DE2847416A1 - METHOD FOR GASIFYING FINE GRAIN FUELS - Google Patents

Description

METALLGESELLSCHAFT AG Frankfurt am Main, October 30, 1978

No. 8237 Lö -WGN / HSZ-

Process for gasifying fine-grain fuels

The invention relates to a method for gasifying solid, baking Containing fuels under a pressure between 5 and 150 bar with free oxygen, water vapor and / or carbon dioxide Gasification means, wherein the fuel forms a fixed bed that moves slowly downward, the gasification means of Introduced below into the fixed bed and the incombustible mineral components of the fuel as solid ash or liquid Slag can be drawn off under the fixed bed. Above all, all baking coals can be used as solid fuels.

The gassing of this type is known and e.g. in Ulimann's encyclopedia der technical chemistry, 4th edition (1977) Volume 14, pages 383 to 386, shown. Details of the ash gasification process can be found, for example, in U.S. patents 3 540 867 and 3 854 895 as well as the German Offenlegungsschrift 2 201 278. The process variant with deduction of liquid Slag is discussed in British Patents 1,507,905, 1,508,671 and 1,512,677.

In these known methods, granular fuel is used a grain size in the range from 3 to 60 mm into the gasification

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given. The object of the invention is to be able to use fuel with a more fine grain size for this process without having to worry about the fuel grains sticking together. According to the invention this is achieved in that largely spherical pellets with a diameter of 5 to 50 mm are formed from fine-grain fuel with a grain size of less than 7 mm with a liquid and the pellets are provided with a largely closed covering layer of fine-grain, non-baking material before they in. to be given the gassing. The fine-grained fuel can be created during the extraction of the fuel or it can also be produced by crushing. A fine-grain fuel with a grain size of about 0.01 to 5 mm is preferably used for pelleting. As a result of pelleting, fuel in powder form can now also be used for pressurized gasification in the fixed bed, either alone or together with granular coal with a grain size of between 3 mm and about 60 mm. The pellets preferably make up the majority of the fuel fed into the gasification.

If granular, baking coal is put into the fixed bed gasification, it is produced in the upper part of the fixed bed when the softening temperature is reached the coal a little gas-permeable zone, since the coal grains melt or at least become doughy. By Up to now, attempts have been made to loosen this carbon layer in the fixed-bed gasification and thus make it gas-permeable.

There has also been no lack of efforts to deprive the carbon of its bath properties, for example by pretreating it oxidatively at temperatures of about 200 to 350.degree. The aim was to influence the entire grain of coal in the desired manner, including through pore diffusion of oxygen. These efforts met with some success, but the treatment times were too long for the coal to oxidize. A gasification operation with high throughput rates was therefore not economically feasible because too much effort was required. . -? _

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Difficulties arise with the method according to the invention this type eliminated. The shell layer around the pellets now ensures that the pellets in the upper part of the fixed bed where relatively low temperatures prevail, keep a sufficiently stable shape. At the same time, the envelope layer is gas-permeable and allows volatile constituents to escape from the interior of the pellet. If the temperatures continue to rise, it stays the cladding layer largely preserved, with slight cracks not being a disadvantage if the fuel becomes plastic and only in a highly viscous mass passes over. In the event of greater softening, the coating layer or the carbon must be reinforced accordingly catalytically active substances can be added before pelletizing, which increase the baking and expandability of the charcoal reduce. After passing through the baking zone, the pellet shell tears open further due to the strong degassing of the carbon substance, so that the coal coke that has now been produced causes the gasification reactions in its entire surface, including the macro and micro structure is exposed. It is also an important result that the gasification product gas is much less tarry Contains components than is possible with the previously known gasification of baking coals under increased pressure was.

The pellets can be prepared in a known manner, see above e.g. in the inclined turntable or in the rotary tube. With these devices, the pellets can also be used with the desired Enveloping layer provided. The pellets can have a diameter of 10 to 30 mm and preferably 8 to 15 mm.

A variety of liquids can be used to form the pellets. For example, water, sulphite waste liquor, water glass, molasses, starch solutions, gas water from the gasification or coking of solid fuels, or milk of lime are suitable. Catalytically active substances can be added to the pelletizing liquid or to the fine-grained solid fuel to be pelletized to increase the reactivity. Such substances are in particular NaCl, KCl, NaCQ ,, K ₂ CO ₅ , oxides or sulfides

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of molybdenum, tungsten, tin, chromium, winding, cobalt or iron or finely ground, thin-layer zeolites. This catalytic Active substances are able to bring about the desired transformations in contact with gases and vapors from the pellets, E.g. to make low-boiling hydrocarbons from ■ higher-boiling hydrocarbons.

In order to reduce the baking and swelling properties of the solid fuel to be gasified, suitable substances can be added to the pelletizing liquid or the fuel to be pelletized. Such substances are, for example, Ma ₂ BO ₇ , NaMOp, KpCrO ,, K ₀ CO, orKNO ,.

To produce the shell layer for the pellets, non-baking Coal, ash, e.g. from gasification or from outside production, dolomite, bentonite, lime, montmorillonite, cement or others inorganic substances are used. Mixtures of finely ground zeolites are also particularly suitable. Be the best these substances are added in fine-grained or dusty form before the end of the pelletizing process.

The shell layer of the pellets should have a thickness of about 0.1 to 2 mm, preferably 0.2 to 0.5 mm. For economic For reasons, efforts are made to keep the covering layer as thin as possible. But it must be used especially with strong coals be sufficiently strong and thick to prevent the flowable charcoal from breaking through.

If necessary, the pellets provided with the covering layer can be dried before they are introduced into the gasification unit. This is best done at temperatures below the softening point of the coal, preferably between 40 and 150 ^° C. The pelletized fuel generally has a noncombustible mineral content of 5 to 40% by weight and preferably 10 to 30% by weight.

The gasification product gas can be used in a variety of ways. After cleaning and conditioning the gas can e.g.

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can be used for syntheses or as hydrogenation gas. Another possibility is to remove the gas, if necessary after removing it solid or gaseous components, to be used as fuel gas and in a combined steam-gas turbine power plant to use.

Examples

A moderately baking and puffy gas flame charcoal with 20% by weight of ash and 8% by weight of moisture was used for experiments. The baking number according to Roga (ISO 335-1974) was 25, the swelling number according to DIN 51741 was 2.5% - the coal was in a grain size between 0 and 1 mm and had an average grain diameter of 0.291 mm. A pelletizing plate 1 m in diameter with an incline of about 50 ° and a speed of 20 revolutions per minute was used to shape the pellets. In each case, pellets with a shell layer were produced, the diameter of which was in the range from 10 to 20 mm. The pellets were ^{dried at 110 °} C. and then the compressive strength was measured. To simulate the conditions in the fixed bed gasification, coking was carried out under shock mode under a nitrogen pressure of 20 bar.

coking took place with shock-like heating to 80O ⁰ C

T he s piel 1

Water was used as the pelletizing liquid, so that the water content of the finished pellets was 15% by weight. The shell layer had a thickness of 0.3 mm and consisted of finely ground own ash the coal. The point compressive strength of the dried pellets was approx. 70 N. After the pressure coking, the pellets were not Baked together, the shell had burst open, the pellet core was structurally stable. The pellets were excellent for pressurized gasification suitable.

Example 2

A 5% calcium sulphite waste liquor served as pelletizing liquid, Finely ground Dolspiit was used for the coating layer

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The coating layer had a thickness of about 0.3 mm. The point compressive strength of the dried pellets reached about 80 N; the test results after pressure coking agreed with those of Example 1. In addition, about 50 % of the sulfur contained in the coal was bound by the dolomite layer.

Example 3

A 20% waterglass solution was used as the pelletizing liquid, cement was used for the coating layer and a thickness of about 0.4 mm was achieved. The dried pellets had a point compressive strength of about 60 N. After pressure coking, the pellets did not adhere to one another and were structurally stable. The covering layer was cracked and partially flaked off. The pellets of Examples 2 and 3 were suitable for gasification in the plague bed without a special loosening device having to be provided in the upper part of the gas generator.

Example 4

For this experiment, also a moderate baking and flatulent gas flame coal with 22 wt.% Ash at 8 wt.% Moisture was used. The baking number according to Roga (ISO 335-1974) was 25, the swelling number according to DIN 51 741 was 3. The coal had a grain size between ο - 1 mm, the mean grain diameter being 0.280 mm.

The pellets produced on the pelletizing plate of the previous examples had a diameter of 10 to 20 mm. As a coating layer, dolomite was applied with a layer thickness of 0.3 mm. A 10% potassium carbonate solution was used as the pelletizing liquid. Before the coating was applied, the pellets had a moisture content of approx. 15 % by weight. Before being used in coking and gasification, the pellets had a potassium carbonate content of less than 0.6 % by weight. .

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During the investigation of the product gas, it was found for 2s that that of that contained in the coal. Tar according to ISO 647-1974 only ca, reached the gas space after leaving the pellets 50% of the liquid hydrocarbons and that the final boiling point of these liquid hydrocarbons, which is usually above 450 ⁰ C, contained only hydrocarbons below 240 ° C boiled.

Furthermore, in a reactivity test under 20 bar and a constant temperature of 800 ^° C., it was found that at a mass flow of 20 l ^ / h 3> 8 vol. $ COp were decomposed, while under otherwise identical conditions, but without the use of potassium carbonate, only values of 2.3% by volume were achieved.

Example 5

In a further experiment, a coal was used whose baking number according to itoga (ISO 335-1974) was 52, while the swelling number according to DIK 51 741 was 7. The coal was one grain between 0 - 1 mm with an average grain diameter of 0.264 mm.

After pelleting, it became with its own fine-grained ash provided in a layer thickness of 0.25 mm. As a pelletizing liquid a 5-6% sodium tetraborate solution was used. This measure reduced the ability of the coal to bake and expand to such an extent that it caked together during pressure coking the pellets failed to appear. The reactivity of the pellets produced in this way was favorably influenced by this measure.

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Claims (1)

Claims 1) Method for gasifying solid, baking fuels under a pressure between 5 and 150 bar with gasifying agents containing free oxygen, water vapor and / or carbon dioxide, the fuel forming a plague bed that moves slowly downwards, the gasifying agents from below into the fixed bed . initiated and the incombustible mineral components of the fuel are withdrawn as solid ash or liquid slag under the fixed bed, characterized in that largely spherical pellets with a diameter of 5 to 50 mm are formed from fine-grain fuel with a grain size below 7 mm with a liquid and the Pellets are provided with a largely closed covering layer made of fine-grained, non-baking material before they are put into the gasification process. 2) Method according to claim 1, characterized in that the pellets have a diameter of 10 to 30 mm, preferably 8 to 15 mm. 3) Method according to claim 1 or 2, characterized in that water, sulphite waste liquor, water glass, molasses, starch solutions, gas water from the gasification or coking of solid fuels, or milk of lime is used as the liquid for forming the pellets. k) Method according to claim 1 or one of the following, characterized in that the pelletizing liquid or the fine-grained solid fuels to be pelleted are catalytically active substances to increase the reactivity, in particular ITaCl, KCl, NaCO ,, K ₂ CO, or oxides of molybdenum, Tungsten, tin, chromium, nickel, cobalt or iron can be added. 030020/0103 5) Method according to claim 1 or one of the following, characterized in that the pelletizing liquid or the fine-grained solid fuel to be pelletized substances are added which reduce the baking and expansion properties of the solid fuel, in particular Na ₂ BzO ₇ , WaWO ₂ f 6) Method according to claim 1 or one of the following,. characterized in that the shell layer of the pellets consists of a non-baking coal, foreign or own ash, dolomite, bentonite, lime, I-iontmorillonite, cement, zeolites or other inorganic substances. 7) Method according to claim 1 or one of the following, characterized in that the shell layer of the pellets has a thickness of 0.1 to 2 mm, preferential prices of 0.2 to 0.5 mm. 8) Method according to claim 1 or one of the following, characterized in that the pellets provided with the shell layer are dried before being introduced into the gasification, in particular at temperatures below the softening point of the coal, preferably between 40 and 150 ° C. 9) A method according to claim 1 or one of the following, dadur ch in that the pelletized fuel has a content of non-combustible mineral constituents of 5 to 40 wt.%, Preferably 10-30 -Grew.%. 030020/0103