Odorized fuel gas mixture for the autogenous processing of metals

Abstract

A fuel gas mixture for the autogenous processing of metals consists of: 0.5% to 20% by volume of a carrier gas consisting of a hydrocarbon or a mixture of hydrocarbons; 100 ppb to 50 ppm by volume of an odorant; with the remainder being hydrogen.

Description

[0001] Odorized fuel gas mixture for autogenous machining of metals

[0002] The invention relates to a fuel gas mixture for the autogenous machining of metals.

[0003] For the oxy-fuel processing of metals, such as flame cutting, flame straightening, gouging, or oxy-fuel welding, predominantly hydrocarbon-based fuel gases such as propane, acetylene, propene, ethene, etc., are used today, as described, for example, in DE 2 823 305 A1. Due to the carbon dioxide emissions produced during the combustion of these gases, these very fuel gases and fuel gas mixtures will soon be subject to a CO2 tax through legislation already being prepared. Regardless of the cost aspect, avoiding climate-damaging carbon dioxide and other emissions, such as carbon monoxide or microparticles (carbon), which are produced as combustion reaction products, is of paramount importance for increasing occupational safety and environmental protection.

[0004] Hydrogen, which has been used as a fuel gas in autogenous welding for over 100 years, offers an alternative to carbon-based fuel gases. Hydrogen is now used in both industrial and manual autogenous welding processes.

[0005] The use of hydrogen in oxy-fuel welding is not without its problems, however, because its diffusion properties mean that hydrogen can easily escape into the environment through even the smallest leaks in improperly installed or frequently used lines or fittings, such as hose connections or rotating seals. This creates the risk of a flammable mixture forming in the vicinity of the work area over time. This risk is further exacerbated by the fact that hydrogen is a completely odorless gas, meaning that its leakage is not easily noticed by the user.

[0006] From a safety perspective, it would therefore be advisable to label hydrogen used in autogenous welding with an odorant, as has long been the practice with gases supplied by public gases, such as natural gas. These gases are mixed with an odorant, for example, organic sulfur compounds like thioethers or mercaptans, to make the gases detectable in the event of leaks. Suitable odorants for this purpose are described, for example, in DVGW worksheet G 280, "Gas Odorization," ISSN 0176-3490.

[0007] It is already known from DE 197 45 851 A1 to add an odorant to the fuel gas acetylene used for autogenous machining.

[0008] WO 90 / 06170 A1 discloses the odorization of oxygen used for welding or cutting with an odorant, for example dimethyl sulfite. The odorized oxygen is produced by first mixing the odorant in a pressure vessel with a condensed gas, for example pressurized liquefied carbon dioxide, to form a mother mixture, which is then fed into the gaseous oxygen.

[0009] A major challenge in oxy-fuel welding is the correct dosage of odorant in the fuel gas. Especially in manual applications, the concentration must not be too high to avoid health risks to the user from odorants, some of which are classified as carcinogenic. Furthermore, odorants can be corrosive to pipes and fittings, shortening their lifespan and / or causing leaks. Conversely, the concentration must not be too low to ensure the user can reliably detect the gas mixture. Therefore, the odorant must be added reliably at a low concentration within a narrow tolerance range, which is technically very complex to achieve.

[0010] The object of the present invention is therefore to create an odorized, hydrogen-containing fuel gas for use in oxy-fuel technology that has good combustion properties, can be reliably detected by the user in the event of a leak, and avoids the risk to the user or plant equipment from an excessively high concentration of odorant.

[0011] This problem is solved with a fuel gas mixture according to claim 1. Advantageous embodiments of the invention are claimed in the dependent claims.

[0012] The fuel gas mixture according to the invention for autogenous processing of metals therefore consists predominantly of hydrogen, to which a carrier gas consisting of a hydrocarbon or a mixture of several hydrocarbons has been added with a volume fraction of 0.5% to 20%, as well as an odorant with a volume fraction of between 0.1 ppm and 50 ppm.

[0013] In the fuel gas mixture according to the invention, hydrogen acts as the actual fuel gas, comprising at least 80% by volume, preferably at least 90% by volume, and particularly preferably at least 95% by volume. The carrier gas, which is a hydrocarbon—preferably gaseous under normal conditions—or a mixture of hydrocarbons—preferably gaseous under normal conditions—acts itself as a fuel gas and therefore does not impair the fuel properties of the hydrogen acting as the main component. Furthermore, it increases the visibility of the hydrogen flame, particularly when operating in bright environments, such as sunlight.The comparatively low concentration of odorant, between 100 ppb and 50 ppm, ensures good visibility of the fuel gas mixture while posing no health risk to the user, having no or negligible corrosion effects on the system, and decomposing odorlessly during the autogenous combustion process. To eliminate any risk to the user, the volume fraction of the odorant in the gas mixture should not exceed 50 ppm.

[0014] The fuel gas according to the invention contains, for example, a volume fraction of a gaseous hydrocarbon or hydrocarbon mixture of between 0.5% and 20%, between 0.5% and 10%, between 1% and 10%, between 1% and 5%, or between 1% and 3%. A volume fraction of less than 5% is preferred. The volume fraction of the odorant is, for example, between 100 ppb and 50 ppm, between 1 ppm and 50 ppm, between 1 ppm and 25 ppm, or between 5 ppm and 15 ppm, for example, about 10 ppm.

[0015] In addition to the carrier gas and the odorant, the fuel gas mixture according to the invention contains hydrogen. For the purposes of this invention, "hydrogen" is understood to mean a gas with a hydrogen content of at least 99.5% by volume, preferably at least 99.99% by volume. Furthermore, traces of inert gases, such as nitrogen or carbon dioxide, may be present in the fuel gas mixture in a volume fraction of less than 0.5%, preferably less than 0.01%, provided that they do not negatively affect the fuel properties of the fuel gas mixture.

[0016] Suitable carrier gases include methane, ethane, ethene, propane, propene, butane, acetylene, or mixtures of two or more of these gases. Preferably, the carrier gas consists of ethene or propane, or a mixture of ethene and propane. Mixtures of hydrogen with ethene and / or propane are very stable and can be stored without problems in containers, especially in pressure vessels such as gas cylinders, cylinder bundles, or pressure tanks, even at pressures of 300 bar and above, for extended periods.

[0017] A sulfur-containing odorant, such as THT (tetrahydrothiophene), TBM (2-methyl-2-propanethiol, tert-butyl mercaptan), or DMS (N,N-dimethylsulfamide), is used as the preferred odorant in the fuel gas mixture according to the invention. However, sulfur-free odorants can also be used in the fuel gas mixture according to the invention.

[0018] The fuel gas mixture according to the invention can be stored as a ready-to-use mixture in containers, for example, pressurized gas cylinders, cylinder bundles, or pressure tanks with a nominal pressure of, for example, between 150 bar and 450 bar, preferably 200 bar or 300 bar. This provides the user with increased safety during use in autogenous machining by means of a timely warning of leaks through a noticeable odor. The fuel gas mixture according to the invention is preferably produced in a two- or multi-stage process. In a first step, the odorant is added to the carrier gas. Commercially available mixers can be used for this purpose. This yields a gas mixture, referred to here as "mother gas," consisting of the carrier gas and a volume fraction of, for example, 100 ppm to 5000 ppm odorant. The mother gas is then mixed with hydrogen at a volume fraction of, for example, between 1% and 5%.

[0019] In order to reliably ensure very low concentrations of odorant in the fuel gas mixture, an intermediate step or several intermediate steps can be inserted in which the concentration of the odorant in the mother gas is reduced by adding a suitable amount of pure carrier gas to the already produced mother gas before the resulting mother gas is mixed with the hydrogen.

[0020] The resulting fuel gas mixture, consisting of a carrier gas volume fraction of 0.5% to 20%, an odorant volume fraction of 0.1 ppm to 50 ppm, and hydrogen, can then be filled into containers such as pressurized gas cylinders, cylinder bundles, or pressure tanks and stored therein for long-term use. The two- or multi-stage production process allows for the reliable production of fuel gas mixtures with a low odorant volume fraction. In particular, this ensures that the specified odorant volume fraction is maintained within a narrow tolerance range of, for example, ±10% with comparatively little effort, thereby minimizing the risk to the user.

[0021] The fuel gas mixture according to the invention is suitable for all known oxy-fuel machining processes, for example, oxy-fuel welding, flame cutting, flame straightening, or gouging. For example, the fuel gas mixture is taken from a pressure vessel, combined with an oxidizing agent, such as air or pure oxygen (with a volume fraction of over 95%), at a machining tool, and reacted, generating a flame used for the oxy-fuel machining of a workpiece. The odorant decomposes odorlessly during the combustion process. According to the invention, any conventional tool for oxy-fuel machining can be used as the machining tool, for example, an oxy-fuel cutting machine, a flame spraying device, a gouging device, or an oxy-fuel welding machine.

[0022] Furthermore, all materials commonly machinable using oxyfuel technology can be processed, in particular unalloyed or low-alloy steels or aluminum alloys. The inventive method is especially suitable for flame cutting unalloyed or low-alloy steels, particularly those with a sheet thickness exceeding 5 mm.

Claims

Patent claims 1. Fuel gas mixture for autogenous machining of metals, consisting of a volume fraction of 0.5% to 20% of a carrier gas consisting of a hydrocarbon or a mixture of hydrocarbons, a volume fraction of between 100 ppb and 50 ppm of an odorant, remainder hydrogen.

2. Fuel gas mixture according to claim 1, characterized in that the carrier gas contains ethene and / or propane or consists of ethene and / or propane.

3. Fuel gas mixture according to claim 1 or 2, characterized in that a sulfur-containing odorant, for example a thiol or a mercaptan, is used as the odorant.

4. Fuel gas mixture according to one of the preceding claims, characterized in that the volume fraction of the carrier gas is between 1% and 10%, preferably between 1% and 5%.

5. Fuel gas mixture according to one of the preceding claims, characterized in that the volume fraction of the odorizing agent is between 1 ppm and 25 ppm, preferably between 5 ppm and 15 ppm.

6. Method for producing a fuel gas mixture according to one of the preceding claims, in which the carrier gas is first mixed with the odorant to form a mother mixture and the mother mixture is then added to the hydrogen.

7. Use of a fuel gas mixture according to one of claims 1 to 5 for autogenous machining of metals.