Designing a Load-Flexible Renewable Ammonia Plant for Variable Green Hydrogen Supply

Authors: Niklas Groll, Gürkan Sin

Conference: 36th European Symposium on Computer Aided Process Engineering (ESCAPE 36)

Codespace: FlexiblePtA_Economics

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Abstract

Decarbonizing ammonia by replacing grey with green hydrogen directly affects the operation of the Haber-Bosch (HB) process. When directly coupled to green hydrogen production from renewable energy, the HB process should be able to operate flexibly to match variable hydrogen supply. This study presents a structured approach for designing a load-flexible HB plant, supported by a rigorous process model. First, we screen 2,000 designs at high (100%) and low (10%) hydrogen loads to assess operability. Only 1,100 designs are feasible for both loads, underscoring the need to account for multivariable interactions during design. Next, we assess the economic feasibility of a base design, comparing HB operation under constant and flexible loads. Flexible operation reduces the levelized cost of ammonia (LCOA) by about 5.8%, primarily by lowering green hydrogen production costs. This cost reduction results from downregulating hydrogen production during periods of high electricity prices. By contrast, HB design improvements yield only small LCOA reductions (about 0.4%), though lower reactor pressure and a larger reactor volume remain the best HB design options to further reduce renewable ammonia costs.

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Concept

The plant consists of two coupled units:

• Electrolyzer (600 MW) – produces green hydrogen. Runs at full load during cheap electricity and at 10% minimum load during expensive electricity.
• Haber-Bosch synthesis loop – converts H₂ and N₂ to NH₃. Follows the same two-mode operation profile as the electrolyzer.

The economic performance is measured via:

• LCOH – Levelized Cost of Hydrogen (EUR/kg H₂)
• LCOA – Levelized Cost of Ammonia (EUR/kg NH₃)

The split between high-load and low-load operating hours is optimized to minimize LCOA. Results are compared across three scenarios: Base Constant, Base Flexible, and Best Flexible (using the best Haber-Bosch design found by simulation).

Repository Structure

.
├── FlexibleHB_Simulation.py       # 1. LHS sampling + AVEVA Process Simulation simulation runner
├── FlexibleHBFeasibleDesign.py    # 2. Feasible design space visualization
├── FlexibleHB_LCOA.py             # 3. LCOH/LCOA economics, optimization, comparison plots
├── ELPriceDistribution.py         # 4. Electricity price distribution visualization
├── Electricity Prices/            # Danish spot price data (DK1/DK2, 2023–2024)
├── Simulation Models/
│   ├── HBPlantEco.simx            # AVEVA Process Simulation Haber-Bosch plant model
│   └── ReactorEconomics.libx      # Reactor economics library
├── Simulation Data/               # LHS simulation output CSVs (generated)
├── Results/                       # Summary CSVs for LCOA comparison
├── Plots/                         # Generated figures (PNG + SVG)
└── Logs/                          # Simulation run logs

Workflow

Run the scripts in order:

Step 1 — Generate simulation data (FlexibleHB_Simulation.py)

Performs Latin Hypercube Sampling (LHS) over 7 Haber-Bosch design variables and runs both the High-load (100%) and Low-load (10%) AVEVA Process Simulation snapshots for each of the 2000 samples. Results are written incrementally to a timestamped CSV in Simulation Data/. Supports resuming interrupted runs with resume=True.

Design variable	Range
Total reactor volume $V_{total}$	50–80 m³
Reactor 1 volume fraction $V_1/V_{total}$	0.1–0.4
Reactor 2 volume fraction $V_2/V_{total}$	0.2–0.4
Reactor inlet temperatures $T_{R1}$, $T_{R2}$, $T_{R3}$	620–700 K
Synthesis pressure $P_R$	200–225 bar

Requires: AVEVA Process Simulation with HBPlantEco.simx open and the simcentralconnect Python package.

Step 2 — Identify feasible designs (FlexibleHBFeasibleDesign.py)

Loads the simulation CSV and produces a $7\times7$ matrix plot of the design space, highlighting in blue those samples where both the High- and Low-load runs converged and returned valid CAPEX values. Saves figures to Plots/FeasibleDesignSpace.png/.svg.

Step 3 — LCOA economics and optimization (FlexibleHB_LCOA.py)

Core analysis script. Key functionality:

• economics_electrolyzer() — calculates LCOH for the flexible electrolyzer (electricity cost, CAPEX, stack replacement, degradation).
• economics_ammonia_flexible() — calculates LCOA for the coupled plant, decomposed into: H₂ electricity, H₂ CAPEX, HB compression, cooling water, catalyst, N₂, and HB CAPEX.
• optimize_splitfactor() — uses scipy.optimize.minimize_scalar to find the fraction of high-capacity operating hours that minimizes LCOA.
• Produces a stacked bar chart comparing LCOA across the three scenarios and saves data to Results/LCOAComparison.csv.

Key economic parameters:

Parameter	Value
Discount rate (WACC)	6%
Economic lifetime	25 years
Electrolyzer capacity	600 MW
Electrolyzer CAPEX	2503 EUR/kW
Specific energy consumption	53.3 kWh/kg H₂
Minimum load fraction	10%
HB plant Lang factor	5.93
Electricity grid fees & taxes	26.26 EUR/MWh

Step 4 — Electricity price distribution (ELPriceDistribution.py)

Visualizes the 2024 DK1 spot price distribution, split at the optimal split factor (~76%/24%). Shows mean prices for the high-load and low-load zones. Saves figures to Plots/ElPriceDistribution.png/.svg.

Dependencies

numpy
pandas
scipy
matplotlib
lxml
pythonnet
./packages/simcentralconnect

Install all dependencies with:

pip install -r requirements.txt

Note: ./packages/simcentralconnect is expected to come from the AVEVA Process Simulation software installation/package bundle.

Data

Electricity spot prices are sourced from the Danish TSO (Energinet) for the DK1 and DK2 price zones, covering 2023 and 2024. Files are located in Electricity Prices/ as semicolon-separated CSVs with EUR/MWh prices in the SpotPriceEUR column.

Citation

The paper is currently under review. Once published, it will appear in Vol. 5 of Systems & Control Transactions as an Original Research Article and Peer Reviewed Conference Proceeding for 36th European Symposium on Computer Aided Process Engineering, Sheffield, UK, 21-24 June 2026.

Until the final bibliographic details are assigned, please cite the work as:

Groll, N., and Sin, G. Designing a Load-Flexible Renewable Ammonia Plant for Variable Green Hydrogen Supply. Under review for publication in Systems & Control Transactions, Vol. 5, Peer Reviewed Conference Proceeding, 36th European Symposium on Computer Aided Process Engineering, Sheffield, UK, 21-24 June 2026.

License

This project is licensed under the MIT License.

MIT License

Copyright (c) 2026 GSI Research Group

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of this software and associated documentation files (the "Software"), to deal
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The above copyright notice and this permission notice shall be included in all
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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SOFTWARE.

Contact

Niklas Groll nigro@kt.dtu.dk

References

• Haber-Bosch process modeling using AVEVA Process Simulation
• Danish electricity market (Energinet)
• European Clean Hydrogen Observatory – Levelised Cost of Hydrogen Calculator

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Last Updated: March 2026