Abstract: A steam distributor includes a front screen equipped with steam perforations wherein the output area of at least some of the perforations can be adjusted to enable active control of the steam jet velocity. The steam velocity can be controlled independently of steam flow. The front screen is includes (i) a first plate that has a first set of apertures and (ii) a second plate that has a second set of apertures, wherein the second plate covers the first plate, and wherein the means fir varying the size of at least one of the perforations moves the first plate, the second plate, or both the first and the second plates in order to change the position of the first set of apertures relative to the second set of apertures.