WO1988000427A1

WO1988000427A1 - Method and apparatus for plasma gasification of liquid materials

Info

Publication number: WO1988000427A1
Application number: PCT/FI1987/000089
Authority: WO
Inventors: Pentti Salmelin
Original assignee: Imatran Voima Oy
Current assignee: Imatran Voima Oy
Priority date: 1986-07-04
Filing date: 1987-06-30
Publication date: 1988-01-14
Anticipated expiration: 1989-01-04
Also published as: FI862836L; FI862836A0; FI75969C; FI75969B

Abstract

In accordance with the method, an electric arc (7) is formed between the electrodes (4, 5), and a gaseous material is fed into the electric arc (7) in order to generate a plasma jet (8). In accordance with the invention, the material to be gasified is fed into the plasma jet (8) through the electrode (4) in order to cool the electrode and to vaporize the material. The apparatus for the plasma gasification of liquid materials comprises two electrodes (4 and 5) between which an electric arc (7) can be formed; a reaction chamber (9) in which the material can be gasified into plasma; and a material feed connection (6) through which the material to be gasified can be fed into the plasma jet (8). The second electrode (4) of the apparatus according to the invention comprises at least one channel (3) through which material to be gasified entering from the material feed connection (6) can be fed into the plasma jet (8) in order to cool the said electrode (4) and to vaporize the material to be gasified. In the method and apparatus according to the invention, the material to be decomposed operates by itself as the plasma gas, and, consequently, decomposes almost completely.

Description

Method and apparatus for plasma gasification of liquid materials

This invention relates to a method in accordance with the 5 preamble of claim 1 for plasma gasification of liquid materials. Furthermore, the invention provides an apparatus for the implementation of the method.

In prior art embodiments, the plasma gasification of liquid 10 materials is implemented by feeding the material to be decomposed into the plasma jet either from the side of the jet or close to the outer electrode of the plasma gun, generally the anode, in order to vaporize and decompose the material in the intense heat and ultraviolet radiation of the 15 arc. The plasma arc is generated and maintained with help of an appropriate plasma gas, for instance, argon or nitrogen. The cathodes of conventional plasma guns are generally manufactured of copper, and, typically, the cathode tip is of tungsten. The cathode requires cooling, which is provided 2C either by an external or internal water circulation inside the cathode construction.

A disadvantage of the prior art technology is that uncertainty remains as to whether the exposure of the material to be 5 decomposed to the influence of the plasma jet is sufficiently long, partly because the plasma jet tends to expel the material to be disintegrated. Furthermore, the full capacity of the jet cannot be utilized because energy transfer from the jet to the decomposition process is incomplete since, for instance, 0 the high temperature (approx. 10 000 °C) of the jet core is not utilized. Factors of uncertainty associated with decomposition give an impetus towards over-dimensioning of process components, reduce the energy and operating economy of the plasma process and increase operating malfunctions and 5 safety risks. Furthermore, a separate cooling system complicates the construction.

The aim of this invention is to overcome the disadvantages of the technique described above and to provide a completely T-hs invention is based on feeding the liquid material to be gasified through an electrode construction, consisting of metal rods, which operates as a feeding channel so that the material to be disintegrated is vaporized in the waste heat ~ of the plasma gun and the steam formed is used as the plasma arc gas.

More specifically, the method in accordance with the invention is characterized by what is stated in the characterizing part 0 Q£ claim 1.

Furthermore, the apparatus in accordance with the invention is characterized by what is stated in the characterizing part of claim 2. τ

The invention provides appreciable benefits.

Due to the method in accordance with the invention, the material to be decomposed cannot avoid the plasma conditions 0 because the material itself is converted into plasma gas. Furthermore, the plasma arc power can be fully utilized. Decomposition is quick and complete, which allows the reaction chamber to be dimensioned purely on the basis of conditions set by the gas reactions. The time requirements necessitated

25 by the gas reactions are in the order of a few milliseconds. The reaction chamber can be compactly designed which further enhances the gas reactions. Owing to effective decomposition, the operating safety of the process is appreciably improved. Compared to prior art embodiments, the method in accordance

50 with the invention does not necessarily require any auxiliary components. In fact, the construction of the plasma gun is simplified because the feeding system simultaneously performs as a cooler.

35 The electrode construction in accordance with the invention operates simultaneously as both the electrode and the material feeder connection. The construction disposes of a separate cooling water system because the waste heat is utilized in improves the energy efficiency. The quantity of inert gases in the process is decreased and the operating costs of the process reduced since a separate plasma gas system is required only in the warm-up and shut-down phases of the decomposing

I 5 process, which furthermore allows a small and simple gas system.

In the following, the invention will be examined in more detail by means of an exemplifying embodiment illustrated by the 10 attached drawings.

Figure 1 shows in longitudinally-sectioned side view an electrode in accordance with the invention.

_ς Figure 2 shows the cross-section of the electrode illustrated in Figure 1.

Figure 3 shows in a longitudinally-sectioned side view a plasma arc unit with an electrode illustrated in Figures 1 20 and 2.

Figure 4 shows in a cross-sectional view another electrode in accordance with the invention.

25 Figure 5 shows in a longitudinally-sectioned side view the electrode in accordance with Figure 4.

With reference to Figure 2, an electrode construction in accordance with the invention will be described. The

30 electrical conductors are a sleeve tube 1, manufactured of copper, and tungsten rods 2. The material to be fed flows in voids 3 remaining between the rods 2 within the approximately round sleeve tube 1 and simultaneously cools the rods 2 and the sleeve tube 1. Finally, the fed material vaporizes close 5 to the electrode end. Heat required for vaporizing is obtained from the heat load exerted on the plasma arc electrode, of which load is normally cooled off by a separate water cooling apparatus. Figure 3^' shows an electrode 4 as part of a plasma arc unit in accordance with the invention. In this configuration, the electrode 4 operates as the anode. The cathode electrode 5 of the embodiment is annular. First, an electric arc 7 is 5 established between the electrodes 4 and 5. .Plasma gas is fed into the electric arc 7 through the anode 4 from a material feed pipe 6 attached to the end of the anode. During the starting phase of the process, plasma gas can be lead to the material feed pipe 6 from a separate plasma gas container, C esξxec±ally if the material to be decomposed is hazardous. An alternative implementation of the process is also possible so that the electric arc 7 is excited sufficiently long in order to warm up the anode 4, which allows subsequent material feed immediately. The material is then vaporized within the 5 anode 4 by the effect of this generated waste heat and directly enters the plasma arc 8.

>

Figures 4 and 5 show a variant embodiment of the invention, in which material feed channels 11 are fabricated into the Q oblong and massive conductive electrode 10. There are five channels 11 in the embodiment illustrated by the figure, however, the quantity of channels 11 may vary according to the material being fed and the cooling requirements of the electrode 10. 5

For the operation of the invention, the polarity of the electrode 4 or 10 is relatively insignificant, allowing the electrode to operate either as the anode or the cathode. Within certain limitations, the apparatus can also be fed

3.3 with AC power, which allows only a temporary assignment of the anode and the cathode.

The construction of the electrode 4 or 10 is not limited to the implementations shown in Figures 2 and 4. Since the 35 principal idea of the invention is to feed the material to be decomposed through the electrode in order to cool the electrode and to vaporize the material, the invention encompasses all oblong-shaped electrode constructions with flow-through may replace the tungsten rods 2 with tubes, achieving a larger flow area due to the round holes of the tubes. The cross- section of the rods 4, as well as of the sleeve tube 1, does not necessarily have to be circular. An electrode construction with concentric tubes is also feasible in fabrication, requiring a support structure for fixing the tubes to each other.

The electrode material used must have a high electrical conductivity and high^" temperature resistance. Several alternative metals and metal alloys are readily available, including such metals as zirconium or hafnium.

Claims

WHAT IS CLAIMED 'IS:

1. A method for plasma gasification of liquid materials, in which method

- an electric arc (7) is formed between electrodes (4) or (5) and,

a gaseous material is fed into the electric arc 0 (7) in order to generate a plasma jet (8),

c h a r a c t e r i z e d in that

- the material to be gasified is fed into the ^ plasma jet (8) via the electrode (4) in order to cool the electrode and vaporize the material.

2. An apparatus for plasma gasification of liquid materials comprising 0 two electrodes (4) and (5) between which an electric arc (7) can be formed.

- a reaction chamber (9) in which the material 5 can be gasified into plasma and,

- a material feed connection (6) via which the material to be gasified can be fed into the plasma jet (8)

c h a r a c t e r i z e d in that

- the second electrode (4) comprises at least one channel (3) through which the material to be ^■55 gasified entering from the material feed connec¬ tion (6) can be fed into the plasma jet (8) with the purpose of cooling the electrode (4) and vaporizing the material to be gasified.

3. An apparatus in accordance with claim 2, c h a r a c t e r i z e d in that the second electrode (4) comprises an oblong sleeve tube (1), within which several

Ϊ oblong, essentially round rods (2) are placed so that oblong

5 channels (3) remain between the rods (1) inside the sleeve tube for the passage of the material to be gasified.

4. An apparatus in accordance with claim 2, c-h a r a, c. t e r i z e d in that at least one channel (11) 10 is- fabricated into the solid structure of the second electrode (10) for material feed.