Plate Heat Exchangers for Vapor Condensing

Yes, a plate exchanger condenses vapor well when the pressure is at or above atmospheric, the vapor is clean, and the duty rewards a close approach. A 2,000 lb/hr flash steam duty at 2 psig condensed against 85 F tower water fits in a frame about 3 ft tall, where a shell-and-tube unit would run 10 ft long. The limit is vapor-side pressure drop, and the quickest screen is port velocity: with the inlet port carrying the full vapor flow above about 100 ft/s, the drop will exceed what most low-pressure services can give up. Size the port first, then the plates.

Because the same mass of vapor occupies far more volume as pressure falls, and velocity through the narrow channels climbs until pressure drop consumes the vacuum. Steam at atmospheric pressure takes about 27 cubic feet per pound; at 2 psia it takes about 174, so a plate pack passing 1,000 lb/hr sees more than six times the velocity and roughly forty times the pressure drop. A loss of 0.5 psi across the condenser raises the process pressure by a quarter of its absolute value. Welded plate units push the envelope into moderate vacuum with larger ports, but deep vacuum duty stays with shell or spiral designs.

Gasketed packs open and grow, brazed packs are sealed and inexpensive, and welded packs are sealed and tough; the elastomer, the braze alloy or the plate metal sets each one's envelope. A gasketed unit with nitrile or EPDM gaskets stops near 300 F and a few hundred psig and must be compatible with the vapor and the CIP solution. A copper-brazed unit tolerates about 450 F but cannot see ammonia or chloride-rich condensate, and cannot be opened once fouled. A welded unit handles 600 F, higher pressures and aggressive solvents at two to three times the price. Choose by the chemistry first and the service temperature second.

Badly, because a channel gap of a few millimeters bridges quickly, and a plugged channel disappears from the surface count with no outside sign other than rising pressure drop. On condensing duty the vapor side is usually the clean one, so the risk sits on the coolant: tower water with silt or biological growth fouls plate channels in months. Keep a strainer with openings smaller than half the channel gap on any plate condenser, and on gasketed units plan on opening and pressure washing at a set interval. Vapor carrying solids, polymer or fibers should not go into a plate at all.

Yes, in a plate pack noncondensable gas spreads unevenly across the parallel channels, so some channels fill with gas and stop condensing while the rest carry the whole duty. From outside you see rising condensing pressure at a steady vapor rate, which looks like fouling and resists diagnosis. Give the condenser a vent at the gas-rich end of the pack and size it for the expected gas flow, and state the noncondensable fraction on the data sheet so the plate pattern and port arrangement are chosen for it. Above a few percent gas by mass, a tube bundle with a defined vent zone is the safer design.

Yes, if the frame was ordered with spare tightening length and the ports and nozzles were sized for the larger vapor flow from the start. Adding plates raises surface but not port diameter, so a frame built for 1,000 lb/hr whose ports already run near the velocity limit cannot grow to 1,500 lb/hr without pushing vapor-side pressure drop past the limit. Specify the future duty when buying the frame and the port size follows. Adding plates also changes the channel count per pass, so the arrangement must be re-checked for condensate drainage rather than simply inserted into the existing pack.