Squeezing Value continued
Even when first developed, Rolls-Royce envisaged a design capable of decades of further development and this has also applied to the industrial variant which is now available in a range of outputs from 27-38 MW. In its industrial configurations the SGT-A35 fleet has now recorded more than 37 million hours in service.
Three variants of the engine and three variants of power turbines are now available to match application requirements. Siemens notes that the two-spool architecture allows maximum operational flexibility and a high tolerance to transient excursions and challenging cycles. The SGT-A35 turbine heat rate can reach 9904 kJ/kWh with a speed of up to 4850 rpm depending on configuration. Up to 110 kg/s of exhaust mass flow is possible at a temperature of around 500°C.
All of the variants can use liquid or gaseous fuel and may be equipped with a Dry Low Emissions (DLE) burner for additional emission controls. By carefully controlling combustion characteristics NOx and CO can be maintained at low levels. “Controlling flame temperature is a big part but also how you manage the DLE combustor,” said Rickert. However, additional post combustion emissions control systems are available such as selective catalytic reduction (SCR). Rickert said: “Those typically deliver emissions below 2 ppm NOx and we are seeing some states in the US that are driving that requirement. We expect that trend to continue growing.”
Immediately behind the SGT-A35 is a free power turbine that is aerodynamically connected to the turbine using the exhaust airflow. There is no connecting shaft. This arrangement allows the free power turbine to deliver the required and variable level of torque to the compressor to meet spontaneous demand while the engine can be run at full power continuously for optimum efficiency.
At the Winchell Lake Compressor Station the free turbine is set to drive a Siemens RFBB36 centrifugal pipeline compressor which has a maximum working pressure of 155 bar with an inlet flange of up to 760 mm and up to five
Maintaining the SGT-A35 at maximum efficiency in operating mode allows the configuration to meet another key requirement for gas compression applications – low operating costs. As Rickert explained: “End users want the most efficient solution to provide the lowest costs of delivering gas from A to B.”
Figure 6. Fuel filters and oil filters are all located on the outside of the package so it is not necessary to access the noise enclosure to maintain the unit.
According to Siemens, the RFBB36 compressor offers some of the highest compression efficiency in the midstream market while delivering the lowest CO2 and methane gas emissions compared to other pipeline compressors.
In a bid to further reduce costs, the SGT-A35 is integrated into a compact, lightweight and easily maintainable package designed for oil and gas applications by the Dresser-Rand business, part of Siemens Power and Gas. “We’ve updated the Dresser-Rand packaging design making it much improved in terms of serviceability,” said Rickert. He notes, for example, that the fuel filters and oil filters are all located on the outside of the package so it is not
necessary to access the noise enclosure to maintain the unit.
Rickert added: “That serviceability of the package means that you have a reduced amount of down-time whenever you have a service event. It allows you to optimise your availability and your up-time.”
Supplied by Siemens’ Dresser-Rand business as a complete package, the power unit arrives on site factory preassembled. The only on-site assembly required is to install the roof-mounted ancillaries such as the air-inlet filtration units, intake assembly and the exhaust.
“There’s a minimal amount of site work to be done, as we have the main package built in the factory and then ship it directly to site,” noted Rickert.
Package design is also suited to the operating environment. While ambient temperature changes don’t really affect the core engine – jet engines are designed to operate in all weather conditions – extreme temperatures can have an impact. Rickert explained: “Cold weather presents some unique challenges, primarily concerning steel which can become brittle. Siemens has extensive experience making the correct steel selection for the package.”
In Alberta, where temperatures have fallen to as low as -61°C other measures may be required: “You need some additional features for servicing,” said Rickert, “for example, if the engine is shut down for servicing you need to be able to keep the package warm, especially in the oil systems to keep the oil from freezing. There are standard solutions that we’ve introduced based on where in the world the unit is going to be operating. Siemens has a lot of experience running engines in colder climates and hotter locations too, so we’ve designed them to go into a variety of locations.”
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