In a first for the company, Siemens’ SGT-700 gas turbines are now destined for a Chinese combined heat and power (CHP) application. Two units are heading to a distributed energy project run by Guangzhou Development Group Co., Ltd. (GDG) for the Taiping Industrial Park in Guangzhou in Guangdong Province. Operated as combined cycle units using natural gas, once operational the turbines will meet the industrial park’s electricity and heat demands while cutting emissions.
This is the second distributed energy project built by Guangzhou Development Group using Siemens equipment. It follows a 2013 development featuring two SGT-400 gas turbines also in Guangzhou.
With a claimed reliability of higher than 99%, Siemens boasts of the SGT- 700 gas turbine’s sturdiness and ease of maintenance as well as its long-term stable operation. In addition, with its high fuel flexibility, low emissions and high residual heat the model is widely used in diverse power and mechanical drive applications, including power generation, oil & gas and industrial power generation.
Roger Ahlin, the product owner of the SGT-700 gas turbine at Siemens, explained: “It’s an industrial machine. First of all it’s very versatile especially for this type of application. It has good efficiency and it has good source data and that is very well proven for evaluation in combined cycle and cogeneration applications; those two features are especially very important in terms of the technical aspects.”
As well as good base load efficiency Ahlin noted: “It’s also good in part load but in this type of application the end user is mainly running in base load. In this case it’s a cogeneration and combined cycle plant, so it’s for the steam and also electricity generation for industrial use on site.”
This project is expected to go into operation in the second half of 2019 with Siemens acting as a sub-supplier to the delivery consortium. The steam turbine does not form part of the Siemens scope of supply.
With 90% overall energy efficiency in CHP mode the gas turbine is rated at around 33-34 MW. In simple cycle power generation under ISO conditions output is 32.8 MWe while in mechanical drive configuration this figure reaches 33.7 MW.
The SGT-700 industrial gas turbine is a robust, highly fuel-flexible gas turbine that provides high-performance with low emissions.
The SGT-700 concept
The SGT-700 concept is based on the 25 MW two-shaft or twin spool SGT- 600 unit but with third-generation DLE (Dry Low Emissions) combustion technology. Specially designed to produce more power, the SGT-700 is an up-rated version of the proven SGT-600 industrial gas turbine. The robust design of the SGT-600, which had already accumulated over three million hours of operation by 2001, was utilized to maintain high availability and reliability, providing an excellent platform for the SGT-700.
In November 2001 the first engine was started and verification tests were initiated before the turbine underwent a number of different development stages at the Finspång test facility in Sweden. Complete disassembly and visual inspection of each component was standard procedure during this first year to validate the design. During these comprehensive tests, 1200 additional measuring points were installed, and the control system was additionally equipped with data acquisition systems.
Subsequently, in April 2003 the turbine was launched commercially for partial release. Three orders taken that year for the first five units were the basis for the evaluation and introduction programme that was applied through 2004 and 2005.
Since then, some 98 units have gone into service around the globe with well over 2 million fleet operating hours recorded to date.
Compared with the SGT-600, the SGT-700 has an increased airflow from 80 kg/s up to 91 kg/s by extending the compressor blading profile and introducing an additional compressor stage.
In addition, a different combustion system has been introduced from the then 45 MW SGT-800, now available in various ratings from 47 MW to 57 MW – a simple and robust DLE system that minimizes nitrogen oxides (NOx) in the combustor. This represents the third generation of DLE, which Siemens says demonstrates 15 ppm NOx on gaseous fuel and 42 ppm NOx on liquid fuel without the requirement for the introduction of water or steam.
The turbine inlet temperature (TIT) was initially increased by a moderate 27°C (from 1115° to 1142°C), and step-wise to the current 1188°C. The compressor turbine also has a modified cooling design in order to handle the increased TIT while the pressure ratio has been increased from 14:1 to more than 18:1. It had an original heat rate of 9999 kJ/kWh. For power generation the heat rate today is 9675 kJ/kWh.
In order to better fit the mechanical drive market, the SGT-700 was designed to operate at a lower speed, from 7700 rpm to 6500, rpm. The turbine has a larger rotor diameter, lower speed and higher output while since launch its efficiency has increased from 34% to 38.7%. Exhaust gas flow is now 96.5 kg/s at an exhaust temperature of 530°C.
This twin shaft/spool machine initially delivered a simple cycle thermal efficiency of 36% at base load on gas.
In July 2004 Siemens performed a successful string tests of its then branded GT10C industrial gas turbine coupled to a 12MV5A compressor. The first two SGT-700 turbines to be delivered and put into commercial operation were for the UGDC Port Said Nile Gas project in mechanical drive configuration. The turbines operate on gas fuel only. Two identical trains were ordered in November 2002 for delivery to a natural gas liquids (NGL) plant owned by the special vehicle company UGDC (United Gas Derivatives Company). Designed for operation in an ambient temperature of 45°C, both turbine-compressor sets were commissioned at the end of 2004.
The first two SGT-700 genset units are still generating power and district heating for the town of Sochi, a major resort on the Black Sea Coast of Russia.
Offering high efficiency, very good off-design efficiency and low degradation, the SGT-700 is designed to match the overall fuel consumption of aeroderivative machines.
Like the SGT-600, the SGT-700 has a two-stage power turbine and a two-stage gas generator turbine. The SGT-700 has 11 stages within its axial-flow transonic compressor, also incorporating the latest aerodynamics and with variable guide vanes for optimized performance over a wide range of operating conditions.
The two-stage, uncooled, free power turbine offers a nominal shaft speed of up to 6500 rpm and it can be matched for different ambient conditions. Again, as with the SGT-600, it features an annular combustor. For mechanical drive, it may operate at 50% to 105% of the nominal speed.
The compressor rotor and the twostage bolted compressor turbine module form a single shaft, which rests in two standard tilting pad-type hydrodynamic bearings.
A separate high-speed two-stage power turbine also forms a single unit, again resting on two standard hydrodynamic bearings. The power turbine is then coupled to driven equipment.
In power generation configuration it has a mass of 169,000 kg, while as a mechanical drive unit it weighs some 63,000 kg. Approximate dimensions are 18.8×4.6×5.8 m and 11.7×4.0×5.8 m for power generation and mechanical drive, respectively.
In contrast to the older types of industrial turbine, which had a relatively low power turbine speed (3600 – 4700 rpm), this industrial gas turbine has a 6500 rpm design speed, putting it on a par with aeroderivative machines which run at 5500 – 6100 rpm. The higher speed of the power turbine was chosen to give a high total efficiency in compressor drive applications – both SGT-600 and SGT- 700 have a high power turbine speed, which results in a high train efficiency and requires no step-up gearbox either.
These turbines are compact, and feature short erection and commissioning times as well as a design based on ease of maintenance. The turbine is skidmounted, with the auxiliaries grouped in self-contained modules while the whole compression package can also be designed to form a single-lift unit. The layout is basically the same for both power generation and mechanical drive applications.
Ahlin said: “It’s a standard package where the auxiliaries and the gas turbine are installed on a single base frame. The generator is placed on the separate foundation, but we deliver a complete unit from our factory in Finspång.”
He added: “Stationary testing of all equipment is conducted in our workshops, all except firing up the package is done before shipping. The core engine itself is fully tested before entering the package.” For example, the machine destined for Guangdong is currently undergoing its final testing stages, and engine testing of the second unit took place in early November.
The turbine was designed with the flexibility to suit both mechanical drive and generator applications with availability and reliability prioritized. During the first year of operations the reliability factor was recorded at 98.9% while the corresponding availability figure was 97.7%.
Siemens claims the SGT-700 provides the best availability within its class, thanks to a robust and well-proven design. The compact twin-shaft engine is easy to maintain and allows for flexible operation with excellent efficiency at part-load conditions. Using the same design for power generation and mechanical drive increases the operational reliability, the company adds.
Now, with the fleet total accumulated hours at more than two million hours of field operation, all of which are equipped with DLE, a reliability of >99.3% is reported.
Designed to offer higher output and efficiency as well as lower emissions and capable of using a wide range of fuels, relatively easy on-site maintenance, low deterioration rates and service costs and short installation times were key design considerations. Its compactness makes it suitable for offshore installations as well as for retrofitting in existing installations. Furthermore, due to its high exhaust temperature and residual heat, it is an ideal platform for combined heat and power such as the Guangdong project.
Ahlin added: “All engines are equipped with the data for logging and also for communication with our service center here in Finspång. We call it our RDS remote diagnostic services. Due to legal or regulatory restrictions in some countries as well as security limitations for some customers, we don’t have data from all the in-service engines available. But we have the possibility to collect this if the customer allows us to do so.”
Third generation DLE
The SGT-700 and SGT-800 are only supplied in DLE-versions since this design allows reliable and fuel flexible operation at a lower investment cost than the non-DLE-designs, Siemens says.
Second generation DLE burners – a split cone with two main fuel pipes – were developed to meet the increased emissions requirements for the on-shore market and were first introduced for the SGT-600 gas turbine in 1991. The SGT-600 combustion system is capable of NOx emission levels below 25 ppm NOx running on gas. The design allows for operation across the full load range without any staging of the combustion. Recently Siemens also incorporated the third generation DLE into the SGT-600 and it too is capable of emissions below 10 ppm NOx.
During the development of the SGT- 700 and 800, the third generation DLE burner was introduced utilizing the same design principle as the previous version, but with the cone now split into four sections and with an additional mixing tube. This same design is used in both engines and only the number of burners differ. The SGT-700 combustion system consists of 18 removable burners in an annular combustor whereas the SGT-800 comes with 30. With the third generation DLE system it is possible to maintain low NOx and CO emissions with a turndown to 50% load, without any staging.
In addition, the combustion system has shown good durability over time with stable emission levels and operating with a wide range of gaseous and liquid fuels.
Most recently, in September Siemens reported that, working together with utility group E.On, it has reached a significant milestone in 3-D printing with the world’s first 3-D printed burner for an SGT-700 gas turbine operating for one year. Located at E.On’s combined cycle power plant in Philippsthal in the German state of Hessen, Siemens said that the results of the test programme “are impressive” after more than 8000 hours of operations and with no reported issues (see GTW Sept-Oct 2018).
Siemens began printing gas turbine burners using selective laser melting technology in 2017 using its intelligent burner manufacturing (IBUMA) programme, also in Finspång. Each burner head is manufactured in one piece compared to traditional methods that required 13 individual parts and 18 welds. Design improvements allow the operating temperature to be kept lower, thus contributing to a longer operational lifespan of the components and, ultimately, the gas turbines, says Siemens, noting that the pilot-gas feed is now part of the burner head instead of the outside fuel pipe, for example. 3-D printing of the DLE pre-mixer allows Siemens to simplify the production process, cutting lead times by around 70%.
Commenting on the project Vladimir Navrotsky, Chief Technology Officer for Siemens Power Generation Services, Distributed Generation, noted: “These early results from the IBUMA burner with E.On validate our belief that this technology is a game-changer.”
He added: “Our achievements using AM are paving the way for greater agility in the design, manufacturing and maintenance of power generation components.”
China’s CHP market
Designed to provide heat and power mainly for light industrial users and support services, users at the Taiping Industrial Park include paper container manufacturing, metal, electrical or machinery product manufacturing. The Economic Development Bureau of Guangzhou City Government constructed the Taiping Industrial Park as part of a strategy for the Pearl River Delta for a large comprehensive energy supply for electric power, fuel, and natural gas.
Commenting on the wider, national policy of vigorously developing natural gas distributed energy, Yao Zhenguo, Executive Vice President of Siemens Ltd., China, General Manager of Power and Gas Division Greater China, said: “With the continuous optimization of the energy mix, China will usher in a boom of efficient and environmentally friendly natural-gas distributed energy.”
Certainly, China is implementing a number of policies designed to promote greater use of cleaner fuels such as natural gas in order to curb air pollution and improve environmental performance. However, volatile gas prices and large regional variations in gas pricing have presented challenges for investors looking to develop gas fired CHP developments in China. Unclear policies have made the bankability of such projects more difficult.
“For this project and that area, gas supply is sufficient. There are many resources in that area for natural gas supply and they can also have LNG from overseas. In Guangdong province the gas supply is perhaps the best in China. But part of the problem is the gas price and it is obviously changing and having an impact on electricity generators,” noted Ahlin.
Nonetheless, fluctuations in market prices and availability of different fuels offers a potential advantage for the SGT-700 with its fuel flexible operation. As Ahlin said: “We have been working a lot with fuel flexibility. For a lot of petrochemical industries we can use various off-gases, heavy hydrocarbons or hydrogen gases for example. Varying from pure propane, the turbine can also be pure ethane, and many other gases and liquids. The SGT-700s have been operating on all these fuels without changing any setting in-between. You have a very robust system that can accept very wide range of fuels.” Several industrial applications of the SGT-700 are already operating in China using alternative fuels for example.
“A lot of it is in the hardware but the ability to operate on a wide variety of fuels is also in the software system – not for this particular plant but for many similar applications where there are offgases available. It’s a very good way of reducing the operating cost if you can use waste gas for power generation. It could be even flare gas; in that respect it could be said to be free fuel for power generation. That is not possible for this specific project, but in many other similar projects,” said Ahlin.
The Chinese government is encouraging CHP and more gas fired projects to leverage the opportunities associated with industrial upgrading to optimize the energy infrastructure. High efficiency, low efficiency and characteristics like fuel flexibility and ease of maintainability make the SGT-700 suitable for a wide range of industrial applications in China. This project in Guangdong perhaps signals the first step on a long road towards cleaner energy development through onsite CHP using industrial gas turbines.