Why Simulation Is Essential in Converter Design

Why Simulation is Necessary

Core reason: the complexity and stringency of the ammonia synthesis reaction

01 Thermodynamic Equilibrium Limitations

• The reaction N₂ + 3H₂ ⇌ 2NH₃ is reversible, exothermic, and involves a reduction in the total number of molecules which creates an inherent trade-off.
• Simulation enables precise calculation of equilibrium ammonia concentration under different temperature, pressure, and composition conditions, providing a theoretical ceiling for selecting optimal operating conditions.

02 Complex Reaction Kinetics

• The reaction rate depends not only on temperature and pressure but also strongly on catalyst type, activity, particle size, and adsorption processes on the catalyst surface.
• Simulation helps build kinetic models to predict the converter size and operating conditions required to achieve a desired production rate with real industrial catalysts.

03 Strong Thermal Effects

• The reaction releases a tremendous amount of heat. In large-scale converters, if the heat is not effectively removed, local overheating (hotspots) can occur.
• Overheating reduces equilibrium conversion rates and may sinter the catalyst, leading to permanent deactivation.
• Managing thermal effects is critical for converter safety and long-term stable operation.

04 High Process Integration

An ammonia synthesis loop is not just a converter, it includes

• Feed gas compression
• Heat recovery from reaction heat
• Product separation
• Recycle loop

These units are tightly integrated, meaning a change in one parameter can impact the entire system.

Roles of Simulation & Analysis

Given the above complexity, simulation plays an irreplaceable role in design and optimization.

01 Converter Design & Optimization

Scale-up and Configuration

• Scaling up from laboratory glass converters to million-ton-per-year industrial converters is not a simple proportional enlargement.
• CFD (Computational Fluid Dynamics) and chemical kinetics models can simulate momentum transfer, heat transfer, mass transfer, and reaction kinetics within the converter.

Hotspot Prediction

• Simulation can accurately predict temperature distribution within the converter, especially in the catalyst bed, identifying potential hotspots.
• This guides internal structural design (e.g., multi-bed with inter-stage cooling), cooling schemes, and operational strategies.

Catalyst Performance Evaluation

• Simulation models allow comparison of catalyst activity and particle size effects on reaction progression and pressure drop, supporting catalyst selection and loading strategies. 

02 Process-Wide Optimization & Energy Efficiency Improvement

Energy Integration

• Process simulation software can model the entire ammonia synthesis loop.
• Simulation calculates the quantity and grade of heat released by the reaction, optimizes the heat exchanger network, and maximizes energy recovery, minimizing external utility consumption (e.g., steam, cooling water).
• This is crucial since energy consumption dominates ammonia production costs.

Operating Condition Optimization

• Virtual experiments can be run to test various pressures, temperatures, recycle ratios, and inert gas concentrations (e.g., argon, methane), identifying optimal operating windows to maximize yield and minimize cost.

03 Safety and Reliability Analysis

Abnormal Condition Simulation

• Simulation models startup, shutdown, load changes, and equipment failures.
• For example, how will system temperature and pressure respond to sudden feed composition changes or compressor instability?
• These insights support the design of safety interlocks and control strategies to prevent accidents.

Equipment Sizing

• Accurate flow, composition, and temperature data from simulation allow precise sizing of related equipment (e.g., heat exchangers, piping, valves, separators).

04 Economic Benefit Evaluation & Decision Support

Risk Reduction

• Detect design flaws before plant construction to avoid costly modifications post-installation.

Cost Prediction

• Accurately forecast raw material and utility consumption, improving cost estimates for feasibility studies and investment decisions.

CFD in Ammonia Synthesis Converter Design

CFD is a numerical simulation technique to solve fluid flow, heat transfer, and mass transfer problems, widely applied in chemical converter design.

CFD simulations of flow fields, temperature profiles, concentration gradients, and catalyst behavior significantly enhance design efficiency, performance, and safety.

01 Converter Design & Optimization

• CFD simulates gas turbulence, mixing, and flow distribution, helping optimize converter geometry (e.g., fixed bed, multi-tubular, fluidized bed) and operating conditions (400–500°C, 200–300 atm).
• Tools like ANSYS Fluent or COMSOL can model multiphase flow (gas-solid), providing quantitative insights into reaction efficiency.

02 Heat & Mass Transfer

• Ammonia synthesis is highly exothermic. CFD predicts temperature gradients and heat transfer to ensure efficient heat removal, prevent catalyst overheating, and avoid equipment damage.
• It also aids in optimizing mass transfer, which directly impacts reaction rate and ammonia yield.

03 Safety & Risk Management

• CFD can simulate abnormal events like gas leaks and localized overheating, supporting safety evaluations and risk mitigation strategies.

04 Economic Performance

• By simulating various design scenarios, CFD identifies optimal configurations to minimize energy consumption and capital investment.
• For example, optimizing gas flow distribution reduces pressure drop and compressor energy consumption.

05 Environmental Sustainability

• Optimized converter designs can reduce CO₂ emissions, as ammonia production accounts for 1–2% of global CO₂ emissions.

06 Scale-up & Commercialization

• CFD captures scale-up effects such as flow maldistribution and temperature gradients, ensuring laboratory findings are translated safely to industrial-scale designs.

07 Innovation and R&D

• CFD accelerates development of next-generation ammonia synthesis technologies, including modeling nano-catalysts and unconventional converters like microchannel or plasma converters.
• Combining CFD with molecular dynamics and AI enables rapid screening and innovative converter design.

08 Process Control & Dynamic Behavior

• CFD simulates dynamic operations (e.g., startup, shutdown, load variation), supporting advanced control strategy development.

KAPSOM employed CFD simulations to optimize key aspects of the ammonia synthesis converter's design, such as the quench gas configuration, interbed cooling, and orifice distribution. This resulted in significantly more uniform gas flow, mixing, and distribution under target conditions, creating a data-driven approach to innovation and guaranteeing long-term operational stability and reliability.