Procedure and installation of loading natural gas treatment to obtain treated natural gas and a fraction of C5 + hydrocarbons

摘要

Process for treating a natural gas of charge (12) dried and decarbonised to obtain a treated natural gas (14) intended to be liquefied and a fraction (16) of C5 + hydrocarbons, the process comprising the following steps: - cooling of natural gas of charge (12) in a first heat exchanger (20) to form a precooled charge current (54). - introduction of the precooled charge stream (54) into a first separator tank (22) to form a precooled gas stream (56) and, eventually, a precooled liquid stream (58); - dynamic expansion of the precooled gas stream (56) into an expansion turbine (24) and introduction of the expanded stream (60) from the expansion turbine (24) into a first purification column (26); - possibly, the expansion of the precooled liquid stream (58) and introduction into the first column (26); - production at the head of the first column (26) of a purified natural head gas (70); - recovery at the bottom of the first column (26) of a liquefied natural gas (74) in the background; - introduction of liquefied bottom gas (74) in a second column for the removal of C5 + hydrocarbons; - bottom production of the second column (30) of a fraction (16) of hydrocarbons; - production, at the head of the second column (30) of a column head gas stream (86) and introduction of the column head gas stream (86) into a second separator tank (40) to form a stream liquid (100) from the bottom and a gaseous stream (90) from the head; - introduction of a first part (102) of the liquid stream of the lower part (100) under reflux into the second column (30) and introduction of a second part (104) of the liquid stream of the lower part (100) at reflux within the first column (26); - injecting at least a part of the head gas stream (90) from the second separator vessel (40) into the purified natural head gas (70) to form the treated natural gas (14), the process comprising the steps following: * overheating of purified head natural gas (70) from the first column (26) in the first heat exchanger (20) by thermal exchange with the natural charging gas (12); * expansion of the liquefied natural bottom gas (74) from the first column before its introduction in the second column (30); * compression of the gaseous stream (86) of the column head in a first compressor (38) and cooling before its introduction into the second separator tank (40); characterized in that the hydrocarbon fraction (16) is a C5 + hydrocarbon fraction, because during the dynamic expansion stage, the precooled gas stream (56) expands to a pressure greater than 35 bar, advantageously greater than 40 bar, more advantageously greater than 44 bar, and because the pressure in the second column (30) is less than 25 bar, advantageously less than 20 bar, more advantageously less than 15 bar, and because it comprises a heat exchange ratio in a second heat exchanger (28 ) of the second part (104) of the liquid stream of the lower part (100) with the liquid liquefied natural gas (74) from the first column (26).