Surface Condenser Design (TEMA Type BEM) 2

[MHS1988]

Hello everyone,

I’m a mechanical engineer working for a vendor that designs and fabricates heat exchangers. While we primarily focus on mechanical design, clients sometimes ask us to guarantee thermal performance as well. This usually involves minor tweaks in HTRI, like adjusting tube layouts or baffle arrangements, to align with our mechanical design.

However, a couple of days ago, a client sent us a process datasheet and asked us to provide our own thermal design. Here are the key design details:

SERVICE: Surface Condenser, TEMA TYPE: BEM, Qty.: 1
Tube Length= 3000mm, SHELL/CHANNEL ID= 1360mm, Tube OD= 25.4mm, Tube Thk.=1.65mm, Tube Pitch=35.5mm, Layout: 30°, No. Tubes: 888 (to be finalized by vendor),
Baffle: Single Seg. 30% Cut (to be finalized by vendor),

Shell Side Data:
Fluid: STEAM, Mass Flow: 16600 kg/hr, Inlet/Outlet Press.: 0.09341/- Bar(absolute), Allow. Press. Drop: By Vendor, Inlet/Outlet Temp.: 44.8/40 °C, Vapor Fraction In/Out: 1/0,
Design Press.: 3 Bar(Gauge), Design Temp.: 120 °C, No. Passes: 1, Inlet/Outlet Nozzle Size: NPS22/NPS3, Material: SS304L, C.A.: 0

TUBE Side Data:
Fluid: COOLING WATER, Mass Flow: 134309 kg/hr, Inlet/Outlet Press.: 3.1/2.6 Bar(absolute), Allow. Press. Drop: 0.5 bar, Inlet/Outlet Temp.: 32/42 °C, Vapor Fraction In/Out: 0/0,
Design Press.: 6 Bar(Gauge), Design Temp.: 120 °C, No. Passes: 4, Inlet/Outlet Nozzle Size: NPS10/NPS10, Material: SS304L, C.A.: 0

I ran the data through HTRI, but no solution was reached. As a troubleshooting step, I left out the cooling water flow rate, and the reported value in HTRI was almost 7 times higher than the specified value in the datasheet. A friend of mine (also a mechanical engineer) checked the data using HYSYS and confirmed the HTRI result. He also used EDR’s design module, which suggested 8 parallel exchangers of this size to meet the requirements.
Now I am wondering whether this kind of exchanger (a Surface Condenser) is just another story and too complex for us to handle, Or is there a possibility that the client’s provided data is incorrect?

I’ve already reached out to their process engineer, but he wasn’t much help. He mentioned that the data came from a licensor, but couldn’t provide further details.

Any insights or advice would be greatly appreciated!
Thanks in advance.

 

[georgeverghese]

This selection of a TEMA BEM configuration for a 4tubeside pass arrangement doesnt make sense from a thermal design point of view, since half the passes will be in co current flow. Hence this is equivalent to a TEMA BEU configuration, and this is a better configuration from a design temp perspective.

 

[pierreick]

Hi,
another possible configuration:

BEU Shell & Tube

www.shell-tube.com

Pierre

 

[MJCronin]

Wild ideas from a disgusted, feral (and cancerous) geezer ...

1.) Google "steam surface condenser" "eng-tips" and "MJCronin" together - What can you learn here ?

2). Since this is your first heat exchanger ever, investigate the term "thermal approach temperature"

3). Go back to the barn and feed your animals, they are hungry and have been waiting for you,..... Najeeb

 

[pierreick]

Wild ideas from a disgusted, feral (and cancerous) geezer ...

1.) Google "steam surface condenser" "eng-tips" and "MJCronin" together - What can you learn here ?

2). Since this is your first heat exchanger ever, investigate the term "thermal approach temperature"

3). Go back to the barn and feed your animals, they are hungry and have been waiting for you,..... Najeeb

Anything excessive is insignificant.
Pierre

 

[shvet]

@MHS1988
1/ Ask the licensor how is it possible that the steam is under vacuum conditions and contains no non-condensibles. Note that there is a huge difference between total condenser and partial condenser.
2/ Pressure drop is less than 1 kPa. How do you suppose the flow will be distributed in reality between 4 (four!) parallel shells? Lets assume that the real non-uniformity between shells will be 10%, in this case 10%=100 Pa will make this condensers work totally different than that had been calculated. Is there a margine to compensate such?
100 Pa is ~ a light breathing out from a human mouth. It's not enough to blow out the flame of a match.
3/ Ask the licensor what reason the design pressure is 6 times higher than the operating pressure. If 300 kPag is related to steaming out conditions than how is it possible that the design temperature is only 120°C low and irrelevant to steaming pressure. When and by what gas is this HE supposed to be pressurized up to 300 kPag?
4/ The water is supposed to be relatively clean (fouling is 5.5 kW/m2-K). What reason the cold side is made of SS?

It is better leave such a complex task to an experienced person and start training the basics on simple ones.

 

[MHS1988]

@MHS1988
1/ Ask the licensor how is it possible that the steam is under vacuum conditions and contains no non-condensibles. Note that there is a huge difference between total condenser and partial condenser.
2/ Pressure drop is less than 1 kPa. How do you suppose the flow will be distributed in reality between 4 (four!) parallel shells? Lets assume that the real non-uniformity between shells will be 10%, in this case 10%=100 Pa will make this condensers work totally different than that had been calculated. Is there a margine to compensate such?
100 Pa is ~ a light breathing out from a human mouth. It's not enough to blow out a burning match.
3/ Ask the licensor what reason the design pressure is 6 times higher than the operating pressure. If 300 kPag is related to steaming out conditions than how is it possible that the design temperature is only 120°C low and irrelevant to steaming pressure. When and by what gas is this HE supposed to be pressurized up to 300 kPag?
4/ The water is supposed to be relatively clean (fouling is 5.5 kW/m2-K). What reason the cold side is made of SS?

It is better leave such a complex task to an experienced person and start training the basics on simple ones.

Thank you so much.
It was very helpful.