Energy-from-Saltwater PDF

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CHAPTER IIReview of Related LiteratureEnergy from SaltwaterAccording to [ CITATION alb09 \l 1033 ]“The main goal was to find an alternative source of energy and to be able to see if seawater can be used as the alternative source of energy”. Based on their findings, they concluded that seawater essen...

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CHAPTER II Review of Related Literature

Energy from Saltwater According to [ CITATION alb09 \l 1033 ]“The main goal was to find an alternative source of energy and to be able to see if seawater can be used as the alternative source of energy”. Based on their findings, they concluded that seawater essentially store electric potential energy which can be harnessed to become a source of power. To harness the said potential energy to usable electrical energy, one has to be near the shore to collect saltwater and it will take a large amount of water for it to become efficient. The main problem is that, it is hard for it to be converted into electrical energy because it needed to be transferred from the shore into the mainland and will need a large amount of metals to serve as electrodes. Despite this hurdle, numerous researches tried to optimize and further develop the technology to minimize the cost in producing electricity from salinity. Saltwater can serve as the electrolyte in a battery, thus generating electricity. A battery has three parts: an electrolyte and two electrodes, which are made by different materials, often metals, but some of the first batteries that made by Alessandro Volta around 1880, used saltwater, silver, and zinc to generate electricity. [ CITATION Sci \l 1033 ] Water is comprised of two elements – hydrogen [ CITATION alb09 \l 1033 ]and oxygen. Distilled water is pure and free of salt; thus it is a very poor conductor of electricity. But saltwater that has salt in it, becomes an electrolyte solution that can conduct electricity. [ CITATION Amr \l 1033 ]

Hydrogen Production Methods A promising candidate for producing elemental hydrogen is electrolysis. It is a decomposition reaction that splits water into hydrogen and oxygen gas by inducing electricity to drive the reaction. Electrolysis reactions undergoes in a unit called electrolyzer which can come in all shapes and sizes that is suitable for small scale to large scale hydrogen production. To drive the reaction, production plants or facilities can get their electricity from renewable or nonrenewable energy sources[ CITATION USD \l 1033 ]. To make electrolysis widely become a standard means of mass production of hydrogen through electrolysis, there are factors that must be addressed which are namely; reduction of energy consumption, cost to build and operate and maintenance of electrolyzers while increasing the device’s efficiency. In order to make electrolysis more sustainable, cost effective and environmental friendly, electricity that is used must came from renewable sources such as solar or wind based powerplants to eliminate greenhouse emissions.[CITATION San13 \l 1033 ] Hydrogen can be produced from diverse, domestic resources including fossil fuels, biomass, and water electrolysis with electricity. The environmental impact and energy efficiency of hydrogen depends on how it is produced. Water electrolysis is one of the simplest methods used for hydrogen production. It has the advantage of being able to produce hydrogen using only renewable energy. To expand the use of water electrolysis, it is mandatory to reduce energy consumption, cost, and maintenance of current electrolyzers. [ CITATION sci \l 1033 ] Generally, for electrolysis to occur at significant rate, it is essential to have a relatively high concentration of the reactant, while process economics dictate that the solvent should be

stable. It is usually essential for the inert electrolyte to be dissociated extensively into cations and anions. [ CITATION sci \l 1033 ]

Hydrogen as Fuel Hydrogen is considered an alternative fuel under the Energy Policy Act of 1992. The interest in hydrogen as an alternative transportation fuel stems from its ability to power fuel cells in zero-emission electric vehicles, its potential for domestic production, its fast filling time, and the fuel cell's high efficiency. In fact, a fuel cell coupled with an electric motor is two to three times more efficient than an internal combustion engine running on gasoline. Hydrogen can also serve as fuel for internal combustion engines. However, unlike FCEVs, these produce tailpipe emissions and are less efficient. The energy in 2.2 pounds (1 kilogram) of hydrogen gas is about the same as the energy in 1 gallon (6.2 pounds, 2.8 kilograms) of gasoline. Because hydrogen has a low volumetric energy density, it is stored onboard a vehicle as a compressed gas to achieve the driving range of conventional vehicles. Most current applications use high-pressure tanks capable of storing hydrogen at either 5,000 or 10,000 psi. Retail dispensers can fill these tanks in about 5 minutes. Other storage technologies are under development, including bonding hydrogen chemically with a material such as metal hydride, or low-temperature sorbent materials. [ CITATION www \l 1033 ]

Hydrogen production may improve the performance of internal combustion engines. It is high energy, has wide flammability limits, and high flame speed which are all desirable traits that can potentially enhance the engine’s combustion. However, hydrogen has low energy density and

it needs to be produced from another energy source pose significant challenges for implementation [ CITATION Mar1 \l 1033 ]. Researchers of University of Connecticut found out that long term stability test and cyclic contamination-recovery test are used to evaluate the PEFC tolerance to various impurities and the recovery strategies following the contamination. The cyclic voltammetry and electrochemical impedance spectroscopy are used to characterize any electrochemical changes due to contamination, and help to understand the contamination mechanisms. Hydrogen pump cell with application of reference electrodes is used to characterize contamination separately on two electrodes. Polymer electrolyte membrane fuel cells (PEMFCs) are a type of fuel cell that converts the chemical energy released by the reaction of hydrogen (fuel) and oxygen into electrical energy and generates water and heat. The fuel delivery system (FDS) is designed to supply hydrogen from a storage tank to the fuel cell stack and, in some designs, reuses the exhausted fuel [ CITATION Zha \l 1033 ].

In the research work of (He, Jinglin, Ph.D., Auburn University, 2011, 200; 3480706) a hybrid FDS used in fuel cell vehicles is proposed, which uses an ejector and a blower dependent upon loads that circulate unconsumed hydrogen to increase efficiency of fuel usage. In addition, stoichiometric ratio (SR) of the hydrogen, defined as the ratio of the supplied hydrogen flow rate to the consumed by the reaction in cells, should be maintained a constant to prevent fuel starvation at abrupt load changes. Moreover, the hydrogen pressure imposed to the stack should follow any change of the cathode pressure to prevent large pressure difference across thin membranes. Furthermore, liquid water, impurities and contaminant species in the anode gas flow channels should be purged out in time to prevent flooding and catalysts poisoning in cells.

(Silva, Isaac Alexander, M.S., University of California, Davis, 2014, 93; 158; 5124) Proposed a method of exhaust heat recovery from a spark-ignition internal combustion engine was explored, utilizing a steam reforming thermo-chemical reactor to produce a hydrogen-rich effluent, which was then consumed in the engine. The effects of hydrogen in the combustion process have been studied extensively, and it has been shown that an extension of the lean stability limit is possible through hydrogen enrichment. The system efficiency and the extension of the operational range of an internal combustion engine were explored through the use of a methane fueled naturally aspirated single cylinder engine co-fueled with syngas produced with an on-board methane steam reformer. It was demonstrated that an extension of the lean stability limit is possible using this system.

The thermochemical recuperation according to (Vernon, David R., Ph.D., University of California, Davis, 2010, 356; 3444080), processes uses endothermic reformation reactions to upgrade a portion of an engine’s primary fuel into a hydrogen-rich gas, thereby converting part of the exhaust heat from an internal combustion engine into chemical potential energy. Enriching the primary fuel air mixture of the internal combustion engine with this hydrogen-rich gas potentially enables combustion with very lean or dilute mixtures, resulting in higher efficiency and lower emissions as compared to standard combustion regimes. It may be possible to simplify thermochemical recuperation system architecture by directly mixing exhaust gases with the fuel in the reformation process to supply a significant portion of the heat and water required. To evaluate the effect of direct exhaust gas mixing on ethanol autothermic reformation, this work experimentally and theoretically investigated dilution with a mixture of nitrogen and carbon

dioxide to simulate an exhaust composition, in combination with a range of inlet temperatures, to simulate exhaust gas temperatures, at a constant steam to carbon ratio.

A CAT C6.6 turbocharged diesel engine was operated in dual-fuel diesel-hydrogen mode. (Kersting, Lee Allan, M.S., North Dakota State University, 2014, 86; 1568051) Hydrogen was inducted into the intake and replaced a portion of the diesel fuel. Hydrogen was added across multiple engine speeds and loads until reaching the knock limit, identified by a threshold on the rate of in-cylinder pressure rise. In-cylinder pressure and emissions data were recorded and compared to diesel-only operation. Up to 74% H2 substitution for diesel fuel was achieved. Hydrogen addition increased thermal efficiency up to 32.4%, increased peak in-cylinder pressure up to 40.0%, increased the maximum rate of pressure rise up to 281%, advanced injection timing up to 13.6°, increased NOx emissions up to 224%, and reduced CO 2 emissions up to 47.6%. CO and HC emissions were not significantly affected during dual-fuel operation. At 25% load an operating condition was observed with low NOx and nearly 0 CO2 emissions, which however exhibited unstable combustion....