A steam accumulator stores heat as high-pressure saturated water charged by a boiler at peak pressure (P1). When batch process demand exceeds boiler capacity, the accumulator discharge control valve opens, lowering the vessel pressure toward header pressure (P2). The excess sensible enthalpy in the water instantly causes a portion of the liquid to flash into dry saturated steam (y = [hf1 - hf2] / hfg2), dampening boiler firing swings.

The upper 10% to 15% of the horizontal drum volume provides essential steam disengagement surface area. When pressure drops, steam bubbles nucleate violently throughout the entire water column (bulk boiling). If water level is too high, the surface area narrows and bubble rise velocity exceeds 1.5 ft/s, entraining liquid slugs directly into the process steam header (priming), which causes severe downstream water hammer.

The internal sparger is a submerged perforated pipe located near the bottom of the accumulator. It injects boiler steam directly into the water mass through hundreds of small nozzles, promoting intense thermal convection and ensuring the entire water volume reaches uniform saturation temperature without cold temperature stratification.

When an isolated steam accumulator cools down during a plant shutdown, the trapped steam condenses into liquid water, which occupies only 1/1600th of the vapor volume. This creates a deep vacuum (up to 29 in. Hg). Because pressure vessels are designed primarily for internal pressure, an unreinforced shell can buckle and implode unless certified for full vacuum per ASME UG-28 or equipped with dual vacuum relief valves.

Boilers forced to modulate rapidly to follow short batch peaks suffer incomplete combustion, high stack thermal losses, and thermal stress, degrading seasonal efficiency by 8% to 15%. A steam accumulator absorbs peak deficits and stores excess steam during lulls, allowing boilers to fire continuously at their peak efficiency baseline.