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Ammonia is a well-known industrial chemical that is manufactured worldwide as a precursor for the production of Urea. The chemistry and technology of Ammonia synthesis is well-known and well established. It was a land mark achievement to fix atmospheric Nitrogen into the soil in the form of Urea as a fertilizer. It has 17.6% Hydrogen and 82.4% Nitrogen making it an ideal fuel for combustion when compared to Gasoline in terms of greenhouse gas emission because Ammonia no carbon. Handling free Hydrogen has always been a concern due to its explosive nature and lightness. Transportation of Hydrogen in the form of Ammonia is relatively cheaper and safer. A non-regulated Ammonia nursing tank at 265 psi pressure holds 3025kg Ammonia, containing 534kg Hydrogen, because a 5900 gallon Hydrogen tube trailer at 3200 psi pressure, contain only 350kgs of Hydrogen. Low pressure Ammonia tank with less than 25% volume contain more than 53% Hydrogen than a high pressure tube trailer. Ammonia has a lower volumetric energy density compared to other fuels.However, after subtracting energy required to elicit hydrogen from each fuel, hydrogen emerges with highest energy density compared to other fuels, and it is the only fuel which is carbon free. These qualities make Ammonia, a potential  substitute for Gasoline.

Ammonia need not be used as direct combustible fuel in internal combustion engines but it can be used as Hydrogen carrier safely and economically. The Hydrogen resulting from the decomposition of Ammonia can be used as fuel in a Fuel cell car as well as in a combustion engine. It can also be used to generate small on site power using a Fuel cell or IC engine. For example, 534kg Hydrogen can generate Electricity up to 10 MW and up to 6Mw thermal energy using a Fuel cell.

Currently ammonia is manufactured using fossil fuel source such as natural gas or naphtha to generate Hydrogen in the form of Syngas.But this can be effectively substituted with renewable source of Hydrogen such as Electrolysis of water using renewable solar thermal power or wind energy. Alternatively a biogas can be steam reformed to generate Hydrogen similar to natural gas. The generated Hydrogen can be compressed and stored.

Nitrogen forms 79% of atmospheric air and it can be obtained by air liquefaction and separation by distillation or by simple membrane separation method to separate air into Nitrogen and Oxygen. The resulting Nitrogen can be compressed and stored for Ammonia sysnthsis.Production of Ammonia using Bosch Haber process is well-known. Ammonia can be transported in pipelines, in tankers by road, rail or ship to various destinations.

Ammonia can be readily be used as fuel using a spark ignited combustion engine with little changes because Ammonia is classified as non-combustible fuel. Alternatively, it can be decomposed in a catalytic bed reactor and separated into Hydrogen and Nitrogen using PSA (pressure swing adsorption) system. The resulting Hydrogen can be stored to run a Fuel cell car like Honda FCX. Ammonia, as a Hydrogen carrier can substitute gasoline as an alternative fuel for transportation and power generation. All necessary technologies and systems are commercially available to make it a commercial reality.

 

Synthesis of Ammonia is one of the  remarkable achievements of Chemical engineering in forties .It is a precursor for Urea, the fertilizer  that  brought about ‘Green revolution’ in agriculture industry and helped to achieve record food production all over the world. It was a milestone in modern chemistry to synthesis a molecule containing I atom of Nitrogen and 3 atoms of Hydrogen, represented by NH3 called Ammonia. The HeberBosch process for the production of Ammonia is a well established mature, commercial technology.

The process uses a Hydrocarbon source such as Naphtha or Natural gas as the feed stock to generate a synthesis gas composed of Hydrogen and Carbondioxide.The gas mixture is separated into carbon dioxide and Hydrogen using PSA (pressure swing adsorption ) technology. The resulting Hydrogen is used to combine with Nitrogen to synthesize Ammonia.

The chemical reaction can be represented by the following equation.

N2 + 3H2 ———- 2 NH3

The above reaction takes place at a pressure of 100-200 bars and temperature of 300-500C in presence of  catalysts. It is an exothermic (heat releasing) reaction and the catalyst bed is cooled and maintained at 400C to be efficient.But this process of Hydrogen generation using Hydrocarbon emits greenhouse gases. Alternatively, Hydrogen can be generated using different methods using renewable energy sources using water electrolysis. Such process may be used in the future for this application.

Nitrogen is derived from atmospheric air. The air we breathe has about 79% of Nitrogen and 21% Oxygen. But these two gases can be separated by liquefying the air by cryogenic process and distilling them into two fractions. Alternatively, they can separated using pressure swing adsorption or membrane separation process, utilizing their density differences. In either way, Nitrogen can be separated from atmospheric air. By combining the above Hydrogen and Nitrogen, it is possible to synthesis Ammonia on a commercial-scale.

The ammonia can be easily split into Hydrogen and Nitrogen by passing Ammonia through a bed of Nickel catalyst at 200-400C as and when required to generate on site Hydrogen. This Hydrogen can be used for power generation or to run our cars using PEM Fuelcell.As we have seen previously, we are now looking for various sources of Hydrogen, and Ammonia is one of the promising sources for couple of reasons. The process and technology of Ammonia production, transportation and usage is well documented and has been practiced for few decades. It does not emit  greenhouse gases.Liquified Ammonia has been widely used in air-conditioning and refrigeration systems. Ammonia can be easily metered into any system directly from the cylinder.

It is easier to use Ammonia directly into a convention internal combustion engines in place of Gasoline and this technology has already been practiced in 1880. Ammonia is pungent and any leakage can be easily identified. The advantage of using Ammonia as a fuel in cars, it does not emit any smoke  but only water vapour.It can be admixed with Gasoline or used as 100% anhydrous Ammonia. It also helps in reduction of NO2 emission, especially is diesel engines.

Ammonia has a great potential as a source of future fuel provided the sources of Hydrogen comes from water using renewable technologies or by photo electrolysis using direct sunlight.

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