Compact high-efficiency boiler and method for producing steam

A method for producing steam in a boiler comprising:

• a lower drum adapted to receive a fluid;
• an upper drum having a heated fluid outlet;
• a plurality of conduits adapted to transfer fluid from the lower drum to the upper drum;
• a combustion chamber having walls comprising at least some of the plurality of conduits;
• a first heat transfer chamber having walls comprising at least some of the plurality of conduits;
• and
• a second heat transfer chamber positioned below the first heat transfer chamber, the second heat transfer chamber having walls comprising at least some of the plurality of conduits;
• the method comprising:
• introducing a heated gas stream to the combustion chamber and heating the fluid in the conduits that comprise the walls of the combustion chamber;
• passing the heated gas stream from the combustion chamber to the first heat transfer chamber and heating the fluid in the conduits that comprise the walls of the first heat transfer chamber;
• passing the heated gas stream from the first heat transfer chamber to the second heat transfer chamber, below the first heat transfer chamber, and heating the fluid in the conduits that comprise the walls of the second heat transfer chamber;
• discharging the heated gas from the second heat transfer chamber;
• and
• generating heated fluid in at least some of the plurality of conduits that comprise the walls of at least one of the combustion chamber, the first heat transfer chamber, and the second heat transfer chamber.