Tuesday, May 8, 2012

Power generation with Ammonia

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 or gas turbine. The mechanical energy is converted into electrical energy in power generation and as a motive force in transportation. The fundamental principles remain the same irrespective of the efficiencies and sophistications 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 utilize 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 utilize 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 portion 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 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 currently 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.