Enable affordable and reliable delivery of low-carbon fuel for the energy transition

Plant Design, Engineering, Construction and Commissioning

J. DAVIDSON, Aspen Technology, Houston, Texas

Liquified natural gas (LNG) is a strategic component of the global energy matrix. Natural gas is uniquely positioned as a transition fuel to support an affordable and secure energy transformation through the displacement of coal-powered electricity generation and supplement renewable electricity. The safe, reliable and environmentally sustainable delivery of LNG to consumer markets requires investment in new and expanded infrastructure. Embedding digital technology and insights—from conceptual design to final investment decision (FID)—allows key stakeholders to understand technical and economic feasibility, evaluate design alternatives, decrease design time and execution, optimize performance and efficiency, and deliver product in a greener, safer and more efficient manner.

PILLARS TO MAINTAIN SUSTAINABLE GROWTH OF THE INDUSTRY

Investment in infrastructure. The LNG market is poised for continued near-term growth, fueled by market demand in Asia, which offers the beneficial impact of displacing coal-fired electricity generation with natural gas and petrochemical demand. McKinsey recently reported that the global demand for LNG is expected to increase as much as 5% per year until 2035.¹ Preventing a supply shortage requires additional investment in both liquefaction and regassification facilities; however, conflicting energy transition scenarios and evolving regulations are a risk for future expansion of the market and may deter investment. Capital discipline and supply chain agility will be required to entice the additional funding needed to meet forecasted LNG demand.  

Capital acumen. According to McKinsey, LNG projects have been penalized with a 10%–20% increase in cost escalation due to raw material pricing, escalating labor costs and rising equipment charges.¹ As such, the market is reliant on long-term supply contracts to reduce project risks between owners and suppliers. Acceleration and improved feasibility of capital projects with data-centric engineering are crucial to overcome these hurdles, offset the shortage in skill engineers and enable continued collaboration across the value chain. 

Reduced carbon intensity. Industry leaders must plan strategically to lower the carbon intensity of their operations in advance of increased future regulations. This can be accomplished via improved site efficiency, optimized energy consumption, electrification of assets with renewable energy, blending natural gas with hydrogen (H₂), leak detection and prevention, and carbon capture technologies.

Ensure capital efficiency and optimal design for greenfield and brownfield liquefaction plants. LNG global trade reached 404 MM tons (t) in 2023, and the market is forecasted to continue to grow at a compound annual growth rate (CAGR) of 3.6% between 2023 and 2040.² As of mid-April 2023, 997.¹ MMtpy of aspirational liquefaction capacity was in the pre-FID stage of project development to support this growth potential.³ To remain competitive in this environment, engineering companies and their partners are leveraging demonstrated modular designs to accelerate project schedules and maximize return on capital investments (FIG. 1).

Improve investment confidence with a holistic approach to reliability, design and operations. The profitability of a project—regardless of size—can be improved with system-wide performance simulation. This quantifies the business impact of planned and unplanned events along a specified timeframe by considering the asset connectivity in the system, material and energy flows between these assets, operational logic, storage elements, volatility in weather, supply, demand prices, shipping, and more. This allows for a primary understanding of financial risks and the opportunity to evaluate alternatives to improve the long-term viability and performance guarantees of the project. Key benefits of system-wide performance analysis include the following: 

• Increase probability to achieve business targets [e.g., production throughput, revenue, levelized costs, net present value (NPV)] 

• Identify challenges (assets or events) in the design and mitigate their risk 

• Compare different technologies and/or system configurations, and determine the optimum choice based on a quantitative analysis 

• Increase availability and utilization of the overall system 

• Generate a digital representation of the system that can be used later for continuous improvement.  

The outputs from system-wide performance simulation help identify performance-cost-risk trade-offs, quantify the expected variability in key performance indicators (KPIs) in the early stages of a project and improve investor confidence.  

Embed economic considerations and optioneering into asset designs. During the design phase, digital tools are essential for engineering and cost estimation. They enable techno-economic feasibility studies and accelerate projects with optimized capital expenditure (CAPEX)/operational expenditure (OPEX), ensuring a balance between safety and production. Performance engineering solutions offer system-wide simulation using equipment models. Engineers can leverage highly accurate state-of-the-art, off-the-shelf process simulators for gas processing and liquification plants.⁴ Key benefits of simulation at the design phase include: 

• Driving down the cost of production and boosting operational efficiencies by simulating the process behavior under multiple scenarios, sizing equipment and estimating costs.  

• Improving energy efficiency by analyzing design, equipment configurations and the impact of ambient temperature and weather conditions.^5,6,7 

• Achieving safe operations by accounting for overpressure protection and evaluating alternatives to debottleneck existing relief networks. 

Improve capital efficiency by understanding costs at the granular level. Cost estimation software can accelerate project execution and increase the accuracy of capital cost estimates from conceptual design to detailed engineering. This tool can effectively determine the best configuration of heat exchanger trains and compressors by assessing benefits (e.g., thermal efficiency, capacity, availability) and costs (e.g., capital, maintenance, energy requirements) for projects in the design phase as well as for equipment re-vamps. Once complete, engineers can streamline cost estimations and the review process to accelerate project timetables and coordinate with contractors to install the equipment.

Case study: Dynamic simulation of a natural gas liquefaction system. An integrated energy company in Asia evaluated the feasibility of scaling up its operational natural gas liquefaction technology from 500 MMtpy to 3 MMtpy–5 MMtpy. The company developed a digital model of the proposed build by leveraging existing designs and simulations from the operational plant. The results from dynamic base case models were in line with the historical design data and proved to be robust through interface testing, confirming the model recovered back to steady-state conditions. In addition, the following four key parameters were evaluated to ensure safe startup, shutdown and maximum efficiency: 

1. A front-end simulation of the natural gas separation system resulted in a recommendation to add a reflux drum temperature control loop and remove the pressure controller valve (PCV) of the reflux drum. 
2. The liquefaction unit cold startup was dynamically modeled, reducing the plant startup time.  
3. The anti-surge period was verified during compressor emergency shutdown to be within the acceptable range of < 1 sec. 
4. The control scheme was analyzed and optimized, improving the operability of the process system. 

These opportunities to improve the performance in the early stage of the asset lifecycle determined the startup time of the plant can be shortened by 6 hr, resulting in an equivalent savings of $200,000 for a 1-MMtpy LNG train. 

Enhanced visualization capabilities with 3D conceptual layout. 3D conceptual models can be integrated with front-end design and cost estimation to ensure constructability, identify the optimal layout, leverage modular or repeat designs, and accelerate optioneering. This revolutionary tool enhances a user’s ability to ingest data, evaluate modifications and prioritize alternative concepts.  

Develop proactive strategies to minimize future variance in facility performance. The capacity of a liquification plant is often limited by equipment constraints from the compressors and cryogenic multi-stream heat exchangers. Having a robust protocol for managing events that would adversely affect these assets’ performance—and training operators to respond effectively to dynamic process changes—can reduce the potential for safety incidents and increase production.

Case study: Evaluating the impact of cooling water temperature variations on LNG production. A large 8-MMtpy LNG terminal in Africa comprises six trains. The site uses a wet liquefaction process to convert natural gas to LNG, relying on seawater as the primary cooling agent. A specialized mixed coolant refrigerant (MCR) extracts heat from the natural gas and is cooled by propane, which is cooled in turn by seawater in an open circuit.

While this system works effectively at moderate temperatures, production rates significantly decrease during summer when seawater temperatures exceed 24°C (75°F). This decline presents operational challenges and impacts LNG output.

Simulation tools were used to investigate the cause of this decline and explore solutions to maintain optimal production throughout the year. A preliminary simulation of the propane loop, scrub tower, MCR loop and liquefaction section was conducted to replicate the impact of the seawater temperature increase on LNG production and validate the models. Next, the seawater exchangers were modeled to determine the impact of geometric dimensioning on the temperature of the fluid output. Finally, a study was conducted to evaluate the repercussions of a seawater temperature increase from 24°C to 28°C on LNG production rate.

The results of this study identified that as a result of the increase in seawater temperature, part of the propane inventory does not condense and remains in vapor state. This reduces the amount of propane available for pre-cooling of natural gas at the heat exchangers and cooling of MCR, resulting in a decreased rate of the natural gas flow and, consequently, a reduction in the quantity and volume of LNG produced.

Conversely, a significant decrease in the amount of C3 evaporated in the propane accumulator was observed following the increase in the pressure of discharge—this was close to the compressor stop threshold. A prescribed discharge pressure at the propane compressor was identified to offset the increase in seawater temperature during the summer season. This setpoint was specified to reduce the amount of C3 evaporated in the propane accumulator and therefore reduce the continuous booster to the propane loop and increase the production rate of the process trains during warmer months.  

Navigate the complexities of the modern energy landscape. As the global LNG market continues to grow and evolve, the adoption of these sophisticated digital and analytical tools will be a key differentiator for industry leaders. LNG producers have the potential to systematically unlock significant value through the evaluation of business trade-offs, improved visibility across the organization and overall energy efficiency, reduced emissions and maximized production. GP&LNG

NOTE

^a Aspen Fidelis 

LITERATURE CITED 

¹ Aggarwal, P., J. Dahl, S. Linder, D. Dediu and M. Smith, “Crunch time in the North American LNG industry: How to meet demand,” McKinsey & Company, December 7, 2023, online: How to meet US LNG demand with EPC strategies | McKinsey 

² Shell, “LNG Outlook 2023,” online: https://www.shell.com/energy-and-innovation/natural-gas/liquefied-natural-gas-lng/lng-outlook-2023.html 

³ International Gas Union (IGU), “2023 World LNG Report,” 14th Ed., July 12, 2023, online: 2023 World LNG Report | IGU 

⁴ Bassoini, G. and H. Klein, “Liquefaction of natural gas and simulated process optimization – A review,” Ain Shams Engineering Journal, Vol. 15, Iss. 2, February 2024, online: https://doi.org/10.1016/j.asej.2023.102431 

⁵ Khan, M. S., I. A. Karimi, A. Bahadori and M. Lee, “Sequential coordinate random search for optimal operation of LNG plant,” Energy, Vol. 89, September 2015, online:  https://doi.org/10.1016/j.energy.2015.06.021 

⁶ Hwang, J., et al., “Application of an Integrated FEED process engineering solution to generic LNG FPSO topsides”, 19th ISOPE International Ocean and Polar engineering Conference, Osaka, Japan, 2009, online: https://onepetro.org/ISOPEIOPEC/proceedings-abstract/ISOPE09/All-ISOPE09/ISOPE-I-09-187/7492 

⁷ Khan, M. S., I. A., Karimi and M. Lee, “Evolution and optimization of the dual-mixed refrigerant process of natural gas liquefaction,” Applied Thermal Engineering, 2016, online: https://doi.org/10.1016/j.applthermaleng.2015.11.092 

ABOUT THE AUTHOR

Jillian Davidson is the Industry Marketing Director for Energy at AspenTech, where she leads strategic initiatives to help global energy companies improve profitability, safety, and sustainability. With more than 10 yr of experience in the oil and gas sector, Dr. Davidson has developed deep expertise in innovation, product development, manufacturing, field support and advanced digital solutions for asset optimization.  

In her current role, Dr. Davidson is dedicated to driving the digital transformation of the energy industry by leveraging advanced technologies that not only optimize assets, but also enable accelerated and improved decision-making. She partners with energy companies across the value chain—from upstream exploration to downstream operations—to deliver tangible opportunities to maximize productivity and minimize environmental impact. 

Before joining AspenTech in 2022, Dr. Davidson held a leadership role at Nalco Water, an Ecolab company, where she was responsible for new product development and executing sales strategies to drive growth in the refining market. She played a key role in navigating market disruptions caused by the pandemic and the energy transition, while overseeing global innovation programs and managing a team of chemists focused on solving complex challenges such as refinery fouling and phase separation. Dr. Davidson holds a PhD in organometallic chemistry from Texas A&M University.

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