Pre Heat Exchanger

[OilHunter]

I'll been trying to figure out what heat exchanger will be suitable for our process. Currently we got plate type but we are facing some problem like blocking of some scales and solid particles..that can caused back pressure. Is there any good designed that can be suitable for this. we got no option but to bypass the pre heat exchanger. is tube/shell type suitable for this.

 

[sshep]

Hello OilHunter,

The selection of plate exchangers is driven by the need to have alot of surface area, but the problem that you have is a common pitfall because the nature of the fouling that might be experienced is often not considered. Maybe a set of strainers upstream can help you.

A shell and tube with proper choice of side (typically fouling fluid on the shell), and type (AES, etc) as approriate to the nature of the fluids being handled is a serious option. It will all depend on the size required- it is probably large or they wouldn't have justified a plate type. The first thing to do is calculate the required area as a starting point for your alternative consideration process.

best wishes always,
sshep

 

[OilHunter]

sshep

thank you very much for the suggestion. considering a strainer upstream of PHE what can be possible problem we might encounter?

 

[sshep]

I would put in two strainers if the load is heavy so that one can be on line while the other is cleaned. You will see the strainer taking more pressure drop via your control valve position becoming more open, then you know you need to clean. This can be cheap if your piping is easy to access. Running a dP indication to the panel is probably a waste of your money. If you have a typical DCS rather just configure a controller high output alarm to anticipate when these strainers are fouling.

If you really want to do it cheap and can bypass the HX for a few hours to bring it off line when needed, just put in a witch hat style start-up strainer. Many of our plate exchangers are protected like this for start-up purposes.

good luck,
sshep

 

[OilHunter]

thank you very much I might consider those tips you have given.. I try to review our design and see if we can adopt the idea..

 

[ash9144]

You want fouling material on the tube side. You can open and easily clean the tubes. Shell side you have to chemically treat or get a new HE

 

[OilHunter]

i think it will be worse if tube got fouling as I saw the nature of scale we got here

 

[Compositepro]

I agree with ash. You almost always want the fluid most prone to fouling on the tube side. Fluid velocity is higher and more uniform to help avoid fouling, and the tube side is far easier to clean if fouling occurs. I'm sure there are exceptions.

 

[rmw]

Your problem is two fold. One is particles. Plate exchangers also function as wonderful strainers if there is anything in the fluid larger than what will pass through the channels.

If your problem is particles, add a strainer and as suggested, either get a duplex type or a self cleaning type.

Your second problem is scaling. If you have scaling with the plate, then you will probably have trouble with scaling of the shell and tube type Hx. Pick the one that you think easiest to clean when this is required. With plate types, sometimes you can cycle them to make the plates flex so that the scale flakes off and is carried away. You can't do this with a S&T.

rmw

 

[OilHunter]

thanks guys your recommendations really helps a lot

 

[sshep]

The first paper in the old HTFS Handbook (GS1: Pitfalls in the Design and Operation of Tubular Exchangers) has a great general advice on exchangers if you can get a hold of a copy.

Incidently I saw that I made a typo about which side to put the fouling fluid on in my first post- it was supposed to say "clean fluid on the shell." Thanks to everyone for correcting that obvious error without making me feel like an idiot.

best wishes,
sshep