Fluidized bed combustion system and method utilizing capped dual-sided

Abstract

A fluidized bed combustion system and method for combusting particulate fuel such as coal together with a sorbent material such as limestone to heat a pressurized liquid and generate saturated vapor, such as steam. The combustion system utilizes at least one concentric dual-sided riser-downcomer unit having a central riser passageway and a concentric outer downcomer passageway located above a dense phase fluidized bed in an enclosure module, the downcomer being configured for directing particulate solids back to the bed. The unit inner and outer passageway surfaces each include a heat exchange panel containing the pressurized liquid for absorbing heat from combustion of the fuel and generating the vapor such as pressurized steam. Primary air is provided below the fluidized bed, while secondary air is provided into the riser passageway. The coal feed particles are substantially completely combusted during their passage through the circulating loop passages, and flue gas is passed outwardly through a cyclone separator, from which any unburned solids are returned to the fluidized bed. The resulting ash and spent limestone are withdrawn from the lower portion of the fluidized bed. Pressurized saturated steam is withdrawn from the unit, while particulates are removed from the flue gas.