GB2160218A

GB2160218A - Method and plant means for partial combustion and gasification of carbonaceous material

Info

Publication number: GB2160218A
Application number: GB08427964A
Authority: GB
Inventors: Sven Santen; Bjorn Hammarskog
Original assignee: SKF Steel Engineering AB
Current assignee: SKF Steel Engineering AB
Priority date: 1984-06-14
Filing date: 1984-11-05
Publication date: 1985-12-18
Also published as: ZA848218B; AU568693B2; NZ210168A; CN85101700A; IN162320B; KR860000355A; BE901159A; JPS614789A; DE3441358A1; AU3525684A; DE3441358C2; SE453751B; GB8427964D0; IT8423373A0; GB2160218B; FR2565992A1; NO844800L; SE8403191L; IT1177080B; ES538144A0

Abstract

The present invention relates to a means and method for partially combusting and gasifying carbonaceous material in which a hot plasma gas flow containing oxidizing agent is generated in a plasma generator and introduced into a reaction chamber, the pulverulent carbonaceous material being introduced concentrically around said hot gas flow with the aid of a transport gas.

Description

SPECIFICATION Method and plant means for partial combustion and gasification of carbonaceous material The present invention relates to a method of partially combusting and gasifying atomized carbonaceous material by introducing oxidizing agent and said carbonaceous material into a reaction chamber while at the same time supplying energy by means of a plasma generator, and to a plasma generator therefor.

It is already known to use oxygen burners for gasifying carbonaceous material, which burners are directed towards the centre of a chamber having a central gas and slag outlet.

However, certain problems arise here in conjunction with the burner design. The rate at which the oxygen is blown in determines the location of the flame front and in order to prevent reverse firing there must be a certain distance betwen the burner nozzle and the flame front This conserably limits the control range. In order to protect the walls of the chamber, a wall of water vapour is sometimes blown around the oxygen inlet, making the flow relatively undisturbed. Carbon powder is blown into the oxygen flow by lances and mixed in the burner. Due to the undistributed flow and the high flow rate, mixing is extremely poor and a long mixing distance is required for water in the carbon particles to be gasified and the particles themselves to be sufficiently heated.

Furthemore, a relatively low reaction speed is achieved in known methods of heating the oxidizing agent and fuel to a temperature at which reactions commence, this being primarily achieved through circulation of hot reaction products. t It is also known per se to use plasma generators for the supply of thermal energy for combustion and gasification of carbonaceous fuel. Pulverized carbon is injected into a carrier gas heated by a plasma generator.

Oxygen, CO2, and/or water vapour are used as oxidizing agent and injected either in the hot carrier gas or used wholly or partially as carrier gas.

The object of the present invention is to effect a process for partial combustion and gasification of carbonaceous material permitting rapid, efficient mixing of the oxidizing agent and the carbon carrier, giving a short mixing distance and a large control range irrespective of the location of the flame front, and achieving a considerably higher reaction speed by the direct supply of thermal energy to the oxidizing agent and fuel used.

Another object of the invention is to produce a combined burner for performing the process according to the invention In the method described in the introduction, the above objects are achieved according to the invention by generating a hot gas flow in a plasma generator and introducing the gas into a reaction chamber the pulverent carbonaceous material being introduced concentrically around said hot gas flow with the aid of a transport gas. The transport gas may consist of oxidizing agent, for instance, combustion products (02, CO2, H20), or recirculated gas.

The plasma gas is given a rotary movement in the plasma generator, so that on leaving the plasma generator vigorous turbulence is achieved in the concentrically flowing carbonaceous material, while at the same time the central flow of hot gas instantaneously heats the material mixture to reaction temperature.

The oxidizing agent preferably consists of 02, CO2, water vapour, air or a mixture thereof, while the carbonaceous material consists of coal dust, coke dust, characoal dust, peat and/or shavings.

The plasma generator for performing the process according to the invention is characterised in that it comprises cylindrical electrodes between which an electric arc may be generated, a supply pipe for the introduction of carrier gas into the plasma generator, means for imparting a tangential velocity component to the hot gas flow generated in the plasma genertor, an outer tube arranged around the plasma generator to form an annular space between the outside of the plasma generator and said outer tube, at least at the outlet end of the plasma genertor, and means for the supply of carbon-carrying material to said annular space.

A pressure chamber may preferably be arranged in connection with the inlet side of the annular space, in which lances are arranged for supply of carbonaceous material to give the carbonaceous material a tangential speed component in order to effect uniform distribution of the material in the annular space.

Alternatively, an inner protective pipe may be arranged with outer guides, for instance in the form of blades to provide a rotary movement, preferably in a direction opposite to that of the plasma gas. In this case the annular space for introduction of the pulverulent material is formed by said outer tube and said inner tube. Besides achieving quicker mixing, this arrangement causes less wear on the plasma generator.

Additional advantages and features of the invention will be revealed in the following detailed description with reference to the accompanying drawings in which Figure 1 shows the plasma generator according to the invention, Figure 2 shows an alternative embodiment of the plasma generator according to Fig. 1 and Figure 3 shows a somewhat modified embodiment of the plasma generator according to Fig. 2.

Fig. 1 thus shows a burner according to the invention, with a plasma generator generally designated 1. The plasma generator is of conventional type with cylindrical electrodes between which an arc is generated. Carrier gas is injected through a supply pipe 2 and is heated upon passage through the arc. Besides acquiring an axial speed component in the plasma generator, the carrier gas also acquires a tangential speed component, so that the plasma gas rotates vigorously when leaving the plasma generator.

Arranged around the front portion of the plasma generator is an outer pipe 4, sealed to the plasma generator at 5. In the embodiment shown the outer pipe is provided with a flange 6 for fitting to a combustion or gasification chamber. This indicates that the outer pipe may be permanently fixed to a wall, thus considerably facilitating removal and replacement of the plasma generator. In this case the outer pipe is preferably water-cooled, and by allowing it to protrude slightly past the chamber wall, the outer pipe can also function as a tuyere.

Dry, pulverulent fuel is introduced through a pipe 7 into the annular space 8 formed between the plasma generator and the outer pipe. According to the embodiment shown a pressure chamber 9 is arranged at the inlet side of the annular space, the orifice of the supply pipe 7 being in this chamber. This ensures more uniform distribution of the material in the annular space.

Fig. 2 shows an alternative embodiment of the plasma generator according to Fig. 1. An inner protective pipe 10 is arranged around the free end 3 of the plasma generator, surrounded by the outer pipe 4. Outside the inner protective pipe 10 are blades 11-14, designed to give the pulverulent material introduced a direction of rotation opposite to that of the plasma gas generated. This provides better and more rapid mixing as well as protecting the plasma generator from wear.

Fig. 3 shows yet another embodiment of the plasma generator according to Fig. 2. The outer pipe, here designated 15, is watercooled, the coolant being supplied at 1 6 to the space 17. In the embodiment shown the outer, water-cooled pipe is in the form of an extended tuyère, intended to repalce a con ventionaltuyre.

The procedure and function of the arrangement are described in more detail in the following.

Carrier gas, preferably comprising a part of the oxidizing agent used, is heated in the plasma generator and leaves the plasma generator as a hot core of rotating plasma gas.

This ignites and causes vigorous turbulence in the pulverulent, carbonaceous material introduced through the annular space 8, preferably by means of oxidizing agent such as water vapour, oxygen, air or a mixture thereof. Contrary to the case with an oil burner, for instance, where firing is effected by the flame front whose location is determined by the flow conditions, the high temperature of the plasma gas ensures stable firing irrespective of other conditions. This provides an extremely wide control range of the plasma generator and considerably quicker initiation of firing and consequently higher total reaction speed.

The hot plasma gas also reduces the need for excess oxygen to achieve substantially complete combustion/gasification. Furthermore, an extremely high flame temperature is obtained, considerably higher than in conventional burners, resulting in a greater reduced percentage of undesired constituents in the gas after combustion/gasification, such as un combusted / ungasified carbon, alcohols, phenols, methane, tar, heavy hydrocarbons, etc.

Yet another decisive advantage is that an excess of thermal energy independent from the combustion is supplied through the plasma generator. This offers considerably greater opportunities of controlling the composition of the reaction products while at the same time reducing the risk of soot deposits.

Claims

1. A method of partially combusting and gasifying atomized carbonaceous material by introducing oxidizing agent and said carbonaceous material into a reaction chamber while at the same time supplying thermal energy by means of a plasma generator, wherein a hot gas flow containing oxidizing agent is generated in a plasma generator and introduced into said reaction chamber and the pulverulent carbonaceous material is introduced concentrically around said hot gas flow with the aid of a transport gas.

2. A method according to claim 1, wherein the oxidizing agent used is 02, CO2, water vapour, air or a mixture of one or more of said components.

3. A method according to claim 1 or claim 2, wherein the oxidizing agent is utilized as transport gas for the carbonaceous material.

4. A method according to any one of claims 1 to 3, wherein the oxidizing agent is partially or wholly heated in the plasma generator to generate said hot gas flow.

5. A method according to any one of claims 1 to 4, wherein coal dust, charcoal powder, peat or shavings are used as carbonaceous material.

6. A means designed for partial combustion and gasification of atomized carbonaceous material by introducing oxidizing agent and said carbonaceous material into a reaction chamber while at the same time supplying thermal energy by means of a plasma generator, for performing the method according to claim 1, wherein the plasma generator comprises cylindrical electrodes between which an electric arc is generated, a supply pipe for the introduction of carrier gas into the plasma generator, means for imparting a tangential velocity component to the hot gas flow generated in the plasma generator, an outer tube arranged around the plasma generator to form an annular space between the outside of the plasma generator and said outer tube, at least at the outlet end of the plasma generator, and members for the supply of carbon-carrying material to said annular space.

7. A means according to claim 6, wherein a pressure chamber is arranged in connection with the inlet side of the annular space, to effect uniform distribution of the carbon-carrying material supplied.

8. A means according to claim 7, wherein the supply pipe for the carbonaceous material is arranged to open tangentially into said pressure chamber.

9. A means according to claim 6, wherein an inner, protective pipe is provided, having obliquely arranged blades to provide a rotary movement and to protect the plasma generator from wear.

10. A means according to any one of claims 6 to 9, wherein the outer pipe is watercooled.

11. A means according to claim 10, wherein the water-cooled outer pipe is in the form of an extended tuyere.

1 2. A method of partially combusting and gasifying atomised carbonaceous material according to claim 1 and substantially as herein described with reference to the drawings.

1 3. A means for partial combustion and gasification of atomised carbonaceous material according to claim 6 and substantially as herein described with reference to the drawings.