Nitrogen injection

In a method for the production of pressurized nitrogen for injection application at high pressure, said method being of the type which comprises combusting natural gas in air, which is compressed prior to the combustion, whereby said combustion forms a flue gas containing nitrogen and carbon dioxide and said combustion binds the oxygen content of the air in the carbon dioxide;

• removing the carbon dioxide from the flue gas by absorption, and then pressurizing the remaining nitrogen to a high pressure required for said injection application, wherein the improvement comprises compressing the combustion air prior to the combustion to an intermediate pressure between said high pressure and atmospheric pressure, the heat energy developed by the combustion being heat exchanged at the intermediate pressure with water for production of steam, which subsequently is utilized for mechanical work for compression to the intermediate pressure and maintenance of said high pressure.