Abstract: Disclosed herein are a fluid sand falling type circulating fluidized bed boiler with a plurality of risers for preventing erosion and corrosion of water tubes and increasing combustion efficiency, and a method of operating the same. The fluid sand falling type circulating fluidized bed boiler with a plurality of risers includes a boiler section into which fuel and oxidizer are injected, a riser section connected to the boiler section so that the fuel and fluid sand supplied from the boiler section are introduced from the bottom of the riser section and flow up, and a relay section provided on the boiler section to supply the fluid sand having passed through the riser section to the boiler section, wherein the fuel is injected from the top of the boiler section and burned while flowing down therein.

Abstract: A boiler for generating steam and/or hot water is provided having a tank containing water, an outlet located proximal to the top of the tank, and a return inlet located proximal to the bottom of the tank. A substantially horizontal combustion conduit in heat transfer relationship with the water extends through the tank proximal to the outlet. A heat source in communication with the combustion conduit heats and drives the heated gas into the combustion conduit. A set of fire conduits in heat transfer relationship with the water and in communication with the combustion conduit, extend though said tank below the combustion conduit. When heated gas is driven into the combustion conduit, the heated gas flows through the combustion conduit, and then flows downwardly and then in a substantially transverse through the fire conduits, and heat is transferred to the water as the heated gas flows through the combustion conduit and fire conduits.