JPH03115117A - Substance application of residual gas in rare gas apparatus - Google Patents

Abstract

PURPOSE: To use the remaining gas produced under a low pressure for an ammonia plant without requiring any extra compression cost by feeding the remaining gas from the rare gas device to an ejector and using the gas flow as a driving medium, performing compression to the pressure of a refoaming process, and returning the gas to a production part for synthetic gas.

CONSTITUTION: Hydrogen for synthesis is manufactured by a steam reforming method from a raw material containing hydrocarbon and the product ammonia is separated from the synthetic circulating gas by partial condensation. Then, circulating flash gas is further processed by a downstream hydrogen recovery device and/or the rare gas device and a gas flow having a pressure higher than the pressure of the refoaming process is sent as the raw material of the refoaming process in this ammonia plant. Namely, the remaining gas from the rare gas device is sent to the ejector, where the gas flow having higher pressure than the pressure of the refoaming process is used as the driving medium for compression to the pressure of the reforming process. Then, it is returned to the synthetic gas production part before the refoaming process.

COPYRIGHT: (C)1991,JPO

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a gas that is produced at low pressure in a rare gas equipment downstream of an ammonia plant and contains mainly hydrogen, nitrogen, methane, and other components as well as a small amount of argon. Concerning how to use substances.

This method can be applied to an ammonia plant where the recycled flash gas is processed in a downstream hydrogen recovery unit and the remaining gas fraction is sent to a rare gas unit.

BACKGROUND OF THE INVENTION Most of the ammonia currently produced is based on syngas obtained by steam re-forming or partial oxidation of hydrocarbons.

The mainstream is the natural gas space ammonia plant developed in the 1960s and 1970s. The following description therefore refers to a natural gas space plant, but is equally applicable to other hydrocarbon-based ammonia plants.

The production of ammonia by the steam re-forming process is
Usually divided into the following process steps:

1. Compression of raw natural gas; 2. Desulfurization of natural gas; 3. - Adding water vapor with the next former to convert most of the hydrocarbons in natural gas into hydrogen, - carbon oxide and carbon dioxide; 4. A secondary reformer adds process air to further convert methane into hydrogen, carbon oxide, and carbon dioxide. 5. A two-stage carbon monoxide converter usually converts carbon monoxide into carbon dioxide. 6. A special absorption tower. 7. Convert the remaining carbon oxides and carbon dioxide contained in the gas into methane in the methanation process. 8. Synthesize the synthesis gas as required. 9. Partial conversion of hydrogen and nitrogen in the synthetic recycle gas to ammonia.

10. Separation of product ammonia from synthetic recycle gas, 11.
Separation of synthetic recycle gas to remove inert methane and rare gas, 12, Recovery of hydrogen and rare gas from separated synthetic recycle gas, 13
, recompression of synthesis recycle gas, and generation of synthesis gas are typically carried out at pressures of 2.5 to 5 MPa. It is known that the raw natural gas often has a fairly high pressure at the battery limit and is therefore allowed to expand up to the pressure of the synthesis gas generator. Most raw natural gas contains a small amount of sulfur, and since this sulfur acts as a catalyst poison in the subsequent steps, it is necessary to remove the sulfur with a desulfurization device. For this purpose, e.g.
For small sulfur contents in the range up to g/Nm3, it is customary to use zinc oxide, which forms zinc sulfide and scavenges hydrogen sulfide. However, not all the sulfur is present as hydrogen sulfide, but some of it is also bound as organic sulfur, for example in the form of mercaptans, so that it must first be converted to hydrogen sulfide with hydrogen. The hydrogen required for this is usually recycled from an intermediate stage of the synthesis gas compressor at a pressure of usually 5 to 10 MPa (as is known). Since this gas is returned to the synthesis gas generator, it must be expanded to intermediate pressure.This expansion takes place without using the existing pressure difference as energy.Natural gas The remaining amount of methane is reduced from 1O to 12% by volume by converting the hydrocarbons contained in the
To do this, use a fuel-heated tube furnace at a temperature of approximately 800°C.
That is, it is mixed with excess process steam in a so-called next reformer. In the downstream secondary reformer, unconverted methane is converted to a residual amount of approximately 0.5% by volume. It is done using. In the downstream usually two-stage carbon monoxide conversion process, the carbon monoxide contained in the gas is converted into hydrogen and carbon dioxide by water vapor at 2[)0°C to 450°C, and the remaining amount is 0.2
0.5% by volume. The removal of carbon dioxide is carried out in special columns by washing with a chemically and/or physically acting washing liquid, the residual amount of which is approximately 0.
It becomes 1% by volume.

Carbon monoxide and carbon dioxide remaining in the gas act as catalyst poisons in ammonia synthesis, so the minimum amount, usually 10N, is
g/Nm” or less.

In most cases, this removal is done at approximately 300°C during the methanation step.
This is done by converting these carbon oxides to methane using hydrogen at temperatures between 350°C and 350°C. After this process step, the synthesis gas reaches its final composition for ammonia synthesis. That is, synthesis gas contains hydrogen and nitrogen in a ratio of 3:1, as well as small amounts of methane, typically 0.5 to 1.5% by volume, and rare gases, primarily argon, from 0.3 to 0.7% by volume. It is contained in a range of % by volume. Here, methane is derived from residual methane from primary forming and/or secondary refluxing, residual carbon oxide from the carbon oxide conversion process, and residual carbon dioxide from the carbon dioxide removal process, as described above. The active gas is mainly introduced along with the process air supplied to the secondary reforming and partly along with the raw material natural gas. Methane and rare gases act as inert gases in the ammonia production reaction, so they accumulate in the synthesis circulation system.

Therefore, it is necessary to continuously remove the same amount of inert gas as enters the synthesis circulation system. This removal depends on the current technical situation, for example in the case of separating ammonia from the synthesis recycle gas by partial condensation, on the one hand by dissolving it in the product ammonia, which dissolves the synthesis pressure Depending on the permissible concentration of inert gas in the synthesis recycle gas and the inert gas concentration, up to 50% of the inert gas can be removed. Furthermore, this removal is carried out by diverting a portion of the synthesis recycle gas, the so-called recycle flash gas, to the other side. This amount of recycled flash gas is generally less than 5% of the synthesis gas fed to the synthesis loop. This recycled flash gas is usually first cooled to minimize its ammonia content. In the past, it was customary to partially utilize this gas for energy purposes only as fuel gas in reforming.

However, since then most ammonia plants have at least some downstream equipment for recovery of the hydrogen contained in the gas. The principle of most of these devices is to remove the residual ammonia contained in the recycled flash gas to be treated, for example by cooling to separate the condensed ammonia and/or by drying the gas after washing with water. Cooled by external refrigeration using a separate refrigeration circulation system or by own refrigeration using the Joule-Thomson effect (e.g. D D47.120) to a temperature at which methane, rare gases and nitrogen condense and hydrogen remains in gaseous form. In both cases, a hydrogen fraction consisting mainly of hydrogen and containing a small amount of nitrogen as well as methane and rare gases in the range of a few percent;
A residual gas fraction consisting of methane, rare gases and nitrogen and a small amount of hydrogen is obtained.

This small amount of hydrogen was partially dissolved in the initial liquid mixture of methane, rare gas, and nitrogen. Furthermore, it is also possible to separate hydrogen using a separation membrane (for example, D
C-O32,910,742+, this method yields a hydrogen-rich gas with a composition similar to cryogenic separation methods. However, the hydrogen loss is higher than the above method, in other words, 40% by volume.
The pressure of the hydrogen recovery device, which produces a higher residual gas fraction with a hydrogen content of less than or equal to 100% hydrogen, is generally selected to be such that the hydrogen fraction obtained can be fed to the suction side of the synthesis gas compressor. The residual gas produced in the above-mentioned process is often used only energetically as fuel gas, for example in the primary foaming of an ammonia plant. However, since the amount of rare gas in this gas is generally between 15 and 25% by volume,
This gas can be subjected to further low-temperature separation to obtain argon and other rare gases contained in the gas in highly pure form, while other gas components are also obtained as relatively pure fractions.

This cryogenic separation is generally carried out using a separate cooling circulation system.

In addition to liquid argon products and other rare gases (e.g. krypton and xenon), this rare gas device is capable of producing hydrogen/nitrogen fractions with a hydrogen content of 40 to 80% by volume and small amounts of argon and methane, with a methane content of 95% by volume. % methane fraction, and nitrogen fractions of varying purity, but generally less (both 95% by volume), the utilization of these gas streams is very limited due to relatively low pressures. These gas streams are generally generated at pressures of 0.4 MPa to 1 MPa.

Its use, for example in an ammonia plant, is therefore only possible after further compression. Separated methane is usually used as fuel gas in ammonia plants. For this purpose, compression to the fuel gas pressure is necessarily required. The nitrogen generated is sent to the low-pressure nitrogen supply network or is recycled, in whole or in part, to the ammonia plant together with the hydrogen/nitrogen fraction. The connection of these return gases to the ammonia production process depends on the pressure of the return gases and the pressure of the natural gas sent to the ammonia plant. If the differential pressure between return gas and natural gas is positive, the connection is made on the suction side of the natural gas compressor. If the differential pressure is not positive, further compression must be applied to raise the pressure to at least the suction pressure of the natural gas compressor.

[Problems to be Solved by the Invention] The purpose of the present invention is to add various residual gases, which are composed of components such as hydrogen, nitrogen, methane, and argon, and are produced at low pressure in rare gas equipment that processes recycled flash gas. The objective is to utilize the material in the synthesis gas generation section of an ammonia plant without requiring additional compression costs.

[Means for Solving the Problems] An object of the present invention is to provide a method that makes it possible to utilize the residual gas of a rare gas device for treating recycled flash gas of an ammonia plant without requiring additional compression costs. It is to be.

According to the invention, this problem is solved when a part of the recycled flash gas generated in the ammonia plant is returned to the synthesis gas generation section after further cooling to separate the condensed ammonia or after removing the ammonia through a water washing device. Higher pressure than this reforming process, preferably 4.0-40
The recycled flash gas of MPa, more preferably 20 to 30 PMa, is passed through a jet compressor by utilizing the pressure difference between it and the synthesis gas generation section (the reforming process is preferably carried out under a pressure of 2.5 to 4.5 PMa). This can be solved by using it as a driving gas for the ejector.

By this jet compressor, various gas flows (preferably from 0.2 to 1.3 MPa, more preferably from 0.4 to 0.0 MPa), consisting of components such as hydrogen, nitrogen, methane, argon, etc. generated in the rare gas device, are (under pressure) is compressed to a pressure that allows it to be connected to a synthesis gas generator.

Components such as hydrogen and nitrogen contained in the recycled flash gas and the gas from the rare gas equipment can be used for ammonia synthesis without any of the necessary compression of natural gas or process air and the consumption of raw materials or energy required for methane decomposition. It can be used as a raw material.

In contrast to the return noble gas, which is sent back unchanged to the synthesis cycle along with the synthesis fresh gas, methane, which acts as an inert gas in the synthesis cycle, is used for subsequent forming and/or secondary reforming. Since it is converted into hydrogen and carbon monoxide by the steam re-forming reaction in the equipment, it no longer reaches the synthesis circulation system together with the new synthesis gas.

According to the present invention, any gas can be used as the driving gas for the jet compressor as long as it has sufficient pressure and is sent to the synthesis gas generation section in sufficient quantity (e.g., in addition to the above-mentioned recycled flash gas, organic sulfur conversion synthesis gas from the intermediate stage of the synthesis gas compressor for use in the production of synthetic gas (or natural gas).

As a typical example, instead of a hydrogen-containing gas such as the above-mentioned recycled flash gas, as a driving gas for the ejector,
A hydrocarbon-containing gas, preferably at a pressure of 5 to 10 MPa, as a raw material gas for the reformer unit can also be used.

[Example] The present invention will be explained in detail with reference to an example. Figure 1 shows an ammonia plant, hydrogen recovery equipment 12, and rare gas equipment 13.
This shows a complex system consisting of Approximately 38.00 ONm3/h of natural gas is sent to the ammonia plant via line 20 as a raw material for ammonia production, and about 4
Compressed to MPa. This gas is sent through line 21 to the desulfurization unit 2, and after approximately 6.850 Nm”/h of gas consisting of recycled flash gas and gas from the rare gas unit 13 is added through line 43, a two-stage cleaning process is carried out. The residual amount of sulfur is reduced to 0.5 mg/Nm" or less. This gas is mixed with approximately 100 t/h of process steam from line 23, and a portion is passed through line 22 to the reformer 3.
send to Catalytic conversion of methane takes place here, resulting in a methane content of approximately 11.5% by volume. When this gas is sent to the secondary reformer 4 through line 24, further conversion of methane takes place, and the remaining amount of methane becomes about 0.3% by volume. The approximately 55.00 ONm"/h of process air required for this purpose is sent through line 25. This crude synthesis gas is sent via line 26 to a two-stage conversion step 5, where the previously formed carbon monoxide is The carbon dioxide is converted into hydrogen and carbon dioxide, with a carbon oxide content of approximately 0.3% by volume.The carbon dioxide-rich gas is sent via line 27 to the carbon dioxide removal unit 6.By activated hot potash solution, the carbon dioxide is is removed from the crude synthesis gas to a residual volume of 0.1% by volume, followed by line 2
Step 8 leads to methanation step 7, where remaining carbon monoxide and carbon dioxide are converted to methane by hydrogen.

Approximately 90
a hydrogen fraction of about 3.900 Nm"/h containing % hydrogen by volume and about 600 Nm"/h containing about 50% hydrogen by volume sent from inert gas unit 13 via line 39.
After mixing with 3/h of hydrogen/nitrogen fraction, the synthesis gas is sent via line 29 to the synthesis gas compressor 8 at a pressure of about 30 MPa.
6 Synthetic recycle gas is compressed into lines 30 and 3.
1. The supply to the ammonia reactor 1O takes place via line 32. Catalytic conversion of hydrogen and nitrogen into ammonia occurs in this reactor 10. After cooling the synthetic recirculation gas and condensing liquid ammonia, the synthetic recirculation gas is sent to the separator 11 through a line 33, where liquid ammonia is formed. Approximately 1520t/d is separated. Before the synthetic recycle gas is recycled through the line 34 to the synthetic recycle gas compression step 9, about 6,000 Nm3/h is extracted from the line 35 to the hydrogen recovery device 12, and an additional 6,000 Nm3/h is transferred to the line 36. is sent to the jet compressor 14 through the The hydrogen recovery device 12 performs low-temperature separation of the recycled flash gas. The hydrogen fraction is returned to the ammonia plant via line 38. The remaining residual gas fraction of about 2.00 ONm 3 /h is sent to the rare gas device 13 via line 37 . Here, further low-temperature separation is carried out, and the product argon (approx. It will be sent back. Nitrogen fraction (approximately 3t/d)
are provided for their respective uses from line 4o.

Consists of methane fraction and generated residual gas, approximately 77% by volume of methane, approximately 9% by volume of hydrogen, approximately 9% by volume of nitrogen, and approximately 5% by volume of argon.
A gas mixture at a pressure of 1.0 MPa (approximately 85 ONn+"/h) having a composition of Approximately 4.4MPa
It is returned to the discharge side of the natural gas compressor 1 via the line 43 at a pressure of .

[Effects of the Invention] The present invention relates to a method for materially utilizing gas from a rare gas device in an ammonia plant.

According to the method of the invention, the gases (methane, hydrogen, nitrogen, argon) produced in the rare gas installation at low pressure are returned to the synthesis gas generation part of the ammonia plant without additional compression costs. The compression required for this purpose is performed by a jet compressor (ejector) with gas as the driving medium and is sent to the reforming process at a pressure higher than the actual pressure.

By applying the present invention, the power of the natural gas compressor can be reduced by about 2%,
Furthermore, the amount of raw material natural gas can be reduced by 2%.

4,

[Brief explanation of drawings]

Figure 1 shows a complex system consisting of an ammonia plant, hydrogen recovery equipment and rare gas equipment. In the figure, 1...Natural gas compressor 2...Desulfurization process 3...-Next reformer-4...Second reformer-5...Conversion process 6...Dioxide Carbon removal device 7... Methanation process 8... Synthetic new gas compression process 9... Synthetic recycled gas compression process 10... Ammonia reactor 11... Separator 12... ... Hydrogen recovery device 13 ... Rare gas device 14 ... Jet compressor (ejector) 20-4
3...Represents each line.

Claims (1)

[Claims] 1. Hydrogen for synthesis is produced from raw materials containing hydrocarbons by a steam reforming method, and at the inlet of the synthesis circulation system, the synthesis gas contains inert gases, especially rare gases and methane, and The ammonia is separated from the synthesis recycle gas by fractional condensation, and the recycle flash gas is further processed in a downstream hydrogen recovery unit and/or rare gas unit, with one or more In an ammonia plant that requires a gas stream to be delivered as feedstock for this reforming process, hydrogen, nitrogen, argon,
The residual gas from the rare gas system, which contains components such as methane and has a pressure lower than the reforming process pressure, is sent to an ejector where it is injected into one or more gas streams with a pressure higher than the reforming process pressure. using as the driving medium,
A method for utilizing residual gas from a rare gas equipment in an ammonia plant as a material, characterized by compressing it to the pressure for a reforming process and then returning it to a synthesis gas generation section before the reforming process. 2. Using a hydrogen-containing gas as the driving medium, and circulating this gas from parts of the plant downstream of the synthesis gas generation section, in particular from the synthesis gas compression step and the synthesis circulation step, to the synthesis gas generation section before the desulfurization step. A method according to claim 1, characterized in that: 3. The method according to claim 1, characterized in that a hydrocarbon-containing gas is used as the driving medium and this gas is sent upstream of the desulfurization step as a raw material for a synthesis gas generation section.