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What do topping and bottoming mean in a coal-fired MHD power plant?
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magnetohydrodynamic power generator
Comparison of the operating principles of (A) a turbogenerator and (B) an MHD generator.
In a coal-fired magnetohydrodynamic (MHD) power generator, the terms topping and bottoming refer to the two stages of a binary cycle designed to maximize efficiency.2
- Topping: This is the initial phase where high-temperature, electrically conducting gas—produced by burning coal—is passed through the MHD generator. During this stage, the gas's kinetic energy is converted directly into electric power as it expands through a magnetic field.12
- Bottoming: Once the gas temperature drops to a point where thermal ionization is no longer sufficient for efficient MHD power production, it is directed to the turbogenerator of a conventional steam plant. This secondary phase captures the remaining thermal energy to generate additional electricity.2
By combining these two processes, an open-cycle MHD system can achieve significantly higher overall efficiency than a standard power plant.12