Gas turbine upgrades can pave the way to millions of tonnes of reduced CO2 emissions annually

The global energy system faces a triumvirate of challenges: meeting the increasing energy demand of a growing global population, delivering energy security to the developed world, and lowering global emissions in line with the Paris Agreement. If we are going to make this happen, it will require a broad energy mix and unprecedented collaboration across all sectors and countries.

Over recent years the majority of the focus has been on the decarbonization impact that renewable energy sources such as wind, solar, hydroelectric and nuclear can make. And rightfully so; energy coming from these sources is the lowest carbon emissions option we have today. However in order to make the impact we need renewables energy sources alone are not enough. For more than a decade, the gas industry has made a case that gas can be a critical factor in the ongoing energy transition as a bridge fuel, primarily by displacing more polluting coal in the energy system and also for providing a stable and reliable energy foundation. A considerable fleet of gas turbines operates worldwide and it goes without saying that these turbines must work at optimum performance to ensure that gas can fully participate in the energy transition.??

So, to maximize the performance of these engines, Siemens Energy has developed some intelligent upgrade packages for its F- and E-Class large gas turbines that, if implemented for just 20% of our fleet, could save up to 2,400,000 tonnes of CO2 emissions each year. Now, that’s an impressive number.

Improving the performance of F-Class gas turbines

One of these turbines is the SGT5-4000F. Since the first 4000F gas turbine was produced in 1996, the first emulator combustion chamber gas turbine manufactured by Siemens has proven reliable and resilient, and that is a fact that the market recognizes. Today, more than 350 4000F units are running at greater than 99.5 percent reliability, with an equivalent operating time of over 17 million hours over the last 25 years. Additionally, the vast majority of our customers trust our partnership by committing to a long-term maintenance contract for their 4000F units.

But enough of the PR. I want to discuss the Advance Turbine Efficiency Package (ATEP). This clever package focuses on improving the combined cycle efficiency, optimizing all four stages of turbine blades to achieve the greatest possible improvement. That optimum performance level is reached by incorporating a vast amount of research from my colleagues in the three main technology fields in gas turbine development. First, in aerodynamics, using the latest tools to optimize the airflow profile and aero features. The second is heat transfer, which improves the cooling air consumption and significantly increases efficiency. Finally, in terms of mechanical integrity, critical areas have been optimized, and the casting process has been simplified. In addition, the base material of the blade is protected by an improved thermal insulation layer. Stage loading has also been optimized, as currently, the 4000F is operated with a frontloaded turbine only.

Depending on site conditions, the ATEP, when operated at constant load, also reduces CO2 emission by up to 18.6 tonnes a year while burning up to 7.3 tonnes a year less fuel. Based on data from four implemented projects and the service pack 4 configuration, efficiency was improved by 1.5 percent, and output increased by 45 MW. And it’s worth remembering that even after the ATEP upgrade package, the GT retains its pre-upgrade minimum load limit.

It’s a straightforward process with just two internal upgrades necessary to achieve this level of performance improvement. First, the gas turbine is upgraded with aerodynamically optimized hot gas path blades and airfoils based on the advanced computational methods used in the HL-class turbine. Also, the load distribution between the four turbine stages is balanced, and the blade tip design is improved to minimize secondary flow losses. As a bonus, turbine cooling air requirements have also been reduced. Together, these upgrades produce a significant improvement in gas turbine efficiency.

Also, with higher cycle temperatures, the thermodynamically optimum compressor pressure ratio increases, so compressor blades with improved geometry are required to handle the increased air mass flow. Other casing and component upgrades are necessary, so the best time to complete these upgrades is during a planned outage.

Going beyond the ATEP upgrade

Of course, the age and condition of the turbine, which is primed for an upgrade, is a factor when considering further upgrade additions to increase performance. Many of these additional upgrades may require tuning of the plant controls. This includes the start gradient optimization package, designed to increase the 4000F turbine start-up gradient to 30MW/min, allowing the turbine to ramp up from synchronization to baseload in roughly ten minutes. Operators with unit start-up emissions limits will be super interested in this option because the high ramp rate reduces the amount of natural gas consumed during start-up.

Turn-down upgrades are also available, which reduce the minimum part-load capability of the turbine without increasing carbon emissions – beneficial for combined cycle applications where part-load efficiency is desired. Alternatively, the turn-up upgrade will increase the gas turbine output to 6 MW in simple cycle operation and up to 9 MW in combined cycle applications above baseload, with higher efficiency. Particularly important, I think, is that this upgrade also allows the turbine to maintain the minimum primary and secondary frequency reserve when operating above the baseload. It’s worth noting that this upgrade is desirable when the turbine is used in peaking service.

Extending the upgrades to the E-class turbines

Although the 50Hz ATEP package was initially targeted at the SGT5-4000F, that has now been extended to the SGT5-2000E. Over 300 of these gas turbines have been sold, with another 200 under license, and it has accumulated over 21 million operating hours with a best-in-class reliability exceeding 99.5%.

Siemens Energy recently upgraded the SGT5-2000E to increase its power output and baseload efficiency. And I am excited particularly about the Advanced Siemens Innovative 3D (Si3D+) program, which introduces a new aerodynamic airfoil design with improved coating technology, again the result of our research experts. The upgrade package significantly increases the gas turbine efficiency, up to 2.6 percent in simple cycle operation and up to 1.6 percent in 1 x 1 combined cycle operation, over prior performance data. These improvements equate to an estimated 20 MW increase in power in a simple cycle and a 38 MW increase in combined cycle operation; you will agree these are big numbers. The upgrade has other advantages to the plant owner, such as extended service intervals, which result in significantly reduced maintenance costs, something that every operator wants, over the lifecycle of the GT and reduced NOx emissions.

Much like the ATEP upgrades, the Si3D+ program does require some internal component changes, and these are best completed during a planned outage. The scope of the Si3D+ includes the replacement of the blades and vanes of the four-stage turbine, new seal rings in stages 2-4 that reduce the amount of cooling air required, and the installation of an improved compressor bearing. And the good news is these upgrades are compatible with the entire range of SGT5-2000E upgrade products.

The Importance of Gas Turbines in the Energy Transition

The development of the international energy market shows that we are making progress with the mission to decarbonize the planet. However, this goal can only be achieved if the energy system remains stable and with a variety of technologies. Improving the efficiency of gas turbines is a key, and coupled with low-emission, hybrid-compatible fuels becomes an extremely powerful combination. Gas turbine upgrades such as ATEP, flexibility enhancements and Si3D+ are a critical milestone in meeting our specific decarbonization goals. With this initiative, Siemens Energy is taking a responsible stance for its service fleet and is making a significant contribution towards decarbonization.