MULTI TUBULAR HEAT EXCHANGER

PROBLEM TO BE SOLVED: To dispense with a pressure vessel as storage tank of steam drain water by preventing possible corrosion of heat exchanger tubes. SOLUTION: There are arranged a shell 2 through which a fluid to be heated passes, first heat exchanger tubes 4 which are arranged on the upstream side end part in the direction of the fluid to be heated flows in the shell 2 while a heated fluid passes therethrough, and second heat exchanger tubes 5 which is arranged at a part except for the upstream side end part in the direction of the fluid to be heated flows in the shell 2 while the heated fluid passes therethrough. Steam fed into the second heat exchanger tubes 5 is condensed while passing through the heat exchanger tubes 5 and a steam drain water thus obtained flows through the first heat exchanger tubes 4. A fluid to be heated on the side of the shell 2 is heated utilizing latent heat as obtained when the steam flowing through the second heat exchanger tubes 5 is condensed. The fluid to be heated on the side of the shell 2 is heated utilizing latent heat of the steam drain water flowing through the first heat exchanger tubes 4.