The patented AET Process Nitrogen Rejection Unit utilizes noncryogenic absorption to separate methane and heavier hydrocarbons from nitrogen containing natural gases. If desired, propane plus NGL product can also be produced.
The absorbed methane and heavier hydrocarbons are flashed off from the solvent by reducing the pressure of the absorber bottoms stream in multiple steps to minimize gas compression. The separated gases leave as the sales gas product. The liquid from the proven, heatless flash regeneration step is returned to the top of the methane absorber as lean solvent. If helium is present, the overhead stream from the methane absorber is further processed in a membrane/PSA unit to produce Grade A helium, and nitrogen product is available at high pressure. For most applications, there are no solvent make-up requirements.
Operating conditions: Wide operating pressure range: 240 psig to 1,200 psig feeds without inlet gas compression. Low pressure drop for N2: 15–30 psi is typical and suitable for noncryogenic helium production and N2 reinjection. Inexpensive metallurgy: Lowest temperature, limited by C3 refrigeration, permits use of predominantly carbon steel metallurgy. Feed pretreatment: CO2 removal is not necessary; glycol injection for dehydration is adequate.
Economics: Low, capital operating costs: When high flexibility for inlet gas flow and composition is desired, the initial and ongoing costs are lower. High methane recoveries: One pass methane recovery typically exceeds 98+%. Low nitrogen content sales gas: Sales gas product at