanty
1 .Department of Chemical Engineering, National Institute of Technology Rourkela,
2.Rourkela-769008, India 2 Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, India