January 2018, Vol. 245, No. 1
Features
ODORIZATION: The Not-So-Sweet Smell Of Safety
Ensuring that natural gas is easily detectable is not just for the sake of customer safety but also concerns economics. For example, the loss of over 607,000 tons of gas by the Southern California Gas Co. (SoCalGas) storage facility near Los Angeles is estimated to have cost the company $665 million in lost gas, according to the San Diego Tribune.
In its raw state, natural gas is comprised of a mixture of inflammable gaseous hydrocarbons, chiefly methane as well as propane, butane and other substances.
Natural gas is lighter than air, non-toxic and is only explosive when mixed in the air at a concentration of between 5-15%. When a leak occurs, whether in an enclosed space, or from a pipeline, tanker, canister or storage facility, the consequences can be serious.
Because natural and shale gas is colorless and odorless, the addition of an artificial odor as a form of alert to a gas escape seemed an obvious solution. Odorization, which was first proposed by German scientist R. Von Quaglio in the 1880s, did not become common until after World War I when it was adopted by many German towns.
However, the practice of adding an artificial odor to gas was slow to spread. It was not until after the 1937 explosion at a Texas school, which killed over 300 students and teachers (when a spark from a sanding machine ignited an undetected gas leak), that gas odorization was widely adopted throughout North America.
In Europe, large-scale gas odorization did not take place until after the discoveries of significant gas finds in the North Sea, which led to natural gas replacing manufactured gas in homes and businesses during the 1970s.
Market Expansion
Natural gas is fast becoming the fuel of choice in power generation since it produces fewer greenhouse gases than other fossil fuels and creates no mechanical impurities such as soot. This makes it much more environmentally friendly than coal or oil.
Natural gas meets 25% of global energy demand, boosted by the growth in North American shale gas from 1.2 Bcf/d in 2007 to 15.2 Bcf/d in 2015 and growth in LNG production to a record 258 million tons in 2016. In recent years, trade in LNG and pipeline gas has grown at an annual average of 6% and 3%, respectively, creating a dynamic market for odorizers.
The odorization process results in the distinctly unpleasant, strong rotten egg smell of escaped gas. The addition of an artificial odor can take place at various points along the gas supply chain.
For instance, producers of natural gas and biogas can add it at the source prior to distribution by pipeline. Others, such as regasification plants and regional distributors, can add odor before gas is delivered to customers by pipeline or in liquid petroleum gas or compressed natural gas formats. In some countries, artificial odors are added at LNG road transport filling stations or at ship bunkering facilities.
Method
Wick-type odorizers range in scale from tiny to large. Where gas is destined for a few or just one large gas customer, the tiny wick odorizer is appropriate. Larger wick odorizers can meet the gas needs of a small town. The odorant is drawn up the wick from the container and into the gas stream. It works on the same principle as the wick in an old-fashioned kerosene lantern.
The absorption bypass odorizes a portion of the gas stream, the amount being dependent on the flow of gas in the line, and runs it through a tank containing liquid odorant. The gas is then passed over the top of the liquid. Variations exist where wicks are used to increase odorant vaporization.
For high-volume systems (and for some smaller volume systems), liquid injection of small amounts of liquid odorant to the moving gas is common. A feature of this method is the adjustable pump which offers a range of injection rates. In modern systems, computers control and vary the injection rates.
Artificial Odors
Since the start of the 20th century, the chemical industry has developed a whole range of artificial odors to be used by pipeline operators based on common compounds such as mercaptans and sulphides. Dimethyl disulfide, made by oxidizing methyl mercaptan, is used for blends of natural gas. Industrial odors added to natural gas include ethyl mercaptan (EM), ethanethiol or Scentinel A, diethyl sulphide (DES), ethylthioethane, tetrahydrothiophene (THT) and scentinel T or thiophene.
Traditionally in Europe, sulfur-based and sulfur-free varieties of odorizing substances have prevailed. THT is the sulfur-based odorant most widely used in the EU, whereas in green Germany sulfur-free odorants dominate. However, since 2001, over 40 gas distributors in Germany, Austria and Switzerland have changed their odorization from THT or mercaptans to a sulfur-free odorant.
Odorization ingredients and their strengths are prescribed by industry standards that form the basis of regulations in both the U.S. and Europe. In the U.S., odorization is regulated by regulation CFR Title, 49 Part, 192.625, and in Europe by regulation G280 (DVGW) prevails.
Industry best practice suggests the concentration of the odorant, also referred to as stentching agent, should be adequate: too much odorant could cause health problems as well as equipment damage, and many false alarms of leaking gas. Too-little odorant risks end-consumers being unable to smell a gas leak.
This enables a leak to be detected well before the gas concentration in the air reaches the lower flammability limit (LFL) of 5% for natural gas and 2% for liquid petroleum gas. These standards are similar across EU member states.
In Russia, the state-controlled gas company Gazprom uses a standard of 10-30 grams of artificial odorant per 1,000 cubic meters of gas, depending on its quality, pressure and temperature as well as the condition of the pipeline, its length and flow rate.
Future
The market for gas odorization products and systems is likely to mirror future growth in demand for gas for power generation, heating and other industrial processes. With U.S. shale gas production expected to account for 60% of the increase in gas supply between now and 2035, the U.S. market will be buoyant for many years to come.
As the number of countries supplying and consuming LNG increases, from the present day 18 and 35, respectively, fresh demands for safety measures including odorization will occur, especially in Mexico, Brazil, China and South Africa, where plans to develop a national gas distribution network are advancing.
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