EP0492269B1 - Gaseous 4-components combustible comprising acetylene and suitable for storage and transportation in liquefied state - Google Patents

Abstract

The object of the invention is an acetylene-containing multi-component fuel gas mixture which can be safely handled as a liquefied gas and has properties as similar to those of acetylene as possible. According to the invention, this is a mixture which, at least when stored, contains in the liquid phase 22 to 32 mol% of acetylene, 1 to 4 mol% of a C3 hydrocarbon, 10 to 20 mol% of ethane and ethylene as the remainder, that is to say about 67 to 44 mol% of ethylene. <IMAGE>

Description

The invention relates to a multi-component fuel gas mixture with a main part of acetylene and a main part of ethylene, the mixture being manageable in cryogenic, liquefied form.

In terms of its application properties, acetylene is an extremely advantageous fuel gas, which is clearly superior to other fuel gases such as methane and propane in terms of properties such as flame temperature, primary flame output and ignition speed. However, based on its molecular structure and the resulting energy content, it has characteristics that place special demands on its storage, transport and consumer supply. Acetylene is a fuel gas with a positive enthalpy of formation and, under certain conditions, continuous decay can only occur under certain conditions without additional energy and without oxygen. For this reason, acetylene must not simply be stored in "normal" gas cylinders with higher pressures because this creates safety-intolerable conditions. The storage problem with acetylene has so far been overcome by dissolving this fuel gas in a solvent and storing it in storage containers at comparatively low pressure (<approx. 25 bar), the said solution also being in a cement-like, porous mass that completely fills the storage container is distributed. However, this particular type of gas storage entails a comparatively poor ratio of the amount of gas contained to the weight transported. For this reason, a large number of proposals are already known that address this fact and try to improve this situation.

• mit möglichst hoher Flammentemperatur und Primärflammenleistung sowie guter Zündgeschwindigkeit,
• mit einer Dichte, die wie beim Acetylen unterhalb der von Luft liegt,
• mit über die Entleerungszeit der zugehörigen Speicherbehälter hinweg konstanten Eigenschaften sowie
• mit Sicherheitseigenschaften, die den Anforderungen in allen möglichen Betriebssituationen gerecht werden.

A well-known solution to this problem is to cool acetylene in pure form or with the admixture of a further gas, if necessary under pressure, below the boiling point, and to make it available as a liquefied gas (see DE-PS 71 45 52 v. 1939). Since safety problems nevertheless arise with pure acetylene and with mixtures with a high proportion of acetylene - above all because gas volumes with extremely high proportions of acetylene are generated via such fuel gas liquids - this solution is unsatisfactory and ultimately gas mixtures are found which compromise safety-related and application-specific requirements. With regard to the needs from the application side, a fuel gas which is as acetylene-like as possible is generally sought, that is to say a fuel gas

• with the highest possible flame temperature and primary flame output as well as good ignition speed,
• with a density that, like acetylene, is below that of air,
• with constant properties over the emptying time of the associated storage tanks as well
• with safety features that meet the requirements in all possible operating situations.

On the basis of these and similar specifications, combustible gas mixtures which can be handled as liquid gas have now been proposed, which result in largely safe handling and at the same time have acceptable combustible gas properties. These include, in particular, three-component mixtures of acetylene, ethylene and propane or propylene (propane or propylene are so-called C₃-hydrocarbons) .These known three-component mixtures can be divided into two groups, with one of the mixing groups in addition to the important acetylene component (components from 15 to 50 vol % are mentioned) high ethylene fractions and in which other high propane or propylene fractions are proposed as the second essential mixture fractions. The third part of the mixture in each group is the gas not yet mentioned, i.e. the C₃ hydrocarbon on the one hand and ethylene on the other (see EP-PS 0 060 769 and Chemical Abstracts, 84 (1976) 26, abstract 18 23 65 n) .

With these mixtures, those which have relatively high proportions of propane or propylene and also relatively high proportions of acetylene (mixtures according to the Chemical.Abstract) have the disadvantage that they are heavier than air and are therefore unsuitable for certain applications, in contrast to pure acetylene , for example for use in basements, underground operations and shipbuilding. On the other hand, the mixtures according to said EP-PS with a high ethylene content (about 70 vol%), about 15 to 25 vol% acetylene and about 10 vol% of a C₃ hydrocarbon, as fuel gases, which are at least partially lighter than Are air, the safety-related behavior of which, however, is critical in certain operating states - depending on the composition of the mixture (as detailed below) is shown) and their performance compared to pure acetylene leaves nothing to be desired.

The problem to be solved by the present invention arises from this problem, namely to create a fuel gas mixture which can be handled as liquid gas and which provides the best possible flame properties, largely in the direction of pure acetylene, which has a lower density in gaseous form than air and which is nevertheless present in everyone Operating situation meets high safety requirements.

This object is achieved with a fuel gas mixture that is in the liquid phase
22 to 32 mol% acetylene,
1 to 4 mol% of a C₃ hydrocarbon,
10 to 20 mol% of ethane and the rest of ethylene,
thus contains about 67 to 44 mol% of ethylene, with higher proportions of C3 hydrocarbon and ethane also tending to be more advantageous toward higher acetylene values.

With this specific mixture of 4 "single" fuel gases, a fuel gas is given which, with good performance and a lower density than air, also has a high level of safety. An essential safety aspect is that, in the fuel gas mixtures according to the invention, the acetylene content in the gas volume present above the stored quantity of liquid gas does not increase beyond critical values even when fuel gas is removed from the gas phase. In the operating situation of gaseous extraction, which can arise not only from standard gas extraction but also from the normal blowing off of a liquid gas storage device when an upper limit pressure is exceeded, this is the case with liquid mixtures Commonly known separation problem, ie that the more volatile constituents are disproportionately removed from the liquid while the less volatile constituents accumulate in the liquid and a not inconsiderable proportion shift occurs with increasing emptying.

In the case of the known three-substance mixtures of ethylene, acetylene and propylene, this means that ethylene is contained in the gas above the liquid because of the greatest volatility. This is especially true at the start of emptying a newly filled liquid gas container. However, with increasing emptying, the ethylene content in the liquid and in the gas decreases disproportionately, and the influence of the second most volatile component, namely acetylene, increases, i.e. its relative proportions increase (everything applies to the withdrawal of gas phase). This leads to the fact that very high levels of acetylene, especially in the gas phase above the liquid phase, are possible with extensive emptying, and the known safety requirements described at the outset, as with pure acetylene, become relevant. To avoid this, high acetylene fractions - that is, acetylene fractions that are significantly above the 50% value - must be avoided. This results in a very restrictive condition for the multi-component fuel gases in question.

Against this background, however, a good result is achieved with the fuel gas mixtures according to the invention, since the proposed 4-component mixtures actually keep the acetylene content in the gas phase comparatively low in the described critical operating situation (gaseous removal up to a high degree of emptying). This property of the proposed fuel gas is probably due to the fact that ethane of volatility is very close to acetylene (boiling temperatures almost the same). Because of the similar volatility behavior, this results in a constant ratio of the two components to one another at the level of the initial ratio in all emptying phases, whereby this also applies above all to the gas phase. In addition, ethylene is again the most volatile part of the liquid phase in the case of fuel gases according to the invention and thus decreases most strongly in the course of emptying, while the C3 hydrocarbon has the opposite property and the contrary behavior and thus counteracts the decrease in ethylene with a C3 increase is. The consequence of this is a far-reaching "stabilization" of the acetylene content in the liquid phase and also in the gas phase over the entire emptying process. This also applies, especially in the worst case of gaseous extraction. In contrast, the case of liquid withdrawal represents the less critical and preferable case in practical use, since the mixture proportions are not subject to any significant change. Overall, the 4-component mixtures according to the invention thus achieve advantages over the known mixtures, above all in the sense of an increased proportion of acetylene, with the same level of safety.

Compositions have particularly advantageous fuel gas mixtures according to the invention
24 to 28 mol% acetylene,
2 to 3 mol% of C₃ hydrocarbon, preferably propylene,
13 to 17 mol% of ethane and the rest (about 61 to 52 mol%) of ethylene.

Fig.1

ein angepaßtes Dreistoffdiagramm sowie einen Näherungsvergleich bekannter 3-Komponentengemische mit den erfindungsgemäßen 4-Komponentengemischen in diesem Dreistoffdiagramm;

Fig.2

Acetylenanteil in der Gasphase bei 97%iger Entleerung eines Speicherbehälters gegen den Ausgangsacetylengehalt in der Flüssigkeit angegeben sind, wobei Drei- und Vierstoffgemische eingetragen sind sowie die Grenzlinie zu höheren Dichten als Luft hervorgehoben ist und wobei die Entleerung über die Entnahme von Gasphase erfolgt.

Fuel gas mixtures corresponding to these compositions have the properties already described, such as good ones Efficiency and high security in a particularly balanced way. This aspect and the fuel gas mixtures according to the invention in general are further explained below with reference to FIGS. 1 and 2:

Fig. 1

an adapted three-component diagram and an approximate comparison of known 3-component mixtures with the 4-component mixtures according to the invention in this three-component diagram;

Fig. 2

The percentage of acetylene in the gas phase given a 97% emptying of a storage tank against the initial acetylene content in the liquid is given, where three- and four-component mixtures are entered and the boundary line to higher densities than air is highlighted and the emptying takes place via the removal of the gas phase.

In the three-substance diagram (isosceles triangle, in which each side is used for the application of a substance) of FIG. 1, the gas mixtures proposed according to the invention are shown as a framed area. The ethane and ethylene fractions have been combined to make a total of 4 components in the three-component diagram. If the ethylene-ethane scale is viewed as a pure ethylene scale, the three-substance mixtures according to EP-PS 0 060 769 can be entered in this diagram for illustration (area within the additionally marked points). It can be seen that the fuel gas mixtures proposed here are equipped with higher proportions of acetylene in comparison to these three-substance mixtures and thus have more pronounced properties of acetylene in the flame properties. Besides only very low amounts of C3 hydrocarbon are provided in the mixtures according to the invention, which keep the density of the resulting fuel gas low. However, a sufficient stabilizing effect for the mixture is nevertheless achieved.

gemäß der folgenden Tabelle, wobei die angegebenen Werte für den jeweiligen thermischem Gleichgewichtszustand bei 6 bar und -60°C gelten:

The proportion of acetylene in the gas phase above the liquid which is relevant for safety reasons develops with gaseous removal in a liquid starting mixture corresponding to the invention

according to the following table, the values given for the respective thermal equilibrium at 6 bar and -60 ° C:

The acetylene concentrations for a three-substance mixture are given in brackets
22% acetylene,
6% propylene and
72% ethylene
given for comparison. It can be seen that the proportion of acetylene in the gas increases significantly with increasing emptying. As can be deduced from the table, this effect is much more pronounced in the three-substance mixtures considered (details in brackets) than in the four-substance mixtures considered (values in the table are calculated values for the respective evacuation state in thermal equilibrium). For safety reasons, however, the proportion of acetylene in the gas phase - as explained above - should remain as low as possible in all emptying stages in order to prevent acetylene decomposition. Here, with the mixture according to the invention with 48.2% acetylene content in the gas at 97%, a value is reached which is clearly below the 50% mark which characterizes a good safety standard.

Exact versions can also be seen in part in FIG. 2, in which acetylene concentrations in the gas phase are plotted with 97% emptying compared to initial concentrations of acetylene in the liquid (emptying by removal of gas). In addition to the 4-component mixtures according to the invention, 3-component mixtures are also entered, in each case the propylene fraction line which represents the limit to higher densities than air is emphasized. The mixture of 22; 2: 15: 61 is included in this diagram as point C. It can again be clearly seen that the comparative three-substance mixtures give significantly higher acetylene fractions in the gas phase at high emptying stages with the same initial concentration of acetylene in the liquid. This safety criterion worsens with increasing initial proportions of acetylene, although for safety reasons no mixture can be tolerated that allows far more than 50% of the acetylene content in the gas phase. From Fig. 2 it follows that with the mixtures according to the invention one about 1/3 higher The proportion of acetylene in the starting liquid can be provided than is possible with known three-substance mixtures, and still maintains the same safety standard with regard to the proportion of acetylene in the gas phase (see, for example, 50% line in FIG. 2).

A liquid gas fuel gas according to the invention, which is optimized in many aspects, consists of
26 mol% acetylene,
3 mole% propylene
15 mole% ethane and
56 mole% ethylene.

This is advantageously stored at temperatures between -60 and -80 ° C and under pressures of 4 to 6 bar and thus also made available to the consumer. For use, this fuel gas is advantageously removed in the liquid state, sent via an evaporator and then fed to the point of use.

In summary, it can be stated that the fuel gas mixtures according to the invention are efficient, meet high safety requirements and are easy to handle as liquefied gases within the limits known for acetylene. They offer the possibility of a safe and efficient fuel gas supply based on liquid gas with advantages such as large storage capacity with comparatively small space requirements and low weight.

Claims (3)

1. A multi-component combustible gas mixture having a main constituent acetylene and a main constituent ethylene, wherein the mixture can be handled in low-temperature, liquified form, characterised in that in the liquid phase, at least at the time of transfer into an associated storage container, the mixture is composed of
      22 to 32 mol.% acetylene,
      1 to 4 mol. % of a C₃-hydrocarbon,
      10 to 20 mol.% ethane and the remainder ethylene thus
      approximately 67 to 44 mol. % ethylene.
2. A multi-component combustible gas mixture as claimed in Claim 1, characterised in that it is composed of
      24 to 28 mol.% acetylene,
      2 to 3 mol.% C₃-hydrocarbon, preferably propylene or propane,
      13 to 17 mol. % ethane and the remainder approximately 61 to 52 mol.% ethylene.
3. The storage of the combustible gas mixtures claimed in Claim 1 or 2, characterised in that the combustible gas mixtures are stored in the liquid state at temperatures below -50°C, preferably between -60 and -80°C, at pressures of between 2.5 and 7 bar, preferably at 4 to 6 bar.

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