Method of Feeding: Multiple Effect Evaporators PDF

Preview

Summary

Name : Mayasti Suraira Student Identity No. : 6514010019 Concentration : Gas Processing Subject : OTK-2 Lecturer : M. Qirom Method of Feeding: Multiple Effect Evaporators 1. Forwarded Feed In forwarded feed multiple effect evaporator the liquid feed is pumped into the first effect and the partially ...

Description

Name Student Identity No. Concentration Subject Lecturer

: Mayasti Suraira : 6514010019 : Gas Processing : OTK-2 : M. Qirom

Method of Feeding: Multiple Effect Evaporators 1. Forwarded Feed In forwarded feed multiple effect evaporator the liquid feed is pumped into the first effect and the partially concentrated solution is sent to the second effect and so on. The heating steam is also sent through the first effect to another effect. This particular strategy is known as forward feed. In the forward feed the concentration of the liquid increases from first effect to the subsequent effects till the last effect. It may be noted that the first effect is that in which the fresh steam is fed, whereas the vapor generated in the first effect is fed to the next evaporator (connected in series with the first effect) is known as second effect and so on.

The forward feed requires a pump for feeding dilute solution to the first effect. The first effect is generally at atmospheric pressure and the subsequent effects are in decreasing pressure. Thus, the liquid may move without the pump from one effect to another effect in the direction of decreasing pressure. However, to take out the concentrated liquid from the last effect may need a pump.

Advantage of Forward Feed Multiple Effect Evaporator : -

-

In this arrangement the feed and steam introduced in the first effect and pressure in the first effect is highest and pressure in last effect is minimum, so transfer of feed from one effect to another can be done without pump. Product is obtained at lowest temperature. This method is suitable for scale-forming liquids because concentrated product is subjected to lowest temperature.

Disadvantage of Forward Feed Multiple Effect Evaporator : -

-

The forward feed configuration can not used in the desalination industry because it has a more complex layout than the parallel feed configuration. It is not suitable for cold feed because, the steam input in effect-1 raises the temperature of the feed, and a small amount of heat is supplied as latent heat of vaporization. Therefore, amount of vapor produced will be less than the amount of steam supplied. Lower amount of vapor in effect-1 produces lower amount of vapor in the subsequent effects. Therefore, the overall economy is lower.

Application of Forward Feed Multiple Effect Evaporator : -

This method of operation is used when the feed is hot or when the final concentrated product might be damaged at high temperatures (in Pharmaeutical Industry). Pulp and Paper Industry Sugar Factory

2. Backwarded Feed The backward feed arrangement is very common arrangement. In this arrangement the dilute liquid is fed to the last effect and then pumped through the successive effects to the first effect. The method requires additional pumps (generally one pump in between two effects) as shown in the fig. 9.6. Backward feed is advantageous and gives higher capacity than the forward feed when the concentrated liquid is viscous, because the viscous fluid is at higher temperature being in the first effect. However, this arrangement provides lower economy as compared to forward feed arrangement.

Advantage of Backward Feed Multiple Effect Evaporator : -

-

This method of reverse feed is advantageous when the feed is cold since a smaller amount of fresh cold, liquid must be heated to the higher temperatures in the second and first effects. The method is suitable for viscous products, because highly concentrated product is at highest temperature, hence lower viscosity ( higher heat transfer  higher capacity)

Disadvantage of Backward Feed Multiple Effect Evaporator : -

Liquid pumps must be used in each effect, since the flow is from low to high pressure.

Application of Backward Feed Multiple Effect Evaporator : -

Milk & Yogurt Factory

3. Parallel Feed Another common evaporator arrangements, which is more common in crystallization is parallel feed where feed is admitted individually to all the effects. The vapor from each effect is still used to heat the next effect.

Application of Parallel Feed Multiple Effect Evaporator : -

This method of operation is mainly used when the feed is almost saturated and solid crystals are the product, as in the evaporation of brine to make salt.

Conclusion : The multiple effect evaporation process can be configured in forward, backward, or parallel feed. The three configurations differ in the flow directions of the heating-steam and the evaporating brine. Selection among the three configurations relies on variation in the salt solubility as a function of the top brine temperature and the maximum brine concentration. At higher temperatures or higher brine concentrations, scale formation takes place inside and outside the tube surfaces....