PURWOX (USA), Inc. C 1997

 System Process

Feeding on waste, solid organic feed materials - primarily solid waste and/or other types of low value waste feeds - are dumped from trucks (exactly as would be received at the landfill) or drums into a slope-sided receptacle. At the bottom of this receptacle is a gravity-fed belt conveyor that takes the solids to a rotating blade-type grinder for size reduction and density control. A magnetic tramp iron collector system is used to remove ferritic/nickel/cobalt materials from the solids stream before commination. The discharge of the grinder feeds a second conveyor belt, which carries the solids to a lock-hopper reception bin atop the pyrolytic converter.

A double-door blast-furnace type feed chamber is used whereby the top door opens with the bottom door hermetically sealed against the reactor chamber. The entire contents of the receptacle chamber drop into a lock hopper after which the top door closes to provide a similar top-seal to the environment. The bottom door of the lock hopper opens allowing its contents to drop to the top of the solids pile in the pyrolytic chamber. Great care is taken in the reactor feed zone design to minimize fugitive emissions of hydrocarbons, carbon monoxide, flammables and particulates.

The pyrolytic converter itself is a slowly moving (downward by gravity only) non-fluidized bed vertical shaft chemical converter, in which the top-fed solids are slowly heated as they progress downward to the bottom of the bed. The primary heat source for the reaction is via a bottom feed circulating “restorer” or recirculation gas stream that is heated externally to the reactor.

Pyrolytic zones change during normal operations, the reactor can be considered to have four distinct process zones as shown in Figure 1.

From the intake port at the very top of the fixed-bed vertical shaft, waste is program-flowed into the sealed atmosphere of the reactor chamber. The waste continuously flows downward. The special carrier restorer gas which contains primarily CO and H2 in combination with rationed water vapor is injected into the reactor chamber by specially designed nozzles. The restorer gas moves upward, penetrating the entire waste volume within the chamber, permeating the waste materials, initiating destruction of the contents up to atomic level and effectively processing the waste.

By turbulent (near sonic) velocity, the hot restorer gas is blasted into the gasification bottom and reacts vigorously with the carbonaceous char-like pyrolysis Zone II residual material.

Zone III is the gasification zone. Here the hot recycle gas basically consists of an equimolar mixture of carbon monoxide (CO) and hydrogen (H2), commonly called syngas, and a controlled amount of water vapor.

Zone IV is the melt separation zone (in reality, the melting zone is merely an extension of the gasification zone). The hot (2000OC) recycle gas provides the heat needed to ensure that metals and ash components of the feed trash fully melt.

At 1000O C to 1400O C, the 100% gasification process of carbon and hydrocarbon waste originates the syntheses gas mixture of CO and H2.

At 1500O C to 1800O C, all inorganic waste components are melted. The ferroalloy and slag are yielded at the reactor's specific output locations.

The water-gas shift reaction tends to dominate at the 1800-1900O C temperature and thus forms mostly syngas. The actual equilibrium is thought to be partly dependent on the type of waste feed. Some slag and metals components catalyze hydrogenation and shift reactions of both char and CO.

The liquid slag (high strength building material) outflows into a water cooled tank and the liquid ferroalloy is received through a separate output.

At the upper 2000O C temperature zone of the reactor chamber, the raw pyrogas together with any remaining mechanical solid particles and gaseous hydrogen compositions of the HF, H2S, HCL types are removed for particulate and pyrogas re-processing then returned to the chamber as restorer gas or as waste for liquidation and gasification.

The following major reactions occur in order of predominance:

C*(activated char) + H20 --> CO + H2 (Water gas shift reaction)
C*(activated char) + 2H2 --> CH4 (Hydrogenation reaction)
C*(activated char) + 2H20 --> CO2 + 2H2 (Methanation reforming reaction)
CO + H20 --> CO2 + H2 (Hydrogen shift reaction)
2CO + 2H20 --> CO2 + CH4 (Methanation shift reaction)