There are many uses for fuel cells — right now, all of the major automakers are working to commercialize a fuel cell car. Fuel cells are powering buses, boats, trains, planes, scooters, forklifts, even bicycles. There are fuel cell-powered vending machines, vacuum cleaners and highway road signs. Miniature fuel cells for cellular phones, laptop computers and portable electronics are on their way to market. Hospitals, credit card centers, police stations, and banks are all using fuel cells to provide power to their facilities. Wastewater treatment plants and landfills are using fuel cells to convert the methane gas they produce into electricity. Telecommunications companies are installing fuel cells at cell phone and radio. The possibilities are endless. 

Fuel Cell as Power Source in Remote Location

Fuel cells are very useful as power sources in remote locations, such as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications. A fuel cell system running on hydrogen can be compact and lightweight, and have no major moving parts. Because fuel cells have no moving parts and do not involve combustion, in ideal conditions they can achieve up to 99.9999% reliability. This equates to around one minute of down time in a two year period.

Since electrolyzer systems do not store fuel in themselves, but rather rely on external storage units, they can be successfully applied in large-scale energy storage, rural areas being one example. In this application, batteries would have to be largely oversized to meet the storage demand, but fuel cells only need a larger storage unit (typically cheaper than an electrochemical device).

One such pilot program is operating on Stuart Island in Washington State. There the Stuart Island Energy Initiative has built a complete, closed-loop system: Solar panels power an electrolyzer which makes hydrogen. The hydrogen is stored in a 500 gallon tank at 200 PSI, and runs a Reli On fuel cell to provide full electric back-up to the off-the-grid residence.

Fuel Cell in Residential Applications

In residential applications, small fuel cell power plants could be installed for the production of both electricity and heat or hot water for the home. 

In addition to homes in developed countries, where the market may first develop, an ideal application for fuel cells is to provide power to remote residential entities that have limited or no access to primary grid power, thereby delaying, if not eliminating, the necessity of expensive, maintenance intensive transmission line installations. These applications will be more common in developing countries, where fuel cells can provide electricity in regions gradually as development warrants and allows.

Fuel Cell in Data Centers

The propagation of  Data Centers through out the U.S. and the developed world, is a sign of continued growth in the digital age and also a significant burden on grid generation and transmission capacity. The power use density for these facilities can be in excess of 100 watts per square foot resulting in very high electrical demands for a relatively small facility. These same facilities are extremely dependent on premium quality and highly reliability power.

The potential for cogeneration at these facilities is low, however the development of the Data Center Campus concept allows cogeneration to be implements beyond the confines of the Data Center in surrounding process, office, or hospitality relate buildings. The waste heat of a fuel cell can be converted to chilled air through the absopbtion chilling process, a definite need for such a data center facility.

In 1999, the First National Bank of Omaha (FNBO) - the nation's largest privately owned bank-installed a 800-kw fuel-cell system as the primary power source for its new 200,000 square foot Technology Center's critical loads. This bank is the nation's seventh largest credit card transaction processor, handling over three million transactions per day, 365 days a year. According to officials at the bank, a single one-hour blackout could cost FNBO's credit card operation as much as $6 million in lost business.
 

Fuel Cell in Transportation

There are numerous prototype or production cars and buses based on fuel cell technology being researched or manufactured by motor car manufacturers.

The GM 1966 Electrovan was the automotive industry's first attempt at an automobile powered by a hydrogen fuel cell. The Electrovan, which weighed more than twice as much as a normal van, could travel up to 70 mph for 30 seconds.

The 2001 Chrysler Natrium used its own on-board hydrogen processor. It produces hydrogen for the fuel cell by reacting sodium borohydride fuel with Borax, both of which Chrysler claimed were naturally occurring in great quantity in the United States. The hydrogen produces electric power in the fuel cell for near-silent operation and a range of 300 miles without impinging on passenger space. Chrysler also developed vehicles which separated hydrogen from gasoline in the vehicle, the purpose being to reduce emissions without relying on a nonexistent hydrogen infrastructure and to avoid large storage tanks.

In 2005 the British firm Intelligent Energy produced the first ever working hydrogen run motorcycle called the ENV (Emission Neutral Vehicle). The motorcycle holds enough fuel to run for four hours, and to travel 100 miles in an urban area, at a top speed of 50 miles per hour. In 2004 Honda developed a fuel-cell motorcycle which utilized the Honda FC Stack.

In 2007, the Revolve Eco-Rally (launched by HRH Prince of Wales) demonstrated several fuel cell vehicles on British roads for the first time, driven by celebrities and dignitaries from Brighton to London's Trafalgar Square. Fuel cell powered race vehicles, designed and built by university students from around the world, competed in the world's first hydrogen race series called the 2008 Formula Zero Championship, which began on August 22, 2008 in Rotterdam, the Netherlands.

After this first race, Greenchoice Forze from the university of Delft (The Netherlands) became leader in the competition. Other competing teams are Element One (Detroit), HerUCLAs (LA), EUPLAtecH2 (Spain), Imperial Racing Green (London) and Zero Emission Racing Team (Leuven).

In 2008, Honda released a hydrogen vehicle, the FCX Clarity. Meanwhile there exist also other examples of bikes and bicycles with a hydrogen fuel cell engine.

A few companies are conducting hydrogen fuel cell research and practical fuel cell bus trials. Daimler AG, with thirty-six experimental units powered by Ballard Power Systems fuel cells completing a successful three-year trial, in eleven cities, in January 2007. There are also fuel cell powered buses currently active or in production, such as a fleet of Thor buses with UTC Power fuel cells in California, operated by SunLine Transit Agency. The Fuel Cell Bus Club is a global cooperative effort in trial fuel cell buses.

The first Brazilian hydrogen fuel cell bus prototype began operation in São Paulo during the first semester of 2009. The hydrogen bus was manufactured in Caxias do Sul and the hydrogen fuel will be produced in São Bernardo do Campo from water through electrolysis. The program, called "Ônibus Brasileiro a Hidrogênio" (Brazilian Hydrogen Autobus), includes three additional buses.


The Type 212 submarines of the German and Italian navies use fuel cells to remain submerged for weeks without the need to surface.

 

Fuel Cell Fueling stations

The first public hydrogen refueling station was opened in Reykjavík, Iceland in April 2003. This station serves three buses built by Daimler Chrysler that are in service in the public transport net of Reykjavík. The station produces the hydrogen it needs by itself, with an electrolyzing unit (produced by Norsk Hydro), and does not need refilling: all that enters is electricity and water. Royal Dutch Shell is also a partner in the project. The station has no roof, in order to allow any leaked hydrogen to escape to the atmosphere.

The California Hydrogen Highway is an initiative by the California Governor to implement a series of hydrogen refueling stations along that state. These stations are used to refuel hydrogen vehicles such as fuel cell vehicles and hydrogen combustion vehicles. As of July 2007 California had 179 fuel cell vehicles and twenty five stations in operation, and ten more stations have been planned for assembly in California. However, there have already been three hydrogen fueling stations decommissioned.

South Carolina also has a hydrogen freeway in the works. There are currently two hydrogen fueling stations, both in Aiken and Columbia, SC. Additional stations are expected in places around South Carolina such as Charleston, Myrtle Beach, Greenville, and Florence. According to the South Carolina Hydrogen & Fuel Cell Alliance, the Columbia station has a current capacity of 120 kg a day, with future plans to develop on-site hydrogen production from electrolysis and reformation. The Aiken station has a current capacity of 80 kg. There is extensive funding for Hydrogen fuel cell research and infrastructure in South Carolina. The University of South Carolina, a founding member of the South Carolina Hydrogen & Fuel Cell Alliance, received 12.5 million dollars from the United States Department of Energy for its Future Fuels Program.

Japan also has a hydrogen highway, as part of the Japan hydrogen fuel cell project. Twelve fueling stations have been built in 11 cities in Japan. Canada, Sweden and Norway also have hydrogenhydrogen highways implemented.

Reference Books

Modern Electric, Hybrid Electric, and Fuel Cell Vehicles

Sponsored Ads

Sponsored Ads

The modern technology used for burning coal to generate electricity has evolved over a period of more than a century and until awareness grew of the environmental damage coal burning could produce, the coal-fired power station developed in a single direction. The basic principle underlying this type of power station is to burn coal in air and capture the heat released to raise steam for driving a steam turbine. The rotation of this steam turbine, in turn, drives a generator; the net result is electricity.

The traditional coal-fired power plant comprises two basic components. The first component is a furnace boiler designed to burn the coal and capture the heat energy released using a system of circulating water and steam. The second part of the system is a steam turbine generator which converts the heat energy captured by the steam into electrical energy. In other words, chemical energy held within the coal is first translated into heat energy and then into mechanical energy, and finally into electrical energy. Modern plants also include additional units to remove dust and acid emissions from the flue gases before they are released into the atmosphere.

 

Boiler

A power plant boiler is a device for converting the chemical energy in coal into heat energy and then transferring that heat energy to a fluid, steam. The efficiency of a coal-fired power plant increases as the pressure and temperature of the steam increases. This has led to a demand for higher temperatures and pressures as technology has developed and this has required, in turn, the development of materials with higher performance under increasingly stressful conditions. The most advanced boilers develop steam with a pressure of around 250bar and a temperature of 600°C.

Early boilers were made from iron, but as the demands on the system increased, special steels were used that could resist the conditions encountered in the power plant. These now dominate in modern boilers. Even so, oxygen dissolved in the water circulating within the boiler pipes can cause serious corrosion in steel at the elevated temperatures and pressures to which it is exposed, so the boiler water must be deoxygenated.

The first part of the boiler is a furnace in which combustion takes place. In the most common type of boiler, pulverised coal is injected with a stream of air into the furnace in a continuous process through a device known as a burner. The coal burns, producing primarily carbon dioxide while incombustible mineral material (ash) falls to the bottom of the furnace where it can be removed (some is also carried away by the hot combustion gases).

The heat generated during combustion (the temperature at the heart of the furnace may be as high as 1500°C) is partly radiant and partly convective, the latter carried off by the hot combustion gases. The radiant heat is collected at the walls of the furnace where water is circulated in pipes. Covective heat in the combustion gases is captured in bundles of tubes containing either water or steam which are placed in the path of the flue gas as it exits the furnace.

In a conventional boiler there is a drum positioned appropriately within the steam–water system containing both water and steam so that steam can develop as the temperature of the fluid rises. The most advanced designs, however, operate at such high temperatures and pressures that they do not pass through a stage in which water and steam co-exist. In these boilers the water turns directly to steam within the water tubes. This type of boiler exploits what is called a supercritical cycle, called so because the thermodynamic fluid (the water) enters what is known as the supercritical phase without passing through a condition in which both water and steam co-exist.

The boiler watertubes in the exhaust gas path are frequently divided into a number of different sections. (These sections have names, such as economiser, reheater or superheater.) The water or steam passes through them is a specific order determined by the design of the steam cycle. Traditional pulverised-coal boilers have been built with outputs of up to 1000MW.

Steam turbine

The steam turbine is the primary mechanical device in most conventional coal-fired power stations. Its job is to convert the heat energy contained in the steam exiting the boiler into mechanical energy, rotary motion. The steam turbine first appeared in power applications at the end of the nineteenth century. Before that steam power was derived from steam-driven piston engines.

The steam turbine is something of a cross between a hydropower turbine and a windmill. It, like them, is designed to extract energy from a moving fluid. The fluid is water, the same as the hydro turbine. In the case of a hydro turbine the water remains in the liquid phase and neither its volume nor its temperature changes during energy extraction. In the case of the steam turbine, energy extraction is from a gas, steam, rather than a liquid and involves both the pressure and the temperature of the fluid falling. This has a profound effect on the turbine design.

Both hydro and steam turbines exist in two broad types: there are impulse turbines which extract the energy from a fast-moving jet of fluid and reaction turbines which are designed to exploit the pressure of a fluid rather than its motion. A hydro turbine will be of one design or the other. In a steam turbine the two principles may be mixed in a single machine and they may even be mixed in a single turbine blade.

It is impossible to extract all the energy from steam using a turbine with a single set of turbine blades. Instead, a steam turbine utilises a series of sets of blades, called stages. Each stage is followed by a set of stationary blades (usually called nozzles) which control the steam flow to the next stage.

A single steam turbine stage consists of a set of narrow blades projecting from a central hub. (In concept, it is something like a steam windmill.) Ten or more sets of blades can be mounted on a single steam turbine shaft. This combination of shaft and blades is called a rotor. The turbine stages are separated by carefully designed stationary blades, or nozzles, which control the flow of steam from one set of rotating blades to the next. The precise shape of the blades in each set determines whether that set is impulse or reaction, or a cross between the two. The hub, blades and nozzles are enclosed in a close-fitting case to maintain the steam pressure.

In a steam turbine impulse stage, energy is extracted at constant pressure while the velocity of the steam falls as it flows across the blades. The steam is then expanded through a stationary control stage to increase its velocity again before energy is extracted from another set of impulse blades. In a steam turbine reaction stage, by contrast, both pressure and velocity of the steam fall as energy is extracted by the rotating blades.

Steam exiting the power plant boiler is at a high temperature and a high pressure. Both temperature and pressure fall as the steam passes through the turbine. The greater the temperature drop and the greater the pressure drop, the more energy can be captured from the steam. Consequently the most efficient power plants condense the steam back to water at the end of the turbine.

Even with a modern design it is impossible to capture all the energy from the steam efficiently with a single multiple-stage turbine. Coal-fired power plants use several. These are usually divided into high-, medium- and low-pressure turbines. The blades in these turbines get larger (longer) as the pressure drops; in fact, the low-pressure turbine may comprise several turbines operating in parallel to gain the most energy without making a single turbine impossibly large. All the turbines may be mounted on a single shaft, but it is common for the low-pressure turbines to be on a separate shaft rotating at a lower speed to reduce the forces exerted at the blade tips. Multiple turbines of this type can have aggregate outputs of over 1000MW.

As with boilers, the demands of modern power plant design have led to the development and introduction of high-performance materials that can cope with the extreme conditions encountered within a steam turbine. The high-pressure turbine blades have to be able to withstand extremes of both temperature and pressure and have to be able to resist the abrasive force of steam. At the low-pressure end of the turbine train the large size of the turbines means that the blade tip speeds are enormous, again requiring specially designed materials to withstand the centrifugal forces exerted on them.

A refinement which improves the overall efficiency is to return the steam to the boiler after it has passed through the high-pressure turbine, reheating it before delivering it to the medium-pressure turbine. Most modern steam turbine plants use this single reheat design (multiple reheat is also possible).

The theoretical maximum efficiency of a coal-fired power station is determined by the temperature difference between the steam entering the high-pressure turbine and the steam exiting the low-pressure turbine. The greater this temperature difference, the more energy can be extracted. With the most advanced technology, utilising the best boiler materials to achieve the highest-steam temperatures and pressures, a maximum efficiency of around 43–45% can be achieved. New supercritical designs may eventually push this as high as 55%. In the near future, however, the best that is likely to be achieved is something between 47% and 49%.

Generators

The turbine shaft, or shafts if there is more than one, are coupled to a generator which converts the rotary mechanical motion into the electrical energy that the plant is designed to provide. Generators, like steam turbines, first appeared during the nineteenth century. All utilise a coil of a conducting material, usually copper moving in a magnetic field to generate electricity.

The generators used in most power stations, including coal-fired power stations, are designed to deliver an alternating current (AC) to a power grid. An AC current is preferred because it allows the voltage to be raised or lowered easily using a transformer. For transmission of power over long distances it is preferable to use a very high voltage and a low current. The voltage is then reduced with a transformer before delivery to the consumer.

The need to generate an AC voltage determines the speed at which the generator rotates. This must be an exact multiple of the grid frequency (normally grids operate at either 50 or 60Hz). For grids operating at 50Hz the traditional generator speed is 50 cycles per second, or 3000rpm. The equivalent 60Hz machine rotates at 3600rpm. This speed, in turn, determines the operating speed of the steam turbine. Large low-pressure steam turbines may operate at half these speeds.

Generators may be as large as 2000MW, and large generators are normally built to suit a particular project. Modern generators operate with an efficiency of greater than 95%. The remaining 5% of the mechanical input energy from the turbine is usually lost as heat within the generator windings and magnetic components. Even though the percentage is small, this still represents an enormous amount of energy; perhaps 50MW in a 1000-MW machine. Hence generators require very efficient cooling systems in order to prevent them overheating. Avariety of cooling mediums are used, including hydrogen which is extremely efficient because of its low density and high specific heat.

The broad outline of generator design has changed little over a century. However new materials have improved efficiencies. The latest developments involve the use of superconducting materials to reduce energy and increase efficiencies.

Coal Fired Steam Power Plant Video

Coal-Fired Steam Power Plant Reference Books:

Steam Plant Operation

Steam Turbines: Theory and Design

Steam Plant Calculations Manual,...

 

Power Plant Engineering