A closer look at the welded heat exchanger used at Rosneft helps prospective users understand how it can help in myriad applications.
The heat exchanger is built around a pack of corrugated heat transfer plates, welded alternately to form channels. The complete plate pack slides inside a four-column carbon steel frame bolted to pressure-retaining heads at the top and bottom. Four removable side panels contain the fluid inlet and outlet connections, and baffles direct the fluid media back and forth through the channels.
The exchanger’s corrugated plate pattern creates a high degree of turbulence. This results in heat transfer efficiency, with an overall greater heat transfer coefficient than that available from a corresponding shell-and-tube unit. This means the welded heat exchangers requires only 25 to 50 percent of the heat transfer area to provide the same effect as a corresponding tubular unit.
When the exchanger is used as a condenser, the vapor enters from the top of the unit and condenses on the cold plates while passing through the plate pack. The condensate exits at the bottom. The cooling media is forced through several passes with a series of baffles. This, together with the plate corrugations, boosts heat transfer efficiency and keeps fouling to a minimum.
In the refinery application, If the vapor contains noncondensable gases, a two-pass arrangement on the condensing side permits gas/liquid separation inside the exchanger, eliminating the need for a separator unit. The main condensation takes place in the first pass. Subcooling of the noncondensable gases takes place in the second pass, which also serves as a mist eliminator.
With its short flow path and large cross-section, the welded unit serves as a suitable thermosiphon reboiler. The feed enters at the bottom of the unit. When the liquid passes between the heated plates, it is brought to boiling point and a mixture of vapor and liquid leaves the unit through the outlet at the top.