Seyfettin Can Gulen

Modern heavy duty industrial gas turbines in combined cycle configuration, with rated efficiencies (at ISO base load) above 60% net LHV, are expected to play a significant role in reducing the carbon footprint of utility scale electricity generation. Even without postcombustion capture (PCC), simply switching from coal-fired generation to natural gas-fired generation reduces carbon dioxide emissions by 60% (on a kg per MWh of generation basis). In simple cycle mode, with efficiencies above 40% net LHV and startup times around 20 min, 300–400+ MW gas turbines can easily serve as peakers to support variable renewable resources, i.e., wind and solar. In this paper, a close quantitative look is taken at the capabilities of gas turbines firing natural gas, hydrogen, or a blend thereof, both in simple and combined cycle configurations. Furthermore, using published data, first-principles calculations, and software simulations, it will be shown that the gas turbine constitutes an efficient and cost-effective technology, with and without carbon capture, as a key player in decarbonization of the electric power sector.

In this article, a close look is taken at the state-of-the-art in steam turbine and steam (Rankine) cycle technology within the framework of conventional steam and gas turbine combined cycle power plants, specifically, the bottoming steam (Rankine) cycle of the latter. Using the second law of thermodynamics and the concept of exergy as a guide, cycle and technology factors are calculated to provide a simple but precise (and unassailable) yardstick to assess where the technology was, where it is at present, and how much farther it can go. In addition, the study takes a critical look at an emerging technology, supercritical CO₂ cycle, that is being touted as a serious contender for steam turbine’s place in the fossil fuel-fired electric power generation portfolio—as a standalone system or as a waste heat recovery capacity (i.e., combined cycle).

Contains discussion and author closure of GTP-17-624.

A detailed look at the gas turbine (GT) technology over the last three decades clearly shows that an asymptotic limit is reached in thermal efficiency in combined cycle (CC) configuration. There is little reason to expect a technology leap anytime soon to change this appreciably as long as the industry sticks to the classic Brayton cycle configuration and the brute force approach of ever higher turbine inlet temperatures (TITs). The changing landscape of electric power generation, especially integration of fossil fuel fired technologies with renewable generation and wide variation in natural gas prices, suggests that it is time to look at the direction of future development efforts differently. This paper looks at the need of a paradigm shift in GT CC technology using thermodynamic and economic arguments.

This paper describes a gas turbine combined cycle (GTCC) power plant system, which addresses the three key design challenges of postcombustion CO2 capture from the stack gas of a GTCC power plant using aqueous amine-based scrubbing method by offering the following: (i) low heat recovery steam generator (HRSG) stack gas temperature, (ii) increased HRSG stack gas CO2 content, and (iii) decreased HRSG stack gas O2 content. This is achieved by combining two bottoming cycle modifications in an inventive manner, i.e., (i) high supplementary (duct) firing in the HRSG and (ii) recirculation of the HRSG stack gas. It is shown that, compared to an existing natural gas-fired GTCC power plant with postcombustion capture, it is possible to reduce the CO2 capture penalty—power diverted away from generation—by almost 65% and the overall capital cost ($/kW) by about 35%.

In 1992, United States Department of Energy's (DOE) Advanced Turbine Systems (ATS) program established a target of 60% efficiency for utility scale gas turbine (GT) power plants to be achieved by the year 2000. Although the program led to numerous technology breakthroughs, it took another decade for an actual combined cycle (CC) power plant with an H class GT to reach (and surpass) the target efficiency. Today, another target benchmark, 65% efficiency, circulates frequently in trade publications and engineering journals with scant support from existing technology, its development path as well as material limits, and almost no regard to theoretical (e.g., underlying physics) and practical (e.g., cost, complexity, reliability, and constructability) concerns. This paper attempts to put such claims to test and establish the room left for gas turbine combined cycle (GTCC) growth in the next two decades. The analysis and conclusions are firmly based on fundamental thermodynamic principles with carefully and precisely laid out assumptions and supported by rigorous calculations. The goal is to arm the practicing engineer with a consistent, coherent, and self-standing reference to critically evaluate claims, predictions, and other futuristic information pertaining to GTCC technology.

Integrated solar combined cycle (ISCC) is an operationally simple, clean electric power generation system that is economically more attractive vis-à-vis stand-alone concentrating solar power (CSP) technology. The ISCC can be designed to achieve two primary goals: (1) replace natural gas combustion with solar thermal power at the same output rating to reduce fuel consumption and stack emissions and/or (2) replace supplementary (duct) firing in the heat recovery steam generator (HRSG) with “solar firing” to boost power generation on hot days. Optimal ISCC design requires a seamless integration of the solar thermal and fossil-thermal technologies to maximize the solar contribution to the overall system performance at the lowest possible size and cost. The current paper uses the exergy concept of the second law of thermodynamics to distill the quite complex optimization problem to its bare essentials. The goal is to provide the practitioners with physics-based, user-friendly guidelines to understand the key drivers and the interaction among them. Ultimately, such understanding is expected to help direct studies involving heavy use of time consuming system models in a focused manner and evaluate the results critically to arrive at feasible ISCC designs.

This paper describes a simplified physics-based method derived from fundamental relationships to accurately predict the dynamic response of the steam bottoming cycle of a combined cycle power plant to the changes in gas turbine exhaust temperature and flow rate. The method offers two advantages: (1) rapid calculation of various modes of combined cycle transient performance such as startup, shutdown, and load ramps for conceptual design and optimization studies, and (2) transparency of governing principles and solution methods for ease of use by a wider range of practitioners. Thus, the method facilitates better understanding and dissemination of said studies. All requisite formulas and methods described in the paper are readily amenable to implementation on a computational platform of the reader's choice.