CS211360B2 - Method of treating the raw gas from the gasification of solid fuels - Google Patents

Abstract

A crude gas, produced by the gasification of solid fuel under a pressure of 5 to 150 bars with gasifying agents comprising free oxygen and water vapour flowing in countercurrent to the fuel and having a temperature of 350 to 800 DEG C, is reacted under pressure in the presence of a hydrogenating catalyst. Various hydrogenating catalysts are described. In a preferred embodiment, substantially no oxygen is required to initiate cracking of the hydrocarbons in the crude gas, resulting in little loss of calorific value by partial oxidation of said gas. Also, most sulphur compounds are converted to hydrogen sulphide, rendering desulphurisation of the treated gas before methanation simple.

Description

The present invention relates to a process for treating crude. gas from solid gasification, in particular coal.

From German publications' writings. Nos. 25 32 197 and 25 32 198 as well as the corresponding U.S. Pat. Nos. 4,056,483 and 4'082,520 disclose a method for post-gasification of hydrocarbons. In this process, the post-gasification is carried out in a reactor which comprises a solid bed of inert solids or. from catalyst material, but with the addition of oxygen. This oxygen causes a partial oxidation of the individual components of the raw gas, thereby raising the temperature and causing gasification and cracking reactions. The resulting post-gasification gas is largely free of tar, phenols, fatty acids, and ammonia.

The pressure gasification of coal in the range of - 0.5 to 15 MPa with solids ash is known from numerous publications, for example U.S. Pat. Nos. 3,540,867 and

854 895 and German Offenlegungsschrift 2,201,278. The granular coal is arranged in a fixed bed and the gasification means flows from the fixed bed from bottom to top. Coal in granular form - or in the form of agglomerates of grain size in the range - for example from 3 to 30 mm - is fed into a pressure reactor, where it gradually passes through a plurality of not very clearly separated zones - becoming increasingly higher - temperature. - mostly oxygen and water vapor, but - in addition - carbon dioxide may also be used:

British Patent Nos. 1,507,905, 1,508,681, and 1,512,677 disclose a variation of pressure blasting - coal, which essentially operates in the same manner, but the ash is removed in a liquid state. The raw gas obtained in this gasification variation has a higher carbon monoxide content and a " lower " water vapor content as compared to the gas obtained by gasification in which the ash remains solid.

In addition to water vapor, the raw gas, from gasification under pressure - coal mainly hydrogen and oxides - contains carbon as well as methane. Numerous other substances, such as condensable hydrocarbons, in particular aromatics, paraffins and naphthenes of different distillation ranges and different compositions, are contained in small amounts.

SUMMARY OF THE INVENTION It is an object of the present invention to de-purify the crude gas in a simple and economical manner, especially the condensable hydrocarbons contained therein, thereby making the gas cleaning and gas water considerably easier. For example, it is then possible, for example, to supply gas water with a simple aftertreatment, e.g.

2113 example by degassing or partial desalination, re-gasification. To control the salt content, part of the condensed gas water can be discharged into the public flow without any purification. Simpler wiring can also be used in the gas purification stage. According to the invention, these advantages are achieved by additionally gasifying the raw gas under pressure in the presence of a hydrogenation catalyst. Preferably, the post-gasification is carried out at a pressure at a temperature approximately equal to the pressure and the temperature of the raw gas.

Accordingly, the present invention provides a process for treating raw gas from the gasification of solid fuels, in particular coal, at a pressure in the range of 0.5 to 15 MPa by gasification means countercurrent to the fuel and containing free oxygen and water vapor, wherein the raw gas coming from gasification at a temperature ranging from 350 to 800 ° C, with all its hydrocarbon and water vapor content, is subjected to a subsequent gasification, characterized in that the gas immediately after gasification is subsequently gasified without adding oxygen under pressure in the presence of a hydrogenation catalyst.

In the process according to the invention, it is important that the post-gasification does not normally add a substantial amount of free oxygen-containing gases to the raw gas, which gases would cause partial oxidation. Indeed, this partial oxidation with oxygen supply would disadvantageously convert a significant portion of the high calorific hydrocarbons into carbon dioxide and water, thereby reducing the calorific value of the produced gas. Therefore, in the process according to the invention, it works without additional oxygen addition during the subsequent gasification. At low temperatures of the raw gas leaving the pressure gasifier, it may be necessary to add a small amount of oxygen in order to raise the temperature of the raw gas to a value at which the catalyst is effective.

Catalysts capable of hydrotreating - the tars contained in the raw - gas - have proved to be useful substances used - in refining techniques - for hydrotreating. A useful hydrogenation catalyst comprises, for example, 3-10% by weight cobalt. It may additionally contain 5 to 15% by weight of molybdenum. The active substances are preferably applied to a porous support, for example of alumina, but zeolite is also suitable. A known embodiment of this type of catalyst is the so-called Cornox catalysts having a specific surface area of more than 80 m ² / g.

Suitable hydrogenation catalysts are also known nickel catalysts, as is known, for example, for producing a rich gas from vaporized liquid hydrocarbons or for methanization. These catalysts are advantageously characterized by 5- to 40% by weight of supported nickel. It has also proved to be very useful to add silicon, magnesium, calcium, iron, sodium, potassium and tungsten oxides to the lysators. The reaction is also supported by the mono-orrillonite treated with the dilute acid. Coke can also be used as a hydrogenation catalyst. or even as carriers.

The post-gasification is carried out in one or more reactors in which the hydrogenation catalyst or catalysts are in a fixed or fluidized bed. In the post-gasification zone, the pressure is in the range of -0.5 to 15 MPa, and it is expedient to feed the raw gas from the pressure gasification to the post-gasification zone without substantially reducing the pressure.

Among the reactors for pressure gasification of fuel, in particular coal, and for subsequent gasification of the raw gas, it is expedient to include a device for removing coarse or fine dust from the raw gas. This removal of coarse or fine dust can be carried out, for example, in cyclones or fabric filters.

Liquid, preferably finely divided, hydrocarbons and / or pulverized fuels, for example coal dust, can also be added to the raw gas to be subjected to post-gasification, grain size less than 2 mm.

The gas produced from the post-gasification practically no longer contains any hydrocarbons condensable at ambient temperature, at most only traces of hydrocarbons having a distillation range of gasoline are possible. The methane content of the produced gas is higher than that of the primary raw gas produced. The increase in the methane content depends to a large extent on the tar content of the gasified coal and on the possible additions of evaporable hydrocarbons to the raw gas. The methane content can be controlled - in a wide range.

On the hydrogenation catalyst used in the aftergassing, the sulfur compounds in the raw gas are virtually completely converted into hydrogen sulfide. For many reasons, it is usually necessary to completely or largely remove the hydrogen sulphide formed before use - the produced gas as fuel gas, reducing gas or synthesis gas. This can be achieved by known chemical or physical scrubbing or adsorption, for example on activated carbon or aluminum oxide. The removal of the hydrogen sulphide is necessary even in the case where the produced gas is subsequently to be catalytically methanized in order to increase its calorific value so that it can be replaced by natural gases.

The process according to the invention is illustrated by the following examples.

Example 1

In a pressurized gasification plant of a known construction (Lurgi gasifier) with an average diameter of 2.6 m, 15 tons of coal with lower calorific values are gasified every hour

275 kj / kg and having the following composition:

C 57.6 wt. %

..... H 4.0% by weight.

. O 5.9 · wt. % · ... ·.

N, 1.1 wt. %

% · Ash · · 29.3 · wt. %

Oxygen in the amount of 270 Nm @ 3 / coal and water vapor in the amount of 4.9 kg / Nm @ 3 of oxygen are introduced as gasification means into the gasifier in which a pressure of 20 bar is maintained.

Crude is obtained. 1420 Nm3 / / t coal with composition · (dry basis):

CO2 27.5 vol% CO ·· 23.1 vol% Ha 37.5 vol% CH4 9.9 vol%.

..... CnHm 0.6 vol. · ° / o · N? · 0.6 vol. ·%.

HaS 0,8% vol. '

In addition, it contains 0.64 Nm3 of water vapor per 1 Nm ^{3 of} dry raw gas and leaves the gasifier at a temperature of 650 degrees Celsius. If this raw gas was cooled. temperature 25 C, would be obtained in the condensate to · 1000 '· Nm? dry raw gas, excluding water, the following components:

tar 34.3 kg oil 15,5 kg benzine 6,4 kg phenols 4.8 'kg fatty acid 0.7 kg ammonia ⁴ . ^{9 k} g

The resulting gas sc without cooling and practically, without pressure loss, leads to a post-gasification reactor which is about half filled with a commercially available Comox catalyst containing 6% by weight of cobalt and 10% by weight of molybdenum on the support. of alumina in the form of 6X6 · mm tablets. . Diameter · shaft · reaction. and the bulkhead height of the catalyst material is 4 m.

The reaction produces gas. · 'Composition' (on a dry basis) .:

CO2 45,8% vol.

CO 10,4 percentage points

H2 28.3% by volume;

CHi · '14.4 otye-in%

H2S 0,1 obЬлпО'УУсЬ '%

N2 + Ar. 1.0% by volume leaving the reactor for post-gasification at a temperature of 670 ° C and no longer containing any higher hydrocarbons. The water vapor content of the gas is 0.7 Nm3 / Nm ^{3 of} dry raw gas. After removal of carbon dioxide and water vapor, a fuel gas of composition is obtained

CO 19, 2 volume%

..... H2 5t ^ 2 volume%

CHi 26.6 vol%

HaS 0,2 vol%

N2 + Ar 1.8 vol. / Axis 'lower' limit · calorific value 17 540 kJ / Nm ³ . Example 2

In the arrangement as in Example 1 and under otherwise the same conditions, the composition coal is gasified

C 63.9 hrs. %

H 4.1 wt%

7.3% w / w

N Щ wt%

S! 4 МпЯ. % ash, 22.3% by weight.

with a lower calorific value of 25,120 kj / kg, air at 1500 Nm3 / t coal and water vapor at 0.42 kg / Nm ³ air at a pressure of 2 MPa.

2,700 Nm ^{3 of} crude gas / t coal is produced

Temperature 585 ° C · and composition (based on good status) CO2 10,6% by volume WHAT 21,3% by volume H2 19,8 'vol% . CH 4.2% by volume CnHm 0,3% vol N2 43,5% by volume HžS 0,3% vol and in addition 0.11 Nm ³ water vapor / Nm ³ su- chélio raw gas. When cooling on

a temperature of 25 ° C would yield the following by-products per tonne of coal:

tar, oil and gas (carbonization) gasoline 37.1 kg phenols 2.6 kg fatty acids 0.6 kg ammonia 3.3 kg

This gas, as in Example 1, is fed without cooling directly to the shaft gasification reactor for subsequent gasification and is subsequently gasified there. The catalyst used is a commercially available nickel catalyst containing 25% by weight of nickel on a silica-based carrier in the form of 6X6 mm tablets. A gas is produced which does not contain higher hydrocarbons and has the following composition:

CO2 13.8 'vol%

CO 17,9%

162 16.0% vol / o

СН4 9.8% vol.

At 42.2% by volume

HzS 0.3 vol%;

it also contains 0.1 Nm ^{3 of} water vapor / Nm ^{3 of} dry gas. After removal of carbon dioxide and water vapor, a fuel gas of the following composition is obtained

CO 20,8% by volume

Hz 18.6% vol / o

CH4 11.4% by volume

At 48.9% by volume

H2S 0,3% vol. With a lower calorific value of 8680 kJ / Nm ³ .

Example 3

17 tons of coal are introduced per hour into a pressure gasifier with liquid slag evacuation with a mean diameter of 1.8 m, which maintains a pressure of 2.5 MPa. The coal has the following composition, based on the dry state after deduction of ash:

C 78.99% by weight

H 5,25% by weight

8,75% by weight

N 1.37% by weight

With 0.43% by weight

Cl 0.38 wt ^. %.

The lower calorific value of this coal is 29 490 kj / kg, the ash content is 4.83 weight 0/0.

350 g / m ^{3 of} oxygen and 1 kg / m ^{3 of} oxygen are supplied to the gasifier per 1 ton of coal as gasification means. The raw gas produced, which is obtained in an amount of 1890 Nm ³ / h (calculated on a dry basis), has the following composition:

CO2 2,3 vol%

CO 58,2% vol

H2 29,3% by volume

CH4 6.8% vol

C _n H _m 0,6% vol

H2S 0.1 vol

N2 + Ar 2.7 volume%.

In addition, it also contains 0, 12 Nm ^{3 of} water vapor per 1 Nm of ³ dry gas. The raw gas leaves the gasifier at a temperature of 650 ° C.

By cooling the raw gas to 25 ° C, the following by-products would be obtained per 1000 Nm ^{3 of} dry raw gas:

tar 39,0 kg oil 8,3kg benzine 9.8 kg ammonia 2.7 kg phenols 2.3 kg fatty acids 3.4 kg

as described in Example 1, the raw gas is reacted without cooling with water vapor in an amount of 0.76 kg / Nm ^{3 of the} raw gas. The reactor is approximately half filled with active coke with a mean diameter of 30 mm. The reaction chamber diameter is 2 m and the coke catalyst bulk height is 4 m.

The gas leaving the post-gasification has a temperature of 670 ^e C and has the following composition:

CO2 33.8 vol%

CO 10,8% by volume

Ha 32.0% vol

CH4 21.0% by volume

H2S 0.1 vol%

N2 + Ar 2.5 vol% lower heating value 12 730 kJ / Nm ³ .

This resulting gas does not contain condensable hydrocarbons; In waste heat boilers and chillers, the gas is cooled down to 30 ° C and then desulfurized by washing with liquid methanol at a temperature of about -25 ° C, removing carbon dioxide. The gas treated in this way has a calorific value of 19 160 kJ / Nm ³ with the following composition:

CO 16,3%

H2 48,2% by volume

CH4 31.7% by volume

N2 -f- Ar 3.8% by volume

This gas is used for methanol synthesis.

Example 4

Repeats pressure gasification of coal as described in Example 3. The crude К gas that arises, in addition to 1 Nm ³ is added 0.28 Nm ³ oxygen and 0.8 kg water vapor к the coal dust in an amount of 1 300 kg tonnes of lump fuel from compressed gasification of coal with a grain size ranging from 0.03 dO 'to 0.3 mm. The elemental analysis of the coal dust corresponds to the elemental analysis of the coal in Example 3.

The crude gas, oxygen, water vapor and coal dust were reacted in the post-gasification as used in Example 3. However, the hydrogenation catalyst consisted of 3.5 wt% cobalt and 10 wt% molybdenum on an alumina support. and has a ball shape of approximately 5 mm.

The product gas leaves the aftergassing with a temperature of 950 ° C and has the following composition:

CO2 20.7 vol%

CO 32,2 vol%

Нз 45,0% vol

CH4 0,4% vol

H2S 0.1 vol%

N2 -f- Ar 1.6% by volume

In post-gasification reactor, po211360

In order to produce synthesis gas from the intermediate gas thus produced, it is subjected to further processing as described in Example 3.

Claims (12)

Process for treating raw gas from gasification of solid fuels, in particular coal, at a pressure in the range of from 0.5 to 15 MPa by gasification means conducted in countercurrent to the gas flow ^. fuel and containing free oxygen and water vapor, wherein the raw gas coming from the gasification at a temperature in the range of 350 to 800 ° C is subjected, with all its hydrocarbon and water vapor content, to post-gasification, characterized in that the raw gas is immediately after gasification, it is subsequently gasified without the addition of oxygen under pressure in the presence of a hydrogenation catalyst. 2. The process according to claim 1, characterized in that free oxygen-free gases are added to the raw gas for post-gasification. 3. Process according to claim 1 or 2, characterized in that the hydrogenation catalyst is provided in a fixed bed. 4. The process of claim 1 wherein the hydrogenation catalyst is in a fluidized bed. 5. A process as claimed in any one of claims 1 to 4, wherein a hydrogenation catalyst containing 3 to 10 weight percent cobalt is used. 6. Process according to claim 5, characterized in that a hydrogenation catalyst is used BACKGROUND OF THE INVENTION containing, in addition to at least one active ingredient, 5 to 15% by weight of molybdenum. 7. A process according to any one of claims 1 to 6, characterized in that a hydrogenation catalyst consisting of silicon, magnesium, calcium, iron, sodium, potassium and tungsten or containing coke as the basic substance or consisting of coke is used. 8. A process as claimed in any one of claims 1 to 7, wherein a catalyst to which montmorrinonite treated with a dilute acid is added is used. 9. Process according to Claims 1 to 8, characterized in that a hydrogenation catalyst containing nickel as active ingredient is used, preferably in an amount of from 5 to 40% by weight. Process according to Claims 1 to 9, characterized in that sulfur compounds, in particular hydrogen sulfide, are removed from the gas produced after the subsequent gasification. 11. The process of claims 1 and 10, wherein the gas produced from the post-gasification is methanized after removal of the sulfur. Method according to one of Claims 1 to 11, characterized in that hydrocarbons and / or pulverized fuels having a grain size of less than 2 mm are admixed with the raw gas before the subsequent gasification.