Staged oxy-fuel natural gas combined cycle

Abstract

Exhaust gas recirculation (EGR) in conventional natural gas-fired oxy-combustion cycles is required to maintain the combustion temperature at an allowable level. However, EGR is not beneficial from the system performance perspective. It is difficult to achieve in oxy-fuel cycles due to the high pressure and increased pressure drop in such systems. Consequently, alternative options to control the combustion temperature need to be considered. In this study, staged oxy-fuel natural gas combined cycle (SOF-NGCC) was proposed, which does not require EGR, and its feasibility was evaluated. A process model was developed in Aspen Plus in order to evaluate the thermodynamic performance of the proposed system and to benchmark it against the Allam cycle and conventional NGCC. The optimum net efficiency of the proposed cycle (47.63-51.32%) was shown to be lower than that for Allam cycle (54.58%) and the conventional NGCC without post-combustion capture (PCC) (56.95%). However, the SOF-NGCC is less complex and requires smaller equipment than the Allam cycle. This is mostly because the combined volumetric flow rate into expanders in both topping and bottoming cycles is approximately 25% of that estimated for the Allam cycle. Moreover, with a backpressure of 35 bar, no further compression is required prior to the CO 2 purification unit.

Techno-economic-environmental assessment of biomass oxy-gasification staged oxy-combustion for negative emission combined heat and power

“…The considered BOXS-CC process consists of a syngas gasification section and two power generation sections: (1) the staged oxy-combustion power cycle and (2) the sCO2 cycle. The power generation sections have been previously validated and investigated extensively by Khallaghi et al [19,21]. The accuracy of the gasification model used in this study is validated based on the wood chip oxy-gasification reported by Dimitriou et al [33].…”

“…To improve the performance of the BOXS-CC system, a sensitivity analysis was performed on the split fraction ( ) in the sCO2 cycle, gasification temperature and combustion temperature. It is worth noting that the effects of the pressure and temperature in the sCO2 cycle have been extensively analysed in the literature [19,21].…”

“…Yet, in this case, the air separation unit (ASU) operation is necessary that increases the capital cost of the plant [18], which is a disadvantage to its commercialisation. The concept of staged combustion has been applied to the natural gas-fired oxy-combustion combined cycle by Khallaghi et al [19]. Such an oxy-combustion cycle was shown to have a comparable efficiency (51.2%) to the state-of-the-art NG-fired oxy-combustion cycles, such as the Allam cycle (55%) [20].…”

Integrated Coproduction of Power and Syngas from Natural Gas to Abate Greenhouse Gas Emissions without Economic Penalties

“…Here, endothermic reforming utilizes the sensible heat of combustion products and can be formally represented using one partial oxidation reactor, as shown in Figure 4 . Compared to the staggered oxy-fuel combustion in some consecutive chambers where oxygen and fuel are distributed in a way to reach maximum admissible temperature in each chamber, followed by an interstage heat transfer “through the wall” to water 17 or supercritical CO 2 , 18 the staggered combustion shown in Figure 5 is controlled by the catalytic endothermic reaction accepting combustion products as its reactants. Both methods help in reducing the recirculation of exhaust gases (combustion products) per unit of released heat to control the maximum combustion temperature, resulting in a more compact unit without loss in efficiency.…”