Practical Design Solutions For Mechanical Drive Steam Turbines

PaperPg. 99-110.Following a review of possible alternative solutions regarding the choice of a mechanical driver; i.e., electric motor, gas turbine or steam turbine, it is demonstrated that the steam turbine as applied in industry is ideally suited for integration in many processes and often provides an optimum heat/power balance. Although it involves a higher initial capital investment, the overall result is an economic optimum. The steam turbine is adaptable within a wide range as regards the specific requirements set by each application. It has a favorable output/speed characteristic and is an independent source of power, unaffected - given proper design - by unusual operating conditions. Emphasizing the need for highly reliable machines, a design concept is presented, founded on a sound philosophy regarding mechanical design, safety and reliability. The system is an intelligent application of the modular design concept, supported by extensive research, testing and advanced computing technology. A description of requirements for applications in various widely differing industries demonstrates the suitability of this design concept. Attention is drawn to considerations leading to the actual choice of a turbine, such as efficiency, impulse or reaction design, and others. In view of this, an unbiased review is given of vital elements such as the rotor and its blading and the underlying design principles. Aspects of blade erosion, axial thrust and blade fixing methods, including the control stage, follow. In the design stage of last stage blading, particular attention is required regarding flow patterns, strength and resonance characteristics, but it is demonstrated that wide range variable speed units with last stage blades larger than 500 mm (20") can be built reliably. A special section is devoted to the elimination of dynamic stresses by suitable blade design and methods such as damping or lacing wire. Mechanical drivers can be coupled to the driven machines either by flexible or solid couplings, the latter being the only sensible solution for units of medium and large outputs, regardless of the number of cylinders. The paper concludes with some design aspects on rotor dynamics and shaft stability considerations