With plasma gasification, an electric arc heats a gas stream (air or nitrogen), at extremely elevated temperatures typically 50000C, thereby supplying the required energy to the process.
The plasma delivers energy needed to maintain the temperature inside the gasification reactor volume at values needed for dissociation of molecules of gases produced by material decomposition. Due to the elevated temperature the ash, metals and glass in the waste are melted, organic components are volatilized, and complex molecules are dissociated. Molten slag is removed from the reactor, and after cooling and solidification, a substance similar to lava is produced. Organic materials, containing mostly chemically bound carbon, hydrogen, and oxygen, are decomposed into syngas that can be utilised as various energy products, for example high quality fuel or electricity. Figure 1 is an illustration of the gasification process.
TECHNOLOGY VALUE PROPOSITION
SANEDI commissioned NECSA to design and build a more environmentally friendly Plasma Waste Gasification (PlasGas) and Plasma Waste to Energy (PlasWen) systems. In plasma gasification a gas stream, typically air or nitrogen, is heated by an electric arc to extremely elevated temperatures (5000 °C or more) to supply the required energy to the process. Current systems are designed to meet varying, site-specific user requirements, which range from technology demonstration units and vitrification of municipal solid waste (MSW) incinerator bottom ash to the production of syngas for electricity generation. Compared to non-plasma methods the advantages of plasma waste treatment can be summarized as follows:
- The energy for gasification is supplied by plasma rather than energy released from combustion and is therefore independent of substances used, to provide flexibility, fast control over the process, and more options in the chemistry of the process. A broad range of waste feedstock can be used for gasification.
- No combustion gases are produced typically generated in conventional autothermal reactors).
- The temperature in the reactor can be easily regulated by controlling plasma power and the material feed rate.
- As sufficiently high temperatures and homogeneous temperature distribution can be easily maintained in the entire reactor, production of higher hydrocarbons, tars, and other complex molecules are substantially reduced.
- High energy density and high heat transfer efficiency can be achieved, by allowing shorter residence times and increased throughput.
- Highly reactive environment and easy control of the composition of reaction products.
- Low thermal inertia and easy feedback control.
- Much lower plasma gas input is required per a heating power unit than in non-plasma reactors, and therefore energy necessary to heat the plasma to reaction temperature is low; also, the number of gases diluting the syngas produced is lower.
- High energy densities, lower gas flows, and volume reduction enable use of plants that are smaller in size than non-plasma reactors.