Development of potassium recovery system for MHD spent seed containing materials

Efficient recovery and regeneration of seed material is an economic and environmental necessity in Coal-Fired Open-Cycle Magnetohydrodynamics (MHD). The potassium seed which is added to enhance the electrical conductivity of the hot combustion gas by thermal ionization, also removes the environmentally offensive sulfur containing gaseous combtistion products by forming K₂SO₄. Approximately 90 % of potassium is recovered in the various downstream components as spent seed and fly ash, with the remaining potassium being contained in the molten ash or slag. Because of the high cost of fresh seed and limited commercial use of K₂SO₄, the disposal of spent seed is not economically feasible. Therefore, a complete potassium recovery system from spent seed and slag is required.

In this work, a multistage countercurrent extraction process to recover watersoluble potassium from spent seed is developed. A lime digestion option is suggested to recover water-insoluble potassium from spent seed insolubles and slag. Spent seed solids used in the bench scale experiments were from the Coal Fired Flow Facility (CFFF), tests LMF4-I and LMF4-K. Results of bench scale dissolution experiments at various process conditions to recover water-soluble potassium from spent seed are reported in this thesis. Data obtained from the experiments are implemented in the process design of a multistage countercurrent system for the extraction of potassium from spent seed solids. Literature data axe used in designing the extraction system based on lime digestion for the recovery of potassium from spent seed insolubles and slag. The preliminaxy economic evaluation of the seed reprocessing scheme is also presented.