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.
Plasma Assisted Cupola

  • 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.
Submerged DC Electrodes

  • 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.

 

Plasma Syngas Polishing
  • 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.