# Applications of Thermal Plasmas for the Environment
## 3 Applications of Thermal Plasma Waste Treatment  
In recent years the number of applications of thermal plasmas has increased significantly. Basic research in the 1990s led to major advances in understanding the fundamental phenomena involved and to a renewed interest in the use of thermal plasmas in materials processing and the environmentally friendly treatment of waste streams [3, 4]. The stricter environmental legislation on the processing of waste streams and the limitations of conventional technologies make plasma technologies increasingly attractive. _Priority is given to environmental quality at affordable costs_ and to the use of innovative thermochemical conversion technologies (gasification and pyrolysis) to _contribute to sustainable development and circular economy in which waste is managed as a resource._  
In Comparison with Conventional Thermal Treatment, the Main Advantages of Thermal Plasmas Treatment of Waste Streams Are:  
* Much higher temperatures. The temperature inside the reactor can be controlled by the torch power, waste feed rate, and plasma gas flow rate;
* Highly reactive environment (reactive species such as atomic oxygen and hydrogen) and reducing atmosphere in the gasification process resulting in reduced NOx emissions;
* Short residence times and high throughput due to the high energy density of the plasma and the high heat transfer efficiency;
* Lower amount of plasma gas per unit of calorific power than of the gas flow in conventional technologies. Therefore, there is less loss of the energy necessary to bring the gas to the reaction temperature, and the amount of gas diluting the syngas produced is lower;
* Deep breakdown of waste into simple compounds, greatly simplifying the cleanup of harmful impurities;
* Possibility of joint treatment of different types of waste without pre-sorting, which is particularly important for the treatment of biomedical waste and other non-sorted toxic waste;
* Because high and homogeneous temperatures can be easily maintained throughout the reactor volume, the production of higher hydrocarbons, tar and other complex molecules is significantly reduced compared to combustion;
* Gasification at high temperature and rapid cooling of the synthesis gas prevent the formation of dioxins and furans (the most dangerous toxic substances);
* Low thermal inertia and easy feedback control. Possibility of quickly adapting the process by modifying the flow rate of the oxidant (air, steam or other plasma gas) and the power of the plasma torches. Ability to create the desired gas atmosphere. In an emergency a quick shutdown of the process is possible;
* Significant reduction in the volume of flue gases and, therefore, the load on the gas cleaning system, and less entrainment of dispersed particles;
* Smaller installations due to the high energy density of the plasma, the lower gas flow rates and the reduced flue gas volume;
* The heat source is electricity rather than the energy released during combustion and is, therefore, independent of the waste being processed. This provides rapid and flexible process control and more possibilities in process chemistry, including the capacity to generate valuable by-products. Easy temperature control in the reactor is made possible by changing the power of the plasma torches and the feed rate of waste and added gases;
* Optimal control of the composition of the final product in stable form. Possibility of obtaining a more calorific and cleaner synthesis gas from the organic part of the waste, which is not contaminated by the typical by-products of conventional gasification (in particular, tar);
* Vitrification of combustion ashes and production of vitrified slag usable as construction material;
* Recovery of value-added products (metals) from the slag. Plasma gasification is a promising method for treating _solid and liquid combustible waste_[3,5]. Plasma methods have been used successfully in industry for decades. Reviews are presented in [3,4].