EP0149930B1 - Process and plant for coal gasification - Google Patents

Description

The present invention relates to the gasification of solid carbonaceous materials and more particularly to the technique according to which powdered coal is injected, together with oxygen and materials for forming a scrubbing slag, in a gasification reactor. consisting of a metallurgical container. This reactor contains a metal bath capable of dissolving carbon, in particular a molten iron bath, playing a role comparable to a catalyst, to give rise to the formation of a combustible gas containing mainly carbon monoxide.

It is known that, in principle, this process is carried out in a container containing a certain volume of molten iron and in which all of the agents and materials intended to intervene in the gasification process are injected by a lance with multiple flow, or separately by different lances, or even by lances and nozzles opening below the surface of the bath.

Overall, the basic reactions differ little from those involved in the pneumatic refining of cast iron by oxygen blown from above, even if these two techniques are also completely foreign both by their goals and their respective implementations . Consequently, it is not surprising that the gasification of coal on liquid metal is usually carried out in a reactor quite similar to a converter of steelworks to oxygen blown from above, or even in such a converter itself. - meme (French patent application No. 2 495 178-from Sumitomo Metal or 2 488 903-from Klockner Werke).

Also, the gasification is carried out sequentially: the slag of the "cast iron refining slag" type, ensures the elimination of the impurities introduced by the coal, in particular sulfur, and is subjected to periodic descaling, while the molten iron bath is used again after reheating.

However, the slag tends to carry with it droplets (or micro-particles) of liquid iron in suspension, so that the simple deslagging causes each time a certain depletion of the iron bath, which can become appreciable after a number of cycles.

With the main aim of achieving "continuous" operation of the gasification operation without consequent loss of iron, the present invention relates to a process for the gasification of carbonaceous material, in particular coal, according to which the carbonaceous material is injected , together with oxygen and materials for forming a purifying slag, using lances in a gasification container containing a metal bath capable of dissolving carbon, in particular a bath of molten iron, process characterized in that said lances are maintained in the emerged position, in that water is also injected into the container and jointly a heat supply is made in order to compensate for the cooling effect of the water injection, in that the supernatant slag is continuously collected on the metal bath as it forms by overflowing a threshold, in that the slag collected is allowed to settle out or allow the gravity separation of the metal droplets present therein in suspension and which collect in the bottom, and in that the slag thus purified is continuously discharged and the metal bath is also recycled continuously liquid metal obtained by decanting the slag.

The process can then be carried out continuously for long periods, the proportion of iron eliminated from the circuit being practically negligible.

• -un réacteur de gazéification destiné à contenir un bain métallique en fusion capable de dissoudre du carbone et pourvu de lances pour l'introduction de matières carbonées, notamment du charbon, d'oxygène gazeux ainsi que des matières de formation d'un laitier d'épuration.
• ―et un décanteur, adjacent au réacteur, destiné à recueillir le laitier formé dans ledit réacteur et communiquant avec ce dernier, d'une part, par un passage qu'emprunte la laitier, et, d'autre part, par un chenal de recyclage dans le réacteur du métal liquide déposé dans le fond du décanteur, et provenant de gouttelettes métalliques en suspension dans le laitier recueilli, installation caractérisée en ce que lesdites lances pour l'introduction des matières dans le réacteur sont maintenues en position émergée, en ce que ledit passage emprunté par le laitier est formé par un seuil de débordement constitué par l'extrémité supérieure d'une cloison séparant le réacteur du décanteur, en ce que ledit chenal est ménagé au travers de cette cloison, et en ce que des moyens sont prévus pour l'introduction d'eau et pour des apports calorifiques, ces derniers n'étant pas susceptibles d'intervenir chimiquement dans les réactions de gazéification.

The subject of the invention is also an installation for installation comprising an integrated assembly with two stages:

• -a gasification reactor intended to contain a molten metal bath capable of dissolving carbon and provided with lances for the introduction of carbonaceous materials, in particular coal, gaseous oxygen as well as materials for forming a slag of purification.
• ―And a decanter, adjacent to the reactor, intended to collect the slag formed in said reactor and communicating with the latter, on the one hand, by a passage through the slag, and, on the other hand, by a recycling channel in the reactor of the liquid metal deposited in the bottom of the decanter, and coming from metal droplets in suspension in the slag collected, installation characterized in that said lances for the introduction of materials into the reactor are maintained in the emerged position, in that said passage taken by the slag is formed by an overflow threshold constituted by the upper end of a partition separating the reactor from the settling tank, in that said channel is formed through this partition, and in that means are provided for the introduction of water and for calorific contributions, the latter not being capable of intervening chemically in the gasification reactions.

In accordance with a preferred embodiment, the recycling channel opens into the reactor below the level of the metal bath so as to allow the metal to flow from the bottom of the decanter to the reactor, according to the principle of communicating vessels.

Advantageously, provision is made to assist this flow by means of supply of motive energy, for example an electromagnetic pump constituted by a linear inductor with a sliding magnetic field housed in the refractory along the recycling channel.

Another means may consist of a gas blowing through a permeable refractory element housed in the bottom of the reactor, in the vicinity of the outlet outlet of the channel, so as to cause an upward mixing of the metal at the level of the channel favoring the flow sought in it. Such a permeable element can perfectly well be of the type described in the published European patent application No. 0021861.

The external calorific intake can be limited to the thermal needs of the fraction of water injected beyond that whose cooling effect is naturally compensated by the internal thermal resources of the reactor, subject, of course, to keep the metal bath in the liquid state, that is to say not to drop below a temperature of the order of 1400-1500 ^° C. in the case of an iron bath.

In this regard, the determinations of the thermal and material balances make it possible in each case to adjust the external calorific contribution to the quantities of water injected according to the introductions of carbon and oxygen, possibly taking into account the search for productivity installation maximum.

Among the possible means of calorific contribution, one will retain those not likely to intervene chemically in the reactions brought into play by the gasification of coal. Thus, we will preferably opt for energy of electrical origin, in particular in the form of an electric arc which is maintained between an electrode and the metal bath itself, as happens in an arc furnace. electric steelworks. Other means of this nature can of course be used, such as a plasma torch or an electromagnetic inductor.

• Qc=quantité du charbon injectée,
• Vu=volume utile pour une charge donnée,
• k=constante de proportionalité dépendant des conditions de mise en oeuvre du procède (granulométrie, qualité du charbon, etc.).

It is remarkable to note that, in view of the experiments they have carried out, the inventors have been led to remember that, for a given volume of metallic bath, the quantity of coal introduced into the bath is linked to the "useful volume" of the bath by a relation of the form:

• Qc = quantity of coal injected,
• Vu = useful volume for a given load,
• k = constant of proportionality depending on the conditions of implementation of the process (particle size, quality of coal, etc.).

It is therefore advantageous, according to a variant of the invention, to associate with the decanter a reactor ensuring the maximum "useful volume" of the bath.

To this end, according to the invention, the decanter is associated with a reactor having an elongated shape, while there is provided a plurality of oxygen lances with spread jets distributed along the reactor so that all of these jets are of interest most of the surface of the metal bath.

• -la figure 1 illustre une installation de base selon l'invention,
• ―et la figure 2 illustre une variante de la figure 1 équipée de moyens d'introduction d'eau,
• -la figure 3 illustre une deuxième variante de l'installation selon l'invention équipée d'une pluralité de lances d'oxygène alignées dans un réacteur de forme allongée.

We will now describe the invention in more detail with reference to the accompanying drawings which illustrate by way of nonlimiting examples and schematically, the invention and its two main variants. On these boards:

• FIG. 1 illustrates a basic installation according to the invention,
• ―And FIG. 2 illustrates a variant of FIG. 1 equipped with means for introducing water,
• FIG. 3 illustrates a second variant of the installation according to the invention equipped with a plurality of oxygen lances aligned in a reactor of elongated shape.

In all the figures, the same elements are designated with identical references.

FIG. 1 shows a double-stage gasification installation comprising a reactor 1 and an associated decanter 2 separated by a half-height partition 3, the assembly being closed by a cover 4 provided with an opening 5 for the outlet of the gases produced.

As can be seen, the reactor 1 is equipped with two emerging lances 6 and 7 respectively for the blowing of gaseous oxygen added with lime and for the introduction of powdered carbon using any transport gas. These lances, cooled by internal circulation of water, of a type known in pneumatic refining, pass vertically through the cover 4 by passages denoted 8, 8 '. All the openings 8, 8 'and 5 of the cover are capped by a gas collecting cover 9 connected to a recovery pipe 10.

The decanter 2 has a lateral opening 11 at a height level approximately equal to that of the upper end of the separating partition 3 and formed at a location on the wall of the decanter remote from this partition. In addition, the bottom of the decanter is substantially raised relative to that of the reactor, and a channel 12, connecting the bottom of the decanter to the reactor, is formed in the refractory partition 3 in a slope inclined downward in the decanter-reactor direction.

The elements which have just been described constitute the basic arrangement of an installation according to the invention.

Its operation is schematically as follows:

The reactor is filled with molten iron 13 to a level between the outlet of the channel 12 and the upper end of the partition 3.

When the lances 6 and 7 are put into service, the injected carbon dissolves in the bath 13 and the rest of the operation is quite comparable to what happens in conventional refining of the cast iron by oxygen blown by the top. This oxygen thus ensures the decarburization of the bath by the formation of gaseous carbon monoxide. The formation of a basic fluid slag 14 based on lime constitutes a sulfur-purifying agent which eliminates this element from the bath 13 as it is introduced by the carbon to be gasified.

The continuous nature of the operation at this stage is ensured by a continuous departure of the slag 14, as it forms, by passing over the partition whose upper end thus constitutes a "single overflow" 15 of the slag .

This expression "only slag overflow" has been consecrated in the past in the field of continuous refining of cast iron which, precisely, implements a double-stage installation reactor-settling tank, in principle and in technology very similar to the gasification plant exemplified here. The reader will be able to realize this for himself by referring to the numerous patents filed on this subject by the applicant, and in particular the French patents No. 1 407 082, 1 427 201 and 1 418 924.

It is recalled in this regard that the technique of "continuous" evacuation of the slag supernatant on a metal bath by overflow of a threshold seems to be well mastered when the slag has a rather frothy consistency. It is known that this result can be easily obtained by an adequate control of the characteristics of the oxygen jet, control which can be easily ensured, for example, by an adjustment of the position in height of the blowing lance. It is also known that a foaming slag contains in suspension a relatively large quantity of iron in the form of droplets or liquid microparticles.

Thus, the deliberately foaming slag 14 that is formed here on the surface of the bath 13 passes, by continuous and regular overflow above threshold 15, from reactor 1 to decanter 2.

During its stay in the decanter, the slag is at rest so that the droplets of liquid iron in suspension have the possibility of separating by gravity from the non-metallic phase and of gathering in the bottom by giving birth then by feeding regularly a bath foot 16. The slag 14 ', which during its progress in the decanter, passes from an initial foaming state to a consistency close to the liquid, reaches the outlet orifice 11 through which it is continuously discharged.

Furthermore, at the bottom of the reactor, the communication channel 12 ensures the recycling of the deposited iron 16 to the main bath 13.

This recycling takes place automatically according to the principle of communicating vessels since, under established conditions, the level of the bath bottom 16 in the decanter is naturally adjusted at all times to that of the main bath 13 in the reactor.

Here, an observation should be made about the start-up phase of the installation.

• -où l'on procède initialement au remplissage du réacteur seul, auquel cas il est nécessaire d'obturer temporairement le chenal 12 par tout moyen approprié (obturateur à tiroir coulissant, etc.) et, de préférence, obturer son extrémité de sortie dans le réacteur. Dans ce cas, la mise en service de l'installation est suivie d'une phase transitoire de mise en régime au cours de laquelle le décanteur voit se former le pied de bain 16 à partir du laitier débordé jusqu'à ce que, le niveau de la surface du bain 16 s'égalisant avec celui du bain principal 13, on ouvre le chenal de communication 12;
• -où l'on procède initialement au remplissage simultané du réacteur et du décanteur, soit séparément si l'on obture le chenal 12, soit en alimentant en métal liquide l'un des deux dans le cas contraire.

There are two possibilities:

• where the reactor is initially filled alone, in which case it is necessary to temporarily close the channel 12 by any appropriate means (shutter with sliding drawer, etc.) and, preferably, close its outlet end in the reactor. In this case, the commissioning of the installation is followed by a transient phase of setting in operation during which the decanter sees the formation of the bath bottom 16 from the slag overflowed until, the level from the surface of the bath 16 equalizing with that of the main bath 13, the communication channel 12 is opened;
• -where one proceeds initially to the simultaneous filling of the reactor and the settling tank, either separately if the channel 12 is closed, or by supplying one of the two with liquid metal otherwise.

In this mode, the start-up phase may be slightly longer, but the transient phase is practically reduced to the time necessary for the first slag which overflows from the threshold 15 to reach the outlet orifice 11.

Whatever the mode chosen, we will of course take care to preheat the vacuum installation properly, in particular the communication channel 12, to avoid untimely phenomena of localized solidification of metal bath.

In accordance with a preferred implementation of the invention, the flow of recycled metal in the channel 12 is assisted. These assistance means may for example be an electromagnetic pump, as shown diagrammatically at 17 in FIG. 1, and constituted by an inductor with a magnetic field sliding along the channel. This inductor is composed of a succession of annular conductors 18 (three in the example shown) housed in the refractory material around the channel 12 and supplied by a three-phase electrical source 19.

According to another variant, these assistance means can be constituted by stirring the bath 13 preferably in the vicinity of the outlet of the channel 12. This stirring can advantageously be obtained by blowing a gas, such as as carbon dioxide (C0 ₂ ) through an air-tight refractory element 20 mounted in the bottom of the reactor and connected to a source of pressurized gas symbolized at 21. Of course, these two types of means can be used separately or jointly, as is the case with the installation in FIG. 1.

As already indicated, these means are known in themselves, as well as in their application to the field of the production of metals. If necessary, reference may be made, for example, to French patent applications PV No. 170198 or PV No. 908871 with regard to electromagnetic pumping and to the published European patent application No. 0081861 with regard to airtight refractory element , such as 20.

The gasification installation illustrated in FIG. 1 allows the production of CO, H ₂ , C0 ₂ type gases, rich in CO, in a continuous manner: the regular evacuation of the slag and the continuous recycling of liquid iron entrained by the slag avoid the accumulation of impurities in the reaction medium (in particular carbon sulfur), as well as the consumption of the metal bath, with slight losses by oxidation in the slag and by dust, but which can easily be compensated if necessary by spaced metal back-ups.

In accordance with a particularly advantageous variant of the invention, illustrated in FIG. 2, a gas rich in hydrogen is produced by gasification of coal from a decomposition of injected water.

But before describing this variant in more detail, it is worth making a few reminders.

From the oxygen oxygen and the water vapor injected, a gas mixture produced according to the following overall reaction is collected in the gasification reactor:

In order to better reveal the elementary phenomena and the heats involved, this reaction can be broken down into:

The combination of reactions (1) and (2) makes it possible to find the well-known reaction of formation of gas to water

Due to the very endothermic nature of the dissociation of water vapor (reaction 1) - the effect of which, as can be seen on the gasification reaction (4), is far from being offset by the combustion of carbon at from the oxygen thus released (reaction 2) -the possibilities of injecting water for the production of a gas rich in hydrogen are relatively limited, and the current techniques of gasification of coal on liquid metal hardly allowing to exceed a content of approximately 20-30% by volume of hydrogen in the gases recovered.

One could think of mitigating the cooling effect of an increased injection of water by a correlative increase in oxygen blowing. Such a measure, however, not only is not easy to control due to the fact that the different reaction equilibria are not established in the same way according to the temperature levels reached in the reactor, but, moreover, the combustion sought carbon then leads to the production of carbon oxides (CO, CO2) which lower the hydrogen content of the recovered gas to bring it back to the values mentioned above.

The fact remains that such a way of operating makes it possible to increase the quantity of gas produced, and therefore also that of coal to be gasified, although limits also appear at this level because this time of the different kinetics between the various chemical reactions put stake.

Certain devices have however been envisaged in an attempt to overcome the limitations of the hydrogen content of the gases produced. Sumitomo Metal Industries Ltd. proposed, in its patents FR.A 2,445,364 and 2,495,178, to make the jets of oxygen and water vapor converge on the surface of the metal bath to create and maintain a "hot spot" at high temperature not likely to affect the thermal resistance of the container refractory. In this case, it would be possible to increase the hydrogen content of the gas produced to more than 30%. However, the means used require very precise adjustments, so that the H ₂ contents greater than 30% indicated in the examples of this patent probably only apply to specific cases and cannot be considered. as a constant and reproducible result based on really well defined characteristics and broad application.

These difficulties are solved by implementing the invention in accordance with an alternative embodiment illustrated in FIG. 2.

As can be seen, the lance 7 for injecting the coal is also used for the introduction of water which, preferably used in the vapor state, can then also serve as a fluid for the pneumatic transport of the coal particles. In addition, the reactor is provided with a graphite electrode 22 passing through a passage 8 "provided for this purpose in the cover 4, preferably in the center of the reactor to limit the harmful effects on the resistance of the refractory walls of the radiation of the electric arc 23 maintained between the bath 13 and the tip of the electrode, which is connected to a terminal of an electrical supply symbolized at 24, the other terminal being brought into contact with the bath 13 by means of a conductive pad 25, located in the bottom of the reactor.

It has already been said that the electric arc 23 is used as a means of heat input which is not capable of intervening chemically on the gasification. This external calorific contribution, which adds to the clean availability of the reaction medium, makes it possible to increase up to values of 40% and beyond the volume content of hydrogen of the gas produced, by making possible the injection of a quantity of much more water than would otherwise be allowed.

The implementation of such a variant thus allows a very appreciable qualitative improvement in the gases obtained, the field of use of which is thus widened towards synthetic chemistry or towards industrial processes requiring highly reducing gaseous agents, for example .

In addition to this variant intended to improve qualitatively the gases obtained, as we have just seen see, the object of the invention is also a quantitative improvement, i.e. an improvement in the productivity of a gasification installation.

The basic principle is based on the double idea that the metal bath must offer, for a given volume, the largest contact surface possible with the blown oxygen and that this oxygen must be blown so as to interest the greatest possible proportion of this surface.

Thus, the inventors have been led to design the variant illustrated in FIG. 3 in which the bath 13, of the same volume as in the previous variants, occupies a reactor 1 of elongated linear shape, The bath 13 therefore has a height " H "weaker than before but, conversely, a much larger free surface 26 above which can be distributed, no longer a single oxygen blowing lance, but several lances 6a, 6b, 6c ... ( three in the example considered) arranged side by side along the reactor and releasing jets whose impact zones on the surface 26 of the bath are substantially tangent to each other. In parallel, a second series of three lances 7a, 7b, 7c, for the injection of powdered coal, are placed obliquely through the large side wall of the reactor and, preferably, each emerge in an oxygen jet in the direction from the surface of the bath.

It is understood that, for a radius "R" of the impact zone of the jet, the optimal size of the reactor shown (having a single row of oxygen lances) is 2R in width and 2NR in length, where N is the number of lances used.

Compared to a reactor of the same capacity but square (or circular) shape with a side 2R (or diameter), the reactor according to the present variant makes it possible to practically triple the metal-oxygen contact surface, which leads to multiplying by three the capacity of the bath to dissolve the carbon quickly, thus increasing proportionally the flow of charcoal that can be injected. This can be expressed, according to the inventors, by saying that the "useful volume" of the bath has also tripled, knowing that this useful volume "Vu" conditions the flow "Qc" of injectable carbon according to the empirical relationship Oc≈k · Vu (previously seen).

The desired increase in productivity is also manifested in the fact that for the same mass of iron bath, the quantity of oxygen and carbon being able to be considerably increased, the instantaneous production of gas collected will be all the more voluminous.

Of course, a gasification installation of this type can also be used for the production of a gas rich in hydrogen, according to the technique described with reference to the variant of Figure 2 (injection of water vapor associated with a compensating calorific contribution ).

It goes without saying that the invention cannot be limited to the examples described, but extends to multiple other variants or equivalents insofar as the characteristics set out in the appended claims are respected.

Thus, the partition 3 separating the reactor from the decanter can be replaced by any other threshold means, the role of this threshold being to promote a calm zone as soon as it leaves the reactor, which makes it possible to implement a decanter of relatively small size. .

Similarly, the metal recycling channel 12 may very well emerge, no longer under the surface of the bath 13, but above. In this case, the respective levels of the main bath 13 and of the bath foot 16 in the decanter are offset in height, and recycling takes place, no longer by balancing the pressures between the reactor and the decanter according to the principle of communicating vessels. , but by simple gravity spill, from the decanter to the reactor.

Similarly, in the case of the water injection variant, the electrode may very well, if it is deemed necessary or simply useful, be placed in the decanter. In any event, it remains preferable to carry out, in one way or another, a chemically neutral calorific contribution to the reaction medium and in particular to the metal bath, which, in addition to its function of dissolving carbon, also plays a role of thermal reservoir essential to the process.

Among the various possibilities of calorific contribution, we will pay particular attention to a technique known for a long time but which, thanks to technical progress, is developing industrially today: electric heating by plasma torch. Applied to the invention, the torch may very well be of the plasma transferred type, with consequently the formation of an electric arc between the metal bath and the electrode, or with plasma gas, this gas possibly being for example steam. of water itself.

Claims (9)

1. Process for the gasification of carbonaceous substance, especially coal, according to which the carbonaceous substance is injected, at the same time as oxygen and substances for forming a purifying slag, with the aid of lances into a gasification vessel containing a metal bath capable of dissolving carbon, in particular a bath of molten iron, which process is characterized in that:

-the said lances (6, 7) are kept in an unimmersed position;

-water is also injected into the vessel and a heat energy input is performed conjointly in order to compensate for the cooling effect of the water injection;

-the slag (14) floating on top of the metal bath (13) is collected continuously as it is being formed, by overflowing a sill (15);

-the slag collected (14') is allowed to decant to permit the separation by gravity of the metal droplets which are present in suspension therein and which collect on the bottom;

-and the slag thus purified is removed continuously and the liquid metal (16) obtained by decanting the slag is recycled, also continuously, into the metal bath.

2. Process according to Claim 1, characterized in that the heat energy input is made without intervening chemically in the reactions brought about by the gasification.

3. Process according to Claim 1, characterized in that the oxygen blown in is distributed over as large as part of the free surface of the bath as possible and in that, for a given bath volume, its free surface is increased to the maximum.

4. Gasification plant for implementing the process according to Claim 1, consisting of an integrated unit with two stages:

-a gasification reactor proper intended to contain a molten metal bath capable of dissolving carbon and provided wcth lances for the introduction of carbonaceous substances, especially coal, of gaseous oxygen and of substances for forming a purifying slag.

-and a decanter adjacent to the reactor, intended to collect the slag formed in the reactor and communicating with the latter, on the one hand, via a passage which is taken by the slag and, on the other hand, via a channel for recycling into the reactor the liquid metal deposited at the bottom of the decanter and originating from the metal droplets suspended in the slag which is collected, which plant is characterized in that:

-the said lances (6, 7) for the introduction of substances into the reactor are kept in an unimmersed position;

-the said passage taken by the slag is formed by an overflow sill (15) consisting of the upper end of a partition (3) separating the reactor from the decanter;

-the said channel (12) is arranged through this partition (3);

-and in that means are provided for the introduction of water and for heat energy inputs, the latter not being liable to intervene chemically in the gasification reactions.

5. Plant according to Claim 4, characterized in that means are provided for assisting the circulation of the liquid metal in the recycle channel.

6. Plant according to Claim 5, characterized in that the said means consist of an electromagnetic inductor (17) with a sliding field along the recycle channel.

7. Plant according to Claim 5, characterized in that with the recycle channel emerging into the reactor under the surface of the metal bath, the said means consist of an air-permeable refractory component (20) fitted into the bottom of the reactor and connected to a source (21) of gas under pressure.

8. Plant according to Claim 4, characterized in that the said means for heat energy input consist of an electric arc (23) maintained between an electrode (22) and the metal bath (13 or 16).

9. Plant according to Claim 4, characterized in that the reactor (1) has an elongate linear shape and in that the means for injecting gaseous oxygen (6a, 6b, etc.) are distributed along the reactor so that the group of the oxygen jets affects the major part of the free surface (26) of the metal bath (13).

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