Abstract: A fluid bed boiler and combustion method are provided having a first fast bed combustion zone followed by a second slow bed combustion zone. Coal, as a typical fuel, and limestone are fed to the first zone, where the coal undergoes combustion and sulfur is captured by the limestone. The solids which flow from the top of the first combustion zone are separated and introduced into a low velocity "slow" bubbling fluid bed in which arrays of heat exchange tubes are immersed. Additional heat transfer to water can be achieved by employing water walls for the first fast bed combustion zone.

Abstract: Apparatus for pulsing the flow of the liquid between the trays of a distillation column with only a small change in liquid level. In the preferred embodiment, a dome-like capping plate is mounted over the upper end of a downcomer conduit and overlaps the portion of the downcomer which extends above the fractionation tray as a weir to form a sealed liquid passageway having the shape of an inverted U. A siphon which starts when liquid is pushed over the top of the weir is broken when the liquid level on the tray falls to the lower end of a U-shaped conduit communicating with the upper volume of the capping plate.