This invention relates to a shell-structured plasma process unit in accordance with the preamble of claim 1.

The unit is used in decomposition, disposal and recombination applications requiring high temperatures and high energy densities.

All prior art plasma unit constructions are almost identical. The plasma burner is located in a cylindrical reaction chamber lined with a refractory material. The material to be decomposed, via different types of feeders, is applied close to the plasma flame into the reaction zone, where gases consisting of the decomposition products are mixed and reacted in the reaction chamber and then exit via a separate gas scrubber to further processing.

The reaction chamber volume is determined by the delay required for the mixing and recombination of the decomposition products ^• as well as by the power of the plasma gun. The delay can be adjusted by regulating the auxiliary gas flows or material feed. In prior art constructions, the reaction chamber volume and the plasma gun power are scaled according to an approximate rule of 4 liters/kW which requires large-volume reaction chambers, e.g., a 2 m3 chamber for a plasma gun of 0.5 M .

The heat radiation load created by the plasma flame implies an extremely good temperature resistance from the reaction chamber. The reaction chambers described in the literature and patent publications are insulated against heat radiation by different kinds of ceramic compounds or by a tile lining.

The decomposition gases exiting from the reaction chamber are cooled and scrubbed in a separate scrubber. The operation of the scrubber is based on air and/or water jets. The scrubber size is roughly 2 or 3 times the size of the reaction chamber.

A disadvantage of the prior art technology is the size of the equipment, which is comprised of two relatively large units.

easily reaches a few tons. Furthermore, the massive construction slows down the heating of the reactor so that the first warm-up may take up to several days and even after a temporary break, will take hours. In some cases due to the cracking risk of the thick lining, liquified gas burners or - other types of burners are required for preheating. If the lining is damaged, it may take several days to repair. Another serious drawback of conventional constructions is that the full capacity of the reaction vessel is not effectively utilized. A material feed dimensioned according to the plasma gun size requires a large reactor. Furthermore, in a big reactor, the mixing of decomposition gases takes a relatively long time (approx. I s), necessitating larger reactor dimensions or decreased material feed rate. A large reactor may contain pockets of low temperature (< 700 °C), which may cause serious damage to the environment and personnel during the waste disposal process. The lining materials may also absorb reaction products, and in disturbance situations also input materials may be absorbed, which, in the destruction of problem wastes, converts the lining materials themselves into problem wastes.

The aim of this invention is to overcome the drawbacks of the technology described above and to provide an entirely novel type of plasma process unit with a shell construction.

The invention is based on constructing the process unit from concentric shell-shaped structures located around the decomposition cylinder so that the gas path is formed into a meandering passage, which combines the decomposition, recombination and scubber zones into the same unit.

More specifically, the method in accordance with the invention is characterized by what is stated in the characterizing part of claim 1.

The invention provides appreciable benefits.

The equipment in accordance with the invention can be designed com act on the basis of its inte rated construction. The

small size of the equipment is advantageous in its light weight and easy transportability. A short warm-up is also achieved, with the shortest warm-up time taking only a few seconds. Compared with conventional constructions, the small size of the equipment results in low-cost maintenance, servicing and repair and also achieves superior durability. Owing to the decomposition cylinder, the material to be decomposed cannot avoid undergoing contact with the plasma jet. Due to the oblong decomposition cylinder, the material will be subjected to plasma conditions for a time an order of magnitude longer than in conventional constructions, which insures an almost complete decomposition. The materials, which are decomposed into an almost gaseous state, are vigorously mixed in the narrow reaction zones and react into final products efficiently and quickly. Due to the effective decomposition and recombination, the delays can be shortened up to a tenth of those conventionally applied. Furthermore, the full capacity of the equipment in accordance with the invention can be optimally utilized. In an equipment with correct dimensioning, the material feed rate is determined by the plasma gun power. The equipment also disposes of auxiliary burners and auxiliary systems required by these. In a disturbance situation, the quantity of undecomposed material remaining in the equipment is essentially less than in conventional equipment because of the effective material decomposition. Moreover, the decomposed materials are easily recovered due to the uncomplicated, unlined and compact equipment.

In the following the invention is exemplified in detail in accordance with the embodiment illustrated by the attached drawings.

Figure 1 shows a longitudinally sectioned view of a possible implementation for a plasma process unit with shell construction.

Figure 2 shows in section A - A the plasma process unit in accordance with Figure 1.

T e support-structure of the process unit is formed by a body 13, fabricated, for instance, of a special steel, to which the other parts of the equipment are mainly mounted. The nucleus of the system is a plasma gun 1 attached to the upper part of the body. The plasma gun 1 comprises the plasma gas feed elements 3, electrical feed elements 4, and cooling elements 2. A material to be decomposed is fed with help of material feed elements 19 into a plasma flame 6 formed by the plasma gun 1. Underneath the plasma gun 1 is a decomposition 0 zone 8, which is delineated by its sides by a decomposition cylinder 9 mounted about the plasma gun 1. The cross-section of the decomposition cylinder 9 is preferably circular because then the cylinder is most effectively filled by the plasma flame 6, and it is possible to achieve the most even 5 temperature distribution together with the most effective material decomposition. The decomposition cylinder 9 is sub¬ jected to a heavy heat load and, consequently, must be manu¬ factured of a special metal, for instance, niobium. Examples of physical dimensions for the decomposition cylinder 9 are 3 given for the cylinder 9 when using a 200 kW plasma gun. In this case, the length of the cylinder 9 is 1000...1500 mm and the diameter is 150...200 mm. The decomposition cylinder 9 is attached to the body 13 of the equipment around the plasma gun 1, by, for instance, bolts and an appropriate sealing. 5 The sealing material can be, e.g., a sufficiently refractory material, for instance, an asbestos-containing compound. When required, the seal can be cooled by a gas flow. The end of the decomposition cylinder 9, opposite the plasma gun 1, is open in order to ^" facilitate the flow of the decomposed 0 gaseous material. A wall 10 surrounding the gas space and located close to the open end is cooled behind the wall 10 with a material 11, for instance, water or some other applicable liquid. The surface 10 limiting the gas space can also be lined with a casting compound (not shown), allowing, the 5 lining compound to be in liquid state during the running process on the plasma flame side, and in solid state closer to the cooled wall 10.

Due to the construction in accordance with the invention, the

shell-shaped structures, for instance, cylinders 9, 14, 15, 16. Each cylinder is attached at its other end to the body 13-so that the decomposition cylinder 9, having the smallest diameter, is attached at its upper end while the second cylinder 14, having the second smallest diameter, is attached at its lower end, and so forth. A gap is left between the body 13 and the unattached end of each cylinder in order to facilitate a gas flow. The gap is determined by the required flow with a preferable size of the radius of the decomposition cylinder 9.

A recombination zone 12 of the gaseous decomposed material entering from the decomposition, zone 8 is formed between the outer wall of the decomposition cylinder 9 and the inner wall of the second cylinder 14. The radial width of the said recombination zone 12 is preferably the size of the decomposition cylinder 9 diameter and its length is in the exemplified construction approximately equal to the length of the decomposition cylinder 9 of the described embodiment. In the embodiment illustrated in the figure, the recombination zone 12 reaches up to the level of the same wall to which the plasma gun 1 and the decomposition cylinder 9 are attached. Next to the recombination zone 12, the gas passage contains the scrubbing zones 7, whose number is determined by the required scrubbing efficiency. In the embodiment illustrated by the figure, there are two scrubbing zones 7, of which the first one is formed between the outer wall of the second cylinder 14 and the inner wall of the third cylinder 15 and the second zone between the outer wall of the cylinder 15 and the inner wall of the fourth cylinder 16.

Mounted at the process unit plasma gun 1 end of the cylinder, are atomizing nozzles 5 of the scrubbing zones 7, via which, for instance, gas or liquid is sprayed in order to scrub the gas entering from the recombination zone 12. As many atomizing nozzles 5 are assembled as required to cover the entire cross- section of the zone. For instance, water is applicable as the scrubbing compound. The equipment according to the drawings comprises 8 nozzles per zone. When required, the scrubber nozzles 5 of the scrubbin zone next to the

recombination zone 12 can be closed in order to convert the scrubbing zone 7 into the recombination zone 12. Thus, the length of the recombination and the scrubbing zones can be adjusted to desired length. The purpose of the scrubbing zone 7 is to quickly cool down the gas entering from the recombination zone 12. Next to the scrubbing zone 7, the gas is conveyed to further processing, for instance, to heat recovery outside the process unit.

The body 13 of the process unit can be completely closed and solid, which requires some of the cylinders to comprise mounting fixtures (not shown) with a non-obstructing con¬ struction to the gas flow in order to connect a lower part 17 of the body to an upper part 18. The mounting fixtures are preferably located at the outer cylinders to minimize their heat loading.

The upper part 18 and the lower part 17 of the body 13 can also be fully separated, in which case the upper part is supported by a separate element (not shown) . An advantage of this embodiment is that the gas flow opening between each cylinder and the body 13 is adjustable. Furthermore, maintenance and servicing of the equipment is easier if the upper and lower parts are constructed as separate elements. The cross-section of the decomposition cylinder 9 need not be circular and is preferably symmetrically formed in relation to the flame. The corners must also be rounded in order to avoid cold pockets.

Neither the decomposition cylinder 9 nor the other cylinders

14, 15, and 16 necessarily need to be a mathematically defined cylinder but, rather, an essential feature is the cylindrical shape of the structural elements. Deviations from cylindrical shape may be required if the cylindrical shells are tapered due to reasons related to flow engineering or the shells are formed conical for the same reasons.

The diameters of the cylinders 14, 15, and 16 can also be chosen so that the diametrically cross-sectional area of each

plasma process unit is constant, which provides an approximate¬ ly equal flow resistance for the gas flow in each zone.

In order to minimize heat loading, the plasma gun 1 can be sur- rounded by an annular gas nozzle (not shown), which ejects gas, for instance, the plasma gas used in the process, in order to cool the inner wall of the decomposition cylinder 9.

The quantity of concentric cylinders may be chosen as desired. However, the invention is characterized in that the space remaining within the innermost cylinder 9 operates as the decomposition zone 8 and it is followed on the gas passage by at least one. recombination zone 12, which furthermore is followed by a sufficient number of scrubbing zones 7 that can be converted into recombination zones by closing the scrubber nozzles 5.

Insufficient tightness between the decomposition cylinder 9 and the plasma gun 1 may cause problems that can -be alleviated by arranging a lower pressure compared to the surroundings of the cylinder with help of, e.g., the atomizing nozzles of the scrubbing zones 7 or by gas suction after the scrubbing zones.

The position of the process unit shown in the drawings, with the material to be gasified as well as the scrubbing compound being fed in the direction of the gravitational field is most preferable; however, other positions are also possible. Special embodiments for cooling procedures and precautionary measures are required for the other positions in possible malfunction situations.