Basic knowledge of odorant

**1. Definition of Deodorant** A deodorant is an organic compound or mixture that possesses a strong, distinctive odor. When added to gas at very low concentrations, it imparts a noticeable, unpleasant smell, allowing the detection of gas leaks when the concentration reaches 5% of the lower explosive limit or becomes harmful to human health. This warning odor plays a critical role in ensuring safety during gas transportation and usage. **2. Requirements for Odorants** To ensure safe handling and prompt leak detection, most gas distribution stations inject odorants into odorless gases. The chosen odorant must produce a distinct, detectable scent when mixed with the gas. It should be non-toxic to humans, piping, and materials it comes into contact with. Additionally, its combustion byproducts must not pose risks to breathing or damage equipment. The solubility of the odorant in water should not exceed 2.5% (mass fraction), and it must have a detectable odor level in the air. Human sensitivity to odors generally increases with temperature, so the amount of odorant used should vary seasonally. The consumption ratio between the coldest and hottest months is typically around 2:1. In hot climates, less odorant is needed compared to colder regions. At the start of production, the odorant dosage is often increased by 2 to 3 times. For short-term use, such as detecting underground pipeline leaks, the odorant may be absorbed by soil, so the amount can be up to 10 times higher than normal. Due to the corrosive nature of sulfides, the amount of odorant added should be carefully controlled. **3. Introduction to Odorants** Ethyl mercaptan (C₂H₅SH) is one of the most commonly used odorants. However, when there is a lot of rust on the inner walls of gas pipes, ethyl mercaptan may gradually lose its effectiveness due to reactions with metal oxides, forming thiolates. Therefore, higher initial dosages are usually required. As a natural gas odorant, ethyl mercaptan has an average annual consumption of about 16–20 mg/m³. For industrial toxic gases containing 20% CO, the annual average consumption is approximately 230 mg/m³. Other options include tetrahydrothiophene (THT) and tributyl mercaptan (TBM). Compared to ethyl mercaptan, THT offers better chemical stability, oxidation resistance, easier storage, longer-lasting odor, no residue after combustion, and less corrosiveness. It became widely used in the mid-1990s with the rise of natural gas. As natural gas expands into more industrial applications, the demand for lower sulfur content in gas has increased. Sulfur-containing odorants are now limited in many cases, and sulfur-free alternatives like acrylates are gaining more attention. These substances have been certified as effective odorants either alone or in combination with other compounds, and are already applied in real-world projects. **4. Methods of Odorization** Odorizing units are typically installed at the end of long-distance pipelines rather than at the starting point, as mainline leaks are rare and can be detected through other means. The odorant storage area should be cool, dry, and well-ventilated. Containers should not be exposed to direct sunlight to prevent pressure buildup. Spare odorant tanks and equipment can be stored in the same room, but odorants must never be stored with flammable materials. The most common method is a drip-type odorizer, which introduces liquid odorant into the gas stream in droplet form, allowing it to evaporate and mix. The reservoir holds enough odorant for one day’s use, and the flow rate is adjusted manually using a needle valve. While this system is simple, it requires manual operation, which can be time-consuming. With advances in automation and detection technology, many automatic odorizing systems are now widely used in engineering practices. These systems offer greater precision and reduce the need for constant manual monitoring.

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