Optimizing technology pathways for Ammonia Fuel: production, transportation, and use

A new paper has just been published by researchers in The Philippines who set out to determine the most environmentally benign way to produce, transport, and use ammonia as a fuel for vehicles.

This latest work provides a detailed life cycle analysis of a broad range of ammonia technologies, evaluating both carbon and nitrogen footprints of each, and identifying the optimal “well-to-wheel” pathway. Their results support the idea that using ammonia for energy presents a safe and sustainable way to bring about the hydrogen economy.

Unlike hydrogen, ammonia is relatively easy to store and handle, and has a higher energy density. In addition, the infrastructure for its production and distribution is well established. Ammonia may be used as a fuel either in internal combustion engine vehicles (ICEV) or in fuel cell vehicles (FCV). Interest in the use of ammonia in vehicles dates back to the mid-20th century.
ACS Sustainable Chemistry & Engineering: Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017

The authors examined four production methods and four fuel uses in this analysis, incorporating data from extensive studies in the academic literature, including the use of ammonia fuel in both internal combustion engines and fuel cell technologies. Three production methods studied were based on Haber-Bosch technology, with biomass, natural gas, or coal feedstocks; the fourth was a biological production process, briefly described below. The fuel uses included fuel cells, as well as ammonia-hydrocarbon mixtures including gasoline, diesel, and DME (dimethyl ether).

For fuel cells, the authors assume that ammonia would need to be ‘cracked’ back into hydrogen before use as a fuel; we have written extensively about such cracking technologies. Alternatively, ammonia could be used as a direct fuel in a solid oxide fuel cell, but that’s beyond the scope of this paper.

In this study, a P-graph model is developed to determine the best well-to-wheel pathway for the use of ammonia as an automotive fuel, using carbon and nitrogen footprints as dual environmental criteria. Multiple fossil fuel-based and biomass-based ammonia production processes are considered, as well as different drivetrain configurations that include internal combustion engine vehicles (ICEV) and fuel cell vehicles (FCV). In the case of ICEV, the model also considers the secondary fuels needed to allow ammonia use in existing engines.
ACS Sustainable Chemistry & Engineering: Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017

This latest publication builds upon years of research coming out of De La Salle University in The Philippines, mainly focused on production technology and nitrogen cycles. Indeed, the lead author, Luis Razon, will present a paper at the forthcoming AIChE 2017 Annual Meeting, in which he’ll demonstrate the scale of future ammonia demand driven by population growth and increased biofuel production, carbon capture, and ammonia energy deployments.

In this paper, various scenarios are analyzed for ammonia demand up to the year 2050, driven by increasing demand for food; mandated use of biofuels; initiation of large-scale carbon capture schemes and the potential use of ammonia as a fuel. Sharp increases in demand, in the order of 1012 kg/year, are projected even with only partial replacement of diesel and gasoline demand for fuel. The other new applications may still account for an additional demand of 100-200 ×109 kg NH3/year — almost equivalent to the projected fixed nitrogen demand for food agriculture.
AIChE 2017 Annual Meeting: Increases in Demand for Fixed Nitrogen from Alternative Energy and Carbon Capture Schemes, Luis Razon, 10/31/2017

Razon’s paper will not be part of the NH3 Fuel Association’s Topical Conference, but rather part of the preceding day’s session on CO2 Industrial, Engineering and R&D Approaches. However, registration for the Topical Conference is now open, with discounts for NH3 Fuel Association members.

Click to enlarge. Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017
What is a P-Graph?
The P-Graph is a tool that allows researchers to build a web of calculations, to create an “unambiguous representation of relationships” for multiple competing pathways. It is, essentially, a way to solve an optimization problem.

The P-Graph “makes it easy to identify alternatives, which can facilitate decision-making … Near-optimal solutions may also share general features that characterize good engineering solutions, which are also robust.”

These researchers used P-Graphs “to determine the optimal system configuration, such that the carbon and nitrogen footprints per km traveled by a representative vehicle are minimized.”

Click to enlarge. Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017
Any individual P-Graph solution can also be represented as a block diagram. These two images above, which communicate the same data, represent the optimal solution to the researchers’ ammonia fuel analysis.

As Razon pointed out in an interview, “the advantage of the P-graph method is we can easily add other combinations” of production methods or fuel uses, “assuming the data is available.” For example, “the ‘real’ optimum may very well be another production method or another use for ammonia that was not included in the analysis [and] other ‘success criteria’ like economics may well shift the optimum to another solution.”

Optimized solution: produce ammonia from biomass, use it in a fuel cell
According to their 2017 findings, however, the “optimum pathway for production and use of ammonia as automotive fuel” begins with a biomass production technology and ends in a hydrogen fuel cell.

Solving the P-graph model identifies the optimal pathway as cyanobacteria-based ammonia production coupled with FCV. This pathway has a carbon footprint of 4.96 g CO2 equiv/km and a nitrogen footprint of 0.325 g reactive N/km. The model also identifies a cluster of near-optimal solutions, for which possible technology improvements are discussed.
ACS Sustainable Chemistry & Engineering: Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017

To avoid digressing into cyanobacterial ammonia production here, I’ll say two things. First, it is similar to other algal biofuel processes. And second, I’ll be writing soon about the significant progress being made on this technology in The Philippines.

Supplemental data is available for the “near-optimal” technology pathways. It may be useful to note that nitrogen emissions (N2O and NOx), which are so often cited as reasons to dismiss ammonia as an engine fuel, are shown to decrease as the proportion of ammonia in the fuel mix increases.

Click to enlarge. Table S6: Summary of flow of streams for the 16 solution structures, Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017

The nitrogen cycle
I’ve previously written about a number of other valuable life cycle analyses, both of production technologies and of fuel comparisons, but I’m glad to note that this research analyzes the nitrogen footprint of these technologies (N2O, NOx, and NH3 emissions) as well as their carbon footprint (CO2 and CH4 emissions).

“The carbon footprint primarily occurs during the fuel production stage of the life cycle … The nitrogen footprint, on the other hand, is primarily attributed to the fuel use phase of the life cycle. It should be noted that, in many cases, such emissions result from emissions of traces of unburned ammonia from engines designed and optimized to run on petroleum-based fuels … improvements in engine technology will be needed to reduce emissions generated during ammonia combustion.”
ACS Sustainable Chemistry & Engineering: Optimization of the Automotive Ammonia Fuel Cycle Using P-Graphs, Razon et al, 08/14/2017

The nitrogen cycle is an under-examined subject, but absolutely vital to sustainability. Fortunately, it is a familiar subject for these researchers: Razon was writing about it in 2014, when he asked: Is nitrogen fixation (once again) “vital to the progress of civilized humanity”?

The excessive use of synthetic fixed nitrogen fertilizers has led to severe environmental effects, but fixed nitrogen is essential to the sustainability of biofuels. Nitrogen fertilizers are also required for biotic carbon capture schemes like bioenergy with carbon capture and storage (BECCS), afforestation, and soil carbon sequestration. Ammonia has been proposed as a non-carbon emitting alternative fuel that has many advantages over hydrogen … ammonia is an enabling technology for alternative fuels and carbon sequestration.
Clean Technologies and Environmental Policy: Is nitrogen fixation (once again) “vital to the progress of civilized humanity”?, Luis Razon, 08/15/2014

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