Efficiency

[Scotty]

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.


Natural Gas Fired Power Plants.
Natural Gas fired (including LNG fired) power plants account for almost 20 % of the world’s electricity generation. These power plants use Gas Turbines or Gas Turbine based combined cycles. Gas turbines in the simple cycle mode, only Gas turbines running, have an efficiency of 32 % to 38 %. The most important parameter that dictates the efficiency is the maximum gas temperature possible. The latest Gas Turbines with technological advances in materials and aerodynamics has efficiencies upto 38 %. In the combined cycle mode, the new "H class" Gas turbines with a triple pressure HRSG and steam turbine can run at 60 % efficiency at ISO conditions. This is by far the highest efficiency in the thermal power field.

http://www.brighthubengineering.com/pow ... er-plants/

Scotty

[Lopez Mike]

And here I am filled with dreams of boosting my numbers from 2% up to maybe 2 1/2%.

On the other hand, I'm not burning coal in China and raining mercury down on the world. The mercury levels in a lot of Tuna are really high.

[Scotty]

2.5 % ???

Single expansion (with feedwater heater) has appr. 7 %, triple expansion should be able to top 15 %.
(you should have a reasonable good boiler, of course).

In comparison to IC you have a bonus of 1.45 - 80 % propeller efficiency against 55 %.

So no reason to despair.
We are in the kilowatt-range - not gigawatt.

Scotty

[Lopez Mike]

I think your numbers are high. The last of the steam locos were talked up as having numbers more like 5%. This on a 4500 hp power plant. A few compounds claimed 8-12%. Even with really good boiler insulation and an insulated steam pipe, what makes it into my cylinder might best be described as a humid day in Atlanta.

As far as compounding, I worked on a 7.5" scale compound locomotive. We had a gauge on the receiver pipe and even on hard climbs we never saw any pressure. The low pressure cylinders were going along for the ride. Little engines like ours might better be describe as complicated condensers.

It's a size thing. The ration of volume to surface area is horrible in my little engine. Like a mouse compared to an elephant. 'Gots to eat a lot!'

I don't despair. But it doesn't escape my notice that I throw a lot of wood into that hole in an afternoon. Lately I have taken to doing a Tom Sawyer thing and making the passengers run the boat. I just sit back and give advice. "Work harder!"

[Scotty]

Hallo Mike,

I don't think the numbers are high, they are for well engineered plants, but realistic.

Let's make a calculation:

30 kg/hr of good hardwood at a LHV of 14 000 kJ/kg --> 420 000 kJ/hr or 116,7 kJ/s or 116,7 kW = INPUT
Sisson Triple at full load: 25 PSe = 18,4 kW = OUTPUT

18,4/116,7 = 15,8 %


Scotty

[Lopez Mike]

Sadly, I burn somewhat less exalted fuel. Lately I've had a run of cedar lumber. Hot but the BTU per cubic foot is terrible. A couple of cubic feet per mile is typical. I dunno about weight. Volume is what counts in my little scow. Sometimes I burn old pallets. Often they are not too bad. Sometimes I burn drift wood and stuff out of a pasture. Perhaps I get some heating value from the bugs and worms. I am only slightly better off than Mr. Allnut harvesting wood from the jungle.

All of that doesn't affect my plant efficiency, however.

The power plant is a 3 x 4 simple with inside admission piston valve. The engine lagging is just mahogany. No real insulation. There is no feedwater heater or economizer. The condenser is oversized at present so the hot well is warm at best. I would do handsprings (within the limits of a 24' boat!) if I thought I was getting 4%. Highly engineered it is not. Reliable, it is. And stunningly simple. I recently turned the operation of the plant over to an eight year old young woman after fifteen minutes of instruction. Discreetly supervised, of course.

I will probably add both an economizer and a feedwater heater before next season and cut down on the area of my condenser. But I get all of my wood for free and am not oppressed by the fuel consumption. I strongly doubt that I will ever see much over 5%.

Heading out just now to haul people at a Tug Boat racing event. In 2 1/2 days of having great fun I will burn an amazing pile of wood. You should see the looks on these people's faces. I suspect that it is the first non-synthetic experience they have had in ages.

[Scotty]

Hallo Mike,

everybody as he likes it.

I just wanted to show you that the numbers are correct.


Scotty