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Tag Archives: Ammonia

We now generate electric city from heat, obtained by combustion of fossil fuel such as coal, oil and gas. But such combustion generates not only heat but also greenhouse gases such as Carbon dioxide and oxides of Nirogen.The only alternative to generate power without any greenhouse gas emission is to use a fuel with zero carbon. However, oxides of Nitrogen will still be an issue as long as we use air for combustion because atmospheric air has almost 79% Nitrogen and 21% oxygen. Therefore it becomes necessary to use an alternative fuel as well as an alternative power generation technology in the future to mitigate greenhouse problems.

Hydrogen is an ideal fuel to mitigate greenhouse gases because combustion of Hydrogen with oxygen from air generates only water that is recyclable. Combining Hydrogen with Oxygen using Fuel cell, an electrochemical device is certainly an elegant solution to address greenhouse problems. But why Hydrogen and Fuel cell are not commonly available? Hydrogen is not available freely even though it is abundantly available in nature. It is available as a compound such as water (H2O) or Methane (CH4) and Ammonia (NH3). First we have to isolate Hydrogen from this compound as free Hydrogen and then store it under pressure. Hydrogen can easily form an explosive mixture with Oxygen and it requires careful handling. Moreover it is a very light gas and can easily escape. It has to be compressed and stored under high pressure.

Generation of pure Hydrogen from water using Electrolysis requires more electricity that it can generate. However, Hydrogen cost can be reduced using renewable energy source such as solar thermal. The solar thermal can also supply thermal energy for decomposing Ammonia into Hydrogen and Nitrogen as well as to supply endothermic heat necessary for steam reformation of natural gas into Hydrogen. On-site Hydrogen generation using solar thermal using either electricity or heat can become a commercial reality. Hydrogen generation at higher temperatures such as Ammonia decomposition or steam reformation can be directly used in Fuel cell such as Phosphoric acid Fuel cell.

Phosphoric acid fuel cell is a proven and tested commercial Fuel cell that is used for base load power generation. It is also used for CHP applications. Hydrogen generation using solar thermal and power generation using Fuel cell is already a commercial reality and also an elegant solution to mitigate greenhouse gases. Large scale deployment of Fuel cell and solar thermal will also cut the cost of installations and running cost competing with fossil fuel.Fuecell technology has a potential to become a common solution for both power generation and transportation.

While Government can encourage renewable energy by subsidizing PV solar panels and discourage fossil fuel by imposing carbon tax, they should give preference and higher tariff for power purchase from Solar thermal and Fuel cell power generators. This will encourage large-scale deployment of Fuel cell as a potential base load power source.

Majority of current power generation technologies are based on thermodynamic principles of heat and work. Heat is generated by  chemical reactions such as combustion of coal, oil or gas with air or pure oxygen. This heat of combustion is then converted into work by a reciprocating engine or steam turbine of gas turbine. The mechanical energy is converted into electricity in power generation and as a motive force in transportation. The fundamental principles remain the same irrespective of the efficiencies and sophistication we incorporated as we progressed. The efficiency of these systems hardly exceeds 30-40 of the heat input, while the remaining 60-70 heat is wasted. We were also able to use this waste heat and improved the efficiency of the system by way of CHP (combined heat and power) up to 80-85%.But this is possible only in situations where one can use both power and heat simultaneously. In a centralized power plant such large heat simply dissipated as a waste heat through cooling towers and in the flue gas. This is a huge loss of heat because a substantial part of heat of combustion is simply vented into the atmosphere in the form of greenhouse gases. If ‘greenhouse gas’ and ‘Global warming’ were not issues of concern to the world, probably we would have continued our business as usual.

Generation of heat by combustion of hydrocarbon is one example of a chemical reaction. In many chemical reactions, heat is either released or absorbed depending upon the type of reaction, whether it is exothermic or endothermic. Sometimes these chemical reactions are reversible. It may release heat while the reaction moves forward and it may absorb heat while it moves backward in the reverse direction. By selecting such reaction one can make use of such energy transformations to our advantages. One need not release the heat and then release the product of reaction into the air like burning fossil fuels.

Ammonia is one such reaction. When Hydrogen and Nitrogen is reacted in presence of a catalyst under high temperature and pressure the reaction goes forward releasing a large amount of energy as practiced in industries using Heber’s process. The heat released by this reaction can be converted into steam and we can generate power using steam cycle. The resulting Ammonia can further be heated in presence of a catalyst by external heat due to endothermic nature of the reaction and split into Hydrogen and Nitrogen.  However, such heat can be supplied only from external sources. One University in Australia is trying use the above principle by using solar thermal energy as a source of external heat. The advantage of this system is power can be generated without burning any fossil fuel or emitting any greenhouse gas. One can use a renewable energy sources such as solar thermal and also use Ammonia as a storage medium.

Ammonia is a potential source of energy to substitute fossil fuels. However, such Ammonia is now synthesized using Hydrocarbon such as oil and gas. The source of Hydrogen is from synthesis gas resulting from steam reformation of a Hydrocarbon. Hydrogen can also be derived from water using electrolysis using renewable energy source. In both the above cases, renewable energy is the key, without which no Hydrogen can be produced without a Hydrocarbon or an external heat is supplied for splitting Ammonia.

Ammonia can also be split into Hydrogen and Nitrogen using external heat.  The resulting Hydrogen can be used to generate power using a Fuel cell or run a Fuel cell car. Nitrogen also has many industrial applications.Thereoefore ammonia is a potential chemical that can substitute fossil fuels in the new emerging renewable economy.

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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