CS258273B1 - Method of ammonia production - Google Patents

Abstract

The solution concerns the production of ammonia from a nitrogen synthesis synthesis mixture at which hydrogen is obtained by hydrocarbon gasification raw materials with oxygen and steam, whereupon is mixed with pure nitrogen to synthesize a mixture that results in ammonia synthesis the hydrocarbon feedstock is gasified by technical oxygen containing not more than 1.25 mol%, preferably 0.25 mol% 0.8 mol%, argon.

Description

BACKGROUND OF THE INVENTION The present invention relates to the production of ammonia from a hydrogen synthesis synthesis mixture which is obtained by mixing technically pure hydrogen and nitrogen, wherein hydrogen is obtained by gasifying the hydrocarbon feedstock with an oxygen-steam mixture.

Oxygen for gasification is usually obtained by rectification of liquefied air, where nitrogen is separated and oxygen is usually about 3 mol% of argon, in hydrogen production by gasification of petroleum residues with oxygen and water vapor argon remains in hydrogen in the amount of 0.41 to 1% mole, which is reflected in the nitrogen synthesis mixture values of 0.31 to 0.75 mole%.

Argon is an inert gas which, together with methane from the gasification of a hydrocarbon feedstock in the production of hydrogen, which also has the character of an inert gas under synthesis conditions, accumulates in the ammonia synthesis gas in the circulating gas, causing part of the circulating gas to be vented and replaced fresh hydrogen. The amount of circulating gas to be discharged is directly proportional to the amount of inert gases present in the fresh synthesis nitrogen gas mixture, which thus directly affects the specific consumption of hydrogen and nitrogen for ammonia production.

To reduce the consumption of hydrogen and nitrogen for ammonia production, the discharged circulating gas from the ammonia production is therefore post-treated to separate the accumulated inert constituents and the hydrogen or possibly nitrogen can be returned to the synthesis. Several methods are known for this purpose, for example cryogenic at low temperatures, separation of components on molecular sieves or semipermeable membranes, or, finally, the additional conversion of hydrogen and nitrogen from the purged circulating gas in separate ammonia synthesis under deteriorated reaction conditions.

All of these known methods have the disadvantage that in order to utilize a portion of the hydrogen and nitrogen from the discharged circulating gases from the ammonia synthesis, they require the construction of new equipment and further energy use. They are used in particular when, in addition to nitrogen and hydrogen, some other inert gas constituents are recovered from the circulating gas to cover these extra costs.

We have now found a method for the production of ammonia, which newly solves the issue of the quality of the circulating gas of ammonia synthesis. A process for the production of ammonia from hydrogen and nitrogen, wherein hydrogen is obtained by gasifying a hydrocarbonaceous feed with oxygen and steam, then mixed with pure nitrogen to form a synthesis mixture which leads to the synthesis of ammonia and circulates as a circulating gas according to the invention The hydrocarbon feedstock for hydrogen production is gasified with technical oxygen containing not more than 1.25 mol%. % of argon, preferably up to 0.8 mol%. argon.

Under the usual conditions of rectification of liquefied air, oxygen containing 1.5 to 3 mol% is generally obtained. argon. The rectification conditions are mainly determined by the requirement for an optimum energy mode of rectification, taking less account of the oxygen quality that is sufficient for the desired purposes.

In the ammonia production process according to the invention, however, the improvement in oxygen quality results in savings in the following technologies, both in the production of hydrogen and nitrogen, and in the production of ammonia, by reducing the oxygen consumption to gasify the hydrocarbon fractions for hydrogen production. the consumption of energy for its production and compression, the consumption of hydrogen and nitrogen for the production of ammonia is reduced, and hence the consumption of energy for the production of hydrogen and nitrogen and their compression is also reduced.

A further benefit will be in reducing the amount of circulating gas discharged, which is usually used for heating purposes, which is uneconomical in terms of the components it contains, especially hydrogen. The lower hydrogen consumption results in a positive reduction in the amount of hydrocarbon fractions, eg black oil, for gasification.

With regard to improving the oxygen quality to an argon content of not more than 1.25 mol%, it can be achieved on existing equipment in several ways, eg by increasing the backflow ratio in the overhead column rectification product, reducing the oxygen recovery from air and increasing the column hydraulic load. While this will somewhat reduce the economic efficiency of rectification of liquefied air, the savings in subsequent technological processes, however, greatly exceed these losses. Improvement of oxygen quality can also be achieved by reconstruction of rectification columns or by construction of new equipment. A reduction in the argon content of oxygen of up to 0.25 mol% can be achieved.

This reconstruction or construction of a new plant is justifiable, provided that the oxygen produced is used predominantly for the oxy-steam cleavage of the hydrocarbon feedstock and for the production of hydrogen for the production of ammonia.

The process for producing ammonia according to the invention is further described in an example which compares the present state of the art with the process according to the invention and demonstrates the effects achieved.

Example

For the production of 1 t ammonia, the following parameters are used in the normal technological regime:

Oxygen composition:

oxygen content: argon content: nitrogen content:

96.75 mol%. 1.75 »mol. 1.50% inol.

Hydrogen gasification of the black oil using the following technical oxygen produced hydrogen of the following composition:

Hydrogen composition:

mixture

hydrogen content: 97.96 mol% Argon content: 0.47 mol% methane content: 0.77 4 mol. nitrogen content: 0.80 i mol. By mixing this hydrogen with nitrogen Nitrogen composition: nitrogen content: 99% hydrogen content: 1% Composition obtained synthesis mixtures: nitrogen content: 24.77% mo. hydrogen content: 74.29 mol%. methane content: 0.58 mol% argoh content: 0.36 mol%

Passing this mixture through the synthesis loop and producing 1 ton of ammonia gave the following results:

consumption of synthesis mixture:

of which:

hydrogen consumption: nitrogen consumption:

729,05 m

062.78 m ^J 666.27 m ³ Amount of discharged gases: 83.12 m

Composition of vented gases mol. %:

nitrogen content: 18.08 mol% hydrogen content: 54.20 mol% methane content: 14.75 mol% Argon content: 10.65 mol% Ammonia content: 2.32 mol%

After adjusting the technological regime in the production of oxygen, which led to a decrease in the argon content, the technological regime in the monitored values was as follows:

Case 1 Case 2 Case 3

oxygen composition (mol%) oxygen content 97.35 97.70 98.13 argon content 1.35 1.20 1.12 nitrogen content 1.30 1.10 0.75

hydrogen composition (mol. S)

hydrogen content 98.06 98.11 98.11 argon content 0.37 0.33 0.30 methane content 0.77 0.79 0.78 nitrogen content 0.80 0.80 0.80 composition of the synthesis mixture (mol%) nitrogen content 24.79 24.79 24.80 hydrogen content 74.35 74.35 74.38 methane content 0.58 0.60 0.59 argon content 0.28 0.26 0.23

The nitrogen to form the synthesis mixture had the same composition as in the normal process mode.

The following results were found when the synthesis mixture was passed through the synthesis loop and for the production of 1 t ammonia:

Case 1 Case 2 Case 3 Synthesis Consumption (m ^)

720.12

715.74

Of which:

hydrogen consumption 2 055.48 2,051.90 2,051.79 nitrogen consumption 664.64 663.84 663.81 amount of vented gases: 73.83 69.29 69,11 composition of vented gases (mol%) nitrogen content 18.08 18.08 18.08 hydrogen content 54.20 54.20 54.20 methane content 16.24 16.80 17.40 argon content 9.16 8.60 8.00 content of ammonia 2.32 2.32 2.32

Over the entire production area, from the oxygen production node to the synthesis loop, these savings were achieved (compared to normal technology) - with 1,000 tonnes of ammonia produced daily.

Case 1

Case 2

Case 3

saving el. energy (kWh / day) 4 538 6 636 6 959 savings of black oil (t / day) 2.5 3.82 3.86 loss on calorific value (GJ / day) 74.7 119.7 105.8 Loss of el. energy at oxygen plant (for production of better oxygen) (kWh / day) 4 459 4 976 5 317 energy cost savings for ammonia production (%) 0.23 0.36 0.38

The total savings also include savings on steam and cooling water. This item is not shown separately in weight units here.

The share of savings in total savings on raw materials and energy is based on the total cost of the entire production line from the oxygen plant to the synthesis loop.

Case 2 and Case 3 differ slightly, since, in addition to the decrease in argon content, there is a slight increase in methane in comparison with Case 1.

Claims (1)

object of the invention A process for producing ammonia from hydrogen and nitrogen, wherein hydrogen is obtained by gasifying a hydrocarbonaceous feedstock with oxygen and steam, followed by mixing with pure nitrogen to a synthesis mixture which leads to synthesis and circulates as a circulating gas, characterized in that the hydrocarbonaceous feedstock for production. The hydrogen is gasified with technical oxygen containing not more than 1.25 mol%, preferably 0.25 to 0.8 mol%, of argon.