System and method for natural gas and nitrogen liquefaction with independent nitrogen recycle loops
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Solution Overview
Problem
Existing liquefier arrangements capable of co-producing liquid natural gas (LNG) and liquid nitrogen (LIN) face limitations in adjusting the warm turbine to cold turbine flow ratio and suffer from efficiency penalties when demand for LNG and LIN changes, requiring a flexible system that can achieve optimal flow ratios and efficient turndown capabilities.
Innovation Solution
A nitrogen-based liquefaction system with independent recycle circuits and a multi-pass brazed aluminum heat exchanger, allowing for flexible co-production of LNG and LIN, featuring a primary recycle circuit, a secondary closed-loop recycle circuit, and a diversion circuit to optimize refrigeration and liquefaction processes, enabling adjustment of the warm to cold turbine flow ratio and efficient turndown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a separate passage is allocated to cool natural gas in a conventional nitrogen liquefier, then LNG and LIN co-production is enabled, but the warm turbine to cold turbine flow ratio adjustment capability is limited and efficiency penalties occur when demand changes
Solution Approach 1:
The system divides the nitrogen recycle flow into separate warm and cold turbine circuits, allowing independent control of each turbine's refrigeration capacity. This segmentation enables the warm turbine to cold turbine flow ratio to be adjusted independently of the overall system capacity, resolving the efficiency penalty that occurs when demand changes in conventional integrated designs.
Solution Approach 2:
The invention introduces dynamic adjustability through variable geometry turbine nozzles and controllable valve arrangements in each recycle circuit. These dynamic elements allow the system to optimize the warm turbine to cold turbine flow ratio in real-time based on varying LNG and LIN demand, maintaining high efficiency across different operating conditions rather than being fixed at design point.
2Temperature
If the feed natural gas pressure is below 450 psia, then the temperature difference in the condensing zone exceeds allowable limits for BAHX designs, but pre-compression increases the refrigeration demand on the warm turbine
Solution Approach 1:
The system segments the natural gas cooling process into distinct temperature zones within the heat exchanger, with dedicated warm and cold sections. This allows the condensing zone to operate with smaller temperature differences that fit within BAHX design limits, while the refrigeration demand is managed separately through the divided turbine circuits that can be independently sized and controlled.
Solution Approach 2:
The invention changes the operating parameters of the warm turbine circuit to match the refrigeration requirements at different natural gas feed pressures. By adjusting the warm turbine inlet temperature, pressure ratio, and flow rate independently of the cold turbine, the system can accommodate various feed conditions without requiring pre-compression, thereby avoiding the associated energy penalty while maintaining acceptable temperature differences in the heat exchanger.
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 achieves flexible co-production of LNG and LIN with improved efficiency by allowing independent adjustment of the warm to cold turbine flow ratio and efficient turndown, reducing thermodynamic penalties and maintaining optimal turbine efficiencies across varying demand conditions.
Implementation Method 1
a multi-pass brazed aluminum heat exchanger (BAHX) configured to liquefy a portion of the primary nitrogen liquefaction stream, recycle portions of the primary nitrogen liquefaction stream and the nitrogen refrigerant in the secondary closed-loop recycle circuit, and to liquefy a natural gas feed stream in separate heat exchange passages
Implementation Method 2
The cold turbine refrigeration primarily is providing refrigeration for liquefaction or pseudo-liquefaction of the nitrogen while the warm turbine refrigeration primarily provides refrigeration for natural gas liquefaction or pseudo-liquefaction
Implementation Method 3
The feed natural gas is preferably pre-compression of the natural gas feed, preferably to a pressure of about 450 psia
Data Source
AI summary
Liquefier arrangements configured for flexible co-production of both liquid natural gas (LNG) and liquid nitrogen (LIN) are provided. Each liquefier arrangement comprises separate and independent nitrogen recycle circuits or loops, including a warm recycle circuit and a cold recycle circuit with a means for diverting nitrogen refrigerant between the two recycle circuits or loops. The warm recycle circuit includes a booster loaded warm turbine, a warm booster compressor and warm recycle compression whereas the cold recycle circuit includes a booster loaded cold turbine, a cold booster compressor and a separate cold recycle compression.