GB Patent 1554637 - PROCESS FOR PRODUCING GASES HAVING A HIGH CALORIFIC VALUE

Claims

WHAT WE CLAIM IS: 25

1 A process for producing gases which have a high calorific value and contain more than 50 W methane by volume, wherein a solid fuel is gasified in a first reactor under a pressure of 5 to 150 bars by a treatment with free oxygen-containing gas and steam, to produce a crude steam-containing gas at an exit temperature of 350 to 700 'C, and wherein said crude gas is reacted under a pressure of 5 to 150 bars with free oxygen-containing gases 30 in a following reactor to produce an intermediate product gas, which contains mainly hydrogen, oxides of carbon, and methane and which leaves the reactor at a temperature of from 6000 to 950 'C, this intermediate product gas being thereafter cooled, freed from sulphur compounds and subjected to methanation.

2 A process as claimed in Claim 1, wherein fuel in dust form and/or a liquid hydrocar 35 bon is or are added to the crude steam-containing gas in said following reactor.

3 A process as claimed in Claim 1 wherein fuel in dust form and/or a liquid hydrocarbon is or are first contacted with oxygen in a reaction chamber and the reaction products are further reacted together with the crude steam-containing gas in said following reactor.

4 A process as claimed in Claim 2 or 3, wherein the fuel in dust form has a particle size 40 of less than 2 mm.

A process as claimed in any one of Claims 2 to 4, wherein the fuel in dust form has a particle size of from 0 03 to 0 3 mm.

6 A process as claimed in Claim 2 or 3, wherein the liquid hydrocarbon is vaporized or formed into a fine spray before it is reacted 45 7 A process as claimed in any preceding claim, wherein exhaust gases having combustible constituents are fed to the reactor for producing the intermediate product gas.

8 A process as claimed in Claim 7, wherein the exhaust gases are used as an atomizing agent for dispersing the liquid hydrocarbon or fuel in dust form.

9 A process as claimed in any preceding claim, wherein the reaction in the reactor for 50 producing the intermediate product gas is carried out under turbulent conditions of flow.

A process as claimed in any preceding claim, wherein said following reactor contains a bed of granules having a particle size of 3 to 80 mm.

11 A process as claimed in any preceding claim, wherein said following reactor contains a bed of granules having a particle size of 5 to 30 mm 55 12 A process as claimed in Claim 10 or 11, wherein the bed consists at least in part of catalytically active substance.

13 A process as claimed in Claim 12, wherein the catalytically active substance is nickel, cobalt, chromium, or an oxide or sulphide thereof.

14 A process as claimed in any one of Claims 10 to 13, wherein the bed or a support for 60 the catalytically active substance consists of alumina, magnesia, a mixture thereof, or a spinel or silicate of aluminium and/or magnesium.

A process as claimed in any one of Claims 10 to 14, wherein the bed is moved by mechanical means.

16 A process as claimed in any one of Claims 10 to 14, wherein the bed is maintained in 65 1,554,637 1,554,637 a fluidized state.

17 A process as claimed in any one of Claims 10 to 16, wherein the bed material is removed from the reactor, freed from combustible residues outside the reactor, and is returned at elevated temperature into the reactor.

18 A process as claimed in any preceding claim, wherein at least part of the heat of reaction of required in the reactor for producing the intermediate product gas is supplied by high-frequency electric heating or electric resistance heating.

19 A process as claimed in any preceding claim, wherein the solid fuel gasified in the first reactor is lump fuel.

20 A process for producing gases which have a high calorific value substantially as hereinbefore described with reference to the accompanying drawing and/or in either of the foregoing Examples.

TREGEAR, THIEMANN & BLEACH, Chartered Patent Agents, 15 Enterprise House, Isambard Brunel Road, Portsmouth P 01 2 AN and 49/51, Bedford Row, London, WC 1 V 6 RL 20 P f lajeitys Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1979.

Published by lhe patent office, 25 Southampton Buildings, London, WC 2 A Afo whi Ch Copies may be obtained.

Description

PATENT SPECIFICATION ( 11) 1 554 637

> ( 21) Application No 27922/76 ( 22) Filed 5 Jul1976 ( 19) I I), ( 31) Convention Application No 2532198 ( 32) Filed 18 Jul 1975 in /i ( 33) Fed Rep of Germany (DE)

t' ( 44) Complete Specification Published 24 Oct 1979

In' ( 51) INT CL 2 CO 7 C 9/04 1/02 i ( 52) Index at Acceptance C 5 E AG ( 72) Inventors: GERHARD BARON HERBERT BIERBACH CARL HAFKE GUNTER POCKRANDT FRANZ BIEGER CLAUS LOHMANN ( 54) PROCESS FOR PRODUCING GASES HAVING A HIGH CALORIFIC VALUE ( 71) We, METALLGESELLSCHAFT AKTIENGESELLSCHAFT, a body corporate organized under the laws of the German Federal Republic, of Reuterweg 14, 6 Frankfurt am Main, German Federal Republic, and RUHRGAS AKTIENGESELLSCHAFT, a body corporate organized under the laws of the German Federal Republic of 60 Huttropstrasse, 4300 Essen 1, German Federal Republic, do hereby declare the invention for which 5 we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:-

This invention relates to a process for producing gases which have a high calorific value and contain more than 50 % methane by volume.

Such gases can be produced starting from gases produced by the gasification of solid 10 fuels, particularly coal, under a pressure of 5 to 150 bars by a treatment with free oxygencontaining gas and steam and, if desired, additional gasifying agents to produce a crude steam-containing gas at a temperature of 350 to 700 'C.

A gas which can be economically converted to a gas of high methane content can be produced by the pressure gasification of coal, including brown coal, by treating the coal 15 with oxygen and/or air and, as further gasifying agents, steam and possibly carbon dioxide.

The pressure gasification of coal is conventionally effected under a pressure of 5 to 150 bars, preferably 10 to 80 bars, and results in a crude steam-containing gas at a temperature of 350 to 7000 C.

Coal is normally gasified under pressure in a reactor by a countercurrent operation in 20 which the fuel to be gasified and the gasifying agents are fed into a reaction chamber of the reactor from opposite directions and move in said chamber in opposite directions This mode of operation has proved desirable because the sensible heat of the product gas is advantageously utilized to heat the fuel to the reaction temperature In the reactor or gas producer, the fuel travels through several zones, the fuel being first dried and then degasi 25 fied in a dry distillation zone before the fuel enters a gasification zone, in which a major portion of the endothermic reactions are carried out In a combustion zone the remaining fuel is finally reacted to a large extent with the free oxygen and an incombustible residual ash consisting of mineral constituents is left and the gasifying agent which flows into the reactor receives sensible heat from that ash Experience has shown that the gasifying agents 30 are suitably supplied at a metered rate which is selected so that the maximum combustion temperatures in the reactor are below the melting point of the ash.

In addition to steam, the crude gas produced by the pressure gasification of coal contains mainly hydrogen and oxides of carbon as well as methane Numerous further substances, such as condensible hydrocarbons, particularly tar having various boiling ranges, are pre 35 sent in smaller quantities Whereas these are often considered as valuable constituents of coal, they are not always desirable in gaseous fuels Unless they can be directly used for the production of energy, they must be fed to a further benefication stage, e g, for hydrogenation The processing of such substances is often problematic because they become available as a result of a gasification in quantities which are not sufficient to enable them to be 40 L 1,554,637 2 utilized economically They are also undesired because they become available together with the aqueous condensate formed from the gaseous constituents during the further processing of the crude gas Considerable expenditure is required to purify this condensate, which contains not only hydrocarbons but, inter alia, also phenols, fatty acids, and ammonia 5 According to the present invention there is provided a process for producing gases which have a high calorific value and contain more than 50 % methane by volume, wherein a solid fuel is gasified in a first reactor under a pressure of 5 to 150 bars by a treatment with free oxygen-containing gas and steam, to produce a crude steam-containing gas at an exit temperature of 350 to 700 C, and wherein said crude gas is reacted under a pressure of 5 to 150 10 bars with free oxygen-containing gases in a following reactor to produce an intermediate product gas, which contains mainly hydrogen, oxides of carbon, and methane and which leaves the reactor at a temperature of from 6000 to 950 MC, this intermediate product gas being thereafter cooled, freed from sulphur compounds and subjected to methanation As the crude gas is converted to the intermediate product gas, the hydrocarbons contained in 15 the crude gas as well as the phenols, fatty acids, and ammonia are converted mainly to hydrogen and oxides of carbon by gasification and cracking and for this reason need not be separated from the crude gas The reaction to produce the intermediate product gas is suitably effected under the same pressure as that used for the production of the crude gas.

Fuels in dust form, particularly coal dust, or liquid hydro-carbons, particularly tar and/or 20 tar oil, are preferably gasified by treatment with oxygen before or in the reactor for producing the intermediate product gas, and the gasification products may be fed to the reaction for producing the intermediate product gas Exhaust gases and undesired byproducts of other processes can also be processed by such thermal gasification treatment with oxygen.

Carbon dioxide may be used as one of the gasifying agents in the production of the interme 25 diate product gas.

The thermal gasification of dust fuels, liquid hydrocarbons, exhaust gases or by-products by treatment with oxygen results in reaction temperatures of 900 to 1400 'C and in the production mainly of hydrogen and carbon monoxide, which subsequently deliver heat to the endothermic reactions carried out in the reactor for producing the intermediate product 30 gas The thermal gasification may be effected in a separate reactor or in the reactor for producing the intermediate product gas.

The dust fuels to be subjected to the thermal gasification have a particle size of from 0 to 2 mm preferably from 0 03 to 0 3 mm Liquid hydrocarbons to be subjected to the thermal gasification are first vaporized or formed into a fine spray Exhaust gases which contain 35 combustible constituents may be used as atomizing agents for dispersing the liquid hydrocarbons or dust fuels.

The reactor for producing the intermediate product gas may be designed in various ways.

In the reactor, the starting materials in the form of dust and gas are suitably subjected to centrifugal forces or turbulent conditions of flow, for example because the reactor contains 40 internal fixtures or a bed of granular material having a particle size of 3 to 80 mm preferably 5 to 30 mm, the granular material consisting of heat-resisting inert material, which serves primarily to agitate the gas and dust particles.

The reactor for producing the intermediate product gas may contain catalytically acting substances, such as nickel, cobalt, chromium or their oxides or sulphides For this purpose, 45 known catalysts are selected which accelerate the cracking of the gases and vapours to hydrogen and oxides of carbon in the reactor for producing the intermediate product gas and which suppress the formation of carbon black Supports for the catalysts may consist of alumina, magnesia or mixtures of these two substances as well as silicates of aluminium and/or magnesium The catalyst support may also consist of aluminium spinel or magne 50 sium spinel To improve the probability of the reaction in the reactor for producing the intermediate product gas, the granular bed may be carried by a movable grate Alternatively the bed may consist of a fluidized bed.

Because the cracking reactions in the intermediate product gas reactor are endothermic reactions, care must be taken that sufficient energy is available for the reaction To this end, 55 the bulk material contained in the reactor may be periodically removed from the reactor and freed from combustible residues whereafter the bulk material is returned at an elevated temperature to the reactor At least part of the energy required for the reaction may be supplied by high-frequency heating or electric resistance heating In most cases, however, it will be possible to supply the required energy by partial oxidation with the oxygen which is 60 fed.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawing which illustrates diagrammatically and by way of example an embodiment thereof and which is a plant diagram of apparatus for producing gases which have a high calorific value and contain more than 50 % methane by volume 65 Referring now to the drawing, there is shown a gas-producing reactor 1, to which coal, e.g, hard coal or brown coal, is fed through a conduit 2 The coal is gasified in the gasproducing reactor 1 using steam and oxygen as gasifying agents which are injected through conduits 3 and 4 into the reactor at the lower end thereof The ash which is produced by the gasification treatment is withdrawn through a conduit 5 The gasification is carried out in 5 the reactor 1 in conventional manner and is effected under a superatmospheric pressure of 4 to 150 bars, preferably 10 to 80 bars.

The crude steam-containing gas produced by the gasification is at a temperature in the range of from 350 to 700 C when it leaves the reactor 1 through a conduit 7 This crude gas may be passed through a cyclone in order to effect coarse separation of dust, if this is 10 required, this optional feature not being shown on the drawing The conduit 7 conducts the crude gas to a second reactor 8 for after-gasification of the crude gas, the pressures in the reactors 1 and 8 preferably being the same.

The reactor 8 is fed at its top 8 a with coal dust through a conduit 9 and with oxygen through a conduit 10, the coal dust and oxygen interreacting in the reactor with the produc 15 tion of high temperatures of 900 to 1400 'C The reaction products together with the crude gas from the conduit 7 then flow through a bed 11 of inert granular material, such as aluminia, which has a particle size in the range from 3 to 80 mm, preferably 5 to 30 mm, and is carried by a grate 12 The coal dust fed to the reactor has a particle size of less than 2 mm preferably from 0 03 to 0 3 mm 20 The bed 11 serves mainly for intensely agitating the gases flowing into the bed so that the probability of reactions between the components of the flowing gases is increased The bed may alternatively consist of catalytically active material for intensifying the gasification reactions taking place in the reactor 8 The gasification reactions comprise reactions of solid fuels and hydrocarbons and, inter alia, phenols, fatty acids, and ammonia, with oxygen and 25 steam to produce hydrogen, oxides of carbon, and methane, these gasification or cracking reactions being endothermic reactions.

The reaction in the reactor 8 is so controlled that the resulting intermediate product gas is at a temperature of 600 to 950 'C as it leaves the reactor The intermediate product gas flows along a conduit 13 to a scrubber-cooler 14 and is subsequently fed to a desulphurizing 30 scrubber 15 The scrubber-cooler 14 may be replaced by one or more wasteheat boilers and/or scrubber-coolers When a shift conversion is required, some of the intermediate product gas is branched off through a conduit 13 a, represented by a dotted line, and fed to a shift converter 16, in which carbon monoxide is catalytically converted with steam to form carbon dioxide and hydrogen in known manner, e g as described in the Specification of U S 35

Patent No 3,069,250 The shift-converted gas is added to the main stream before it is fed to the desulphurizing scrubber 15.

The desulphurization in the scrubber 15 may also be carried out in conventional manner, e.g, by the "Rectisol" process in which the gas is scrubbed with a scrubbing agent, such as methanol, at a temperature below O C to remove impurities, mainly sulphur compounds 40 and carbon dioxide Such scrubbing processes have been described in the Specifications of

U.S Patents Nos 2,863 527: 3,531 917; and 3710,546 The thus purified gas leaves the scrubber 15 through a conduit 17 and is reheated to a temperature of 250 to 350 'C in a heat exchanger 18 The gas then flows into a plant 19 for catalytic methanation In this plant, which is also conventional (see e g the Specifications of U S Patent No 3511,624 and 45

British Patent No 820257) methane and steam are produced from oxides of carbon and hydrogen.

The gas leaving the methanating plant 19 through a conduit 20 is cooled in the heat exchanger 18 and may be used as a fuel gas which contains more than 50 % methane by 50 volume In order to enrich its methane content, the gas is suitably passed through a scrubber 21, in which carbon dioxide is removed to a large extent so that a gas which has a further increased calorific value and usually contains more than 80 Cc methane by volume is available in a conduit 22.

The invention will now be further illustrated by the following Examples of the operation 55 of plant similar to that shown in the drawing.

1,554,637 A 1,554,637 Example 1

A gas producer having an average diameter of 2 6 m and operated under a pressure of 20 bars is fed with 15 metric tons (t) of coal per hour The coal has the following composition based on water and ash-free matter: 5 Proximate Analysis Moisture 251 9 kg /t.

Ash 298 5 kg /t.

Tar 143 0 kg /t.

Water removable by 10 dry distillation 80 3 kg /t.

Phenols 8 0 kg /t.

Fatty acids 1 8 kg /t.

Net calorific value 7,044 5 kcal Ikg.

Elemental Analysis of Pure Coal 1 s kg /t.

C 762 6 H 55 8 o 157 4 N 13 2 20 S 10 7 Cl 0 3 257 standard m 3 oxygen per metric ton of coal and 5 5 kg steam per standard m 3 of oxygen are fed as gasifying agents into the gas producer Crude gas is produced at a rate of 1913 standard m 3/h on a dry basis and has the following composition in percent by volume: 25 CO 2 28 2 H 2 S 0 4 C 2 H 4 0 4 CO 20 1 H 2 38 9 30 CH 4 11 1 C 2 H 6 0 6 N 2 + Ar 0 3 The crude gas contains also 0 5 standard m 3 steam per standard m 3 dry gas and has an exit temperature of 600 'C 35 Cooling of the crude gas to 250 C would make the following by-products available per metric ton of water and ash-free coal:

Tar 59 kg.

Oil 32 kg.

Gasoline 16 kg 40 Ammonia 13 6 kg.

Phenols 8 kg.

Fatty acids 1 8 kg.

The crude gas is fed without cooling to an after-gasification reactor 8 and is reacted therein with 0,04 standard m 3 oxygen and 0 4 kg steam per standard m 3 of crude gas About 45 one-half of the reactor is filled with alumina balls having an average diameter of 30 mm, the reaction chamber being 2 m in diameter and the alumina balls forming a bed 4 m high.

As a result of the reaction in the reactor 8, a temperature of about 1000 'C is attained near the oxygen inlet The gas leaving the reactor is at a temperature of 700 C and has the following composition in percent by volume: 50 CO 2 32 9 H 2 S 0 3 CO 12 0 H 2 40 8 CH 4 13 3 55 N 2 + Ar 0 7 Thus intermediate product gas is free from condensible hydrocarbons and no longer contains free oxygen The gas is cooled to 30 C in waste-heat boilers and coolers and is then desulphurized by being scrubbed with liquid methanol at about -25 C, whereby about one-half of the content of carbon dioxide is also removed The desulphurized gas is rehe 60 ated to 300 C and is then methanated in contact with a catalyst which contains 50 % nickel by weight on a magnesium spinel support The methanation is effected under a pressure of bars and results in a gas which has a high calorific value and contains about 62 % methane per volume on a dry basis In order to increase the methane content to 96 % by volume of dry gas, the gas is scrubbed with hot potassium carbonate solution to remove its content of 65 carbon dioxide to a large extent.

Example 2

0.09 standard m 3 oxygen and 0 8 kg steam are added to the crude gas produced in accordance with Example 1 per standard m 3 of said crude gas, and coal dust having a particle size of 0 03 to 0 3 mm is also added at a rate of 300 kg per metric ton of the lump fuel fed to the gas-producing reactor 1 The coal dust has the same analysis as the coal used in Example 1 5 Crude gas, oxygen, steam, and coal dust are reacted in the reactor 8 such as is diagrammatically shown in the drawing and as used in Example 1 The resulting gas is at a temperature of 750 'C as it leaves the reactor 8 and has the following composition: in percent by volume:

C 02 30 7 10 H 2 S 0 2 CO 15 6 Hz 46 6 CH 4 6 4 N 2 + Ar 0 5 15 H 20 0 74 standard m 3 per standard m 3 of dry gas This gas is subjected to the further processing described in Example 1 The gas leaving the methanation plant has a high calorific value and contains 57 8 % methane by volume of dry gas This methane content can be increased to 96 5 % by volume if the gas is scrubbed to remove carbon dioxide to a large extent 20 In the Specification of our co-pending Patent Application No 27923/76, of even date herewith, we have described and claimed a process for producing a synthesis gas which contains carbon monoxide and hydrogen, the process being substantially the same as that of the present Application save that the methanation step is omitted (Serial No 1554638)