Many people are unaware that natural gas is a mixture of several colorless and odorless gases. What are these components, what is the composition of natural gas, and how do they transform the odorless gas into a "rotten-egg-smelling" mixture?
In the detailed guide about natural gas, we have already explained how it is formed, extracted, and utilized.
Since it is a highly flammable mixture of different gas components, natural gas is an excellent energy source. However, it is important to mention that the composition of the gas changes after extraction and before it is used by households and businesses, due to an intermediate step.
Before becoming suitable for consumption, natural gas companies mix the gas with crude oil. This process is essential for the removal of by-products. It enhances the quality and purity of natural gas, thereby improving its heating value and making it a more efficient energy source.
The most common by-products are:
These by-products are not wasted as they can be reused. However, besides ethane, propane, and butane, there are many other gases and by-products found in natural gas.
Another by-product, for example, is water (approximately 10-40 mg/m3 in natural gas), which is also extracted. If this step is not taken, there could be a risk of freezing, especially in the case of LNG (liquefied natural gas).
After the extraction of various by-products, natural gas reaches its complete purity, but an important step is still required before distribution.
Due to its colorless, odorless nature and its flammability, it is considered highly dangerous, as even a small amount can cause accidents. Besides water, air also poses a significant risk: if the gas content exceeds 5%, the two compounds form an explosive mixture. However, it is important to note that air is needed for the combustion of natural gas, approximately 10 m3 of air for every 1 m3 of natural gas.
That is why it is odorized with a 50-50 mixture of tetrahydrothiophene (THT, (CH2)4S) and tert-butyl mercaptan (TBM, (CH3)3CSH) - this gives it the distinctive "rotten-egg smell."
Odorization is carried out in national gas transmission systems, the service providers and traders already receive odorized gas. Its energy content depends on the heating value and quantity. This is measured in megajoules (MJ), by multiplying the heating value (which depends on the gas composition, MJ/m3) by the quantity (m3).
In case of perfect combustion, the gas has a blue flame, without any harmful combustion by-products, soot, or ash.