3 replies to this topic

[millanyc]

Hi,

I'm rating an existing heat exchanger (AET). Its pre-heating Urea product coming from urea plant using a steam coming on top of a condensate collection drum. Flowrate of steam is not controlled. Steam is generated condensate collected from Steam user flashes on the condensate drum. The exchanger is located on top of the drum.

Downstream of the steam side of the exchange is a steam condenser that condenses the steam which return the condensate to the condensate drum.

My question is since there's no temperature control on both side of the exchanger, I was thinking of the best method I should do in order for me to determine if the existing exchanger is still adequate for the increase f steam flow coming form the collection drum.

The first option i tried is since my area is fixed it should be able to provide the same duty as it was before. So I rated my exchanger using the same duty it was design before, and let htri calculate the the outlet temperature of the steam and urea side of the exchanger. However, I'm still not sure if this will be correct as I know the duty of the exchanger will change because your U value changes. Doing this method will generate a -60% over design. Meaning the exchanger won't be able to performed at the expected duty.

I tried rating the exchanger using the process condition I have from our Heat and Material balance. And the exchanger over design is 55%. The exchanger was used to heat the urea from 90 to 170 deg F, From our new HMB urea enters the exchanger at 82 deg F and leaves at 143 deg F

The existing data sheet of the exchanger shows a steam flow of 4090 lbs/hr saturated at 1.5 kg/cm2A and 230 deg . The revamp steam flow is now 13,000 lbs/hr at the same steam condition.

Any help will be highly appreciated

Thanks
Millany

[Nirav]

You are increasing flow by almost 3 times. If same heat exchanger is used, how can it accomodate such a huge flow compared to what it is designed for.

You said you'r getting 60% overdesign. However, what is actual dP (pressure drop) on steam side? I guess it will be very high which will practically not allow this much flow of steam.

Edited by Nirav, 29 October 2012 - 01:26 AM.

[millanyc]

Yes, If HE is to perform the design duty of the heat exchanger, steam side pressure will be very high. High enough for the steam pressure to have a negative outlet pressure.

What I did was to reduce my specified duty and let htri calculate the outlet pressure of steam and process side of HE until I get a 0% over design since I dont have temperature control on either side of the heat exchanger.

Heat transfer area will be the same, but Q will be reduce because of the change in the U value corresponding to the change in my Process Condition.

Not 100% sure if its correct. But I think it make sense.

[millanyc]

Sorry, I need to correct my post.

Yes, If HE is to perform the design duty of the heat exchanger, steam side pressure drop will be very high. High enough for the steam pressure to have a negative outlet pressure.

What I did was to reduce my specified duty and let htri calculate the outlet temperature of steam and process side of HE until I get a 0% over design since I dont have temperature control on either side of the heat exchanger.

Heat transfer area will be the same, but Q will be reduce because of the change in the U value corresponding to the change in my Process Condition.

Not 100% sure if its correct. But I think it make sense.