Solar Turbines has announced the commercialization of the Mercury 50 gas turbine. This advanced, 4 MW unit represents a breakthrough in recuperative gas turbine technology, and will, says Solar, address barriers commonly faced in distributed generation applications.

At the Power-Gen International conference and exhibition in 1997, Solar Turbines unveiled its programme to develop a new 4 MW-class recuperated gas turbine called the Mercury 50. Six years on, and again at Power-Gen International, Solar announced that the Mercury 50 has reached commercialization.


The Mercury 50 is the newest addition to Solar’s product line and it represents a technological breakthrough in recuperative gas turbine technology.
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The unit incorporates several state-of-the-art combustion and materials technologies which, says Solar, have resulted in a host of environmental, operational, economic and siting advantages.

Solar’s new unit is one of several advanced gas turbine technologies that have recently attained – or are close to – commercialization and which were developed under the US Department of Energy’s (DOE) Advanced Turbine Systems programme. This programme began in 1992 and aimed to develop 21st Century gas turbines that were efficient, clean and less expensive to operate than gas turbines of today. While manufacturers such as GE and Siemens-Westinghouse focused on utility-scale machines, Solar concentrated on the development of small-scale industrial machines for distributed generation applications.

The Mercury’s low emissions signature and high power density are features that Solar believes will allow it to help utilities and other organizations overcome barriers to distributed generation. “The Mercury 50 recuperated gas turbine will enable energy service providers, utilities, and industrial and commercial power users to incrementally expand their generating capabilities quickly for highly reliable, low cost power service to satisfy growing requirements for distributed generation,” said Greg Barr, vice president of power generation for Solar Turbines.

The Mercury 50 is the latest addition to Solar Turbine’s product line and represents a breakthrough in recuperative gas turbine technology

Extensive evaluation

The Mercury 50 will be introduced with a nominal power rating of 4600 kW with a heat rate of 8863 Btu/kWh, and is available in a gas-only configuration. The unit has an exhaust temperature of 374°C (705°F), an exhaust flow of 64 152 kg/h (141 430 lbs/h) and an efficiency of 38.5 per cent. The rated turbine inlet temperature of the Mercury 60 is 1163°C (2125°F).

Since its initial launch, the unit has undergone an extensive field evaluation programme which has resulted in a series of product improvements that have been incorporated into the engine, recuperator and package. The field evaluation sites provided Solar with valuable data regarding the operation of the generator sets over a variety of conditions including a range of ambient temperatures, different fuel properties, as well as numerous customer-driven operating scenarios. The most significant improvements to the product have been those that have extended recuperator durability and improved turbine rotor dynamic stability.

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The Mercury 50 has completed more than 40 000 hours of operating experience at field evaluation sites in California, Colorado, Illinois and South Carolina in the United States and in France and Australia. The principal DOE host site for demonstration of the Mercury 50 was at Rochelle Municipal Utilities in Illinois, USA. Field evaluation units were also installed at a remote phosphate mining site in Queensland, Australia, and at Solar’s San Diego Harbor Drive test facility in the USA.

Since the initial field evaluation, the recuperator material has been upgraded and structural design integrity has been enhanced to improve durability. The gas turbine rotor was shortened and the centre X-frame was replaced with a hot strut design to improve dynamic stability. Performance improvements were also made in the compressor and turbine sections.

Recuperated cycle

The Mercury 50 is a single shaft recuperated machine with a ten-stage axial compressor and a two-stage turbine. The recuperator cycle works by recovering turbine exhaust heat and using the energy to preheat the engine’s combustion air. This type of cycle helps to yield high turbine efficiencies at modest temperatures and pressure ratios. The Mercury is equipped with Solar’s primary surface type recuperator with a Inconel Alloy 625 construction. The recuperator allows the engine to develop an efficiency of 38.5 per cent at ISO conditions.

Axial compressor: The ten-stage compressor has a compression ratio of 9.1:1 and is equipped with variable inlet guide vanes and stators. Inlet airflow is 17.9 kg/s (39.2 lb/s) and rotor speed is 14 179 r/min (50 Hz), 14 186 r/min (60 Hz).

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Annular combustion chamber: The Mercury 50’s Ultra Lean Premix recuperated combustion system, with eight fuel injectors and a torch ignitor system, represents a substantial technology development milestone in Solar’s on-going efforts to achieve further emissions reductions. Solar Turbines led the gas turbine industry in the development of low emissions combustion technology and has now sold over 1140 turbines with its SoLoNOx dry low-NOx combustion system. These units have accumulated a total of 22 million hours of operation in a variety of applications worldwide. The Mercury 50 is available with a 5 ppm nitrogen oxide (NOx) guarantee, with the carbon monoxide (CO) and unburned hydrocarbons (UHC) guarantees both at the 10 ppm level.

Control: The generator set is controlled by a Turbotronic 4 control system equipped with a ControlLogix processor and a standard display with discrete event log, strip chart, historical trend and maintenance screen. The system carries out a number of functions including gas turbine and generator control, vibration and temperature monitoring, auto synchronizing, kW control, voltage control, reactive power control and generator protection.

The Mercury 50 generator set package consists of a single skid containing all major turbine systems which is designed to maintain turbine, reduction drive and generator alignment. It has a natural gas fuel system, integrated lube oil system and a direct drive AC start system.

Low emissions

Solar believes that the Mercury 50’s performance characteristics mean that its appeal will go beyond traditional industrial

cogeneration or combined heat and power (CHP) applications. The Mercury 50 is well suited for commercial CHP or BCHP applications, where steam loads are less than 11 340 kg/h (25 000 lbs/h) and chilled water and/or hot water is required. The Mercury 50 is also well suited for intermediate peaking applications, such as economic dispatch for municipal utilities and rural electric cooperatives, distributed generation applications such as utility grid support, shoulder management for municipal and rural electric cooperatives and load following.

Like many manufacturers producing equipment for the distributed generation market, Solar points to the recent blackout in the USA and a decline in investment in transmission and distribution as providing an opportunity for the Mercury 50. Transmission grid bottlenecks and load growth together present a compelling case for utilities and industrial and commercial end-users to invest in distributed generation technology. According to organizations such as the World Alliance for Decentralized Energy (WADE), investment in distributed generation is a low-cost alternative to investment in transmission and distribution infrastructure.

Nevertheless, barriers to distributed generation still exist in the USA and other parts of the world – for example, a key barrier to the expanded use of 5-15 MW machines in the US has been that emissions have been too high to permit easily. The Mercury 50 has been specifically designed to overcome such barriers and, says Solar, will open up a large number of new utility use opportunities. The machine can be used to serve load growth, to relieve areas of transmission and distribution congestion and to enhance system reliability, and can operate in environmentally sensitive areas.

Solar Turbines points out that one of the advantages of distributed generation solutions is size. The Mercury 50 unit can be transported to various locations as needs change, making it a flexible, low-risk resource for utilities. Siting is also simplified by the fact that these units have very low emissions, and the Mercury 50 requires very little in the way of site utilities.

The Mercury 50 has low emissions of NOx, CO, sulphur dioxide (SO2), particulate matter and toxics. This means that it can be sited where other generation options would be prohibited. In the USA, this is particularly valuable in nonattainment areas under the Federal Clean Air Act.