Low-dioxin waste treatment process set for launch in Japan
15 Jan 2000
A process that turns many types of waste into a combustible gas is about to receive its first use in Japan, thanks to an agreement between its developer, German firm PKA Umwelttechnik, and Toshiba. The process produces 'substantially lower' emissions of dioxins and oxides of sulphur and nitrogen than comparable waste treatment systems, claim the company.
Known as a pyrolysis and gasification system, the process can handle shredded plastics from cars, old tyres, plastic waste and contaminated soil. These are first fed into a rotary kiln, heated externally to 500-600oC. The organic gases produced by the kiln pass into a thermal cracker, which 'almost entirely' destroys any dioxins in the feed and breaks large molecules down into smaller, more combustible units. A cleaning system then strips out any chloride or sulphur impurities, leaving a clean, combustible gas. This can be used to heat the kiln, or sold on to external users.
The solid residues left in the kiln are also not wasted, the companies say. The residues consist of metal scrap and a carbon-rich material known as char. The former can be recovered, smelted and reused; while the latter is itself a chemical resource. It can be used as a reduction material in furnaces, or can be fed into a gasification unit to produce synthesis gas, a mixture of carbon monoxide and hydrogen, which can be used as a fuel for the kiln in this process, or sold on or a chemical feedstock.
The system has been verified in Germany, and PKA is currently building its first two commercial-scale plants at Aachen and Freiberg. More are in the planning stage, it says. The deal with Toshiba, meanwhile, will 'provide a core product' for the Japanese firm's new waste treatment and recycling business unit. The company will start marketing the system at the end of this year, and aims to have ten orders in place by the end of 2000.
