Siemens blends past and present for next generation gas-fired power efficiency

Siemens new HL-class turbines are a synthesis of old and new technologies but ultimately they add up to an efficiency gain that equips gas-fired power plants well for the challenge of balancing a renewable energy-dominated power sector.

The HL represents an evolutionary development step derived from its proven SGT-8000H technology and is achieving greater thanà‚ 63 per cent efficiency with a mid-term goal to reach 65 per cent.

Power Engineering International recently attended Siemensà‚ in Berlin to view the latest of the German giant’s gas turbines.

Siemens CEO Global Sales Power and Gas, Karim Amin (right),à‚ told a press gathering in Berlin, the requirement is for the operation to be very flexible to complement the intermittence of renewables, with the HL-class having a ramp up of 85 MW per minute in simple cycle.

“We have a very optimised service process and that was important in the criteria and you will see the service of this turbine is extremely efficient and cost effective as well. And there are allowances for start and stop segments.”

The HL-engines are designed to fulfil the requirements of base load units as well as of peakers ” which makes them a perfect fit for energy systems with a rapidly increasing share of fluctuating renewables. The naming HL-class underlines that the engines are based on Siemens proven H-Class design and are the technology carrier from 63% to 65%.

To achieve top performance, Siemens developed advanced combustion technologies, innovative multi-layer coatings, super-efficient internal cooling features as well as an optimized water-steam cycle. Engineers designed the frame using the latest in digital technology, for example 3D-printed components for prototype testing and validation.

The new Siemens HL-class consists of three engines: SGT5-9000HL, SGT6-9000HL and SGT5-8000HL. In simple-cycle operation the air-cooled SGT-9000HL gas turbine will provide a capacity of 567MW for the 50-Hertz market and 388 MW in the 60-Hertz version. SGT5-8000HL will provide 481 MW in simple-cycle operation.

The turbines are designed to plug in to Siemens’ suite of digital products ” running on MindSphere, the cloud-based Siemens operating system for the Internet of Things (IoT).

“It’s designed to allow for the digitization road map we have,” Amin told attendants at the press tour. “You can connect it through IoT, Mindsphere and it has more than 3000 sensors. At the end of the day, the impact is the highest efficiency large output together with a smaller footprint.”

What does this do to CAPEX, OPEX, and fuel economics?

“We think that when you look at certain gas process for this instance, it can reduce the cost of electricity by around 5 per cent compared to the existing rate, amounting to around EUR15-20m a year. It has a visible impact on the economics of EPA for a traditional asset that runs from 15 -25 years.”

When asked if the development of the new product might indicate some confidence in a turnaround for the fortunes of gas power in Germany and Europe in general, Amin explained success was contingent on certain criteria.

“For a considerable period of time in Germany and Europe gas power was not being dispatched. Now you are seeing with ancillary services, reactive power and grid stability some of these plants started running again and now it all depends on the economic values that are attached to them.”

“How much was the capex when they were built, how much have the prices changed, and the services cost attached to that and so on. Whatever plant is more efficient gets dispatched first and our job as a service organisation is to provide service upgrade packages that makes it less costly to open again.”

Amin and his colleagues spent a year analysing potential ways forward for gas-fired power offerings. Did the advances being made in rival technologies such as battery storage inform their approach?

Siemens HL Class gas turbine
“Siemens is working on storage from a much broader aspect. Storage and renewables are going to change the landscape one more time completely once there is an efficient scalable, economic storage solution.”

Siemens is accelerating its drive in technological upgrades and competitiveness by transferring newly developed key technologies to its entire gas turbine portfolio. At the initial launch of the technology, Willi Meixner, CEO of the Siemens Power and Gas Division neatly encapsulated the motive in developing it.

“Driven by digitalisation, speed in technology development is rapidly gaining momentum in the power generation arena,” he said. “It took us 10 years from 2000 to 2010 to increase the efficiency of our combined cycle power plants from 58 to 60 per cent, a further six years to reach 61.5 per cent in 2016 and now we are taking the next step to 63 per cent and beyond. But we know that speed and efficiency alone are not sufficient ” reliability and cost effectiveness of our solutions as well as partnership, support in financing and insurability are also key to our customers”.

In the near future, all Siemens’ customers will benefit from further efficiency and performance increases. This approach is part of a series of activities to help Siemens` customers compete in a rapidly changing market ” working to significantly reduce lead and construction times through standardization and modularization.

Guido Schuld, Siemens’ Product Family Owner (Large Gas Turbines), said the thinking behind the HL-Class came from a wide variety of people under the company’s roof.

“Unlike the usual procedure at Siemens, this mixed group of people together contributed to the development of a new turbine class,” said Schuld. “For example, we looked at new ways of manufacturing, but analysed also which technologies will likely be available in five or six years from now, and made sure these turbines are ready to incorporate these new production technologies. People from manufacturing and colleagues from technology & innovation were key in these assessments.”

“We considered how difficult this market is developing so our strategy department began looking at how it might evolve in the future. On top of this we also looked at new manufacturing methods, such as digital printing and of course some components are not yet ready. Turbine blades are still made in a conventional way. We are considering what manufacturing tech might be available in three or four years’ time and that the engine architecture of the HL Class allows for the incorporation of this new methods.”

Schuld (right) also provided a detailed account on what the HL comprised and how its new-found efficiencies are being gained.à‚ 

“So if it’s just an evolution how do you achieve efficiency levels above 63 per cent? The answer is on the compressor side, especially improvements on the combustion side and the turbine section itself.”

“From the compressor side, this is the third generation of a so-called family compressor ” the first generation for a 5000F engine was a 60 HZ and then developed for a H-Class family of 50 to 60 Hz and this is the third generation. It makes use of advanced 3D blading which improves the efficiency of the entire compressor, and allows us (despite having a higher compressor ratio of 24:1 compared to 20:1 for the 8000H) to reduce the number of stages of the compressor, meaning less complexity.”

The HL class comes with 12 compressor stages, while the H Class had 13 compressor stages. To further reduce complexity the HL-class has one inlet guide vane and two variable guide vanes in comparison to the SGT-8000-H series which had one inlet guide vane and three variable guide vanes. It amounts to less complexity with higher efficiency.

To achieve top performance, the turbines operate at high combustion temperatures. For this purpose, Siemens’ specialists have developed advanced combustion technologies, innovative multi-layer coatings, super-efficient internal cooling features as well as an optimized water-steam cycle.

More gains are made in the hotter parts of the engine and the combustion system. Siemens refers to the ACE, or Advanced Combustor for High Efficiency ” the concept is once again aimed at the development of the H-Class family’s PCS or Platform Combustion System.

“Concept-wise we have a pilot burner in the middle surrounded by a number of pre-mixed flames,” explains Schuld. “What we did here is increase the number of premixed flames compared to the SGT-8000H series.”

“With the H-Class we had eight and with the HL we have 25 premix flames helping us to reduce NOX, because final temperature has to go up if you want to improve the efficiency of the engine of the entire internal combined cycle. It also helps us with the part load.”

“This engine can go down to a part load of 30 per cent which again serves the market when more renewable energy is coming inward. It not only delivers fast ramp-up but low part-load operation capability.”

“To show how similar the concepts are, the HL part oxygen completion burner has already been tested one year ago in an SGT-8000H series engine installed here at our test centre in Berlin. We took the new burner and operated at the conditions of the SGT-8000H series.”

“We see a new concept with more premixed burners and flames and full oxygen mixing and also the transition piece shortened in order to reduce residence time of the combustion gasses within the combustor itself.”

“With turbine blades, it’s a real challenge with air cooled engines and improving efficiency. You must get the firing temperature up.”

When increasing burning temperature, there are two ways to protect the blades ” one is improved cooling and the other is improved protection.

“Improved cooling to some extent is easy as you just use more cooling air. But when you use more cooling air, the efficiency of the engine goes down because the air isn’t available for combustion in power generation.”

“What we realised is the importance of the thermal barrier coating on the blade, making it thicker. The thermal barrier coating has a different thermal behaviour than the base material of the actual blade. It’s a ceramic material and during start up and shut down experiences thermal stresses.”

Siemens came up with a technology to increase the thermal coating with so called laser engraving, thin cuts in the thermal barrier coating, and this helps to reduce the stresses on the coating, which avoid spallation ” the biggest risk of damage to coating.

They also found a second route cause of spallation. During commissioning of the engine, on the compressor side, there are gradable or metallic seals. In commissioning there is controlled rubbing of the compressor and small metal pieces that go into the engine.

“Even if you try to clean everything there will always be some metal dust remaining in the engine. The first time you try to start up the engine the metal dust melts and gets plucked through the thermal barrier coating of the main area and, if you have metal deposits there, it changes the thermal coating behaviour and causes spallation.”

“We noticed this as you see spallation a lot during the first couple of hundred operating hours and after than you don’t see it any longer. What we came up with is a very simple concept. We have a sacrificial layer on the main one and that just disappears within the first couple of hundred operating hours and below that layer you have the proper, original barrier coating then protected.”

“You also have to improve cooling of the blade without consuming more air. We bought a manufacturing license from a US-based company called Microsystems. This technology allows us to manufacture very sophisticated cooling channels inside the blade. This was up until now not possible but reduces the amount of cooling air needed.”

It means major changes from theà‚ SGT-8000H seriesà‚  with an internally cooled blade needed because of the higher exhaust temperature to improve the overall combined cycle efficiency. With the HL class there is an exhaust temperature of around 680 degrees Celsius compared to theà‚ SGT-8000H series range of 630 to 640 degrees Celsius.

“An additional change with the HL class is the thermal barrier coating is used for the first seven air foils as against the H8000 where it only applies for the first six air foils. It’s a free standing blade, which we use to reduce losses and improve the overall combined cycle efficiency.”

This is not to mention the benefit to customers in available spare parts, along with it being much more flexible to market changes. It will allow plant owners to react quicker as we can use the same casing.

Testing and validation is vital for Siemens in the development of the offering. Executives highlighted the role of the company’s EUR100m Clean Energy Centre in that responsibility.

The centre has a focus on combustion and component testing and allows Siemens to test combustion parts under real engine conditions.

“The approach results in improved technology and a proof point for customer in endured durability,” according to Schuld. “Also for the insurance companies it provides increased insurability “it’s much easier for the customer to achieve financing and bankability in their projects.

All blades can be replaced even without a rotor lift of the engine for the turbines. There is also a roll in roll out concept for the turbine build carriers so no requirement to lift the rotor out with the batteries.”

In terms of maintenance improvement concept, the first combustor inspection combined with a stage 1 over inspection is only necessary after 33,000 base operating hours “or between 6-10 years for the first inspection.”

There is also the operational regime change to be factored in. Some units bought five years ago as baseload are now daily start twice a day, which meant changing the starting process.

“So for the H-class you would have to perform the combustor inspection after 900 starts but this has been extended to 1250 starts, really addressing the requirements of customers according to the market changes.”

“After 66,000 base operating hours we do a major overhaul, looking at the combustor turbine compressor and the casing.”

If you were to isolate one outstanding motive for the HL-Class, it would be that requirement for adaptability to the new renewable energy dominated environment, this technology finds itself in.

“We really believe we have an engine which addresses new market requirements with more renewables coming into the market. You need engines with fast ramp-up so they can operate in combination with proliferation of power generation from renewables and on the other hand the high efficiency also allows for customers who still have baseload plants to substantially improve life cycle cost of the engine compared to other frames, the proof of service concept and also digitalisation.”

“I refer to the engine as future proof which means it is designed to plug into the Siemens cloud MindSphere and as more and more applications become available that will result in more improvement for customers from an operational flexibility point of view.”

Looking at the market in general Schuld said there are some requirements for capacity in the UK and also in Germany. He acknowledged that the market in the EU has been stagnant for quite some time.”

Developing further on that Amin pointed to a more positive scenario outside Europe.

“Countries in Asia and the Middle East like Pakistan and Saudi Arabia, one of the biggest gas turbine markets in the world, are clearly going for H-Class in their recent tenders and saying they aren’t doing F-Class any more. Even China is now saying its going for H-Class and above.”

“We see 120 or 130 units per year and the years to come will remain at this range. The only thing is the make-up of these units is clearly changing, with less in the middle range and more in the higher classes or decentralized classes. When we talk about where the HL will fit, in Europe it is a capacity discussion while in other markets its not capacity they opt for, it is base load because of the higher efficiency and lower capex.”

“Gas is a good partner for renewables. Renewables are here to stay and will grow and our position is that gas is a good partner because you get into high levels of efficiency and its much faster to install from an EPC perspective. It’s cheaper and more flexible compared to all the other alternatives.”

What’s driving the pace of change to increase because its taken such a lot of time to get to 60 per cent efficiency?

On that theme, Amin is unequivocal.

“From a commercial point of view, customers were not paying too much attention to total cost of ownership or tariff-based models. There was a lot of specific price discussion and dollar per kilowatt was driving decisions in the industry and their capex played a major role.”

“This is changing. They didn’t pay attention to efficiency before because of abundant hydrocarbons and gas. Also the tools. We were always doing stuff in two dimensions, and designing in two dimensions. Now 3d, additive manufacturing and digitalization is helping a lot. It’s a race for efficiency ” you need to be ahead of the game otherwise you don’t survive.”

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