Some energy services and industrial processes-such as long-distance freight transport, air travel, highly reliable electricity, and steel and cement manufacturing-are particularly difficult to provide without adding carbon dioxide (CO2) to the atmosphere. Rapidly growing demand for these services, combined with long lead times for technology development and long lifetimes of energy infrastructure, make decarbonization of these services both essential and urgent. We examine barriers and opportunities associated with these difficult-to-decarbonize services and processes, including possible technological solutions and research and development priorities. A range of existing technologies could meet future demands for these services and processes without net addition of CO2 to the atmosphere, but their use may depend on a combination of cost reductions via research and innovation, as well as coordinated deployment and integration of operations across currently discrete energy industries.

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Net-zero emissions energy systems

Ammonia for power

Models show that to avert dangerous levels of climate change, global carbon dioxide emissions must fall to zero later this century. Most of these emissions arise from energy use. Davis et al. review what it would take to achieve decarbonization of the energy system. Some parts of the energy system are particularly difficult to decarbonize, including aviation, long-distance transport, steel and cement production, and provision of a reliable electricity supply. Current technologies and pathways show promise, but integration of now-discrete energy sectors and industrial processes is vital to achieve minimal emissions. Net emissions of CO2 by human activities - including not only energy services and industrial production but also land use and agriculture - must approach zero in order to stabilize global mean temperature. Energy services such as light-duty transportation, heating, cooling, and lighting may be relatively straightforward to decarbonize by electrifying and generating electricity from variable renewable energy sources (such as wind and solar) and dispatchable ("on-demand") nonrenewable sources (including nuclear energy and fossil fuels with carbon capture and storage). However, other energy services essential to modern civilization entail emissions that are likely to be more difficult to fully eliminate. These difficult-to-decarbonize energy services include aviation, long-distance transport, and shipping; production of carbon-intensive structural materials such as steel and cement; and provision of a reliable electricity supply that meets varying demand. Moreover, demand for such services and products is projected to increase substantially over this century. The long-lived infrastructure built today, for better or worse, will shape the future. Here, we review the special challenges associated with an energy system that does not add any CO2 to the atmosphere (a net-zero emissions energy system). We discuss prominent technological opportunities and barriers for eliminating and/or managing emissions related to the difficult-to-decarbonize services; pitfalls in which near-term actions may make it more difficult or costly to achieve the net-zero emissions goal; and critical areas for research, development, demonstration, and deployment. It may take decades to research, develop, and deploy these new technologies. DOI Link: https://doi.org/10.1126/science.aas9793

Net-zero Emissions Energy Systems

Ammonia synthesized using hydrogen from renewable sources offers a vast potential for the storage as well as transportation of renewable energy from regions with high intensity to regions lean in renewable sources Ammonia can be used as an energy vector for an emissionless energy cycle in a variety of ways Ammonia at the point of end use can be converted to hydrogen for fuel cell vehicles or alternatively utilized directly in solid oxide fuel cells, in an internal combustion engine or a gas turbine One ton of ammonia production requires 9–15 MWh of energy However, its conversion back to useful form or direct utilization can lead to substantial energy losses In this paper, we present an overview of the current processes and technologies for ammonia synthesis and its utilization as an energy carrier We have performed an estimation of the round-trip efficiency of different routes for ammonia utilization at the point of end use along with some sensitivity analysis, and we discuss the outcomes resulting 

Ammonia as a Renewable Energy Transportation Media

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1551&context=etd

Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel

An overall stoichiometric mixture of air, gaseous ammonia, and gasoline was metered into a single cylinder, variable compression ratio, supercharged cooperative fuel research (CFR) engine at varying ratios of gasoline to ammonia. The engine was operated such that the combustion was knock-free with minimal roughness for all loads ranging from idle up to a maximum load in the supercharge regime. For a given load, speed, and compression ratio, there was a range of ratios of gasoline to ammonia for which knockfree, smooth firing was obtained. This range was investigated at its rough limit and also at its maximum brake torque (MBT) knock limit. If too much ammonia was used, then the engine fired with an excessive roughness. If too much gasoline was used, then knock-free combustion could not be obtained while the maximum brake torque spark timing was maintained. Stoichiometric operation on gasoline alone is also presented, for comparison. It was found that a significant fraction of the gasoline used in spark ignition engines could be replaced with ammonia. Operation on about 100% gasoline was required at idle. However, a fuel mix comprising 70% ammonia/30% gasoline on an energy basis could be used at normally aspirated, wide open throttle. Even greater ammonia to gasoline ratios were permitted for supercharged operation. The use of ammonia with gasoline allowed knock-free operation with MBT spark timing at higher compression ratios and higher loads than could be obtained with the use of gasoline alone. DOI: 10.1115/1.2898837

The Fuel Mix Limits and Efficiency of a Stoichiometric, Ammonia, and Gasoline Dual Fueled Spark Ignition Engine

Engine-out and post-catalyst emissions of ammonia, hydrocarbons, nitric oxide, carbon monoxide, and nitrous oxide are measured for an ammonia and gasoline dual fueled spark ignition engine. An ordinary three-way catalytic converter can be used to clean up these emissions. The clean-up region occurs between stoichiometric and 0.2% rich. Ordinary exhaust gas oxygen sensors are usable with ammonia and gasoline in much the same way as they are with gasoline alone.Copyright © 2009 by ASME

Exhaust Emissions From a Stoichiometric, Ammonia and Gasoline Dual Fueled Spark Ignition Engine

An overall stoichiometric mixture of air, gaseous ammonia and gasoline was metered into a single cylinder, variable compression ratio, supercharged CFR engine at varying ratios of gasoline to ammonia. The engine was operated such that the combustion was knock-free with minimal roughness for all loads ranging from idle up to a maximum load in the supercharge regime. For a given load, speed, and compression ratio there was a range of ratios of gasoline to ammonia for which knock-free, smooth firing was obtained. This range was investigated at its roughness limit and also at its knock limit. If too much ammonia was used, then the engine fired with an excessive roughness. If too much gasoline was used, then knock-free combustion could not be obtained while the maximum brake torque spark advance was maintained. Stoichiometric operation on gasoline alone was also investigated, for comparison. It was found that a significant fraction of the gasoline used in spark ignition engines could be replaced with ammonia. Operation on mostly gasoline was required near idle. However, mostly ammonia could be used at high load. Operation on ammonia alone was possible at some of the supercharged load points. Generally, the use of ammonia or ammonia with gasoline allowed knock-free operation at higher compression ratios and higher loads than could be obtained with the use of gasoline alone. The use of ammonia/gasoline allowed practical operation at a compression ratio of 12:1 whereas the limit for gasoline alone was 9:1. When running on ammonia/gasoline the engine could be operated at brake mean effective pressures that were more than 50% higher than those achieved with the use of gasoline alone. The maximum brake thermal efficiency achieved with the use of ammonia/gasoline was 32.0% at 10:1 compression ratio and BMEP = 1025 kPa. The maximum brake thermal efficiency possible for gasoline was 24.6% at 9:1 and BMEP = 570 kPa.Copyright © 2006 by ASME

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The Operating Features of a Stoichiometric, Ammonia and Gasoline Dual Fueled Spark Ignition Engine

A method for simulating conventional time gating in low-coherence optical imaging processes in highly scattering media is given. The method uses monochromatic instead of broadband light, and spatial filtering is substituted for time gating. The process enables the study of imaging techniques in scattering media to be carried out in an easy and highly controllable way. Experimental results are given.

Realization of time gating by use of spatial filtering

Apparatus, methods and systems reside in the decomposition of ammonia into a hydrogen gas mixture. An ammonia-rich gaseous mixture containing ammonia and oxygen enters into a conduit within which combustion and decomposition of the mixture is initiated, thereby liberating hydrogen. A mixture of gaseous products resulting from the reaction is expelled from the outlet of the conduit, the mixture including non-combusted hydrogen gas, which may then be used for other purposes. In the preferred embodiment, the incoming reactants including ammonia and oxygen are heat exchanged with the outgoing product mixture containing non-combusted hydrogen gas.

Shawn M. Grannell

Papers

The Fuel Mix Limits and Efficiency of a Stoichiometric, Ammonia, and Gasoline Dual Fueled Spark Ignition Engine

Exhaust Emissions From a Stoichiometric, Ammonia and Gasoline Dual Fueled Spark Ignition Engine

The Operating Features of a Stoichiometric, Ammonia and Gasoline Dual Fueled Spark Ignition Engine

Realization of time gating by use of spatial filtering

Ammonia flame cracker system, method and apparatus