Flexibility And Performance : Staying in “tune” with changing market conditions by steve hartman Steve Hartman is general manager, Thermal Services Engineering, GE Energy.
Today’s dynamic, rapidly changing energy markets pose significant and ongoing challenges for utility executives, managers and power plant operators. As businesses seek ways to decrease costs while maintaining or growing revenue, power plant asset owners need to remain flexible as conditions change. Recent advances in software technologies and engineered performance for gas turbines can help plant personnel adapt to market conditions, even as variables such as the economy, fuel sources and regulations continually shift. One factor that plant owners and operators must consider is the shift to cleaner sources of fuel, which may impact utilization and capacity factors.
Since 1987, nearly 70% of new electricity generation in the United States has come from gas-fired generating units, according to “The Future of Gas,” a study managed by the Massachusetts Institute of Technology Energy Initiative. This is due to the cleaner-burning nature of natural gas as a fuel source and the efficiency improvements made possible by new combined-cycle gas turbine technology. Consequently, there has been a trend toward oversupply of gas-fired generating capacity during the last 20 years, causing lower capacity factors across the fleet. The recent economic downturn has added to this market condition, creating a significant drop in electricity demand. In developed countries, demand may take three years or more to return to pre-recession levels, according to some estimates.
In addition to changing utilization, the United States is on the cusp of a significant national policy shift toward greater regulatory oversight and stricter environmental protection requirements. For example, according to the American Public Power Association, Congress is currently considering 35 different proposed pieces of legislation with various emission standards that could take effect between now and 2017. This does not include state and local regulations that may develop in parallel with national standards.
Whatever the regulatory course, oil, gas and power companies will face new requirements around emissions and clean water, as well as regulation of other pollutants. Power generation providers (some exposed to extreme operating conditions) must invest in assets to maintain continuity of service, even as emerging regulations add new considerations for plant operators and industrial executives. Electrical generation, transmission, distribution, metering and consumption also is undergoing a shift that ultimately will change the way communities use power. As the power grid is wired for two-way communication, consumers increasingly will depend on cleaner, smarter and more efficient sources of power.
Over the next 10 years, renewable power generation is predicted to grow at a rate three times that of other traditional sources, such as coal or gas, according to the U.S. Energy Information Administration. This reinforces the need to upgrade the world’s aging energy infrastructure. At a capacity factor well below fossil units, these new power sources will require much more reliable sources of backup power more frequently. Wind farms and solar generating stations, for example, cycle naturally during the day. The likelihood of grid disturbances or power fluctuations will increase as these new sources of power are integrated.
Traditional fossil plants must prepare for such transients and be able to either take advantage of new ancillary markets around spinning reserve, nonspinning reserve, VAR support or as a unit that can provide additional reserve margin for enhanced grid stability. All of these issues can increase the frequency of plant trips and raise operations and maintenance (O&M) costs. Other potential consequences may include penalties and fines due to emissions excursions or operational issues as a result of changing fuel mix, changes in frequency of the grid or other grid dynamics. Amidst all these challenges, generating stations must ensure that they are available to dispatch quickly and reliably when called upon ideally without adding significant hardware or protection systems.
Addressing the Flexibility Challenge
The story is not all doom and gloom, however. Unpredictable market conditions also provide power generation asset owners with opportunities to take advantage of both the flexibility and performance of their units. To respond to these rapidly changing market conditions, power generation suppliers have come to companies like GE in search of a range of tailored, cost-effective solutions that alleviate growing concerns around technology flexibility.
GE introduced its OpFlex enhancements to help maximize turbine and plant operating envelopes enabling customers to meet the demands of a changing power market. With highly variable fuel costs and market capacity, plants are seeking ways to maximize revenue potential during peak conditions and reduce operating costs during off-peak periods. A key part of these enhancements is corrected parameter control (CPC), a new, robust turbine control methodology leveraged from the DLN1+ combustor program. Traditional gas turbine control uses a single temperature control curve where multiple operational boundaries are implicit in a feed-forward control schedule. This schedule is not corrected for changing ambient conditions, and so must be conservative to still accommodate operation across a wide ambient range; otherwise, it must be adjusted or tuned seasonally to ensure proper turbine operation.
CPC changes the way the turbine is controlled. Through measurement of traditional noise parameters (e.g., humidity) and separation of operational boundaries into four separate control algorithms, turbine operation can be much more tightly controlled. This, by itself, enables reduced variation in turbine NOx and CO emissions and an expanded low-emission operating envelope. CPC is then coupled with an emissions signal from a unit’s CEMS, or equivalent, to provide real-time emissions feedback. This enables control parameters that are normally set and left static following initial combustor tuning to now be actively controlled as both load and ambient conditions vary. Turbine performance can now further be optimized while still maintaining low emissions, thus increasing turbine operating flexibility.
The variation in emission levels is reduced, thus enabling operation closer to limits with no increase in risk of exceeding limits. It is also critical for the unit to perform reliably and remain within allowable emission requirements. OpFlex enhancements, for instance, provide operators with a “slider bar” option that allows refined control of NOx emission targets and will automatically maintain the emissions at the operator setpoint, while maximizing unit performance.
Improving the Efficiency Equation
Also essential when considering gas turbine power plant flexibility and performance is the option to improve overall output and efficiency of the unit. As power plants age, asset owners expect overall equipment degradation as well as the inability to provide as much power as newer, more advanced machines. One way that customers have taken advantage of new technologies avoiding both massive capital investment and strict permitting processes required for new generating stations is by maximizing the existing gas turbine footprint and supporting systems through upgrades of the existing machine’s compressor and/or hot gas path. Customers with older versions of GE’s F-class machines can improve the overall performance and recover lost efficiencies due to aging equipment or natural degradation over time.
Hot gas path upgrades can improve hardware performance and enhance unit flexibility. These changes can dramatically improve unit performance, recovering up to 1% of lost efficiency. This can create significant fuel savings per megawatt-hour of generation, as well as 20 or more additional megawatts of power, should the owner decide to increase the overall output of the machine. Owners gain not only increased performance, but also decreased fuel costs and lower total O&M costs per megawatt-hour. Operators also gain the flexibility to provide the grid with additional power if the unit is called upon for more generation. In addition, the replacement components often extend the overall life of the asset, reducing the likelihood of equipment downtime due to maintenance or unplanned replacement of aging components.
Energy markets are changing quickly in today’s environment. Global business is in dramatic flux as the economy gains strength, the pace varying by geography. As conditions rapidly change, power plant asset owners can take advantage of technology advancements to keep pace. Whether owners seek improved flexibility or better performance, they should consult with partners who can help them operate in a cleaner, smarter, more efficient manner. By improving overall unit performance and flexibility, owners can best position their portfolio of power generation assets to increase revenue, lower O&M costs and maintain compliance, regardless of market uncertainties around the corner.