GAS INTRODUCTION HOOD

PROBLEM TO BE SOLVED: To restrict the capacity of a gas introduction hood for a double pipe heat exchanger for cooling decomposed gas to be small to the utmost. SOLUTION: The foregoing double pipe heat exchanger includes many headers having an ellipsoidal cross section, and the headers 3 is connected with a bottom plate 5 that forms an upper cover of a gas introduction hood. The gas introduction hood includes an inside lining 11, an inside contour 13 of which lining forms a central inner space 12 which space is open, expanded toward the bottom plate 5. The lining 11 extends continuously through a flange-equipped surrounding cylinder 6 fixed to a lower surface of the bottom plate 5, and the inside contour 13 of the lining 11 extends continuously up to the bottom plate 5.