System and method for reducing nitrogen content of GSP/expander product streams for pipeline transport
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Solution Overview
Problem
Natural gas processing systems face challenges in reducing nitrogen content in sales gas streams to meet pipeline specifications, as existing methods like nitrogen rejection units (NRUs) are costly and not economically feasible for small nitrogen excesses, and dilution is expensive and inefficient.
Innovation Solution
Integrating a nitrogen rejection unit (NRU) into a conventional gas subcooled/expander process system, where a portion of the process stream feeds a single fractionating column to reduce nitrogen content, allowing the treated gas to be reintroduced for further processing, thereby achieving pipeline-compliant sales gas without additional dehydration or carbon dioxide removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional stand-alone NRU unit is used to remove nitrogen, then nitrogen content is reduced to acceptable levels, but capital cost and operating cost increase significantly
Solution Approach 1:
The patent combines the NRU nitrogen removal function with the existing GSP demethanizer system by integrating a nitrogen rejection column into the process. Instead of using a separate stand-alone NRU unit, the system merges nitrogen removal with the existing fractionation infrastructure, sharing equipment such as heat exchangers, compressors, and control systems. This integration achieves the required nitrogen content reduction while avoiding the high capital and operating costs of a complete standalone NRU installation.
2Manufacturing precision
If dilution with other gas is used to meet nitrogen specification, then pipeline specification is met, but cost increases and gas quality is compromised
Solution Approach 1:
The patent extracts nitrogen from the sales gas stream through the integrated NRU system. The nitrogen rejection column separates nitrogen from methane and other hydrocarbons, allowing nitrogen to be removed and discarded while the purified gas is returned to the sales stream. This extraction approach meets pipeline nitrogen specifications without requiring dilution, thereby preserving gas quality and avoiding the costs associated with blending lower-quality gas.
3Manufacturing precision
If a complete stand-alone NRU is installed, then large percentages of nitrogen are removed, but the system is not economically feasible for small nitrogen excesses
Solution Approach 1:
The patent applies partial action by using the existing GSP demethanizer infrastructure to handle nitrogen removal rather than implementing a complete standalone NRU system. The integrated approach uses a portion of the existing fractionation capacity and shared equipment to achieve the necessary nitrogen reduction for streams with only moderate excess nitrogen (3-10% nitrogen content). This partial implementation achieves sufficient nitrogen removal while maintaining economic feasibility by avoiding unnecessary capital investment in a full standalone system.
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
This approach reduces nitrogen content in sales gas to acceptable levels at lower capital and operating costs compared to standalone NRUs, while maintaining NGL production and potentially enhancing recovery, with costs 25-50% less than conventional NRUs.
Implementation Method 1
The NRU feed stream passes through a single fractionating column and other processing equipment to produce a treated gas stream with reduced nitrogen content
Implementation Method 2
a subcooler reduces the temperature of a process stream prior to feeding the top of a demethanizer column
Data Source
AI summary
A system and method for removing nitrogen from an intermediate stream in a gas subcooled process operation that processes natural gas into a sales gas stream and a natural gas liquids stream. The system and method of the invention are particularly suitable for use with gas subcooled process operations where the sales gas stream exceeds pipeline nitrogen specifications by up to about 3%, such as for reducing the nitrogen content of sales gas streams to levels permissible for pipeline transport.