Oxyfuel combustion

Carbon dioxide capture and storage is especially studied in connection with electricity generation, where different technology routes - post-combustion capture, pre-combustion capture and oxyfuel combustion - are under research and development. Carbon dioxide capture is also crucial in connection with hydrogen production... 

Steam power plants with oxyfuel combustion (the fuel is combusted with a mixture of CO2 and pure O2) CO2 is captured from the flue gas. 

Oxyfuel-combustion. The fuel is converted to heat in a combustion process. This is achieved with pure oxygen as an oxidiser. Mostly C02 and water vapour are produced in the flue gases, and thus C02 can be easily separated by condensing the water vapour. 

There are three main ways to capture C02 in the NGCC process post-combustion C02 capture, oxyfuel combustion, and precombustion C02 capture. 

In oxyfuel combustion, the natural gas is combusted with a concentrated oxygen stream (-95% 02). The flue gas from the combustion process is not diluted with N2 but consists of mainly C02 and steam. The steam in the flue gas can be condensed, and C02 can be sent direcly to the sequestration plant without further separation. 

Figure 11.10. Schematic representation of an NGCC power plant with Graz (oxyfuel combustion) cycle.

The primary challenge facing the oxyfuel combustion with ASU is the requirement of advanced GTs that use C02/H20 as the working fluid, which has different expansion characteristics than nitrogen used in conventional turbines. Existing GTs... 

Figure 11.13. Schematic representation of the AZEP (oxyfuel combustion) concept. HX, heat exchanger BFW, boiling feed water.

Oxyfuel combustion with flue gas recirculation represents a method of CO2 capture that could be implemented today. In this technique, input air is replaced by a mixture of recycled nitrogen-free flue gas (mainly CO2) and pure oxygen. The recirculated CO2 maintains an optimal oxygen concentration in intake gas, which, for a retrofit, would be near that of ambient air. The major cost and energy penalty in such a plant results from the operation of the oxygen plant, which consumes approximately one-third of the electricity output of the power station. At the current price of oxygen (US 4 per 100 the oxygen... 

To avoid the surface catalytic effects, a water-cooled probe must be used when sampling high temperature combustion products. This is of particular importance to oxyfuel combustion where measured species concentrations are much higher due to the elimination of nitrogen. Recommended probe materials and cooling requirements to avoid reaction of the various gases inside the probe are given elsewhere [48]. 

Oxyfuel combustion, where coal is burned in oxygen rather than air, means that the flue gas is mostly CO2 and hence it can more readily be captured by amine scrubbing—at about half the cost of capture from conventional plants. 

Jordal, K., Anheden, M., Yan, J., and Stromberg, L. 2004. Oxyfuel combustion for coal-fired power generation with CO2 capture—Opportunities and challenges. Proceedings of Greenhouse Gas Control Technologies Conference, GHGT-7, Vancouver, British Columbia, Canada, September 5-9. 

Tan, X., Li, K., Thursfield, A. and Metcalfe, I.S. (2008) Oxyfuel combustion using a catalytic ceramic membrane reactor. Catalysis Today, 131,292-304. 

For gas combustion processes, the lower-energy flame spray process uses oxyfuel combustible gas as a heat source to melt the coating material, which may be in the form of rod, wire, or powder. In the higher-energy, high-velocity oxyfuel combustion spray (HVOF) technique, internal combustion of oxygen and fuel gas occurs to produce a high-velocity plume... 

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