Russian scientists developed a technology, which provides plasma processing of solid wastes into motor fuel components without emitting any toxic or hazardous substances.

Nowadays the most widely used technology for disposing of solid wastes is burning natural gas (or other combustible gases) in fluid-bed facilities under temperature of 850 degrees Centigrade. This burning temperature is relatively low, thus causing formation of extremely dangerous poisons, such as dioxins (p-dibenzodioxins) and furans (p-dibenzofurans), which concentrations in off gases may vary between 7000-45000 nanograms per cubic metre, while European Union standards provide a maximum of 0.1 nanograms per cubic metre. Apart from dioxins and furans, off gases may contain other substances, which can harm human health – aldehydes, phenols, volatile metal compounds and etc. Refuse incinerators have some techniques to get rid of aforementioned substances, but they require expensive components.

Another burning problem is toxic ashes from incinerators, requiring special burial techniques. All mentioned drawbacks of waste burning technology resulted into ban of building new refuse incinerators in European Union and the United States, while active incinerators will be dismantled and replaced with ecologically friendly plants, using advanced and environmentally safe techniques.

Russian engineers from “Eco-Technologies of Experimental Engineering” design bureau together with collaborators from Kurchatov Institute developed a plasma complex, which allows processing of solid wastes without emitting dioxins and furans – off gases contain about 0.01 nanograms of said substances in cubic metre, which is ten times lower than existing standard require. Such results can be achieved due to high temperatures inside working zones of plasma jets – up to 5 000 degrees Centigrade, that is why wastes immediately pass from solid to gaseous state, forming synthesis gas (a mixture of carbon monoxide with hydrogen). Other burning remains include basalt-like bottom ash, known as ecologically safe construction material, used for production of mineral fibres (thermal insulation) and road surface.

 

 

Moreover, working plasma jets emit significant amounts of excessive heat, which can be utilized during high-pressure steam production, which in its turn is used for producing up to 600 kilowatt-hours – enough to cover energy, spent for plasma jet operation. As can be seen from the above, the plasma jet, which processes solid wastes, can work in closed cycle using its own energy, when stable regime is reached.

As a working substance, plasma jets usually use various plasma-supporting gases, such as air, carbon dioxide, methane and gas mixtures. Carbon dioxide, which is emitted during plasma-involving processing of solid wastes, is used as working substance, thus reducing emissions of this greenhouse gas to the atmosphere. By changing working substance, we can regulate concentration of main gas products of solid waste processing (hydrogen and carbon monoxide), and isolate necessary components (hydrogen, for instance), or forward them for further processing – making motor fuels by means of Fischer-Tropsch process (a catalyzed chemical reaction in which synthesis gas, a mixture of carbon monoxide and hydrogen, is converted into liquid hydrocarbons of various forms), for instance.

Plasma waste processing doesn’t require any size classification for wastes and can process wastes with up to 45% moisture content, including agricultural wastes (manure, rice husk, straw, cake and etc), silts from sewage water treatment stations and heavy petroleum residues.

Experimental plasma jet plant has been put into operation in Haifa, Israel, in 2006.

Source: Science & Life

Kizilova Anna