Whats the Difference Between Gas Turbine and Steam Turbine?
• Steam turbine uses high pressure steam as the working fluid, while the gas turbine uses air or some other gas as the working fluid.
• Steam turbine is basically an expander delivering torque as the work output, while a gas turbine is a combined device of compressor, combustion chamber, and turbine executing a cyclic operation to deliver work as either torque or thrust.
• Steam turbine is only a component executing one step of the Rankine cycle, while gas turbine engine executes the whole Brayton cycle.
• Gas turbines can deliver either torque or thrust as the work output, while steam turbines almost all the time delivers torque as the work output.
• The efficiency of the gas turbines is much higher than the steam turbine due to higher operating temperatures of the gas turbines. (Gas turbines ~1500 0C and steam turbines ~550 0C)
• The space required for the gas turbines is much less than steam turbine operation, because steam turbine requires boilers and heat exchangers, which should be connected externally for heat addition.
• Gas turbines are more versatile, because many fuels can be used and working fluid, which has to be fed continuously, is readily available everywhere (air). Steam turbines, on the other hand, require large amounts of water for the operation and tend to cause problems in lower temperatures due to icing.
Gas Turbine vs Steam Turbine
Turbines are a class of turbo machinery used to convert the energy in a flowing fluid into mechanical energy by the use of rotor mechanisms. Turbines, in general, convert either thermal or kinetic energy of the fluid into work. Gas turbines and steam turbines are thermal turbo machinery, where the work is generated from the enthalpy change of the working fluid; i.e. The potential energy of the fluid in the form of pressure is converted into mechanical energy.
Based on the direction of the fluid flow turbines are categorized into axial flow turbines and radial flow turbines. Technically a turbine is an expander, which delivers mechanical work output by the decrease in pressure, which is the opposite operation of the compressor. This article focuses on the axial flow turbine type, which is more common in many engineering applications.
The basic structure of an axial flow turbine is designed to allow a continuous flow of fluid while extracting the energy. In thermal turbines, the working fluid, at a high temperature and a pressure is directed through a series of rotors consisting of angled blades mounted on a rotating disk attached to the shaft. In between each rotor disks stationary blades are mounted, which act as nozzles and guides to the fluid flow.