Thermal Plasma Assisted Gasification of Polymers

Gasification of various hydrocarbons with help of thermal plasma is studied at the Institute of Plasma Physics (IPP). Such treatment can be way of recycling of polymer waste with production of high purity synthesis gas (syngas) mainly composed of hydrogen and CO. A plasma torch with hybrid stabilization of arc used in the reactor allows higher efficiency for gasification than other processes. This work is a preparation of the experiment for gasification of polyethylene (PE). Basic description and analysis of the gasification reactor is done. Analysis of reaction taking place is made. On the base of derived information optimal composition flow rates and power balance of the process are calculated. Introduction Polymers are well-known thanks to their large range of application. Every year approximately 200 Mt of polymers is produced and we have to investigate for the future of such waste. Recycling is a complicate process, depending on the polymer’s nature as thermosetting plastic and thermoplastics, but also on additives contained in the plastic. Nowadays polymers are mainly recycled as a combustible material to produce electric energy. The treatment using plasma technology offers many exceptional advantages that other polymer treatment processes cannot achieve. The high temperature of reaction allows rapid treatment of any kind of polymers, whatever the composition or physical properties. Thermal plasma offers the possibility of decomposition of polymer by pure pyrolysis in the absence of oxygen as well as flexible variation of reaction gases to achieve desired product. Further advantages come as high efficiency of gasification process and high purity of produce gases from usage of plasma generated from water. To accomplish this performance, a new plasma torch specially adapted for material treatment has been developed at the IPP [1]. In a common gas torch using steam as gas, the enthalpy of plasma, given by ratio of net arc power to gas flow rate, was usually not higher than 10 MJ/kg, meaning plasma temperature lower than 4000 K [2]. But the plasma flow rate is high and ensures good mixing of plasma with treated material in the case of waste treatment or spraying application. The stabilization by water vortex provides a low flow rate but high plasma enthalpy, more than 200 MJ/kg, meaning plasma temperature more than 15 000 K. Utilization of both systems in this hybrid torch offers high enthalpy, high temperature and possibility to increase the mass flow rate substantially. That’s why this experimental torch is very efficient for destruction and gasification of solid waste materials. Preliminary study of polymer treatment in reactor Plasgas with help of this hybrid gas/water-stabilized torch will be explained in this resume. WSP®H500R–New development The hybrid torch has been developed in the perspective to fill a gap existing between operation regimes of gasand liquid-stabilized torch [1]. This torch uses a non-transferred DC arc and is called hybrid because of using both technical structure, gasand liquid-stabilization. A picture and the characteristics of the hybrid WSP500H can be seen in figure 1 [3]. In the Figure 2 the schematic of plasma torch is shown. Inert argon in a cathode chamber prevents any chemical reactions on the cathode surface. The water mainly determines power balance in torch and store most of the energy taken from arc. It is because high enthalpy of hydrogen and oxygen as the energy is stored not only in thermal form and due to ionization but also in chemical form due to dissociation. Water injected in the system plays two roles. The first objective of the water is to cool the chamber. Secondly the water is the arc-stabilizer. The water vortex is produced by tangential injection. Proximity between water and plasma causes evaporation and an ablation of the water, which will provide additional material to plasma stream. That’s why this experimental torch is very efficient for destruction and gasification of solid waste materials. 176 WDS'09 Proceedings of Contributed Papers, Part II, 176–181, 2009. ISBN 978-80-7378-102-6 © MATFYZPRESS