Gas leak detection : what is the science behind gas odorization ?

Processed natural gas is both colorless and odorless which makes leaks impossible to detect. The technology of adding a sulfur additive to natural gas was discovered in the late 19th century. However, the widespread natural gas odorization became a common practice much later. The New London school explosion in 1937 is one of the biggest accidents that happened in Texas, United States. The school had been using gas heaters that were supplied from a residue gas line. The gas leak from the gas line spread in the enclosed crawlspace that ran the entire building and remained undetected until a spark exploded the building.
 
In the aftermath of the tragedy, the first odorization regulation emerged in Texas and then at federal level and is now a widespread documented rule and practice stating that distributed fuel gases should be odorized so that a leak shall be detected before reaching 20% of the LEL.  

Since the onset of the first concerns on potential leakage, the authorities in most countries have taken precautions to ensure the safety of the gas supply. Even though overall regulations on mandatory gas odorization and its standards have evolved in various ways in different parts of the world. Natural gas odorization practices in Europe mainly use the technology of pure THT (TetraHydrothiophène), while in United States blends based on TBM (Tertio Butyl Mercaptan) are used most often. However, the difference in gas odorization-related practices does not stop there: each country has a different requirement at every stage of the gas distribution chain. The odorant requirements and practices can vary on whether odorization is required at transit, transportation or distribution points. In addition, each country’s regulations can define the level of odorant concentration and olfactory degree.

French law requires that gas network operators deliver odorized gas to all consumers However, the in current practice all transported gas is odorized and it is recognized by French authorities as the best practice in safety studies. Meanwhile in Belgium and Denmark regulations do not require odorization of transported gas, whereas, in Spain, it is mandatory to odorize gas during transportation.

The raw materials used to formulate Arkema gas odorants conform to the ISO 13734 standards for natural gas odorisation. Most of those are produced out of Lacq industrial complex, which is located on a sour gas field. This location gives the site direct access to a continuous underground source of hydrogen sulfide (H₂S) – a key raw material for THT and mercaptans production.

Each type of gas requires tailored odorants of specific properties:

We offer the world's largest comprehensive range of odorants for gases and associated local services for natural gas (THT, Spotleak^®), LPG (ethylmercaptan, Vigileak^®) and industrial gases including exhaust gases in the steel industry and inert gases (Codetect^®, etc.)
 

•  Natural gas & Bio-methane​​​​​​​

1. THT (TetraHydrothiophene)
2.  Spotleak^® product line has a wide range of blends based on TBM, custom tailored mixed with IPM, NPM, MES, DMS, and THT

• Propane, Butane, LPG

Odorization of LPG is a complex process with particular constraints. LPG odorant is injected in the liquid phase but it has to be balanced with the gaseous state above the liquid. Therefore, LPG odorization demands a complex combination of odorant properties in order to ensure its safety. Historically, the main technology is based on Ethyl Mercaptan, but Arkema has developed two other grades Vigileak^® (7030 and Z), an innovative new group of gas odorants for LPG, offering higher chemical stability versus Ethyl Mercaptan and an easier handling profile.
 

• Industrial gas

For facilities using both industrial and natural gas, it is important to distinguish the two in case of a leak. Therefore, in the case of Steel industry, Arkema developed Codetect^®, a special formulation to enable CO containing gases in case of leaks on those specific networks. Arkema can propose other adapted technologies for industrial gases such as oxygen, CO_², hydrogen, and nitrogen.
 

Specific parameters to consider:

Each process having its own constraints, it is of utmost importance to review all process conditions and risks associated with gas leakage to perform the odorant selection according to:

 

• Chemical stability

For example, when odorizing natural gas for transportation, it is required to select the odorant of a high chemical stability to reduce possible risks of odor fade along the pipeline network. In this case, pure THT is often chosen for its high chemical stability. On the other hand, in the US regulations requires odorization only at distribution level, which largely consists of short networks at lower pressure, in which case, TBM based odorants are mainly used. Arkema specialist can give you the accurate advice for your specific conditions.
 

• Minimize sulfur content 

In order to reduce SOx emissions, but also to extend the life of the equipment, minimizing the sulfur content can be a key driver. Vigileak^® and Spotleak^® blends can be used instead of Ethyl Mercaptan or THT to minimize fuel sulfur content. Nevertheless, special precautions have to be taken, for example, for injection rate control.
 

• Industrial context

CO containing gases are transported and distributed in short, low pressure pipelines, though in an aggressive environment (dust, iron oxide particles). Codetect^® was developed for this purpose combining high odor intensity and good stability in those networks, it allows better detection for toxic CO containing gas leaks not being covered by portable or fixed detectors (neighbors to steel manufacturing plants).
Other parameters such as the type of injection technology used, possibility to use inert gas or odorant blanketing or even climate parameters can be taken into account in the appropriate selection of the odorant.

Arkema’s odorant product facilities are located in France, Netherland and US where the product is packaged according to transportation modality: road tankers, ISO tanks for bulk deliveries, barrel/drum containers, SBC (Semi Bulk Containers) of fitted size for deliveries. Those strategic production and storage location gives access to ports and ease the shipping worldwide while ensuring safe and reliable supply to an industry for which odorization represent a critical operation without which gas cannot be commercialized.
 
Proposing customers the most appropriate odorant delivery option is the key because of the complexity and time constraints of the operation. In North America, Arkema owns and operates a full fleet of trucks for highly flexible delivery: from bulk tankers down to micro bulk trucks for “Milk Man” deliveries.
 
Odorization is a complex logistic process that requires long distance shipping from Europe to Americas and Asia. Arkema promotes using returnable packaging via its network of decanting and storage facilities. For example, we deliver the odorants in bulk ISO containers first, where we offload it in order to fill SBC packaging. This allows so serve the customer with shorter lead times and optimized returnable packaging rotation.

Over the years of experience in odorization, Arkema’s team has developed an expertise on highly sensitive odorization operations. Odorflex^® is a one-stop shop service package that covers all odorization operations’ needs:

• Accurate selection of the right odorant
• Assistance to odorant sampling and analysis
• Odorant handling training, from basic information about odorization to spill drills
• Technical recommendations for new installations
• On site operations for sampling, repacking, redistribution, odor control
• Odorflex^® OED: odorant equipment decommissioning or cleaning before inspection
• Odorflex^® EOT, equipment odorant transfer.

Some of our specialized distributors are manufacturers for the odorisation industry allowing us to cover a worldwide equipment supply.

We are involved in technical committees and developing actively solutions for the use of hydrogen as renewable energy source and Carbon Capture Storage (CCS) to decarbonize the fossil resourced based industry.
 
Carbon capture and storage aim at capturing, transporting and permanently storing CO_² that would be otherwise emitted into the atmosphere. CCS technologies offer significant strategic value in the transition to low carbon economy by reducing carbon footprint of industrial activities and enabling the development of low carbon hydrogen as new energy vector.
 
Indeed, we are also particularly interested in the "blue" hydrogen market development, where the CO² emitted during hydrogen production is captured and stored to reduce its carbon impact. We are therefore looking to adapt our odorant solutions for this CO_² in order to detect leakages during onshore transport but distinguishing it from natural gas.