Abstract: The present document describes a boiler for heating a cold fluid with a hot fluid. The boiler comprises a lower drum, an upper drum, a plurality of right tubes for conveying the cold fluid, where each of the right tubes are fluidly connecting the lower drum and the upper drum, where the right tubes form a right wall and where each of the right tubes comprises at least one left inwardly extending portion extending toward a left wall and a plurality of left tubes for conveying the cold fluid, where each of the left tubes fluidly connect the lower drum and the upper drum, and where the left tubes form the left wall facing the right wall, where each of the left tubes comprises at least one right inwardly extending portion, each extending toward the right wall.

Abstract: A boiler comprises a boiler gas exhaust providing an exhaust for recuperated gases; and a secondary heat exchanger comprising: an economizer cold fluid inlet connected to a source of cold fluid; an economizer cold fluid outlet fluidly connected to the economizer cold fluid inlet and located thereabove, the cold fluid circulating upwardly from the economizer cold fluid inlet towards the economizer cold fluid outlet; a hot gas inlet for receiving the recuperated gases from the boiler gas exhaust; and a hot gas outlet fluidly connected to the hot gas inlet through the secondary heat exchanger, the recuperated gases circulating from the hot gas inlet toward the hot gas outlet; wherein the recuperated gases cross the secondary heat exchanger and exhaust by the hot gas outlet, the cold fluid being heated between the economizer cold fluid inlet and the economizer cold fluid outlet thereby resulting in a preheated fluid.

Abstract: The present document describes a boiler for heating a cold fluid with a hot fluid.