Nitrogen removal technology

Paul Boughton

HNNG Development LLC, leaders in nitrogen removal technology for the global natural gas industry, has recently commissioned independent industry consultant, Muse Stancil, to compare the operational benefits and economics of technologies for the removal of nitrogen from otherwise uneconomic natural gas reserves.

Nitrogen removal technologies represent a significant opportunity to develop domestic reserves of natural gas - those which contain too much nitrogen to be transported by the natural gas pipeline network and thus remains shut-in, underdeveloped, or undeveloped.

Most natural gas pipelines have a quality specification that sets a limit on either the nitrogen or total content of inert gases, or establishes a minimum heating value for gas delivered into the pipeline.

In the US, the specification typically limits total inerts in the gas stream to a maximum of 4 mol%, including nitrogen. Thus, high nitrogen natural gas is generally defined as any natural gas stream having a nitrogen content greater than 4 mol%.

Nitrogen takes up pipeline capacity for which no revenue is received and inhibits the flow of gas into pipelines, between pipelines and, potentially, to the ultimate consumers of the gas.

The report concludes that, when compared to the Engelhard PSA-type process, HNNG's AET Process is more attractive on all but the smallest size plants processing gas with the lowest N2 content.

When compared with the BCCK cryogenic-type process, the AET Process is the best choice for processing when N2 content is less than 30 mol%, regardless of plant size.

As facilities increase in size above 10 MMscf/d for N2 contents above 30 mol%, the BCCK process is indicated to be slightly more economical.

However, the much longer delivery time for cryogenic equipment should be considered when there is little difference in processing costs as compared to the AET Process, and for larger plants this time value of money is even more important.

Globally there are over 1,500 gas fields with a 'high' nitrogen content (5-40 per cent by volume). These include:

* Approximately 16 per cent (24 trillion cubic feet) of the USA's identified gas reserves.
* More than 100 trillion cubic feet (Tcf) in Russia.
* At least 4 Tcf in China.

Gas prices have increased over the past few years to well above the $3.00-4.00 per Mcf generally required to exploit this high nitrogen resource base. These high nitrogen natural gas reserves are becoming increasingly attractive as the market need for natural gas continues to grow. Global demand is expected to increase by 50 per cent over the next 20 years, with natural gas prices projected to remain strong, partly as a result of declining domestic gas supplies in Europe and North America.

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