Siemens STC-SI Compressor Series

Single-Shaft – Air Compressor with Integrated Coolers

Isothermal compressor: extraordinary efficient and reliable

The Siemens STC-SI compressor is the result of decades of compressor development experience. The design is a combination of proven single-shaft and integrally-geared compressor technology. Siemens’ new three-stage, single-shaft turbo compressor is available in various frame sizes and covers a volume flow up to 1,000,000 m3/h. The Siemens STC-SI compressor, with the highest efficiency levels in the market, will mainly be used as main air compressor in air separation plants.


  • High efficiency – up to four percent greater than existing products on the market
  • Optimized for Siemens steam turbine drive speeds; also compatible with Siemens electric motor
  • Graded frame sizes for customer process requirements
  • Designed for stability with operating speeds below the second critical speed
  • Optimized maintenance concept, including easy cooler bundle handling
  • Designed to minimize total cost of ownership and life cycle costs
  • Shipping dimensions minimized for overseas and inland transportation limitations
  • The volute casing can be easily disassembled for transport
  • Short delivery times

Design Concept

Flexible use: As a stand-alone main air compressor or in combined trains with booster air compressor

The Siemens STC-SI compressor was designed as the main air compressor for steam turbine and electric motor drives. The primary application is in large gasification plants, together with a booster air compressor driven by a common steam turbine. This arrangement was an essential piece of the overall design. Siemens is the market leader for this combination of main air and booster air compressor trains with a double-ended steam turbine. The integrally-geared STC-GV booster air compressor can be customized with multiple process sections depending on a customer’s process requirements.


Highest efficiency in the market
One of the outstanding features of the Siemens STC-SI compressor is its energy efficiency – the best available on the market. This compressor series was designed for highest efficiency and reliability which is essential for large air separation units; for example, in coal-to-liquid, gas-to-liquid or IGCC plants. Siemens has been a preferred supplier for air separation equipment for EPCs and plant operators for more than 60 years.

Reliable operation

The single-shaft STC-SI turbo compressor has been optimized for Siemens’ steam turbine drive. This enables steam from other processes to be reused – a plus for the running costs and the environment. Depending on the project-specific requirements, the Siemens STC-SI compressor can be alternatively driven by an electric motor via an external speed increasing gear box.

Simple and quick maintenance

The short, stiff cooler bundle can be easily drained and is highly accessible if maintenance is required. With Siemens’ motorized cooler bundle removal device, customers benefit from simple assembly and disassembly, as well as the advantage of a low crane hook height.
The Hirth connection allows for wear-free disassembly of the first-stage impeller without the need to rebalance the impeller once it is reinstalled. A special tool is provided for this feature.  The front bearing is readily accessible without removing the upper casing or the first impeller.