BKU Kettle Type
U-Tube Exchangers

About 1,030 lb per hour of low-pressure steam for every 1,000,000 BTU per hour of boiling duty, using 970 BTU per lb latent heat. Boiling duty is the vapor rate times the latent heat of the process fluid, plus the sensible heat to bring feed up to its boiling point. Condensate collects in the lower tube pass and drains to the bottom nozzle on the front head, so the trap sits there and is sized for that flow with a margin for startup. An undersized trap floods the lower pass, the flooded tubes stop boiling, and kettle output falls off exactly when demand rises.

Wide, because the pool stays at its boiling point whatever the duty; the limit is on the heating side. At low load a steam-heated kettle has its control valve throttle steam pressure down, saturation temperature falls with it, and the temperature difference shrinks until boiling becomes uneven across the bundle. Hot oil turns down more gracefully because flow can be cut without losing temperature. Tell HeatX the lowest sustained load when you Request a Quote.

Because disengagement needs a wide liquid surface with a vapor space above it along the full bundle length, and only a horizontal shell provides both. Stand the same shell on end and the liquid surface shrinks to the shell cross-section, surface velocity jumps and carryover follows. A horizontal kettle also lets the weir hold a level over the entire bundle rather than over its bottom tubes only. Vertical thermosiphon reboilers exist, but they are a different exchanger with separation done in the column. For a U-tube kettle, plan a horizontal footprint with the front head clear for the bundle pull.

Square or rotated-square pitch, at or above the TEMA minimum of 1.25 times tube OD, with the open lanes left for vapor to escape upward. Triangular pitch packs more tubes in to the shell but closes the vertical lanes, so vapor generated on lower rows blankets the rows above and the upper tubes run at a worse coefficient than the rating assumed. Square pitch also leaves cleaning lanes for the scale that concentrating service builds on the outside of the tubes. On a kettle, tube count per shell diameter is the wrong figure to optimize; stable boiling on every row is the one that matters.

Only when downstream equipment cannot tolerate the entrainment a correctly sized vapor space still leaves, or when the shell cannot be made large enough. A mesh pad under the vapor outlet knocks out the fine droplets gravity will not, and it is cheap to add at build. It is not a substitute for disengagement height: a pad over a flooded or foaming surface loads up and its pressure drop climbs. Pads must also be removable for cleaning, which means a flanged access or a removable nozzle section designed in from the start.