Natural Gas Processing is a vital aspect of the energy industry, and Nitrogen Rejection Units (NRUs) play a crucial role in ensuring that the natural gas product meets industry specifications. If you’re tasked with choosing between a single column and a dual column NRU, you might find yourself pondering which option offers the best balance of efficiency, complexity, and cost. This post aims to shed light on these two NRU configurations, helping you decide which is more suitable for your specific needs.

An NRU, or Nitrogen Rejection Unit, is an essential component of natural gas processing. Its primary function is to separate nitrogen (N₂) from natural gas streams using cryogenic distillation. By doing so, it improves the heating value (Btu/scf) of the gas, aligning with typical sales gas specifications, which generally require less than 4.0mol% inerts (including N₂ and CO₂). NRUs are also crucial for meeting the stringent requirements for LNG production, which demands a nitrogen content of less than 2.0 mol%.

The presence of nitrogen in natural gas decreases its heating value, making it less efficient and less desirable for end-users. Additionally, pipeline and LNG production specifications require low levels of nitrogen to improve safety and efficiency. By removing excess nitrogen, NRUs enable natural gas streams to meet these specifications, ensuring they are market ready.

Single Column NRUs

• N₂ Content: More than 25%
• Design: Simple and typical
• Equipment: Minimal equipment required, leading to lower CAPEX and straightforward operation
• Efficiency: Generally higher efficiency compared to dual column setups (for N2>25%)

If the natural gas stream contains more than 25% nitrogen, the single column is the best option for enhanced efficiency, simplicity, and cost-effectiveness.  It might be the right solution even for those gases with less than 25% nitrogen if the capacity is low, the operation prioritizes simplicity and cost-effectiveness over enhanced efficiency. For end-users with gases where nitrogen isn’t necessarily high (N2<25%) with straightforward processing needs and the operation prioritizes simplicity and cost-effectiveness over enhanced efficiency a single column system can be adequate.

Single Column NRUs

• Design: Less complex with less equipment
• Efficiency: Higher efficiency, leading to less power consumption (for N2>25%)
• Commonality: More common than dual column systems

Dual columns should be considered if your gas streams have lower nitrogen content (N2<25%). If efficiency and power savings are critical to your operation, then a dual column NRU is worth considering. Even though there is additional complexity and equipment leading to higher upfront equipment costs, the enhanced performance, which saves substantial compression power offsets these costs leading to an overall reduction in CAPEX.

Dual Column NRUs

• Efficiency: The two-column design requires substantially less horsepower, making it more energy-efficient.
• Performance: It met all the specified performance criteria, including Nitrogen and Methane specifications in the product streams.
• Flexibility: The design provides flexibility in the feed gas composition, ensuring reliable operation even at higher Nitrogen concentrations.

Downstream of NGL Recovery:

Both single and dual column NRUs are typically implemented as standalone systems, but they can also be integrated with NGL (Natural Gas Liquids) recovery systems. Integrating with NGL recovery can optimize the overall efficiency of gas processing and offer additional opportunities for power savings.

Power Requirements:

Power savings is a critical factor in the design and operation of NRUs. While dual column systems generally offer better efficiency and lower power consumption, for nitrogen content less than 25% in the feed gas, it’s essential to evaluate your specific operational needs and constraints.

When deciding between a single column and a dual column NRU, consider the following:

• Single Column NRUs are ideal for operations that prioritize simplicity and cost-effectiveness. This design is a good techno-economical fit for natural gas streams with high nitrogen concentration, or where simplicity is a higher priority than performance.
• Dual Column NRUs are suitable for end-users with natural gas streams with low nitrogen content and looking for improved efficiency and power savings.

Ultimately, the choice between a single column and a dual column NRU will depend on your specific processing requirements, budget, and long-term operational goals. For tailored advice and to explore how these systems could fit into your existing setup, consider consulting with our NRU and cryogenic distillation experts to ensure you make the most informed decision.