CO₂ and H₂O diluted oxy-fuel combustion for zero-emission power

Abstract

Concerns about climate change have encouraged significant interest in concepts for zero-emission power generation systems. These systems are intended to produce power without releasing CO2 into the atmosphere. One method to achieve this goal is to produce hydrogen from the gasification of fossil or biomass fuels. Using various membrane and reforming technologies, the carbon in the parent fuel can be shifted to CO2 and removed from the fuel stream, followed by direct CO2 sequestration. The hydrogen fuel can be used directly in gas turbines fitted with low-NO x combustors. A second approach to producing zero-emission power is to replace the nitrogen diluent that accompanies conventional combustion in air with either CO2 or H2O. In this concept, CO2 or H2O is added to oxygen to control combustion temperatures in oxygen-fuel reactions. In the absence of nitrogen, the primary combustion products for any hydrocarbon under lean conditions are then simply CO2 and H2O. Thus, merely cooling the exhaust stream condenses the water and produces an exhaust of pure CO2, ready for sequestration. The dilute oxy-fuel combustion strategy can be incorporated in power cycles that are similar to Brayton or Rankine configurations, using CO2 or H2O as the primary diluent respectively. While the relative merits of the various strategies to zero-emission power are the subject of various technical and economic studies, very little work has focused on defining the combustion issues associated with the dilute oxy-fuel option. In this paper, the expected combustion performance of CO2 and H2O diluted systems are compared. Experimental results from a high-pressure oxy-fuel combustor are also presented.

Oxyfuel combustion for CO2 capture in power plants

“…Richards et al (2005) calculate the equilibrium concentration of CO in the CES cycle combustion products to be 5-7 times lower than for CO 2 moderated combustion. At 1650 K, 10 bar and ϕ = 0.98 the equilibrium concentration of 12 ppmv is reached in 4 ms. For a CO 2 recycle, 200 ppmv in 20 ms are reported as in Section 4.…”

“…Though low emissions of CO and O 2 are favoured at low flame temperatures, a kinetic approach revealed that the equilibrium concentrations are not reached at a fixed residence time of 40 ms. Higher pressure reduces the equilibrium concentration due to Le Chatelier's principle and leads to faster reaction rates. Richards et al (2005) investigate the CO emissions of an oxyfuel gas turbine combustor with a combined network of perfectly stirred reactor and a plug flow reactor (PSR/PFR) model. For a recycle stream consisting mainly of CO 2 at 10 bar and a flame temperature of 1650 K the equilibrium concentration of 200 ppmv is reached in 20 ms for ϕ = 0.98 .…”

Laminar flame speeds of H 2 /CO with CO 2 dilution at normal and elevated pressures and temperatures

“…Therefore, it is essential to study the fundamental burning properties of syngas over a wide range of composition under representative operating conditions of advanced gas turbines. With the development of carbon capture and storage (CCS) technique [2], burning syngas with large amount of CO 2 becomes an effective way to reduce NO X emission (e.g. in oxy-fuel combustion).…”

Chemical kinetics mechanism for oxy-fuel combustion of mixtures of hydrogen sulfide and methane

“…It should be noted that AramcoMech 1.3 does not contain a model for formation of nitrogen oxides (NOx). However this is not expected to be a major problem when dealing with oxy-fuel combustion, since a number of studies have found NOx formation to be negligible for realistic O 2 purities [16][17][18].…”