EP0240483A1 - Process and apparatus for the concurrent gasification of coal - Google Patents

Abstract

The invention relates to the gasification of co-current coal and a gasifier. The gasifier (11) comprises a vertical sealed tank, the lower third of which is divided into several identical vertical compartments (12). Coal is loaded at the top (17). The hot reactive gas, under pressure, is mainly introduced at the top (18), the rest at lower levels (21, 22). In turn, we stop the evacuation of gas (24) from a compartment (12), we blow the gas produced to unclog the filters (25, 26) and remove the ashes, we extract the ashes from the bottom (23 ) and cold reactive gas is blown against the current to complete the combustion and cool the ashes. This gasifier allows the use of coal coming from all sources and does not require purification downstream.

Description

The present invention relates to a process and apparatus for gasifying coal by feeding coal and reactive gas to the top of a reactor, the gas and solid streams moving downward co-current in most of the reactor, and completion of the reaction by introducing a quantity of reactive gas against the current at the base of the reactor. The reaction takes place in a fixed bed, under pressure and with non-molten ash.

By coal is meant in this descriptive specification any carbonaceous material of a wide range of particle sizes, without resorting to upstream coal preparation such as crushing, grinding, screening, etc. On the other hand, coal can have any composition without resorting downstream to equipment for purifying or recovering by-products (sulfur compounds, tars, phenols, liquid hydrocarbons). The process of the invention allowing the elimination or the transformation of all the harmful quantities of the by-products "in situ" during the gasification.

By "fixed bed" is meant in this specification a non-turbulent bed which does not undergo than a slow downward movement due to the effect of gravity.

Most of the gasification processes for coal with a fixed bed, operating on an industrial scale, at low or high pressure, are counter-current systems.

A good representative example is the LURGI process, the gasifier of which is shown in FIG. 1. In the LURGI process, the calibrated coal with low agglutinative power is introduced at the top of the reactor, from where it moves in a fixed bed downwards under the effect of gravity and the ash is extracted at the base. Water vapor and oxygen are introduced to the base of the reactor and allowed to rise against the current and the gases produced are discharged from the top of the reactor.

This counter-current process has the advantage of providing a fairly good recovery of the heat of the gases resulting from the reaction by transferring part of the heat to the fresh masses placed in the oven. In addition, thanks to the countercurrent circulation of the fresh oxidizing gas, the reaction is almost complete. There is therefore a minimum loss of active material in the ashes.

On the other hand, since the reaction focus is at the bottom of the reactor and the temperature decreases as one goes up in the reactor to meet fresh coal, one arrives at an area where the temperature is close to 500 ° C and where the slow rise in temperature favors the formation of a liquid phase which causes the agglutination of the coal particles preventing a regular descent of the ashes. To avoid this agglutination, the LURGI process requires, upstream, the choice of coal with low agglutinative power. In addition, inside the gasifier, LURGI had to provide a mixing arm, which must stir the fixed bed of coal.

If the size of the coal is uneven, there is an irregular distribution of the gases, hence the need to choose a calibrated coal (for example, with a particle size between 10 and 30 mm) and a screening plant and 'removal of fines upstream.

The reaction center is located at the bottom of the reactor. In order to prevent the temperature therein rising too high, the oxidizing gas distribution grid must be cooled by the use of a large excess of steam, which results in a negative effect on the energy and economic balance.

The decreasing temperature gradient in the reactor causes the by-products to gradually evolve and mix with the product gas and thus 70 to 95% of the sulfur contained in the coal can be found in the form of gaseous sulfur compounds in the gas discharged to the top of the reactor. This gas therefore requires downstream a purification installation which must not only rid the product gas of sulfur compounds, but also other annoying non-gaseous products, such as tars, fractions of liquid hydrocarbons, ammonia, etc.

US Patent 3,920,417 describes a gasifier where the coal and reactive gas descend co-current in the lower part of the reactor. On the other hand, the upper part of the reactor consists of a coal preheating zone against the current, with a very lively hearth at the base of this zone and a temperature which decreases to meet fresh coal, which itself is introduced right at the top of the reactor. In this zone, therefore, all the drawbacks of the counter-current process are encountered, that is to say agglutination and the formation of tars and sulphurous gases. In addition, this process is limited to the implementation of non-sticky coal, of a well-determined caliber, and the tars and other undesirable liquids are reinjected into the reactor by means of a steam injector, thus linking the quantities of steam to those of the tar formed.

The combustion furnace in the gasifier of this patent gives off a very high temperature (around 1800 ° C). Indeed, we want to obtain molten ash. However, given the introduction of steam downstream from that of the oxidizing gas and the endothermic reaction which follows, there is every reason to fear that the liquid ash generated upstream will be cooled, inevitably causing the solidification of the ash, the formation of large bottom ash and blockage of the reactor. Moreover, the brick baffles serving as filters for the liquid ash being solidified will quickly be clogged and the gas will not be able to find a homogeneous passage through the reactor towards its discharge point. Finally, since the gasifier does not include an airlock, it cannot operate under pressure.

German patent 54.995 describes a gasifier with a fixed bed where the coal as well as the major part of reactive gas are introduced by the open top of the gasifier and descend while cocurrent in it. To avoid clumping, additional amounts of air, steam and carbon are injected at other lower levels. The gases produced are extracted using a gas suction extractor and therefore vacuum. This gasifier, fitted with sliding doors, a water guard and seating holes to ward off blocked bottom ash, cannot operate under pressure. This patent describes the possibility of heating the air by means of superheated steam, but the risk of agglutination implies that the temperature of the gas remains below 500 ° C. This gasifier therefore does not provide means avoiding the sticking of bottom ash and the agglutination of coal. In addition, the process of this patent, which does not envisage a final phase of reaction against the current, evacuates with the ashes residual quantities of carbon, which represent a loss or require a recycling.

French patent 783.087 describes a wood gasifier for OTTO motor vehicles. Combustion takes place at a fixed bed and at a co-current. The fireplace is divided into several compartments for a better distribution of the air injection nozzles and a softening of the incandescent bed. In addition to the compartmentalization of the hearth, the description of this patent emphasizes the compartmentalization of the upper part of the gas generator into several chambers (claim 10), one above the other, at least one of which has a drying zone and a distillation zone. The distillation zone gives off tar and other undesirable liquid products which must be recycled to ensure their elimination which remains partial, which constitutes a major drawback. In addition, the French patent process can only operate at very low pressure (1.5 bar), does not include an airlock, does not provide a continuous ash extraction device and must therefore be stopped regularly to evacuate the ashes and be cleaned before setting up a new load. Designed for the use of wood, if the wood had to be replaced by charcoal, the agglutination of this one, in the drying zone, would be inevitable, because nothing is planned to prevent it.

German patent 1,048,658 describes six reactors operating with cocurrent, dry ash and using fine particle size coal. In each reactor, the coal is fluidized in turn by blowing against the current, through the incandescent bed, in order to generate a sorting of particles by gravity, in order to direct the ashes downwards. This blowing is preceded and followed by a blowing of water vapor over the bed to remove oxygen and avoid the formation of explosive mixtures. This blowing is carried out in all the gasifiers simultaneously.

US patent US 1,505,065 describes a gasification of fatty carbon for the production of a gas with a low calorific value, rich in hydrogen and as poor as possible in carbon monoxide. The gasifier has two zones: an upper carbonization zone and a lower production zone. In the carbonization zone, the coal is loaded at the top and flows down. The reactive gas (air + excess water vapor) is mainly introduced between the two zones, so that it produces an incandescent focus in the middle of the gasifier and the reactive gas rises partially against the current in the carbonization zone. , gradually reheating the fixed bed of charcoal above and another part of this gas descends, co-co-occurring with the glowing charcoal. In this lower production zone, it is planned to inject additional quantities of reactive gas. Since this process has an upper zone of progressive heating, it is not suitable for sticking coals. It cannot operate under pressure due to the lateral evacuation of ash and dust. It cannot prevent the entrainment of ashes in the gases towards the stacks which will quickly become blocked; cleaning them is difficult.

European patent application 0089329 describes a process for gasifying coal under pressure, but it comprises two reactors which operate alternately by reversing. This process has several drawbacks. Having two reactors and many valves, it is much more expensive to implement and difficult to operate. Operating in reverse, it requires a steam sweep after each cycle, either every 2 to 4 minutes, in order to separate the reactive gases, either air or oxygen and steam and the combustible reaction gases by purging the installation. Cyclical inversion and permanent temperature fluctuations make refractories fragile, which requires their replacement more frequently. Finally, the recovery of the heat contained in the gases produced is mandatory here, which does not allow the direct use of hot gases at the outlet of the gasifier, such as for example in synthesis or in the production of reducing gas in the steel industry, without using an independent and expensive heater.

In order to remedy all the drawbacks of these known methods, the applicants have developed a carbonation process for coal, with a fixed bed, by reaction with a reactive gas under pressure, in which the coal is charged in an upper loading zone. of a vertical gasifier at a point near its top from which it flows downwards under the effect of gravity, characterized in that it is subjected, upon introduction into the gasifier, to a shock thermal by reacting it with reactive gases, at a temperature much higher than the coal agglutination temperature and close to the ash melting temperature and under a pressure of at least 2 bars (0.2 MPa), said reactive gases being introduced into the gasifier for the most part at a first level close to the point of introduction of the coal and, in addition, at least at a level lower than said first level, the gases moving downwards by cocurrent with coal, a certain quantity of cold reactive gas is introduced into the evacuation zone at the base of the gasifier, at the point of extraction of the ashes, from which this quantity goes upwards against the current to complete the gasification of the residual carbon and cooling the ash, and in that the gas produced by the gasification is evacuated, after filtration, from the evacuation zone to a level higher than the extraction point of the ash.

According to a preferred embodiment of the process of the invention, the evacuation zone is compartmentalized in the direction of flow of the bed into at least three equal compartments and the evacuation rate of the gas produced is controlled so to be identical in all compartments except one, in turn, where the gas evacuation is stopped. Indeed, one stops in turn, in one compartment after the other, the evacuation of produced gas, and one blows there briefly and vigorously, in opposite direction of the evacuation, of the cold produced gas and / or the steam to clean the filter and to ash ash upstream of the filter in said compartment. During the gas evacuation stop, a determined quantity of ashes, identical for all the compartments, is evacuated from the bottom of the compartment concerned, and at the same time, fresh reactive gas is blown into the ash extraction orifice. to complete the gasification of the residual carbon and cool the ash.

After having passed the coal, as defined above, in a sealed airlock, it is loaded into a loading area located near the top of a vertical gasifier. The carbon is distributed uniformly over the fixed bed and allowed to flow down under the effect of gravity.

If the coal contains a significant quantity of sulfur-containing products, it is mixed with a calcium or magnesium material, either before the introduction into the airlock of the coal, or via a separate airlock before the dispersion of the coal.

Depending on the type of gas that one wishes to obtain at the end of gasification, the reactive gas is air or oxygen and steam for the production of combustible gas, hydrogen and oxygen for the production of rich gas, blast furnace gas and oxygen for the production of reducing gas, or other oxidizing gases.

These reactive gases are pressurized. Indeed, the pressurized gasification process has several advantages over gasification at atmospheric pressure or at reduced pressure. Since the amount of gas produced is significantly higher than the amount of reactive gas introduced, pressurizing the introduced gas represents an economy compared to pressurizing the larger gas produced. Moreover, this latter pressurization is necessary to transport the gases in the piping to their destination. In addition, the transport of pressurized gas requires less expensive piping and the smaller the diameter the higher the pressure. Finally, gasification under pressure requires a much smaller volume of gasifier than gasification at atmospheric pressure, resulting in a considerable gain in investment. For these reasons, the reactive gases are put under a pressure of at least 2 bars, up to, for example, 40 bars, before their introduction into the gasifier.

They are brought to high temperature by heat recovery, for example between 600 and 1200 ° C. The largest part of these gases (for example 50 to 75%) is introduced into the gasifier loading area at a level close to the coal loading and distribution point, preferably at a level higher than the latter.

As a result, the coal, upon its introduction into the gasifier, is subjected to a thermal shock, the fine particles spontaneously ignite and the larger pieces burst by decrepitation into multiple smaller particles, thus releasing the volatile matter, and the distillation residues, such as tars and phenols, decompose under the effect of temperature and are recovered in the form of useful gas.

The gases formed descend by cocurrent in the bed of solids. Given this co-current flow, there is a risk of an incomplete reaction. This is why one or more complementary quantities of the reactive gases are introduced at at least one other level below the loading zone. For example, a second quantity of reactive gases, 10 to 30%, is introduced at a second injection point, for example peripheral, and again 0 to 20% at a third injection point, which can be central.

Thanks to secondary and tertiary injections, etc., the gasification reaction continues efficiently throughout the height of the solid mass and the temperature of the reaction medium is maintained at a high and controlled level.

The thermal shock of the first injection and the continuation of the reaction by the other injections disintegrate the carbon without clumping it, whatever its composition.

As mentioned above, the preferred embodiment of the process of the invention provides for the partitioning, in the direction of flow of the bed, of the evacuation zone into at least three compartments of identical dimensions, preferably four to eight compartments, for example six equal compartments.

Each compartment is provided with an outlet for the evacuation of the produced gas and an outlet for the ash. The flow rate of these evacuations is controlled. The gas discharge rate is controlled so as to be identical for all the compartments, with the exception of one of them, where the gas discharge is periodically stopped. Indeed, one stops, in turn, in one compartment after another the evacuation of product gas. While the evacuation of the gas from the compartment concerned is stopped, a blow of gas produced cold and / or steam in the opposite direction to the direction of normal evacuation is briefly blown under pressure. This blast is used to clean and unclog the filter (s) and to unclog the ashes beyond the filter in the compartment at rest.

After blowing the gas, we proceed to the evacuation of a specific quantity of ash. This quantity will be the same for all compartments that are put to rest in turn.

The distribution of the material of the descending bed into equal compartments as well as the double control of the gas and ash evacuation rate ensures a regular descent in all points of the whole of the fixed bed, despite a varied particle size of the coal at the start, and this without having to use a costly mixing arm which is difficult to operate at high gasifier temperatures.

Since ashes are removed from one compartment at a time and these ashes remain stationary in the other compartments, clogging filters during the evacuation of these gases is reduced to a minimum, the mass of ash forming filter-mass.

While the ash is being removed, cold reactive gas is injected into the bottom of the compartment, into the ash outlet. The purpose of this injection is, firstly, to gasify the residual carbon contained in the ashes, and, secondly, to completely cool the ashes before their evacuation with total recovery of the sensible heat in the reactor. As a result, the coal is fully gasified in a single step, in a single gasifier and no recycling of the ashes is necessary.

The gas evacuated from each compartment at a regular rate is collected in a common manifold and leaves the gasifier at high temperature. It can then either transfer its sensible heat to the reactive gases in heat exchangers and produce the steam necessary for the reactions in a recovery boiler and then pass through a washer where any impurities are extracted, or be used by a consumer, directly, as is, at high temperature, or heated in independent heaters.

Indeed, the gas produced by the process of the present invention does not require any downstream purification installation, since the undesirable products: tars, liquid hydrocarbons, phenols, sulfur compounds, or else are decomposed by the thermal shock of the at the start, or else react with the calcium material and are eliminated with the ashes.

As briefly noted above, in order to remove sulfur compounds from the manufactured gas, especially when using sulfur-rich coal, in the process of the invention, provision is made for the addition of a controlled quantity of calcium or magnesium materials, for example lime. This addition can be done either at the same time as the coal, or separately. The sulfur compounds are thus fixed at more than 90% in solid form in combination with the ash and the gas leaving the gasifier is free of by-products and other elements harmful to use. It is therefore not necessary, in most use cases, to install gas cleaning equipment.

The present invention also relates to an apparatus suitable for carrying out the method described above, in this case a gasifier.

The coal gasification apparatus according to the invention comprises, in combination, a sealed vertical tank, the lower part of which is divided into at least three compartments of equal dimensions by means of vertical radial partitions leaving the tops of these compartments in communication with the non-compartmentalized upper part of the tank, the tank being provided with:
- a sealed means of loading coal near the top of the tank and a means of distributing it on the fixed bed,
a means for introducing hot reactive gas, for the most part, at a first level, close to the point of introduction of the coal into the enclosure of the tank,
- at least one means for introducing an additional quantity of reactive gas to at least one level below said first level,
- a means of extracting a controlled quantity of ash from the bottom of each compartment, a common and sealed means of collecting and evacuating ash and a means for introducing into each compartment a last part of reactive gas into the ash extraction means,
- a means of evacuating the gas produced from each compartment, which means is located at a level higher than that of extracting the ashes, a means of filtering the gas, a means of controlling the flow of gas and stopping its evacuation, a means for introducing cold product gas in counter-current when stopping the evacuation, the different gas evacuation means, one per compartment, being connected to a common collector means.

The gasifier advantageously comprises four to eight equal compartments. These compartments preferably occupy 20 to 40% of the total height of the gasifier.

The sealed coal loading means is advantageously an airlock, the coal of which is brought to the distributor by means of a metering device, for example an Archimedes screw.

The main means of introducing the reactive gas is preferably situated at a level higher than that of the distribution of the coal on the fixed bed and it is advantageously peripheral around a central means of distribution of the coal.

The complementary means for introducing reactive gas preferably comprises a peripheral means located approximately halfway up the gasifier and a central means in the middle and at the top of the compartmentalized sector.

The means for extracting the ash from each compartment preferably comprises a means for grinding any clinkers.

The means for filtering the gas produced preferably comprises a large mesh filter, for example 3 mm and a special filter in metallic refractory material, or ceramic retaining fine dust particles, for example 0.1 mm and more.

The means for evacuating the product gas is preferably a nozzle per compartment provided with a flow control and stop member and with a cold product gas introduction orifice against the current when stopping. gas evacuation, the different nozzles being combined downstream of the adjustment means in a common peripheral collecting means.

The gasifier is preferably provided with a means of adding calcium or magnesium material to the coal. This means involves the addition of calcic or magnesium matter to the coal before its introduction into the sealed loading means (airlock) or else a separate airlock, the two solid loads mixing in the middle of the top in the distribution and dispersion means. homogeneous, for example a dispersing disc.

• La Fig. 1 est un schéma d'un gazogène connu selon le procédé en contre-courant de LURGI.
• La Fig. 2 est une coupe verticale d'un gazo­gène suivant l'invention.
• La Fig. 3 est une coupe horizontale le long de la ligne III-III du gazogène de la Fig. 2.
• La Fig. 4 est une coupe verticale, à l'échelle agrandie, d'une tuyère d'évacuation de gaz.
• La Fig. 5 est un schéma de fabrication de gaz combustible par le procédé et l'appareil de l'invention.
• La Fig. 6 est un schéma de fabrication de gaz réducteur en substitution au coke en sidérurgie par le procédé et l'appareil de l'invention.
• La Fig. 7 est un schéma de fabrication de gaz de substitution au gaz naturel (SNG) par le procédé et l'appareil de l'invention.

With the aid of the appended figures, in which the same numbers refer to the same members, an embodiment of the gasifier according to the invention is described, as well as a few manufacturing diagrams illustrating the use and operation of the gasifier of the invention. .

• Fig. 1 is a diagram of a known gasifier according to the LURGI counter-current process.
• Fig. 2 is a vertical section through a gasifier according to the invention.
• Fig. 3 is a horizontal section along the line III-III of the gasifier of FIG. 2.
• Fig. 4 is a vertical section, on an enlarged scale, of a gas discharge nozzle.
• Fig. 5 is a diagram of the production of combustible gas by the method and the apparatus for the invention.
• Fig. 6 is a diagram of the production of reducing gas in substitution for coke in the steel industry by the method and apparatus of the invention.
• Fig. 7 is a diagram of the production of natural gas substitution gas (SNG) by the process and the apparatus of the invention.

Fig. 1 is a diagram of a gasifier known from LURGI operating under pressure and against the current.

The reactor 1 comprises at its top an airlock 2 for loading calibrated coal which flows downwards, in a fixed bed, and which is distributed by the distributor 3. A rotary mixing and crusher arm 4 brews the fixed bed and prevents its agglutination. The reactive gas (oxygen + water vapor) is introduced at 5 at the base of the reactor 1 and goes upwards against the flow of the coal. Around this point of introduction 5 of the reactive gas, the gasifier is provided with a jacket 6 for water cooling. The counter-current reaction depletes the coal of its combustible material and transforms it into ashes which are evacuated via the rotary grate 7 and the orifice 8 at the bottom of the reactor 1 towards the sealed airlock of the ashes 9. The gas produced is evacuated from the top of reactor 1 through port 10.

Fig. 2 shows a vertical section of a gasifier according to the present invention. It comprises a vertical reactor 11, the lower part of which is divided into six vertical compartments 12 of identical dimensions (cf. Fig. 3). The gasifier 11 is provided with a port 13 for loading coal at its top. The coal is in a sealed airlock 14 (cf. Fig. 5), from where it is loaded by the metering device 15 in the form of an Archimedes screw towards a vertical distributor 16 which disperses it by the disperser 17 on the fixed coal bed. This disperser 17 is therefore located in the center and at the top of the enlarged cavity of the reactor 11. Most of the reactive gas is introduced, for example 60%, through the orifice 18 situated at a higher level than that of the disperser 17, whence the gas surrounds the distributor 16 and the disperser 17. This reactive gas is brought beforehand to a temperature of 600 to 1,200 ° C. by heat recovery or by reheating. The coal dispersed in the center by the disperser 17 is therefore directly subjected to a violent thermal shock resulting from the reaction. The fine particles ignite spontaneously and the larger pieces burst by decrepitation into multiple smaller particles which fall on the fixed bed having released the volatile matter and the residues of distillation (tars, phenols). These products decompose under the effect of the temperature in situ and are transformed into useful gas. When the coal used contains a significant quantity of sulfur-containing product, a calcium or magnesium material, for example calcium carbonate, is loaded into the reactor at the same time as the coal. This can be done in two ways: either mixing the calcium or magnesium material with carbon in the same airlock, or alternatively loading this material in a separate sealed airlock 19, as shown in FIG. 5, and via a separate metering device 20, the calcium or magnesium material is brought to the vertical central distributor 16 from where it is dispersed at 17 at the same time as the coal. Since the gaseous and solid streams (carbon + calcium or magnesium matter) move cocurrently, the calcium or magnesium matter reacts with the sulfur to finally form calcium sulphate (or magnesium) which is evacuated with the ashes. Thus, the gas produced is also freed of any sulfurized material and it does not no more downstream purification or recovery facilities are required. The coal and possibly the calcium or magnesium matter and the reactive gas descend co-current in the reactor. In order to ensure a good reaction of all the active material in the coal, an additional quantity of hot reactive gas, for example 25%, is introduced halfway up the reactor 11 through peripheral orifices 21. It is preferable to introduce another final quantity of hot reactive gas, for example 15%, through a central orifice 22 in the middle and at the top of the compartmentalized part of the reactor. All these quantities of reactive gases descend, co-co-occurring with the coal.

Finally, to completely complete the reaction of the residual carbon in the ashes, a certain quantity of cold reactive gas is injected, this time in counter-current, into the ash extraction orifice 23. This final quantity will ensure, in Besides, the cooling of the ashes.

As described above, the lower part of the reactor is divided into six vertical compartments of identical dimensions, by means of vertical radial partitions (cf. Fig. 3). Each compartment 12 is in communication with the non-compartmentalized upper part of the reactor 11. Thus, the fixed bed which previously descended into a single solid mass is divided into six equal parts in the six compartments. This division of the fixed bed is an important factor in the homogeneous distribution and regular descent of the mass of coal and ash.

The mass of coal and ash and the gases are therefore distributed in identical quantities in the six compartments 12 where they are removed. The gas produced is evacuated from five of the six compartments 12 by a nozzle 24 (see more particularly Fig. 4). Each nozzle contains two filters, one 25, in the form of a large mesh grid to retain the larger particles, which have a diameter greater than 3 mm and the other 26, made of metallic or ceramic refractory material to retain the particles of dust with a diameter between 0.1 mm and 3 mm. As an extension of the filters 25 and 26, the nozzle 24 has an orifice 27 with a plug 28, through which the filter or filters can be inserted or removed for cleaning or replacement. Further on, the nozzle 24 is provided with an orifice 29 through which one blows, briefly and vigorously, a blow of gas produced cold and / or steam. The nozzle also includes a valve 30 which regulates or stops the gas discharge rate. Finally, the six nozzles open into a common manifold 31 from which the gas produced leaves the gasifier at high temperature. Its destination depends on the type of gas produced and its use, as explained in the manufacturing diagrams in Figs. 5 to 7.

The ashes and what they still contain as carbon descend homogeneously into the six compartments. Each compartment 12 has at its bottom an orifice 23 for extracting the ashes. In this orifice a crusher-extractor 32 (cf. Fig. 5) enters the compartment, grinds the ashes if they are agglomerated and extracts them in a controlled manner to the common sealed airlock of the ashes 33 from which the ashes are removed. , for example by means of a conveyor belt 34. The ash release orifice 23 is provided with a means of introduction against the current, of a certain amount of cold reactive gas as already described above.

The valves 30 of the nozzles 24 control the gas discharge rate so that this rate is identical in all the nozzles except one, where gas evacuation is stopped. In fact, one stops, in turn, in one compartment after another, the evacuation of the gas produced by closing the valve 30. While the evacuation of gas from the compartment 12 concerned is stopped, one breathes there. , through orifice 29, in counter-current, a short and vigorous blow of gas produced cold under pressure and / or water vapor. This blast cleans and unclogs the two filters 25 and 26 of the nozzle 24 in question and rubs the ash beyond the filter 25 in the compartment 12 concerned.

After blowing the gas, a predetermined quantity of ash is removed from the orifice 23 by means of the grinder-extractor 32. This quantity will be the same for all the compartments during shutdown, in turn, of the gas outlet. While the ash is being extracted, a certain amount of cold reactive gas is introduced through the orifice 23 for extracting the ash, which rises against the current and completes the combustion of the residual carbon in the ashes and cools them.

This double control of the gas and ash evacuation flow rate, which will be identical for all the compartments, ensures a homogeneous distribution and a regular descent of the whole of the fixed bed, distributed in six compartments, whatever the particle size or the composition of the coal at the start.

Since the ashes are removed from one compartment 12 at a time and these ashes remain stationary during this time in the other five compartments, the clogging of the filters in them is reduced to a minimum and the gas evacuation of these five compartments is unhindered.

FIG. 5 represents a diagram for manufacturing combustible gas and thus illustrates an example of the use and functioning of the gasifier of the invention.

Charcoal is loaded into the airlock 14, then it is transported by the metering device 15 to the distributor 16 where it encounters the calcium material that was loaded in the airlock 19 and transported by the device 20 to the same distributor 16. The carbon and the calcium material mix and are dispersed together by the disperser 17 on the fixed bed.

The compressor 35 sends reactive gas, air or oxygen, via the pipe 36 to the heat exchanger 37. Water vapor from the boiler 46 is introduced therein at the same point. reagents are warmed to about 700 ° C. They leave the exchanger by the pipe 38 which is divided into three pipes each provided with its valve, namely: the continuation of the pipe 38, provided with the valve 39, feeds the top of the reactor 11, the pipe 40, provided with the valve 41 feeds the medium of the reactor 11 and the pipe 42, provided with the valve 43 opens at the center and at the top of the compartmentalized part. The flow rate of the valves is adjusted so that most of the hot reactive gas, for example 60%, feeds the top of the reactor through the orifice 18, while a second part, for example 25%, feeds the periphery at mid-height of the reactor by the peripheral orifices 21 and a third part, for example 15%, feeds the center of the part compartmentalized by the orifice 22.

The coal and the calcium material dispersed by the disperser 17 are subjected as soon as they enter the reactor cavity to a thermal shock by reaction with the hot reactive gases and the temperature reaches about 1,000 ° C. These gases are introduced via the orifice 18 located at a higher level than the surrounding disperser. Small particles ignite and the large pieces burst and the whole of the fixed bed and the gas flow descend slowly co-flowing.

Unlike counter-current processes, this co-current descent cannot alone guarantee that the combustible material in the coal is exhausted. This is why the second quantity of reactive gas is introduced peripherally at the middle of the reactor and a third quantity in the center at the top of the compartmentalized part.

The ashes descend into the compartments and are evacuated to the common airlock 33, then disposed of.

The gas produced, combustible gas, leaves the reactor 11 via the nozzles 24, the flow control valves 30, the manifold 31 and the pipe 44 towards the heat exchanger 37. It transfers its heat there by heat exchange to the gas reactive and warms it. The gas produced leaves the heat exchanger 37 through the pipe 45, heats the recovery boiler 46 and the exchanger 47 and is washed in the washer 48 which receives cold water through the pipe 49. The gas washed and cooled passes through the pipe 50 to the exchanger 47 and from there through the pipe 51 to the user. Part of this cooled gas leaves the pipe 50 through the pipe 52 to the gas booster 53. The compressed gas at 53 passes through the pipe 54 and is divided into six pipes 55, each provided with a valve 56. When stops the evacuation of gas in one compartment at a time, in turn, by closing the valve 30, the corresponding valve 56 is opened and the product produced under pressure is blown briefly and vigorously against the current, to unclog filters and remove ash from the affected compartment.

Note that part of the reactive gas, after compression but before heating in the heat exchanger 37, is led by the pipe 57 provided with its valve 58, towards the ash extraction orifice 23. When stopping the evacuation of gas in a given compartment, fresh pipe gas is introduced through this pipe 57 against the current in the concerned compartment where it completes burning the residual carbon and cooling the ash.

Fig. 6 shows a diagram of the production of reducing gas in substitution for coke in the blast furnace and thus illustrates another example of the use and operation of the gasifier of the invention.

In this diagram, the system for loading coal and calcium and the ash removal system are identical to that in FIG. 5 and will therefore no longer be described a second time here. Besides, all the elements which correspond to those of FIG. 5 have the same number.

The diagram in FIG. 6 differs from that of FIG. 5 mainly by the reactive gas supply system and product gas discharge.

In Fig. 6, part of the gas produced by the blast furnace (reactive gas) and which essentially consists of CO, CO₂ and N₂ is sent by pipe 59 to the compressor 60 and by pipe 61 to the gas heater 62, supplied with gas fuel through the pipe 63 and the combustion fumes of which are discharged at 64. The hot blast furnace gas leaves the heater 62 through the pipe 38 which is divided into two or three pipes each provided with its valve to supply the gasifier. By the continuation of the pipe 38 and of the valve 39, most of this hot reactive gas, for example 60%, feeds the top of the reactor through the orifice 18 situated above the point of dispersion of the coal 17. By the pipe 40 and the valve 41, another part of the reactive gas, for example 25%, feeds the mid-height of the reactor through the periphery orifices Finally, via the pipe 42 and the valve 43, a last part of the hot reactive gas, for example 15%, feeds the center 22 of the reactor at the top of the compartmentalized part.

As for oxygen, necessary for the reaction, it is introduced at three points close to the introduction of blast furnace gas, namely at the head at 118, halfway up at 121 and at the center at 122.

The reducing gas produced by reaction of the gas from the blast furnace with the coal and which essentially consists of CO, H₂ and N₂ leaves the compartments 12 through the nozzles 24, the valves 30, the manifold 31 and the pipe 44 and in turn feeds the blast furnace in the reduction gas production zone. The use of blast furnace gas in the gasifier and the refueling of the blast furnace with reducing gas allows a saving of coke which can reach 50%.

Fig. 7 shows a diagram for manufacturing natural gas substitute gas (Substitute Natural Gas SNG) and thus illustrates a third example of the use and operation of the gasifier of the invention.

In this diagram, the system for loading coal and calcium and the ash removal system are identical to that in FIG. 5 and will therefore not be described again here. Besides, all the elements which correspond to those of FIG. 5 have the same number.

The diagram in FIG. 7 differs essentially from FIG. 5 by the reactive gas supply system and the product gas evacuation system.

In Fig. 7, hydrogen passes through the pipe 65 to the heater 66, supplied with fuel through the pipe 67 and whose combustion products tion are evacuated via pipe 69. The heated hydrogen feeds the reactor through pipe 38 which is divided into three pipes each provided with its valve. By the continuation of the pipe 38 and the valve 39 most of the hydrogen, for example 60%, feeds the top of the reactor through the orifice 18 situated above the point of dispersion of the coal 17. Through the pipe 40 and the valve 41, another part of the hydrogen, for example 25%, feeds the mid-height of the reactor through the peripheral orifices 21. Finally, by the pipe 42 and the valve 43, a last part of the hot hydrogen, for example 15%, feeds the center 22 of the reactor at the top of the compartmentalized part.

On the other hand, oxygen passes through the pipe 69 which is divided into two or three pipes each provided with its valve. The pipe 70 and its valve 71 supplies the top of the reactor with most of the oxygen. It joins the supply of hot hydrogen through an independent orifice 118. A second part of the oxygen feeds via the pipe 72 and the valve 73 halfway up the reactor and joins the hot hydrogen there through independent peripheral orifices 121. Optionally, a third part of oxygen is introduced into the center through an independent orifice 122.

The gas produced essentially consists of a mixture of CH₄, CO, H₂, CO₂. It leaves the compartments 12 via the nozzles 24, the valves 30, the manifold 31 and the pipe 44 and is sent to the recovery boiler 76 from where it is sent to the CO converter 77, at the washing of CO₂ 78, where the CO₂ is eliminated by the pipe 79. Then, the gas freed from CO₂ passes through the hydrogen separator 80, from where part of the pure hydrogen passes through the booster 81 and is recycled towards the reactor by the pipe 65. The residual gas passes through the pipe 82 and the booster 83 to the final methanation reactor 84. From there, the outgoing gas, consisting mainly of methane, is sent to the natural gas distribution network. A certain quantity of raw gas, taken at the outlet of the boiler 76, is sent to the compressor 53 and through the pipe 54, which is divided into six pipes 55 provided with their valves 56 to introduce brief blows under pressure into the nozzles 24, each time that the evacuation of the gas is stopped from one compartment at a time, in order to unclog the filters and to ash out the ashes in the compartment concerned.

The three manufacturing diagrams shown in Figs. 5, 6 and 7 show that the various gases produced leaving the gasifier can be used directly, as they are, without requiring a purification or recovery installation downstream of the reactor. Likewise, the loaded charcoal can be of any size or composition. Even if it is rich in sulfur products, it suffices to load a quantity of calcium matter so that the flux which moves in co-current promotes the reaction of the sulfur with the calcium matter and allows its evacuation with the ashes.

The thermal shock that the coal undergoes upon its introduction into the reactor, causes it to explode, volatilizes the volatile materials and decomposes them so that they are transformed into useful gas. There are therefore no more harmful by-products in the gas produced.

The cocurrent reaction at high temperature avoids all agglutination problems, which are specific to all the processes which include at least one initial phase of countercurrent reaction. On the other hand, the final counter-current phase of the present invention completely completes the reaction of the residual carbon in the ash and at the same time ensures the cooling of the ashes with total recovery of the heat in the reactor.

In addition, the gasifier according to the invention has considerable economic advantages. It consists of a single vertical tank. Operating under pressure, its volume is reduced, the gases are compressed before the volume increase due to the reaction in the gasifier, the net energy yield is very high and its needs in fluids and energy are very limited. If we compare it, for example, to the LURGI reactor, which is commercially very widespread, we see that there is no need to moderate the exothermic combustion reaction as LURGI does by injecting steam. This represents a pure loss of energy, which does not exist in the present process. In addition, the LURGI process requires the choice of a calibrated carbon, of non-caking property and poor in sulfur products. Despite these strict fuel quality requirements, LURGI must provide an enormous dynamic crusher-crusher arm to ensure a certain regular descent of the fixed bed. On the other hand, in the gasifier of the present invention, the static partitioning of the lower part of the gasifier and the regulation of the gas and ash evacuation flow rate described above ensure a homogeneous distribution and a regular descent of the mass without problems. of the fixed bed.

Finally, let’s add up to a non-negligible saving factor which consists in the freedom to use all-coal, cheaper, without limitation either from the point of view of its physical characteristics (particle size) or chemical (agglutinative power, sulfur content) . All these factors make it possible to manufacture purified gases at low cost and satisfying the most recent anti-pollution regulations.

Claims (16)

1.- Process for the gasification of coal, with a fixed bed, by reaction with a reactive gas under pressure, in which the coal is loaded into an upper zone for loading a vertical gasifier at a point near its top (13) d '' where it flows down under the effect of gravity, characterized in that it is subjected, upon introduction into the gasifier, to a thermal shock by reacting it with reactive gases, at a temperature considerably higher than the coal agglutination temperature and close to the ash melting temperature and at a pressure of at least 2 bars (0.2 MPa), said reactive gases being introduced into the gasifier for the most part at a first level (18) close to the point of introduction of the coal and in addition to at least one lower level (21, 22) to said first level (18), the gases moving downward cocurrently with the coal, a certain amount of gas cold reagent being introduced into the discharge area at the base of the g azogen, at the ash extraction point (23), from where this quantity goes up against the current to complete the gasification of the residual carbon and cool the ash, and in that the gas produced by the gasification is evacuated, after filtration, from the evacuation zone to a level (24) higher than the ash extraction point. 2.- Method according to claim 1, characterized in that the evacuation zone is compartmentalized in the direction of flow of the bed into at least three equal compartments (12) and the evacuation rate of the gas produced is controlled by so as to be identical in all compartments except one, in turn, where the gas evacuation is stopped. 3.- Method according to claim 2, characterized in that one stops, in turn, in a compartment (12) after the other the evacuation of product gas and that there (29) blows briefly and vigorously , in the opposite direction to the evacuation, of the cold product gas and / or of the steam to clean the filter (25, 26) and to ash the ash upstream of the filter (25, 26) in said compartment (12). 4.- Method according to claim 3, characterized in that during the gas evacuation stop, the bottom (23) of the compartment concerned is evacuated, a determined quantity of ash, identical for all the compartments, and, at the same time In time, fresh reactive gas is blown into the ash extraction orifice (23) to complete the gasification of the residual carbon and to cool the ash. 5.- Method according to any one of claims 1 to 4, characterized in that calcium or magnesium material is added to the coal. 6.- Apparatus (11) for carbonating carbon comprising, in combination, a sealed vertical tank, the lower part of which is divided into at least three compartments (12) of equal dimensions by means of radial vertical separations leaving the tops of these compartments in communication with the non-compartmentalized upper part of the tank, the tank being provided with:
- a sealed means (14) for loading the coal near the top of the tank and a means of its distribution (17) on the fixed bed,
- a means for introducing (18) hot reactive gas, for the most part, at a first level, close to the point of introduction (17) of the coal into the enclosure of the tank,
- at least one quantity introduction means (21) of reactive gas at least at a level lower than said first level,
- a means for extracting (32) a controlled quantity of ash from the bottom of each compartment, a common and sealed means for collecting (33) and evacuating (34) the ash and a means introducing (57) into each compartment a certain amount of cold reactive gas into the ash extraction orifice (23),
- a means of evacuation (24) of the gas produced from each compartment (12), which means is located at a level higher than that of the ash extraction orifice (23), of a filtration means (25, 26) of the gas, of a means of control (30) of the gas flow and of stopping its evacuation, of a means of introduction (29) of gas produced cold in counter-current during the stopping the evacuation, the different gas evacuation means, one per compartment, being connected to a common collecting means (31). 7.- Apparatus according to claim 6, characterized in that it comprises four to eight compartments (12) equal and in that these compartments occupy 20 to 40% of the total height of gasifier. 8.- Apparatus according to any one of claims 6 and 7, characterized in that the sealed means (14) for loading the coal is an airlock, the coal of which is brought to the distributor (16) by means of a device dispenser (15). 9.- Apparatus according to any one of claims 6 to 8, characterized in that the main introduction means (18) of the reactive gas is located at a level higher than that of the distribution of coal (17) on the bed fixed and it is peripheral around the distribution means (17) of the coal which is central. 10.- Apparatus according to any one of claims 6 to 9, characterized in that the complementary means of introduction (21) of reactive gas comprises a peripheral means (21) located approximately halfway up the gasifier and a central means (22) in the middle and at the top of the compartmentalized sector. 11.- Apparatus according to any one of claims 6 to 10, characterized in that the ash extraction means (32) of each compartment comprises a means of grinding any bottom ash. 12.- Apparatus according to any one of claims 6 to 11, characterized in that the filtration means (25, 26) of the gas produced comprises a large mesh filter (25) and a special filter (26) of refractory material metallic or ceramic retaining fine dust particles. 13.- Apparatus according to any one of claims 6 to 12, characterized in that the means for discharging the gas produced is a nozzle (24) per compartment, provided with an adjustment member (30) and stop flow and an introduction orifice (29) of cold product gas against the current during the gas evacuation stop, the various nozzles (24) being joined downstream of the adjustment means (30) in a common peripheral collecting means (31). 14.- Apparatus according to any one of claims 6 to 13, characterized in that the reactor is provided with an addition means (19) of calcium or magnesium material to carbon. 15.- Apparatus according to claim 14, characterized in that the means for adding the calcium material to the coal is a means located upstream of the introduction of the coal into the sealed means (14) of loading. 16.- Apparatus according to claim 14, characterized in that the means for adding calcium or magnesium material is an airlock (19) separate, and in that the two solid loads, carbon and calcium or magnesium material, mix in the middle of the top in the distribution means (16) and homogeneous dispersion (17).

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