Triple Expansion Steam Engine

Posted by PITHOCRATES - November 6th, 2013

Technology 101

Pressure and Temperature have a Direct Relationship while Pressure and Volume have an Inverse Relationship

For much of human existence we used our own muscles to push things.  Which limited the work we could do.  Early river transport were barges of low capacity that we pushed along with a pole.  We’d stand on the barge and place the pole into the water and into the river bed.  Then push the pole away from us.  To get the boat to move in the other direction.

In more developed areas we may have cleared a pathway alongside the river.  And pulled our boats with animal power.  Of course, none of this helped us cross an ocean.  Only sail did that.  Where we captured the wind in sails.  And the wind pushed our ships across the oceans.  Then we started to understand our environment more.  And noticed relationships between physical properties.  Such as the ideal gas law equation:

Pressure = (n X R X Temperature)/Volume

In a gas pressure is determined my multiplying together ‘n’ and ‘R’ and temperature then dividing this number by volume.  Where ‘n’ is the amount of moles of the gas.  And ‘R’ is the constant 8.3145 m3·Pa/(mol·K).  For our purposes you can ignore ‘n’ and ‘R’.  It’s the relationship between pressure, temperature and volume that we want to focus on.  Which we can see in the ideal gas law equation.  Pressure and temperature have a direct relationship.  That is, if one rises so does the other.  If one falls so does the other.  While pressure and volume have an inverse relationship.  If volume decreases pressure increases.  If volume increases pressure decreases.  These properties prove to be very useful.  Especially if we want to push things.

Once the Piston traveled its Full Stroke on a Locomotive the Spent Steam vented into the Atmosphere 

So what gas can produce a high pressure that we can make relatively easy?  Steam.  Which we can make simply by boiling water.  And if we can harness this steam in a fixed vessel the pressure will rise to become strong enough to push things for us.  Operating a boiler was a risky profession, though.  As a lot of boiler operators died when the steam they were producing rose beyond safe levels.  Causing the boiler to explode like a bomb.

Early locomotives would burn coal or wood to boil water into steam.  The steam pressure was so great that it would push a piston while at the same time moving a connecting rod connected to the locomotive’s wheel.  Once the piston traveled its full stroke the spent steam vented into the atmosphere.  Allowing the pressure of that steam to dissipate safely into the air.  Of course doing this required the locomotive to stop at water towers along the way to keep taking on fresh water to boil into steam. 

Not all steam engines vented their used steam (after it expanded and gave up its energy) into the atmosphere.  Most condensed the low-pressure, low-temperature steam back into water.  Piping it (i.e., the condensate) back to the boiler to boil again into steam.  By recycling the used steam back into water eliminated the need to have water available to feed into the boiler.  Reducing non-revenue weight in steam ships.  And making more room available for fuel to travel greater distances.  Or to carry more revenue-producing cargo.

The Triple Expansion Steam Engine reduced the Expansion and Temperature Drop in each Cylinder

Pressure pushes the pistons in the steam engine.  And by the ideal gas law equation we see that the higher the temperature the higher the pressure.  As well as the corollary.  The lower the temperature the lower the pressure.  And one other thing.  As the volume increases the temperature falls.  So as the pressure in the steam pushes the piston the volume inside the cylinder increases.  Which lowers the temperature of the steam.  And the temperature of the piston and cylinder walls.  So when fresh steam from the boiler flows into this cylinder the cooler temperature of the piston and cylinder walls will cool the temperature of the steam.  Condensing some of it.  Reducing the pressure of the steam.  Which will push the piston with less force.  Reducing the efficiency of the engine.

There was a way to improve the efficiency of the steam engine.  By reducing the temperature drop during expansion (i.e., when it moves the piston).  They did this by raising the temperature of the steam.  And breaking down the expansion phase into multiple parts.  Such as in the triple expansion steam engine.  Where steam from the boiler entered the first cylinder.  Which is the smallest cylinder.  After it pushed the piston the spent steam still had a lot of energy in it looking to expand further.  Which it did in the second cylinder.  As the exhaust port of the first cylinder is piped into the intake port of the second cylinder.

The second cylinder is bigger than the first cylinder.  For the steam entering this cylinder is a lower-pressure and lower-temperature steam than that entering the first cylinder.  And needs a larger area to push against to match the down-stroke force on the first piston.  After it pushes this piston there is still energy left in that steam looking to expand.  Which it did in the third and largest cylinder.  After it pushed the third piston this low-pressure and low-temperature steam flowed into the condenser.  Where cooling removed what energy (i.e., temperature above the boiling point of water) was left in it.  Turning it back into water again.  Which was then pumped back to the boiler.  To be boiled into steam again.

By restricting the amount of expansion in each cylinder the triple expansion steam engine reduced the amount the temperature fell in each cylinder.  Allowing more of the heat go into pushing the piston.  And less of it go into raising the temperature of the piston and cylinder walls.  Greatly increasing the efficiency of the engine.  Making it the dominant maritime engine during the era of steam.

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Neutrons, Electrons, Electric Current, Nuclear Power, Nuclear Chain Reaction, Residual Decay Heat and Pressurized Water Reactor

Posted by PITHOCRATES - July 18th, 2012

Technology 101

We create about Half of our Electric Power by Burning Coal to Boil Water into Steam

An atom consists of a nucleus made up of protons and neutrons.  And electrons orbiting around the nucleus.  Protons have a positive charge.  Electrons have a negative charge.  Neutrons have a neutral charge.  In chemistry and electricity the electrons are key.  When different atoms come together they form chemical bonds.  By sharing some of those electrons orbiting their nuclei.  In metals free electrons roam around the metal lattice of the crystalline solid they’re in.  If we apply a voltage across this metal these free electrons begin to flow.  Creating an electric current.  The greater the voltage the greater the current.  And the greater the work it can do.  It can power a television set.  Keep your food from spoiling in a refrigerator.  Even make your summers comfortable by running your air conditioner. 

We use electric power to do work for us.  Power is the product of voltage and current.  The higher each is the more work this power can do for us.  In a direct current (DC) system the free electrons have to make a complete path from the power source (an electric generator) through the wiring to the work load and back again to the power source.  But generating the power at the voltage of the workload required high currents.  Thick wires.  And a lot of power plants because you could only make wires so thick before they were too heavy to work with.  Alternating current (AC) solved this problem.  By using transformers at each end of the distribution path to step up and then step down the voltage.  Allowing us to transmit lower currents at higher voltages which required thinner wires.  And AC didn’t need to return to the power plant.  It was more like a steam locomotive that converted the back and forth motion of the steam engine into rotational power.  AC power plants generated a back and forth current in the wires.  And electrical loads are able to take this back and forth motion and convert it into useful electrical power.

Even though AC power allows us to transmit lower currents we still need to move a lot of these free electrons.  And we do this with massive electric generators.  Where another power source spins these generators.  This generator spins an electric field through another set of windings to induce an electrical current.  Sort of how transformers work.  This electrical current goes out to the switchyard.  And on to our homes.  Simple, really.  The difficult part is creating that rotational motion to spin the generator.  We create about half of our electric power by burning coal to boil water into steam.  This steam expands against the vanes of a steam turbine causing it to spin.  But that’s not the only heat engine we use to make steam.

To Shut Down a Nuclear Reactor takes the Full Insertion of the Control Rods and Continuously Pumping Cooling Water through the Core

We use another part of the atom to generate heat.  Which boils water into steam.  That we use to spin a steam turbine.  The neutron.  Nuclear power plants use uranium for fuel.  It is the heaviest naturally occurring element.  The density of its nucleus determines an element’s weight.  The more protons and neutrons in it the heavier it is.  Without getting into too much physics we basically get heat when we bombard these heavy nuclei with neutrons.  When a nucleus splits apart it throws off a few spare neutrons which can split other nuclei.  And so on.  Creating a nuclear chain reaction.  It’s the actual splitting of these nuclei that generates heat.  And from there it’s just boiling water into steam to spin a steam turbine coupled to a generator.

Continuous atom splitting creates a lot of heat.  So much heat that it can melt down the core.  Which would be a bad thing.  So we move an array of neutron absorbers into and out of the core to control this chain reaction.  So in the core of a nuclear reactor we have uranium fuel pellets loaded into vertical fuel rods.  There are spaces in between these fuel rods for control rods (made out of carbon or boron) to move in and out of the core.  When we fully insert the control rods they will shut down the nuclear chain reaction by absorbing those free neutrons.  However there is a lot of residual heat (i.e., decay heat) that can cause the core to melt if we don’t remove it with continuous cooling water pumped through the core. 

So to shut down a nuclear reactor it takes both the full insertion of the control rods.  And continuously pumping cooling water through the core for days after shutting down the reactor.  Even spent fuel rods have to spend a decade or two in a spent fuel pool.  To dissipate this residual decay heat.  (This residual decay heat caused the trouble at Fukushima in Japan after their earthquake/tsunami.  The reactor survived the earthquake.  But the tsunami submerged the electrical gear that powered the cooling pumps.  Preventing them from cooling the core to remove this residual decay heat.  Leading to the partial core meltdowns.)

Nuclear Power is one of the most Reliable and Cleanest Sources of Power that leaves no Carbon Footprint

There is more than one nuclear reactor design.  But more than half in the U.S. are the Pressurized Water Reactor (PWR) type.  It’s also the kind they had at Three Mile Island.  Which saw America’s worst nuclear accident.  The PWR is the classic nuclear power plant that all people fear.  The tall hyperboloid cooling towers.  And the short cylindrical containment buildings with a dome on top housing the reactor.  The reactor itself is inside a humongous steel pressure vessel.  For pressure is key in a PWR.  The cooling water of the reactor is under very high pressure.  Keeping the water from boiling even though it reaches temperatures as high as 600 degrees Fahrenheit (water boils into steam at 212 degrees Fahrenheit under normal atmospheric pressure).  This is the primary loop.

The superheated water in the primary loop then flows through a heat exchanger.  Where it heats water in another loop of pumped water.  The secondary loop.  The hot water in the primary loop boils the water in the secondary loop into steam.  As it boils the water in the secondary loop it loses some of its own heat.  So it can return to the reactor core to remove more of its heat.  To prevent it from overheating.  The steam in the secondary loop drives the steam turbine.  The steam then flows from the turbine to a condenser and changes back into water.  The cooling water for the condenser is what goes to the cooling tower.  Making those scary looking cooling towers the least dangerous part of the power plant.

The PWR is one of the safest nuclear reactors.  The primary cooling loop is the only loop exposed to radiation.  The problem at Three Mile Island resulted from a stuck pressure relief valve.  That opened to vent high pressure during an event that caused the control rods to drop in and shut down the nuclear chain reaction.  So while they stopped the chain reaction the residual decay heat continued to cook the core.  But there was no feedback from the valve to the control room showing that it was still open after everyone thought it was closed.  So as cooling water entered the core it just boiled away.  Uncovering the core.  And causing part of it to melt.  Other problems with valves and gages did not identify this problem.  As some of the fuel melted it reacted with the steam producing hydrogen gas.  Fearing an explosion they vented some of this radioactive gas into the atmosphere.  But not much.  But it was enough to effectively shut down the U.S. nuclear power industry. 

A pity, really.  For if we had pursued nuclear power these past decades we may have found ways to make it safer.  Neither wind power nor solar power is a practical substitution for fossil-fuel generated electricity.  Yet we pour billions into these industries in hopes that we can advance them to a point when they can be more than a novelty.  But we have turned away from one of the most reliable and cleanest sources of power (when things work properly).  Using neutrons to move electrons.  Taking complete control of the atom to our make our lives better.  And to keep our environment clean.  And cool.  For there is no carbon footprint with nuclear power.

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In the Great Electricity-Generating Race it’s Coal by a Nose over Natural Gas with Solar Power Still in the Barn

Posted by PITHOCRATES - July 15th, 2012

Week in Review

Natural gas is running to catch up and pass coal in the great electricity-generating race.  While solar power is struggling to win a participation ribbon (see The Huge Shift in Our Energy System That’s Happening Right Now in 1 Chart by Alexis Madrigal posted 7/13/2012 on The Atlantic).

As long as Americans have made electricity, they’ve gotten more of it from coal than from any fuel. While petroleum and natural gas have played huge roles in our energy system, coal’s been responsible for more than 65 percent of the fossil-fuel electricity we’ve generated for most of the last 50 years. (And for big chunks of the 20th century, we made half of all the electricity in this country by burning coal.)

But natural gas is in the process of overtaking coal as the top fuel in America — and fast.

There’s a reason coal dominated for so long.  And still does.  For awhile at least.  Generating electricity from coal is more efficient than generating electricity from natural gas.  Coal plants are heat engines.  They produce heat to boil water.  Natural gas plants are more like the jet engines on an airplane.  Where we use the products of combustion, expanding gases, to spin a turbine.  We don’t use it to boil water.  So we waste much of the heat generated from combustion.  Resulting in lower efficiencies than a coal-fired plant.

However, thanks to hydraulic fracturing (aka fracking) the supply of natural gas is exploding (pardon the pun).  Causing prices to tumble.  And because natural gas is now so plentiful and so cheap the poorer efficiencies are less important.  Economically speaking.  So power companies are expanding their natural gas turbines.  Which helps them avoid headaches with the environmentalists.  For natural gas burns cleaner than coal.  So for the foreseeable future it will be roughly 50-50 between coal and natural gas.  But what about renewable energy you ask?  Like solar power?  When will solar power provide 50% of our electricity needs?

Each percentage point of share is roughly 40 million megawatt hours a year. By comparison, all solar projects in 2010 (the last year stats were available) produced 1.3 million megawatt hours.

About 40 million megawatt hours a year per percentage point?  Looking at the chart it looks like coal is currently at 52%.  And natural gas is at 45%.  Or thereabouts.   If you do the math that’s about 3,880 megawatt hours between the two of them.  Or approximately 96.97% of all fossil-fuel generated electricity.  While the 1.3 million megawatt hours of solar power provides about 0.032% of our fossil-fuel generated electricity.  So when will solar power provide 50% of our electricity needs?  Probably never.

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Windmills, Waterwheels, Steam Engine, Electric Power, Coal, Heat Engine, Steam Turbine, Generator and Coal-Fired Power Plant

Posted by PITHOCRATES - July 11th, 2012

Technology 101

By burning Coal to Boil Water into Steam to Move a Piston we could Build a Factory Anywhere

We created advanced civilization by harnessing energy.  And converting this energy into working power.  Our first efforts were biological.  Feeding and caring for large animals made these animals strong.  Their physiology converted food and water into strong muscles and bones.  Allowing them to pull heavy loads.  From plowing.  To heavy transportation.  To use in construction.  Of course the problem with animals is that they’re living things.  They eat and drink.  And poop and pee.  Causing a lot of pollution in and around people.  Inviting disease.

As civilization advanced we needed more energy.  And we found it in wind and water.  We built windmills and waterwheels.  To capture the energy in moving wind and moving water.  And converted this into rotational motion.  Giving us a cleaner power source than working animals.  Power that didn’t have to rest or eat.  And could run indefinitely as long as the wind blew and the water flowed.  Using belts, pulleys, cogs and gears we transferred this rotational power to a variety of work stations.  Of course the problem with wind and water is that you needed to be near wind and water.  Wind was more widely available but less reliable.  Water was more reliable but less widely available.  Each had their limitations.

The steam engine changed everything.  By burning a fuel (typically coal) to boil water into steam to move a piston we could build a factory anywhere.  Away from rivers.  And even in areas that had little wind.  The reciprocating motion of the piston turned a wheel to convert it into rotational motion.  Using belts, pulleys, cogs and gears we transferred this rotational power to a variety of work stations.  This carried us through the Industrial Revolution.  Then we came up with something better.  The electric motor.  Instead of transferring rotational motion to a workstation we put an electric motor at the work station.  And powered it with electricity.  Using electric power to produce rotational motion at the workstation.  Electricity and the electric motor changed the world just as the steam engine had changed the world earlier.  Today the two have come together.

You can tell a Power Plant uses a Scrubber by the White Steam puffing out of a Smokestack

Coal has a lot of energy in it.  When we burn it this energy is transformed into heat.  Hot heat.  For coal burns hot.  The modern coal-fired power plant is a heat engine.  It uses the heat from burning coal to boil water into steam.  And as steam expands it creates great pressure.  We can use this pressure to push a piston.  Or turn a steam turbine.  A rotational device with fins.  As the steam pushes on these fins the turbine turns.  Converting the high pressure of the steam into rotational motion.  We then couple this rotational motion of the steam turbine to a generator.  Which spins the generator to produce electricity.

Coal-fired power plants are hungry plants.  A large plant burns about 1,000 tons of coal an hour.  Or about 30,000 pounds a minute.  That’s a lot of coal.  We typically deliver coal to these plants in bulk.  Via Great Lakes freighters.  River barges.  Or unit trains.  Trains made up of nothing but coal hopper cars.  These feed coal to the power plants.  They unload and conveyor systems take this coal and create big piles.  You can see conveyors rising up from these piles of coal.  These conveyors transport this coal to silos or bunkers.  Further conveyor systems transfer the coal from these silos to the plant.  Where it is smashed and pulverized into a dust.  And then it’s blown into the firebox, mixed with hot air and ignited.  Creating enormous amounts of heat to boil an enormous amount of water.  Creating the steam to turn a turbine.

Of course, with combustion there are products left over.  Sulfur impurities in the coal create sulfur dioxide.  And as the coal burns it leaves behind ash.  A heavy ash that falls to the bottom of the firebox.  Bottom ash.  And a lighter ash that is swept away with the flue gases.  Fly ash.  Filters catch the fly ash.  And scrubbers use chemistry to remove the sulfur dioxide from the flue gases.  By using a lime slurry.  The flue gases rise through a falling mist of lime slurry.  They chemically react and create calcium sulfate.  Or Gypsum.  The same stuff we use to make drywall out of.  You can tell a power plant uses a scrubby by the white steam puffing out of a smokestack.  If you see great plumes puffing out of a smokestack there’s little pollution entering the atmosphere.  A smokestack that isn’t puffing out a plume of white steam is probably spewing pollution into the atmosphere.

Coal is a Highly Concentrated Source of Energy making Coal King when it comes to Electricity

When the steam exits the turbines it enters a condenser.  Which cools it and lowers its temperature and pressure.  Turning the steam back into water.  It’s treated then sent back to the boiler.  However, getting the water back into the boiler is easier said than done.  The coal heats the water into a high pressure steam.  So high that it’s hard for anything to enter the boiler.  So this requires a very powerful pump to overcome that pressure.  In fact, this pump is the biggest pump in the plant.  Powered by electric power.  Or steam.  Sucking some 2-3 percent of the power the plant generates.

Coupled to the steam turbine is a power plant’s purpose.  Generators.  Everything in a power plant serves but one purpose.  To spin these generators.  And when they spin they generate a lot of power.  Producing some 40,000 amps at 10,000 to 30,000 volts at a typical large plant.  Multiplying current by power and you get some 1,200 MW of power.  Which can feed a lot of homes with 100 amp, 240 volt services.  Some 50,000 with every last amp used in their service.  Or more than twice this number under typical loads.  Add a few boilers (and turbine and generator sets) and one plant can power every house and business across large geographic areas in a state.  Something no solar array or wind farm can do.  Which is why about half of all electricity produced in the U.S. is generated by coal-fired power plants.

Coal is a highly concentrated source of energy.  A little of it goes a long way.  And a lot of it produces enormous amounts of electric power.  Making coal king when it comes to electricity.  There is nothing that can match the economics and the logistics of using coal.  Thanks to fracking, though, natural gas is coming down in price.  It can burn cleaner.  And perhaps its greatest advantage over coal is that we can bring a gas-fired plant on line in a fraction amount of the time it takes to bring a coal-fired plant on line.  For coal-fired plants are heat engines that boil water into steam to spin turbines.  Whereas gas-fired plants use the products of combustion to spin their turbines.  Utilities typically use a combination of coal-fired and gas-fired plants.  The coal-fired plants run all of the time and provide the base load.  When demand peaks (when everyone turns on their air conditioners in the evening) the gas-fired plants are brought on line to meet this peak demand.

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