Two novel oxy-fuel power cycles integrated with natural gas reforming and CO2 capture

Abstract

Two novel system configurations were proposed for oxy-fuel natural gas turbine systems with integrated steam reforming and CO 2 capture and separation. The steam reforming heat is obtained from the available turbine exhaust heat, and the produced syngas is used as fuel with oxygen as the oxidizer. Internal combustion is used, which allows a very high heat input temperature. Moreover, the turbine working fluid can expand down to a vacuum, producing an overall high-pressure ratio. Particular attention was focused on the integration of the turbine exhaust heat recovery with both reforming and steam generation processes, in ways that reduce the heat transfer-related exergy destruction. The systems were thermodynamically simulated, predicting a net energy efficiency of 50-52% (with consideration of the energy needed for oxygen separation), which is higher than the Graz cycle energy efficiency by more than 2 percentage points. The improvement is attributed primarily to a decrease of the exergy change in the combustion and steam generation processes that these novel systems offer. The systems can attain a nearly 100% CO 2 capture. r

Study on Co-combustion Characteristics of Superfine Coal with Conventional Size Coal in O<sub>2</sub>/CO<sub>2</sub> Atmosphere

“…During the O 2 /CO 2 combustion, coal is burnt in a mixture of O 2 and recycled flue gas (mainly CO 2 and H 2 O), to yield a rich CO 2 stream. Previous results have shown that the replacement of N 2 by CO 2 can cause significant differences in the area such as burning stability, char burnout, heat transfer and gas temperature profiles [4][5][6]. The flame propagation speed, flame stability and gas temperature in O 2 /CO 2 environment are lower and the unburned carbon content is higher than those in air environment.…”

A preliminary investigation of cryogenic CO2 capture utilizing a reverse Brayton Cycle

“…The net energy efficiency (produced power / heating value of natural gas) for such a system is predicted to be over 65%, and the associated required heat exchanger area is approximately 460 m 2 per MW of electricity produced [9] . The same group developed two other novel oxy-fuel power cycles integrated with natural gas, with predicted net energy efficiencies of 50~52% (including the additional energy needed to produce the oxygen), and a CO 2 capture rate of nearly 100% [10] . Studies for pre-combustion are also ongoing.…”

“…In order to capture 90% of the CO 2 , in the gas mixture into its liquid form, the process consumes about 0.395 MJ per kg of CO 2 with a resulting CO 2 purity of over 99% [13] . The advantages of cryogenic CO 2 capture techniques, as readily recognizable from the above examples, are: (1) the energy penalty of solvent regeneration and generated pressure drop can be neglected [4][5][6][7][8][9][10][11][12][13] ; (2) CO 2 can be captured in the liquid or solid phase, enabling compression without the huge energy consumption associated with gaseous compression, and providing a convenient means for storage and transport [4][5][6] ; (3) the compression, expansion and refrigeration technologies in the cryogenic CO 2 capture system are all relatively mature industrial processes, and can be easily utilized on an industrial-scale [10,13] ; (4) various refrigeration byproducts will be produced in some systems, such as high purity N 2 , and these can reduce the operation cost of the plant [14] . Nevertheless, to extract CO 2 from the other components in the flue gas (typically as N 2 , CO 2 , H 2 O, NO x , SO x ), a very low-temperature is required, resulting in the following problems [4][5][6][7][8][9][10][11][12][13] : (1) a large amount of energy is consumed for the refrigeration, leading to a high energy penalty for capture, and the process covers a large range of operating conditions from normal to supercritical states; (2) in the anti-sublimation processes, CO 2 will be frozen on the cold surfaces of the flow channels or heat exchangers, potentially causing several operational problems, such as plugging; (3) for the pre-combustion power plant and the oxy-fuel power plant, a large amount of additional energy is consumed in the hydrogen production or air separation unit; (4) acidic gas, such as NO x , SO x , may damage the devices, and shorten their operational life time.…”

Thermodynamic analysis of the advanced zero emission power plant

“…Currently the use of cryogenic air separation units is considered due to the requirement of high performance and sufficient purity of the oxygen. In the literature different concepts of the natural gas fueled units with oxy-combustion, such as [3][4][5], can be found. However, in most of presented structures the application of oxy-combustion involves a significant efficiency drop at the level of 7-9 p.p.…”