CA1187702A - Process for converting coal and/or heavy petroleum fractions into hydrogen or ammonia synthesis gas - Google Patents

Abstract

ABSTRACT

A PROCESS FOR CONVERTING COAL AND/OR HEAVY PETROLEUM
FRACTIONS INTO HYDROGEN OR AMMONIA SYNTHESIS GAS.

Hydrogen or ammonia synthesis gas consisting substantially only of hydrogen and nitrogen is prepared from coal and/or heavy petroleum fractions by gasification with steam and an oxygen-containing gas, cooling the thus-formed crude gas by quenching and/or steam production, scrubbing the cooled gas to remove soot and other solid impurities, re-heating by heat exchange with exit gas from a subsequent conversion step, shift-converting the re-heated, soot-free crude gas to convert its CO by passing the gas through one ore more catalyst beds of one or more sulfur-resistant shift catalysts, removing acid gases (notably H2S and CO2) from the shift-converted gas and finally subjecting the gas to a catalytic methanation to convert remaining amount of carbon oxides to methane. If the process is used for preparing ammonia syngas, the gasification is conveniently carried out with oxygen-enriched air and steam.

Description

15805-15812/KP/io '7~2 Haldor Tops0e A/S, Lyngby, Denmark.

A process for converting coal and/or heavy petroleum fractions into hydrogen or ammonia synthesis gas.

Field of the invention -The present invention relates to a process for converting a raw material of coal and/or heavy petroleum fractions into hydrogen or an ammonia synthesis gas, so-called syngas, substantially only consisting of hydrogen and nitrogen .

Background of the invention The last step in ammonia synthesis is the conversionof the ultimate syngas of nitrogen and hydrogen, most frequently in the stoichiometric proportion 1-3, but sometimes in another proportion and often accompanied by '7'7B~

small amounts of impurities, notably argon and methane, at high pressure by the aid of a catalyst, especially consisting of iron and various promoters, e.g. the ammonia synthesis catalyst type KM prepared and supplied by Haldor Tops0e A/S.
An example of the preparation of a~monia synthesis gas from natural gas and air has been described by H.F.A.
Tops~e, H.F. Poulsen and A. Nielsen in Chemical Engineering Progress, vol. 63, No~ 10, 67,73 (October 1967). A useful review of ammonia technology is found in the book "Ammonia", edited by A.V. Slack and G. Russel James, Marcel Dekker IncO, New York and Basel 1977.
The need of ammonia, not least for fertiliæ~r and raw material for fertilizers, is heavily increasing. At the same time, the growing scarcity of energy and increasing cost of recovering natural gas has rendered it desirable to use other raw materials for the preparation of the synthesis gas as well as hydrogen, viz. either coal (including pit coal, anthracite, lignite, peat and coke including petroleum coke), or heavy petroleum fractions, whereby they are gasiied by the aid of oxygen and steam. When using coal the gasification reactions are:

C + H20 ~ -- CO + H2 (1) C + ~ 2 > CO (2) whereby by-products may issue such as methane and possibly other hydrocarbons and sulfur compounds, notably hydrogen sulfide and carbonyl sulfide, originating from the sulfur contaminations of the coal, and possibly small amounts of nitrogen, argon and possibly tar substances.
-The gasification of mineral oils is more complicated, i.a. because of the fact that especially the heavy ractions consist of complex mixtures of higher paraffins, olefins and aromatics. An ideal example is the general reaction CnHm + n/2 2~ nCO -~ m/2 H2 (3) but even a thermal cracking with partial oxidation of the heavy hydrocarbons ta}Ces place so as to form free carbon:

~ ~ ~'7'i'~

CnHm ~ nC + m/2 H2 (4) In practice both reactions (3) and (4) take place when using oxygen since less than the stoichiometric amount is used in practice. Other possible reactions by the partial oxidation of mineral oils are, i.a.:

CnHm + (n~m/4)O2 ~ - nCO2 + m/2 H~O (5) CnHm + nCO2 ~ ~ 2m CO + m/2 H2 (6) CnHm + m/4 2 ~ j nC + m/2 H20 (7) and by the partial oxidation of liquid hydrocarbons with superheated steam: ~

CnHm + nH20 ~--- nCO + (m/2 ~ n~ ~2 (8) and additionally as secondary reactions reaction (1) and C + CO2 ~ `-2CO (9) Since a normal residence time in the gasification reactor is insufficient to allow reactions (1~ and ~9) to run to completion, there will always be some soot left in the raw gas at the conclusion of the gasification; when using heavy fuel oi~ the amount of soot may be up to 3% of the weight of the raw material.
The further working up of the raw gas formed by the gasification into the desired synthesis gas in recent time mostly takes place via two paths differing in principle;
both have been described by Samuel Strelzoff in an article in Hydrocarbon Processing, December 1974, pages 79-87.
In one of the reaction paths the raw gas is cooled in a waste heat boiler and is thereafter cooled to below the dew point in a soot removal system. Thereupon sulfur is removed and the hydrogen sulfide is worked up, e.g. in a Claus plant. The next step is the conversion of carbon monoxide into carbon dioxide by the so-called shift process:

77~;Z

CO + H20 ~--- CO2 2 (10) which when using this reaction path always takes place by the high-temperature-shift-reaction (at least 330C) by the aid of high-temperature shift catalysts, optionally followed by a low-temperature-shift-reaction (down to about 200C) by the aid of a low-temperature shift catalyst.High-temperature shift catalysts mostly consist of oxides of Fe and/or Cr. If this type of shift catalyst is used, the content of CO may be brought down to about 3.5 mol%. If the reaction is carried out in two steps using a low-temperature shift catalyst in the second step, the content of CO may be brought down to about 0.3 mol%, calculated on the dry gas. The low-temperature shift catalysts used in such embodiments of the process always contain Cu and ZnO and optionally Cr2O3 or ~12O3. These catalysts are exceedingly sensitive to poisoning with sulfur and a very profound removal of all sulfur compounds from the gas therefore is needed before it can be conducted to the low-temperature shift reactor. Since CO is a catalyst poison for ammonia catalysts, the residual CO
remaining after the shift reaction must be removed and this normally takes place, in this reaction path, in the cryogenic manner by washing with liquid nitrogen. If a low-temperature shift catalyst has been used, it is also possible to remove CO by methanation, i.e. conversion into methane by the reaction CO + 3H2 ~ CH~ + H2O (11) Methanation is economically justified onlv when the content of carbon monoxide is low and therefore cannot be used when the shift reaction is solely conducted over a high-temperature shift catalyst. Before the nitrogen wash or methanation carbon dioxide must be removed from the gas, which can be done by a further wash. By wash with liquid nitrogen carbon monoxide, remaining amounts of methane, argon, and other gaseous impurities are removed and at the same time part of the needful nitrogen is added to the synthesis gas. In practice the nitrogen is proviaed by first fractionating atmospheric ~3t7~7~

air into an oxygen fraction and a nitrogen fraction and thenusing the former for the partial oxidation and the latter fox the nitrogen wash.
In the other reaction path the crude gas formed by the gasification is cooled directly by the so-called quenching and at the same time soot removal takes place. By quenching thexe is in the present specification always meant cooling of the gas by direct contact with liquid water;
it usually has a temperature of 150-250C and is under a pressure corresponding thereto. The content of water in the crude gas after the soot removal is sufficient to justify CO-conversion by the shift-reaction at this stage. Since the gas still contains sulfur it is necessary to use a sulfur-resistant shift catalyst and as the sulfur-resistant shift catalysts known at the time of the development of the method were all high-temperature shift catalysts, the CO
conversion in this case is normally carried out at high temperature. This normally takes place in two steps; thereafter removal of sulfur compounds is carried out, notably H2S, and of CO2, usually in a single washing process.
The hydrogen ~ulfide is worked up, e.g. in a Claus plant~
The purified gas contains about 4.8 mol% CO and is finally washed with liquid nitrogen whereby the ammonia synthesis gas obtains the needful amount of nitrogen.
In both cases there is obtained a synthesis gas which in known manner is compressed and converted to ammonia.
; Largely, the two processes set the same demands on energy and require about the same capital investment for the installation o~ the necessary plants.
When preparing hydrogen the ultimate gas purification does not take place by wash with liquid N2 but contrariwise normally with a copper liquor scrubbing, and the CO removed is recycled to the inlet of the shif-t section.
Swedish patent publication No. 394 192 (Patent No.
3S 7215398-4), claiming priority from British patent application No. 549~7/71 of 26th November 1971, describes and claims a process for converting and purifying a raw gas, obtained by the partial combustion of a fuel and mainly c`~

containing hydrogen, carbon monoxide and soot particles, in order to obtain a hydrogen-rich gas stream. The raw gas is cooled at 220-300C. The cooling may commence by quenching but is concluded in a waste heat boiler which it must enter at a temperature of at least 900C. After the cooling the soot present in the gas may optionally be removed partially by wash with hot oil or passage through cyklones. C0 is converted in the soot-containing gas by passing the same along (not through) catalyst beds in one or more reactors having a complicated construction with a plurality of wire mesh discs separated and supported by distance members;
this construction ensures that the soot remains in the gas instead of being deposited on the catalyst: If a plurality of shift conversion reactors are used, the gas is cooled between them at 220-300C, preferably by quenching. When the C0 conversion has been completed the gas is cooled in a cooling zone in which soot and ash are removed. The soot free gas is washed to remove condensate, it is purified for acid components (H2S and CO2) and the remaining amount of carbon oxides is methanated. Swedish specification 394192 states that the process is economic because a cooling and re-heating before shift conversion is not needed and also says that it is advantageous that soot does not need to be removed before the shift conversion, and also that the sulfur compounds may be removed after that conversion.
It may be advantageous in some respects to let the soot remain in the gas during shift conversion but in other respects it is highly disadvantageous, viz. because it necessitates the said complicated construction of the reactor(s) in order to avoid blocking or destruction of the catal~st with soot. The fact that - ior the same reason -the gas must pass along the catalyst bed instead of passing through it is also a disadvantage because it results in an inadequate contact between gas and catalyst and thereby a low conversion per volume of catalyst; this necessitates capital costs for higher amounts of catalyst and larger reactors that would otherwise be required.

'7~

It is the object of the invention to provide a conversion of cheap fuels into hydrogen or ammonia syngas which avoids the disadvantages just mentioned and which can be carried out at any desired tem~erature between the dew point and the highest possible temperature determined by the thermodynamic equilibrium considerations, and in which both the energy consumption and the investment costs for the plant may be reduced. This is obtained by a novel combination of measures known ~er se,and in this combination, like according to the abovementioned Swedish publication shift conversion is carried out before purification for acid components (H2S and CO2) and is used for CO-removal.

Brief description o_ the invention The said objective is achieved by the present process which is characterized by the following combination of steps in sequence:
(a) gasifying the raw material at an elevated temperature with an oxygen-containing gas and steam to form a crude gas, (b) cocling the crude gas from step (a) by quenching and/or steam production, (c) scrubbing the cooled crude gas to completely remove soot and other possible solid impurities, (d) re-heating the cooled, soot-free crude gas at a desired temperature by heat exchange with exit gas from a subsequent step of converting carbon monoxide, (e) subjecting the washed, soot-free, re-heated crude gas to a shift conversion to convert CO into CO2 and H2 by one or more passages through one or more catalyst beds of one or more sulfur-resistant shift catal~sts, that of reaction being utilized for heat exchange with the gas in step (d), (f) removing hydrogen sulfide and carbon dioxide from the shift-converted gas, and (g) subjecting the gas thus substantially freed of acid gas components to a catalytic methanation to convert remaining amounts of carbon oxides into methane.

7~)2 This process differs from that known from the abovementioned Swedish patent publication in several respects.
Firstly, the present process can utilize simple conventional reactors and does not need complicated reactors as in the prior art. Since soot is removed from the gas before the shift conversion, the gas can pass through the catalyst bed without risk of depositing soot on the catalyst particles, whereby the catalyst is utilized much more efficiently. In contradistinction to the prior art the gas is cooled and re heated before shift conversion; however as heat e~change is used to utilize the heat of the exothermal shift reaction to preheat the gas, this cooling-reheating is not any noticeable drawback. It is not necessary to limit the use of quenchin~ in step (b) to quench the gas to a temperature above 900C; thereby the quenching and cooling by steam production can be adjusted to each other in any desired manner, whereby this adjustment can be utilized to add precizely a desired amount of water (steam) to the gas. The said prior art prescribes that the gas temperature at the exit from each shift reactor should preferably be 360-460C, whereas the present process may be controlled to a gas temperature of 190-280C at the exit of the last shift reactor. This lower exit temperature ensures a higher degree of conversion of CO.

Detailed description of the preferred embodiments The pressure during the gasification may be any desired pressure between atmospheric pressure and ~00 bar.
Gasification of coal will in many cases take place at atmospheric pressure whereas when gasifying heavy petroleum fractions one will fre~uently employ elevated pressure. If the process is to be used for the preparation of ammonia synthesis gas it will often be expedient to have the crude gas leave the gasification step at a pressure within a comparatively high pressure range, which may be maintained fairly unaltered during the entire conversion of the crude gas to syngas whereby the pressure increase of the latter ~7~

with a view to its final conversion to ammonia, which normally takes place at a pressure of, e.g., 150-250 bar, can be carried out in a single compression step. Thus, it may be advantageous to obtain the crude gas with a pressure in the range of 30-125 bar, preferably 50-80 bar.
Cooling in step (b) may take p]ace solely by the generation of steam or solely by quenching, whereby part of the soot removal is caused already at this stage.
But according to the invention the cooling conveniently is carried out by a combination of quenching and cooling by the production of high pressure steam. By the combined method of cooling it is obtained that the content of water-vapour may be predetermined at a desired level by choosing the correct ratio of the amounts of heat removed partly by the quenching, partly by the steam production. This is particularly valuable for the subsequent shift conversion because there in this process step is optimally used a steam content which is lower than that normally obtained by quenching alone.
In many cases it is advantageous to quench the crude gas at a temperature in the range of 400-800C and to carry out the remainder of the cooling by production of steam.
Even though part of the solids are removed by the quenching, a soot removal is carried out by scrubbing with water.,The soot removal may take place in any conventional manner.
Before the CO conversion by the shift reaction the soot-freed gas is heated at the desired temperature by heat exchange between inflow and outflow for the CO conversion system. In itself, the reaction may take place at any temperature between the dew point and the maximum temperatures determined by the equilibrium temperature. As mentioned hereinbefore, it is desirable for thermodynamic reasons to use the lowest possible conversion temperatures whereas the temperatures on the other hand are limited by the dew point, for example with an addition of about 30C but also the temperature limits for the activity of the catalyst must be taken into consideration.

77~2 The shift conversion may take place in one or more shift reactors and with one or more sulfur-resistant shift catalysts. In principle it is a low-temperature shift reaction, at least in the last part of the shift process, and there is used a special catalyst which is able to function, in a sulfur-containing atmosphere, both as a high-temperature shift catalyst and as a low-temperature shift catalyst at temperatures down to about 190C. The availability of such a catalyst is an important prerequisite for the invention.
A particularly suitable catalyst has been described in ~erman patent publication No. 1928389. According to the invention there is therefore conveniently emp~oyed a catalyst with or without catalyst support and consisting o~ (a~ at least one alkali metal compound prepared from an acid having a dissociation constant below 1 x 10 3, and (b~ a hydrogenation-dehydrogenation component of at least one element belonging to group VB (vanadium, niobium, tantalum~, VIB (chromium, molybdenum, tungsten) and VIII (iron, cobalt, nickel, the noble metals) in the Periodic Table, or a compound thereof, the ratio a:b being 1:0.001 to 1:10. The catalyst may be sulfided. Component (a) advantageously may be a potassium salt or cesium sulfide. As component (b) there is preferably employed a combination of metals or metal compounds, particularly conveniently nickel and tungsten, or molybdenum, cobalt and molybdenum, or iron and chromium.
As ~entioned the shift conversion takes place under conditions, especially with respect to pressure, temperature and steam content and possible nitrogen content in the gas, so as to obtain a final temperature only a little above the dew point of the gas. More precizely the conditions according to the invention may be adjusted so as to obtain the lowest possible end temperature which is sufficiently much above the dew point of the gas to protect the catalyst against condensation of water vapour~ The shift conversion particularly conveniently takes place under conditions so as to obtain a final temperature of 30-60C above the dew point of the gas, preferably about 40C above the dew point.

~'7'7~

In practice it is usually possible to carry out the shift conversion, or its last part, at-temperatures in the range of 190-280C.
It is advantageous that the shift conversion thus may be conducted at least partly and at least so far as its last part is concerned by low temperatures beca~se this involves a higher degree of conversion carbon monoxide into carbon dioxide than by using higher temperatures since reaction (10) is thermodynamically favoured towards the right by lower and toward the left by higher temperatures. Instead of a content of about 3.5%
CO it is possible by the present process when using a low-temperature active shift catalyst even by the presence of gaseous sulfur compounds to come down to a content of about 0.5~ CO or lower. Hereby there is obtained a higher yield of hydrogen. It involves the further advantage that the remaining amount of CO may be removed by methanation by reaction (11). Methanation of such small amounts of CO is possible in an economical manner and there is obtained the ~0 advantage that one avoids capital costs, operation costs and energy consumption for the cryo-unit with cooling at temperatures between -175 and -200C necessary when removing carbon oxides by nitrogen wash. As mentioned it isnot Fossible to remove so high amounts of CO as 3.5~ in an economic manner by methanation.
As will be understood from the statement hereinbefore on the known processes for preparing ammonia synthesis gas from petroleum fractions, it is most advantageous to carry out the shift conversion before the removal of sulfur because then one can remove sulfur (particularly in the form of hydrogen sulfide) simultaneously with carbon dioxide in one washing process for removal of acidic gases. Hitherto is has not been possible to use low-temperature shift catalysts in the presence of sulfur because they were all sulfur sensitive and very rapidly became sulfur-poisoned. The abovementioned sulfur-resistant catalysts not only are sulfur resistant but even require the presence of a certain minimum amount of H2S.

'7~

An advantage of the conversion process used is that even by low water/dry gas ratios it causes no significant methanation according to the formulae (11) and (12).
Substantial ~ethanation would involve loss of synthesis hydrogen. It is true that the methane formed could be utilized in the process as fuel but too large-amounts of methane will influence the energy economy in adverse direction, firstly because it is compressed to high pressure but used under low pressure, secondly because the very removal ~e.g.
in a cryogenic extraction unit for purge gas) requires supply of energy.
The conversion of the carbon monoxide o~ the crude gas so as to form hydrogen as stated usually takes place by the aid of a catalyst usable in the shift reaction both at low and high temperature, e.g. at 190-480C and which allows or even requires the presence of sulfur. The flow rate of the gas is not a critical factor and it is possible to use the space velocities that are comrnon in such reactions, e.g. in the range of 300-30,000 volumes of gas per volume of catalyst per hour (Nm3/m3/h). Even if the shift reaction may take place at high temperature, for the reasons stated it is most advantageous to conclude it at so low a temperature as possible, yet above the dew point, as condensation of liquid water on the catalyst may damage it.
Because of the sulfur tolerance of the catalyst the acid gases, i.e. mainly carbon dioxide and hydrogen sulfide, may be removed after the shift reaction which for the stated reasons of energy economy is the most advantageous.
The removal may occur in known manner and a number of suitable methods are described in a paper "Merits of acid-gas removal processes !- by K.G. Christensen and W.J. Stupin, Hydrocarbon Processing, February 1978, pages 125-130. As examples may be mentioned here absorption in a solvent ; containing polyethyleneglycol-dimethyl ether (~he "Selexol"
process), absorption in a promoted, hot potassium carbonate solution (the Benfield process), absorption in potassium salt solutions (the "Catacarb" process), absorption in methanol (the "Rectisol" process), absorption in diglycol amine, and absorption with various other amines.

77~2 The low temperature at the completion of the shift reaction allows as stated a high degree of conversion of CO
so that the residual content of the carbon oxides, CO and CO2, after elimination of the acid gases is suf~iciently low to allow them to be removed advantageously by methanation.
~hereby one avoids a nitrogen wash which is expensive because of the large consumption of cooling energy.
The process and the catalyst used moreover have the advantage that there is obtained a more complete conversion of carbonyl sulfide to CO2 and H2S, which are easily removed by the elimination of the acid gases, whereby the washed gas will not contain sulfur compounds disturbing subsequent processes such as for instance the ammonia synthesis.
Purification of the shift-converted gas for acidic gases, i.e. notably H2S and CO2, may be carried out by a number of known methods. After removal of the acidic gases still a little CO remains and possibly also a little CO2 may remain in the gas. Both are almost completely removed by the said methanation treatment which ta~es part, so far as CO is concerned, by reac'ion (11), whereas CO2 is methanated according to the scheme C2 + 4H2 ~ CH4 2 (12) If the process is used for preparing hydrogen i-t is hereby completed. If it is used for the preparation of ammonia synthesis gas, nitrogen must be added. This can take place by the direct addition of N2 but according to the invention it may very advantageously take place by using oxygen-enriched air as oxygan source for the gasification of the raw material, whereby the nitrogen will be present in the gas during the entire sequence of reactions from (b) to (g).
This has the advantage that there is thereby obtained a dilution of the crude gas whereby the equilibrium content of methane in the crude gas, under conditions of equal total pressure and equal temperature, will become lower than under conditions where the gasification is carried out with pure oxygen. The presence of nitrogen in the crude gas also gives '7~

an increase of the heat capacity f the gas and a decrease of the dew point, which again involves that the shift conversion may be carried out at a lower temperature, whereby there is obtained a favourable thermodynamic equilibrium of the conversion, viz. a higher conversion into H2 than otherwise would be the case. By using oxygen-enriched air in the gasification there is finally achieved a saving in the purchase of pure oxygen or the erection of a plant for oxygen production.
In the conventional nitrogen wash in connection with, e.g. the above known processes there is obtained a content of N2 in the purified gas of about 10%, after which more N2 is added to obtain the stoichiometric ratio H2 to ~ for the ammonia synthesis. Gasification with oxygen-enxiched air accordingly is not advantageous in connection with nitrogen wash because a content of N2 beyond about 10% will merely condense in the washing column, resulting in a considerable increase of the needful cooling energy.
The process of the invention is particularly usable when using heavy petroleum fractions as starting material.
The crude gas is formed by the gasification of the hydrocarbon material either with pure oxygen, if hydrogen is to be prepared, or, for the preparation of ammonia syngas, preferably with oxygen-enriched air, in both cases while adding steam according to the exothermal reactions ~3) and (8). Typically the temperature hereby increases to 1300-1400C. The crude gas formed by the gasification is cooled, ; and for the reasons explained hereinbefore preferably by a combination of quenching and a further cooling in a boiler. During the cooling one can thus partly utili~e the heat content of the crude gas in a waste heat boiler to prepare high pressure steam. After thecooling the gas is cooled further in a soot scrubber to remove soot and possible other solids in known mannerO The cooling takes place to a temperature near the dew point of the crude gas.
The temperature obtained and the concentration of steam obtained in the gas depends upon the total pressure and of the relative proportion of the amounts of heat removed by ~ ~'7~2 the quenching and steam production, respectively. Expediently these parameters are so adjusted mutually that the steam concentration becomes precizely that which is optimum ~or the subsequent shift conversion.
If hydrogen is to be produced by the present process there is also used pure oxygen for the gasification. If ammonia synthesis gas is to be producedl it is instead advantageous to use oxygen-enriched air obtained by mixing atmospheric air and oxygen. The proportion may be calcu]ated in such a way that the synthesis gas obtained after the methanation process and an optional admixture of a hydrogen~
rich fraction, obtained either by the process of the invention from a crude gas formed by gasification ~ith steam and pure oxygen or obtained from an extraction unit for purge gas, contains substantially the stoichiometrical amount of nitrogen for formation of ammonia, i.e. a ratio H2:N2 of about 3:1. However, also other ratios hydrogen to nitrogen can come into question.
The process of the invention will now be illustrated by a calculated Example of the preparation of ammonia synthesis gas from a heavy oil which is gasified with enriched air.

Example The following streams are assumed to be gasified:
Fuel oil: 32.2 t/h (C 8503%, H 10.5~, S ~.0%, N 0.2~) Enriched air: 55,281 Nm3/h (2 ~3~9%~ N2 55%~ ~r 1.1%
85 kg/cm2g, 600C, prepared by admixing 98.5% 2 with air.
Steam 13.0 t/h Hereby there is formed a crude gas having the following composition (leaving water vapour out of consideration):

7~2 Mol%
H2 34.0 N2 24.2 Ar 0.5 CH4 0.25 COS O . 0 1 Temperature 1365 C, pressure 80 kg/cm g, flow rate 125,920 Nm3/h calculated as dry and 135,360 Nm3/h calculated as wet gas.
The exit gas is quenched to 650C and is cooled further in a boiler at 340C. Thereby is formed about 42 t/h saturated steam at 115 bar.
After the boiler the gas is further quenched in a scrubber at a dew point of 240C whereby there is achieved a ratio water to dry gas of 0.78. The total amount of quenching water is 71,830 kg/h.

CO conversion The purified gas leaving the soot-scrubber is heated at 280C ~y heat exchange between inflow and outflow and is conveyed through three CO-converters after each other, all being reactors having downwards flow and fixed catalyst bed.
The c ~ osition of the dry yas (mol%) after the converters ~ and other data are seen in the following Table:

Converter 1 Converter 2 Converter 3 H2 49.2 51.2 51.4 N2 18.6 17.8 17.8 30 CO 5.2 1.1 0.7 C2 25.9 28.8 29.0 Ar 0.4 0.4 0.4 CH4 0.2 0.2 0.2 H2S 0.5 0.5 0.5 35 COS100 ppm 21 ppm 13 ppm 7~

Converter 1 Converter 2 Converter_3 Discharge stream Qf dry gas, Nm /h 164,000 170,710 171,410 Temp. in/out 5C) 280/441 250/280 245/24 H O/dry gas, inlet 0.78 0.37 0.32 The heat of reaction is utilized to generate high pressure steam to preheat boiler feed water in so far as possible. Optionally there may be used an absorption cooling unit to win heat down to 120C.

Removal of acid gases The process gas is con~eyed to a plant for removing acid gases, e~g. a Selexol unit, where CO2 and H2S are removed and separated off, whereby there is obtained an H2S-rich stream which is utilized in a Claus plant.
The gas thus purified is thereupon methanated to remove remaining CO and CO2.
The composition (mol~) after the elimination of acid gases and methanation as well as other data are seen in the following Table:

After elimination After of acid gasesmethanation

2 73.0 72.04 N2 25.2 26.06 CO 1.0 C2 ~.1 Ar 0.5 0.52 CH4 3 0.25 1.38 Discharge of dry gas, Nm /h 120,440 116,400 Temp. in/out ~C~ 320/389 Pressure 70 kg/cm g q,i~;

Ammonia synthesis The methanated gas is mixed w.ith an H2-rich gas coming from a purge gas recovery unit and after compression the synthesis gas obtained is conveyed to the synthesis loop.
The synthes:is converter, which operates at a pressure of 160 kg/cm g, is a converter as described in DK patent application No. 1041/77 with steam boiler and preheater for boiler feed water for chilling the exit gas from the converter.
The purge gas is conveyed to a cryogenic purge gas recovery unit in which the major part of ~r and CH4 are removed by condensation and the hydrogen-rich fraction is recycled to the suction side of the compressor.
Gas composition (mol~) and amounts of flows are as follows:

Hydrogen-rich Make up gas Convertex gas from residual for synthesis inflow outflow gas extraction unit H2 89.96 73.57 64.6252.97 N2 8.39 24.55 21.5517.67 NH3 3.82 17.99 Ar 0.98 0.56 3.00 3.40 CH4 0.67 1.32 7.01 7.97 dry gas stream Nm3/h 10,890127,290 457,270 402,350

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for converting a raw material of coal and/or heavy petroleum fractions into a gas con-sisting substantially only of hydrogen or of hydrogen and nitrogen, wherein the conversion is carried out by the following combination of steps in the order stated:
(a) gasifying the raw material at an elevated temperature with steam and an oxygen-containing gas or an oxygen - and nitrogen-containing gas to form a crude gas, (b) cooling the crude gas from step (a) by at least one treatment selected from quenching and steam production, (c) scrubbing the cooled crude gas to com-pletely remove soot and other solid impurities possibly present, (d) re-heating the cooled, soot-free crude gas at a desired temperature by heat exchange with exit gas from a subsequent step of converting carbon mon-oxide, (e) subjecting the washed, soot-free, re-heated crude gas to a shift conversion to convert CO to CO2 and H2 by at least one passage through at least one catalyst bed of at least one sulfur-resistant shift catalysts, heat of reaction being utilized for heat exchange with the gas in step (d), (f) removing hydrogen sulfide and carbon dioxide from the shift-converted gas, and (g) subjecting the gas thus substantially freed of acid gas components to a catalytic methanation to convert remaining amounts of carbon oxides to methane.

2. A process for converting a raw material of coal and/or heavy petroleum fractions into a gas con-sisting substantially only of hydrogen, wherein the con-version is carried out by the following combination of steps in the order stated:
(a) gasifying the raw material at an elevated temperature with an oxygen-containing gas and steam to form a crude gas, (b) cooling the crude gas from step (a) by at least one treatment selected from quenching and steam production, (c) scrubbing the cooled crude gas to com-pletely remove soot and other solid impurities possibly present, (d) re-heating the cooled, soot-free crude gas at a desired temperature by heat exchange with exit gas from a subsequent step of converting carbon mon-oxide, (e) subjecting the washed, soot-free, re-heated crude gas to a shift conversion to convert CO to CO2 and H2 by at least one passage through at least one catalyst bed of at least one sulfur resistant shift catalysts, heat of reaction being utilized for heat exchange with the gas in step (d), (f) removing hydrogen sulfide and carbon dioxide from the shift-converted gas, and (g) subjecting the gas thus substantially freed of acid gas components to a catalytic methanation to convert remaining amounts of carbon oxides to methane.

3. A process as claimed in Claim 1 or 2, wherein the crude gas is cooled in step (b) by a combination of quenching and production of high pressure steam.

4. A process as claimed in Claim 1 or 2, wherein the gas is quenched in step (b) to a tempera-ture of 500-800°C.

5. A process as claimed in Claim 1 or 2, wherein there is used two or more reactors for the CO shift con-version in step (d) and the gas is cooled between the reactors by heating boiler feed water and producing high pressure steam.

6. A process as claimed in Claim 1 or 2, wherein the shift conversion is carried out under conditions so as to obtain the lowest possible final temperature which is sufficiently much above the dew point of the gas to protect the catalyst against conden-sation of steam.

7. A process as claimed in Claim 1 or 2, wherein the shift conversion is carried out under conditions so as to obtain a final temperature of 30-60°C above the dew point of the gas.

8. A process as claimed in Claim 1 or 2, wherein the shift conversion is carried out under conditions so as to obtain a final temperature of 40°C
above the dew point of the gas.

9. A process as claimed in Claim 1 or 2, wherein the shift conversion is completed at a temperature in the range of 190-280°C.

10. A process as claimed in Claim 1 or 2, wherein the sulfur-resistant catalyst for the shift conversion is catalyst consisting of (a) at least one alkali metal compound prepared from an acid having a dissociation constant below 1 x 10-3, (b) a hydrogenation-dehydrogen-ation component of at least one element of group VB, VIB
and VIII in the Periodical Table or a compound thereof, the ratio a:b being 1:0.001 to 1:10, and (e) a support.

11. A process as claimed in Claim 1 or 2, wherein the sulfur-resistant catalyst for the shift conversion is catalyst consisting of (a) at least one alkali metal compound prepared from an acid having a dissociation constant below 1 x 10-3, (b) a hydrogenation-dehydrogen-ation component of at least one element of group VB, VIB
and VIII in the Periodical Table or a compound thereof, the ratio a:b being 1 0.001 to 1:10

12. A process as claimed in Claim 1, wherein oxygen-enriched air is used in step (a) as the oxygen source for the gasification.