Life Cycle Inventory and Assessment Datasets on the Operational Sustainability of the Ammonia Process

This article presents data affiliated with life cycle inventories, environmental impact and operational sustainability used in, the influence of raw material availability and utility power consumption on the sustainability of the ammonia process [1]. Scenario specific operating conditions were used to simulate the ammonia process based on unique constraints occurring within the Trinidad and Tobago energy sector. The data was collected using AspenⓇ Plus simulations and validated against plant operating data. The data consists of an economic cost evaluation as well as environmental impact using the CML-IA Baseline midpoint approach. The data was derived from life cycle inventories aligned to input/output material and energy flows within the ammonia process as well as life cycle assessment databases utilizing Ecoinvent v3.4. The data can be applied to the wider ammonia supply chain, aiding in achieving greater sustainable development within ammonia-based process industries.


Value of the data
• The data available gives insights into the sustainable assessment of operational ammonia plants and the impact of operating conditions on reducing environmental burden. • The data can be used within the ammonia supply chain demand such as the fertilizer industry, to further investigate sustainable operations. • The data can be easily compared with other ammonia process technologies to understand how operational efficiency can improve overall sustainability.

Data
The data presented here illustrate the datasets utilized from Ecoinvent Databases for the ammonia process system boundary definition as well as raw and processed data (available through supplementary files at http://dx.doi.org/10.17632/7krrvxtsmm.2 ) aligned to input-output flows developed using process modelling.

Aspen Plus Simulation
The ammonia process was simulated using Aspen® Plus and validated against plant operating data. The Front End, Back End and Ammonia Refrigeration sections of the process were simulated using the Peng-Robinson thermodynamic fluid package. For carbon dioxide (CO 2 ) removal, the Electrolyte non-random two-liquid -Redlich-Kwong and Perturbed-chain statistical associating fluid theory Equations of state were employed to simulate the CO 2 capture using proprietary solvents.
In the front-end section of the process, hydrogen is produced in two stages. In the primary reforming step, compressed natural gas is mixed with steam and converted to hydrogen and carbon oxides (mainly CO and CO 2 ). In secondary reforming, the reformed gas stream is mixed with air stoichiometrically to maintain the required amount of nitrogen required for ammonia synthesis, and hydrogen is produced whereby heat generated within the partial oxidation of methane facilitates the steam reforming and water gas shift reactions. All reforming reactions were modelled using equilibrium reactors with set approach temperatures. Waste heat recovery was considered downstream the hydrogen generation unit through high-pressure (HP) steam generation. Finally, CO is converted to CO 2 in two stages through low and high temperature water shift conversion. These reactions were modelled using a R-STOIC reactor with set conversions.
From the front-end section of the plant, reformed gas is further cooled through heat recovery and sent to the CO 2 removal section using proprietary solvent scrubbing. Both absorption and stripping processes were modelled as equilibrium RADFRAC applications and the equilibrium constants within the Aspen Plus library were used. The CO 2 was removed and sent to the lowpressure flash section and the lean solvent was recycled to the absorber.
In the back-end section of the plant, methanation was considered whereby residual carbon oxides were converted to methane using hydrogen. Methanation reactions were modelled using a R-STOIC reactor with 100% conversion. The effluent was flashed and mixed with recycle hydrogen from the purge gas recovery unit and recycle gas from the refrigeration section, and sent to the ammonia synthesis converter. The ammonia synthesis converter was modelled as four equilibrium reactors (to represent 4 beds) and three heat exchangers with set approach temperatures and duties.
The synthesis gas was first preheated and sent to each bed whereby the heat of reaction was removed through heat recovery. The discharge was further cooled in the ammonia refrigeration section, whereby the produced ammonia was removed using cold ammonia gas recovered from purge gas as well as cold liquid ammonia product in a counter-current heat exchange process. This was simulated using a series of shell and tube heat exchangers, exchangers, flash drums and compressors. Detailed process descriptions and simulation assumptions are available [1] .

Scenario Descriptions
Four (4) scenarios were developed based on current operational issues facing traditional ammonia processing within Trinidad and Tobago; Scenario 1-Availability of Raw Material, Scenario 2-Optimization of Purge Gas Recovery, Scenario 3-Optimization of Ammonia Synthesis, and Sce- nario 4-Utility Optimization. Carbon capture and Utilization (CCU) was also examined within Scenario 1 in an effort to investigate potential avenues for reduced environmental burden. Raw input/output material flows as well as energy integration were collated and normalized to the functional unit-10 0 0kg/h ammonia, forming the basis of life cycle inventories (LCI) for each scenario. Detailed scenario descriptions and objectives are available [1] .

Economic Evaluation
Operational costs attributed to natural gas utilization, cooling water, steam generation, demineralized water and electricity as well as ammonia product revenue were estimated for each simulation using cost data supplied by market trends as well as literature [3][4][5][6][7] . Operational profit and Incremental savings were calculated following Eqs. 1 and 2 :

LCA Methodology
The defined system boundary for the ammonia process is given in Fig. 1 . Table 1 gives the LCA datasets used within the Ecoinvent v3.4 database for various material flows. Scenario specific LCI was aligned to each LCA datasets and used to investigate the environmental impact of the ammonia process across eleven (11) environmental impact categories ( Table 2 ) using the CML-IA baseline Life Cycle Impact Assessment (LCIA) midpoint methodology [8] . In an effort to  ( Table 3 ) was used. An economic allocation was utilized based on the cost prices of both ammonia and CO 2 to illustrate the effects of carbon capture and utilization as an environmental benefit for the ammonia process. Detailed analysis of the system boundary and relevant assumptions are given [1] .