science

Sour gas

Sour gas is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sour gas rather than just read about it. In short: Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide (H2S). Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure.

Key takeaways

Sour gas belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sour gas to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sour gas from memory before moving on to harder problems.

Reference excerpt

Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide (H2S). Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure. However, this threshold varies by country, state, or even agency or application. For instance, the Texas Railroad Commission considers a sour gas pipeline one that carries gas over 100 ppm by volume of H2S. However, the Texas Commission on Environmental Quality has historically defined sour gas for upstream operations – which requires permitting, reporting, and possibly additional emission controls – as gas that contains more than 24 ppm by volume. Natural gas that does not contain significant amounts of hydrogen sulfide is called "sweet gas". Although the terms "acid gas" and "sour gas" are sometimes used interchangeably, strictly speaking, a sour gas is any gas that specifically contains hydrogen sulfide in significant amounts, whereas an acid gas is any gas that contains significant amounts of acidic gases such as carbon dioxide (CO2) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being toxic, hydrogen sulfide in the presence of water also damages piping and other equipment handling sour gas by sulfide stress cracking. Natural gas typically contains several ppm of volatile sulfur compounds, but gas from one well in Canada is known to contain 90% hydrogen sulfide and others may have H2S contents in the tens of percent range.

Methods for sweetening

Within oil refineries or natural gas processing plants, the removal of hydrogen sulfide and other organosulfur compounds is referred to as "sweetening". The sweetened product lacks the sour, foul odors of mercaptans and hydrogen sulfide. Before raw natural gas containing hydrogen sulfide or carbon dioxide can be used, the raw gas must be treated to remove those impurities to acceptable levels, commonly by an amine treatment process. The removed H2S is most often subsequently converted to by-product elemental sulfur in a Claus process or it can be treated in a wet sulfuric acid process unit where the by-product is sulfuric acid. Alternatively, the highly concentrated H2S gas, the by-product of the amine treatment plant, can be recompressed by gas compressor units specifically designed to handle highly toxic gas and injected back in the reservoir. In addition to utilizing an amine or Claus process, liquid redox is becoming increasingly popular. Another product removed during sweetening is carbonyl sulfide.

See also Rectisol Shah gas field, Abu Dhabi

References

Worked examples

Example 1 — a first encounter with Sour gas

Start with the simplest possible case. Write down what Sour gas claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sour gas before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sour gas ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sour gas

In research: Sour gas appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sour gas in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sour gas is common in secondary-school and first-year university syllabi. It links to neighbouring topics Natural gas, so understanding it makes those chapters shorter.
In everyday life: Look for Sour gas outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sour gas in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sour gas means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sour gas out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sour gas in simple terms?

Why does Sour gas matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sour gas?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sour gas.