Safe production and management of VOC standard gases during the preparation process
With the development of the economy and the increasing demand for VOC standard gases in the market, there are more and more types of VOC standard gases, and their complexity is also increasing. Their application fields involve petrochemical, exploration, metallurgy, mechanical manufacturing, electronics, coal, electricity, environmental protection, and other fields (process gases or VOC standard gases). In recent years, unexpected accidents often occur during the preparation process of VOC standard gases, which not only cause personal injury but also result in huge property losses for colleagues. Therefore, understanding and mastering the properties of gases and materials, designing filling processes reasonably, developing strict operating procedures, and clearly identifying the hazards of gas cylinders are necessary to ensure safety during the preparation and use of VOC standard gases.
1、 Design of filling system
Incompatible gases cannot be filled on a filling system. Design two independent filling systems to separate incompatible gases. If incompatible gases are simultaneously connected to a manifold, when a valve leaks, high-pressure gas will flow into a low-pressure incompatible gas cylinder, causing a reaction and combustion or explosion. At the same time, operator errors may also lead to unimaginable dangers, as acidic gases cannot be connected to the same system as alkaline gases.
2、 Incompatibility of gases
1. Oxidative gases and combustible gases are incompatible. Common oxidizing gases include oxygen (O2), laughing gas (N2O), nitric oxide (NO), nitrogen dioxide (NO2), nitrogen trifluoride (NF3), fluorine gas (F2), chlorine gas (CL2), etc. Common combustible gases include hydrogen (H2), methane (CH4), other hydrocarbons (alkanes, olefins, alkynes, etc.), carbon monoxide (CO), ammonia (NH3), and hydrogen sulfide (H2S).
2. Acidic and alkaline gases are incompatible. Common acidic gases include hydrogen chloride (HCL), hydrogen bromide (HBr), and sulfur dioxide, while common alkaline gases include ammonia (NH3) and amine (RNH2).
3. Oxidative gases and reducing gases are incompatible.
3、 Incompatibility between gas composition and materials
Gas incompatibility with gas cylinders, valves, and pipeline materials under certain conditions can lead to the following hazards:
1. Corrosion
1) Moisture corrosion
For example, HCL and CL2 are prone to corroding steel cylinders in the presence of water, and the introduction of water may come from customer use without closing the valve, as well as during the filling process or water pressure inspection; NH3, SO2, and H2S also exhibit similar corrosion. Even dry hydrogen chloride and chlorine gas cannot be stored in aluminum alloy cylinders at high concentrations.
2) Stress corrosion
When CO, CO2, and H2O coexist, carbon steel cylinders are highly susceptible to corrosion. Therefore, when preparing VOC standard gases containing CO and CO2, the gas cylinder needs to be dried, and the raw gas should also use high-purity gas or gas without moisture.
2. Generating hazardous compounds
1) Acetylene reacts with copper alloys containing more than 70% copper to form metal organic compounds.
2) Monohalogenated hydrocarbons such as CH3CL, C2H5CL, CH3Br, etc. cannot be contained in aluminum alloy gas cylinders. They will slowly form metal organic halides with aluminum and explode when exposed to water. If the gas cylinder contains water, hydrocarbons and hydrogen can be detected in the prepared VOC standard gas.
3. Explosion reaction is caused by incompatibility between gas and valve sealing material or pipeline material. Valves with combustible sealing materials cannot be used for oxidizing gases. This is easily overlooked when preparing VOC standard gases. This includes how to calculate the oxidizability of VOC standard gases.
4、 Review and analysis of accidents in the preparation of incompatible gases
The following are known accidents in recent years: 1996- Taiwan, China, China, N2O/H2, explosion/casualties; 1997- Canada, CO/Air, explosion; 1997- UK, CH4/Air, explosion/casualties; 1997- South America, CH4/Air, pressure gauge destroyed; 1997- United States, 4% H2/Air, hidden danger accidents; 2003- Germany, N2O/CO, personnel injured; 2004- France, halogenated hydrocarbons/Air, hidden danger accidents; 2007- Lanzhou, China, CH4/Air, casualties.
In the above accidents, most of them are combustible gases in the air, which are mostly used in the detection of environmental gases in chemical plants and coal mines. The cause of the accident may be incorrect operations; Or incompatible gases can be simultaneously connected to a system, causing backflow due to valve leakage; Or it could be a concentration calculation error; Or it may be caused by incorrect filling sequence. For the analysis of explosion accidents of carbon monoxide mixtures, people often attach importance to the toxicity of carbon monoxide and neglect its combustibility. The preparation of combustible gases in the air often occurs, so it is very important to establish strict operating procedures. Wuhan ISOTOPE Technology Co., Ltd. Service hotline: 19526388246
