Waste processing

The present invention relates to the treatment of organic waste. Treatment in this case means the thermal decomposition of said waste. In particular, it aims to reduce the volume of waste and the associated problems of handling and storing it. More specifically, it refers to a new method of treating solid sulfur containing waste and an apparatus for that purpose. The thermal decomposition of waste in this process actually means its pyrolysis. Not only does the present invention achieve the desired reduction in volume, but it also offers advantages such as the removal of sulfur and any radioactive material from the emitted gas in the most efficient and straightforward manner. Therefore, the present invention is particularly useful for the treatment of products formed by ion exchange in nuclear facilities. Such substances are subject to a certain level of radioactivity and would therefore require the usual measures to be taken in such cases before final disposal and deposition.

Each year, the nuclear industry generates a large amount of waste, which is classified as ion-exchange products contaminated with radioactivity. In Sweden, before such waste is finally disposed of in the bedrock, it is treated in various ways. This work is technically complex and, as a rule, involves an increase in volume. This increases their storage costs. In this context, a reasonable reduction in volume would be commercially advantageous.

Ion exchange products are organic matter. It consists predominantly of a styrene polymer with grafted sulfuric acid and amino groups. As a result, this material is flammable but requires combustion air and therefore produces sulfur and nitrogen oxides which need to be separated in some way. In addition, the relatively high temperature generated during combustion allows partial evaporation of radioactive cesium. Radioactive residues are also present to some degree in the resulting fly ash. This makes it necessary to have high quality filters. Accordingly, the incineration process involves both technical and economic problems.

Pyrolysis is an alternative to combustion. However, the pyrolysis methods known to date are in some respects insufficient for this field of technology. Until now, no one has been able to develop a pyrolysis process that can comprehensively solve the problem of sulfur and nitrogen-containing radioactive waste and achieve this in economically acceptable conditions. The following are examples of known technologies in this sense:

SE-B 8405113-5 discloses pyrolysis in a liquid bed in a single process followed by conversion of the resulting gaseous resins into a non-combustible gas using limestone as a catalyst.

U.S. Pat. No. Nos. 4,628,837, 4,636,635 and 4,654,172 describe pyrolysis of ion exchange resins, which consists of two technological operations in which the purpose of each operation is the pyrolysis of the ion exchange product itself, i.e. a solid. In general terms, both operations take place at relatively low temperatures. In addition, none of these descriptions provides a comprehensive solution to the problem of solid organic waste containing sulfur waste. This is achieved only in a manner according to the invention.

✓

The main object of the present invention is to provide a method for treating solid waste of the above type. In this way, dead (in biology) suitable precipitates formed during the pyrolysis are obtained. This enables efficient waste reduction.

It is another object of the present invention to provide a method which, in addition to reducing the volume mentioned above, enables efficient treatment of the evolved gas.

It is a further object of the present invention to provide a method which, among other things, enables extremely high radioactivity retention of the precipitates formed during pyrolysis.

It is a further object of the present invention to provide a technically direct method that is at the same time economical. This applies both to reducing the volume of solid waste and to managing the emissions.

The above objectives are achieved by working in a manner that can be described in general terms as two-stage pyrolysis. It is essential that the first non-high temperature pyrolysis step is for the treatment of solid waste and the second stage the higher temperature gas. These two pyrolysis steps are followed by another, during which the gas is allowed to affect the sulfide-forming metal. This is desirable after the intermediate step in which the gas reducing conditions are provided.

More particularly, the method of the present invention is characterized in that:

(a) pyrolysis of waste at temperatures up to 700 ° C, preferably up to 600 ° C, to produce compounds containing organic sulfur and solid precipitates containing radioactive material recovered from the waste;

(b) separating the gas from the precipitate formed during the pyrolysis. Thereafter, pyrolysis, otherwise known as cleavage, proceeds further. It breaks down the organic sulfur compounds in the gas into low or low carbon carbon compounds and inorganic sulfur compounds;

(c) the gas formed during the process operation (b) is stored in a reducing medium formed in the solid reduction layer so that any sulfur oxides contained therein can be reduced to hydrogen sulfide; and

(d) the process gas (b) or (c), if performed, is considered to be capable of producing sulfides in a metal environment under conditions such that the sulfur compounds formed during the prior process could form sulfides with that metal.

In other words, pyrolysis of solid waste is carried out at a temperature of up to 700 ° C, preferably up to 600 ° C during the initial technological operation. The term pyrolysis must be understood in its ordinary sense, that is, as the formation or thermal decomposition of a substance without the actual use of oxygen, or at least in such a small quantity that it does not permit true combustion. This means that during pyrolysis, the carbonaceous waste is converted into a relatively fluffy pyrolysis residue that can be collected at the bottom of the pyrolysis reactor and then rendered substantially smaller by compression. In addition, practically all radioactive materials, including, but not limited to, the above temperatures, are maintained¹³'Cs, remains in the precipitate formed during pyrolysis. This enables the elimination of additional radioactivity at minimal cost and expense. Any fly ash from the resulting gas can be removed in a known manner using a ceramic filter in the pyrolysis reactor. This enables the radioactive materials in the fly ash collected in the filter to be returned to the precipitate formed during pyrolysis.

By applying the present invention in practice, it has become possible to achieve very high radioactivity retention in the precipitate formed during pyrolysis. In this sense, testing with ion-exchange media from nuclear power plants has resulted in near-10⁶: l expressed detention. This means that the purification factor is 10. In addition to said radioactive material, pyrolysis precipitates contain carbon and, possibly, iron compounds such as iron oxides and iron sulfides. Tests for this purpose have shown that sulfur retention in pyrolysis precipitates exceeds 90%.

The pyrolysis of process (a) does not have any critical lower bound, but is determined by efficiency and / or cost. For convenience, however, the lower limit can generally be set at 400 ° C and, therefore, in the most preferred embodiment of the invention, the process operation a) is carried out in the range 400 ° C to 700 ° C, preferably 400 ° C to 600 ° C; ° C-600 ° C, e.g. 450 ° C-550 ° C.

In addition, since the process of the present invention as a whole has proven to be extremely effective in both solids and gas emissions, it is desirable to carry out the process a) without using any catalyst for the decomposition of carbon compounds in the waste. Of course, such a method according to the present invention is very cost-effective since the cost of the catalyst in similar cases often represents a significant proportion of the total cost.

The technological pyrolysis operation a) can be performed in a known manner. This is especially true for the type of pyrolysis reactor. For example, pyrolysis can be carried out in a liquid layer. However, in general terms, in the context of the practice of the present invention, particularly good results have been achieved by the use of instant pyrolysis. The term instant pyrolysis is used here in its usual sense, that is, to describe a relatively fast-moving matter. In other words, we are faced with a very short stay in a technological device. This time is usually less than 30 seconds and is usually even shorter, such as less than 15 seconds. It is particularly useful to perform instant pyrolysis in a gravity or instant reactor having a residence time of from 3 to 15 seconds, more preferably from 4 to 10 seconds, for example from 5 to 8 seconds or about 6 seconds. The appropriate length of stay in a technological device can be easily determined by the professionals on a case-by-case basis.

In this case, it should be understood that solid waste does not mean a solution of the substance in question. In addition to being necessarily dry, they may also contain substances that contain some moisture, for example up to 50% and usually 30% to 50%, which is common in ion exchange products. However, in the case of instant pyrolysis, prior to technological pyrolysis, a) conditioning of the material may be useful. This means drying this material

LT 361δ B i

to some degree, and possibly its crushing into powder. Particularly good results have been observed for the initial pyrolysis process a) using powdered material.

The gas generated by the pyrolysis process (a) contains products of the decomposition of organic waste, which are known as tars. These tars contain pure hydrocarbons and water vapor or organic sulfur compounds and amines if the waste is of the sulfur and nitrogen ion exchange product type. The second technological operation (b) involves the separation and pyrolysis of the gas from the precipitate. This process is selected at a temperature which, among other things, enables gases containing sulfur-containing organic compounds and relatively large amounts of carbon atoms to be decomposed into compounds with low or lower carbon content and to inorganic-sulfur compounds. If the waste contains nitrogen, inorganic compounds with nitrogen are also formed. In other words, the temperature at which technological operation b) is carried out is selected depending on the composition of the gas obtained during technological operation a). This usually means that the temperature for the process b) is higher than for the process a) but provided that no decomposition catalyst is used. If the temperature in process a) is high, this may, for example, mean that the temperature in process b) will be higher than 700 ° C. However, if the degradation catalyst is used, process b) may be carried out at a temperature slightly below process a) or at least below the upper limit of process a). It can be at temperatures above 600 ° C and more preferably above 650 ° C. Preferred for fragmentation paLT 3616 B

- reaching the upper limit of the temperature is not very important. This ceiling is more likely to be determined by processing technology (material science) or economic factors. This can, for example, make it difficult to use materials that maintain temperatures above 1500 ° C for reasons of economy. In this context, temperatures up to 1500 ° C are desirable. However, 1300 ° C is the optimum temperature range and therefore a comfortable temperature range, especially without the use of a catalyst, will be above 700 ° C to 1300 ° C. Especially suitable for the technical operation b) is carried out in a temperature range of above 700 ° C to 1000 ° C, and preferably above 700 ° C to 850 ° C.

When the catalyst is used, suitable desirable temperatures are from 600 ° C to 1300 ° C, more preferably from 650 ° C to 1300 ° C, and most preferably from 650 ° C to 1300 ° C, such as from 650 ° C to 850 ° C. C.

The circumstances of pyrolysis under process (b) are not as significant as under process (b), as it is important to completely break up the sulfur and any nitrogen and low carbon compounds into lower carbon compounds, avoiding any interfering side reactions or by-products. formation. In this context, pyrolysis undergoing technological operation (b) can alternatively be called fragmentation in a generally accepted terminology. A large amount of soot is formed during splitting. The higher the temperature, the more soot is formed. It is possible that soot formation · will require high temperature filtration of the gas evolved during digestion, which is done by conventional means. However, in a simpler and less time consuming way, the above-described pre-split condensation of tar is described. In addition, condensation facilitates the separation of organic compounds with sulfur.

Analogous to the above, the technological operation b) is conveniently carried out in certain cases, using a catalyst which has hitherto been used in similar cases. A suitable catalyst for process (b) is lime, such as dolomite lime.

When the process gas (a) contains tar products and water, the most appropriate method of carrying out the present invention, prior to process (b), facilitates gas condensation in which the tar-like products are condensed and separated and in addition to the above-mentioned technological operation b) with gas. In this context, resin products are carbon compounds which, after a technological operation, (a) are in the form of a gas and which fall out to be more or less viscous in the form of a resin mixed with water. This condensate can be separated by fractional condensation, which produces high-calorie low viscosity tar, water and viscous rich sulfur tar. Further improvements in the pyrolysis or digestion process of process (b) are related to the above-mentioned tar separation and therefore require higher costs.

If the gas emitted during pyrolysis contains sulfur oxides, especially S0₂, they must be handled appropriately and remember the stringent requirements that currently exist for the release of sulfur oxides and other sulfur compounds.

io

This is achieved in a simple and efficient manner by utilizing the method according to the invention in an integrated process. During process operation b) the gas formed during process operation c) is allowed to enter the layer of the solid reducer, creating the reduction conditions under which the sulfur oxides are reducing! to hydrogen sulfide and to carbon disulfide. In a process according to the present invention, carbon has proved to be a particularly suitable reducing agent. In addition, the use of carbon produces certain harmless end products, including carbon dioxide, which can in principle be released directly into the atmosphere.

Those skilled in the art can select a temperature for the reduction to be carried out in the course of process operation c) that will enable the desired subsequent reactions to be carried out. This means that the suitable temperature for the reduction is in the range of 700 ° C to 900 ° C and the optimum temperature is approximately 800 ° C.

In addition, the technological operation (c) also involves the reduction of the oxides of nitrogen, provided that they are present in the gas after the technological pyrolysis operations. If a carbon or a similar type of high temperature filter is used to clean the gas from the carbon black after the technological operation b), it can be considered as a means used in the additional technological operation c) according to the invention.

Finally, the technological operation d) allows the gas to enter the sulphide-forming metal layer. To this end, conditions are created under which the remaining sulfur compounds form sulfides of this metal. In this case, it is the gas resulting from process (c), of course, if it is either from the second process pyrolysis (b). In each case, u

is the conversion of hydrogen sulfide to metal sulfide. Iron, which is capable of forming sulfides in metal, is desirable, as it is a cheap material and in this case produces harmless products. It is preferably in the form of iron disulphide or pyrite. Other metals, such as nickel, are also suitable. Those skilled in the art can select the temperature of the technological operation d) to enable further desired reactions. However, a particularly suitable temperature range is from 400 ° C to 600 ° C, and in most cases the temperature is 500 ° C.

Highly volatile organic gas, which does not condense during the process and is produced during the digestion, also penetrates into the gear units used in process (c) and into the gear unit used in process (d). For these release products, these are subject to recycling or separation requirements in Sweden. If such gas is oxidised, it can be destroyed by oxidation (combustion), eg catalytic oxidation. Oxidation is suitable for pyrolysis of ion-exchange products, since the discharged gases do not contain chlorine and therefore do not form any dioxins.

It has been previously mentioned that both solid and gaseous end products of the present invention are suitable for processing. The resulting ash is suitable for further processing by simple pressing. Practical application of the present invention has shown that it can be reduced by up to 75%. In addition, the resulting gas is rich in light organic compounds, which means that a large amount of heat is released during combustion. In addition, this type of gas is not harmful to the environment. These are carbon dioxide, nitrogen and hydrogen in gaseous form and water vapor. This means that the method according to the invention as a whole has unmatched advantages over known methods.

To effectively utilize this technique and to prevent leakage of radioactive, unpleasant, or hazardous gas to the system, which may pose a risk to service personnel, it is suggested to operate under a certain degree of vacuum or negative pressure. For this purpose, it is convenient to use a suction or exhaust gas type pump during the technological operation.

The present invention further relates to an apparatus for implementing it. Such apparatus consists of:

A) Reducer for solid waste pyrolysis. Preferably, the pyrolysis is carried out at 400 ° C to 700 ° C, and preferably at 400 ° C to 600 ° C;

B) a pyrolysis or fission reactor for pyrolysis of the gases emitted from reactor A). This is preferably done between 700 ° C and 1300 ° C if the catalyst is not used and between 600 ° C and 1300 ° C, if the catalyst is used;

C) an additional layer of solid reducer in which any sulfur dioxide in the gas is to be reduced; and

D) a metal layer capable of forming sulphides, which produces metal sulphide in the presence of gases evolved during process operations B) or C).

In addition, with regard to the apparatus for carrying out the present invention, all features of the above-described method and the proposed methods of its application are applicable to the apparatus and therefore no detailed description thereof is required.

Nevertheless, it is worth noting the following extremely important embodiments of this apparatus.

Specifically, the reactor for pyrolysis is a gravitational type reactor.

It is desirable to install a capacitor for the condensation of the tar products in the gas in front of reactor B.

A reactor A) is preferably provided with a filter for separating any fly ash from the gas.

It is desirable to install a filter in the apparatus for removing soot from the gas emitted from reactor B).

It is desirable to install a press for reacting the pyrolysis residue formed in reactor A).

It is convenient to install a burner to burn the above mentioned gas behind layer D).

Description of the figure

The drawing schematically shows an apparatus of the present invention.

The device shown below consists of the following parts and functional units. The solid waste is fed into a gravity-type first pyrolysis reactor 1 by means of a feed mechanism Z. After the solid waste pyrolysis in the above reactor 1, the solid pyrolysis residue (ash) is conveyed by screw means 3 to a container which is additionally equipped with a press.

The gas generated during the pyrolysis in reactor 1 is passed through a ceramic filter 5 and passed through a tube 6 to a second pyrolysis reactor, where it is subjected to pyrolysis under the conditions described above. In the illustrated embodiment of the apparatus according to the present invention, there is further provided a capacitor 8 which has all the necessary connections that can be used if the gas contains resinous products which must be condensed before the pyrolysis reactor 7. In this case, these resinous products are pulled from the condenser 8 by means of an exhaust pipe 9.

In reactor 7, the pyrolysed gas is led through a tube 10 to a reducing carbon layer 11, where sulfur oxides are reduced to form hydrogen sulfide and carbon disulfide.

Subsequently, the reduced gas from the layer 11 is directed by a tube 12 to a metal layer 13 capable of forming sulfur, such as iron. The metal sulphide formed thereafter can be removed from the bottom of this layer 13 by a tube 14. If the metal in the layer is iron, it means that the metal sulfide that is extracted is mainly pyrite.

The embodiment of the apparatus according to the invention may further comprise a burner 15 for final oxidation or combustion of the exhaust gas and a pump 16, which in this case is placed between the layer 13 and the burner 15 and is designed to create negative pressure in the apparatus.

i

DEFINITION OF INVENTION