Introduction to double-column Nitrogen Rejection Unit NRU
Guofu Chen, PEs, PMP, Certified HYSYS Expert
Process Engineering Expert at Carbon Capture, Hydrogen, LNG and Midstream with PMP & Computer Programming Expertise
Introduction
It is estimated that 25% of the United States natural gas reserves contain unacceptably large quantities of nitrogen. Nitrogen is inert and lowers the BTU value of natural gas. It also takes up capacity in pipelines that could be used for valuable methane. Thus, nitrogen needs to be rejected from the gas through a Nitrogen Rejection Unit NRU. Typically, the feed to nitrogen rejection unit comes from the top of the DeMethanizer column of a cryogenic NGL recovery unit.
Process Description
The feed gas is first cooled against the HP column reboiler and further cooled in the main cryogenic heat exchanger before introducing to the HP column. The bottom methane rich liquid is subcooled and sent to an intermediate location of LP column. The top Nitrogen rich liquid is sent to the top of the LP column after being subcooled against nitrogen vapor. Nitrogen vapor out of the top of LP column first subcools the nitrogen rich liquid and then the methane rich liquid, and ultimately the cold is fully recovered in the main cryogenic heat exchanger.
The LP column reboiler and HP column condenser is physically one heat exchanger. On the LP column side, methane liquid is reboiled and on the HP column side, the nitrogen rich vapor is condensed. The bottom methane liquid from the LP column is pumped to the subcooler 1 and finally sent to the main cryogenic heat exchanger after the cold being recovered.
Result
In the feed, the nitrogen content is 30%, after the first HP column, it becomes 22.5% and finally in the LP column, N2 is reduced to 4%, which is generally well accepted pipeline specification in the United States.
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Reference: Muhammad Tahir Ashraf, PARAMETRIC OPTIMIZATION OF DOUBLE COLUMN NITROGEN REJECTION UNIT
Chemical Engineer
3 年Hi, it looks awesome! Could I please have access to further information and the reference parameters?
Process Engineer at EPRF || Aspen Certified Expert User || Chemical Engineer
3 年That's great, it really helps me. Kindly share the material and energy balance sheet of each and every stream, so it would be easier to simulate. Thank you!
Process Engineer at Mega Methanol Plant
7 年NICE
Retired
7 年Nice.
Gofu, What is the feed N2 content? Product BTU recovery% and heavy hydrocabon recovery using this process? MTR can handle upto 50 % N2 in the , product BTU recovery 90%, heavy hydrocarbon recovery more than 95%. I would like to hear from you on NRU. Thanks