A boiler is disclosed in which the furnace is divided into a lower furnace and an upper furnace. The lower furnace uses water-cooled membrane walls, while the upper furnace uses steam-cooled membrane walls that act as superheating surfaces. A steam-cooled circuit includes a steam separator, a primary superheater, and the steam-cooled membrane walls of the upper furnace. During start-up, a diversion path is opened that reduces dry steam flow through the primary superheater and increases dry steam flow through the steam-cooled membrane walls of the upper furnace. This protects the steam-cooled membrane walls from excessive thermal stresses during start-up.

A boiler is disclosed in which the furnace is divided into a lower furnace and an upper furnace. The lower furnace uses water-cooled membrane walls, while the upper furnace uses steam-cooled membrane walls that act as superheating surfaces. A steam-cooled circuit includes a steam separator, a primary superheater, and the steam-cooled membrane walls of the upper furnace. During start-up, a diversion path is opened that reduces dry steam flow through the primary superheater and increases dry steam flow through the steam-cooled membrane walls of the upper furnace. This protects the steam-cooled membrane walls from excessive thermal stresses during start-up.

Transition castings are disclosed which comprise a steam tube, a water tube, and a pass-through tube, which are joined together by membranes. The ends of the tubes on one vertical end are aligned in a plane, while the ends of the tubes on the other vertical end are aligned in alternating planes, or put another way are angled instead of being in a straight line. The transition castings are used in a transition section of a boiler in which the furnace is divided into a lower furnace and an upper furnace. The lower furnace uses water-cooled membrane walls, while the upper furnace uses steam-cooled membrane walls that act as superheating surfaces. The transition section joins the lower furnace and the upper furnace together.

Transition castings are disclosed which comprise a steam tube, a water tube, and a pass-through tube, which are joined together by membranes. The ends of the tubes on one vertical end are aligned in a plane, while the ends of the tubes on the other vertical end are aligned in alternating planes, or put another way are angled instead of being in a straight line. The transition castings are used in a transition section of a boiler in which the furnace is divided into a lower furnace and an upper furnace. The lower furnace uses water-cooled membrane walls, while the upper furnace uses steam-cooled membrane walls that act as superheating surfaces. The transition section joins the lower furnace and the upper furnace together.

A boiler includes an upper steam drum, an optional intermediate drum, and a lower drum. Each drum is divided by an internal divider into a clean section and a concentrated section. Downcomers connect the upper steam drum to the lower drum, and tubes are connected to convey a heated steam-water mixture from the lower drum into the upper steam drum (through the optional intermediate drum, if provided). An optional superheater has an input terminal connected to receive steam from the clean section of the upper steam drum. An attemperator may be provided to attemperate superheated steam output from an output terminal of the superheater, and the attemperation fluid may optionally be provided from the concentrated side of the upper steam drum.

A boiler includes an upper steam drum, an optional intermediate drum, and a lower drum. Each drum is divided by an internal divider into a clean section and a concentrated section. Downcomers connect the upper steam drum to the lower drum, and tubes are connected to convey a heated steam-water mixture from the lower drum into the upper steam drum (through the optional intermediate drum, if provided). An optional superheater has an input terminal connected to receive steam from the clean section of the upper steam drum. An attemperator may be provided to attemperate superheated steam output from an output terminal of the superheater, and the attemperation fluid may optionally be provided from the concentrated side of the upper steam drum.

An arrangement in a recovery boiler having a furnace for combusting waste liquor and a flue gas duct comprising vertical flue gas channels, at least part of which is provided with heat recovery units for recovering heat from flue gases. The heat recovery units have a width of substantially the width of the flue gas duct, whereby downstream of the furnace the first flue gas channel is provided with a superheater. In addition to the superheater, the first flue gas channel is provided with one of following heat recovery units: an economizer, a boiler bank, or a reheater. The superheater and a second heat recovery unit are located one after the other in horizontal introduction direction of the flue gas, so that in a flue gas channel the flue gas flows in the vertical direction downwards and heats the superheater and the second heat recovery unit simultaneously.

An arrangement in a recovery boiler having a furnace for combusting waste liquor and a flue gas duct comprising vertical flue gas channels, at least part of which is provided with heat recovery units for recovering heat from flue gases. The heat recovery units have a width of substantially the width of the flue gas duct, whereby downstream of the furnace the first flue gas channel is provided with a superheater. In addition to the superheater, the first flue gas channel is provided with one of following heat recovery units: an economizer, a boiler bank, or a reheater. The superheater and a second heat recovery unit are located one after the other in horizontal introduction direction of the flue gas, so that in a flue gas channel the flue gas flows in the vertical direction downwards and heats the superheater and the second heat recovery unit simultaneously.

A modification of a power boiler is disclosed, which comprises water walls enclosing the furnace for heating water and producing steam; a superheater system provided above the furnace for superheating steam; an additional superheater mounted in the furnace for further superheating steam from the superheater system. A modifying method of a power boiler is also disclosed, which comprises steps of mounting an additional superheater on water walls in a furnace; connecting an output of a superheater system to an inlet of the additional superheater; and connecting an outlet of the additional superheater to a turbine for producing power at an improved plant heat rate.

A modification of a power boiler is disclosed, which comprises water walls enclosing the furnace for heating water and producing steam; a superheater system provided above the furnace for superheating steam; an additional superheater mounted in the furnace for further superheating steam from the superheater system. A modifying method of a power boiler is also disclosed, which comprises steps of mounting an additional superheater on water walls in a furnace; connecting an output of a superheater system to an inlet of the additional superheater; and connecting an outlet of the additional superheater to a turbine for producing power at an improved plant heat rate.