Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2001-05-24
2003-06-10
Bos, Steven (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C065S134400, C065S134500, C065S134800, C065S355000, C588S011000, C588S900000
Reexamination Certificate
active
06576807
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 takes place in introducing the waste. 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, according to the invention, said waste is introduced into said reactor (into the gas phase of said reactor) in association with dual cooling. This can be thought of as cooling the device per se for feeding said reactor with waste and indirect cooling via said device of the waste that is being introduced. Said device for feeding said reactor with said waste is cooled firstly on its side passing through the gas phase and secondly, and advantageously independently, on its side where the waste arrives.
The first cooling is intended above all to protect said feeder device from corrosion which develops where it is in contact with the gas phase; the second cooling is intended above all to minimize the amount of heat transferred to the incoming waste, in order to minimize vaporization of liquid waste and prevent solid waste sticking together, where this can lead to the feeder device becoming clogged.
In order to implement such cooling, the structure of the feeder device has provision to circulate cooling fluids, generally cooling liquids. In a particularly preferred variant of said dual cooling, in order to implement at least the first cooling, a circuit is provided for at least one cooling fluid, which fluid is maintained at a temperature higher than the dew point of the gas phase through which the device passes. This is intended to avoid any condensation of said gas phase on the walls of said feeder device. This condensation phenomenon is clearly harmful, given the problems of corrosion. It can also give rise to electric arcing and thus raise serious problems when heating the bath of glass by induction. In this advantageous variant, the “hot” cooling fluid is advantageously superheated water.
The advantage of using such a “hot” cooling fluid is clear when it comes to implementing the first cooling (adjacent to the gas phase through which the device passes). When implementing the second cooling (on the side where the waste arrives), the use of such a “hot” cooling fluid can clearly be envisaged only if the waste is capable of withstanding the temperature of such a “hot” fluid. In general, the second cooling is implemented using a “cold” cooling fluid, such as water at ambient temperature.
Now that the principle of the main improvement provided by the invention to the method of direct vitrification has been stated (i.e. the principle of dual cooling implemented where the waste is introduced), the way in which it is carried out can be varied 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) or with a bath of glass that is built up as the reaction progresses starting from an initial minimum fill. In this second variant, which is preferred, the reactor starts up with an initial bath of glass of small volume (a starter bath) and it is subsequently fed both with waste and with substances for constituting a bath of glass. Said waste and said substances are indeed advantageously introduced as a mixture, and the waste can be thought of as one of the precursors of substances constituting said bath of glass. The reactor is thus fed continuously with waste and with substances for constituting the bath of glass, and indeed with additives therefor. Once a certain level has been reached, both types of feed are stopped and the bath of glass built up in this way is emptied out.
The waste, which in characteristic manner is cooled on being introduced, is incinerated at the surface of the bath of molten glass, in the presence of oxygen, said oxygen is delivered into the gas phase so as to act as an oxidizer therein.
Advantageously, in order to optimize the incineration in question, the amount of oxygen introduced is greater than the theoretically required stoichiometric quantity. Advantageously, the quantity introduced lies in the range 1.25 to 1.5 times said stoichiometric quantity. In any event, said quantity is controlled and does not interfere with the negative pressure that is maintained inside the reactor in conventional manner for obvious safety reasons. Said negative pressure is maintained by sucking out the combustion gases, with said suction being implemented under conditions which minimize the amount of waste, and above all the amount of ash, that is entrained.
The distribution of said oxygen within the gas phase overlying the bath of molten glass is advantageously optimized. In particular, steps are taken to ensure proper mixing of waste and oxygen when said waste is introduced. Thus, said waste is advantageously introduced immersed in a flow of oxygen. To obtain such a result, it is advantageous to use at least one oxygen feed circuit in the structure of the device for feeding said waste. In general, such a circuit operates in addition to means for feeding oxygen into the gas phase of the reactor, which means are indep
Brunelot Pierre
Choi Kwan-Sik
Lacombe Jacques
Merlin Serge
Roux Patrice
Berkowitz Marvin C.
Bos Steven
Kuhar Anthony
Nath Gary M.
Nath & Associates PLLC
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