1. Solid fuel combustion TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A AAA A A

2. Solid fuel combustion process Three stages of mass loss: Drying (removal of water): endothermic Devolatilization: vaporization of volitile hydrocarbon compounds, gas-phase diffusion flames. Char combustion: heterogeneous (solid phase fuel, gas phase oxidizer) combustion of fixed carbon.

3. Water in fuel Water content in fuel: free (within pores) or bound (adsorbed into interior structure). Green wood: 45% water, free and bound. Lignites: up to 40% water Bituminous: 1-5%, mostly bound.

4. Devolatilization process Volatiles formed from heating in the absence of oxygen (pyrolisis). Volatiles formed from heating in the absence of oxygen (pyrolisis). Depending on fuel, volatile release begins around 250-300 o C Depending on fuel, volatile release begins around 250-300 o C Volatiles include CO, CO Volatiles include CO, CO 2, hydrocarbon vapors, H 2, chemically-produced water. Above 900 o C, devolatilization complete: fixed carbon (char) and ash remain.

5. Devolatilization analysis Could apply droplet-based analysis to devolatilizing fuel particle: made difficult by different saturation (boiling) temperatures of different compounds. Could apply droplet-based analysis to devolatilizing fuel particle: made difficult by different saturation (boiling) temperatures of different compounds. Often modeled as a first-order reaction: Often modeled as a first-order reaction:

6. Char combustion Surface (heterogenous) global reactions: Surface (heterogenous) global reactions: gas-phase reactions: gas-phase reactions:

7. Solid fuel combustion technology Fixed-bed combustion: wood stoves, stoker-fired furnaces, refuse/biomass burners. Old technology. Fixed-bed combustion: wood stoves, stoker-fired furnaces, refuse/biomass burners. Old technology. Suspension burning: pulverized coal (PC) combustion. Fuel is ground to sub-mm sizes, injected into combustion chamber. Suspension burning: pulverized coal (PC) combustion. Fuel is ground to sub-mm sizes, injected into combustion chamber. PC combustion process, technology similar to spray combustion. PC combustion process, technology similar to spray combustion. PC can be scaled to large sizes (200 tons coal/hr), more responsive to load. PC can be scaled to large sizes (200 tons coal/hr), more responsive to load.

8. Fluidized-bed (FB) combustion: fuel particles are suspended in a gas stream. Bed appears like a boiling liquid. Fluidized-bed (FB) combustion: fuel particles are suspended in a gas stream. Bed appears like a boiling liquid. Two main types: bubbling FB and circulating FB. Two main types: bubbling FB and circulating FB. Relatively new combustion technology. Main advantages: Relatively new combustion technology. Main advantages: Control of Sox and NOx within combustion chamber. No need for post-combustion scrubbers. Control of Sox and NOx within combustion chamber. No need for post-combustion scrubbers. Enhanced fuel flexibility: high-moisture, high ash fuels can be burned without problems of instability, loss-of-ignition, slagging. Enhanced fuel flexibility: high-moisture, high ash fuels can be burned without problems of instability, loss-of-ignition, slagging.