Plate type heat exchanger 3

[schick]

Does anyone have experience using plate type heat exchangers for cooling Industrial Diesel Engines?

I'm looking for pros and cons about the Raw Water portion of the system. We'll be pumping river water and/or ocean water and haven't heard of anyone using these types of coolers.

Traditionally we've been using shell in tube coolers, but we're looking to make a more compact package, that easier to service.

Any and all comments welcome!!

Schick

 

[jistre]

I'm assuming you're talking about plate and frame exchangers.

Be careful with your water supply. The passages in a plate and frame exchanger are typically MUCH smaller than those in a shell and tube. Their essential design is to spread the fluid streams out into sheet-like flows that run across either face of the flat plates. In addition, the plate is designed with ridges and such to direct fluid and further increase the surface area. This is what allows their large transfer area in a compact design; in essence, it creates a whole bunch of tiny tubes that have common walls that heat can transfer across. The trade-off for this compact design is that the effective diameters of the passages through these exchangers are much smaller than what you see in a typical shell and tube. Because of this, you'll see that viscous fluids don't always perform well in them. More importantly if I understood your cooling fluid, is that they're much less forgiving of particulates, scaling, biological growth, etc., and will readily clog. They really play best with clean, relatively inviscid fluid streams.

There are some models of these exchangers that are designed with slightly larger passages for fluid streams with particulates and such, but they still prefer fluids that are cleaner. I'd take a long hard look at all the ways untreated water might foul the exchanger.

 

[schick]

My concerns exactly. I am hoping to hear both success and horror stories, so we can decide whether or not to pursue this method.

 

[jistre]

Wish I could help you with stories, but I've never used these types of exchangers with anything other than clean process fluids. Good luck!

 

[SNORGY]

The presence of chlorides in both sources of water discussed would concern me almost as much as the solids, given that the standard plate pack offered would likely be austenitic. However, I have used P+F with acceptable success in water that was rather cruddy on both sides (fresh untreated water cross exchanged with warm water laden with sulphur solids). If you plan to do this, my thoughts would be to err on the side of high dP and flow velocity across the plate pack, even if it means being a bit tight on the heat transfer area.

Regards,

SNORGY.

 

[rmw]

To rephrase what Jistre has said, P&F Hx's make wonderful strainers. Some of the tighter models won't pass a particle any larger than a BB. And, that includes pipe scale, and, of course with river water, .... well, the stuff in raw river water is just too numerous to list-some of it live and some dead.

IF and I put that as a capitalized IF, you don't intend to put a first class strainer; and by first class I mean cleanable on line strainer system then don't use a P&F. If you make the right preparations other than the biological fouling mentioned by jistre, they should work fine. But then again, you would have to account for the same type of biological fouling in any Hx you used S&T of P&F.

I know of a nuclear plant that had several (something near double digits) large P&F's on Mississippi River water and were successful with it (near you jistre). So it can be done, but must be done carefully.

I was involved with the strainers at a hydro plant (I can't remember what the downstream Hx's were) on the Miss River (right upstream of you jistre), and they were a nightmare but mostly because the original designers never anticipated the silt loading that they would eventually see. Most of the problems were with the valving for the strainers, not the strainers themselves. Garden variety ball valves just weren't suited for this service. Their actuators wouldn't cut it initially until higher pedigree actuators were installed.

I have seen P&F's in unstrained clean water service clogged up (inlet channels completely full) of pipe scale from steel pipes upstream.

But, all that said, I wouldn't hesitate to use a P&F in such an installation, but it would be carefully and meticulously designed.

Also, P&F's aren't real tolerant of varying flows especially on the dirty side. Design your system to keep the flow up to design flow on the river water side and you will have less problems. Slowing the flow down allows what silt there is in the river water (strainers aren't 100% efficient - HA!) settle out in the small passages affecting heat transfer and service life. You may have no choice to let the flow vary on the engine side because the engine thermostats will have control of that. Keep the river water flow constant, however.

DO not try to design in a 'fouling factor'. That is a term for S&T's and works against P&F's. Adding a 'fouling factor' adds surface area (plates) and slows the velocity down in the plate passage channels. The secret of keeping the plate passage channels clean is keeping velocity high. Letting it drop by adding a 'fouling factor' or by varying the flow is GUARANTEED to plug up your Hx on the river water side.

I have also used the more open style of plates in industries like the sugar industry (just south of you jistre) where it is mandatory due to stuff in the syrup and viscosity reasons. This is probably not an answer for you shick as you are not having to deal with higher viscosity fluids albeit just as dirty. I don't recommend these for your application. Clean up the river water and use it for you needs.

rmw

 

[schick]

Thanks SNORGY!

it's actually a marine engine and heat exchanger that we're using and the plates are Titanium. Generally they're used on pleasure craft (fun boats) but we're looking at using it in an industrial application.

BTW, what is P+F? How large were the sulphur solids?

We're dredging (underwater excavation) and sometimes we have suspended dirt and silt in the raw water. That's why we're planning on using a centrifugal filter, unless someone has a better "proven" idea.

 

[SNORGY]

Schick:

P+F = Plate & Frame (Alfa-Laval, etc.)

Sulfur solids would be those that would typically be picked up by cyclonic separation (Krebbs etc.). Not sure how big they are individually on average, other than they are quite visible to the naked eye.

Please be cautious with my advice. I don't see any real busts in your propose application, but there are several folks on this site who are more knowledgeable with heat transfer components than I am. I am a generalist who can "make things work by doing a whole bunch of other stuff", but not a heat transfer component specialist.

Regards,

SNORGY.

 

[rmw]

I don't know if they still make it or not but Hayward had a rotating shoe type of self cleaning strainer that I would go looking for if I had your project. I have used it in some pretty nasty services and it usually treated me well.

Nice thing about it is that it will clean itself when it needs cleaning, not when someone decides to do it (or not.)

Titanium plates are an excellent choice. Your P&F (that is what Snorgy meant by P+F) vendor will be able to tell you what is the maximum partcle size the specific Hx for your application will pass.

rmw

 

[schick]

rmw

Thanks!! Super helpful.

We've got a separate pump planned for the raw water, and our equipment generally runs continuous (23-24 hr/day) at full speed. So I think we'll be ok. I'm not sure how close we are to being as dirty as the Miss but it would probably be comparable, and with the cyclonic filter we'll get the majority of the particulate.

 

[willard3]

I no longer use plate and frame HX when there is any question of water quality on either side.

P&F are more efficient (not much, really) but take forever to clean. Shell and tube does the same job and are easy to clean.

 

[rmw]

P&F's are superior when close approaches are required. If you don't need a close approach, S&T would be fine.

Actually, P&F's came to us from the dairy industry where there was the requirement to take the equipment apart for cleaning daily. S&T's just couldn't be cleaned to the dairy industries standard.

But that said, that doesn't mean I disagree with willard3. I am just not sure I'd make that statement about an S&T.

rmw