Heat exchanger with by-pass

Claim 1

An in-line exhaust gas heat exchanger for use with a vertical exhaust stack having a lower portion below the heat exchanger and an upper portion above the heat exchanger, comprising: (a) a pair of concentrically spaced vertically disposed cylindrical segments forming a vertical central passageway having a diameter substantially equal to the inside diameter of the exhaust stack upper and lower portions, and a vertical annular passageway between the cylindrical segments having a cross-sectional area greater than that of the central passageway, both said passageways being in open communication with upper and lower portions of the exhaust stack at the respective ends of the heat exchanger, a pair of oppositely disposed coaxial upper and lower end coupling members attachable to the exhaust stack upper and lower portions respectively and a plurality of vertical load carrying stringers connected between the coupling members to support the weight of the upper exhaust stack; (b) fluid carrying heat exchange coils disposed in the annular passageway and having fluid inlet and outlet ports; (c) a temperature probe means in communication with the exhaust gas passing through at least one of said passageways; (d) a butterfly valve disposed in the lower end of the central passageway; (e) means operably connected to the butterfly valve and responsive to the output of the temperature probe means for controlling the position of the butterfly valve within preselected limits; and (f) said lower end coupling member being provided with a trough in communication with the annular passageway for trapping condensation moisture, and a drain attached to the lower portion of said trough and in communication with said trough for draining same; wherein the position of the butterfly valve may be controlled by preselected temperature limits detected by the temperature probe means.