Q3 2009 / Helium extraction and production techniques

Three essential steps are needed to produce helium from natural gas by any production facility (Figure 1) – extraction, purification, and liquefaction. 

Step 1: Helium extraction

Any natural gas containing helium must first be cryogenically processed to remove moisture, carbon dioxide, sulfur compounds, and heavier hydrocarbons to prevent freezing at low temperatures. 

To accomplish this, the first step is to partially condense natural gas into two phases – liquid and gas to collect the heavier hydrocarbons. 

Step 2: Purification

However, because helium is soluble in natural gas, even as the natural gas is condensed, a significant quantity (along with some nitrogen) is also dissolved in the remaining liquid state natural gas. Unless that dissolved helium is also extracted, it will leave the plant along with the natural gas and be lost.

That’s why two major techniques were developed to separate the remaining quantities of helium left in the natural gas. The first technique is one in which helium is concentrated with the nitrogen 

 through the use of one or more distillation columns. With this technique the nitrogen and helium leave the top of the column, and the liquid natural gas exits the bottom of the column.

The second technique is called “flashing” (Figure 2). This technique involves dropping the pressure on the liquid natural gas that now contains dissolved nitrogen and helium. Since helium is more volatile than natural gas, much of the dissolved helium returns to the gaseous phase. 

The use of either technique depends on the composition of the natural gas and the concept of the design engineers. Generally, flashing is more energy intensive and distillation more capital intensive. Engineers may even combine these technologies in the design of some plants.

The composition of recovered helium stream at this point can range from a few percent up to 12% helium from Liquefied Natural Gas (LNG) plants and Nitrogen Rejection Plants (NRU’s). The LNG plants are those outside the U.S. in which the natural gas is liquefied for transportation purposes. The NRU plants are those containing a high concentration of nitrogen that must be removed to meet natural gas utility pipeline specifications (Figure 3). 

The recovered “crude” helium stream at this point is compressed to between 300 and 500 psig. The gas will likely still contain components of nitrogen, small amounts of methane, and trace impurities (in the ppm range) of gases such as hydrogen and neon.

Hydrogen, moisture, and carbon dioxide removal

Hydrogen is removed at this stage by adding a small quantity of air or oxygen and allowing it and the oxygen to convert to moisture through the use of a catalyst.

In a few facilities hydrogen is removed later on in the process – in a liquefier along with neon, using activated carbon at 20ºK for gas adsorption.

However, most systems employ a catalytic conversion technology in which air or oxygen is blended into the impure stream. The stream is then passed over a catalyst which causes the hydrogen to combine with the oxygen to produce water. This catalytic reaction generates heat, and if the hydrogen concentration is above a certain range, two beds of catalyst are provided with a cooling device inserted in between them.

The still crude helium stream must be free of moisture and carbon dioxide. However, helium recovered from purging or other downstream operations are sometimes again returned to this area of the process for a second re-purification. Process dryers are used to remove the moisture and any trace amounts of carbon dioxide from the combined streams.

Nitrogen removal

Next, the still impure helium stream is upgraded to 80 to 85% purity by cooling it to cryogenic temperatures and thereby condensing a large portion of the remaining nitrogen in the Nitrogen Condenser (Figure 4). Here, the gas stream is cooled to liquid nitrogen temperatures condensing most of the nitrogen. Both streams are warmed back to ambient temperature and the nitrogen gas typically vented. The pressure drop of the nitrogen provides most of the refrigeration due to the Joule-Thompson effect, supplemented by the addition of purchased liquid nitrogen for an additional cooling action. 

Any trace amounts of remaining nitrogen in the helium is removed by adsorption.

Pressure Swing Adsorption Technology (PSA)

PSA consists of multiple vessels constructed in parallel filled with a molecular sieve on a preassembled skid containing automatic valves, piping, and a surge tank. PSA is now available from multiple sources, is easy operate, and adaptable to the larger helium plants now under construction. PSA removes all of the remaining impurities in the gas stream, except for neon and hydrogen, to less than 1 ppm(v/v).

The feed stream is routed through one vessel where all the impurities are adsorbed on the molecular sieve. After approximately 10 to 15 minutes, the feed is then routed through a fresh vessel and the initial empty vessel is de-pressured allowing the molecular sieve to release the adsorbed components.

However, during the venting of the PSA vessels, an important amount of helium contained in this de-pressured gas must still be recovered. This is accomplished by compressing the gas and returning it to the inlet of the nitrogen condenser. At this point the helium exiting the PSA is nearly pure except for trace amounts neon and possibly hydrogen.

The neon and any hydrogen is eventually removed by adsorption on carbon at a temperature of -424Fº (20ºK) resulting in inherently pure liquid helium.

Step 3: Liquefaction

Except a few very small plants, all helium production plants completely liquefy the helium for sale to their customers ? the major industrial gas companies. Transportation in liquid phase is the only economical means to distribute large quantities of helium (Figure 5). 

Liquefaction consumes the largest quantity of energy on a unit cost basis, in the whole process of extraction and purification. Helium contains only a small amount of latent heat. Since it is the coldest of gases in its liquid state, it is also easily vaporized. Therefore, the liquefier must be sized to liquefy not only the pure feed gas, but also recover and liquefy any liquid vaporized in handling and filling the liquid containers.

The refrigeration to liquefy helium consists of a vacuum, super-insulated cold box containing brazed heat exchangers, and gas-bearing turbo-expanders connected to oil-flooded screw compressors.

Liquefiers are designed with efficient rotary machines such as gas-bearing turbo-expanders with a service life of more than 200,000 hours.

There are only two key firms offering large helium liquefiers today – Linde Kryotechnik and Air Liquide (Figure 6). 

Helium production economics

In U.S. facilities, one of the largest costs is the royalty paid to the natural gas owner – usually 1/8 of the value of the crude helium. The large base load plants are mostly also owned by the gas owners who may not recognize royalty separately as a cost.

The second largest unit cost of capital is the investment assigned to the unit cost of helium. It usually determines the economic size of a recovery and purification facility due to its inelastic cost. With few exceptions, helium production, along with liquefaction is not justified for production rates of less than 100 Million Standard Cubic Feet per Year (MSCFY) (TABLE 1). 

The third largest cost is energy consumption. This consists mostly of compression in the processing and liquefaction. Most facilities consume liquid nitrogen as a refrigerant that is either purchased or produced on-site.

Helium today has numerous applications ranging from its use in parade balloons to MRIs and space research. As a strategic commodity the manufacture, production, and distribution of this incredibly valuable gas will no doubt gain increasing importance in the future as more high-tech applications make use of its unique properties.

Understanding the basics of its manufacturing steps will aid designers and end users as well as those involved with supply and distribution in making better decisions.

A short history of helium extraction production

To fully understand helium production today, it is useful to look at the logic and justification for the helium extraction plants built over the last 50 years.

All helium produced is produced as a by-product recovered from natural gas. Table 1 is a chronological list of all the commercial helium plants built, and the major justification for those facilities. There are only a few locations where the helium concentration is high enough (usually above 1%) to justify a helium-only plant.

Major quantities of helium first became available because of a U.S. government extraction program inspired by the perception of helium as a strategic material. The program began in the 1960’s. Since then, a number of natural gas plants requiring nitrogen removal and base load liquid natural gas (LNG) plants have been built which concentrated the small quantities of helium to high enough levels for extraction.

In 1962, the first commercial gaseous helium plant was built for Kerr-McGee by Air Products and was put into operation at Navajo, Arizona. The reservoir contained a gas with approximately 6-8% helium in nitrogen, with a small quantity of other components. In that era, helium was extracted and distributed in cylinders, tube trailers, and railcars. Liquefaction was not yet applied to production facilities.

In 1963, the government initiated the Helium Conservation Program. The Department of Interior contracted with a number of energy companies to build helium extraction facilities to save unneeded helium lost as the natural gas was consumed. The Program also included the construction of a government-owned and managed pipeline connecting plants from North Central Kansas through the Oklahoma and Texas Panhandle to collect the recovered crude helium (55% minimum) and store it in a depleted natural gas reservoir near Amarillo, Texas.

Although the primary goal was helium extraction, to accomplish that, heavier hydrocarbons had to be removed which also had a value. In addition, for some plants, nitrogen also had to be removed to balance the loss of BTU’s as well as meet pipeline specifications. These came to be known as Nitrogen Rejection Units (NRU’s). The design, construction, and operation of these facilities boosted the development of the technology for helium extraction and eventually led to the large, wound heat exchangers now used for large LNG plants.

However, the Department of Interior cancelled the program in 1973. Now, the crude helium producers were free to use the Bureau of Mines reservoir for a fee, which most did.

After 1977, helium demand continued to grow at an average compounded growth rate of approx 8-1/2%/year. This meant that an increasing demand was becoming supplied by privately held crude helium firms contracted by industrial gas companies. This led to the installation of helium purification and liquefaction plants at various locations along the helium storage pipeline.

During the 80’s and 90’s helium demand continued to grow and natural gas production was also increased, further increasing the number of extraction plants.

In the earlier government-sponsored helium extraction plants, helium was the key product, but in these newer facilities, helium was considered a by-product. During this period the construction of large-base LNG plants began in the Middle East. Their natural gas contained what could be described as trace quantities of helium. The liquefaction of natural gas (the primary product) also produced concentrated helium as a by-product.

Meanwhile, in the U.S., the crude helium storage reservoir and pipeline network still continued to provide a valuable service right up to present. The production plants tied into the system now use it as a giant flywheel, continuing to extract helium during market turndowns and drawing at high rates during high demand periods.

About the author – James E. West

James E. West is President of Nishi Associates, Bethlehem, PA. West has participated in the technology and business aspects of industrial gases and cryogenic technology for over 40 years. He has designed, operated and constructed a variety of helium recovery and production systems. Currently he and his associates offer technical and business solutions to users, producers and distributors of industrial and specialty gases. He can be reached at by phone at 610-984-7604 or by email at: jim@nishicorp.net.