Method of controlling a process of generating power by oxyfuel combustion

Abstract

A method of controlling a process of generating power in a power plant with a boiler by combusting carbonaceous fuel with substantially pure oxygen. At full load conditions, the method includes introducing a first carbonaceous fuel feed stream into a furnace, introducing a first substantially pure oxygen feed stream into the furnace for combusting the first carbonaceous fuel feed stream with the oxygen, and recirculating a portion of the exhaust gas discharged from the furnace at a first recirculation flow rate to the furnace, to form, together with the first substantially pure oxygen feed stream, a first inlet gas stream having a predetermined average oxygen content, thereby discharging exhaust gas from the furnace at a first discharge flow rate. In second load conditions, corresponding to at most 90% load, the method includes introducing a second carbonaceous fuel feed stream into the furnace, introducing a second substantially pure oxygen feed stream into the furnace for combusting the second carbonaceous fuel feed stream with the oxygen, and recirculating a portion of the exhaust gas discharged from the furnace at a second recirculation flow rate to the furnace, to form, together with the second substantially pure oxygen feed stream, a second inlet gas stream, so as to discharge exhaust gas from the furnace at a second discharge flow rate, and controlling the second recirculation flow rate to be from the first recirculation flow rate to a value providing the second discharge flow rate to be substantially as high as the first discharge flow rate.

Description

technical field [0001] The present invention relates to methods of controlling power generation processes through oxyfuel combustion. More particularly, the invention relates to controlling oxyfuel combustion under varying load conditions. Background technique [0002] Oxygen-enriched combustion is proposed for removal of CO from the exhaust of power generation boilers such as pulverized coal (PC) boilers or circulating fluidized bed (CFB) boilers 2 one of the methods. Oxy-fuel combustion is based on burning a carbonaceous fuel with substantially pure oxygen, typically at least 95% pure, so that carbon dioxide and water are the major constituents of the exhaust gas emitted by the boiler. Thus, when fuel is combusted with air, carbon dioxide can be captured relatively easily without having to separate it from the nitrogen-based gas stream. [0003] The oxygen feed rate and fuel feed rate into the combustion system are regularly controlled in order to obtain nearly complete...

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Problems solved by technology

[0008] For oxyfuel combustion, especially when the mass flow of the exhaust gas is less than that of air combustion, operation at low loads can lead to a distorted flow pattern of the exhaust gas, increasing the risk of runnability problems, e.g. caused by the low velocity region of the exhaust passage Problems caused by excessive dirt or dust accumulation

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