Steam for Power

Turbine technology being central to energy-producing industry, research and development efforts is directed towards cost-savings (increased efficiency, reliability, and component lifespan), sustainability (alternative fuels, lower emissions), and cost-competitiveness (particularly for the emerging technologies) [1]. This blog post is the first in a series of three that will focus on steam, gas and hydraulic turbines for power generation.

Going back to the Archimides era we will find the idea of using the steam as a way to produce work. However, it was not until the industrial revolution when the first reciprocating engines and turbines developed to take advantage of steam power. Since the first impulse turbine development by Carl Gustaf de Laval in 1883 and the first reaction type turbine by Charles Parsons one year later, the development of turbines have sky-rocketed, leading to a power output increase of more 6 orders of magnitude[2].

Steam turbines can be intended for either radial- or axial-flow, but the modern ones are mainly axial-flow units, particularly in large power plant applications, and they are generally large in size. The rotors are usually multistage arrangements designed to handle high pressures in the first stages and lower pressures in the later stages [3]. The two major axial-flow turbine stage configurations are impulse and reaction. The distinction is based upon relative pressure drop across the stage, where one stage consists of one row of stationary blades/nozzles, and one row of rotating blades. In the impulse turbine design (pressure drop occurs across stationary blades), the magnitude of the relative velocity of the steam remains unchanged, but the absolute velocity exiting the rotor is greatly reduced. The reaction design velocity triangle differs from the impulse design in that there is increase in relative velocity which corresponds to a pressure drop across the rotating blades and a loss of enthalpy.

steam turbine

As the steam flows over the rotor blades, depending on pressure or velocity absorbance we get a pressure compounding (each nozzle row coupled with one moving blade row) or a velocity compounding (one nozzle row direct steam to multiple moving blade rows) impulse turbine. There are also intermediary designs that incorporate both pressure and velocity compounding.

High computing capacity and continuous development of CFD have now allowed researchers to gain new insight into steam turbine problems. Reliability is of critical importance in steam power generation [2], and so current research surrounding steam turbines is focused around a few fundamental areas. However, as stated in “Full Steam Ahead” [4] advances in steam turbine R&D tend to favour larger-scale machines, which means that on the lower end (3 MW to 10 MW), a lot of manufacturers are using old technology.

The challenge for OEMs is to explore existing opportunities to use the latest design methods and technology to develop competitive machines. Find more about SoftInWay and AxSTREAM platform, and take advantage of working with a leading R&D player on the turbomachinery field.

References
[1] Joel Bretheim and Erik Bardy, “A Review of Power-Generating Turbomachines”, Grove City College, Grove City, Pennsylvania 16127
[2] McCloskey, T.H., 2003, Handbook of Turbomachinery, 2nd ed., Logan Jr., E., Ed., and Roy, R., Ed., Marcel Dekker, Inc., New York, NY, Chap. 8
[3]Logan Jr., E., 1981, Turbomachinery: Basic Theory and Applications, Marcel Dekker, Inc., New York, NY
[4] Valentine Moroz, “Full Steam Ahead”, November/December 2016, Turbomachinery International, p.31

 

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