Abstract: An evaporation cycle of a natural circulation steam generator. An evaporator is in flow connection with a downcomer pipe and includes a first evaporative section and a second evaporative section connected in parallel with the first evaporative section and arranged at a higher level than the first evaporative section. The evaporator cycle is not associated with another external source of motive force than heat from the gas flow to assist the flow of the water in the evaporator, and the evaporator has a vertically extending outlet collector for collecting the steam and water from the first and second evaporative sections to the riser pipe. The outlet collector includes a lower portion and an upper portion above the lower portion. The first evaporative section is in direct flow connection with the lower portion and the second evaporative section is in direct flow connection with the upper portion.

Abstract: An evaporation cycle of a natural circulation steam generator. An evaporator is in flow connection with a downcomer pipe and includes a first evaporative section and a second evaporative section connected in parallel with the first evaporative section and arranged at a higher level than the first evaporative section. The evaporator cycle is not associated with another external source of motive force than heat from the gas flow to assist the flow of the water in the evaporator, and the evaporator has a vertically extending outlet collector for collecting the steam and water from the first and second evaporative sections to the riser pipe. The outlet collector includes a lower portion and an upper portion above the lower portion. The first evaporative section is in direct flow connection with the lower portion and the second evaporative section is in direct flow connection with the upper portion.

Abstract: A method of and a system for combusting fuel in an oxyfuel combustion boiler. Fuel is fed to a furnace of the boiler. Oxidant gas that includes a mixture of substantially pure oxygen and recycled flue gas is fed to the furnace, prior to the feeding of the oxidant gas. At least a portion of the oxidant gas is preheated to generate preheated oxidant gas. The fuel is combusted with the oxidant gas in the furnace so as to generate steam and to produce the flue gas, and at least a portion of the steam is superheated to generate superheated steam. The preheating of the at least a portion of the oxidant gas is performed by using a heat exchanger that transfers heat from a portion of the superheated steam to the oxidant gas.