4. A new generation of plasmatrons – hybrid plasmatrons with a combined discharge

 

There are three types of plasmatrons – arc, high frequency (HF) and microwave (MW).

Arc plasmatron power reaches 250 MW.

MW plasmatrones’ power barely reaches 30 kW with frequency of 2,45 GHz or 100 MW with frequency of 915 MHz.

HF plasmatrons’ power reaches 1 MW but these have limitations in application due to their specifics.

Thus, arc plasmatrons are the most convenient for the range from 100kW to 250MW (fig. 4.1).

However they have a list of disadvantages:

• High temperatures in the arc channel (up to 12000°C - 15000°C);

• Sharp inhomogeneity of temperature and other plasma parameters in the working volume;

• Rigid requirements for the cathode and insulation materials used for protection of the working chamber;

• Rapid erosion of a cathode and the appearance of impurities with its volatilization;

• High probability of an emergency arc breakdown and the necessity of taking measures to stabilize it;

• Impossibility to supply the reagents directly in the active zone of the discharge;

• Low efficiency of conversion of the thermal arc energy into the energy of the workflow.

It is said that MW-plasmatrons are the most perspective in the plasma-chemical processes. The main advantages of these are:

• Volumetric plasma;

• More active plasma-chemical media that allows increasing the rate of a chemical reaction;

• Lack of electrodes and contaminating impurities;

• Low working temperatures in a reaction zone and less rigid requirements for the insulation materials.

• An opportunity to work in an impulse mode.

MW plasmatron disadvantages are low power and, consequently, efficiency, low working pressure (less than 100 Torr), high plasma-forming gas consumption, plasma is homogeneous only at low temperatures.

 

            TWINN, LLC specialists have created a multipurpose MW-plasma module. It was the first time volumetric plasma or plasma of a large size was obtained that is stable in continuous and impulse working modes in a pressure range from 70 Torr up to several atmospheres when large volumes of solid, liquid and gaseous materials pass though plasma.

            The new MW-plasma module works as a basis for the development of a new type of plasmatron with a combined discharge (hybrid plasmatron) (fig.4.2).

            Low power of a standard MW energy source is compensated by the introduction of the direct current into the MW plasma discharge. The total power of these plasmatrons can exceed the  power of existing MW generators in ten times retaining main advantages from both MW and arc plasmatrons.

            A plasmatron with a combined discharge is characterized by:

• An opportunity  to provide with a required power in plasma though passing direct current discharge through the volumetric MW;

• Lack of cathode erosion  (electric current emission occurs from the entire surface area of the cathode at temperature below 1000°C );

• Control of the channel plasma length;

• Independent control for MW and arc power;

• Possibility to supply the reagents (solid, liquid and gaseous) directly in the active zone of the discharge;

• Low consumption of working gas.

The pilot hybrid plasmatron system with the total power of 17 kW (including 5 kW of MW power) was tested for handling cereal with efficiency of 2 tons/hour.

TWINN, LLC has three RU patents, one European and one Eurasian for the hybrid plasmatron.

Hybrid plasmatrons may serve as a basis for development of high-performance plasma-chemical industry. Power of the first step of hybrid plasmatrons can reach 50 kW using standard MW plasmatrons ( power 6 kW ) or 300 kW using WM plasmantrons with power of 30 kW. Using 100 kW plasmatrons with the frequency of 915 MHz power of hybrid plasmatrons can reach up to 2-3 MW. Hybrid plasmatrons with power from 300 kW to 3 MW can cover up to 70% of potential requirements in the plasma-chemical field. 

The further increase of performance and effectiveness of plasma-chemical systems with hybrid plasmatrons can be achieved by the increase of working pressure (up to 5-10 atmospheres and more), the use of cascade and combined schemes. Introduction of impulse plasma-chemical technologies seem quite perspective allowing the realization of a broad spectrum of the threshold, illiquid and chemical reactions.

Hybrid plasmatrons can increase the effectiveness of all known plasma technologies and bring in an important contribution in the development of plasma-chemical field.