SE435998B - KIT FOR HEATING OF PROCESS AIR FOR INDUSTRIAL PROCESSES - Google Patents

Description

In a plasma generator generated by a plasma generator, some of the constituent atoms and molecules are ionized and these ionized particles are highly reactive. However, when plasma gas produced from an air stream passes to normal conditions at a lower temperature, in addition to nitrogen A and oxygen, nitrogen oxides are also obtained. Nitrogen oxides are known to be very toxic and give rise to the formation of nitric acid, which can destroy the process equipment. In the previously known heating of blast air intended for blast furnaces, no consideration has been given to the formation of nitric oxide due to the fact that the generated plasma gas is blown directly into the blast furnace, where a vending machine is obtained during the passage through the blast furnace charge. The object of the present invention is to obviate the above-mentioned disadvantages and to provide a method for heating process air without the process air being polluted and without the above-mentioned nitric oxide formation being obtained and which also results in a cheaper heating compared to a conventional fossil heating by fossil heating.

This is solved according to the invention in the initially described method mainly by passing water vapor through a plasma generator and in it heated to a high temperature to form a plasma gas, which is then mixed with said process air stream.

Namely, it has surprisingly been shown to the person skilled in the art that no nitric oxide formation occurs even in the mixing zone when the hot plasma gas V generated by water vapor is mixed with air. The invention will be described in more detail below with reference to the accompanying drawings, which for exemplary purposes show some applications of the invention, Fig. 1 showing a schematic view of a device according to the invention, fig. Fig. 2 shows a schematic view of a ball interaction with strip rust provided with the hot air generation proposed according to the invention and Fig. 3 shows a section along the line III - III through the device according to Fig. 2.

Fig. 1 thus schematically shows a plasma generator denoted by 1. The plasma generator 1 has a supply line 2 for a gas stream intended for heating, which is preferably constituted by water vapor. Upon passage of the electric arc generated in the plasma generator, the gas reaches a plasma state and so-called plasma gas is formed. Immediately after the plasma generator, seen in the direction of flow, a water-cooled mold 3 is provided with associated lances 4 for supplying any additive material. Immediately after the mold, the stream of the volume of air intended for heating is supplied to the plasma gas having a very high temperature, which takes place through an inlet 7, which opens into what can be termed a mixing or reaction zone 8. Fig. 2 shows application of the invention to a ball mill with strip rust. In the ball interaction shown here, an endless belt 11 consisting of a large number of interconnected, trolleys rolling on rails 12 intended for transport of agglomerated iron ore slag, so-called pellets through an oven 13. The supply of pellets to the carriages 12 takes place continuously via a roller screen 14. In the said order, the carriages 12 pass two drying zones 15, 16, a preheating zone 17, a sintering zone 18 with two post-sintering zones 18a, 18b and two cooling zones 19, 20. The bottom surfaces of these carriages 12 are air-permeable and can, for example, be lattice-shaped or mesh-shaped.

As process air for the ball interaction, for example, cooling air from another part of the process can be used. The air is fed by means of a cooling fan 21, whereby the air is first blown into the cooling zones 19, 20. A small part of the air flows through the last cooling zone 20, is fed by means of a drying air fan 22 to the first drying zone 15 to flow upwards through the layer of pellets in the carriages and through an extraction fan 23 into a chimney 24.

Most of the sucked-in air is led up into a pipe or housing 25, after which it flows down through ducts 25a, 25b to burners 26 and 26 arranged in the sintering zone 18, respectively. 27. A suitable distribution may be 4 pairs of burners in the preheating zone and 7 pairs of burners in the sintering zone.

A small part of the cooling air is caused to flow down through the carriages in the second post-sintering zone 18b, so that the sintering process is also completed in the lower pellet layers in the carriages.

(If; "fl ~, __, ______U _ .. _, .'_'_ í 8301698-0 Under the sintering zones 18a, 18b, a recuperation fan 28 is arranged, from which the air is fed through a duct 29 to the second drying zone 16 to after passing through the carriages filled with pellets, together with the air from the sintering zone by means of an exhaust fan is blown out through the chimney.

When applying the technique proposed according to the invention to such a ball interaction, 6 of the burner pairs in the sintering zone are suitably replaced with plasma generators designed according to Fig. 1, whereby the necessary heating of the air is achieved without nitric oxide formation.

The volume of atomizing air normally used for the oil burners is sufficient for use in the plasma generators proposed according to the invention. No further process technical change, such as the installation of additional fans and compressors, is therefore required if the process air heating of the ball mill takes place in the manner proposed according to the invention. The only thing required is thus an installation of the plasma torches proposed according to the invention with associated electrical equipment and accessories, as well as connection to a source of water vapor or other gas.

Fig. 3 shows a cross section through the device in Fig. 2 along the line III - III, which passes through the sintering zone.

It can be seen that the carriages 12 with wheels 31 run on rails 32. The air heated to 900 ° C flows from the cover down through the ducts 25a and 25b to the area of the burners, where it is heated, and then enters the furnace area 33. and down through the pellets filled with pellets.

Fig. 3 shows the arrangement with plasma generators designed according to the invention as shown in Fig. 1. The function of the plant will become clearer in connection with the embodiment shown below. 8301698-0 It should be noted that the described application of the invention is only one of many conceivable technical applications that can be realized thanks to the fact that the problem of nitric oxide formation has now been solved in a satisfactory manner.

The invention will now be further elucidated by means of an exemplary embodiment in connection with the ball interaction schematically represented in Figs. 2 and 3.

Example Production in the ball mill is assumed to amount to 420 tonnes of pellets / hour. Earlier in the process, used air with a temperature of about 900 ° C is used as the intake air. As is well known, the sintering process itself requires a temperature of about 1300 ° C. However, incoming pellets must not be subjected to a sudden increase in temperature to 1300 ° C.

Therefore, the device is so designed, as is also apparent from the above detailed description, that in a first drying zone a drying air is used which has a temperature of about 25,000 whereupon the air temperature is slowly increased in preheating-A zones. After the sintering zone, reheating zones are arranged, which is required so that even the pellets at the bottom have time to sinter. Thus, it is mainly in the sintering zone itself that there is reason to replace previously used oil burners with the plasma generators proposed according to the invention.

With the said production capacity, a power supplement of 39 MW is required, corresponding to 3.4 tonnes of oil / hour for heating approximately 70,000 Nm3 of air / hour.

The belt kiln plant in the exemplary embodiment has 11 pairs of burners, of which 7 are in the sintering zone. In this application of the invention, the last 6 pairs of burners are preferably replaced _, __ _.______ _____ \ 2.9 _______._._ _ ._ .l .____._... 4 8301698-0 with 6 pairs connected plasma torch. The volume of the gas stream that passes the plasma generators for the formation of the plasma gas usually constitutes only about 10% of the final volume of process air used for the sintering. The inlet temperature of this gas stream is therefore not critical.

A prerequisite for successful process development at such investment-heavy facilities as ball mills is, of course, that any improvements can be achieved with the least possible intervention in the existing facility. These requirements are met in the present case where the oil burner units only need to be replaced with the plasma generators together with electrical equipment for their electricity supply and certain minor additives.

The energy requirement when using plasma burners and oil burners is largely the same. However, the efficiency of plasma burners is higher than the efficiency of oil burners.

The important thing in this context, however, is that fossil fuels, for which prices have risen very quickly, can be replaced by the invention with the significantly cheaper electricity.

Claims (3)

samsas-o 8 P a t e n t k r a v A method of heating process air intended for industrial purposes to a predeterminable temperature, by mixing the process air stream with a heated gas stream in such proportions that a predetermined temperature is reached in the resulting gas stream, characterized in that water vapor is passed through a plasma generator and in this is heated to a high temperature to form a plasma gas, which is then mixed with said process air stream. 2. A method according to claim 1, characterized in that the plasma gas generated in the plasma generator is mixed into the process air stream immediately after the plasma generator. 3. A method according to any one of claims 1 or 2, characterized in that the gas stream heated in the plasma generator constitutes about 10% of the process air stream.