Effect of Rapid Steam Take-Off on Natural Circulation and Water Level in Boilers

Abstract

A theory is presented for predicting the transient behavior of bubbles in the downcomer and riser loop. It is found that a sudden drop in boiler pressure could seriously reduce the circulation velocity and this is attributed to steam formation in the downcomer tube. The reduction of the circulation velocity tends to prolong existence of individual bubbles in the water phase and therefore increases the water level swell. Transient behavior of circulation velocity in the riser, and water level responses in the steam drum were measured in a two-tube experimental boiler following a step increase in steam control-valve opening for various boiler pressures.