(423d) Thermal Desorption of Mercury from Coal Using a Draft Tube Spouted Bed

Thermal desorption of mercury from coal with a scalable, high throughput spouted bed desorber provides an effective method of pre-treatment for coal-fired power plants. A novel draft tube spouted bed desorber capable of processing a wide particle size distribution of pulverized coal was developed through sequential design iterations and a series of tracer visualization studies. Baseline experiments were performed for a conventional conical-cylindrical spouted bed and draft tube spouted bed. The mean particle residence time distribution and turnover rate were measured with variable particle sizes, fluidizing conditions, and reactor and draft tube geometries within a clear half-circular system. Effective heat and mass transfer rates were determined for a conventional spouted bed, straight draft tube, and modified draft tube geometry using surrogate pulverized coal. A self-contained, high-temperature spouted bed desorber test section was fabricated and demonstrated with bituminous, subbituminous, and lignite pulverized coal. Desorbed mercury species were continuously measured at temperatures between 150 °C to 350 °C, at several fluidizing gas flow rates. Several pulverized coal feeds with variable particle size distributions (between 10–500 µm) were fed into the spouted bed desorber under the range of operating conditions. The mercury thermal desorption rate for each coal type was determined as a function of particle size, temperature, and superficial gas velocity. Using the experimental data, process design and economics were evaluated for thermal desorption of mercury from a commercial scale coal-fired power plant.