NON-COMBUSTION TECHNOLOGIES FOR POPs CONTAMINATED PLASTICS

The following technologies have the capability to either destroy POPscontaminated plastic in an environmentally sound manner or separate the POPs from the plastic allowing the POPs to be destroyed and the plastic recycled.

GAS-PHASE CHEMICAL REDUCTION (HYDROGEN REDUCTION)

Gas-Phase Chemical Reduction (GPCR) was initially developed to destroy POPs waste such as PCBs. GPCR was developed in the 1980s in Canada, and operated at laboratory scale before being commercialized and operated at full commercial scale in the 1990s. A large-scale facility in Kwinana, Western Australia, operated for 5 years during the 1990s successfully, destroying that state’s entire stockpile of PCBs and much of Australia’s POPs stockpile. The same technology was developed further and later established at pilot and commercial scale in Canada, USA, and Japan, and has the demonstrated capability to destroy all POPs to high destruction efficiency (DE) levels.

GPCR technology is based on the use of hydrogen at elevated temperatures (approx. 875 o C) and low pressure to achieve thermochemical reduction of organic compounds. The contaminated bulk solids material is placed in a sealed chamber called a Thermal Reduction Batch Processor (TRPB), where the POPs are thermally desorbed and carried into the reactor by the heated hydrogen gas. Liquid POPs are preheated and injected directly into the TRBP. Bulk contaminated soils and sediments are processed in a TORBED Reactor System, a modified version of the TRPB allowing higher throughput.

Pre-treatment of some wastes is necessary, and the system requires electricity, hydrogen, water, and caustic for scrubbing. The 3rd generation of the technology (developed by Hallett Environmental & Technology Group Inc. of Ontario, Canada) can also generate energy from excess hydrogenrich methane process gas that significantly exceeds the parasitic require-

Figure 32. GPCR unit running in Western Australia 1996.

Figure 33. Thermal Reduction Batch Processor (TRPB) of the GPCR unit.

ments of the process and allows energy export. The reactions that occur generate methane and subsequently the methane is converted to hydrogen gas in a self-regenerating, recirculating process gas system.

The general chemistry of conversion of a hydrocarbon structure containing chlorine and possibly oxygen can be expressed in the following way:

Methane is converted into hydrogen via the steam reforming and gaswater shift reactions, which are expressed as follows:

The process residues include scrubber liquor and water that is suitable for industrial discharge, and solid materials (metal drums, etc.) that are decontaminated and suitable for landfill. Emissions are primarily hydrogen chloride, methane, and other hydrocarbons, including benzene. An online mass spectrometer can analyze all reactor exit gases to ensure full dechlorination, and the gases, following scrubbing of the hydrogen chloride, can then be recirculated fully or split between the reactor and boiler fuel feed. The system can operate in modular, transportable and fixed modes, including transportable TRBPs to deal with on-site decontamination of POPs-contaminated sites.

A double TRBP system can process around 75 tons of solids per month. Liquid inputs can be processed at 2-4 liters per minute. A semi-mobile TORBED reactor can process around 300-600 tons per month. The main

Figure 34. GPCR destruction efficiency for dioxins in waste.

Figure 35. Bulk loading of plastic waste to the TRBP is possible.

advantages are complete destruction of all POPs, self-regeneration of hydrogen process gas, mobility and small footprint (1,000m2) for systems with a 70 ton/month throughput for smaller stockpiles or contaminated sites, low amounts of solid process residual and a long history of successful commercial utilization. Recent cost estimates for establishing a GPCR plant are around USD $50 million to construct and USD $1 million to train personnel.This is around 10% of the cost of a modern waste incinerator. A new pilot-scale reactor is being developed in Canada to treat Automotive Shredder Residue (ASR), which is polymer material heavily contaminated with brominated flame retardants from car upholstery.

One of the advantages of this process to destroy POPs-contaminated plastics is that surplus hydrogen can be developed and used to process waste, as well as generate power. It also has few of the feedstock limitation of other technologies, allowing for loading of bulk materials into the TRBP .