An improved heat exchanger which resists fouling of the heat exchange surface by minimizing the temperature difference between the heat exchanger surface and the fluid stream in contact with the heat exchange surface. In one embodiment, a heat exchanger comprises an outer shell, the outer shell comprising a first inlet operable to pass a first fluid stream, an inner shell at least partially disposed within the outer shell, the inner shell comprising a second inlet and an outlet operable to pass the first fluid stream, and a heat exchange surface comprising a plurality of tubes operable to pass a second fluid stream.