CS199271B2 - Process for preparing synthesis gas - Google Patents

Abstract

1528368 Synthesis gas production SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ BV 3 Dec 1975 [5 Dec 1974] 49639/75 Heading C5E In a process for the production of synthesis gas by the partial combustion of coal, tar is separated from the crude gas produced, gasified by partial combustion with the production of soot, and the soot formed is separated from the gases and combusted together with the coal. Preferably, before gasification, the tar is separated into two portions, one containing solids such as ash and unconverted carbon and the other free from solids. The solids-free portion is gasified with oxygen and steam, and the soot separated from the gaseous products by washing with water. The soot/water mixture thus formed is mixed with the solids containing tar and recycled to the coal combustion reactor for partial combustion with the coal. The coal used may be lignite, bituminous coal or anthracite.

Description

The present invention relates to a process for preparing synthesis gas by partial combustion of coal.

During the preparation, tar also separates from the resulting synthesis gas. At least a portion of this tar is then gasified by partial combustion while forming soot. The soot is then separated from the resulting gas and at least a portion of it is partially combusted together with the coal.

Process for preparing synthesis gas by incomplete combustion of coal with an oxygen-containing gas at a temperature in the range of 700 to 1100 ° C, during which a tar-containing tar is formed which is separated from the gas, at least a portion of the tar being gasified by incomplete combustion with oxygen-containing gas at at a temperature in the range of 1000 to 1500 ° C at a pressure in the range of 1 to 10 MPa to form carbon black; which are separated from the gas and at least a part of which is incompletely burned together with the coal, s? · To improve the gasification of the tar according to the invention, the solids are removed from 25 to 75% of tar by settling in the remaining 75 to 25% of tar, at least part of the tar from which the solids have been removed is gasified by incomplete combustion and at least part of the soot in the case of incomplete combustion of tar, it is introduced into the tar in which the solids have settled, and this mixture is incompletely combusted with coal.

The raw material used for this process is a solid carbonaceous material. By solid carbonaceous material is meant a solid fuel that essentially. it consists of free and chemically bonded carbon. In addition, the fuel may comprise hydrogen, oxygen, sulfur, nitrogen, metals and / or ash. Starting materials of this type include, for example, lignite, tar coal, medium tar coal, anthracite and coke.

In the context of said method, the coal is first pulverized into small pieces or. into a powder and then processed by partial combustion. The partial combustion of coal while producing tar can be carried out in some suitable manner, such as. for example, the Lurgi process or the Synthan process. These methods have been described in "The Oil and Gas Journal" 26 August 1974, p. 80 a. 84. In particular, the Lurgi process is used for the first phase of the process associated with the present invention. This method is detailed. explained in "Ullmanns Enzyklopadie der technischen Chemie", Vol. 10, pp. 418-424. During partial combustion, the coal is converted by means of oxygen, air - or oxygen - enriched air into a gaseous mixture consisting mainly of hydrogen and. carbon monoxide. In addition, greater or lesser amounts of nitrogen, carbon dioxide, water, methanol, hydrogen sulfide and carbonyl sulfide may be present in the gas mixture, depending on the nature of the coal, the composition of the gas used for combustion, and the gasification method used. Oxygen is predominantly used as the oxidizing gas, since this produces a gas. of high calorific value. ..........

An amount of 0.2 to 0.4 m ^{3 of} oxygen should be used per kg of coal. During partial combustion, steam is most often introduced as a temperature moderator. Suitably, 2 to 9 kg of steam per 1 Nm ^{3 of} oxygen are added to the reaction mixture.

After coal gasification, which is most often at temperatures in the range of 700-1100 ° C, the resulting gas is discharged from the gasification reactor. This gas is predominantly at a temperature in the range of 370 to 600 ° C and, in addition to the required portions 112, Co and CH 4, it also contains undesirable impurities such as tar. oil, diesel, phenols, water, ammonia, hydrogen sulfide, carbon dioxide, wall and ash.

In order to remove impurities from this gas, the raw gas was cooled to a temperature of between 40 and 200 ° C, most often in an indirect heat exchanger with water. Steam is formed during this cooling. In this cooling process, tar, oil, diesel, phenols and water condense, while coal and ash are trapped in the condensed liquid. From the remaining gas is. this condensed liquid is separated. The tar containing oil, diesel, phenols, ash and coal is recovered from the separated liquid by fractional distillation. The gas may be purified from other impurities, hydrogen sulfide, carbon monoxide, COS, CS2 and HCN.

At least a portion of the tar formed is re-gasified by partial combustion to form soot. . Oxygen or air may be used for this partial combustion, either enriched or. not enriched with oxygen. The tar is predominantly gasified using oxygen. This gasification can be carried out in any suitable manner. Overview of known methods for the preparation of hydrogen and carbon dioxide gas. Partial combustion of liquid fuels is given in the "Chemiker Zeitung" March 3, 1972, pp. 123-134. The gasification method of Shell is predominantly used for tar gasification. This process is described in "Chemical Economy and Engineering Revision", December 1973, Volume 5, No. 12, pp. 22-28.

In the case of partial combustion of tar, it is most frequently dosed as a temperature moderator. steam. Its added. the amount is 0.5-3 kg per kilogram of tar.

The oxygen or oxygen-containing gas is preheated to 200-500 ° C prior to entering the reaction zone where the tar is partially combusted. After preheating, the hot oxidizing gas is mixed to some extent with the tar and this tar-gas mixture is injected into the reactor at high pressure. The overpressure is 1-50 atm compared to the reactor pressure. The reactor is usually an empty 0-vessel, the interior of which is. made of heat resistant material. Most commonly used is described in British Patents 780,120, 832,385, 850,409 and 967,885.

The partial combustion of tar is most often carried out at temperatures in the range of 1000 to 1500 degrees Celsius, which is the resulting temperature of the reaction between tar and oxygen and possibly steam.

The pressure maintained in the reactor may vary within a certain range, and is typically maintained in the range of 0.1 to 10.0 MPa. So that the conversion of the introduced tar to gas is what. preferably, the tar droplets must remain in the reactor for some time. A suitable residence time has been found to be between 1 and 15 seconds.

After tar conversion. for gas. is a reaction product consisting essentially of H2, CO, CO2, N2 and H2O discharged from the reactor.

This gas has a high temperature, generally about 1100 ° C, contains ash, soot and hydrogen sulfide. During the gasification, it is formed from 1. kg of tar. 0.05 to 0.20 kg of soot. In order to remove impurities, the gas is cooled after leaving the reactor. This cooling is effected efficiently by injecting water, steam or a portion of the cooled and cleaned product gas. In connection with the present invention, the cooling is partially or totally carried out in a regenerator in which the waste heat of the gases leaving the reactor is used to generate steam.

The gas is thereby cooled to a moving temperature. in the range of 120 to 250 ° C.

The solids content of the cooled gas is kept low by appropriate selection of reactor conditions. However, further reduction of the solids content is still required, for example by desulfurization as well as by converting the carbon monoxide contained in the gas with water to carbon dioxide and hydrogen. Finally, the gas is fed to a gas scrubber in which it is scrubbed with liquid, most often water. An arrangement of this type of device is described in British Patent 826 209.

Treatment of the gas by scrubbing according to this method is obtained. a substantially solid-free gas having a temperature of 20-80 ° C. . The dry, non-solid gas has a composition within certain limits as shown in Table I below.

Table I

component % vol. H2 15—50 WHAT 15—30 CO2 7—30 CH4 0— 5 I-I2S 0,05- 0.5 N2 + A 1—55

This gas is further purified to remove H2S and possibly at least a portion of CO2.

This purification is carried out in a known manner

H2S and CO2 are predominantly removed from the gas using the ADIP process or SULFI199271

NOL processes as described in British Patents 1 444 963, 1 131 · 989, · 965 358, 957 260 and 972 140.

The solid and HZS-free dry gas then has the following composition, as shown in Table II.

Table II

component % vol. H2 15—50 WHAT 15—30 CO2 7—30 CH4 0— 5 H2S 0,001—0,010 N2 + A 1—55

As previously described, tar is formed as a by-product in coal gasification. This tar typically contains 1 to 25% solids, which are ash and non-convertible or partially transferable coal particles.

Since a high solids content prevents subsequent tar gasification, at least a portion of the solids is removed from the tar portion. The removal can be carried out in any suitable manner, say by settling solids from one part of the tar to the other. Most often, the solids are removed from 25 to 75% of tar by, for example, settling into the remaining 75 to 25% of tar. Another suitable method used to remove solids from tar is to wash the tar with hot water, most often at 125 ° C.

Part of the tar from which the solids have been removed is particularly suitable for gasification by incomplete combustion.

The part of the tar from which the solids have not been removed, or the part which has been enriched by impurities in the settling process and which now contains more solids than originally contained, is usually recirculated and partially combusted either together with coal or separately, according to of what is required.

Accordingly, in the context of the foregoing description, 25% to 75% of the tar is directly gasified and 75% to 25% of the tar is recirculated and partially combusted with coal.

As mentioned previously, during the gasification of tar by partial combustion, soot is formed. These carbon blacks are separated from the resulting syngas and a portion of them is combusted together with coal to obtain a H 2 and CO 2 gas. The methods described in British Patents 826,209 and 1,267,896 are most commonly used to separate carbon black from gas.

If a portion of the tar formed during the partial combustion of coal is recirculated back to the partial combustion process of coal, it is preferable to mix at least a portion of the carbon black with a portion of the tar and partially heat the resulting mixture of tar and carbon black with the coal. Carbon black is particularly suitable for use even when part of the tar contains solids, in particular ash or only partially converted coal. It is suitable to use 3 to 10 parts by weight of tar per 1 part by weight of carbon black.

The carbon black may be directly mixed with the tar or first with water and then with the tar. In the first case, the resulting raw gas from incomplete combustion of a portion of the tar is contacted with another portion of the tar, so that the soot is transferred to that portion. In this case, the raw gas is first cooled to a temperature of between 50 ° C and 200 ° C. The tar to be mixed with the carbon black usually has a temperature in the range of 50 ° C to 200 ° C. In the latter case, the carbon black-containing water having a carbon black content of 0.5% to 10% and a temperature in the range of 100-150 ° C is contacted with the tar, which is usually 100-150 ° C.

In the first case, it is most often used

0.001 m3 of tar per Nm ^{3 of} carbon black gas. .

In the latter case, it is advisable to mix 1 m ^{3 of} water with a carbon black content of 1 m ^{3 of} tar.

From 1000 kg of coal, using the process described in the present invention, after drying and removal of H2S and CO2, 1500 to 3300 Nm ^{3 of} synthesis gas can be obtained having the following composition:

% vol.

N230—45

CO19—24

CH48—30

............... N2 + A1—45

The invention will now be further illustrated by the following example.

Example ‘

The starting material was coal, which had the following composition:

% by weight

C72.95

H4.88

O10.08

S 1133%

N '1.56 ° / o ash · 8.44

This coal contained 34.7% by weight of volatiles and also 2% by weight of volatile matter. water. The coal was converted to gas by partial combustion with tar, which contains some solids and which is recirculated from the next stage of the process. Per kg of ash-free water and coal, 0.06 kg of tar was added and 0.356 kg of oxygen and 1.524 kg of steam were used. The oxygen feed temperature was 250 ° C and the steam temperature was 263 ° C.

The gasification was carried out at a temperature between 700 and 1100 ° C and at a pressure of 4.0 MPa.

After cooling the resulting gas to 125 ° C, tar was removed from the gas.

0.1 kg of tar was obtained from 1 kg of coal. Plate% 'Vol.

het contained 15% solids by weight. 'After' '.dried out .. had. · Resulting. gas. the following composition:

component % vol: H2 ' 29.3 WHAT 15.5 CO2 31.7 CH4 '- 22.1 H2S 0.5 N '- + · A' 0.9

From 1 kg. water and coal · ash-free · 2.08 Nm * · of this gas.

Solids. · Was ··· left. deposit 50% of the tar into the remaining tar. ·. Then. they were both. These tar parts are separated from each other. The pure tar was transferred in a separate reactor by partial combustion with 1.057 kg of oxygen and 2.5. Kg of steam per kg. · Synthetic gas tar. containing carbon black. Temperature. in this · · process was. · 1100. ' ^Q C 'and · pressure' 4.0 · MPa.

Crude synthesis. the gas was "cooled" to 180 degrees "Celsius" in the "indirect" heat exchanger using water. The cooled gas was then scrubbed with water and the result was. that the soot was absorbed in water. 0.15 kg of carbon black was produced from 1 kg of tar.

Dry '' synthesis. gas that. it did not contain carbon black, it had the following composition.

H2

WHAT

CO2

H2S

N2 + A

48.0

25.2

25.6

0.2

1.0

1 kg of tar produced 2.57 Nm of ^{1 * 3} gas.

The tar portion into which the solids had deposited was mixed with the carbon black containing water at 125 ° C by stirring. ° C, whereby the carbon black was mixed into the tar. The soot tar 'and' purified water were. separated. The 'solids-containing mixture of carbon black and tar' was 'recirculated' to the 'phase of the process' in which 'the partial combustion of coal' takes place.

The synthesis gas obtained directly from coal was mixed with the synthesis gas obtained. from purified tar. Thus, 2,228 " Nm ^{< 3} > of dry synthesis gas was obtained from 1 kg of coal ^; who had the following. Ingredients:

component % vol. Hz. 30.4 WHAT 16.1 CO2 31.3 CHí 20.8 H2S 0.5 N2 + A 0.9

OBJECT OF THE INVENTION

Claims (3)

A process for preparing synthesis gas by incomplete combustion of coal with an oxygen-containing gas at a temperature in the range of 700 to 100 ° C 1100 ° C, during which a solid-containing tar is formed which is separated from the gas, at least. part of the tar is gasified. incomplete combustion with an oxygen-containing gas at a temperature in the range of 1000 to 1500 ° C and a pressure in the range of 0.1 to 10. MPa, forming carbon black, which is separated from the gas and at least a portion thereof. '' incompletely burned together with coal, characterized by that for improvement. Tar gasification. from 25 to. 75% of the tar removed the solids by settling in the remaining 75 'to 25' of tar, at least part of the tar from which the solids have been removed is gasified by incomplete combustion; and. at least a portion of the soot formed by incomplete tar combustion is introduced. to. tar, in which the solids have settled, and this mixture is incompletely combusted with coal. 2. The method referred to in point 1,. characterized. by per 1 part by weight. soot is used. 3 to 10 parts by weight of tar.