Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2001-05-24
2004-11-09
Hendrickson, Stuart L. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S900000, C110S236000, C110S243000, C110S251000, C423SDIG001
Reexamination Certificate
active
06815572
ABSTRACT:
The present invention relates to a method and to apparatus for incinerating and vitrifying waste, in particular radioactive waste.
Said invention lies within the context of processing dangerous combustible waste for which it is appropriate to fix the ash in stable manner. To neutralize waste of that type, it has long been the practice to operate in two stages, each of said stages being implemented in an independent apparatus:
a first step of incinerating said organic waste, in divided solid and/or liquid form, in an incinerator apparatus; and
a second stage of fixing the ash recovered from said first stage, said second stage being implemented in suitable apparatus that contains a bath of glass maintained in the molten state.
Nevertheless, for several years, waste processing methods have been described in which said two stages of incinerating said waste and fixing the resulting ash have been implemented in a single apparatus. In this context, a term that is used is “direct vitrification”.
Results obtained in said context by the Applicants have been described in particular at the “Korean Atomic Industrial Forum” (KAIF) '98, which was held Apr. 14 to 17, 1998 in Seoul, South Korea. Said results demonstrated the feasibility of a direct vitrification method, in which the waste is burned for the most part at the surface of a bath of molten glass, in an oxidizing atmosphere, with the ash that is generated being trapped and fixed in said bath of molten glass; since said method was implemented in a cold crucible, said bath of molten glass was heated by induction.
Continuing their work on direct vitrification, the Applicants have designed and developed the present invention which can be considered as being an improvement of said direct vitrification as presently known. The improvement which constitutes the main subject matter of the present invention can be thought of both in terms of a method and in terms of apparatus, and it involves the quality of the bath of glass. Said improvement which, in order to clarify the present description, can be referred to as the “main” improvement, is advantageously implemented with other improvements that, in the same spirit, can be referred to as “secondary” improvements. Said main and secondary improvements are described below in general terms and then in greater detail with reference to the accompanying figures.
Thus, in a first aspect, the present invention provides a method of processing organic waste (i.e. combustible waste) in divided solid form (to facilitate insertion and combustion) and/or in liquid form, the method being implemented in a single reactor containing a bath of molten glass surmounted by a gas phase; said processing method comprising: incinerating said waste in the presence of oxygen at the surface of said bath of molten glass (said waste falling onto said surface, decomposing thereon, and the resulting gaseous products of said decomposition being burned in said oxygen-containing gas phase); and vitrifying said incinerated waste in said bath of molten glass. In this respect, the method of the invention is a direct vitrification method.
In characteristic manner, said method further comprises injecting oxygen into said bath of molten glass, in sufficient quantity to minimize or to avoid any formation of metal within said bath of glass; advantageously, in sufficient quantity to minimize or to avoid any formation of metal within said bath of glass and to subject bath of glass to moderate stirring.
Said oxygen which is introduced in original manner into the bath of molten glass is introduced into the process reactor in addition to the oxygen being delivered in conventional manner as oxidizer into the gas overlying said bath, in order to ensure that the waste is incinerated.
In characteristic manner, in the context of the method of the invention, not only does said oxidizer in the gas phase react, but so also does the oxygen within the bath of glass, said oxygen serving to adjust the oxidation-reduction (redox) potential of said bath of glass (thus serving to limit the reducing nature of the glass).
By controlling the redox potential of the bath of glass in this way, it is possible within said bath of glass to prevent oxides being reduced and thus to prevent metals being formed. The presence of such metals within said bath is very harmful to the uniformity of said bath, and thus to the quality of the vitrification obtained. In addition, the presence of metal can give rise to real difficulties when performing heating by induction . . . .
The oxygen injected into the bath of glass to minimize or even to avoid the formation of metal is advantageously injected in sufficient quantity also to ensure that said bath of glass is stirred somewhat. The person skilled in the art knows how to optimize the quantity of oxygen required for these purposes. In any event, the quantity must be sufficient to obtain the desired effect concerning the value of the redox potential, and indeed the desired effects concerning the value of said potential and also the looked-for stirring effect, but it must not be excessive, insofar as the bath of glass while being stirred and mixed must nevertheless remain a bath of glass and must not be transformed into a foam . . . .
Oxygen has been mentioned as the oxidizer involved in the gas and as the oxidant gas introduced into the bath of glass, and this is appropriate insofar as said oxygen is generally delivered as a “pure” gas. Nevertheless, it is not entirely beyond the scope of the present invention to use a gas that contains oxygen, and in particular to use air, optionally enriched in oxygen, as the oxidizer and as the oxidant gas.
The oxygen delivered as oxidizer into the gas phase is advantageously optimized for the incineration in question, so as to be present in a quantity that is greater than the theoretically required stoichiometric quantity. Advantageously, this oxygen is present in a quantity that lies in the range 1.25 to 1.5 times said stoichiometric quantity. Nevertheless, said quantity is controlled and does not interfere with the negative pressure that is maintained within the reactor in conventional manner for obvious safety reasons. Said negative pressure is maintained by sucking out the combustion gases, where said suction is implemented under conditions such as to minimize the amount of waste, and above all the amount of ash, that is entrained.
Once the principle of the main improvement provided by the invention to the direct vitrification method has been accepted (i.e. the principle of injecting oxygen into the bath of glass), the way in which it is implemented can be subject to several variants, in contexts that are somewhat different.
In particular, the method of the invention can be implemented with a bath of glass that is practically pre-constituted (i.e. present in the reactor before the waste is introduced therein), or with a bath of glass that is constituted progressively from some minimum initial fill. In this second variant, which is preferred, the reactor starts by containing an initial bath of glass that is of small volume (a starter) and it is subsequently fed both with waste and with substances for forming a bath of glass. Said waste and said glass-forming substances are also advantageously introduced as a mixture . . . with the waste being treated as one of the precursors of substances for making said bath of glass. The reactor is thus fed continuously with waste and with substances for forming the bath of glass, and indeed with additives therefor. Once a certain level has been reached, both types of feed are stopped and the resulting bath of glass can be emptied out.
In a preferred variant implementation of the method of the invention, the oxygen which is injected into the bath of glass is introduced into the reactor beneath the surface of said bath of glass. Thus, the means for injecting said oxygen do not pass through the gas phase in said reactor, and are therefore subject to one type of corrosion only: the corrosion inherent to said bath of glass.
This type of comment applie
Brunelot Pierre
Choi Kwan-Sik
Lacombe Jacques
Merlin Serge
Roux Patrice
Berkowitz Marvin C.
Goldberg Joshua B.
Hendrickson Stuart L.
Korea Electric Power Corporation
Lish Peter J
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