Next Generation Gasification
- AST Process – A/C Electrodes
- Conventional Plasma Torch
- Plasma Assisted Cupola
- D/C Graphite Electrode Furnace
- D/C Graphite Electrode Furnace with A/C glass furnace bottom
- Plasma Syngas Polishing.
A/C Graphite Electrode Furnace
- Arc rotates between three electrodes
- Rotation of arc imparts stirring to bath, increasing furnace efficiency
- Brush-arc mode for electrodes concentrates heat at bath’s surface where most needed for gasification reactions
- Electrode consumption slower compared to DC furnaces
- Graphite electric arc furnace most commonly used type in steel making and metal smelting operations
- AST’s extruder type feeder introduces waste at side of furnace, eliminating extraneous air in the system, resulting in cleaner, richer syngas.
Conventional Plasma System
- The original test model for plasma assisted waste gasification. It used a molten metal bed gasifier and a DC plasma torch
- Main drawbacks were the limited plasma torch power and the inherent energy inefficiencies of plasma torches which have to be water cooled to prevent melting
- Used for most early experiments. Georgia Tech data is cited most often.
- A coke fired cupola that relies on air blast to combust
- Plasma torches is to keep the cupola bottom from freezing
- System requires shredding, sizing and baling of waste to prevent turbulent air from blowing small items out of the stack. Can not handle fines
- Process is difficult to control. Syngas chemistry is highly variable. Large amounts of air dilutes syngas, thereby reducing its BTU value
- Does not allow easy separation of slag and metals.
- Both describe a DC graphite arc furnace where the Cathode and Anode are both above the bath, and discharge through the bath
- Waste must be shredded and sized before injecting into the furnace
- Waste injection is from the top of the furnace between the two electrodes and requires nitrogen which dilutes and contaminates the syngas
- Processes have shortened refractory life issues due to exposure to the arc’s thermal radiation.
- A plasma torch is used in the process after the gasifier stage ostensibly to break up large, undesirable molecules in the syngas
- There are several variations on this arrangement, mainly dealing with the type of gasifier used and the exact placement of the torches.
- Figure shown is for Plasco system.
