8 replies to this topic

[addy1]

Hi Guys....

I want to design a condenser (Vertical orientation) for a system in which uncondensable gas is liberated along with the solvent vapors. The gas will be sucked by a blower and vented off. So I need the vent line sizing also Can anybody help me out.


Thanks and Regards,
Addy.

[ankur2061]

Addy,

Without posting all the stream data (shell / tube), configuration (1-2, 2-4 pass) along with the stream pressures and temperatures how do you expect anyone to answer your query.

Regards,
Ankur.

[addy1]

Hi Ankur...

I wanted to know the approach actually means Is it the same as we design a normal heat exchanger or any thing extra details has to be considered...

I'll elaborate my query a little bit.

Mine is a simple batch system in which two reactants (A and B are dissolved in Toluene in a 3.0 KL reactor with 80% occupancy of the reactor and the reaction mass is refluxed for two hours through a graphite type condenser (Block type) in which water at ambient temperature(~35 deg C) is used as coolant. As per reaction chemistry about 1 mole of Ammonia gas is liberated during the reaction during reflux. The condenser is vertically oriented and both the condensate and the vent gas lines are connected from the bottom and the vent line is connected to a blower. The vapor line is 4" in dia. The reflux line is 1.5" and the vent line is 1". I want to look at the condenser and the venting system design.


Thanks and Regards,
Addy.

Edited by addy1, 22 October 2011 - 08:56 AM.

[ankur2061]

Addy,

I still don't understand how a vapor vent line is connected from the bottom? Normally a vapor vent is always from a high point. Maybe I am missing something. Is it possible to upload a sketch of your system for sake of clarity?

Regards,
Ankur.

[addy1]

Please find the simple flow diag of my setup actually looks like...

Attached Files

•  CopyofPIDTemplate.jpg   16.14KB   50 downloads

[ankur2061]

Addy,

From your sketch it is apparent that you are expecting some non-condensibles in the reflux line. Also it is apparent that since the vent line is at the highest point from the reflux line no non-condensibles are expected to be returned into the reactor.

If you do an ideal mass balance across the condenser

Vapor in to condenser = Condensible liquid from Condenser + Non-condensibles to vent

In such a case you need to know what are the non-condensibles from the vapor line flowing to the condenser to find out the vent flow rate.

I would probably provide a vapor-liquid separator in the vent line going to the blower to prevent any liquid droplets being carried over to the blower. Alternatively, I could make the vapor line big enough to have very low vapor velocities in the vapor line which would prevent any liquid carryover to the blower.

It is important to note that blowers are meant for handling vapor / gas and are generally very poor at handling wet gas or gas entrained with liquid unless specifically designed for such service.

Hope this helps.

Regards,
Ankur.

[addy1]

Thanks for ur help Ankur...

But actually my question is
1) Where exactly in the condenser area calculation we are considering the non condensable gas load?
2) How can we find whether the given condenser area is sufficient or not (For vapor it is fine)

Because the main constraint here is the gas must be removed as fast as it is formed in the reaction or else it is pressurizing the reaction and resulting in some unwanted product formation. As per chemistry about 1K.mole of gas is formed in the reaction which occupies huge in terms of volume and the condenser is around 10 sq.m in area.

[ankur2061]

Addy,

From your sketch the condenser appears to be a plate and frame type of condenser. Plate-and-frame exchangers are a specialized design and only the manufacturers of these can provide the exact area. As a general note, two-phase (vapor + liquid) Flow at the outlet of the condenser will require a careful evaluation of the condenser heat transfer area.

Generally only a datasheet is provided which contains stream data at the inlet and outlet conditions for the stream. This data could include flow rate (condensible as well as noncondensible), composition of the inlet stream (including the noncondensibles), the pressure and temperature conditions at the inlet and outlet and the allowable pressure drop.

I would certainly not try to design such a condenser because a lot of the design for plate-and-frame exchangers is very proprietary in nature specially when there could be two-phase flow at the exchanger outlet.

If you have access to some specialized heat exchanger software such as HTRI or HTFS with the plate-and-frame heat exchanger module, maybe you can try it.

This is the best that I can help you.

Regards,
Ankur.

[Profe]

Hi Addy

About your concerns:
I think what you need is to design a vertical condenser with a condensate receiver drum provided with an outlet valve for noncondensables.
The design of this type of condensers can be found in the book of Donald Q. Kern "Process Heat Transfer"

Attached is a diagram of this type.

Good luck.

Attached Files

•  Non condensables.png   35.98KB   35 downloads