FI78173C - Ways of producing so-called. master gas - Google Patents

Description

78173

The so-called method to produce a sample gas

The present invention relates to a process for the preparation of concentrated gas, so-called for the preparation of a model gas containing oxygen and a perfume in the form of an organic sulfur compound, e.g. dimethyl sulfide, DMS, and used for perfuming oxygen gas for use in the shipyard and other workshop industries.

Patent application FI-871046 describes a procedure for adding a perfume to oxygen gas to draw the attention of the environment to the risk of explosion if oxygen enrichment occurs in the air. According to the described method, concentrated gas is produced in special rooms, the so-called a sample gas by adding to the pure oxygen gas a perfume in the form of an organosulfur compound, e.g. dimethyl sulfide DMS having a concentration of 1,000 to 10,000 ppm. The sample gas is then added to the oxygen gas, which is distributed to the user so that the amount of perfume in the operating gas has a concentration of 5-50 ppm. The concentration of DMS in the flue gas tank is the highest possible, partly due to the risk that the DMS may condense in the tank, partly due to the risk that the mixture may ignite and burn due to unauthorized pressure rise or that the tank steel may ignite.

In the case of condensation, the maximum concentration of DMS can be calculated, which can be in gas tanks of different pressures and temperatures without condensation of DMS.

Assuming that the gas tank is filled to a pressure of 200 bar and that the temperature during use is at least o + 15 ° C, the maximum concentration of DMS at a vapor pressure of 2,180 ppm (0.218%) is limited. The uptake of gas from the gas tank must not take place so rapidly that the temperature falls below the condensing temperature due to adiabatic expansion.

2,781 73

There is no risk of ignition in a pre-filled flue gas tank if there is not too much DMS, but its concentration is close to the saturation limit of 0.218% at a temperature of o + 15 ° C, even if the tank contains DMS mixed with pure oxygen, as the mixture does not exceed the flammability limits. Namely, the flammability limit of DMS mixed with 20 ° C and 1 bar oxygen is 2.0% and in air 2.2%. The lower flammability limit is said to not change as the pressure increases. Ignition experiments of DMS mixed with 150-200 bar oxygen show that the mixture was not allowed to ignite even at concentrations up to 0.5%.

The concentration of DM $ in the gas gas tank is thus limited according to the vapor pressure of DMS. If it is required that the sample gas tank be used for min. At a temperature of + 15 ° C, a suitable DMS concentration of 200 bar is 0.2%.

If the sample gas contains only oxygen and DMS, problems arise in filling the sample gas tanks. In that case, it is unavoidable that a certain part of the filling step, at least in a certain part of the tank, takes place in a concentration range where the mixture is flammable. There is a risk of ignition and explosion.

It is an object of the present invention to provide a filling method which eliminates this danger. The invention is mainly characterized in that the tank for malignant gas is filled with a mixture of nitrogen gas, helium gas or some other inert gas and dimethyl sulfide at a concentration of 0.5 to 2.5% dimethyl sulfide, and that pure oxygen is then added to the malignant tank until the desired working gas is reached. 200 bar. A mixture of nitrogen or helium gas and DMS is produced by means of an evaporation column. Nitrogen or helium gas is first fed to the bottom of the column. The column is filled with filler pieces. DMS is pumped to the top of the column, which is allowed to drain down over the fillers through the column. On its way down, the DMS encounters nitrogen or helium gas. DMS-saturated nitrogen or helium gas can then be removed from the top of the column and added to the beaker.

3,78173

Filling with Type 11 or helium can take place at a temperature of 15 C without the risk of condensation at the following alternative pressures and DMS concentrations.

Pressure, bar_20_30_40_50_60 DMS content% 2.18 1.45 1.09 0.87 0.725

However, at a pressure of 50 or 60 bar, a high nitrogen or helium content is obtained in the final product, which is why these alternatives are not always useful, e.g. in the case of a cutting process. After this filling, pure oxygen is added to the mixture until the pressure is 200 bar. In order for the mixing of oxygen to take place homogeneously throughout the tank, the tank is provided with a so-called an immersion tube 1a closed at its lower end and provided with small holes along its entire length of the jacket surface.

If the melt gas tank as the first option A is filled with nitrogen or helium mixed in DMS to a pressure of up to 20 bar with a DMS content of 2% and then with pure oxygen up to a pressure of 200 bar, the gas composition varies during the filling phase according to the pressure below.

Pressure, baa r ia_20 25 ao 36 40 <s so eo 100 200 QMS% 2 '.6 1.33 1.1 * 1 0.8 »0.8 0.67 0.4 0.2 Ν ^ / Ηθ% 98 78 , 4 66.3 56 4 »43.6 39.2 32.7 19.6 9.8 n 0 20 33.3 42.9 SO 55.6 60 66.7 80 90 u 2 ™

The question is whether the mixture is flammable at some point in the filling step. The table shows that at 25 bar the DMS content is 1.6% together with the composition of the air. The flammability limit of DMS is 2.2% at 1 bar and 2.0% in pure oxygen. Assuming that the limit does not vary significantly with pressure, the outside of the limits of the combustible mixture is maintained throughout the filling phase.

4,78173

However, one may ask whether the safety margin is sufficient. Therefore, two alternatives have also been calculated, namely option B with 1.33% DMS in nitrogen or helium at 30 bar and option C with 1.00% DMS in nitrogen or helium at 40 bar.

According to Option B, the gas composition during the filling process varies according to the table below.

Pressure, bar »o <o» om to »o 100 1180 180 200 DMS% 1.33 1.00 0.00 0.67 0.67 0.60 0.40 0.31 0.36 0.2 N2 / He% 90.7 74 69.2 49.3 42.3 37.0 29.0 22.0 10.6 14.0 no / 0 25 40 00 07.1 62.6 70 70.0 01.2 06 u 2 lo

According to option C, the variations that occurred during the filling phase are as follows.

Pressure, bar 40 00 eo n oo 100 120 iqo 170 200 Q | Y | 5 ^ 1 0.0 0.67 0.67 0.00 0.40 0.33 0.29 0.24 0.2 N ^ 99 79.2 06.0 06.0 49.6 39.6 33.0 20.0 33.3 19.0 2 O 20.0 33.3 42.0 60.0 60.0 67.0 71.4 76.6 00 o2%

The attached diagram shows the flammability limits for the different DMS and oxygen contents of the mixture, based in part on data from the literature (curve D) and in part on the basis of this data and the ignition tests performed (curve E).

In addition, the lines along which the mile gas tank is filled according to the above-mentioned options A, B and C can be seen. The choice of alternative depends on the desired safety margin and the desired degree of purity of the finished product. In addition to oxygen and 0.2% DMS, the model gas now also contains nitrogen or helium according to the above options.

5,78173

When the sample gas is metered into the oxygen stream, which is perfumed with a mixture gas / pure oxygen ratio of e.g. 1: 100, the perfumed oxygen contains 220 ppm DMS. In addition to this, it also contains nitrogen or helium, the amount of which depends on the selected option A, B or C according to the table below.

Vaihtoehto_A_B_C

He or N 2 pressure in bars in the flue gas 20 30 40

He or N 2 content in the final product 0.1 0.15 0.2 This means that the degree of impurity of the finished, scented oxygen increases by 0.1, 0.15 or 0.2 percentage points. This should be perfectly acceptable and should not have any negative effects. Scented oxygen can also be used in 1 cutting processes. The use of helium almost completely eliminates the small decrease in 1 eu window velocity that can occur when nitrogen is used as an impurity in the 1 eu window gas. However, nitrogen can be used well in welding and other heating processes. The purity of the oxygen produced today is often a few tenths of a percentage point above the guaranteed. Of course, instead of the mentioned gases, nitrogen and helium, another inert gas can possibly be used.

The values given for the DMS concentration 11e at the filling and closing pressures of the tank are not limited to the above-mentioned examples, but conversions of their values are possible, which is also shown in the curves of the accompanying figure. In addition, the mixture gas sample gas / pure oxygen ratio when perfuming the oxygen gas for the user may deviate from the given example without the degree of impurity becoming unacceptable.

Claims (3)

6 78173 Patent Requirements 1. The method of concentrated gas, the so-called for the production of a model gas containing oxygen and an organic sulfur compound, e.g. dimethyl sulphide a, used for perfuming oxygen gas distributed to the user, characterized in that the model gas container is first filled with a mixture of dimethyl sulphide and an inert gas, e.g. nitrogen or helium gas dimethyl sulphide at 0.5 to 2.5% and that pure oxygen gas is then added to the mixture until the desired working pressure in the tank is reached. Process according to Claim 1, characterized in that the concentration of dimethyl sulphide (DMS) in the DMS nitrogen or helium gas mixture is preferably 1 to 2% and that the working pressure of the tank after filling with pure oxygen is preferably 200 bar. Method according to Claim 1 or 2, characterized in that the gases pass through the so-called through a submersible tube closed at its lower end and provided with small holes throughout its casing.