Waste heat boiler for offshore plant

The present invention relates to a waste heat boiler for an offshore plant, recovering sulfur which comprises a main body part having water contained therein to a specific height; an inlet formed on one side of the main body part to introduce high-temperature combustion gas passed through a combustion room; an outlet for discharging the combustion gas which has exchanged heat while passing the main body part; a plurality of tubes connected between the inlet and the outlet while being submerged in the water of the main body part to make high-temperature combustion gas exchange heat while passing; and partitions installed vertically at regular intervals in the main body part to form a plurality of cells with a small unit volume. The present invention prevents damage to the tubes by making the tubes for passing high-temperature combustion gas not exposed out of water because the water contained in the main body part of the waste heat boiler forms steps owing to the partitions even if the waste heat boiler is tilted or moved.