3 replies to this topic

[sks]

Hi dears,
HETP and HTU both are calculated in determination of Paked Tower Height.....how can we compare these two....and which one is more useful in design?

thanks

[siretb]

HTU is the heigth of a transfer unit. The HTU(overall) is directly related to the kg(overall), the mass transfer coefficient.
Be aware that it is possible to define a HTU(gas side) and a HTU(liquid side) and that the HTU(overall) is greater than both. HTU(overall)=HTU(v) + Lambda HTU(l), where lambda is the stripping factor. You will find useful definitions in Perry's handbook (chapter 14 in the 7th edition). It's worth a look at, there is a worked out example.
For design purpose, you need to define the number of transfers unit you need
NUT(v)=Integrate[dy/(y*-y)) and then knowing the HTU(v) determine the H you need H=NUT(v) * HUT(v)

The HTU is usually determined by experiment, or taken from vendor's data.

The HETP is the heigth of a theor. plate. This concept is more vague, but can be very useful. For instance if you have determined that you need, say 10 plates (Mc Cabe & Thiele, a process simulator, or else) and that a given packing will yield 2 theor. plates per meter (that's a HETP of 0.5 m) then you need 5 meters of packing

there is a relationship HETP = HTU * Ln(lambda)/(lambda - 1) where lambda is, again, the stripping factor.

Now, and I will express only my own view, and some will disagree.
I think that HETP is more useful for distillation. I use HETP for distillation.
I think that HTU is more useful for gas absorption and stripping

[sks]

HTU is the heigth of a transfer unit. The HTU(overall) is directly related to the kg(overall), the mass transfer coefficient.
Be aware that it is possible to define a HTU(gas side) and a HTU(liquid side) and that the HTU(overall) is greater than both. HTU(overall)=HTU(v) + Lambda HTU(l), where lambda is the stripping factor. You will find useful definitions in Perry's handbook (chapter 14 in the 7th edition). It's worth a look at, there is a worked out example.
For design purpose, you need to define the number of transfers unit you need
NUT(v)=Integrate[dy/(y*-y)) and then knowing the HTU(v) determine the H you need H=NUT(v) * HUT(v)

The HTU is usually determined by experiment, or taken from vendor's data.

The HETP is the heigth of a theor. plate. This concept is more vague, but can be very useful. For instance if you have determined that you need, say 10 plates (Mc Cabe & Thiele, a process simulator, or else) and that a given packing will yield 2 theor. plates per meter (that's a HETP of 0.5 m) then you need 5 meters of packing

there is a relationship HETP = HTU * Ln(lambda)/(lambda - 1) where lambda is, again, the stripping factor.

Now, and I will express only my own view, and some will disagree.
I think that HETP is more useful for distillation. I use HETP for distillation.
I think that HTU is more useful for gas absorption and stripping

@siretb

thanks a lot dear.....

regards
sks

[sheiko]

Now, and I will express only my own view, and some will disagree.
I think that HETP is more useful for distillation. I use HETP for distillation.
I think that HTU is more useful for gas absorption and stripping

I don't disagree but could you please tell why?