Integration methods of gas processing plant and nitrogen rejection unit for high nitrogen feed gases
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Solution Overview
Problem
Existing gas processing plants face challenges in achieving low CO2 levels in feed gas for nitrogen rejection units due to high nitrogen content, requiring costly revamps or additional units, and existing amine units often produce wet gas that needs further drying.
Innovation Solution
Implementing an ultra-lean physical solvent system that uses a nitrogen reject stream for stripping, allowing deep CO2 removal without heating and producing a dry overhead gas, thereby reducing residual CO2 content to 1000 ppmv or lower, meeting NRU feed gas specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an amine unit is used to remove CO2 from feed gas, then CO2 removal is achieved, but the treated gas becomes wet and requires additional drying equipment
Solution Approach 1:
The patent extracts the CO2 removal function from the traditional amine unit and places it in a dedicated physical solvent unit positioned before the NRU. This separation allows the amine unit to be optimized for chemical CO2 removal while the physical solvent unit handles the specific requirement of producing dry gas for the NRU, eliminating the need for additional drying equipment.
Solution Approach 2:
The physical solvent unit acts as an intermediary between the amine unit and the NRU. It receives CO2-rich feed gas from the amine unit, performs physical absorption of CO2 to produce ultra-lean CO2 levels, and outputs dry gas suitable for NRU processing. This intermediary function resolves the contradiction by providing both deep CO2 removal and dry gas output without requiring the amine unit to be modified or additional dryers to be added.
2Manufacturing precision
If existing amine units are revamped for deep CO2 removal, then CO2 concentration is reduced to meet NRU specifications, but capital requirements and operating costs increase significantly
Solution Approach 1:
The patent segments the CO2 removal process into two distinct functional units: an amine unit for initial CO2 removal and a physical solvent unit for deep CO2 removal to ultra-lean levels. This segmentation allows each unit to be optimized for its specific function, avoiding the high capital costs associated with revamping an existing amine unit for deep CO2 removal. The physical solvent unit is a relatively simple, low-cost addition that achieves the required CO2 concentration without extensive modifications to existing infrastructure.
3Manufacturing precision
If a new amine unit is added downstream of the NGL recovery unit, then deep CO2 removal is achieved, but the treated gas becomes wet and requires molecular sieve drying
Solution Approach 1:
The patent applies preliminary action by performing deep CO2 removal in the physical solvent unit before the gas enters the NRU. This preliminary treatment ensures that the gas is already at ultra-lean CO2 levels and is dry, eliminating the need for downstream drying equipment. The physical solvent unit is positioned strategically in the flow to perform this preliminary action, preventing the formation of wet gas that would otherwise require molecular sieve drying.
4Productivity
If solvent circulation and heating duties are increased in amine units, then CO2 removal capacity is enhanced, but operating costs and capital requirements increase
Solution Approach 1:
The patent replaces the thermal-mechanical CO2 removal mechanism of amine units with a physical absorption mechanism in the physical solvent unit. Physical solvents rely on pressure and temperature differentials rather than thermal reactions, eliminating the need for high heating duties and extensive solvent circulation systems. This substitution achieves deep CO2 removal with significantly lower energy input, as the physical solvent simply requires pressure reduction and flash separation to release absorbed CO2, without the need for high-temperature reboiling.
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 enables deep CO2 removal at lower capital and operating costs, simplifies process flow, and eliminates the need for downstream dehydration, making it suitable for both new and existing gas processing facilities.
Implementation Method 1
uses an ultra-lean solvent in an absorber to produce a CO2-loaded solvent and a CO2-depleted feed gas
Implementation Method 2
The flash unit is used to flash the CO2-loaded solvent and to produce a flashed solvent
Implementation Method 3
the stripping column uses the N2 waste stream as a stripping gas for the flashed solvent to thereby produce the ultra-lean solvent
Data Source
AI summary
Gas processing plants and methods are contemplated in CO2 is effectively removed to very low levels from a feed gas to an NRU unit by adding a physical solvent unit that uses waste nitrogen produced by the NRU as stripping gas to produce an ultra-lean solvent, which is then used to treat the feed gas to the NRU unit. Most preferably, the physical solvent unit includes a flash unit and stripper column to produce the ultra-lean solvent.