GEOTHERMAL ENERGY
GEOTHERMAL ENERGY:
It is the energy contained as heat under the surface of the planet.
This heat is found in enormous and practically inexhaustible quantities, but it is highly dispersed.
It can be exploited if it is sufficiently concentrated.
When this concentrations are closed to the surface, at the depth of 5-10km, the heat contained in the masses of magma in liquid or solid form, is released in the process of cooling.
When the magma makes its way back to the surface, they cause phenomena like volcanoes, geysers, earthquakes and fumaroles.
The GT energy is brought to the surface either through water or steam, that circulates through the hot subterranean rock, minerals, absorbing heat along the way.
Energy from GT source is natural, clean and renewable. This is the 2nd largest non-hydro RE source.
GEOTHERMAL ENERGY
comes from radioactive decay in the core of the Earth, which heats the Earth from the inside out, and from the sun, which heats the surface. It can be used in three ways:
Geothermal electricity - by pumping a fluid (oil or water) into the Earth, allowing it to evaporate and using the hot gases vented from the earth's crust to run turbines linked to electrical generators.
Geothermal heating, through deep Earth pipes
Geothermal heating, through a heat pump.
Technology
Technologies are
Geophysical prospecting technique
Geological model of GT system
Drilling technology; drill upto 5,000 meter depth where steam pressure is sufficiently high.
Design of geothermal fields that consist of water-steam-gas(CO2) dominated reservoirs
Methodology
Drilling of GT wells in reservoirs with temperature upto 4000C – surveying and site selection (using µω technology)
Providing drilling services, such as, cementing, pumping, logging and GT well logging
Gathering feedback on well operation
Undertaking turn-key projects that involve well design, drilling engineering, well testing and analysis and finally OAM
Developing odor-abatement technology to stop annoying smells
Global Scenario
GT energy has been used globally to provide heat for human use for 1,000 of years
It has been used to produce electricity to many countries around the world. Central and South America are particularly reach in potential GT resources
It has been predicted that GT energy can be a major RE resource for at least for 58 countries; 39 countries could be 100% GT-powered; 43 countries could be 50% GT-powered; 44 could be 20% and 47 could be 10%.
Upto now 67 nations are using GT energy including Japan, Italy, New Zealand, Mexico and United States.
The direct worldwide use of GT energy was estimated to be 15,200 MWt delivering 53,000 GWht/yr for the year 2002. Reasonable projections suggest that at least a 10% per year growth in GT energy applications should occur through 2010, which would lead to 20,100 MWe and 39,250 MWt of GT power worldwide by 2010. Using advanced technology, 35,000 and 72,000 MWe generation capacity could be installed.
GT energy can provide economically beneficial energy to many countries of the world. It has no pollutions. The 95% availability factor for GT electric power generation can along with bio-energy can serve as stabilizing base load resource of RE.
HYDROGEN ENERGY
The most likely long-term candidate for energy storage from the intermittent RE source is the hydrogen. This can convert electricity derived from RE into fuel. Remote sources of RE in areas of rich wind, solar or GT energy potential can be hydrogen factories. The reasons to consider hydrogen as the source of RE energy are multiple:
It protects air quality, climate and has energy security.
It can address all the issues of sustainable energy based on quality and services.
Hydrogen could provide a fundamental means for energy storage from intermittent energy sources, such as, wind and solar and could be a key element in exploiting the full potential of RE.
It offers flexibility in terms of volume of energy and power stored and released
It can be used as a transport-fuel.
Hydrogen may provide a means of tackling greenhouse gas emissions from the transport sector
RENEWABLE HYDROGEN PRODUCTION
Three main methods for inexpensive hydrogen generation.
Reformers - methanol, ethanol, natural gas, petroleum distillates, liquid propane and gasified coal. The hydrogen is produced from these materials by a process known as reforming.
Enzymes - Another method to generate hydrogen is with bacteria and algae. The cyanobacteria, an abundant single-celled organism, produces hydrogen through its normal metabolic function.
Solar- and Wind- powered generation - photovoltaics (PVs), solar cells, or wind turbines are used to electrolyze water into hydrogen and oxygen. A truly zero-emissions way of producing hydrogen for a fuel cell.
Currently hydrogen is derived from fossil fuels and, therefore, causes the emission of GHG pollutants that are connected with climate change.
The resulting hydrogen be considered as renewable or the fuel cell considered as clean, only when eligible technology available.
PRODUCTION OF HYDROGEN BY GASIFICATION PROCESS
The biomass feedstock is first dried and sized.
The feedstock is then gasified to produce syngas, mainly composed of CO, hydrogen, CO2, steam, some methane and small quantities of hydrocarbons.
The syngas is then cleaned, and hydrocarbons are converted to CO and hydrogen by steam reforming.
The reformed gas then undergoes shift reactions. Two shift reactors in series, the first at 4500C and the second at 2300C are used to react the CO with steam to form hydrogen.
Hydrogen is then recovered from the gas steam by pressure swing absorption (PSA - PSA desorbs all the gases except hydrogen).
97% of the hydrogen passing through the PSA is recovered which has 99.999% purity.
The hydrogen can then be liquified or compressed for transport.
Gasification and gas cleaning equipment is still at the pre-commercial stage. Reforming, shift reaction and PSA equipment is commercially available at large-scale, and is widely used for industrial hydrogen production, mainly from natural gas.
Hydrogen Storage
The main storage options for hydrogen are as compressed gas at low and high pressure, or as liquid hydrogen.
Underground storage is suitable for very large gas volumes.
Compressed hydrogen can be stored above ground in pressure vessels at various ranges of sizes and pressures.
Hydrogen Transport
Hydrogen can be transported as a compressed gas either in dedicated pipelines or by container or as liquid hydrogen by tanker.
Transport of both compressed and liquid hydrogen by road is used in industry. Liquid hydrogen is favored for long distances and compressed gas is suitable for short distances.
Use of Hydrogen
Hydrogen can be used as fuel in internal combustion engine vehicles (ICEV), in fuel cell vehicles (FCV). Three basic hydrogen production changes have been assessed globally. Two of them are based on offshore wind electricity and one based on biomass gasification. The use of renewable hydrogen in fuel cell vehicles has better prospect for zero emission fuel chain. Hydrogen and its use in fuel cell is likely to play a major role in a sustainable energy future.
FUEL CELL
A fuel cell is an electrochemical device which brings together hydrogen and oxygen, or air in the midst of a catalyst to produce electricity, heat and water. The single cell fixture consists a single electrolyte sandwiched between electrodes. This inner sandwich is then placed in-between current collectors which usually serve as the poles of the cell. A fuel cell generates current by transforming (usually by using the catalyst in the electrodes) hydrogen gas into a mixture of hydrogen ions and electrons on the anode side of the cell. Because of the insulating nature of the electrolyte, the anions transfer through the electrolyte to the cathode side of the cell while the electrons are conducted to the current collectors and through a load to do work. The electrons then travel to the cathode side current collector where they disperse onto the electrodes to combine with incoming hydrogen anions, oxygen, or air in the presence of a catalyst to form water completing the circuit.
BACKGROUND
The fuel cell was first invented in 1839 by Sir William Grove, a professor of experimental philosophy at the Royal Institution in London. His invention was the precursor to the phosphoric acid fuel cell by enclosing platinum in tubes of hydrogen and oxygen gas while submerging the tubes in sulfuric acid. Unfortunately, he was hampered by the inconsistency of cell performance (a common feature of cells today), but realized the importance of the three phase contact (gas, electrolyte and platinum) to energy generation.
After over 150 years of research, fuel cells can be divided into five major categories named after electrolyte alkaline, solid polymer, phosphoric acid, molten carbonate and solid oxide. Heat accelerates chemical reaction rates and thus the electrical current.
SOLID OXIDE FUEL CELL
• Solid oxide fuel cells (SOFC) operate at the highest temperature (1000 - 1100 degrees Celsius).
• not the most reactive because of the low conductivity of its ionic conducting electrolyte (yttria-stabilized zirconia).
• Now, the chemical to electrical efficiency to 50%, but because of the conductivity and the heat, it has been used mainly in large power plants
• requires no expensive catalysts, or additional humidification and fuel treatment equipment which excludes the cost of these items.
• Drawback is the cost of the containment which requires exotic ceramics which must have similar expansion rates.
MOLTEN CARBONATE FUEL CELL
The molten carbonate, which operates at 600 degrees Celsius can use CO as a fuel input on the cathode side but needs hydrogen on the anode.
Carbonate ions are produced at the cathode and flow across the membrane to react with hydrogen and form two electrons, water and carbon dioxide. In an actual system, because of the internal heat, the cell can reform methanol into hydrogen for the anode reaction and use the carbon dioxide and extra hydrogen (burned in the presence of air) as fuel for the cathode reaction. A MCFC operates with better performance under pressurized conditions. Nickel compounds are used for the electrodes while the electrolyte contains a mixture of 68% lithium carbonate and 32% potassium carbonate in a porous gamma-lithium-aluminum oxide matrix. The efficiency using this system has risen to 50%
PHOSPHORIC ACID FUEL CELL
Phosphoric acid fuel cells (PAFC) are the oldest type. Many different acids have been used in order to boost performance such as sulfuric and perchloric acids, but when the temperature increases above 150 degrees Celsius, high rates of oxygen reduction are possible which enable phosphoric acid to perform best.
The heat generated is not enough for cogeneration of steam, but is able to warm water and act as a heater for an increased overall efficiency.
The electrolyte is flanked by porous graphite carbon coated with Teflon to allow gases to the reaction sites.
The efficiency of this system is much lower than that of other systems at 40%, but because of its history, it can be controlled better. PAFCs are now in production and sell for $2875.00 per kilowatt by International Fuel Cells.
ALKALINE FUEL CELL
The most temperamental of all fuel cells, it can produce the maximum amount of energy (80% efficiency ) when used as a water heating device).
They use KOH (potassium hydroxide) electrolytes because it is the most conducting of all alkaline hydroxides, Hydrogen at the anode reacts with the electrolyte creating water and two electrons which both meet at the cathode with oxygen to complete the circuit.
The electrolyte constantly flows through the cell which provides cooling by convection the porous (and catalyzed) graphite electrodes from which it picks up hydroxyl ions and a small amount of water in the process.
SOLID POLYMER FUEL CELL
Solid polymer fuel cells operate at around 80 degrees Celsius like AFCs at 60% efficiency, it comes in second only to alkaline. The perfluorinated sulfuric acid membrane is sandwiched between two platinum catalyzed porous electrodes.
Many automotive companies have decided to use methanol as a fuel for fuel cells by reforming it into hydrogen because of the capacity of safe hydrogen storage and transportation that methanol provides.
The drive towards new advancements in fuel cells occurred due to the oil crisis of 1973 and todays automotive industry The automotive interest occurred mostly because of the political pressure to lower emissions to cut the increasing degradation of air quality caused by cars.
Other than public concerns, fuel cell research has remained largely academic, but the devices needed to handle and store hydrogen as well as the reforming process from other fuels have been well employed by industry because of the use of hydrogen in producing ammonia and other products.
Telecommunication companies are now buying fuel cells for backup power as well as for cooling equipment.
CELL THEORY
Two main electrochemical reactions occur in a fuel cell. One at the anode and the other at the cathode.
At the anode;
and at the cathode;
which together give the result:
CELL DESIGN ISSUES
Hydrogen is extremely difficult to contain, so the tolerances between materials, the density of materials and their thickness in the hydrogen circuit must be controlled so as not to allow the fuel to escape.
The cross section of Oxygen flow needs to be large enough for the small fraction of oxygen in air (and carbon monoxide in the case of the MCFC) to react at a rate which would support current demand. If oxygen is used, then the circuit must be free of any ignition source.
The presence of water in the system must be controlled. Water is needed for the electrochemical processes of the electrolyte, but proves a barrier to reaction gases.
A fuel cell generates power though a voltage difference and current, therefore electrical separation of the poles is required in order not to short the cell thus subverting all current through the short and not through the load.
The gas pressures and gas and cell temperatures must also be monitored for their influence on performance and for safety.
Temperature control is important during all fuel cell operation, but is especially important when a stack of cells is placed together. Because thinner cell design has always been an objective of designers, the cooling of these cells has also required designing.
ENERGY SUBSTITUTION
