Ce diaporama a bien été signalé.
Nous utilisons votre profil LinkedIn et vos données d’activité pour vous proposer des publicités personnalisées et pertinentes. Vous pouvez changer vos préférences de publicités à tout moment.

Hydrogen energy

15 710 vues

Publié le

Publié dans : Technologie, Business
  • Identifiez-vous pour voir les commentaires

Hydrogen energy

  1. 1.  Hydrogen has highest energy content per unit of mass of any chemical fuel and can be substituted hydrocarbon in a broad range of application.  Its burning process is non polluting.  Heating value of 28000 kcal/kg is three times greater than hydrocarbon.  Easy in production because it is produced from water found in abundance.  Hydrogen is highly flammable.  Hydrogen at ordinary pressure and temperature is a light gas with a density only (1/14) that of air and (1/9) that of natural gas under the same Condition.  By cooling to extremely low temperature of -253 ˚C, the gas is condensed to a liquid with a specific gravity of 0.07, roughly (1/10) that of gasoline.  The flame speed of hydrogen burning in air is much greater than for natural gas, and the energy required to initiate combustion is less.  Mixture of hydrogen and air are combustible over an exceptionally wide range of compositions; thus the flammability limits at ordinary temperature extends from 4 to 74 % by volume of hydrogen in air.
  2. 2. On the basis of source use and energy source hydrogen production are following type-  Electrolysis or electrolytic production-In electrolysis water spit in to H2 andO2 when electric current pass through in this process two type of electrolyzer used  Tank type electrolyzer.  Bipolar or filter press electrolyzer.  Thermo – Chemical Methods.  Some thermo chemical cyclic process.  Westinghouse ElectrochemicalThermal Sulfur Cycles.  Ispra Mark 13 Cycles.  Iodine Sulphur Cycle.  Fossil Fuel Methods  Solar energy methods.  Bio photolysis method.  Photo Electrolysis method.
  3. 3.  The process of splitting water into Hydrogen & Oxygen by means of a direct electric current is known as electrolysis. This is the simplest method of hydrogen production.  Although only the water is split, an electrolyte (KOH solution) is required because water itself is a very poor conductor of electricity.  Theoretically 1.23 volts are required for this process but in real situation due to the slowness of the electrode processes higher voltages are required for the electrolysis.  Theoretically 2.8 KW-hr of electrical energy should produce from one Cu.m of hydrogen however the actual electrical energy requirement is generally from 3.9 to 4.6 KW-hr per Cu.m. this means that efficiency of electrolysis is roughly 60 to 70%.  To increase the efficiency the electrode surface must be able to catalyze the electrode processes. Platinum & nickel are normally deposited on the electrode.
  4. 4.  Diaphragms prevent electronic contact between adjacent electrodes and passage of dissolved gas or gas bubble; from one electrode compartment to another , without appreciable resistance to the passage of current within the electrolyte.  Asbestos is the most suitable material for cell diaphragms.  Three major factors determine the usefulness of an electrochemical cell for hydrogen production. 1. Energy Efficiency. 2. Capital cost of the plant. 3. Lifetime of the cell and its maintenance requirements.  A number of advantages can be gained from operating electrolyzer at higher pressures a follows: 1. Reduction in specific power consumption. 2. Delivery of gas at pressure, thus eliminating the cost of gas compressor. 3. Reduction in the size of electrolysis cell.
  5. 5.  Two types of electrode arrangements are used by industry for the electrolysis of water. On this basis they are classified as follows: 1. Tank type electrolyzer, and 2. Filter press or bipolar electrolyzer. Tank type electrolyzer:  The first application in the industry used the tank electrolyzer, in which a series of electrodes, alternating anodes (+) and cathodes (-) are suspended vertically and parallel to one another in a tank filled with a 20-30 % solution of KOH in demineralized water.
  6. 6.  Alternate electrodes are surrounded by porous diaphragms impermeable to gas but permeable to the cells electrolyte, that prevent the passage of gas free from one electrode compartment to another.  All the anodes are connected to the same positive terminal of the direct current voltage source and all the cathodes are connected to the same negative terminal.  The major advantage of tank type electrolyzers are two fold relatively few parts are required and those needed are relatively inexpensive  Another advantage of this arrangement is that individual cells may be isolated for repair or replacement simply by short circuiting the two adjacent cells with a temporary busbar connections.  Disadvantage is that inability to handle high current densities because of cheaper components parts.  Inability to operate at high temperatures because of heat losses from large surfaces areas of connected cells.
  7. 7. Filter Press Electrolyzer (Bipolar Electrolyzer):  This is the most widely used electrolysis system because of its superficial resemblance to a filter press.  Except at the ends of the cell, the electrodes are bipolar that is, one face of each plate electrode is in anode and the other face is the cathode.  Because of the cells can be made relatively thin, a large gas output is achieved from a relatively small volumes.
  8. 8.  The filter press electrolyzer is generally preferred because it occupies less space and can be operated at a higher current densities than the tank type.  The economics are thus more favorable, since a large production is possible in the plant.  The filter press electrolyzers require a much closer tolerance in construction and are more difficult to maintain.  Breakdowns in this system are rare, but when they occur it is difficult and repair may take considerable time.  If an individual asbestos diaphragm is damaged, the entire battery must be dismantled.  High cell voltage imply high energy costs, and low current densities imply that the electrolyzers give small yields per unit time, leading to relatively high capital costs. For these reasons hydrogen produced electrolytically is at present twice as expensive as hydrogen produced from fossil fuels.
  9. 9.  It is generally desirable to circulate electrolyte through the cell, thereby separating the gas and the electrolyte and in many designs, this is accomplished in a separating drum mounted on the top of the electrolyzer.  The filter press electrolyzer is generally preferred because it occupies less space and can be operated at a higher current densities than the tank type.  The economics are thus more favorable, since a large production is possible in the plant.  The filter press electrolyzers require a much closer tolerance in construction and are more difficult to maintain.  Breakdowns in this system are rare, but when they occur it is difficult and repair may take considerable time.  If an individual asbestos diaphragm is damaged, the entire battery must be dismantled.  High cell voltage imply high energy costs, and low current densities imply that the electrolyzers give small yields per unit time, leading to relatively high capital costs. For these reasons hydrogen produced electrolytically is at present twice as expensive as hydrogen produced from fossil fuels.
  10. 10.  The overall efficiency for the conversion of primary energy from fossil & Nuclear fuels into hydrogen by electrolysis is dependent, in the first place on the efficiency of the generating electricity.  This efficiency is 38% for modern fossil plants and 32% for nuclear installation.  The higher conversion efficiency might be possible if the heat produced by the primary fuel could be used directly to decompose water, without the intermediary of electric energy. Such direct decomposition into hydrogen and oxygen is possible, but it requires a temperature of atleast 2500˚C.  But due to temperature limitation and conversion process equipment, direct single step water decomposition is not possible.  However a sequential chemical reaction series can be devised in which hydrogen and oxygen are produced, water is consumed and all other intermediates are recycled.The operation is called as thermo chemical cycle.  It is so called because energy is supplied as heat at one or more of the chemical stage, and hydrogen and oxygen are produced separately in different stages.  For practical reasons , primarily the availability structural and containment materials, the maximum temperature considered to be about 950˚C.
  11. 11.  Heat energy then be converted into hydrogen energy with efficiency of 50%, this is a marked improvement over what is possible by electrolysis.  At present no commercial process for the thermal splitting of water to hydrogen and oxygen is in operation.  Several workers have proposed many multistep reaction sequence that thermally decompose water at lower temperatures. 2CrCL2 + 2HCL 2CrCl3 + H2 2CrCL3 2CrCL2 + Cl2 H2O + Cl2 2HCL + ½ (O2) As can be seen, in this reaction sequences, only water is split, all other materials are completely recycled.
  12. 12.  Numerous candidate cycles have been suggested during past few years. Here , we shall consider only three cyclic processes which are as follows: 1. Westinghouse ElectrochemicalThermal Sulfur Cycle. 2. Ispra Mark 13 Bromine sulfur cycle. 3. Iodine Sulfur Cycle. Westinghouse ElectrochemicalThermal SulfurCycle. H2So4 H2O + ½ (O2) + SO2 2H2O +SO2 H2+ H2SO4  It is clear by summing reaction that overall process decomposes water into hydrogen and oxygen and involves only sulphur oxides as recycling intermediates.  Although electrical power is required in the electrolyzer, much smaller quantities than those necessary for conventional electrolysis.
  13. 13. Ispra Mark 13 Cycle: 2HBr H2+ Br2 (Electrolysis) Br2 + SO2 + 2H2O 2HBr + H2So4 H2SO4 H2O + SO2 + ½ (O2) (Thermolysis)  The somewhat lower cell voltage in the Westinghouse process is counterbalanced by the advantage of the higher concentration of sulphuric acid obtained in the Mark 13 process.  It should be also mentioned that incorporation of an additional element Bromine in the Mark 13 process may also be advantageous, since it offers more possibilities in the industrial operation of the process. Iodine Sulphur Cycle:  Among the purely thermo chemical cyclic processes , those belonging to the iodine sulphur family are of most interest at thee present stage.  The following three stage process has been developed by General Atomic Co. in particular:
  14. 14. 2HI H2 + I2 I2+ SO2 + 2H2O H2SO4+ 2HI H2SO4 H2O+ SO2+ ½ (O2)  The main difficulty in this process lies in the fact that, if side reactions are to be avoided , the two acids can be obtained only in dilute solution in the second stage, and are difficult to separate even on the laboratory stage.  The difficulties associated with this process have led in recent years to numerous investigations and suggestions for modifying the process.
  15. 15.  Mostly a gaseous mixture of CO and Hydrogen is formed in the first stage, in the production of hydrogen by using a fossil fuel.  This is popular method of hydrogen production through which about 94% hydrogen is produced by following different processes- 1. Steam reforming of gas 2. Partial oxidation of heavier hydro carbon. 3. Coal gasification 4. Pyrolysis 5. Biomass gasification CO + H2O = CO2 + H2 + 1440 KJ/KG  To remove the CO, the mixture is submitted to the water gas shift reaction with steam. The CO is therefore converted into CO2 with the formation of additional hydrogen and energy.
  16. 16.  Hydrogen Production by the Iron Process. Fe + H2O FeO + H2
  17. 17.  Steam Gasification Process and Its application
  18. 18.  Gas Generators for Present Day Industrial Coal Gasification
  19. 19.  Hydrogen production from solar energy there is two methods are considered – 1. Bio photolysis and 2. Photo Electrolysis. Bio photolysis:  This method utilizes living systems (or material derived from such systems) to split water into its constituents hydrogen and oxygen.  In normal photosynthesis in green plants the green plants the green pigment chlorophyll takes of the energy from sunlight and in a complex series of reactions breaks up water molecules into oxygen gas, hydrogen ions and electrons.  The oxygen is evolved from the green plant, but the hydrogen ions and electrons are removed by interaction with carbon dioxide (from the air) to produce simple sugars.  Certain single cell green/ blue green algea are able to make enzyme hydrogenase. They decompose water in sunlight to yield hydrogen and oxygen.
  20. 20.  Instead of using living algae to obtain hydrogen from water, a more convenient approach is to utilize biological materials obtained from plants or bacteria. One advantage is the ability to vary the conditions to optimize hydrogen production.  An ultimate objective of research on the decomposition of water by sunlight is the efficient simulation of biological processes without using biological materials. Photo Electrolysis:  In photosynthesis , a current is generated by exposing on or both electrodes to the sunlight. Hydrogen and Oxygen gases are liberated at the respective electrodes by the decomposition of the water , just as an ordinary electrolysis.  Atleast one of the electrodes in the photosynthesis is usually a semiconductor; a catalyst may be included to facilitate the electrode processes.  Research is being directed at increasing this efficiency by selection of electrode materials, electrolyte solutions and electrode catalysts.  Electrolysis is a more attractive way of producing hydrogen with solar radiation since it can be operated intermittently and therefore needs no storage.
  21. 21.  The solar electricity needed for electrolysis can be produced either photoelectrically or thermoelectrically. Both technologies are available today. HYBRIDE ELECTROLYSIS
  22. 22.  The need for storage is due to the almost inevitable mismatch between the optimum production rate of the energy and the fluctuation in demand for energy by the users.  In the electric energy system storage, presents considerable difficulty because electricity itself is not readily storable.  One of the advantages often claimed for a hydrogen energy systems is that hydrogen is storable. However, it must be realized that storage of hydrogen is not an easy problem compared with storage of liquids fuels such as gasoline or oil. It is only when it is compared with electricity that storage of energy as hydrogen seems relatively easy. There are five principal method of hydrogen production.  Compressed gas storage  Liquid storage or cryogenic storage  Line pack system  Under ground storage  Storage as a metal hydride
  23. 23.  Storage can be effected in a gaseous or liquid state, or in the structure of solids. According to the field application, it is necessary to distinguish between storage on a large scale and on a small scale. The former applies particularly to stationary application and the letter also to mobile ones. Compressed Gas Storage:  Hydrogen is stored in high pressure cylinders.  This method of storage is rather expensive and very bulky because very large quantities of steel are needed to contain quite small amounts of hydrogen. Liquid Storage:  A more practical approach is to store the hydrogen as liquid at a low temperature.  Liquid hydrogen boils at -253˚C and therefore must be maintained at or below this temperature in storage.  It is commonly regarded as necessary to use vacuum- insulated storage vessels and super insulated vessels.  A problem concerning storage of liquid hydrogen is the considerable amount of energy required to convert hydrogen gas into the liquid phase.
  24. 24.  To maintain the temperature at such a low limit some kind of primary refrigeration, such as a liquid nitrogen plant, to precool hydrogen. The net result is that about 25-30% of the heating value of hydrogen is required to liquefy hydrogen. Line Packing:  The use of line pack storage in the natural gas industry provides a relatively small capacity storage system, but one with a very fast response time that can take care of minute by minute or hour by hour variations in demand.  A hydrogen transmission and distribution system running on hydrogen would have a similar capability. Underground Storage:  The cheapest way to store large amounts of hydrogen for subsequent distribution would probably be in underground facilities similar to those used for natural gas; these facilities would include depleted oil and gas reservoirs.  More expensive alternatives would be caverns produced by conventional mining or by dissolving out salt with water.
  25. 25.  Since hydrogen gas tends to escape readily through a porous material, some geologic formations that may be suitable for storing natural gas may not be suitable for hydrogen. Metal Hydrides (Storage in chemically bound form) :  Considerably interest has been shown recently in the possibility of storage of hydrogen in the form of a metal hydride.  A number of metals and alloys form solid compounds , called metal hydrides, by direct reaction with hydrogen gas.  When the hydride is heated, the hydrogen is released and the original metal(or alloy) is recovered for further use.  Thus , metal hydrides provide a possible means for hydrogen storage.  An important property of metal hydrides is that the pressure of the gas released by heating a particular hydride depends mainly on the temperature and not the composition.  Several studies are being made to find a metal hydride that would satisfy the requirements for hydrogen storage.These requirements include the following:
  26. 26. 1) The metal (or alloy) should be fairly inexpensive. 2) The hydride should contain a large amount of hydrogen per unit volume and per unit mass. 3) The hydride should be formed without difficulty by reaction of the metal with hydrogen gas, and it should be stable at room temperature. 4) The gas should be released at a significant pressure from the hydride at a moderately high temperature (preferably below 100˚C)  Three of the more promising hydrides are those of Lanthanum nickel ( LaNi5), Iron titanium (FeTi), and magnesium nickel (Mg2Ni) alloys.  In practice, energy densities of from 500 Wh/Kg (already achieved) to a maximum of 1000 Wh/Kg can be attained.
  27. 27. Pipe Lines:  Presently only few companies are capable to transport hydrogen by pipelines at different locations.  It is of interest to compare the design of a pipeline for hydrogen with those of a pipeline for natural gas.  The heating value of hydrogen is only 12.1 MJ/Cu.m as compared to natural gas having the value of 38.3 MJ/Cu.m.  This implies that to deliver the same quantity of energy, three times the quantity of hydrogen must be transmitted.  On the other side one finds that the capacity of the pipeline depends upon the square root of the density of the gas.  As the density of the hydrogen is (1/9) times that of natural gas , so that it indicates that the energy content of hydrogen is same as that of natural gas for the same size pipe.  As we know that if we want to supply hydrogen to long distance then we have to do same with the help of compressor station.  As the hydrogen compressor s have to handle three to four times the volume of gas large compressor are required and they consume more power also.
  28. 28.  The design of rotary compressors commonly used for natural gas lines appears to be more inadequate for hydrogen operation.  In the case of design of a pipeline of hydrogen transmission the cost of fuel used to drive the engines for compressors is also the highly deciding factor, because the compression energy is so much higher than that of natural gas.  One of the principal concerns about hydrogen transmission is the fear of hydrogen embrittlement of the pipeline material.  A number of metals lose their mechanical strength on exposure to hydrogen; the phenomenon called hydrogen embrittlement, is specially significant for steel in hydrogen under pressure.  Operating experience with common pipeline steels at pressure upto 3.5 Mpa has shown no problems of consequence.  However the behavior at higher pressure is uncertain, and more experimental work needs to be carried out to gen some definite data.
  29. 29. Liquid HydrogenTransportation:  Hydrogen in bulk can be transported and distributed as the liquid.  Doubled wall , insulated tanks of liquid hydrogen with capacities of 7000 gal or more are carried by road vehicles and upto 34000 gal by rail road cars.  Distribution of liquid hydrogen by pipeline , jacketed with liquid nitrogen , has been proposed.  The cost would be substantially greater than for gas pipeline, but it might be justifiable for certain fuel applications where the liquid is required. Metal HydrideTransportation:  Hydrogen is transported in the form of solid metal hydrides.  The main draw back is the weight of the hydride relative to its hydrogen content.
  30. 30. Hydrogen Gas can be utilised in the following ways:  For residential uses  For industrial uses  For as an alternative transport fuel  For as an alternative fuel for aircraft.  For electric power generation (Utilities) For ResidentialUses:  Electricity for lighting and for operating domestic appliances could be generated by fuel cell in which Hydrogen is used as a fuel.  Hydrogen can be used in domestic cooking with the help of changing in the design of burner, including the hole size and air supply system.  Hydrogen can be useful in radiant space heaters, because of the possibility of flameless combustion on a catalytic surface. These devices would be operate spontaneously when the gas was turned on and no pilot light or other ignition system would be required. Because of the low combustion temperature , nitrogen oxide formation would be negligible and venting would be unnecessary.
  31. 31. Industrial Uses:  Many potential uses for hydrogen in industry, either as a fuel or a chemical reducing (oxygen removal) agent if the economics were favorable.  Hydrogen gas could also be used with advantage, instead of coal or coal derived gases, to reduce oxide ores (iron ore) to the metal (iron) RoadVehicles:  The use of hydrogen as a fuel in I.C. Engines has attracted interest as a means of conserving petroleum products and of reducing atmospheric pollution.  Because of fuel as a gas, the conventional carburetor of a S.I Engine must be modified for use with hydrogen.  The hydrogen gas under pressure is injected through a valve directly into the engine cylinder, and the air is admitted through the another intake valve. Since they both supplied separately, an explosive mixture does not occur except in the cylinder.  The engine power output is controlled by varying the pressure of hydrogen gas .  The hydrogen is required to be stored as a compressed gas.  Another modification arises from the high speed of the hydrogen flame in the air; this require that ignition time be retarded compared to gasoline engine.
  32. 32.  They can utilize a higher proportion of the energy in the fuel than gasoline engine.  The amount of CO and hydrocarbons in the exhaust would be very small since they would originate only from the cylinder lubricating oil.  However the nitrogen oxides level due to high combustion temperature may be high, it may be reduced by reducing the combustion temperature by injecting water vapour into cylinder from the exhaust .  The other way to utilised hydrogen as a fuel is thee use of fuel cells. Electricity generated by the fuel cells could be utilized to operate electric motors to propel the vehicles.  For vehicles the storage of hydrogen can be as compressed gas, liquid and metal hydrides. Air Craft Application:  The earliest application of liquid hydrogen fuel is expected to be in a jet air craft; this possibility was demonstrated in a subsonic air craft in 1957.  The main advantage is the much lower overall weight of the fuel and the storage tank than for ordinary jet fuel.
  33. 33.  The volume of liquid hydrogen would be greater than regular jet fuel, but this could be accommodate on the large aircraft.  The cool liquid hydrogen could be used directly of indirectly to cool the engine and the air frame surfaces of a high speed aircraft.  If the hypersonic aircraft is developed , the liquid hydrogen may be the only practical fuel.  Because of the smaller total weight it is possible to achieve shorter take off runs, steeper climbing paths and/or smaller engine thrust.  It may also be possible to decrease the size and weight of the engines.  Hydrogen’s favorable diffusion properties and high thermal conductivity lead to better mixing even with shorter combustion chamber.  The wide range of ignition for hydrogen air mixtures (5 to 75 % by volume) makes the engine more readily controllable, especially under partial loads, and reduces the emission of noxious substances.  The heat required to vaporize and heat up the hydrogen for the engines can be obtained through the certain sections of the outer skin of the wings. In this way the boundary layer is cooled so as to produce laminar flow, resulting in a lowering of the aerodynamic drag and hence of the fuel consumption, this could not be achieved to the same extent in any other way.
  34. 34. Electric Power Generation:  It is unlikely that hydrogen would serve as a major fuel for electrical power generation by a utility. However, its substitution for natural gas in peak hours is possible.  Hydrogen could also be used as a means for storing and distributing electrical energy.  This also comprises the production of electricity by using hydrogen in fuel cell systems.  It is also important that the conversion efficiency of the fuel cells is independent of the load factor over a wide range, so that a high efficiency can be obtained even with partial loads.  Furthermore , with fuel cells which are at high temperatures high grade waste heat can be used for thermal energy production.  Presently the research and development work is in progress with the object of developing fuel cell power stations for the centralized and local generation of electricity.
  35. 35.  Not Explosive In Open Air  Not Decomposing  Not Self-Igniting  Not Oxidizing  NotToxic  Not Corrosive  Not Polluting  Not Cancer Causing
  36. 36.  Currently more expensive  Hydrogen is more difficult to store and distribute.
  37. 37.  The BHU Murugappa - Chettair research center Chenni and IIT Kharagpur are leading institute.  BHU develop metal hydride with storage capacities 2.4 weight%  MNRE stared projects in 22 universities / institute  In IISc Bangalore research work on progress on hydrogen based fuel cell  Some other project in progress in private sector BHEL installed 200 kw fuel cell based power plant
  38. 38. ThankYou