Integrated Nitrogen Rejection for Gas Subcooled Expander Operations
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Solution Overview
Problem
Natural gas streams often exceed pipeline nitrogen specifications, leading to costly dilution or the installation of expensive nitrogen rejection units (NRUs) to reduce nitrogen content, which may not be economically feasible for small nitrogen excesses in sales gas.
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 produce a treated gas stream with reduced nitrogen content, which is then reintroduced into the system, allowing for nitrogen reduction without additional dehydration or carbon dioxide removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional stand-alone NRU unit is installed to remove nitrogen from sales gas, then nitrogen content in sales gas is reduced to pipeline specifications, but capital cost and operating cost increase significantly
Solution Approach 1:
The patent combines the NRU nitrogen removal function with the existing GSP gas subcooled process by integrating a fractionating column and heat exchanger into the conventional workflow. The NRU feed stream is taken from the GSP process stream, and the treated gas stream is returned to the GSP feed, merging two separate processes into one integrated system that reduces nitrogen while avoiding the need for a completely standalone NRU unit
Solution Approach 2:
The integrated system allows the fractionating column and heat exchanger to serve dual purposes: they perform nitrogen removal while also contributing to the overall gas processing and cooling functions already present in the GSP system. This multi-functionality reduces the need for separate dedicated equipment for each function
2Manufacturing precision
If a two-column NRU system is used to remove large percentages of nitrogen, then nitrogen specification is met, but equipment cost and complexity increase
Solution Approach 1:
The patent applies partial action by removing only the excess nitrogen that exceeds pipeline specifications rather than attempting to remove all nitrogen or using an aggressive two-column system designed for high nitrogen removal. This approach uses a single fractionating column with controlled operation to achieve just enough nitrogen removal to meet the 4% specification threshold
Solution Approach 2:
The system segments the nitrogen removal task by taking only a portion of the process stream (about 10-20%) to feed the fractionating column for nitrogen removal, while the majority of the stream bypasses this section. This segmentation allows a single column to handle the nitrogen removal burden without requiring a full two-column 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 pipeline specifications at lower capital and operating costs compared to standalone NRUs, while maintaining NGL production and potentially enhancing NGL 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
Through use of this embodiment of the invention, a portion of the process stream that normally feeds the top of the demethanizer column after passing through the subcooler serves as the NRU feed gas stream
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.