Commercial helium production is a multi-step process. To separate helium from other gases, it must be extracted from natural gas. It must be processed to remove contaminants and then extracted using cryogenic technology to liquefy the gas. This rigorous process ensures high-quality helium manufacture for numerous industries.
Helium is the second most abundant gas in our cosmos after hydrogen gas. However, the specific kind of helium gas utilised in applications like gas chromatography is taken from natural gas. This is an issue of depleting resources that causes helium gas shortages. Helium, a remarkable gas with diverse applications, is crucial in numerous industries. Ever wondered how this valuable resource is manufactured commercially? Join us as we uncover manufacturing intricacies and explore helium's significance in various industries.
Did you know? When a balloon is filled with helium and released, it will rise until it attains a height of about 33,000 feet (10 km).
Where Is Helium Found on Earth?
Helium gas is abundant in space because it is a byproduct of fusion reactions inside stars. But the amount of helium gas found on earth for being used in various essential applications is limited. Helum-4, a particular type of helium gas, exists naturally underground through the radioactive decay and disintegration of elements like uranium and thorium. Fortunately for us, part of the helium-4 gets trapped and combines with the natural gas present in layers beneath the earth's surface. Subsequently, wells are dug to release helium-4, which is then extracted from the earth.
Problem with the Natural Extraction of Helium
Natural gas contains helium gas in varying amounts, ranging from less than 1% to 4% by volume. Considering the limited quantity of helium gas, the supply chain is vulnerable because of the rising demand for helium worldwide. Since there aren't many natural gas reserves with significant helium gas concentrations, extracting helium from these reserves is likely to be expensive. This is because of the small amounts of gas that would be produced. The upgrading of natural gas can be done in several ways. Helium content is extracted using a cryogenic distillation technique when the gas has more than 0.4% helium by volume. After being extracted from natural gas, helium is refined again to a purity of 99.9 % before being used commercially.
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Steps For Extracting and Processing Helium
Below are typical steps for extracting and processing helium:
1. Pre-treating
Since this technique uses a critically frigid cryogenic section during the procedure, any contaminants that might solidify—such as carbon dioxide, water vapour, and bound heavy hydrocarbons—must initially be eliminated from the natural gas in pretreatment to avoid blocking the cryogenic piping.
The process of pre-treating technique is as follows:
- A pressure of 54 ATM is applied to the natural gas. It then enters into a scrubber, exposing it to a jet of monoethanol-amine, which captures and removes carbon dioxide.
- The gas stream travels through a molecular sieve, which separates the bigger water vapour molecules from the flow. This allows the smaller gas molecules through. The water is back-flushed out of the sieve and expelled.
- As the gas flows over a bed of activated carbon, residual heavy hydrocarbons in the stream accumulate on its surfaces. Activated carbon is replenished regularly. Methane and nitrogen now make up the majority of the gas stream, with trace quantities of helium, hydrogen, and neon.
2. Separating
Using a fractional distillation technique, natural gas is divided into its main constituents. The vertical columns used to separate are known as fractionating columns, and this term is often abbreviated to fractionation. Nitrogen and methane are isolated from one another in two phases during fractional distillation, leaving a mixture of gases with a significant amount of helium. Until the separation process is complete, each component's concentration level is raised at each stage. This procedure, which removes excess nitrogen from natural gas, is sometimes known as nitrogen rejection in the natural gas industry.
The process of separating nitrogen and methane using a separation technique is as follows:
- Methane and nitrogen from the cryogenic region enter a plate-fin heat exchanger from one side, and the gas stream exits from the other. While methane and nitrogen are heated up, the entering gas stream is cooled.
- After passing through an expansion valve, the gas stream is allowed to expand quickly as the pressure lowers to around 10–25 atm. This expansion rapidly cools the gas stream, which causes methane to liquefy.
- The gas stream—now partly liquid and partly gas—enters the bottom of the high-pressure fractionating column. Extra heat is lost when the gas ascends through the column's inner baffles.The methane continues to liquefy, generating a methane-rich composition at the bottom of the column, and the bulk of the nitrogen, along with other gases, travels to the top.
- The mixture of liquid methane, known as crude methane, is pumped out of the high-pressure column's bottom before being cooled in the crude sub-cooler.
- Before entering the low-pressure fractionating column, it first travels through another expansion valve, which reduces the pressure to around 1.5 atm. Most residual nitrogen gets separated as liquid methane moves down the column. This yields a liquid that contains slightly more than 4% nitrogen and the remaining 86% methane. Pumping off, warming, and evaporating this liquid enhances natural gas. The top portion of the low-pressure column is piped to release gaseous nitrogen, which is either vented or trapped for additional processing.
- In the meantime, a condenser cools the gases from the high-pressure column's top. The upper part of the low-pressure column is fed with a large portion of nitrogen that has condensed into vapour. The unused gas is called crude helium. About 50–70% of it is helium, 1–3% is uniquified methane, traces of neon and hydrogen, and the rest is nitrogen.
3. Purifying
To eliminate most other components, crude helium must be refined further. Given the purity of the raw helium and the finished product's intended use, this is typically a multi-stage process incorporating various separation techniques.
The process of purifying technique is as follows:
- To begin with, the raw helium is cooled to roughly -193° C. Most of the nitrogen and methane condense into a liquid at this temperature and are drained out. Now around 90% of the gas mixture is pure helium.
- To add oxygen, the air is introduced into the gas mixture. Most of the hydrogen in this mixture reacts with oxygen in the air to generate water vapour. This is after being heated in a preheater and passed via a catalyst. Water vapour condenses and is drained out when the gas is cooled.
- The gas mixture enters a pressure swing adsorption (PSA) unit consisting of numerous parallel-operated adsorption tanks. There are hundreds of small pore-filled particles inside each vessel. Some gases get trapped within the particle pores when the gas mixture flows through these particles under pressure. The air pressure is reduced to release the trapped gases, and the gas flow is reversed.
- Depending on the containers' dimensions and the gas concentration, this cycle continues after a few seconds or minutes. This technique eliminates most of the leftover methane, nitrogen, and water vapour from the gas mixture. At this point, the helium is 99.99% pure.
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Conclusion
Deep down, it was created thousands of years ago due to the radioactive disintegration of heavy metals like uranium and thorium. It rises, gets caught in gas pockets, and is removed from gas fields. Two steps are involved in preparing the helium present in natural gas.
The first process is removing crude helium from the natural gas stream. This generally contains between 50% and 70% helium by volume after extraction.
In the second phase, crude helium is refined to create pure helium in various commercial grades.
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