DD208412A1 - METHOD OF DISPOSING AN ARGONIC NITROGEN METHANE MIXTURE - Google Patents

Abstract

A process for the decomposition of an argon-nitrogen-methane mixture, which was obtained from flash gases of synthetic processes, preferably the ammonia synthesis and optionally an argon-containing, pretreated fraction of an air separation plant was mixed in an argon-rich fraction while obtaining highly enriched nitrogen and methane by cryogenic rectification in a single separation column. This is achieved by removing the argon-rich fraction as a side stream, the highly enriched nitrogen as the top product and the highly enriched methane as the bottom product from the separation column.

Description

VEB Leuna-Werke 'Leuna, 20. 8. 1982

"Walter Ulbricht"

LP 8250

Title of the invention

Process for the decomposition of an argon-nitrogen-methane-Geraisch it

Field of application of the invention

The invention relates to a rectificative process for obtaining an argon-rich fraction and highly enriched nitrogen and methane by decomposition of an argon-nitrogen-methane mixture obtained from flash gases of synthetic processes, preferably a Aminoniaksvnthese, and the optionally an argonhaitiiie, pretreated fraction of an air separation plant admixed has been.

Characteristic of the known technical solutions

Methods for the decomposition of flash gases with the main components hydrogen, nitrogen, argon and methane are known. Common to all these processes is the fact that in each case one component is isolated in each case in the order of its volatility. "Hach appropriate pretreatment of the Sntspannungsgases (DD-PS 122 368, 135 115 and 146 579) is in a first separation column or a separator the hydrogen dissipated «

¹ ft "J ξ" 3 ϊ? Ί 13

_ ₂ "tiuyyi ν

The remaining bottom product is fed into a second separation column, the methane withdrawn at the bottom and fed to the braid nitrogen-argon mixture supplied to a third separation column at the bottom of argon obtained (Technique H, (1959) 6, 438; Chem * Technik Ij (1967) 8 »449; Air and Refrigeration 2 (1980) 83).

Another method (GB-PS 901 580) provides for the removal of nitrogen from the top of the second separation column, while the bottom product consisting of argon and methane is decomposed in a third separation column and argon is withdrawn at the top thereof.

Another possibility is given by obtaining three fractions in a first separation column (US Pat. No. 3,333), where at the bottom the main amount of methane, at the top the hydrogen and argon, nitrogen, including portions of methane, oxygen and carbon oxide, are withdrawn as side stream This sidestream is fed to a second separation column, where an argon contaminated with nitrogen, methane, oxygen and carbon monoxide is recovered at the bottom. After a chemical purification of this bottom product, the remaining nitrogen-argon mixture is fed to a third separation column Swamp "highly enriched argon is recovered *

The methods mentioned are very complex in terms of apparatus and / or energy and, due to the stepwise isolation of the individual components and the resulting large product streams, result in considerable losses of argon with the individual components or fractions.

Object of the invention

The aim of the invention is to reduce the product flows and to reduce the argon losses in the recovery of argon from flash gases by multistage cryogenic rectification.

Explanation of the essence of the invention

3s was thus the task, by changing the product supply and - removal on the separation column for the decomposition of the argon-nitrogen-methane mixture. to make the extraction of argon through cryogenic rectification more favorable «

This object is achieved by a process for the decomposition of an argon-nitrogen-methane mixture, which was obtained from flash gases of synthesis processes, preferably ammonia synthesis, and if necessary an argon-containing, pretreated fraction of an air separation plant was zugemisGht in an argon-rich fraction while obtaining highly enriched Nitrogen and methane inventively achieved in that the decomposition of the varying in its amount and the concentrations of its components mixture takes place in a single separation column, wherein the mixture introduced in liquid or gaseous form in the separation column, the argon-rich fraction in liquid or gaseous form as side stream, the highly enriched nitrogen as liquid or gaseous top product and the highly enriched methane as Suinpfprodukt be taken from the separation column - the argon-nitrogen-methane mixture, the up to 2% by weight Y / erstoff ent and in which the concentrations of the argon in the range of 15 to 30 mol% of the nitrogen in the range of 10 to 55 1Kol-% and the methane in the range of 30 to 60 Mo1- $ fluctuate, is preferably at a pressure of approx 350 to 400 kPa and a temperature of approx. 100 K Few trays fed into the separation column above the sump «Between the middle of the separation column and the beginning of the upper third, the sidestream is drawn off at a point where it discharges more than 75 mol. % Argon contains'' ^Oe : L ca' 97 K, preferably in liquid form. "With increasing reflux ratio the argon content can be raised to more than 99 mol / 3 · The side stream of the separation column contains less than 1.10 *" ° Mo 1- $ methane, the head product

less than 0.05 Mo1- $ argon and the bottom product less than 0.2 mol% argon. "The reflux ratio of the separation column will be according to the argon content in the side stream, and the amount and rate of side stream withdrawal will depend on the argon content of the argon nitrogen -Methane mixture regulated. The argon-rich fraction may be added to another column for additional concentration. "

embodiment

58 kmol / h of a composition of gas fluctuating in composition by an average of 32 mol% of nitrogen, 22 mol% of argon and 46 mol% of methane were placed in a separating column consisting of 30 plates at 100 K and 375 kPa on 27 · Fed into the soil (calculated from the head of the separation column). The methane-rich bottoms product with less than 0.3 mol% argon and nitrogen was drawn off liquid (about 27 kmol / h). At a minimum reflux ratio of 3? which was applied here in modified form as the ratio of the sum of all liquid molar amounts to the sum of all gaseous molar amounts at the condenser, a liquid sidestream (~ 17 kmol / h) at 97 K at 16 ° C. was found, with an average of 81 molar argon dissipated «The argon content can be raised to over 99 mol% as the reflux ratio is increased. The remaining 14 kmol / h of nitrogen with a residual argon content of 0.035 mol% were taken off at 90 K at the top of the column, optionally liquid or gaseous.

Claims (5)

η ο Erf indungsanspicucrr - U '-J "ί ί ^ * 1, Process for the decomposition of an argon-nitrogen-methane mixture, which was obtained from flash gases from synthesis processes and optionally admixed with an argon-containing, pretreated fraction of an air separation plant, in an argon-rich fraction while simultaneously obtaining highly enriched nitrogen and methane by cryogenic rectification, characterized in that the decomposition of the mixture, which varies with respect to its quantity and the concentrations of its components, takes place in a single separation column, the Gemis.ch being introduced into the separation column in liquid or gaseous form, the argon-rich fraction in liquid or also gaseous form as side stream highly enriched nitrogen as liquid or gaseous top product and the highly enriched methane as bottom product are removed from the separation column * 2 »Process according to item 1, characterized in that the .Geschisch up to 2 mol% of hydrogen and the concentrations of the argon in the range of 15 to 30 Mo1-% and the methane in the range of 30 to 60 mol% fluctuate - 3. The method according to Pkt · 1 and 2, characterized in that the introduction of the mixture into the separation column a few floors above the bottom and the removal of the side stream between the middle and the 3eginn the upper 'third of the column, at a point at which the side stream contains more than 75 mol% of argon, » 4. The method according Pkt * 1 to 3, characterized in that in the side stream of the separation column less than 1 * 10 * "° Moi% methane, in the head product 'vveniger than 0.05 i / Iol-% argon and.im Bottoms are less than 0.2% by mole of argon enthalxen * 5. The method according Pkt «1 to 4>, characterized in that the reflux ratio of the column according to the argon content in the side stream and the amount and speed of the side stream withdrawal depending on the argon content of the argon-nitrogen-methane mixture are regulated»