3 replies to this topic

[luckusct]

hi
ive been given a project to design an evaporator(multiple effect) to concentrate water solution from tds(total dissolved solids) 70000mg/l to 250000 tds product. how do i decide how much effects to employ?

[Art Montemayor]

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[katmar]

There is no easy way. Like many problems in chemical engineering it is a trade off between capital cost and running costs. With more effects you will save steam, but your capital equipment cost will go up.

[Jiten_process]

There is no easy way. Like many problems in chemical engineering it is a trade off between capital cost and running costs. With more effects you will save steam, but your capital equipment cost will go up.

Exactly. Here it becomes more client-oriented issue. Sometimes client asks low capital investement and sometimes clients are so consicous about utility. So, as Katmar said, it is trade off which we have to explain to client.

general guidlines, you first find out boiling point of your feed and product and try devide it equally to various effects by assuming no. of effects initially. Then find out evaporation in each effect and flow rates in and out off each effect. Then you have to find out wetting rate for each column, generally there is guidlines of wetting rate for tubes in evaporator, if calculated wetting rate comes out less than the guidlines then you have to decrease the no. of effect and recalculate the data.

As far as classroom assignment is concern you can take up any example of book and try calculate for various effects because practically there is more of technology in evaporation which is tough to expose for any technology supplier.

these all my views...
all the best.