**5. Conclusions**

Despite their harmful e ffects on the environment, fossil fuels will continue to be the primary source of power production. A comprehensive discussion of the technologies to reduce emissions from fossil fuels is presented in this review. Post-combustion carbon capture technology requiring separation is the best technology to retrofit the existing fossil fuel power plants. Pre-combustion carbon capture is more suitable in an integrated gasification combined cycle. A post combustion carbon capture process can be applied to the running power plants without much modification.

The separation of CO2 from the gas stream in these processes requires additional energy which leads to an increase of the electricity price. Several technologies are available for separating CO2 from the gas stream. Separation is less costly in precombustion processes because of the higher partial pressure of CO2 in the gas stream. Among the separation technologies, the absorption process has become almost matured, but it requires attention to corrosion of equipment and high cost for regeneration of the solvent. An adsorption process for separation cannot be applied at large scales due to the low CO2 adsorption and capacity and influence of gases on the adsorbents. New adsorbents should be developed to remove the barriers. Membrane technology is less energy intensive than other processes, though it is less e ffective at low concentration of CO2. Also, more research is necessary to determine membrane behavior at high capacity. Formation of clathrate hydrate to separate CO2 from gas mixture needs more attention. Proper additives or promoters should be developed to use in the process to make this process more competitive.

Carbon capture with water condensation is economically more viable to implement due to a simpler design and higher plant e fficiency and better environmental aspects for the life cycle compared to the pre- and post-combustion capture methods. LCA shows that oxyfuel combustion has much less effect on the environment compared to other methods. The combustion characteristics are di fferent in this case from traditional combustion. Due to the di fferent characteristics, further research is necessary to make this technology competitive with others. There still is limited knowledge of many important aspects of oxy fuel combustion. Along with the theoretical achievement, it is necessary to find more experimental data in order to validate theoretical models.

Further research is necessary to properly understand the oxy fuel combustion-based near-zero emission power cycles like the Allam cycle. Successful commercial implementation of these cycles will be a significant step in reducing emissions, thus meeting the challenge of global climate change. Chemical looping combustion has also the potential to become a cost-e ffective way to reduce emissions. It requires attention as a novel technology in this sector. The availability of suitable oxygen carriers and appropriate designing of the reactors can make this process comparable with others. LCA of these new methods is also necessary to properly understand their impact on the environment.

**Author Contributions:** Conceptualization, N.S.S. and Y.H.; methodology, Y.H.; investigation, N.S.S.; writing—original draft preparation, N.S.S.; writing—review and editing, Y.H.; supervision, Y.H.

**Funding:** This research received no external funding.

**Acknowledgments:** The research fund provided by Central Michigan University is gratefully acknowledged. The authors wish to express their gratitude to the anonymous reviewers for providing constructive feedback.

**Conflicts of Interest:** The authors declare no conflict of interest.
