1. The Challenge of Gas as a Conductor: For the MHD process to work, the moving fluid must be an electrical conductor. Most gases are naturally excellent insulators. Even at high combustion temperatures, gases do not contain enough free electrons to conduct electricity efficiently.
2. The Process of Seeding: To overcome this, "seeding" is used. Small amounts (about 1% by mass) of an easily ionizable alkali metal, such as Potassium or Cesium, are added to the hot flue gas.
• Alkali metals have a very low ionization potential, meaning their outer electrons can be stripped away easily by heat.
• Once ionized, these metals release a large number of free electrons into the gas stream.
3. Resulting Effect: The addition of these ions dramatically increases the electrical conductivity of the gas, allowing it to act as a moving conductor. As this conductive "plasma" moves through the magnetic field, an electromotive force (EMF) is induced across the electrodes, generating power according to Faraday's Law of Induction.
Without seeding, the gas would remain an insulator, and the MHD system would fail to generate any electricity.