Dual-Column Cryogenic Fractionation for High-Flow Nitrogen Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing nitrogen rejection units (NRUs) face challenges in efficiently removing nitrogen from natural gas streams, particularly at high flow rates and varying nitrogen concentrations, leading to increased capital and operating costs, greenhouse gas emissions, and reduced flexibility in handling carbon dioxide and nitrogen variations.
Innovation Solution
A system and method utilizing two fractionating columns with independent reboiler and condenser duties, allowing for flexible temperature control and reduced compression requirements, capable of processing high nitrogen concentrations and integrating natural gas liquids (NGL) extraction, and optionally recovering helium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single fractionating column is used for nitrogen rejection, then capital expenditures are reduced, but the system cannot handle wide variations in nitrogen concentration and requires strict CO2 removal
Solution Approach 1:
The single fractionating column is segmented into two distinct sections: a lower section for CO2 removal and an upper section for nitrogen rejection. This segmentation allows the system to handle both CO2 tolerance and nitrogen separation functions within one column, providing flexibility for varying nitrogen concentrations while avoiding the need for multiple separate columns and reducing capital expenditures.
2Manufacturing precision
If cryogenic temperatures are used for nitrogen rejection, then nitrogen separation efficiency is improved, but CO2 freezes causing blockage and process disruption
Solution Approach 1:
The fractionating column is divided into functional sections with the lower section dedicated to CO2 removal at moderate temperatures and the upper section for nitrogen rejection. This segmentation prevents CO2 from reaching the cryogenic temperatures needed for nitrogen separation, eliminating freezing and blockage issues while maintaining nitrogen separation efficiency.
Solution Approach 2:
CO2 is removed in the lower section of the column before the feed stream reaches the upper nitrogen rejection section. This preliminary action prevents CO2 from entering the cryogenic zone where it would freeze and cause blockages, allowing the upper section to operate at optimal temperatures for nitrogen separation.
3Device complexity
If the first column overhead stream is used to provide reboiler duty for the second column, then system complexity is reduced, but the system cannot handle wide variations in nitrogen content
Solution Approach 1:
The single column is segmented into independent functional sections with separate heat balance zones. The lower CO2 removal section and upper nitrogen rejection section can operate with different heat requirements, allowing the system to accommodate wide variations in nitrogen content while maintaining relatively simple overall system structure.
4Manufacturing precision
If higher compression is applied to meet pipeline specifications, then gas quality is improved, but operating expenditures increase
Solution Approach 1:
Nitrogen is removed as a liquid side stream near the top of the column before the gas requires final compression for pipeline delivery. This preliminary removal of the inert component reduces the volume of gas that needs to be compressed to meet pipeline specifications, thereby reducing compression energy requirements while maintaining gas quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system efficiently removes nitrogen from natural gas streams at high flow rates, reduces overall compression requirements by up to 40%, and integrates NGL extraction, while maintaining low greenhouse gas emissions and increased carbon dioxide tolerance, despite higher initial capital costs.
Implementation Method 1
two fractionating columns with independent reboiler and condenser duties, allowing for flexible temperature control
Implementation Method 2
A system and method utilizing two fractionating columns with independent reboiler and condenser duties, allowing for flexible temperature control
Data Source
AI summary
A system and method for removing nitrogen and producing a high pressure methane product stream from natural gas feed streams having wide variations in nitrogen and methane content are disclosed. Optional add-on systems may be incorporated into the nitrogen and methane separation to produce an NGL sales stream to reduce excess hydrocarbons in the nitrogen vent stream, or to recover helium. The system and method of the invention are particularly suitable for use with feed streams in excess of 50 MMSCFD and up to 300 MMSCFD and containing up to 100 ppm carbon dioxide. Typical power requirements for compressing the methane product stream to produce a suitably high pressure stream for sale are reduced according to the systems and methods of the invention.