| If you’ve ever read a book to a small child on the subject of food or digestion, you’ve probably come across the analogy that our stomachs are like a furnace and our digestive system much like an engine. We explain to the youngster that what we eat is important, because our body needs the right fuel in order to operate properly. If little Susie or Danny insisted on eating only candy day after day, their bodies would become weak and sick.
In much the same way a coal power plant is like a living organism, eating fuel in order to function. But instead of meats and vegetables, it eats coal, and the coal handling department of a power plant acts as a dinner table. It’s where the food is placed and prepared before it enters the diner’s mouth.
The coal our power plants consume comes from one of two places, underground mines or strip mines. It all depends on the particular geology of the area from which the coal is harvested. According to the US Energy Information Administration, underground mines are more common in the eastern United States, while strip mines are more common in the western states. The coal from underground mines is excavated by means of shafts and tunnels which are dug deep beneath the earth’s surface in order to provide access to the buried coal deposits. In strip mines the deposits are just below the surface, so the topsoil is merely stripped away with heavy earthmoving machinery, like bulldozers, to reveal the coal. In both types of mining activity excavating machines and conveyors are required to remove the coal from the mine so it can be loaded for shipment to its ultimate destination.
Once harvested, coal is shipped to power plants primarily by train, river barge, or ship. Its journey can cover thousands of miles. It culminates in delivery to a power plant, where it is unloaded by means of a huge piece of machinery called a rotary dumper. This machine is capable of grabbing onto 100 ton railcars and turning them upside down. The coal spills into a large collection hopper positioned next to the railroad track.
If the coal has found its way to a plant located near a waterway, that means of transport was most likely have been made by flat barge or ship. In this case a large crane with a clamshell bucket is used for unloading. The crane drops its bucket into a pile of coal located within the ship’s hold, takes out a large bite, then hoists and dumps its contents into a large collection hopper next to the crane.
To get an idea of how coal flows within the coal handling system of a power plant, let’s refer to the flow chart in Figure 1.
Figure 1 – Schematic Diagram of the Coal Handling System
Collection hoppers and have slanted bottoms which allow coal to easily spill out onto a conveyor belt. Within the plant coal is transported by means of conveyors into what’s known as a “breaker building.” This building lives up to its name because it contains a very large machine whose job it is to break the chunks of raw coal that have been harvested from mines into smaller chunks which the boiler can work with.
Once broken down, the coal will go to one of two places, either directly into silos or coal bunkers in the power plant building for short term storage, or into an outside storage pile, usually a prominent feature of a power plant due to its formidable size. The coal pile can be several stories tall and much larger than a football field. It acts as a reserve supply should the regular delivery of coal be interrupted by labor strike, natural disaster, or equipment failure. When necessary, the coal is removed from the pile and sent into the plant to fill the coal silos. Coal from the silos is used to feed the power plant boilers.
Next week we’ll continue to follow coal’s journey, on its way to arguably one of the most important pieces of equipment in a power plant, the boiler.
Posts Tagged ‘coal power plant’
Try this for a tongue-twister: Coal fired electric utility power plant boiler… If you’ve been reading along with us for the last couple of weeks, you now have a pretty good idea of what these are and what they do.
These boilers are contained within furnaces in coal fired power plants. The furnace’s job is to combine coal and air to create a combustion process. It is like a big, insulated enclosure that keeps the heat energy from the combustion process from escaping before it can be absorbed by the water and steam in the boiler tubes. The heat energy is then funneled to the steam turbine to spin an electrical generator, creating the energy which will eventually find its way into our homes and businesses.
During the operation of the boiler, coal and air must be introduced into the furnace at carefully measured rates to maintain a proper fuel-to-air ratio which will enable the release of heat energy from the coal at a safe, controlled rate. Fuel-air ratio is the amount of coal entering the furnace divided by the amount of air entering the furnace. If this ratio isn’t precisely maintained, conditions may be right for an explosion to occur. Specifically, the ratio has to fall within an “explosive range.” Once within this range, all that is needed is an ignition source, such as hot ash, or even mere static electricity, and the result may be a furnace explosion.
There are certain times at which furnace explosions are more likely to occur than others, such as when the boiler is being started, operated at less than full capacity, or shut down. When a furnace explodes, a pressure wave moves out from the center of the blast. This pressure wave will bear up against the sides of the furnace with great force, and if the pressure is high enough the sides of the furnace, which are made of heavy steel components, will actually bend and split open. Boiler tubes may even rupture, releasing high pressure steam and water into the power plant and furnace. At the very least, the boiler will be down for expensive repairs and no electricity can be produced by its turbine generator. This down time can last for many months and results in lost revenue to the energy producer.
Aside from an explosive fuel-to-air ratio, there are other potential causes of furnace explosions. For example, poor coal quality can lead to incomplete combustion, or the flame going out completely, encouraging unburned coal particles to settle and accumulate in the furnace. The accumulation of coal can grow to the point where it forms an explosive mixture when combined with the right amount of air.
So how can boiler explosions be prevented? The National Fire Protection Association (NFPA) looked into the problem and developed an industry standard. This standard is known as NFPA 85, Boiler and Combustion Systems Hazards Code. Its purpose is to contribute to operating safety and prevent uncontrolled fires, explosions, and implosions of coal fired boilers. NFPA 85 lays out guidelines to follow when designing, building, and operating boiler fuel handling systems, air handling systems, and combustion control systems. Following its guidelines will certainly significantly decrease the probability of explosions occurring.
Another means of explosion prevention includes implementing a boiler operator training program. These enable attendees to better understand operating procedures and equip them with the knowledge to safely control the combustion process, particularly when a furnace explosion is most likely to occur. This training can be done with a combination of classroom instruction along with time on a simulator and may be followed up with hands-on training in the plant itself.
Lastly, boiler explosions can be prevented by implementing an effective inspection and maintenance program to locate and repair or replace boiler components, averting the possibility of a potential disaster occurring. Things such as check lists can be used to ensure that nothing is missed. This is a strategy that all pilots must use before starting their planes, and it is now being used in hospitals as well to cut back on the rate of patient infection due to carelessness on the part of hospital staff.
Hey, we’re all human, and humans are not perfect. But remember that an ounce of prevention is truly worth a pound of cure, and then some. A properly placed check on the list could mean lives will be saved.
Did you ever have someone you considered to be a great friend and then things suddenly went bad between you? One day you’re chums and then the magic fades, soon to disappear? Sound like some marriages you’ve heard about?
Well, it wasn’t too long ago that coal was considered to be America’s affordable answer to our fuel needs. It was a friend of grand proportions, there when you needed it. It remains an abundant resource, so abundant in fact that according to the US Energy Information Administration (EIA) we are sitting on coal reserves so vast they can provide us with sufficient energy to get us through the next 250 years at current rates of consumption. It was for these reasons that electric utilities decided decades ago to use coal as the primary source of fuel to generate electricity, and as it stands now just over 50% of our electrical energy is generated by burning coal.
So how did coal go from being friend to foe? Well, just as when you’ve known someone for awhile their “baggage” becomes more apparent, it eventually became apparent to Americans that burning coal comes with some nasty baggage of its own, known as byproducts. These unwelcome components of the burning/oxidation process were found in the plumes of smoke that billowed out of power plants’ smokestacks. So just what are these byproducts? Well, some of it is the same stuff that’s left over at the bottom of your barbecue grille after a cookout, and some of it comes with scientific names like sulfur dioxide (SO2), nitric oxide (NO), and nitrous oxide (N2O). Let’s look at these in more detail.
Ash is the residue that’s left behind after coal is burned. Fly ash is a type of ash that is made up of some very light particles and it can get carried away by the hot gases coming off the fire in a power plant boiler. Some of those particles manage to leave the smokestack and enter the environment.
Sulfur dioxide, or SO2, is formed when the sulfur in coal combines with oxygen in the air during burning. When the SO2 leaves the smokestack, it can combine with moisture in the atmosphere to form acid rain. Most of us know what acid rain is, but for those that don’t, acid rain does things like rust metal, dissolve marble monuments, and in general disrupt the balance of Earth’s eco systems.
Nitric oxide, NO, and nitrous oxide, N2O, are chemical compounds composed of nitrogen and oxygen that fall into the group commonly referred to as NOx, pronounced “knocks.” NOx is formed when nitrogen and oxygen in the air combine at the high temperatures released when coal is burned inside power plant furnaces. NOx is bad because its compounds are key ingredients in the formation of both acid rain and smog.
Over the last thirty years emissions of these byproducts have come under increasing scrutiny by federal and state regulators in their quest to curb them and their impact on our environment. As a result, electric utilities have had to comply with ever-tightening regulations. To comply, coals with lower sulfur content have been used, often brought in over very long distances from mines in the US and even foreign countries like Columbia. Utilities have also been installing expensive pollution control equipment in their coal fired power plants. But these changes make operations more expensive, eating into the utilities’ profits. Now we may not like the idea of utilities earning a profit, but this is a necessary reality to some extent in order to keep their business solvent. They’re not in it for the fun of it, after all. And I’m sure you guessed by now that the net result of the regulatory agencies’ mandates is that our electric bills just keep escalating.
Now much of what lies behind the current unfavorable status of coal powered plants is that when operating on our native soil they have high visibility. We don’t like to be reminded of the negatives that accompany the production of energy. Put that same plant in another faraway country and the byproducts cease to be an issue. It’s happening over there after all, and we don’t have to be confronted with it. We neglect to remind ourselves that the earth’s atmosphere is for the most part a contained unit, and that means that what happens there is happening here, whether there happens to be on the other side of the globe or not.
Next week we’ll continue our explorations into coal, examining the impact of the low sulfur variety on electric utility power generation.
The last few weeks we’ve been discussing some of the technical and environmental drawbacks of alternative sources of electrical energy and nuclear power generation. This week we’ll take a look at another drawback, that of energy sprawl.
So what exactly is “energy sprawl?” It’s an easily understand concept, but one that is often overlooked by proponents of the alternative energy movement. Energy sprawl is simply the amount of land which is taken over by alternative power sources in order to generate a given amount of electricity, and that number is dauntingly large.
For example, let’s revisit the subject of wind turbines. According to the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy, each turbine is to be spaced five to ten turbine diameters apart in a wind farm, depending on local conditions. Now the blades of a 2 megawatt (2 million watt) wind turbine are about 260 feet in diameter, and for our example we’ll space them at the prescribed minimum distance of five diameters. The math for this one is easy, 260 times five, which equates to spacing of 1333 feet, or just over a quarter of a mile. That’s right, if you build a wind turbine farm with a whole bunch of these 2 megawatt turbines, they’ll have to be spaced a minimum of a quarter mile apart. You’ll need a lot of acreage.
So based on the calculations above, we’d have to build a wind farm where each 2 megawatt turbine is surrounded by a circle of empty land 1333 feet in radius. We know from geometry that the area of a circle can be calculated by multiplying pi, that is 3.1416, times its radius squared, and this translates into a minimum area of about 5.6 million square feet per 2 megawatts of power generated, or about 2.8 million square feet per megawatt. Just to put this into perspective, a football field has an area of 57,564 square feet. So what we’re actually talking about here is a little more than 48 football fields worth of land per megawatt of electricity generated!
Let’s turn our attention now to solar power generation. We want to generate electricity with their photo-voltaic (PV) panels, and these panels are made of special materials that convert the sun’s energy directly into electricity. Great concept, but here again we’re talking a lot of land. According to the NREL, it’s estimated that 6.4 acres are required to generate 1 megawatt of electricity using PV panels. Since one acre equals 43,560 square feet, we’d need a total of 278,784 square feet of land area per megawatt. After we’ve done the math we discover that this equates to almost five football fields of area per megawatt of electricity generated.
We’ve now established that loads of land space is required to operate multiple options for alternative energy, and you’re probably wondering how this all compares to land usage for fossil fuel (i.e. coal, oil, natural gas) and nuclear power generation. Well, a typical 1000 megawatt coal fired power plant occupies about 148 million square feet. This translates to around 148,000 square feet per megawatt, which is just over two and a half football fields per megawatt. As for a 1000 megawatt nuclear power plant, we’re talking about 28 million square feet that’s typically occupied by an operating plant, and that translates to almost 28,000 square feet per megawatt, or a little less than half of a football field per megawatt.
Math established, it’s a hands down victory for fossil fuel and nuclear plants compared to wind turbine and solar energies when it comes to land usage. Last time I checked tillable land acreage was going down, not up, around cities where electricity demand is highest. Do we start pushing farther outward to build wind turbine and PV farms on vast expanses of land currently occupied by forests or used to grow our food? Which would you rather do, eat or have electricity?
This week we’re continuing our discussion on alternative energy by introducing another voice. A couple of articles ago you were urged to seek a second opinion on the realities of alternative energy. The following article in the Washington Post by Robert Bryce will constitute another attempt to get a full understanding of the picture. Consider it your third professional opinion on the matter…
Five myths about green energy
By Robert Bryce
Americans are being inundated with claims about renewable and alternative energy. Advocates for these technologies say that if we jettison fossil fuels, we’ll breathe easier, stop global warming and revolutionize our economy. Yes, “green” energy has great emotional and political appeal. But before we wrap all our hopes — and subsidies — in it, let’s take a hard look at some common misconceptions about what “green” means.
1. Solar and wind power are the greenest of them all.
Unfortunately, solar and wind technologies require huge amounts of land to deliver relatively small amounts of energy, disrupting natural habitats. Even an aging natural gas well producing 60,000 cubic feet per day generates more than 20 times the watts per square meter of a wind turbine. A nuclear power plant cranks out about 56 watts per square meter, eight times as much as is derived from solar photovoltaic installations. The real estate that wind and solar energy demand led the Nature Conservancy to issue a report last year critical of “energy sprawl,” including tens of thousands of miles of high-voltage transmission lines needed to carry electricity from wind and solar installations to distant cities.
Nor does wind energy substantially reduce CO2 emissions. Since the wind doesn’t always blow, utilities must use gas- or coal-fired generators to offset wind’s unreliability. The result is minimal — or no — carbon dioxide reduction.
Denmark, the poster child for wind energy boosters, more than doubled its production of wind energy between 1999 and 2007. Yet data from Energinet.dk, the operator of Denmark’s natural gas and electricity grids, show that carbon dioxide emissions from electricity generation in 2007 were at about the same level as they were back in 1990, before the country began its frenzied construction of turbines. Denmark has done a good job of keeping its overall carbon dioxide emissions flat, but that is in large part because of near-zero population growth and exorbitant energy taxes, not wind energy. And through 2017, the Danes foresee no decrease in carbon dioxide emissions from electricity generation.
2. Going green will reduce our dependence on imports from unsavory regimes.
In the new green economy, batteries are not included. Neither are many of the “rare earth” elements that are essential ingredients in most alternative energy technologies. Instead of relying on the diversity of the global oil market — about 20 countries each produce at least 1 million barrels of crude per day — the United States will be increasingly reliant on just one supplier, China, for elements known as lanthanides. Lanthanum, neodymium, dysprosium and other rare earth elements are used in products from high-capacity batteries and hybrid-electric vehicles to wind turbines and oil refinery catalysts.
China controls between 95 and 100 percent of the global market in these elements. And the Chinese government is reducing its exports of lanthanides to ensure an adequate supply for its domestic manufacturers. Politicians love to demonize oil-exporting countries such as Saudi Arabia and Iran, but adopting the technologies needed to drastically cut U.S. oil consumption will dramatically increase America’s dependence on China.
3. A green American economy will create green American jobs.
In a global market, American wind turbine manufacturers face the same problem as American shoe manufacturers: high domestic labor costs. If U.S. companies want to make turbines, they will have to compete with China, which not only controls the market for neodymium, a critical ingredient in turbine magnets, but has access to very cheap employees.
The Chinese have also signaled their willingness to lose money on solar panels in order to gain market share. China’s share of the world’s solar module business has grown from about 7 percent in 2005 to about 25 percent in 2009.
Meanwhile, the very concept of a green job is not well defined. Is a job still green if it’s created not by the market, but by subsidy or mandate? Consider the claims being made by the subsidy-dependent corn ethanol industry. Growth Energy, an industry lobby group, says increasing the percentage of ethanol blended into the U.S. gasoline supply would create 136,000 jobs. But an analysis by the Environmental Working Group found that no more than 27,000 jobs would be created, and each one could cost taxpayers as much as $446,000 per year. Sure, the government can create more green jobs. But at what cost?
4. Electric cars will substantially reduce demand for oil.
Nissan and Tesla are just two of the manufacturers that are increasing production of all-electric cars. But in the electric car’s century-long history, failure tailgates failure. In 1911, the New York Times declared that the electric car “has long been recognized as the ideal” because it “is cleaner and quieter” and “much more economical” than its gasoline-fueled cousins. But the same unreliability of electric car batteries that flummoxed Thomas Edison persists today.
Those who believe that Detroit unplugged the electric car are mistaken. Electric cars haven’t been sidelined by a cabal to sell internal combustion engines or a lack of political will, but by physics and math. Gasoline contains about 80 times as much energy, by weight, as the best lithium-ion battery. Sure, the electric motor is more efficient than the internal combustion engine, but can we depend on batteries that are notoriously finicky, short-lived and take hours to recharge? Speaking of recharging, last June, the Government Accountability Office reported that about 40 percent of consumers do not have access to an outlet near their vehicle at home. The electric car is the next big thing — and it always will be.
5. The United States lags behind other rich countries in going green.
Over the past three decades, the United States has improved its energy efficiency as much as or more than other developed countries. According to data from the Energy Information Administration, average per capita energy consumption in the United States fell by 2.5 percent from 1980 through 2006. That reduction was greater than in any other developed country except Switzerland and Denmark, and the United States achieved it without participating in the Kyoto Protocol or creating an emissions trading system like the one employed in Europe. EIA data also show that the United States has been among the best at reducing the amount of carbon dioxide emitted per $1 of GDP and the amount of energy consumed per $1 of GDP.
America’s move toward a more service-based economy that is less dependent on heavy industry and manufacturing is driving this improvement. In addition, the proliferation of computer chips in everything from automobiles to programmable thermostats is wringing more useful work out of each unit of energy consumed. The United States will continue going green by simply allowing engineers and entrepreneurs to do what they do best: make products that are faster, cheaper and more efficient than the ones they made the year before.
Robert Bryce is a senior fellow at the Manhattan Institute. His fourth book, “Power Hungry: The Myths of ‘Green’ Energy and the Real Fuels of the Future,” will be out Tuesday, April 27.
To visit the Washington Post article above go to: http://www.washingtonpost.com/wp-dyn/content/article/2010/04/23/AR2010042302220.html
This week’s blog is a re–publication of a web article by Alex Salkever which appeared on April 6, 2010, in Daily Finance, an AOL Money and Finance site. It’s an excellent followup to last week’s blog on wind turbine energy, which raised concerns as to the feasibility of its widespread use. It’s always good to have multiple sources of information when assessing the value of anything, such as when you seek a doctor’s second opinion, and this article serves that purpose. Enjoy!
Too Green, Too Soon? Renewable Power May Destabilize Electrical Grid
By Alex Salkever
Boy, that was fast. Only five years into the world’s renewable energy push, many utility companies are so concerned about grid instability that they’re saying they can’t accept any more electricity from intermittent sources of power. Translation: Solar power only runs in the day time and can’t re relied on for so called “baseload” capacity. Wind power primarily produces current at night and, likewise, can’t be relied upon for baseload capacity. Geothermal, meanwhile, is perfect for providing baseload. But geothermal projects take an excruciatingly long time to build out. And then there have been the recent spate of earthquake scares around geothermal sites.
The upshot: Utilities such as Hawaiian Electric in President Obama’s home state are voicing concerns about plans to integrate more solar and wind power into the grid until they develop methods to more effectively absorb intermittent sources of power without destabilizing the whole shebang. In Europe, Czech utility companies are concerned that “feed-in tariffs,” which require power companies to repurchase all home- and business-generated renewable power at elevated rates, might wreak havoc on the Central European grid.
This growing push-back from utilities could prove to be shock to energy project developers, lawmakers and homeowners. In the U.S., project developers and state lawmakers have assumed that the ambitious laws mandating as much as 40% of some states’ power come from renewable sources within the next few decades would ensure huge demand for green power as utilities scaled up their use of such resources from low single-digit levels. Likewise, homeowners have tended to assume that if they could put a panel on their roof (or a windmill on their property), they would be guaranteed a market for the extra power produced.
Storing Excess Power in Ice, Salt or Even … Caves?
The ability to sell back power to a utility at retail rates (meaning the rates they charge the public) is dubbed “net metering,” and many states have limitations on what percentage of total baseload power on a grid a utility must buy back. It was broadly assumed net metering would go away in hurry when the Green Revolution came of age. Now, that appears unlikely. The alleged problems with absorbing intermittent green power point to a more fundamental issue with the existing power grid — namely, that the system isn’t really ready to handle a significantly more distributed power production footprint.
One possible remedy would be for utilities to build more power storage systems, and many new forms for those are on the drawing boards. One solution could be massive battery installations from the likes of A123 Systems. Another could be a system such as that offered by Ice Energy, which uses cheap power at night to make ice, reducing the power requirements of air conditioning systems in the daytime. This effectively arbitrages the price differential between nighttime and daytime power generation — something that potentially could be a huge boon for wind power. Other, more exotic “battery” systems that have been proposed include storing power in molten salt or injecting compressed air into sealed caves, both of which create potential energy that can later be used to power electric generators.
Power storage is already being recognized as essential to new renewable energy projects. A wind farm on Maui will be the first in the country to have an added power storage component in the form of a bank of lithium-ion batteries. But most green power developers are still having trouble competing with coal and natural gas fired plants on a level playing field — even without adding in the costs of power storage. If the issues of dealing with intermittent power sources are as disruptive to grid stability as some traditional utilities are claiming, the Green Revolution may be a case of “too much, too soon” — at least until the engineers can figure out better, cheaper ways to capture sunshine and wind in a bottle.
From DailyFinance: http://srph.it/dAoxAj