Which seed materials can be used in magnetohydrodynamic power generation?

In magnetohydrodynamic (MHD) power generation, a "seed" material is a readily ionizable alkali additive injected into the hot gas to increase its electrical conductivity to an adequate level, typically 10 to 50 siemens per metre.1

Commonly used seed materials include:

• Cesium: This material has the lowest ionizing potential (3.894 electron volts), making it highly effective for ionization.1
• Potassium: Often used in the form of potassium carbonate, this is a more cost-effective alternative to cesium, despite having a higher ionizing potential (4.341 electron volts).1
• Sodium: Another alkali material that can be utilized as a seed.1

Typically, these additives are injected into the hot gas at a concentration of about 1 percent by mass. Because the amount of seed material used is small, economic operation of an MHD power plant requires the implementation of a system to recover as much of the seed material as possible. In coal-fired systems, the use of seed material also provides environmental benefits by helping to reduce sulfur dioxide emissions through the formation of potassium sulfate.12