Pros and cons of different Nitrogen Removal Unit (NRU) technology

Abstract For any gas or LNG plant, higher levels of nitrogen within your feed gas mean lower profitable volumes or additional capital investment. Nitrogen Removal Units (NRU) can be expensive to build and difficult to operate. The challenges facing the gas industry are highlighted by the Gas Technology Institute (GTI, USA) in their estimates that 11% of current daily gas production and 16% of all known gas reserves in the USA contain some nitrogen. Recent gas reservoir discoveries around the world were also found to contain significant levels of nitrogen up to the 15% range. Also, some current production techniques for maintaining crude recovery from a reservoir utilize the injection of nitrogen as enhanced oil recovery (EOR) method. Gradually and eventually, the equilibrium nitrogen dissolved in the crude will come to the surface as associated gas when the nitrogen breaks through. Gas companies typically set maximum concentration limits on nitrogen content in the pipeline between 4.0 and 7.0 percent depending on the local product specifications. Therefore, in general, nitrogen levels of greater than 7.0 percent must undergo removal. The author's focus in this paper is on the selection/design criteria to be considered for the selection of an optimum NRU technology.  1) Feed gas nitrogen concentrations,  2) NRU inlet pressure,  3) NRU capacity,  4) Product Specifications,  5) Approaches for the final disposition of the recovered hydrocarbon stream: (e.g., as fuel gas, re-injection or recycle back to feed gas),  6) Environmental NOx emissions impact,  7) Allowable methane concentration in the nitrogen vent. The author summaries all currently available technologies including both commercially demonstrated NRU technologies as well as the future developments. All of those available technologies to be introduced by the author by way of process flow diagrams, descriptions, technology highlights, pre-treatment requirements, strength and weakness and technology licensor/vendor lists are:  • Cryogenic Distillation,  • Membranes (Membrane Technology and Research (MTR),  • Molecular Gate System,  • Solvent Absorption,  • Nitrogen Sponge,  • Pressure swing adsorption (PSA), Carbon Molecular Sieve (CMS),  • Lean Oil Absorption,  • Chelating chemical.