Posts Tagged ‘utility power plant’

Coal Power Plant Fundamentals – Combustion

Sunday, February 13th, 2011
     Ever have a small child threaten to hold his breath until he passes out and he actually managed to do it?  It’s not that unusual.  And if his body were prevented from acting in self preservation, that is, taking in breaths while he was unconscious, leading to his eventual awakening, he would die.  While the human body can survive about a month without eating and three days without water, under normal conditions it can survive only a matter of minutes without breathing.  Power plants, too, require oxygen to function, and this process is called combustion.

      Human lungs, along with the diaphragm which works to expand and release the lung cavities, enable our bodies to breathe in air, then expel the waste product, carbon dioxide.  Oxygen is needed to metabolize, that is burn, our food, enabling the food cells’ energy to be absorbed by our bodies and converted into energy to live.  Like us, coal power plants need to breathe in oxygen in order to convert coal’s latent energy into a usable form.

     Previously we learned how coal is fed to a coal mill where it is pulverized into a fine powder.  This powder is then sucked out of the mill by the exhauster and blown through a serpentine path of pipes leading to the burners on the furnace.  The burners will then act upon the coal, combining it with the oxygen in our atmosphere to create a chemical reaction capable of releasing coal’s energy in the form of heat.  All this activity looks to a bystander like a massive, sustained fire in the furnace.  See Figure l.   

Figure 1 – Coal Power Plant Combustion

     The boiler is contained within the furnace and is situated so it is exposed to fire from the combustion process.  Heat energy from the fire transfers into the water in the boiler, much like when you boil water for tea in a kettle on your stovetop.  If you’ve ever boiled water, you know that once it gets hot enough it will turn into steam, and the same for our furnace boiler.  The steam emitting from the boiler will cause a turbine-generator to spin, and the end result will be electricity for our use.  In the simple diagram of Figure 1,  waste products from the combustion process, like carbon dioxide, go up the smoke stack and are released into the atmosphere.  Incidentally, this is the same type of carbon dioxide that we exhale from our bodies when we breathe.  

     Please keep in mind that Figure 1 is a very simplified diagram.  In reality waste products leaving the furnace go through various pollution control devices where most pollutants are removed before they reach the smoke stack.  These details, and many more, are the type of information that would be covered during my training seminar, Coal Power Plant Fundamentals.    

     Next time we’ll learn how the heat energy in steam is converted into mechanical energy capable of spinning a turbine generator to make electricity.



Fossil Fuel, From Friend to Foe

Sunday, June 27th, 2010

     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.