Plasmatron with steam as the plasma gas and process for stable o

Details Plasmatron with steam as the plasma gas and process for stable o Plasmatron with steam as the plasma gas and process for stable o

1994-10-17

1996-03-12

Niebling, John

Hazardous or toxic waste destruction or containment

Containment

Solidification, vitrification, or cementation

588205, 588212, 588227, 204169, 42218604, 42218622, A62D 300

Patent

active

054988268

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention refers to plasmatrons which are operated with steam as the plasma gas as well as to a process for stable operation of such plasmatrons.
Plasmatrons, which are used for chemical conversion, are predominantly operated with a gas, which is chemically inert with respect to the plasmatron materials, as a plasma gas. Plasma pyrolysis processes, for example, use hydrogen as a plasma gas.
In addition, it has already been known to use steam as a plasma gas for various chemical conversions and on various performance levels, e.g. in the case of coal gasification, (East German Patent 215 325, German-Offenlegungsschrift 3 330 750, German-Offenlegungsschrift 3 605 715).
Moreover, it has already been suggested that toxic waste products, in particular waste products containing fluorinated hydrocarbons or chlorinated hydrocarbons, should be annihilated by a chemical reaction in a steam plasma jet.
In connection with examinations concerning chemical processes in specific fields of application of chemical conversion in a hydrogen plasma atmosphere, it turned out that these chemical processes are caused, on the one hand, by the hydrogen ions and, on the other hand, by the oxygen ions of the steam plasma.
Steam plasmas are advantageous insofar as they have a high concentration of chemically reactive, highly excited oxygen and hydrogen species at comparatively low temperatures of approx. 3000.degree. K., which means that they will be particularly suitable for a series of conversion processes. In the case of all plasmatrons, the thermal load is high so that, due to thermal and/or chemical erosion, a service life will result which prevents continuous operation of a plasmatron without intensive cooling. This concerns primarily the electrodes, but also the gas chamber, the plasmatron housing, the connecting pieces and, depending on the respective structural design, also other components. The coolant used for such plasmatrons is normally water having a temperature of approx. 20.degree. C.
In the case of plasmatrons which are operated by making use of steam as a plasma gas, erosion at the parts which are exposed to, or rather which are in contact with the arc is particularly high in comparison with the use of other plasma gases. Hence, this high erosion load affects especially the cathode and the anode. The comparatively high loss of electrode mass will result in a short service life of the electrodes of the plasmatron operated with steam as a plasma gas so that, due to the frequently necessary exchange of electrodes, a continuous operation will practically be impossible.
For the industrial use of steam plasmatrons, another disadvantage is a phenomenon which is characteristic of such plasmatrons, viz. that abrupt operating troubles in the mode of operation of the plasmatron occur in rapid succession. These troubles manifest themselves in fluctuations or interruptions of the steam flow rate, changes in the arc length, strongly fluctuating arc voltage and arc current strength and a strongly fluctuating plasma enthalpy resulting therefrom. This will cause fluctuations in the chemical conversion in the plasma reactor, i.e. it will impair the product quality as well as the efficiency of the plasmatron. Up to now, measures which are usually taken in the case of plasmatrons, viz. reducing the erosion at the electrodes by intensifying the cooling, have normally failed to show any effect, or they at least failed to show a sufficient effect in the case of plasmatrons working with steam as a plasma gas.
Hence, the present invention is based on the task of improving a plasmatron, which is operated with steam as a plasma gas, in such a way that the service life of the plasmatron components subjected to high thermal loads will be lengthened and that a stable operation of the plasmatron with little fluctuations or with no fluctuations at all can be achieved without any essential increase in the operational expenditure. In particular, the differences existing in the case of plasmatrons with steam plasmas in compari

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