Scholarly article on topic 'Use of NH3 fuel to achieve deep greenhouse gas reductions from US transportation'

Use of NH3 fuel to achieve deep greenhouse gas reductions from US transportation Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Doo Won Kang, John H. Holbrook

Abstract The transportation sector is one of the largest sources of greenhouse gases (GHGs) emissions in the United States. This study identifies scenarios for dramatically reducing future GHG emissions from the US transportation sector, specifically from light-duty vehicles (LDVs), by phasing in ammonia (NH3)-fueled vehicles in place of vehicles using petroleum-based fuels. Projected US LDV carbon dioxide (CO2) emissions from the Annual Energy Outlook (AEO) 2013 reference case projections prepared by the United States Department of Energy serve as the reference case for this study. Two scenarios, in addition to the AEO reference case, have been developed in this study to illustrate the GHG emissions mitigation potential of implementing NH3-fueled vehicles in the US LDV transportation sector through 2040. This study uses the software tool LEAP (the Long range Energy Alternatives Planning System), with which alternative scenarios can be created and evaluated by comparing their energy requirements and environmental impacts. Aggressive implementation of NH3-fueled vehicles replacing gasoline vehicles to account for 100% in 2040 achieves reduction of about 30% of the cumulative LDV CO2 emissions from 2010 through 2040 produced in the reference case. It eliminates most of the annual LDV CO2 emissions projected in the reference case in the year 2040, with a 96% reduction from reference case levels, equivalent to a reduction of approximately 718 million metric tons CO2 equivalent in that year’s emissions. The current study demonstrates that NH3-fueled vehicles could be a promising near-term alternative for LDV because of its significant contribution in reducing CO2 emissions compared with vehicles of carbon based fuels.

Academic research paper on topic "Use of NH3 fuel to achieve deep greenhouse gas reductions from US transportation"

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Energy Reports

journal homepage: www.elsevier.com/locate/egyr

Use of NH3 fuel to achieve deep greenhouse gas reductions from US c^ark

transportation

Doo Won Kanga'*, John H. Holbrook0

a Engineering School, Carnegie Mellon University, United States b NH3 Fuel Association, United States

article info

abstract

Article history: Received 11 May 2015 Received in revised form 4 August 2015 Accepted 4 August 2015 Available online 24 August 2015

Keywords: NH3-fueled vehicles CO2 emissions Global warming LEAP

The transportation sector is one of the largest sources of greenhouse gases (GHGs) emissions in the United States. This study identifies scenarios for dramatically reducing future GHG emissions from the US transportation sector, specifically from light-duty vehicles (LDVs), by phasing in ammonia (NH3)-fueled vehicles in place of vehicles using petroleum-based fuels.

Projected US LDV carbon dioxide (CO2) emissions from the Annual Energy Outlook (AEO) 2013 reference case projections prepared by the United States Department of Energy serve as the reference case for this study. Two scenarios, in addition to the AEO reference case, have been developed in this study to illustrate the GHG emissions mitigation potential of implementing NH3-fueled vehicles in the US LDV transportation sector through 2040. This study uses the software tool LEAP (the Long range Energy Alternatives Planning System), with which alternative scenarios can be created and evaluated by comparing their energy requirements and environmental impacts.

Aggressive implementation of NH3-fueled vehicles replacing gasoline vehicles to account for 100% in 2040 achieves reduction of about 30% of the cumulative LDV CO2 emissions from 2010 through 2040 produced in the reference case. It eliminates most of the annual LDV CO2 emissions projected in the reference case in the year 2040, with a 96% reduction from reference case levels, equivalent to a reduction of approximately 718 million metric tons CO2 equivalent in that year's emissions.

The current study demonstrates that NH3-fueled vehicles could be a promising near-term alternative for LDV because of its significant contribution in reducing CO2 emissions compared with vehicles of carbon based fuels.

© 2015 The Authors. Published by Elsevier Ltd.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Global warming is the result of greater concentrations of greenhouse gases (GHGs), especially carbon dioxide (CO2) building up in the atmosphere. This atmospheric build-up of GHGs is largely the result of combustion of fossil fuels and other human activities, as reaffirmed by the Intergovernmental Panel on Climate Change this past September (Intergovernmental Panel on Climate Change, 2013).

A significant portion of CO2 emissions come from the cars and trucks we drive. Since our vehicles largely run on gasoline and diesel, as fuel is burned, CO2 is released. The transportation sector contributed 27% of the total US greenhouse gases (GHGs)

* Corresponding author.

E-mail addresses: doowonk@andrew.cmu.edu (D.W. Kang), john.holbrook@charter.net (J.H. Holbrook).

emissions in 2010. Within the transportation sector, light-duty vehicles (LDVs), including passenger cars and trucks, contributed 62% of those transportation sector emissions (US Environmental Protection Agency, 2012).

Many potential fixes to this problem have been proposed, including implementation of electric vehicles (EV). The battery technologies required by EVs, however, are relatively immature and expensive (though improving).

There is an alternative way of powering cars and trucks that has not gotten much attention to date—Ammonia (NH3) fueled vehicles (NH3 Fuel Association, 2015). NH3-fueled vehicles have the potential to reduce CO2 emissions to levels far below those achieved by some other alternative-fueled cars, such as those fueled with natural gas, or ethanol derived from corn. In the case of EV's, the CO2 footprint of those vehicles will depend on the nature of how the electricity was produced, e.g. a coal burning power plant versus, say, a hydroelectric plant.

http://dx.doi.org/10.1016/j.egyr.2015.08.001

2352-4847/© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4. 0/).

This study identifies scenarios and requirements to dramatically reduce future CO2 emissions from the US transport sector, specifically from LDV by adopting NH3-fueled vehicles.

2. Why ammonia-fueled vehicles?

Anhydrous Ammonia (chemical formula NH3) is composed of one nitrogen atom and three hydrogen atoms—thus there are no carbon atoms involved in the oxidation reaction when ammonia is combusted. NH3 is a liquid fuel at room temperature and moderate pressures, nearly identical in physical properties to liquid propane. Ammonia can be used in internal combustion engine (ICE) vehicles with straightforward modifications, and is environmentally friendly, as it produces primarily only molecular nitrogen (N2) and water vapor (H2O) at the tailpipe, even when only low-cost emissions controls are used. Problems of unburned ammonia and NOx emissions in the engine's exhaust are removed by a selective catalyst reduction (SCR) system in NH3-fueled vehicles (Desrochers, 2013).

Ammonia can be produced by the catalytic reaction of nitrogen from air (which is 78% N2) and hydrogen from water, usually via electrolysis (Iowa Energy Center, 2013). Currently, however, the bulk of the world's ammonia production is carried out using hydrogen produced by steam reforming of natural gas, a fossil fuel. Ammonia can be produced at an affordable cost using any energy source, including fossil fuels, such as relatively clean natural gas, as well as non-fossil fuels such as renewable wind, solar, hydro and nuclear energy (Tallaksen and Reese, 2013; Kubic, 2006).

The mode of operation of NH3-fueled vehicles is similar to conventional gasoline-fueled internal combustion-engine vehicles: Liquid ammonia, stored in an onboard fuel tank at moderate pressure (150 psi), is burned with air in order to move an engine's pistons, producing power which is harnessed to drive the vehicle's wheels. This familiar technology means NH3-fueled vehicles can generally be built and maintained in the same way as the current vehicle fleet. NH3-fueled vehicles, clearly however, unlike conventionally-fueled vehicles, do not directly release any carbon dioxide (Iowa Energy Center, 2013).

The transition to NH3-fueled vehicles, unlike electric vehicles will be relatively simple. Most conventional cars on the road, including diesels, can run on a mixture of 90% gasoline (or diesel) and 10% liquid ammonia (nh3car, 2015), and could easily be modified to run on a mixture of up to 85% ammonia. This has already been demonstrated in spark ignited engines (Zacharakis-Jutz and Kong, 2013; HEC-TINA, 2015). The concept of the NH3-fueled vehicles is quickly becoming a reality, and an engine that could run on 100% ammonia in a very near future is currently under development (NH3 Fuel Association, 2013; Knight, 2011; Hollinger, 2015).

Regarding safety any safety concerns associated with ammonia fueled vehicles, studies have illustrated that ammonia would be safer than both gasoline and propane, another fuel sometimes used in LDV (Duijm et al., 2005; Quest Consultants Inc, 2009; Thomas and Parks, 2006). Ammonia has been commonly used as an industrial and agricultural chemical for over a century, and procedures have been developed to ensure NH3 can be handled safely (Thomas and Parks, 2006). Ammonia dissipates rapidly when released because it is lighter than air. The US Department of Transportation assigns a ''non-flammable liquid'' designation to liquid ammonia carried in tanker trucks on highways.

The infrastructure for large-scale production and distribution of ammonia already exists worldwide, as ammonia is a major input to the chemicals industry, commercial refrigeration, NOx control, and especially agriculture as an essential nitrogen fertilizer. There are over 2000 miles of underground, low carbon steel pipelines in the United States heartland, operating 24/7 and operating at moderate pressures (e.g. compared to natural gas pipelines) and exhibiting

an excellent safety and leak avoidance. NH3 retail ''filling stations'' are widespread, particularly in rural areas. There is a network of approximately 800 such fueling stations in the state of Iowa alone. These ''gas stations'' would require reasonably modest changes to adapt to ammonia fueled cars as well, including converting them to be attendant operated. Ammonia can be easily stored in large pressurized ''bullet'' tanks at relatively low pressure, similar to liquefied petroleum gas (LPG) (Iowa Energy Center, 2013). At even greater volumes approaching 50,000 tons of storage, NH3 is stored in atmospheric-pressure, self-liquified ''terminals'' which are located along the ammonia pipelines mentioned above.

Ammonia-fueled vehicles offer comparable range per tank of fuel as vehicles using conventional fuels partly because NH3 combustion is more efficient (produces more horsepower for equal energy content of fuel) than gasoline or diesel (HEC-TINA 2015), making them similarly convenient to use.

2NH3 + 3O2 ^ N2 + 6H2O.

The above equation shows that 1 mole of combusted NH3 produces 3-1 /2 moles of hot gas reaction products. That is better than H2 and hydrocarbon combustion, including gasoline and diesel.

In near future, NH3 fuel engineers would have developed direct NH3 fuel cells, which should further increase mpg of NH3 fuel cells LDV.

3. Reference case

Projected US LDV CO2 emissions from Annual Energy Outlook 2013 (AEO2013) reference case projections prepared by the United States Department of Energy will serve as the reference case forthis study (US Energy Information Administration, 2013). AEO 2013 provides projections of vehicle stocks, energy use, carbon dioxide emissions, and other parameters through the year 2040. US LDV stocks, average vehicle miles per gallon, vehicle miles traveled, and carbon dioxide emissions are projected in AEO 2013, shown in Table 1.

Even in 2040, 81% of LDV, in the AEO 2013 reference case projection, will still be fueled with gasoline. Interestingly, although LDV stocks increase by 26% in 2040 relative to 2010, and vehicle miles traveled increases 11% in 2040 over 2010, LDVs consume less fuel in 2040 than in 2010 because the average vehicle efficiency (expressed as miles per gallon) increases by 72% between 2010 and 2040. The net result of these changes is that overall CO2 emissions from LDVs decrease through 2040, and by 2040 are more than 20% lower than 2010 emissions.

4. Mitigation strategies

4.1. Mitigation scenarios

Two scenarios, in addition to the AEO reference case, have been developed in this study to illustrate the CO2 emissions mitigation potential of implementation of NH3-fueled vehicles in the US LDV transportation sector through 2040. Table 2 shows the assumptions regarding phasing in NH3-fueled vehicles in the US through 2040 for each scenario. The reference case of AEO projection does not exclude electric vehicles and fuel cell hydrogen vehicles, which are expected to have a similar effect on reducing CO2 emissions.

4.2. Software tool to be used for analysis

To calculate CO2 emissions reductions of emissions mitigation strategies, this study uses the software tool LEAP (the Long range Energy Alternatives Planning System), with which alternative

Table 1

US LDV stocks, average vehicle miles per gallon, vehicle miles traveled, and CO2 emissions (2010-2040) (US Energy Information Administration, 2013).

Item 2010 2020 2030 2040

Total LDV stock (million) 225 239 262 284

Average vehicle miles per gallon 21.0 24.1 31.3 36.1

Vehicle miles traveled (VMT) 11,803 11,992 12,662 13,111

CO2 emissions (million metric tons CO2 equivalent peryear) 1060 929 825 804

Table 2

Scenario assumptions for LDV in the US through 2040. Reference case Reference case of AEO 2013

Alternative 1 case NH3-fueled vehicles replacing gasoline vehicles to account for 10% of the vehicle fleet in 2020, 30% in 2030, and 50% in 2040, respectively Alternative 2 case NH3-fueled vehicles replacing gasoline vehicles to account for 10% of the vehicle fleet in 2020, 50% in 2030, and 100% in 2040, respectively

Fig. 1. Schematic of analytical approach.

scenarios can be created and evaluated by comparing their energy requirements, costs, and environmental impacts. LEAP is a software tool for energy policy analysis and climate change mitigation assessment developed at the Stockholm Environment Institute—United States (Stockholm Environment Institute, 2013).

4.3. Analysis approach

Fig. 1 illustrates the analytical approach used in the study to estimate potential reductions of CO2 emissions in the US transportation sector through 2040 through development and application of the mitigation strategies considered, with future transportation sector activity as described in AEO2013 serving as the basis for analysis.

5. Results

5.1. Mitigation effects

Table 3 and Fig. 2 show US LDV CO2 emissions through 2040 for each mitigation scenario using LEAP program. The estimated reference case LDV CO2 emissions calculated using the LEAP model in this study are between one and seven percent, depending on the year, different than those in the AEO 2013 reference case. The discrepancies in LDV CO2 emissions results between this study and AEO 2013 arise from the different assumptions used in the calculation of CO2 emissions in both cases. These differences, however, do not affect the overall analytical conclusions reached by this study.

The Alternative 1 case could reduce cumulative LDV CO2 emissions from 2010 through 2040 by about 20%, while the Alternative 2 case achieves reduction of about 30% of the cumulative LDV CO2 emissions from 2010 through 2040 produced in the reference case. The Alternative 2 case eliminates most of the annual LDV CO2 emissions in 2040 projected in the reference case, with a 96% reduction from reference case levels, equivalent to approximately 718 million metric tons CO2 equivalent for a year.

5.2. Cost-benefit results

Besides emitting zero greenhouse gases from vehicles, NH3 fuel could provide additional environmental benefits from the reduction of well-to-tank carbon emissions associated with the production and delivery of conventional fuels. Assuming around 21 g of CO2 are emitted per megajoule of gasoline produced (Bandi-vadekar, 2008), an estimated well-to-tank CO2 emission for a gasoline vehicle in America is approximately 1.5 metric tons of CO2 per year, based on an average fuel economy of about 21 miles per gallon for the gasoline vehicle on the road in America and an average annual distance traveled per vehicle of 12,000 miles (US Environmental Protection Agency, 2011). Table 4 shows well-to-tank CO2 emissions of LDV under the AEO 2013 reference case. The cumulative well-to-tank CO2 emissions for gasoline engine LDV from 2010 through 2040 are approximately 7781 million metric tons CO2 equivalent.

Compared to gasoline vehicles, NH3-fueled vehicles do not produce carbon dioxide during operation. Although CO2 would be emitted during, mostly truck delivered, NH3 fuel delivery, it would be less than a few percent than that of the well-to-tank CO2 emissions associated with gasoline fuel production and delivery in America shown in Table 4 (Bandivadekar, 2008).

Current industrial ammonia production plants, which run on fossil fuels, produce approximately 1.2-1.8 metric tons of CO2 per ton of ammonia produced (Ganley et al., 2007; Wood and Annette Cowie, 2004). Assuming that NH3-fueled vehicles have equivalent fuel energy input per mile of gasoline vehicles, one NH3-fueled vehicle, if fueled with conventionally-produced NH3, will cause emissions by ammonia-producing factories of somewhere between 4.2 and 6.1 metric tons CO2 per year, which is 7%-36% less than that emitted by a similar gasoline vehicle. However, once advanced ammonia production methods (e.g. solid state ammonia synthesis, Ganley et al., 2007) that are now working at the lab scale are commercialized in the very near future, if nonfossil sources of electricity are used, no CO2 emissions will be emitted during ammonia production process. This is also true with the electrolyzer and Haber-Bosch approach.

The retail price of gasoline on February 6, 2015 was $2.17 per gallon, according to US Energy Information Administration (2015). The average bulk ammonia price in 2014 was estimated at about $584 per metric ton (Apodaca, 2015). The estimated retail price of ammonia by comparing the wholesale price of gasoline with the retail price of gasoline is $2.13 per gallon. Advanced ammonia production methods would be expected to decrease ammonia production costs, and thus prices (Ganley et al., 2007; Yoon, 2013).

Table 5 shows required amount of ammonia in selected years to fuel each of the LDV NH3-fueled vehicles penetration scenarios outlined above, plus estimates of the amount of electricity required to make ammonia in each scenario, assuming a commercially mature solid state ammonia synthesis method. This study assumes

2010 2015 2020 2025 2030 2035 2040

Fig. 2. US LDV CO2 emissions through 2040 under scenarios including implementation of NH3 as a fuel.

Table 3

US LDV CO2 emissions through 2040 under scenarios compared with AEO 2013 reference case (Unit: million metric tons CO2 equivalent per year).

Cumulative (2010-2040)

Reference case (AEO2013) Reference case in this study Alternative 1 case Alternative 2 case

1060 1035 1035 1035

929 921 832 832

825 792 565 413

804 752 393 34

27,552 26,817 21,879 18,556

Table 4

Well-to-tank CO2 emissions for US gasoline engine LDV through 2040 for AEO 2013 reference case (Unit: million metric tons CO2 equivalent per year).

Case 2010 2020 2030 2040 Cumulative (2010-2040)

Reference case (AEO2013) 308 268 227 215 7781

Table 5

Required ammonia and electricity to make ammonia through 2040 for each mitigation scenario.

Case 2010 2020 2030 2040

Alternative 1 case

Ammonia (million metric tons) 0 61 156 247

Electricity (TWh) 0 430 1095 1731

Alternative 2 case

Ammonia (million metric tons) 0 61 261 495

Electricity (TWh) 0 430 1825 3462

7000 kWh of electricity to produce one metric ton of ammonia, based on reports that the solid state ammonia synthesis method consumes around 6000-8000 kWh of electricity to produce one metric ton of ammonia (Ganley et al., 2007; Yoon, 2013). For the same energy content, liquid ammonia has 2.3 times the mass of gasoline (Grannel, 2008).

Projected in the AEO 2013 reference case, electric power capacities and electricity generation in America through 2040 are given in Table 6 (US Energy Information Administration, 2013). To implement the Alternative 2 case, additional electricity generation of 11% in 2020, 42% in 2030 and 74% in 2040, respectively, than those of AEO 2013 reference case, while electricity increases of 11% in 2020, 25% in 2030 and 37% in 2040, respectively, for the Alternative 1 case. Installation of additional electric power generation capacity sufficient to produce the ammonia required,

Table 6

Projections of power capacities and electricity generation in America through 2040 in AEO 2013 reference case.

Case 2010 2020 2030 2040

Fossil fuel (Coal, gas and oil)

Power generation capacity (GWe) 720 699 756 835

Electricity output (TWh) 2608 2579 2836 3028

Nuclear energy

Power generation capacity (GWe) 101 111 114 113

Electricity output (TWh) 807 885 908 903

Renewable energy

Power generation capacity (GWe) 148 175 182 229

Electricity output (TWh) 394 557 601 753

Power generation capacity (GWe) 969 985 1051 1178

Electricity output (TWh) 3809 4021 4345 4684

particularly CO2-free electricity, would be a major challenge in aggressive deployment of NH3-fueled vehicles.

If ammonia for NH3-fueled vehicles was produced with nuclear energy and renewable energy, the GHG emissions produced would be near-zero. However, if ammonia for NH3-fueled vehicles were produced with electricity generated by fossil energy, significant GHG emissions during power generation would result. The same problems would occur with electric vehicles and fuel cell hydrogen vehicles.

Gasoline vehicles can be retrofitted to run on mostly ammonia at a cost of between $1000 and $5000 (Yoon, 2013; Proefrock, 2007). Only LDVs already on the road would need to be converted at those prices. ''New'' NH3 LDV's would cost the same as petroleum LDVs. Governmental subsides could encourage the public to adopt NH3-fueled vehicles until automakers can produce NH3-fueled vehicles on a large scale.

6. Conclusion

This study demonstrates that NH3-fueled vehicles could be a promising alternative for LDV public/commercial conversion to fossil-free fuels because of its significant contribution in reducing CO2 emissions compared with vehicles of carbon-based fuels.

Furthermore, NH3-fueled vehicles could be quickly deployed in large scale since the infrastructure for large-scale production and distribution of ammonia already exists worldwide and gasoline vehicles can be retrofitted to run on mostly ammonia at a modest cost.

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