Steam injection and methane steam reforming to enhance performance of existing natural gas combined cycles


The growth in worldwide energy demand is currently facing a lot of difficulty for installing new power generation facilities due to the limited funding and implementation of stringent environmental regulations. As such, it is important to assess the energy and economic feasibility of upgrading such systems’ capacity for them to cope with future energy requirements. Basically, electricity generation can be boosted through the installation of new power plants or upgrading of existing facilities, with the latter being the best option with reference to the subject matter.

The number of natural gas combined cycle (NGCC) installations is increasing over time, credit to impressive technological advances. As such, an increase in plant efficiency and a concurrent reduction in investment cost has been reported. The vital role being to ensure power grid stability in the future.

Recently, Professor Roberto Carapellucci from the University of L’Aquila together with Dr. Lorena Giordano of the Italian National Agency for New Technologies, Energy and Environment proposed a new concept for upgrading existing NGCCs by integrating an additional unit based on gas turbine. This additional unit allows the production of steam to be injected into the existing NGCC combustor (Option A) or syngas from methane steam reforming. The syngas is used to partially replace the natural gas at the inlet of the existing gas turbine combustor (Option B), or even to feed the supplemental gas turbine (Option C). Irrespective of waste heat recovery route, the power output augmentation arises from the capacity of the additional gas turbine and the increased output of the existing NGCC. The latter comprises the additional power production of the gas cycle due to steam or fuel injection, and that of bottoming steam cycle, resulting from the greater exhaust gas flow rate entering the heat recovery steam generator. Their work is currently published in the research journal Energy.

Briefly, the study evaluated the feasibility to improve both the efficiency and power output of NGCCs, by comparing the upgrading options envisaged from the energy and economic points of view. The reference study case was represented by a single shaft NGCC, based on a heavy-duty gas turbine and a three pressure and reheat steam cycle. A preliminary sensitivity analysis was used to assess the influence of operating conditions of the additional unit on the energy and economic performances of marginal power production. Considering commercial gas turbines, further investigations address the design of upgrading options and the comparison of their techno-economic performances referred to the additional or the overall power productions. Finally, focusing on Option A, the part-load operation of the additional gas turbine is examined to evaluate penalties on marginal efficiency and marginal cost of electricity.

The researchers observed that, in Option A, the maximum power increase states at around 45%, due to constrains on the maximum allowable condenser overload (+15%). Conversely, options based on methane steam reforming (Options B, C) allow higher marginal performance of the repowered NGCC, because of the combined chemical and thermal heat recovery.

In summary, Carapellucci-Giordano study concluded that the Option A provides the best economic performance combined with the highest operational simplicity, while the Option C is the preferred technical solution for a greater increase in plant capacity. Furthermore, in option A, by applying a part-load strategy based on inlet guide vane angle and fuel control to the gas turbine of the additional unit, the repowered power plant undergoes a slight decrease in marginal efficiency but it still outperforms, from an economic point of view, the existing NGCC in the whole range of part-load operation.

About the author

Lorena Giordano is a permanent researcher at Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA).

She graduated cum lode in Environmental engineering at University of L’Aquila in 2007; in 2010, she received the PhD in Mechanical, Energy and Industrial Engineering from the same university. From 2011 to 2014, she was post-doctoral researcher at Department of Industrial and Information Engineering and Economics. Her research activity mainly focused on renewable energy islands with hydrogen storage, thermo-economic optimization of heat recovery steam generator in steam-gas combined cycles and integration of carbon capture technologies in fossil fuel power plants. From 2015 to 2017, she was post-doctoral researcher at Laboratoire Réactions et Génie des Procédés (Nancy, France), where she was involved in the research project EU-FP7 M4CO2. In this respect, she worked on techno-economic evaluation and life cycle analysis of membrane systems for post-combustion capture, with the aim to figure out innovative membrane processes, able to cope with technical targets of CO2 removal. In 2018, she was post-doctoral researcher in the Chemical Engineering Department of Delft University of Technology. She worked on the conceptual design of pre- and post-combustion CO2 capture systems based on advanced mixed matrix membranes within the European H2020 project MEMBER.

Her current research interests include techno-economic analysis of power generation systems based on renewable energy technologies, design and analysis of fossil-fuel power plants with reduced CO2 emissions, pre-and post-combustion carbon capture technologies in fossil fuel power plants and low-temperature waste heat recovery in industrial processes.

About the author

Roberto Carapellucci is Full Professor in Management of Energy Conversion Systems at the Department of Industrial and Information Engineering and Economics of the University of L’Aquila since December 2016. He has more than 30 years of teaching and research experience. Roberto teaches two courses at the B.Sc. Degree in Industrial Engineering and M.Sc. Degree in Mechanical Engineering. He has been author of more than 100 scientific papers on various topics, including advanced power generation, energy systems modeling, renewable technologies, carbon capture. He is referee for several international peer-reviewed journals. He received Awards from the American Society of Mechanical Engineering (ASME) for the role of Track Energy Organizer (15-18 topics, 35-45 sessions, 170-220 technical presentations) in the ASME International Mechanical Engineering Congress & Exposition in years 2016, 2018 and 2019. He has been a member of the Executive Committee of the ASME Advanced Energy Systems Division (AESD) since July 2019. He has been the chair of the Systems Analysis Technical Committee of the ASME AESD for years 2018-2019. He has been a member of the Systems Analysis Technical Committee of the ASME AESD since November 2011. He organized plenary presentations in International Conferences on the topics “Thoughts on the Future of Power Generation: A Low Carbon Perspective”, “Thoughts of the Future of Energy in Buildings: An HVAC Perspective”, “Metal Oxide-Based Thermochemical Redox Processes for Producing Solar Fuels and Storing Thermal Energy”.


Roberto Carapellucci, Lorena Giordano. Upgrading existing gas-steam combined cycle power plants through steam injection and methane steam reforming. Energy, volume 173 (2019) page 229-243.

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