Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – Chemical conversion to a stable solid for disposal
Patent
1995-03-17
1996-07-16
Mai, Ngoclan
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
Chemical conversion to a stable solid for disposal
588240, 588216, 110237, 110346, G21F 900
Patent
active
055368964
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the field of processing organic waste, "processing" in the present case referring to the breaking down of said waste via the thermal route with the primary aim of affording opportunities for reducing its volume to thereby lessen handling and storage problems. More particularly, it concerns a new method and new apparatus for processing solid organic sulphur-containing waste in which the thermal breakdown embraces pyrolysis of the waste. The new method of the invention not only achieves the aim of volume reduction, but also provides, for example, such benefits as the elimination of the sulphur content from the exhaust gases, and similarly any radioactive content, in an effective and straight forward manner. The invention is therefore especially useful for the processing of ionic exchange media from nuclear facilities, which media display a certain degree of radioactivity and therefore would otherwise require conventional measures in relation to ultimate waste disposal and deposition.
BACKGROUND OF THE INVENTION
The nuclear industry annually produces a significant amount of waste which is classified as radioactively contaminated ion exchange media. In Sweden, such waste is managed in various fashions in the individual nuclear facilities prior to ultimate disposal in bedrock chambers. This management is technically complex and as a rule leads to increased volumes which influences storage costs. A process resulting in diminished volume at reasonable cost should therefore be commercially interesting.
Ion exchange medium is an organic material. The base is usually a styrene polymer with grafted sulphonic acid and amine groups. The material is therefore burnable, but air is supplied during combustion and sulphur and nitrogen oxides are formed which in turn must be separated in some manner. Additionally, during combustion the temperature becomes sufficiently high for radioactive caesium to be partially vapourised. The residual radioactivity will also accompany the resulting fly ash to some extent. This necessitates a very high performance filter system. Accordingly, both technical and economic problems are associated with the combustion technique.
An alternative to combustion is pyrolysis. However, previously known pyrolysis methods in this technical field are deficient in several aspects and in particular no one has earlier succeeded in devising a pyrolysis process which provides a comprehensive solution to the problem of sulphur and nitrogen-containing radioactive waste, and to do so under acceptable economic stipulations. The following can be mentioned as examples of the known technology in this respect:
SE-B 8405113-5 which describes single stage pyrolysis in a fluidised bed followed by conversion of tars in the resulting gas to non-condensable gas using limestone as catalyst.
U.S. Pat. No. 4,628,837, U.S. Pat. No. 4,636,335 and U.S. Pat. No. 4,654,172 which all describe pyrolysis of ion exchange resins where the pyrolysis is certainly carried out in two stages but where both of these stages are directed towards pyrolysis of the ion exchange media itself i.e. the solid product. Speaking generally, both stages moreover are carried out at relatively low temperatures. Furthermore, none of these specifications recites any comprehensive solution to the problem of solid organic sulphur-containing waste such as is the case with the method of the present invention.
DESCRIPTION OF THE INVENTION
The principal objective of the present invention is to provide a method for processing solid wastes of the abovementioned type, which method results in a "dead" (to use a biological term), compactable pyrolysis residue and thereby an effective reduction in the volume of the waste.
Another objective of the invention is to provide a method which, in addition to the abovementioned volume reduction, affords effective processing of the resulting exhaust gases.
A further objective of the invention is to provide a method which also affords an extremely high retention of the radioac
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Hesbol Rolf
Holst Lars E.
Mai Ngoclan
Studsvik Radwaste AB
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