Unlocking Higher Efficiency Turbines Through Pressure Gain Combustion
NETL’s ground-breaking research on a process to increase the efficiency of power-producing turbines is attracting research partners from some of the nation’s leading academic institutions as well as the U.S. Air Force, and the results could someday mean lower consumer electricity bills.
Modern turbines are engineering marvels that provide affordable and reliable energy for the nation. Today’s state-of-the-art combined cycle power generation – an assembly of heat engines that work together from the same source of heat to convert it into mechanical energy – are capable of efficiencies of 60 percent or higher. But, there is always room for improvement. NETL researches are eyeing efficiencies of 65 percent and beyond, a step-change that could translate to a reduction of electricity costs by more than 15 percent.
For example, NETL researchers are exploring pressure gain combustion (PGC) - a process that creates high temperatures and increases pressure in a turbine.
Turbines work by combusting compressed air with a fuel to create a high-pressure and high-temperature gas stream that expands and spins turbine blades. The blades, in turn, drive generators that produce electricity. Historically, efficiency gains have been realized through continually increasing firing temperatures, which are now approaching 3,100 degrees Fahrenheit.
While burning hotter is the key to higher efficiencies, current materials have reached their structural limits. PGC concepts take a different approach and allow researchers to increase gas pressure during combustion, which can also increase thermal efficiency, improving overall plant efficiency. Pursuing PGC applications are intended to augment traditional approaches to improve efficiency through a higher firing temperature. In fact, designing energy systems that incorporate both PGC and a higher firing temperature approach would work synergistically, making the 65 percent combined cycle efficiency goal, or higher, realistically possible.
Developing this next-generation pressure gain combustion technology will be key to keeping the United States at the forefront of turbine development and ensuring energy dominance. The goal of NETL’s research is to develop PGC systems designed for potential integration with combustion gas turbines in combined cycle applications.
One proposed method for achieving this goal is by developing a rotating detonation engine (RDE), which creates a controlled, continuous detonation wave that rotates around the inside of a modified gas turbine combustion chamber. The RDE would replace the traditional combustion process that results in a loss of pressure. Because the detonation is so rapid, the turbine reacts as if the flow were steady. In this way, RDEs avoid the pressure loss and resulting decrease in efficiency that occurs with conventional gas turbine engines.
While PGC applications hold enormous potential for achieving higher turbine efficiencies, this method is still not completely understood, but NETL researchers are hoping to soon change that. The goal of NETL research effort is to provide theoretical, computational, and experimental analysis to better understand RDE concepts and begin to optimize various aspects of the technology to realize its potential for improved thermal efficiency.
To advance to a more applied technology, NETL has adapted its unique high-pressure combustion rig to study an RDE combustor. Working with the Air Force Research Laboratory (AFRL), NETL installed and is now testing an RDE at pressures above atmospheric. While testing at elevated pressures is not unique, NETL’s enclosed system with ducted exhaust is a more realistic representation of real gas turbine-like operation compared to other facilities currently operating in the United States. In addition to the full-scale RDE test rig, NETL has smaller rigs that use 3-D printed metal parts to study fundamental aspects of the RDE.
Beyond the Lab’s in-house efforts, NETL researchers have collaborated with AFRL to evaluate performance of a turbine when placed downstream of an RDE, duplicating conditions in an actual gas turbine engine.
This work performed at NETL is essential to advancing the technology because it is too risky from a business perspective for industry to explore on its own. DOE’s funding of internal, academic, and private sector research in PGC helps to offset some of this risk and has facilitated ongoing collaborations on this innovative technology. These relationships help to accelerate the application of PGC and similar technologies in the private sector.
For instance, NETL’s Advanced Combustion Program provides funding through the University Turbine Systems Research Program to support studies at the University of Michigan, University of Purdue and Penn State University. NETL’s Advanced Turbine Program and Advanced Combustions Systems Program currently support a six-year study (2014-2019) at Aerojet-Rocketdyne to explore the potential of RDEs for combustion in a high-efficiency gas turbine engine.
The Laboratory’s ground-breaking PGC research has attracted the attention of academia and industry, and several NETL-funded projects have achieved significant success, including work with Aerojet Rocketdyne, Penn State University, the University of Michigan, Oregon University, and Purdue University. Working with its partners, NETL’s effectiveness will lead to combined cycle power plants with higher efficiency and reduced emissions for greater energy security, environmental improvements, and a stronger economy.