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Aggressive Goals for Gas Turbine Development

This chapter describes nine aggressive goals—in power generation, aviation, and oil and gas—that should be pursued as a high priority in order to substantially accelerate the ability to develop advanced technologies that can be introduced into the design and manufacture of gas turbines. The selection criteria for the goals are described in Chapter 1.¹

POWER GENERATION

Power generation turbines for the electrical grid are generally used in one of two different configurations: (1) combined cycle to meet base load power demand, and (2) simple cycle to meet transient and peak power demand. A combined cycle power plant employs both gas turbines and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a simple cycle plant. The waste heat from the gas turbine that escapes through the exhaust in a simple cycle gas turbine is routed to a heat recovery steam generator, where the heat of the exhaust gas is used to generate steam for the steam turbine. In a combined cycle configuration, two gas turbines are often paired with a single steam turbine. Combined cycle power plants are generally designed for base-load (full-power) operation because they lack the agility to ramp up and down rapidly. It is challenging to efficiently integrate a plant designed for base load with renewable energy sources that provide intermittent power. Although the plant efficiency of a gas turbine operating in simple cycle is less than a gas turbine operating in combined cycle, a gas turbine operating in simple cycle has far greater operational flexibility in terms of its ability to accommodate swings in power while operating under partial load.

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¹ Each application area has a different number of goals: power generation has five, aviation has one, and oil and gas has three. Neither the distribution of the goals among the three application areas nor the ordering of the goals for a particular application is indicative of (1) the relative importance of one application area versus another or one goal versus another, or (2) how resources should be allocated among research related to different applications and goals. Rather, for example, the committee concluded that there are five key goals of comparable importance that are applicable to power generation gas turbines, whereas there is one overriding goal that pertains to aviation gas turbines. Within the power generation and oil and gas application areas, the ordering of the goals was selected to facilitate the explanation of each goal because in some cases the details associated with one goal provide a foundation for understanding other goals.

Aggressive Power Generation Goals for Future Development

The five power generation goals below are relevant to simple cycle and combined cycle gas turbines. Each of these goals directly addresses a key criterion used to select aggressive goals for gas turbine development:

• Efficiency
• Compatibility with Renewable Energy Sources
• CO₂ Emissions
• Fuel Flexibility
• Levelized Cost of Electricity

Power Generation Goal 1: Efficiency

Large state-of-the-art gas turbines for power generation are currently operating with a combined cycle efficiency of 63 percent or more and a simple cycle gas efficiency of about 40 percent. Increased efficiency gains are probably more important for power generation and aviation applications than for those used in oil and gas applications.²

In addition to improving efficiency, achieving this goal would reduce environmental impact to the extent that reducing fuel burn results in a commensurate reduction in emissions of interest (i.e., NO_x, carbon monoxide [CO], CO₂, and particulate matter). This may be difficult to achieve with respect to NO_x because some approaches to improving efficiency involve increasing combustion temperatures, which tends to increase the formation of NO_x. Achieving this goal would also reduce life-cycle costs to the extent that reduced fuel consumption exceeds the cost of implementing associated design changes.

The technical risk of this goal is high because achieving 70 percent combined cycle or 50 percent simple cycle efficiency may require the introduction of revolutionary rather than evolutionary technology. Changes to the underlying configuration of the turbine may be required. Development, testing, and validation may be paced by the ability to design and manufacture the necessary hardware. Solutions may require new materials, which have historically required longer development timelines.

Power Generation Goal 2: Compatibility with Renewable Energy Sources

Integration with renewable energy sources will be most critical for turbines being used to meet transient and peak power demands. However, all future turbines would benefit from the ability to use renewable fuels and supplement power from renewable sources.³

Achieving this goal would increase compatibility with renewable energy sources and reduce environmental impacts because a fast start capability and flexible operations will enable grid operators to quickly balance the electrical output of gas turbines with the variable quantity of power supplied by wind and solar. The demand for

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² Background information on efficiency is presented in Chapter 1, in the section “Background Information for the Performance Improvement Criteria.”

³ Background information related to the growth of renewable energy sources and the importance of ensuring that future gas turbines are compatible with renewable energy sources appears in Chapter 1, in the sections “Global Market Trends” and “Background Information for the Performance Improvement Criteria.”

fast start may be impacted with the introduction of grid-scale energy storage systems such as batteries. Hybrid gas turbine/battery systems may reduce the number of turbine starts and extend the time available to bring gas turbines online. Such systems have the potential to reduce fuel burn, maintenance costs, and harmful emissions.

Achieving this goal would improve fuel flexibility, as one aspect of an integrated energy infrastructure with renewable energy sources is the ability to burn renewable fuels.

The technical risk of this goal is medium to high depending on the nature of the renewable fuels that gas turbines would be expected to use as fuel; using 100 percent hydrogen would pose the highest technical risk. Compatibility with electrical generators powered by renewable fuels would also be challenging due to the rapid and frequent fluctuations in the amount of electricity available from renewable energy sources.

Power Generation Goal 3: CO₂ Emissions

There is growing pressure to reduce emissions of various types from power plants. Reducing emissions of CO₂ is of primary importance, however, because the threat posed by global warming and the corresponding drive to decarbonize the energy industry makes the status quo increasingly unacceptable. New gas turbine designs that reduce CO₂, however, will not be competitive if they come at the cost of decreased performance or if they prevent gas turbines from meeting standards for NO_x and other harmful emissions.⁴

In addition to reducing environmental impact, achieving this goal would increase compatibility with renewable energy sources and the future electrical grid by enabling greater use of renewable fuels.⁵

The technical risk of this goal is medium because high efficiencies generally require operating at higher pressures/temperatures, where NO_x formation rates are accelerated. New combustion paradigms are required to enable acceptable NO_x, while still maintaining adequate turndown.

Power Generation Goal 4: Fuel Flexibility

Fuel flexibility is particularly important for power generation and oil and gas applications.⁶ In addition to improving fuel flexibility, achieving this goal would reduce environmental impact by decreasing the reliance on conventional carbon-based fuels, and moving toward zero or near-zero net carbon emissions.

Achieving this goal would increase compatibility with renewable energy sources and the future electrical grid by having the ability to burn fuels, such as biofuels, derived from renewable energy sources.

The technical risk of this goal is high because of the target to burn 100 percent hydrogen.

Power Generation Goal 5: Levelized Cost of Electricity

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⁴ Background information on CO₂ emissions is presented in Chapter 1, in the section “Background Information for the Performance Improvement Criteria.”

⁵ Issues associated with reducing CO₂ emissions through the use of renewable fuels are addressed in the next goal, on fuel flexibility.

⁶ Background information on fuel flexibility is presented in Chapter 1, in the section “Background Information for the Performance Improvement Criteria.”

The levelized cost of electricity is defined as

Levelized cost is becoming one of the key criteria to determine whether a utility company decides to purchase and operate a gas turbine. It is likely that sales of gas turbines will be negatively impacted once the cost of renewable energy is consistently undercutting the cost of gas turbines. Two recent assessments predict that this could happen in the 2020 to 2024 time frame.^8,9

It will be challenging both to meet the increasing performance goals and to remain cost competitive with the renewable energy sources. The ever-changing power generation landscape makes it increasingly difficult to predict gas turbine research with the highest potential paybacks. For example, large and unforeseen reductions in the cost of renewable energy could potentially mitigate or reverse long-term projected growth in the demand for gas turbines for power generation.

Given record-low prices for renewable energy, Bloomberg New Energy Finance has stated that “some existing coal and gas power stations, with sunk capital costs, will continue to have a role for many years, doing a combination of bulk generation and balancing, as wind and solar penetration increase. But the economic case for building new coal and gas capacity is crumbling, as batteries start to encroach on the flexibility and peaking revenues enjoyed by fossil fuel plants.”¹⁰ Even so, the pace at which changes in power sources could take place would depend on many factors, such as the pace at which lower-cost renewable sources of energy could be scaled up and deployed and the rate at which demand for electricity is growing.

This research area would directly reduce life-cycle costs.¹¹ The technical risk of this goal is high because the increased efficiency targets will require more expensive solutions such as higher performing materials and more complex component geometries leading to higher manufacturing costs.

AVIATION

Aircraft engines convert the chemical energy stored in jet fuel to useful propulsive power. Propulsive power is defined as the product of the thrust force and the flight velocity. Gas turbines are used for aircraft propulsion in one of three configurations or architectures, either as a turbojet, turbofan, or turboprop. In each of these cases, a gas turbine serves as the core of the aircraft engine. Turbojet engines use the core exhaust as the direct source of thrust, with essentially all mechanical energy produced by the turbine module used to drive the compressor module (and electrical generators for the aircraft electrical system). Turbofan engines use some of the mechanical energy produced by the turbine module to drive a fan that provides thrust (in addition to the turbine exhaust). The fan is located within the engine nacelle directly in front of the core. The diameter of the fan blades is larger than the diameter of the core. Air passing through the fan flows around the core and merges with the turbine exhaust before exiting the engine. A turboprop is similar to a turbofan, except that a propeller external to the engine nacelle is used to provide thrust instead of the internally mounted fan.

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⁷ Energy Information Administration, 2018, EIA uses two simplified metrics to show future power plants’ relative economics, Today in Energy, March 29, https://www.eia.gov/todayinenergy/detail.php?id=35552.

⁸ McKinsey and Company, 2019, Global Energy Perspective 2019: Reference Case (Summary), https://mck.co/2NH3yGg, January.

⁹ D. Dudley, 2018, Renewable energy will be consistently cheaper than fossil fuels by 2020, report claims, Forbes, January 13, http://bit.ly/2PWOFCi.

¹⁰ Bloomberg New Energy Finance, 2018, “Tumbling Costs for Wind, Solar, Batteries Are Squeezing Fossil Fuels,” March 28, http://bit.ly/34CtcTE.

¹¹ Background information on life-cycle costs appears in Chapter 1, in the section “Background Information for the Performance Improvement Criteria.”

Modern commercial engine architectures use either turbofans or turboprops, and they contain two rotors or spools. The first rotor, or low spool, contains the fan or propeller, the lower pressure compressor, and the low-pressure turbine. The second rotor, or high spool, contains the high-pressure compressor, the combustor, and the high-pressure turbine.

In a turbofan, the ratio of air flow around the core to the air flow through the core is called the bypass ratio. Aircraft engines with large fans are called high bypass ratio turbofans. The efficiency of a turbofan increases with bypass ratio. Modern commercial aircraft have engines with high bypass ratios (5 to 12). High bypass ratio turbofans convert the kinetic energy of the core air flow to propulsive power more efficiently than turbojets and turbofans with low bypass ratios (1 to 4). High-speed military fighter and attack aircraft require high thrust and a compact engine, so they are powered by small bypass ratio turbofans, which have higher thrust-to-weight ratios than the large bypass ratio turbofans or the turboprops used to power commercial aircraft (and military transports and patrol aircraft). Turboprops are used for aircraft that fly at low speeds and that require high efficiency.

Aggressive Aviation Goal for Future Development

There is one overriding goal for aviation, which follows.

Aviation Goal 1: Fuel Burn

The overall efficiency of aircraft gas turbine engines is the product of thermal efficiency and propulsive efficiency. The thermal efficiency is the ratio of the rate of kinetic energy change of the working fluid to the rate of thermal energy added to the cycle. The drivers of thermal efficiency are the cycle pressure ratio, turbine inlet temperature, and individual component performance. The propulsive efficiency is the ratio of propulsive power and the rate of kinetic energy change in the working fluids in the core and fan streams. The main driver of propulsive efficiency is the fan pressure ratio. Advanced technologies that enable propulsive efficiency improvements are specific to the aviation industry and were not considered by this committee.

Some of the advanced technologies that improve the thermal efficiency of gas turbines for power generation and oil and gas applications will also improve efficiency of gas turbines for aircraft.

Today’s best-in-class commercial turbofans achieve 30 to 40 percent overall efficiency. Improving the overall efficiency of an aircraft engine will result in lower fuel burn. Achieving overall efficiency and, hence, fuel burn improvements of 25 percent relative to today’s best-in-class turbofan engines would yield 40 to 50 percent overall efficiency. Reducing the engine weight and drag would also result in lower fuel burn. These advanced engines would require more efficient thermodynamic cycles, such as pressure gain combustion (PGC), more novel engine architectures, and more innovative airframe–engine integration architectures.

Today’s best-in-class turbofan engines achieve approximately 50 to 55 percent cruise thermal efficiency. Turbofan engines that power narrow-body aircraft have approximately 50 percent thermal efficiency, whereas turbofan engines that power wide-body aircraft have approximately 55 percent thermal efficiency. If current trends hold, by 2030 advanced technologies will enable thermal efficiency improvements of 20 percent relative to today’s best-in-class engine cores, which would yield approximately 60 percent and 65 percent cruise thermal efficiency for engines that power narrow- and wide-body aircraft, respectively. Figure 2.1 shows that core thermal efficiency has increased by 0.4 percent per year since 1970. Likewise, Figure 2.2 shows that propulsive efficiency has increased by 0.3 percent per year since 1970. Thus, if current trends hold, by 2030 the propulsive efficiency of new entrants to the market would be 75 percent or higher, 5 to 10 percent more than current best-in-class turbofans.¹²

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¹² National Academies of Sciences, Engineering, and Medicine, 2016, Commercial Aircraft Propulsion and Energy Systems Research: Reducing Global Carbon Emissions, The National Academies Press, Washington, D.C.

Achieving this goal would improve overall efficiency via hot section technologies that enable higher turbine inlet temperatures or lower turbine cooling air levels. In particular, advanced materials and coatings would enable turbine materials to withstand higher gas temperatures in the turbine main gas path while enabling the engine to meet its mission life requirements.¹³ Higher turbine inlet temperatures, however, will increase NO_x production in the combustor. An alternative path to higher thermal efficiency is to reduce the turbine cooling air levels for the same turbine inlet temperature. Reducing the magnitude of the turbine cooling air flow will reduce the turbulent mixing between the coolant and the main gas path flow, which improves turbine efficiency. Reducing turbine cooling flow would also reduce the thermodynamic cycle penalty associated with rerouting compressed air to the turbine. Novel turbine cooling strategies and advanced, high-temperature materials and coatings technology would enable turbines to operate with lower cooling levels while enabling the engine to meet its mission life and emissions requirements.

Achieving this goal would also reduce environmental impact by decreasing CO and CO₂ emissions. The combustion of hydrocarbons and air yields CO₂ and water vapor as the primary byproducts. Higher engine efficiency reduces the fuel consumption rate, and, in turn, the generation of CO₂. The chemical reactions for jet engines that operate at high power (i.e., during takeoff and, to a lesser extent, during cruise) with well-mixed combustion chambers run down to a state of chemical equilibrium, where there are additional products, including CO. Improved engine efficiency will lower CO concentrations at chemical equilibrium for a well-mixed combustion chamber. Incomplete combustion, due to inadequate mixing and reaction of fuel and air molecules, will result in higher CO concentrations than the equilibrium value at combustion chamber pressure and temperatures. Combustion system design, rather than thermal efficiency, sets the CO concentrations above their chemical equilibrium values.

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¹³ The main gas path consists of those areas of an engine where compression, combustion, and expansion take place.

At low power (i.e., ground idle and flight idle, which takes place during descent), the combustor flow is not as well mixed, so the combustion process generates higher CO concentrations than at high power.

Achieving this goal while maintaining fuel flexibility regarding the use of sustainable aviation fuels¹⁴ in place of current fossil-based jet fuel would reduce net life-cycle CO₂ emissions. The aviation industry is pursuing an approach in which sustainable aviation fuels could be used as drop-in fuels, which means that their use would not require any changes in aircraft or engine fuel systems or airport fuel storage and distribution systems. The International Civil Aviation Organization (ICAO) is striving to eliminate growth in net CO₂ emissions even as air transportation increases. ICAO has determined that stabilizing CO₂ growth will require reductions in aircraft fuel burn, improvements in air traffic management, and substantial use of sustainable aviation fuels.¹⁵

Achieving this goal would also reduce life-cycle cost by lowering fuel consumption. Fuel costs are a significant operating expense for airlines. Jet fuel cost has varied from 33 percent to 24 percent of direct airline operating costs from 2013 to 2018 and was projected to be 25 percent of airline direct operating costs in 2019.^16,17

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¹⁴ Sustainable aviation fuels are also known as sustainable alternative jet fuels.

¹⁵ International Civil Aviation Organization (ICAO), 2019 Environmental Report—Aviation and Environment, http://bit.ly/2CiE8tq, accessed November 5, 2019.

¹⁶ International Air Transport Association (IATA), 2019, “Fuel Fact Sheet,” June, Montreal, Canada.

¹⁷ Although the discussion of this goal is framed in terms of improvements to gas turbines for commercial aircraft, accomplishing this goal would inevitably lead to reduced fuel burn by military aircraft.

The technical risk of this goal is medium for strategies that consist of (1) developing and deploying additive manufacturing technology, enabling more advanced turbine thermal management techniques, and (2) developing high-temperature materials and coatings, which enable higher turbine inlet temperatures or lower turbine cooling levels.

An alternative path for achieving greater than 20 percent thermal efficiency improvement relative to today’s best-in-class turbofan engines is to change the thermodynamic cycle of the aircraft engine to one that contains pressure gain combustion (PGC). Implementation of PGC has the potential to yield greater than 25 percent thermal efficiency improvement over today’s turbofans.¹⁸ However, the pulsating pressure waves that are a feature of PGC engines may damage the turbine components, compromising engine reliability, durability, and safety. As a result, this approach would increase the technical risk of this goal to high.¹⁹

OIL AND GAS INDUSTRY

Gas turbines for oil and gas applications are of many different types and sizes, typically producing power in the range of 1 to 40 MW. They are used to power natural gas pipeline compressors, gas lift and reinjection compressors, process plant compressors, water and crude oil pumps, and various power generation applications. The applications can be offshore or land based. These applications typically are fueled by natural gas that is available on site. Liquid fuels may also be used, typically for start-up. All oil and gas applications require gas turbines to regularly operate over a wide range of loads, while maintaining a high efficiency. Some applications also require gas turbines to be shut down and restarted at various frequencies, while other applications are best served by gas turbines that operate continuously.

The number of gas turbines used to drive pipeline compressors far exceeds the number of gas turbines used for any other particular oil and gas application. As a result, improvements in gas turbines for pipeline compressors would have the greatest impact on the oil and gas industry. The committee therefore concluded that the highest-priority goals and research areas for gas turbines in the oil and gas industry are related to gas turbines that drive natural gas pipeline compressors. It is expected that improvements in technologies for these gas turbines would ultimately benefit gas turbines for other oil and gas applications as well.

The United States operates today a network of more than 3 million miles of natural gas pipelines (see Figure 2.3). These pipelines connect production and storage facilities to each other and to consumers. Centrifugal compressors are the most common type of compressor used on pipelines. They are the key to providing high pipeline availability and low energy consumption for energy transport. These gas turbines typically use the gas transported in the pipeline as fuel. Backup fuel is usually not needed.

Aggressive Oil and Gas Goals for Future Development

There are three goals related to oil and gas applications:

• Fuel Flexibility
• Condition-Based Operations and Maintenance (CBOM)
• Flexible Power Demand and Efficiency

Oil and Gas Goal 1: Fuel Flexibility

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¹⁸ C.A. Nordeen and L.S. Langston, 2018, “There’s a new cycle in town,” Mechanical Engineering 140(7):36-41, http://msaidi.ir/asme/201807.pdf.

¹⁹ PGC is addressed in more detail in Chapter 3, in the sections “Research Topic 6.1: Gas Turbines with Pressure Gain Combustion: Technology” and “Research Topic 7.1: Gas Turbines with Pressure Gain Combustion: System Layout.”

Currently natural gas pipelines contain only trace amounts of hydrogen, and increasing the amount of hydrogen would have to overcome many challenges. For example, the characteristics of hydrogen combustion are very different than with natural gas.²⁰

Achieving this goal would improve fuel flexibility by allowing current and future gas turbine installations in pipeline applications to operate on various mixtures of natural gas and hydrogen. It would also reduce environmental impact by reducing the use of carbon-based fuels.

The technical risk of this goal is medium for hydrogen–natural gas fuel mixtures up to about 50 percent hydrogen. Developing a combustion system that can operate on mixtures with more than 50 percent hydrogen would have high technical risk.

Oil and Gas Goal 2: Condition-Based Operations and Maintenance (CBOM)

Condition-based operations and maintenance (CBOM) of gas turbines, for the purpose of this report, are defined as the capability to optimize the operation, maintenance, repair, and overhaul of gas turbines throughout their life cycles. CBOM is particularly important for oil and gas operators to reduce both preventive and corrective maintenance, especially for maintenance that requires shutting down a turbine and interrupting service. CBOM for

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²⁰ Background information on fuel flexibility and the combustion of hydrogen is presented in Chapter 1, in the section “Background Information for the Performance Improvement Criteria.”

oil and gas applications would be of particular value for gas turbines that operate at partial loads for long periods of time. Advanced CBOM algorithms would assess online operating data to calculate the remaining useful life, the probability of failure, and the cost of overhaul and repair. Operators and OEMs could then use this information to decide when to shut down a unit for maintenance.

Achieving this goal would reduce life-cycle cost by enabling operators to minimize the amount of time turbines are shut down for maintenance, facilitate flexible operations from partial load to peak power conditions, and improve availability, thereby increasing operational efficiency. Typical periods for scheduled maintenance today are every 6 to 12 months. The ability to operate gas turbines in pipeline operations for extended periods of time (e.g., 3 years or more) without shutdown or maintenance is particularly important for very remote and unmanned gas turbine applications. As CBOM capabilities mature, unmanned compressor stations will become more practical and their use will likely expand, which will further increase the value and utility of related technologies. Advanced CBOM capabilities would also be of particular value for gas turbines that experience peak load operating conditions that exceed normal operating conditions.

Achieving this goal would also improve the overall efficiency of transporting natural gas by reducing maintenance intervention and unplanned shutdowns. Even gradual improvements in reducing scheduled or unscheduled downtime would have significant financial benefits to the operator by increasing annual operating hours. Avoiding unplanned shutdowns also reduces environmental impact by reducing the need for blowdown of individual gas turbine units or an entire compressor station to clear them of natural gas, thereby releasing natural gas into the environment. Reducing maintenance and overhaul requirements for gas turbines would also enhance the position of gas turbines as the pipeline prime mover of choice over reciprocating engines (which have more frequent but less costly overhauls) and electric motors (which tend to have less maintenance).

The technical risk of this goal is medium because of the time periods involved. Compared to gas turbines for power generation or aviation—and to existing gas turbines of oil and gas applications—3 years is a very long time to operate a gas turbine without scheduled maintenance.

Some of the failure modes of gas turbines for natural gas pipeline are due to changes in fuel composition, some are due to air inlet filtration issues, and some are related to the operation of the gas turbine itself. During maintenance shutdowns, gas turbine internal components are visually inspected through special borescope openings in the compressor, combustor, and turbine casings. This is necessary to detect early signs of damage or degradation that could lead to failure and unplanned shutdowns. Continuous monitoring of gas turbines using new sensors and sophisticated models for diagnostics would allow the time between regular shutdowns to be greatly extended.

Oil and Gas Goal 3: Flexible Power Demand and Efficiency

Many oil and gas operations require gas compressors and the gas turbines that drive them to operate over a wide range of loads and speeds. Currently, minimizing the formation of harmful emissions under these varying operating conditions is achieved largely by maintaining the firing temperature and bleeding off air from the axial compressor directly into the exhaust system. While this maintains satisfactory emissions over a wider load range, it significantly reduces efficiency.

Electric motors have a high efficiency under partial load but require the supply of external electricity to compressor stations that are often remote. In general, operators prefer a gas turbine driver over an electric motor because the natural gas fuel is readily available.

To better equip natural gas pipelines to support the integration of renewable energy sources, gas turbines for pipeline compressor stations may need to start, stop, and operate under partial load more frequently in the future.²¹ Keeping natural gas compressors under pressure while they are shut down avoids releasing natural gas to the

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²¹ Despite the increasing number of starts and stops, rapid start times are not and will not become an important performance parameter. Natural gas pipelines themselves represent a significant energy storage medium that mitigates sudden changes in the demand for natural gas.

environment. Commercially available natural gas compressors, however, cannot hold pressure indefinitely when shut down. In addition, blowing down compressor stations that are driven by reciprocating engines and in some cases electric motors is necessary to reduce the power requirements prior to start. Research to reduce the need for blowing down all classes of natural gas compressors is ongoing.

In addition to improving gas turbine efficiency under partial load, achieving this goal would reduce life-cycle cost by reducing fuel consumption and by improving the ability of gas turbines to serve applications where it would otherwise be required to use compressors driven by electric motors, which have relatively large capital costs if there are no nearby electric power lines. Improvements necessary to meet this goal may also reduce maintenance costs.

Achieving this goal would reduce environmental impact by reducing CO₂ emissions and, possibly, other harmful emissions.

The technical risk of this goal is medium, as many relevant concepts are known, although they have not yet matured to the point that they could be introduced into production. New concepts are developing and are at low technology readiness levels (TRLs) but could be developed to TRL 6 by 2030. Even gradual improvements would create immediate and significant advantages for gas turbines in pipeline compressor applications.

GOALS: INTERRELATIONSHIPS AND RECOMMENDATION

The interrelationships among the goals are illustrated in Figure 2.4. The red arrows (with an arrowhead at each end) show where the accomplishment of two goals are mutually supportive to a substantial degree. This is the case with the efficiency goals for power generation, aviation, and oil and gas and, separately, for the fuel flexibility goals for power generation and oil and gas.

The green arrows (with a single arrowhead) show where the accomplishment of one goal will substantially support the accomplishment of another goal. For example, improving efficiency will directly reduce CO₂ emissions.

The committee identified two sets of related goals (efficiency and fuel flexibility) that are of the highest priority. In Figure 2.4, the goals highlighted in green are most directly related to efficiency, and goals highlighted in blue are most closely related to fuel flexibility:

• Efficiency
  • Power Generation Goal 1: Efficiency
  • Aviation Goal 1: Fuel Burn
  • Oil and Gas Goal 3: Flexible Power Demand and Efficiency
• Fuel Flexibility²²
  • Power Generation Goal 4: Fuel Flexibility
  • Oil and Gas Goal 1: Fuel Flexibility

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²² Government and industry are supporting substantial efforts to develop and scale up the production of alternative fuels for aviation. One of the requirements for such fuels, however, is that they meet current specifications for jet fuels so that the alternative fuels can be used in current fuel distributions systems and in the current fleet of aircraft engines. In other words, in aviation the ability to use alternative fuels is being accomplished by tailoring alternative fuels to meet the needs of gas turbines rather than changing the design of gas turbines to meet the needs of alternative fuels. As a result, for aviation applications, developing gas turbines that can accommodate a variety of different fuels is not a high-priority research and development goal.

2. Condition-Based Operations and Maintenance. Develop the ability for condition-based operations and maintenance to increase periods of uninterrupted operation for natural gas pipeline compressor stations to 3 years or more without reducing availability or reliability.
3. Flexible Power Demand and Efficiency. Design gas turbines for pipeline compressor stations (and other oil and gas applications) that can handle large load swings and operate at partial load with efficiency that exceeds the efficiency of stations that use compressors driven by electric motors.