Patent ID: 8006651

Claim:
An economizer for installation in a flue gas stream to recover heat energy from the flue gas stream, the economizer comprising: a flow duct having an inlet end and an outlet end, the flow duct defining a primary flow passage for flue gas traveling in an upward direction; an inner shell arranged about the flow duct to define a secondary flow passage for flue gas traveling in a downward direction, wherein the flow duct includes at least one redirection port for providing flow communication between the primary flow passage and the secondary flow passage; a damper arranged in the primary flow passage above the at least one redirection port, the damper redirecting upwardly traveling flue gas through the at least one redirection port and into the secondary flow passage, wherein the redirected flue gas travels in a downward direction through the secondary flow passage; a bundle of heat exchange tubes enclosed within the inner shell in the secondary flow passage, the heat exchange tubes carrying a heat exchange medium, wherein the flue gas interacts with the bundle of heat exchange tubes as the flue gas travels in the downward direction through the secondary flow passage such that condensate is formed, the condensate flowing in the downward direction by force of gravity; and an outer shell arranged about the inner shell to define a tertiary flow passage for flue gas; the inner shell having a discharge opening below the bundle of heat exchange tubes for providing flow communication between the secondary flow passage and the tertiary flow passage; wherein the flow duct includes at least one merge port above the damper for providing flow communication between the tertiary flow passage and the primary flow passage, whereby cooled flue gas reenters the primary flow passage.