DE1592356A1 - Process for the production of ammonia synthesis gas - Google Patents

Description

1 5 9? 3 5 R

METALLGESELLSCHAFT ι vi ^ *. ν / ο-J Frankfurt (Main), December 2, 1966

Aktiengesellschaft DrWer / GM

Patent Department
Pro v. No. 5162

Process for the production of ammonia synthesis gas

It is known to make coke oven gas usable for the ammonia synthesis that the im. The hydrogen contained in the gas is isolated from the other components by a gas separation plant using low temperatures. This is done by cooling the gas, whereby various components are already condensing, and by washing the cold gas, which has been separated from eoidensate, with liquid nitrogen. In this way, a very pure synthesis gas with about 75.VoI. % H ₀ and 25 vol.% N ₀ generated. The pure nitrogen required for this is obtained by the well-known air separation. The oxygen produced at the same time in the air separation cannot always be used and must then be blown off into the air. The power consumption of the process is quite high. In addition, the coke oven gas must be cleaned very well for the low-temperature gas decomposition. In particular, CO ₀ , H ₀ O and NO must be removed as completely as possible, since these impair the operation of the gas separation.

Recently, a gas separation process has become known in which the cooling of the gas is effected by cold regeneration (E. Karwat, Erdöl trad coal, natural gas and petrochemical 17.439-447; (1964)).

BATH ORIGINAL

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There are 3 cold storage tanks in alternation. In the first cold storage takes place the cooling of the incoming gas by releasing the sensible heat to the cold storage mass, whereby various components freeze out and stick to the surface of the storage masses.

In the second cold storage unit, the condensed components are re- evaporated through expansion and possibly flushing and ψ suction at low pressure.

The storage mass is cooled down again in the third cold store Purified gas, the temperature of which has previously been further reduced by a work-performing expansion to a medium pressure.

Certain amounts of CO ₀ , H ₀ O and other impurities can be separated out without difficulty, so that prior intensive cleaning of the coke oven gas is not necessary. The raw hydrogen produced in this way can already be used directly for various purposes. For the production of NH synthesis gas, however, a subsequent liquid nitrogen scrubbing has also been provided so far. This process requires an air separation plant in order to prepare the pure nitrogen as a synthesis gas component and to be able to carry out the fine cleaning of the synthesis gas.

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It has now been found that the air separation unit can be dispensed with. if the nitrogen is cached into the raw gas by means of flue gas. As a result of the elimination of fine cleaning and washing with liquid nitrogen, the raw gas must be cleaned in another way after deep-freezing in the heat accumulators before it is introduced into the ammonia synthesis. According to the invention, this purification consists in eliminating the oxygen content by catalytic combustion of hydrogen, converting the CO in a conversion to H ₀ , washing out the resulting CO ₀ and washing out the residues of CO and CO ₀ in a known manner be methanated. In this way, a synthesis gas with about 1 to 1, 3% inert is generated, as is also common in other processes.

One advantage of the process according to the invention is that the CO in the starting gas can also be used for the synthesis gas. Technical progress consists in adding the nitrogen required for the synthesis gas to the gas in the form of flue gases. This is expediently done before the deep-freeze decomposition, in the CO ₀ , CH. and other impurities can be frozen out, but can in part also take place after deep-freeze disassembly. The costly air separation with its high power requirement is completely avoided.

The flue gas is cooled down before it is mixed with the coke oven gas, in two different ways through direct cooling and washing with water, whereby

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impurities such as SO ₀ and dust are also washed out. The O ₀ content

Ct Δ

of the flue gas means a certain loss of hydrogen in the catalytic combustion, but when using coke oven gas the amount of O ₀ with the flue gas is usually smaller than that already in the coke oven gas.

Ct

handene. In the case of nitrogen-containing raw gases, the flue gas addition can be kept smaller because the nitrogen in the starting gas, in contrast to the previous gas separation processes with liquid nitrogen scrubbing, is retained in the synthesis gas. Instead of flue gas, other gases with a _{high N 0 content can of course also be used.}

Instead of coke oven gas, similar gases, the CO and H ₀ and also higher-boiling components such. B. contain methane, such as

for example refinery waste gases, for the NH "-synthesis.

An arrangement which is particularly advantageous in some cases is obtained when _{a cracked gas is used as the N 0} -containing gas, which is produced by splitting

Ct

of residual gas, coke oven gas or another gas containing hydrocarbons with the help of L, uft. With such an arrangement it is It is possible to make some of the hydrocarbons contained in the coke oven gas usable for the generation of synthesis gas. Advantageously, this Fission gas is already generated under such a pressure that it can be mixed with the compressed coke oven gas before it enters the deep-freeze.

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Let the invention be described in more detail with reference to the flow sheet and the following example explained ^

The only roughly pre-cleaned coke oven gas flowing through line 1 is fed through line 2 with cooled and scrubbed flue gas. The mixture enters the deep-freeze section 4 through line 3, which works with heat storage devices 4a, 4b, 4c. In this plant, the gas is compressed to the required pressure ■, cooled in a memory 4a and purified and cooled by reducing the pressure and the temperature in the turbine 4d the storage mass in the memory 4c from.

The frozen out on the storage mass ingredients are by expansion and exhaust, and possibly rinsing with a CO ₀ - and left and H _o O-free gas, for example, with a small portion of the prepurified gas, 4b removed from the heat storage in the position as residual gas by Line 5 the plant. The pre-cleaned gas (synthesis raw gas) exits through line 6 and, if necessary after the addition of further flue gas, is brought to the appropriate pressure for further gas treatment through line 2 b in the compressor 7.

In the heat exchanger 8, the gas is heated by hot converted gas, and then passed into the catalytic combustion 9, where the temperature increases by reacting the O ₂ with H «as much as for the conversion

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is required. The subsequent conversion of the carbon monoxide with Depending on the CO content, steam is preferably in one or two stages two-stage, executed.

For this purpose, steam is added to the heated gas through line 10 before it enters the first conversion stage 11 arrives with an iron oxide catalyst. That ^ hot convert gas flows through line 12 to heater 21 and on Line 13 to the heat exchanger _8 and through line 14 into the 2nd Kanvertieungsstufe 15, which is useful as a low temperature conversion with a copper oxide catalyst is formed and in which the CO content is reduced to 0.1-0.5% will..

Since the low-CO gas then reaches the CO ₀ scrubbing 16 after further utilization of its sensible heat. This can "preferably be carried out as hot potash washing, which uses part of the sensible heat of the converted gas to regenerate the scrubbing liquid. The scrubbed carbonic acid leaves through conduit 17 the plant. The narrow CO content of the scrubbed gas is now between 0.1 - 0.3%.

This gas passes through line 18 to the heat exchanger 19 and through line 20 to the gas heater 21, where it is brought to the temperature of about 250 ° required for the methanation and through line 22 into the methanation 23, in which the remaining CO and CO _{2 content} is hydrogenated on a nickel catalyst with H ₂ to methane.

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Through line 24, heat exchanger 19, line 25 and after cooling the Gas, the synthesis gas generated in this way reaches the compressor 26, in which the gas is brought to the pressure required for the NH "synthesis 27 ^. That generated ammonia leaves the plant through line 28, while the Sy.itheserestgas is discharged through 29.

Instead of the described gas separation with regeneration, another known gas separation process, which works for example with switchable heat exchangers, can be used.

example

3 For the generation of 1200 t NH _Q , 180 500 coke oven gas are required, to which 27 650 NM of raw gas are to be added. In the deep-freeze decomposition 4, in which this

Mixture is compressed to approx. 5-10 ata, 147 290 Nm raw hydrogen from it with a pressure of about 2, 5 - 5 ata gewonnep, which subsequently

3 can be further processed into pure synthesis gas. Thereby 60 860 Nm fall Residual gas, which is sucked out of the heat accumulator 4c of the regenerative cooler and given off as heating gas.

The gases have the following analyzes:

BATH 109809/1593.

Coke oven gas Flue gas - Synthesis raw gas Residual gas co % j 2.5 11.3 - - 12.60 ° 2 0.5 2.1 - 0.97 0.07 CO 6.0 - 7, 10 0.62 ^H 2 52.0 85.6 67.40 5.82 CH ₄ 25, 5 1.0 * 0.57 74.40 CnHn 1.5 - 4.45 ^N 2 6, 96 23, 72 2.02 Ar 0.04 0.24 0.02

A well-known system with 3 regenerators is provided for deep-freeze decomposition. The coke oven gas / flue gas mixture enters the already cooled one at 10 ata and 35 C, with CO ₀ , HO and higher hydrocarbons practically completely and CH. for the most part remain in solid form on the surface of the Regenrat or Masse. The vapor pressure of the CH. at -187 ° C is 0.057 ata, which at 10 ata corresponds to a residual CH content of 0.57%. The partial pressure of N ₂ in the gas as it emerges from the regenerator 4a is 2,372 ata. It is thus lower than the vapor pressure of N ₀ = 2.5 ata at -187 ° C., so that no N _{0 is} condensed.

In turbine 4d, the gas is expanded to 5 ata while performing work, with the temperature goes down to 191 C. The handling 4e is used for the exact setting the desired temperature. At -191 C the vapor pressure of the CH is. 0.037 ata. The CH partial pressure in the gas behind the turbine is Q, iO285 ata,

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from which it can be seen that no further deposition of solid CH ₄ occurs. At this lower temperature, the gas flows through the regenerator 3, cools it down and heats itself up to approx. 31 ° C.

The regenerator 4b, in which the gas mixture has just been cooled with the condensation of the higher constituents, is regenerated to a pressure of about 0.3 ata by decompression and suction, the like

where COgi H _? O, CNHm and CH ₄ evaporate and take their heat of evaporation from the regenerator mass as it cools down. After this regeneration, the regenerator is then cooled further with the cold gas from the turbine, whereby the gas, which still contains the last CH. and other higher-boiling substances from the regenerator, is added to the residual gas until it is pure enough _{for water processing in the NH 3 synthesis.}

Since the synthesis raw gas already contains the nitrogen required for the synthesis gas is contained, there is no need to add 2 more smoke gas. After compaction to 27 ata and preheating in the heat exchanger 8 to 207 C, the oxygen contained in the gas is converted into hydrogen in the catalytic combustion reactor 9 implemented, the temperature increasing to 362 C. Then be the Gas 47 t of steam (30 ata, 340 ° C) mixed in, so that the mixture with 355 C in

the first conversion stage 11 occurs, in which / by the reaction to

380 ° C heated,

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_ ₁₀ _ 159235a

After submitting palpable. Heat in the heater 21, the heat exchanger 8 and a non-dedicated feed water heater, the gas enters the low-temperature conversion stage 15 at 218 ° C. The finished converted gas has only 0.18% CO (based on dry gas). After using its tub for feed water heater 1.md for the regeneration of the washing liquid of the subsequent COgWäscne, it enters the CO ₂ wash 16 at 100 C, in which the carbon dioxide is reduced to a residual content of 0.15% by washing with hot potash solution Will get removed. The scrubbed gas is heated in the heat exchanger 19 and the heater 21 and enters the methanation at 300 C, in which the residues of CO and CO ₉ bits are converted to a maximum of 10 ppm with hydrogen. The analysis of the synthesis gas prepared in this way is

H ₂ % 74.10

N ₂ 24.70

CH ₄ o.95

Ar pO, 25

The amount of synthesis gas is 141.500 Nm / h.

By exploiting its heat in the heat exchanger 19 and, after further cooling and drying of the gas in the Synlliesegasverdihhter 26 is 24 ata 3 ^r '- compacted ata and so enters the NHL synthesis 27, in which H ₂

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and convert N "to NH". The synthesis residual gas, which is used to remove the inert Components CH. and Ar must be released, can be used as fuel gas, e.g. for steam generation, and e.g. with the exhaust gas from the Cold storage 4 b are combined.

- 12 claims

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Claims (4)

Claims 1.) A method for converting carbon monoxide hydrogen and methane "contained gases such as coke oven gas, refinery gas, cracked gas or the like. Zui an ammonia synthesis gas, characterized in that the raw gas according to the required N ₂ : H ₂ ratio S« M 3 £ ehgats % eil Np-rich flue gas or cracked gas is added, and that the Mixture in a known (regenerative system from cold storage to extensive condensation of methane, then freed of oxygen by catalytic combustion with hydrogen, then enriched in the hydrogen content by converting the carbon monoxide it contains with water vapor and after washing out most of it of the carbon dioxide is finely purified by hydrogenation of the residues of CO ₀ and CO to methane. Ct 2.) The method according to claim 1, that a gas generated by splitting coke oven gas, residual gas, refinery off-gas or other hydrocarbon-containing gases with air is used _{as the N 2 -rich flue gas.} 3.) The method according to claim 2, characterized in that the cleavage takes place under such a pressure that the cracked gas can still be fed to the crude gas mixture compressed before the freezing. 109809/1593 -13- 4.) The method according to claim 1 to 3, characterized in that a part of the flue or fission gas is introduced into the raw gas mixture after deep freezing. BATH 109809/1593 Lee r be e