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What is a Power Plant? Type of Power PlantsСтр 1 из 8Следующая ⇒
What is a Power Plant? Type of Power Plants Energy & Power Plants / By Ricky / Mechanical Engineering Introduction Energy comes in various forms but electrical energy is The Power Plant Power or energy (let me remind you at this juncture that In the industrial use of the word, the term power plant Types of Power Plants There are several different types of power plants used
Apart from these main two types there are plants which use Types of Nuclear Power Plants Pressurized Water Reactors Boiling Water Reactors https: //www.brighthubengineering.com/power-plants/2267-types-of-power-plants-generation-of-electrical-energy/
Clean Coal Fired Energy Plants – What is Involved? Energy & Power Plants / By Aggeliki K. / Mechanical Engineering Clean Coal Technologies Coal is considered a highly polluting energy source – for many it is the worst. This is attributed to the fact that it is the most carbon-intensive fossil fuel available. The burning of coal results in dangerous emissions including carbon dioxide that is responsible for global warming, sulfur dioxide, the main responsible for acid rain and a number of other dangerous toxins and cancer-causing dioxins. The newly introduced clean coal operation technologies are aiming at reducing the amounts of these pollutants escaping into the atmosphere. They are targeted mostly toward the reduction of carbon dioxide since global warming is the most severe environmental impact. The first clean coal energy plant, actually a pilot plant using US FutureGen technology and operated by a Swedish firm called Vattenfall, started operating in 2008 in Spremberg, Germany. The facility uses the technique of carbon capture and storage to clean coal. More specifically, carbon dioxide is captured and then compressed into a liquid state and stored. This way the CO2 does not escape into the atmosphere. The technique is described in more detail below, along with other clean coal technologies that are currently under development. Conclusion There is a great deal of concern regarding the future of these technologies. Greenpeace suggests that no coal-fired power plant is ever truly clean. All that clean coal techniques manage is to circulate the pollutants and finally release them back into the environment. Apart from that, the economic viability of these technologies is in question. Research on clean coal technologies is taking place " for over 10 years and $5.2 billion have already been spent in the US alone" (Greenpeace). It is expected that it will take hundreds of millions of dollars and many more years before they are commercially available. Despite the concerns, clean coal technology is now shifting toward a newly modified coal gasification technique that may provide what is called " zero emissions" or actually low emissions of carbon dioxide and other pollutants. Although the US DOE planned to have commercial designs for power plants using the technology by 2012, the project was postponed. https: //www.brighthubengineering.com/power-plants/116012-operating-clean-coal-power-plants/ Natural Gas and its Uses Natural gas is mainly composed of methane and a small percentage of other hydrocarbons (e.g. ethane). This simple composition makes natural gas a valuable energy resource and a great asset to the global economy. Its use is becoming more and more popular since it can be used in a variety of sectors (industrial, commercial, residential, electric power generation, transportation, etc.). More specifically: GAS 1
A Small Conclusion Despite the disadvantages, it is remarkable that the entire cycle of producing, processing, transporting and using natural gas provides us with a total energy efficiency of almost 90%. It is by far the best choice among the fossil fuel energy sources from all aspects. https: //www.brighthubengineering.com/power-plants/114797-pros-and-cons-of-natural-gas-use/ How They Work Gas engines are four stroke engines using the Otto cycle and in principle work exactly like the petrol or gasoline engine. Air and gas mixture ignites at the end of the compression stroke using a spark. Large gas engines use a fuel rich pre-combustion chamber to amplify the sparks energy. Large engines also use turbo-charging to boost power and output. The difference is in the fuel system. Unlike the carburetion system or fuel injection system in today’s gasoline engines, the gas suction is by venturi effect and mixed in a gas mixer in the suction manifold. Electronic fuel gas valves for individual cylinders give much better load control. The higher capacity engines use electronic controls to control air fuel ratio and load to get the best efficiencies and prevent knocking. Combustion with high excess air or lean burning reduces the gas temperatures resulting in lower NOx emissions. Large engines also use turbo charging to boost outputs and torques. V shaped cylinder arrangement as in large diesel sets are the normal configuration for large capacity engines. An optimized cooling system for jacket cooling, lube oil, and inlet air increases efficiency. GAS 4 The gas engine can be for power generation only or for combined heat and power utilizing the exhaust heat. What goes against gas engines are:
The gas engine has some specific advantages over gas turbines in the lower power output range. Advantages of Gas Engines 1. Fuel Flexibility. The biggest advantage is that gas engines can burn natural gas and a variety of other gases. The limited availability of many of the organic and process gases necessitates the use of natural gas as a standby source. Switching from one source is rather easy in the gas engine. They can burn low calorific value gases, low methane number gases, and gases that have fluctuating fuel composition like landfill gas. 2. Fuel Pressures. Gas pressure requirement of a gas turbine is high often in the range of 17 to 20 bar. If the supply gas pressure is low, this requires the addition of a gas pump that increases investment and operation costs. Supply of gas from biomass or other organic sources are at low pressures. Gas engines operate with low inlet gas pressures in the range of 200 mbar. 3. Speed. As an internal combustion engine, gas engines run at much lower speed, 750 or 1500 rpm against the 14000 RPM for smaller gas turbines. There is no need of a gear box. This is much less stress on the rotating elements, combustion path, and bearings, making gas engines cheaper. This also results in a much higher Mean Time Between Outages. 4. Ambient Effect. Gas turbine output reduces with the increase in ambient temperature. Gas engine output reduces only when the ambient temperature reduces the effectiveness of the cooling system. 5. Startup. Gas turbines require high power to start-up, to bring the rotor to synchronous speed. This requires a backup power or stand by DG set, or compressed air pressure or gas pressure. Gas engines can crank start from battery power. 6. Efficiency. In the lower power range, gas turbine efficiencies are in the range of 28 % in the open cycle mode. Present day large capacity gas engines provide greater than 40 % efficiency. 7. Exhaust Temperature. Gas turbine exhaust temperature is in the order of 450 °C. Unless there are exhaust heat recovery devices, the exhaust stack and ducts design should be for these high temperatures. This will also require a higher stack to avoid heat dissipation problems. Gas engines in the stand-alone mode have much lower gas temperatures in the range of 150 °C. 8. Emissions. The lower combustion temperature and lean air burning produces less NOx. 9. Maintenance. Skills required for maintenance follow the well-developed IC engine lines and is thus available in almost all parts of the world. Gas engines are very reliable and run for almost 100 % availability resulting in low costs. Gas turbines require high technology and more time for maintenance. 10. Cost. All of the above makes gas engine a lot cheaper, with lower capital costs and lower O& M costs. For low output power generation with environmentally friendly fuel gases, gas engines are a better option than gas turbines. https: //www.brighthubengineering.com/power-plants/108429-reciprocating-gas-engines-for-biomass-powerplants/ Introduction Hydropower in any country is regulated both during the construction and operational stages. Since the safety of hydropower and dams is a significant part of FERC’s mandate, safety gets a top priority. Prior to construction, the commission staff inspects and sanctions programs and stipulations for the project. Staff engineers are responsible for both examining the project and then for inspecting it on a regular basis. Prompt approval for any type of energy scheme is uncommon. This is true in the case of small hydropower, too. (Some cases have required more than fifteen years for approval.) This has been a major restraint in the growth of significant private energy substructure in the U.S. Nevertheless a novel, reassuring movement is arising in the hydropower industry. Recognizing the requirement for clean, inexhaustible energy, FERC is implementing plans to hasten the licensing procedure for small hydropower projects.
Conduit Exclusions A small passage hydroelectric installation which is around 15 MW, and in certain projects of a municipality of a capacity up to 40 MW, using an artificial conduit functioning chiefly for non-hydroelectric aims may be entitled for a conduit exception. The applicant should have the realty (real estate) concerns essential to formulate and control the project, or an alternative to obtain the interests. The installation cannot use federal lands. The channel on which the scheme is being developed is not considered a project work. Requests for exceptions of small hydroelectric conduits are unconditionally free from the obligation for an Environmental Assessment or Environmental Impact Statement to be arranged by the Commission. On the other hand, this does not signify that the Commission cannot require an EA or EIS to be developed if the proposed project seems to have contrary consequences on the environment. MW Exceptions A small-scale hydroelectric project of 5 MW or less might be entitled to the 5 MW exclusion. The applicant must intend to set up on or lend capacity to an existing project situated on a non-federal dam constructed before 2005, or even at a natural water feature. This exemption is allowed for projects which are situated on federal lands, but they should under no circumstance be situated at a federal dam. The claimant must have all the realty interests or an alternative to hold stakes in any non-federal grounds. Licenses A permit from the Commission is needed to build, operate, and maintain a non-federal hydroelectric project. Such projects must have the following features: (a) Be situated on crossable waters of the United States; (b) Reside on U.S. lands; (c) Make use of excess water or water authority from a U.S. government dam; or (d) Be situated on a watercourse above which Congress has trade Clause authority; (e) Where project building or elaboration took place on or after August 26, 1935. Such project should also consider effects on the interests of interstate or overseas commerce. Licenses may be given for a period which might be up to 50 years and must be renewed toward the end of each period. A license provides the licensee with the ability to hold lands or other permissions required to build, operate, and preserve the hydroelectric project. Conclusion There is no doubt that we are at crossroads with regard to the views of hydropower’s future from its past and present dictatorial environment. The reaction to present disputes and altering actuality will, to a great degree, decide the importance of small hydropower as a significant element of the U.S.'s inexhaustible energy content in the future. Present advances for licensing onhand projects seem to be allowing for preferred tractability, with the option of enhanced efficiencies owing to the superior class of data obtainable for projects with important post-ECPA (Electronic Consumers Protection Act) procedures. On the other hand, the scarcity of propositions for new small and additive capacity to established hydropower add-ons is a red flag. Large fiscal and regulative roadblocks are blocking growth of new generation, formulating less than 3% which is equal to 560 MW out of 21, 000 MW, of the onhand small conservative hydropower not needing the building of new dams, which does not enthuse policy-makers. An appraisal of present policies and processes to assure they are not producing unneeded hurdles to enhancing this existing capacity would be sensible. https: //www.brighthubengineering.com/power-plants/104294-federal-energy-regulatory-commission-and-private-hydropower/ Japan and Earthquakes To the Japanese, earthquakes are nothing new. The entire land mass that Japan rests on is present in a region that experiences earthquakes each year. This has led them to adopt building architectures that are capable of withstanding earthquakes all the way to 6.0 on the Richter scale. But the earthquake of the magnitude 9.0 that Japan saw on March 11th was something out of the blue. It was the worst earthquake that the industrialized world has ever seen. This earthquake not only triggered a tsunam, i but also damaged the Fukushima I reactor to such an extent that many were afraid of a possible Chernobyl-like incident, or something even worse. For those who came in late, here is a brief description of the series of events that has left all countries with nuclear power plants in deep thought about the future of nuclear energy. On March 11th of 2011, an earthquake of magnitude 9.0 on the Richter scale hit Japan. The earthquake caused damage to the Fukushima nuclear reactors. The damage stopped the power source to the reactors before they could shutdown. As designed, the backup generators kicked in and the reactor proceeded with its shutdown process. However this earthquake triggered a tsunami that ravaged a huge area of land and made its way to the Fukushima nuclear reactors. The tsunami reached the reactor and damaged the backup power supply before the nuclear reactor shutdown totally. This was something that was not expected when the reactor was designed, although it was designed to withstand earthquakes up to the magnitude of 8.2. The incomplete shutdown led to the explosion of two reactors (not a nuclear explosion, but an explosion due to the build up of gases inside the reactor). The damage caused to the nuclear reactor was so bad that the core of the nuclear reactor was exposed in the days that followed. This led to the increase in nuclear radiation level around the surrounding areas. FUKUSHIMA 1 Introduction The development of fuel cells has given the energy conversion industry a good potential for a greener future. Nanotechnology on the other hand, has promoted fuel cell technology to a higher level, where fuel cells are more efficient, inexpensive, and suitable for a wider variety of applications than before. At this point, it is crucial to examine the enviromental effects of these promising, yet potentially risky advances. What is Nanotechnology? A brick is the smallest building block in construction. Whatever you do, the strength of the building is limited to the strength of the brick. The brick itself is made of minute particles of clay bonded together. One has limited control over how the particle of clay forms. Each particle of clay in turn is formed from molecules joined together in a particular pattern dictated by the forces of nature. What happens if it is possible to arrange these molecules in a pattern that provides greater strength? You get stronger clay and a stronger brick. This results in a much thinner, but stronger wall. This technology of arranging molecules the way we want is a basis of nanotechnology. In the early days, paint was available in a limited variety of colors for you to choose. Now most of the paint shops have mixers that allow the users to choose the color they require. The manufacturers have to produce and stock only a few basic colors, reducing production and inventory costs at much greater satisfaction to the consumer. The future of nanotechnology will be the personal nano-factories, like the paint mixers, that allow you to produce any material that you require. The shops have to carry only stock in molecular form. Advances in nanotechnology are moving at an exponential rate. It will eventually encompass every field of human activity including energy. Solar cells Solar cells absorb photons from the sun’s rays. Currently available materials can absorb photons only in a limited wavelength. This is why efficiency levels are very low in solar cells. With nanotechnology, it is possible to have materials with different molecular structures in a single solar cell, resulting in absorption of photons in much wider wavelengths. Because of the much smaller particle sizes, the area available for absorption of energy is also considerably higher. This can considerably improve efficiency from the current 12 % to more than 50 %. Printable roll-on solar panels using nanotechnology are almost on the market. Higher power ratings per panel reduce the area requirements. The basic cost of the panel itself maybe high, but the balance of system costs is considerably less than other solar panels. For more details, go to the NanoSolar website. Ultra Capacitors Capacitors are another form of energy storage. Because of the huge surface area requirements, the use of capacitors has been limited to low energy applications. Because of the very small size of nano-particles, it is possible to produce highly porous electrodes, which tremendously increase the surface area, leading to production of ultra-capacitors that can have much higher charging and discharge rates at higher voltage levels. These ultra-capacitors will be the energy source for equipment with heavy power requirements, including automobiles and trucks. These will be part of the micro grid that is set to revolutionize the electricity distribution system as well. EnerG2 has more information about ultra-capacitors. Coal Fired Power Plants Coal based power accounts for almost 41 % of the world’s electricity generation. Coal fired power plants operate on the modified Rankine thermodynamic cycle.The efficiency is dictated by the parameters of this thermodynamic cycle. The overall coal plant efficiency ranges from 32 % to 42 %. This is mainly dictated by the Superheat and Reheat steam temperatures and Superheat pressures. Most of the large power plants operate at steam pressures of 170 bar and 570 °C Superheat, and 570 ° C reheat temperatures. The efficiencies of these plants range from 35 % to 38 %. Super critical power plants operating at 220 bar and 600/600 °C can achieve efficiencies of 42 %. Ultra super critical pressure power plants at 300 bar and 600/600 °C can achieve efficiencies in the range of 45% to 48 % efficiency. Renewables Hydro turbines, the oldest and the most commonly used renewable energy source, have the highest efficient of all power conversion process. The potential head of water is available right next to the turbine, so there are no energy conversion losses, only the mechanical and copper losses in the turbine and generator and the tail end loss. The efficiency is in the range of 85 to 90 %. Wind turbines have an overall conversion efficiency of 30 % to 45 %. These two renewable sources, though efficient, are dependent on availability of the energy source. Solar thermal systems can achieve efficiency up to 20 %. The moving path of the sun and the weather conditions drastically alter the incident solar radiation. The efficiency on an annual basis, around 12 %, is considerably less than on a daily basis. Geo thermal systems, on the other hand, also use the Rankine cycle with steam temperatures at saturation point. Since there is no other conversion loss, this plant can achieve efficiencies in the range of 35 %. Nuclear The efficiency of nuclear plants is little different. On the steam turbine side they use the Rankine thermodynamic cycle with steam temperatures at saturated conditions. This gives a lower thermal cycle efficiency than the high temperature coal fired power plants. Thermal cycle efficiencies are in the range of 38 %. Since the energy release rate in nuclear fission is extremely high, the energy transferred to steam is a very small percentage – only around 0.7 %. This makes the overall plant efficiency only around 0.27 %. But one does not consider the fuel efficiency in nuclear power plants; fuel avaliabity and radiation losses take center stage Diesel Engines Diesel engines, large capacity industrial engines, deliver efficiencies in the range of 35 – 42 %. The power industry is trying to increase this conversion efficiency of power plants to maximise elctricity generation and reduce environmental impact. https: //www.brighthubengineering.com/power-plants/72369-compare-the-efficiency-of-different-power-plants/ NOx and CO The process of combustion itself generates some undesirable gaseous emissions like NOx and CO. These, though not necessarily a part of the basic reaction, are present in everyday combustion. Advances in combustion technology and operation philosophy have seen considerable reduction of these emissions. This is really eliminating an unwanted emission and a success of clean coal technology. CO2 emissions CO2 still emits into the atmosphere. Commercial scale capturing of CO2 ( Carbon Sequestering Systems ) and sending it to underground reservoirs is yet to be viable. CO2 emission will continue to be the main burden of coal, unless large scale forestry takes place to absorb the emissions. New Combustion Process Advanced technologies like Integrated Coal Gasification, Circulating Fluidized Bed technology, and coal washeries improve the utilization and efficiency of coal combustion. This also makes it easy for capturing the emissions and residues. Even though these are termed clean coal technologies, they are in fact only making the coal combustion cleaner. Residue Utilization Utilizing the captured residue, substituting for other natural resources, is an environmentally better disposal method. Technologies like:
Even though this is only a smaller percentage of the residue or emissions captured, this is a constructive clean coal method. Nature has taken millions of years to sequester the carbon into coal. In a few milliseconds, man has found the means to release it back to the atmosphere. The Pandora’s box has been opened, and we can only wait for Hope. A real clean coal with no emissions or environmental effects is impossible, but a cleaner coal is a must. https: //www.brighthubengineering.com/power-plants/71371-clean-coal-fired-power-plants/ Low Level Waste These wastes include some types of process equipment, protective clothing such as boiler suits and gloves along with rubble from decommissioned buildings. It is not considered as being dangerous to health. Intermediate Level Waste This waste is more radioactive than the low level waste and is made up from metal or alloy cladding fitted around fuel rods sludges from various processes, and resins used in coating components. High Level Waste These are prevalent in spent fuel and are highly contagious. Fuel rods are replaced periodically and the used ones are highly contagious containing uranium, plutonium along with minor actinides such as curium and neptunium isotopes. NUCLEAR WASTES 1 https: //www.brighthubengineering.com/power-plants/66637-nuclear-energy-current-and-long-term-storage-of-radioactive-waste/ The Treatment of Syngas The syngas exits the top of the coal gasifier and is passed to the gas treatment plant which consists of coal tar removal, gas water reactor and cooling, dust filtration, and SOx scrubbing processes. Most of these residues can be further processed and sold to chemical and building industries. After treatment, the gas then passes through the CO2 extraction plant where the CO2 is separated and stored, ready for transport to a long term storage area. Following this process the zero CO2 syngas is piped to the gas turbines in the turbine hall. Desorber Tower This is another pressure vessel of similar design to the absorber tower including the ceramic packed sections. The liquid from the absorber tower is fed into the top of this tower, falling downwards through the packed sections. Steam is introduced into the bottom of the desorber, bubbling up through the liquid mixture cascading downward, and passing through the packed sections. The CO2 is stripped from MEA, and passes out the top of the desorber tower for dehydration and cooling and then is sent to storage facilities or to further processing. The MEA gathers at the bottom and is pumped into a reboiler where it is regenerated, and from here it is recycled into the absorber tower along with make-up MEA. Uses of Captured CO2
Note: The various methods for storage of CO2 will be covered in the next article on fossil fuelled power plants. CO2 https: //www.brighthubengineering.com/power-plants/64165-capturing-power-plant-co2-emissions-for-long-term-storage/
Introduction Electricity, in particular thermal power generated using fossil fuels, produces the largest amounts of industrial greenhouse gas emissions. This is because fossil fuels contain carbon which when burned in air produces CO2. In this series on power stations we look at three different types of fuel supplied to the thermal power stations, this first article being on coal fuel, then natural gas and ending with biomass fuel. We will examine the different methods of producing electricity and, fume treatment, both the present and future methods. Coal Supply The UK coal industry was dismantled by Maggie Thatcher’s Government in one of the bitterest disputes between a government and the trade unions ever witnessed. Since then mines have been continuously shut down until now we have only four surface mines and four deep mines operating in Britain today. However we still use coal in our homes and for power generation fuel, so now most of the steaming coal used in the power stations is imported from as far away as Russia, South Africa, and Australia. The coal arrives in Britain by ship and is transported by rail to the power station stockpile. Power Station Stockpile It is distributed into heaps in the stockpile by a bucket wheel machine. This is a device with large buckets arranged in a circle on the end of a rotating head. From the heaps the coal is loaded onto an enclosed conveyor. Coal Pulverisers From the stockpile a conveyor system conveys the coal to the pulverisers. The coal pulverisers are really large ball mills having numerous hollow steel balls weighing over a ton each and about 750mm diameter. The pulveriser drum rotates causing the balls to move in a circular motion inside as the coal is fed into the drum. The coal is not large lumps like we use at home, but in small pieces of between 25 and 50mm known as steaming coal. Water Tube Boilers The pulverised coal, now really coal dust is blown by the primary air fan to the boiler coal burners and into the furnace. Forced draught fans propel the combustion air from the top of the boiler room through an air heater into the furnace combining with the coal dust. The mixture ignites and boils the water in the boiler tubes, turning it first to wet steam in the steam drum and then to superheated steam, in the superheater, which is now used to power a steam turbine. Steam Turbines The steam turbine can be one of several mechanical arrangements; the one shown is an in-line, reheat, single casing arrangement which has three stages. Superheated steam enters the High Pressure (HP) stage; the expanded steam is returned to the boiler and reheated before it enters the Intermediate Pressure (IP) stage. From here the exiting steam passes onto the dual Low Pressure (IP) stage where it expands before exiting to a vacuum condenser and hotwell from which the condensate is pumped into the boiler feed system. This steam turbine drives a generator producing electricity which after passing through transformers is fed to the National Grid. Ash and Fume Extraction The furnace ashes are gathered and sold to the construction industry, with any surplus usually going to a disposal site. The furnace combustion gasses pass through the superheater, economizer, and air heater before being discharged out the flue after being purified by the fume extraction system. CO2 Emissions to Atmosphere At present there is government legislation that will prevent any future power plants in Britain to be built without a method of CO2 abatement such as Carbon Capture and Sequestration (CCS). This involves isolating the CO2 by scrubbing with an ammonia solution and then impounding this gas in an underground or undersea cavern such as a disused deep coal mine pit or exhausted oil/gas reservoir. The amine solution can be recycled and reused. The other method of reduction of CO2 emissions is to make the plant as efficient as possible; much like the one I have described using pulverised coal and energy efficient turbines. In addition to these measures, mixing biomass such as wood sawdust or pellets with the coal dust supply to the furnace will also reduce CO2emission levels. What is a Power Plant? Type of Power Plants Energy & Power Plants / By Ricky / Mechanical Engineering Introduction Energy comes in various forms but electrical energy is The Power Plant Power or energy (let me remind you at this juncture that In the industrial use of the word, the term power plant Types of Power Plants There are several different types of power plants used
Apart from these main two types there are plants which use |
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