Ammonia might just be the ticket for a more sustainable future
Ammonia (chemical formula NH3) can be found naturally in the environment, but it is also widely used in industry and commerce.
For living creatures, it is an essential precursor for synthesizing amino acids and nucleotides and is necessary for numerous biological activities. Ammonia is also a product of bacterial activity in the soil and is created as part of the nitrogen cycle in the environment.
But, for human use, it is essential as the main ingredient in the manufacture of fertilizers for food production. In fact, it has been argued that developing its synthesis at scale is one of the most important discoveries of all time. Although, it has also been pointed out that widespread overuse of ammonia-based fertilizers has degraded the nitrogen cycle and contributed to environmental damage.
While there are some serious environmental concerns about its widespread use, ammonia might just be in a position to save combustion engines and make renewable technologies truly sustainable in one fell swoop!
But how? Let's find out.
Can ammonia be used as a fuel source?
In short, it most certainly can. At least, that is what a growing body of experts on the subject is beginning to explore.
Ammonia has been used extensively for many years as a refrigerant in refrigeration systems and manufacturing things like fertilizers, household cleaning products, and disinfectants, to name but a few products.
However, due to its carbon-free nature and potential use as a fuel to lower CO2 emissions, ammonia has recently begun to attract the attention of researchers, scientists, engineers, and technologists. As a special hydrogen storage medium (with three hydrogen atoms) and method of transportation and distribution, it can be extremely helpful in resolving several problems relating to hydrogen energy options and the hydrogen economy.
This is because it uses the same existing transportation and distribution methods that industries are already using without requiring any infrastructure changes. In the past ten years, attempts to employ ammonia in gas turbines and internal combustion engines have significantly increased.
As a potential fuel source, ammonia has some significant advantages: -
- It is both carbon-free and relatively safe for the environment (excluding carbon costs for its production, more on that later).
- It has three hydrogen atoms and could perhaps be employed as a hydrogen carrier.
- Compared to many other fuels, their manufacturing, storage, transportation, and distribution are significantly simpler.
- It is practical and affordable for use in applications.
- It could serve as a substitute for kerosene, diesel, and gasoline.
- It can be considered for all combustion systems, including gas turbines and engines.
- It might be a viable fuel for renewable energy production in remote places.
Why is ammonia a good choice as an alternative fuel source?
It is estimated that about 1/3 of the world's total energy consumption comes from the transportation sector, where fossil fuels are predominantly utilized to manufacture common transportation fuels like diesel, gasoline, jet fuel, etc.
While one of the most utilitarian fuel sources ever discovered by humans, their extensive use has resulted in very high amounts of greenhouse emissions, widely believed to cause severe environmental damage. Although manufacturers and governments are making significant efforts to move to electric and hybrid vehicles, one concern is that this shift cannot be completed quickly due to infrastructure, economic, and raw material challenges.
According to many studies, not nearly enough is being done or quickly enough.
Additionally, using diesel and gasoline-powered generators in residential, commercial, utility, and off-grid applications raises the consumption of fossil fuels and CO2 emissions. To move to a hydrogen-based economy more quickly, the use of ammonia in combustion processes like gas turbines and internal combustion engines may prove critical.
Several attempts have been made over the past few years to use ammonia in gas turbines and internal combustion engines.
For example, as part of an ongoing microgrid proceeding, the California Public Utilities Commission met with industry stakeholders to discuss alternatives to diesel generators and is considering replacing diesel generators with ammonia-driven ones by 2021.
Under this plan, 350 MW of diesel generators used in 63 substations are earmarked to be replaced with ammonia-fueled ones.
Japan has also started a comprehensive action plan for ammonia use in manufacturing, mainly in power production. A Japanese marine company has announced starting a project on ammonia-fueled ships and fuel supply systems for it.
Many more ammonia applications are introduced in more detail in the following sections. It is anticipated that ammonia-driven systems will soon meet 1 percent of Japan's electricity consumption.
An ammonia-fueled gas turbine program has also been started for power generation in Japan.
However, like many things in life, there are no solutions, only compromises. Despite the clear advantages of ammonia, it does come with some unique challenges related to its toxicity, flammability, and combustion in traditional engines, turbines, and power generators.
Besides, while ammonia is carbon-free, the most common process used to manufacture it is incredibly carbon-intensive. Not only that, but the release of ammonia and nitrogen oxides into the atmosphere is just as bad for global warming as CO2, if not worse. Clearly, to use ammonia effectively, it will be necessary to develop green manufacturing methods.
That being said, the potential benefits of using ammonia as a fuel may outweigh its drawbacks. These include, but are not limited to: -
- The three hydrogen atoms and one nitrogen atom that makes up ammonia can be manufactured readily on demand using fossil fuels or renewable energy sources.
- It can store and transport hydrogen.
- Ammonia transportation is significantly safer than hydrogen transportation.
- It contains roughly 48 percent more hydrogen by volume when liquefied than hydrogen.
- Its use produces no carbon dioxide emissions because it is carbon-free.
- It can be used as a fuel, working fluid, refrigerant, hydrogen carrier, fertilizer, feedstock, chemical, cleaning agent, and a variety of other things.
- Due to its characteristic fragrance, it may be quickly found when a leak develops. However, inhaling large quantities of ammonia can be fatal to living creatures.
- It is a promising fuel for burners, gas turbines, power plants, and engines. For such engines, only minor changes are required.
How is it better than hydrogen?
We've already covered a few reasons above, but one of the ammonia's key benefits is that it can be considered a non-biological "energy currency." This term derives from its use for a molecule in every living cell called adenosine triphosphate (ATP).
In your body, this substance is a sort of one-size-fits-all energy source for various biological functions of the body.
Some consider anhydrous ammonia (NH3) to be the best "energy currency" for green electricity since it can be used to store and distribute energy with great ease. In terms of renewable energy, the ability to store electricity 'in a bottle' so that it may be used in times of shortage is clearly incredibly beneficial.
Mainly, as we've discussed previously, its advantage is its hydrogen content.
Hydrogen has long been considered by some to be the "green" fuel holy grail despite being extremely rare in its pure form on Earth. It is environmentally friendly because it is made from renewable resources, the most popular of which is the electrolytic cracking of water.
Additionally, "brown" sources like the refinement of petroleum, are also used to make hydrogen. To date, the vast majority of synthetic hydrogen in the world is created either as byproducts of refining petroleum or by steam-reforming of natural gas. Both of these processes contribute carbon emissions to the atmosphere.
So, why would anyone consider using anhydrous ammonia rather than hydrogen?
After all, on a weight-by-weight basis, hydrogen has a higher LHV (lower heating value) energy content than ammonia (51590.7 BTU/lb or 120 MJ/kg vs 8082.5 BTU/lb or 18.8 MJ/kg).
However, this neglects the fact that ammonia is a far superior hydrogen carrier in terms of volume than even liquefied hydrogen. This is because liquid hydrogen has an energy density of around 8.491 MJ/liter compared to ammonia's far superior 11.5 MJ/liter.
Despite having 17.65 percent of hydrogen by weight, ammonia has around 48 percent more hydrogen by volume than even liquid hydrogen due to the fact that it has three hydrogen atoms bound to each nitrogen atom.
Hydrogen is frequently viewed as an energy commodity, although it may ultimately be unworkable for several reasons.
One of the main issues is that compressed hydrogen gas has a poor energy density, which makes transportation and storage expenses. It can take more energy in fuel than hydrogen generates to transport compressed hydrogen gas over long distances, depending on the method used.
Obviously, liquefied hydrogen has a higher energy density than compressed hydrogen gas. Still, since hydrogen has a low boiling point (-423 oF/-253 oC), it requires a lot of energy to liquefy and maintain refrigeration.
About 30 percent of the energy contained in the liquid hydrogen is needed for liquefaction, and only 10 percent to 15 percent is needed to compress the hydrogen to 800 bar.
Another factor is that hydrogen molecules are challenging to contain, as they are so tiny. Unlike gases with more giant molecules like ammonia and propane, hydrogen will slowly seep out of hoses at a far higher pace. Metals can also become embrittled by hydrogen, necessitating routine replacement of metallic tanks, valves, and tubing.
Due to the weight of the high-pressure hydrogen tanks, compressed hydrogen can only be delivered in small amounts—about 400 kg (0.4 tonnes).
Ammonia, for many, makes more sense.
For a start, ammonia behaves and stores quite similarly to LPG, with a boiling point of -28.03 °F (-33.35 °C). By contrast, the primary ingredient of LPG, propane, has a boiling point of -43.73 °F (-42.07 °C).
Another benefit of ammonia over hydrogen is that the risk of explosion or fire is so low that the MSDS labels list it as a non-flammable gas with an NFPA flammability rating of 1. Also, because of ammonia's aroma, even extremely modest rates of leakage are easily detectable by the human nose.
If leaks of ammonia do occur, they readily diffuse into the atmosphere, where they are ultimately eliminated by photodissociation. Also, since ammonia doesn't cause embrittlement, metallic tanks, valves, and tubing don't need to be replaced on a regular basis.
Can engines be converted to run on ammonia?
In short, yes they can (in theory).
Called a dual-fueled ammonia vehicle conversion, it is physically identical to a compressed natural gas vehicle conversion in its basic form.
Only 150 PSI of liquid ammonia is held in a new onboard tank, however. After the engine has been started and warmed up using gasoline, ethanol, etc., regulators, valves, and an electronic control system meter the flow of ammonia to the engine as necessary.
When liquefied, ammonia has about half the volumetric energy of gasoline. When the energy contribution of the gasoline's energy is taken into account, this indicates that an ammonia tank the size of your existing gas tank will carry you more than 2/3 of the distance of operating on gasoline alone between fill-ups.
The engine is started with a tiny amount of gasoline, and as the load increases, ammonia is added to generate more energy. The engine control electronic module takes care of everything automatically.
However, there are not many publically available conversion kits widely available, if any. Currently, fleet cars and other major market applications are the focus of any conversion development. However, private car conversions will likely be on the way because of rising gas prices.
As for costs to make a conversion, this is a little tricky to answer.
However, changing a vehicle to run mostly on compressed natural gas is identical to converting it to run largely on ammonia. So, for private cars, the parts and labor would likely cost a few thousand dollars (or less, depending on your country).
But, the investment would likely be worth it.
Any cost savings would be based on how much gasoline and ammonia cost (just like LPG and gasoline). Ammonia currently costs around about $0.23 a liter, or $0.85 a gallon. However, you are not likely to find it at your local gas station anytime soon.
But, even a converted vehicle can still run on regular gasoline if an ammonia top-up is few and far between. Just like an LPG-dual fuel vehicle, you would be able to operate it normally on 100% gasoline by simply flipping a switch, unlike LPG-converted cars; for many natural gas vehicles, this is not feasible.
Is ammonia fuel safe for the environment?
One of the most significant industrial chemical reactions ever created is the Haber-Bosch process, which turns hydrogen and nitrogen into ammonia. Due to the method, ammonia fertilizer became widely available, contributing to a rise in global population by hastening the rate at which agricultural yields rose.
According to Statista, somewhere in the order of 150 million metric tons of ammonia were produced in 2022. About 50% of the world's food output depends on ammonia fertilizer, which accounts for about 80 percent of the ammonia currently manufactured.
The remaining ammonia is used to create other compounds, such as explosives, polymers, textiles, and medications.
According to chemical engineer Karthish Manthiram of the Massachusetts Institute of Technology, the Haber-Bosch process is involved in creating almost every synthetic substance we use that contains nitrogen atoms. All of those nitrogen atoms originated from ammonia, thus every one of the things we use has a significant carbon dioxide footprint.
Even while the Haber-Bosch process is a significant technological breakthrough, it has always been an energy-hungry one, resulting in its enormous carbon footprint.
The reaction consumes around 1 percent of the world's total energy production while operating at temperatures of around 500 °C and pressures of up to 20 MPa. According to the Institute for Industrial Productivity, it releases up to 450 million tons of CO2, give or take, a year.
That's more than any other industrial chemical-making reaction and is estimated to total around 1.8 percent of yearly worldwide CO2 emissions. This is primarily because ammonia production is currently heavily reliant on the use of fossil fuels for raw materials and energy.
The International Energy Agency, the International Council of Chemical Associations, and the Society for Chemical Engineering and Biotechnology published a joint report in 2013 that found that the CO2 emissions from the hydrogen production make up more than half of those from the entire ammonia production process.
And this trend is only set to grow (literally and figuratively) as our need for ammonia fertilizer is growing. The Food and Agriculture Organization of the United Nations projects that by 2020, demand for nitrogen fertilizer will have increased from 110 million tons in 2015 to over 119 million tons.
But, there is some light at the end of the tunnel, sustainability-wise.
How can ammonia be produced sustainably?
Around the world, chemists and engineers are working to develop sustainable ammonia production methods. Some are attempting to create hydrogen without using fossil fuels and to power the reaction with renewable energy sources.
Others are looking for a Haber-Bosch alternative that produces ammonia more efficiently, with fewer emissions. Researchers acknowledge that although progress has been sluggish, it has been worthwhile.
In an interview with Chemical and Engineering News in June of 2019, Douglas MacFarlane, an electrochemist at Monash University, "ammonia as it’s produced today for fertilizers is effectively a fossil-fuel product.”
“Most of our food comes from fertilizers. Therefore, our food is effectively a fossil-fuel product. And that’s not sustainable,” he explained.
Researchers have been experimenting with using renewable energy and feedstocks to create the lucrative chemical in modest sizes at green ammonia factories across the world, including in Japan, England, Australia, and the US.
These businesses mostly employ the standard Haber-Bosch process, but they produce hydrogen and power the reactions using water electrolysis and alternative energy sources rather than fossil fuels.
These strategies have been tested since last year in a pilot facility at the Fukushima Renewable Energy Institute run by the Japanese company JGC. They have partnered with the National Institute of Advanced Industrial Science and Technology (AIST) to launch the green ammonia demonstration plant through a federal program known as the SIP Energy Carriers.
The plant can run on solar energy, electrolyzes water to produce hydrogen, and conducts a Haber-Bosch-type reaction utilizing a new ruthenium catalyst that JGC and AIST created.
According to Mototaka Kai, project manager at the factory, "the major advantage of our process is that hydrogen is produced at a much lower pressure than the conventional process."
According to Mototaka, the hydrogen pressure is about 5 MPa, which is about 1/3 to 1/4 that of a conventional Haber-Bosch plant. There are two benefits to this decreased pressure. One is that it is safer because the reaction is taking place at a lower pressure.
Additionally, it uses less energy to pressurize the system. The factory currently makes 20–50 kg of ammonia each day.
Another interesting approach is being developed by Siemens in the UK in collaboration with researchers at the University of Oxford, the UK’s Science and Technology Facilities Council, and Cardiff University. This project aims to run a demonstration plant using the typical Haber-Bosch process, powering it with the wind.
Siemens first aims to demonstrate that it can produce ammonia sustainably and with a speedy scale-up. The corporation also sees the facility as a testing ground for ongoing technological advancements, such as the creation of Haber-Bosch catalysts and tests on ammonia combustion.
So far, the strategy has been successful.
The small facility, housed in shipping containers, uses wind-generated electricity to power a hydrogen electrolysis unit, which produces hydrogen that is used to create ammonia. This could be a potential solution for solving one of the major problems with renewable energy sources; they are, by their very nature, intermittent.
However, combining wind farms with ammonia synthesis might be a very good way to "bank" generated energy.
According to Wilkinson, burning ammonia made from renewable sources could be a solution. In addition to producing fertilizer, Siemens and JGC are interested in green ammonia production since it can be used to create carbon-free fuel.
Ammonia can be transported and stored similarly to gasoline, and it is less hazardous to handle than gaseous hydrogen, another potential carbon-free fuel.
“Ammonia is what I like to call a nexus molecule,” Manthiram explained. “It’s useful as a fertilizer. It’s useful for food. It’s useful for energy storage.”
All very interesting, but these businesses are still primarily using Haber-Bosch to synthesize the chemical, regardless of how they intend to use the ammonia generated by their green plants.
The reaction involves mixing hydrogen and nitrogen gas over an iron catalyst, at high temperatures and pressures. The process is also pretty inefficient.
Each metric ton of ammonia packs about 5 MW h of energy. “The best, most efficient Haber-Bosch plants work at around 10 MW h per metric ton of ammonia,” MacFarlane explained. “So we’re approximately only 50% efficient. It’s wasting a lot of energy for what you get.”
So, if ammonia is ever considered a sustainable replacement for conventional fuels, an alternative to the Haver-Bosch process must be fully fleshed out first.
But, that is a subject for another time.
Ammonia certainly has some promise as "green" fuel for the future. It has many benefits over existing fuels and is widely available.
However, it will only really become a viable alternative once a less energy-intensive process to synthesize it can be found. But, with rapidly rising fossil fuel costs around the world, it may only be a matter of time before a solution is developed in short order.
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