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
