The much discussion on NRU (Nitrogen Rejection/Removal Unit in LNG processing. Let understand this today in this post as why is it required and its process.
👉 This is a low-temperature rectification (distillation) process that utilizes the different volatilities of methane and nitrogen to achieve separation.
👉 Most pipeline standards require that natural gas contain less than 4% nitrogen.
👉 Nitrogen rejection is done to increase the heating value of the gas
👉 This is basically combination of Column, Cold box and compressor (if required)
Why is it required to remove from LNG:
👉 If there is too much nitrogen present in a pipeline, there is a danger of vapor lock or combustion. Nitrogen also dilutes the heating value of the gas, resulting in a lower BTU and decreased value. High-nitrogen natural gas is essentially stranded, as it cannot feasibly be transported through pipelines to market.
👉 Nitrogen rejection is a difficult technical separation because of the similar molecular size of nitrogen (N2) and methane (CH4) and the lack of a selective reactivity such as there is with carbon dioxide or hydrogen sulfide in an amine plant.
Process of Rejection in NRU:
Pressure swing adsorption
Cryogenic separation
Lean oil absorption
👉 Pressure swing adsorption (PSA) uses an adsorbent to selectively separate nitrogen from methane. This adsorbent can be selected to either adsorb the methane or nitrogen, depending on the gas qualities. Once the adsorbent is saturated, the gas is regenerated from the adsorbent with a combination of pressure and thermal changes. PSA is used for gas dehydration, carbon dioxide removal, nitrogen rejection, and hydrocarbon dew point control.
👉 Cryogenic separation employs low temperature thermodynamic separation based on the comparative boiling points of methane (-259°F) and nitrogen (-320°F) . As the mixture cools, methane will condense before nitrogen, allowing the two to be separated. Cryogenic separation processes are extremely efficient, especially in large installations. Nitrogen concentrations can be reduced to as low as 1% with less power consumption than other methods.
👉 Lean oil absorption absorbs the methane away from the nitrogen in a higher molecular weight hydrocarbon and then regenerates the absorbed methane either through staged pressure reductions or through thermally-driven distillation.
Let see the snap which describe best to understand. Also wait for a video which explaining to understand process in NRU
#NRU
#LNG
#Refinery
#Piping
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2moThanks for sharing