A vaporizer is provided for vaporizing liquid in a fluid stream. The vaporizer
includes at least two heat exchangers serially arranged in a direction of flow
of the fluid stream through the vaporizer for vaporizing liquid in the fluid stream
in stages. The heat exchangers each comprise a first plurality of thermally conductive
flow channels through which the fluid stream flows and a second plurality of thermally
conductive flow channels through which a heating stream flows and which are in
heat exchange relationship with the first plurality of thermally conductive flow
channels. A liquid supply means is provided for adding liquid to a downstream heat
exchanger. The added liquid mixes with the vaporized stream exiting an upstream
heat exchanger for vaporization in the downstream heat exchanger.
