Project Phase 1 - Fall 2024

Project Overview

Northern Flow Engineering presents a conceptual design for a 14 MTPA liquefied natural gas (LNG) export facility located in Kitimat, British Columbia. This project addresses the growing international demand for cleaner energy by proposing a scalable, sustainable LNG plant targeting Asian markets (China, Japan, South Korea).

Description of Selected Design

1. Inlet Scrubber and Compression

Upon arrival at the plant, natural gas undergoes inlet scrubbing to remove any liquids that may enter the system during specific operations, such as pigging. 

A recycle loop ensures continuous operation in case of flow disruptions, protecting the system. Higher pressure enhances natural gas liquids (NGL) recovery, reducing energy requirements for liquefaction.

Alternative designs, such as single-stage compression, were explored but found less favorable due to reduced NGL recovery and increased downstream energy requirements.

2. Amine Absorption and Regeneration

The amine absorption unit removes CO₂ and H₂S to meet LNG specifications (4 ppm H₂S, 50 ppm CO₂). Monoethanolamine (MEA) was selected as the solvent due to its high efficiency in CO₂ removal. 

MEA was chosen over other solvents due to its superior CO₂ absorption capability, despite higher energy requirements.

3. Molecular Sieve Dehydration and Mercaptan Removal

Following acid gas removal, gas enters molecular sieve beds for dehydration and mercaptan removal. Three types of sieves are used:

• 4A Molecular Sieve: Removes water to prevent freezing in downstream exchangers.
• 5A and 13X Molecular Sieves: Remove light and heavy mercaptans to meet LNG sulfur specifications.
• A three-bed system (3×50%) ensures continuous operation, with one bed regenerating at any time using heated gas.

4. Mercury Removal

Mercury is removed to prevent corrosion in aluminum heat exchangers. The process uses a silver-impregnated molecular sieve, with a 2×50% bed configuration for continuous operation. The system is designed to reduce mercury levels below 0.01 μg/m³.

5. Refrigeration and NGL Fractionation

Natural gas is cooled to -30°C using a propane refrigeration cycle, allowing heavier hydrocarbons to condense and be separated in the Low-Temperature Separator (LTS). Recovered NGLs are fractionated to maximize revenue:

• De-Ethanizer: Removes ethane-rich vapors, which are either reinjected or considered for separate sales.
• LPG Production: Remaining liquids (propane, butane, and heavier hydrocarbons) meet LPG specifications.

6. Propane Pre-Cooling

The propane pre-cooling system further cools the gas stream to -35°C using a brazed aluminum heat exchanger (BAHE). This section features:

• Four-stage propane compression and expansion cycle for improved energy efficiency.
• Three-stage economizer design to optimize refrigerant utilization.

7. Liquefaction – Mixed Refrigerant Process

The APCI C3-MR process was selected based on a Kepner-Tregoe decision analysis. Liquefaction occurs in a coil-wound heat exchanger (CWHE), utilizing:

• Mixed refrigerant separation into heavy and light components for efficient cooling.
• Two-stage compression cycle to optimize refrigerant recycling.               

Compared to alternatives (POCLP and Shell DMR), C3-MR was chosen for its cost-effectiveness, flexibility, and energy efficiency.

8. Nitrogen Removal and Final LNG Processing

To meet LNG storage and transport requirements, nitrogen is removed by flashing the LNG at reduced pressure. This serves two purposes:

• Prevents LNG stratification during shipping.
• Enhances energy content per unit volume.