Steam power energy conversion efficiency?

[NoQ]

Just noticed, searched but didn't find anything. Boilers consume 390kW. Steam engines produce 510kW. With the standard 13:10 boiler:steam engine ratio, effectively ~100% of the fuel energy consumed by boilers is turned into electricity. Even if steam engines were implemented as a perfect Carnot cycle, then for hot temperature 100C~=373K and cold temperature 15C=~288K, their energy conversion efficiency would be around (1 - (288/373)) ~= 23%. So while not being a perpetuum mobile, they're still significantly unrealistic.

I suspect this could be fixed without affecting game balance, by changing scale of fuel energy per item, and then scaling the non-boiler fuel-consuming machines accordingly.

[Yoyobuae]

Boilers consume 780kW from fuel energy but only produce 390kW thermal energy.

[NoQ]

Hmm, okay. The in-game tip says 390kW:

Screenshot

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50% is still unrealistic though^^

[torne]

Boilers have an efficiency stat that's not shown in the UI and vanilla boilers are 0.5. For some reason the UI shows the post-efficiency-multiplier value as the energy consumption when it's actually the energy production.

[Nich]

Coal plants are about 56% efficient I believe (coal -> electricty) but they use supper heated steam.

[OdinYggd]

Hmm, okay. The in-game tip says 390kW:

Screenshot

Screen Shot 2017-01-19 at 4.33.48 PM.png

50% is still unrealistic though^^

No its not.

Real life power stations operate coal fired boilers with efficiency exceeding 80% being possible.
http://www.brighthubengineering.com/pow ... fficiency/

Stoker fired and hand fired boilers have considerably less efficiency, ranging from 50%-70% typical assuming the boiler is kept clean and is fired in a manner that encourages clean combustion. That black smoke so well known to steam power? BAD! REALLY BAD! IT DOESN'T HAVE TO BE THAT WAY! Seriously, it shouldn't be that way. I've fired a steam tractor on coal before and have no trouble keeping the smoke to a minimum with black smoke almost entirely gone. Quite a bit of training material from the era of steam power remains available for viewing that describes what a fireman should look for when stoking his boiler in order to maximize fuel economy.

The engine efficiency in-game is certainly a theoretical marvel though. Even the most efficient stationary engines to be built in the days of steam power- the mighty Corliss engines, could not hope to compare to 100% efficiency. Though frictional losses ate up some, the bulk of the loss is in under-expansion of the steam and the latent heat remaining in the exhaust steam. This loss still exists in a modern power station using turbines, and a great deal of complexity is added purely to attempt to capture that energy back into the boiler for reuse. Devices such as heat recovery boilers, feedwater heaters, and condensers are commonplace.

Interestingly enough, your well-known steam locomotive had an engine efficiency to the tune of a mere 8-12%. Entirely because of mechanical limitations on how much the steam was allowed to expand before being exhausted, and because in order to generate torque for moving the train the steam would enter the cylinder at high pressure and leave it again while still at a fairly high pressure.

[NoQ]

Guys, we're derailing into boilers which was never the point :/
I was talking about steam engines.

upd: Yep, i messed up this previous message myself, sorry, it didn't make sense. The original question still stands though.

[OdinYggd]

Guys, we're derailing into boilers which was never the point :/
I was talking about steam engines.

upd: Yep, i messed up this previous message myself, sorry, it didn't make sense. The original question still stands though.

I hadn't even considered the losses of the Generator

I was only talking about the boiler's efficiency, and the engine's efficiency.

Actually surprised myself a bit with the answer. The efficiency problem is almost entirely the engine, while boiler efficiency has only really changed a little in the past 100 years despite tremendous improvements in safety and power density.

[Yoyobuae]

Actually surprised myself a bit with the answer. The efficiency problem is almost entirely the engine, while boiler efficiency has only really changed a little in the past 100 years despite tremendous improvements in safety and power density.

Well, boiler just converts chemical energy to heat (ie. combustion), then transfer that heat to water/steam. Only inefficiencies would be in heat escaping, but it's easy enough to get good thermal isolation.

Heat engines on the other hand...

[ssilk]

Hm.
The right solution might be that boilers produce energy with nearly about 100% efficiency, but steam engine consumes it with efficiency of 50%. And changing according values. That wouldn't affect the game too much.

But in the end it's just like if I take half of the recipe and bake a half cake or if I bake a cake and cut into half.

[Nich]

HAHAHAHAHAHAH NO.... basic Boilers are about 10-15% efficient. A 100% efficient boiler is impossible due to enthalpy or entropy (cant remember which). An ideal boiler would have the exhaust gas = the input water temp and exit water temp = exhaust gas input temp, but even then energy is lost to the laws of thermodynamics. The fact that the water exit temp is 100 C and the input gas temp is 2000 C screams inefficiency. If you super heated the steam to 1500ish or so then we could talk about efficiency.

[aober93]

HAHAHAHAHAHAH NO.... basic Boilers are about 10-15% efficient. A 100% efficient boiler is impossible due to enthalpy or entropy (cant remember which). An ideal boiler would have the exhaust gas = the input water temp and exit water temp = exhaust gas input temp, but even then energy is lost to the laws of thermodynamics. The fact that the water exit temp is 100 C and the input gas temp is 2000 C screams inefficiency. If you super heated the steam to 1500ish or so then we could talk about efficiency.

Pls read https://wiki.factorio.com/Boiler

[OdinYggd]

HAHAHAHAHAHAH NO.... basic Boilers are about 10-15% efficient. A 100% efficient boiler is impossible due to enthalpy or entropy (cant remember which). An ideal boiler would have the exhaust gas = the input water temp and exit water temp = exhaust gas input temp, but even then energy is lost to the laws of thermodynamics. The fact that the water exit temp is 100 C and the input gas temp is 2000 C screams inefficiency. If you super heated the steam to 1500ish or so then we could talk about efficiency.

I think you need to study up a little more on thermodynamics and how they apply to boilers.

It is plenty possible to achieve 80% efficiency just in good design and operation. At 80% efficiency, your biggest losses come from combustion efficiency followed by residual heat remaining in the exhaust gases- as it is very much true that the exhaust cannot be colder than the outlet temperature of the steam.

Digging into this a little I actually was surprised myself to learn that all along the boiler efficiency wasn't really that bad and the bulk of steam power's inefficiency came from the engine proper.

Effectively, the engine cannot expand the steam fully to atmospheric pressure. Mechanical practicalities, this is sort of unavoidable unless you use a large compound engine arrangement to expand it in multiple stages. There is also latent heat being wasted- a large portion of the energy wasted at the engine exhaust is in the energy spent just boiling the water. Very few practical means of recovering that energy exist, the bulk of them focusing on using that remaining heat to pre-heat the incoming water.

Of course a stoker-fired boiler probably would not reach 80% boiler efficiency, as this requires modern combustion equipment such as gas oil or pulverized coal firing to ensure constant clean combustion. Typically stokers operate from 50-70% efficient depending on the design and the skill of the fireman. So Factorio's 50% efficient boilers aren't as unrealistic as you'd think.


But the engine efficiency, what a problem.

The typical non-compound steam engine, using valve arrangements such as the Stephenson or Walschaerts would vary from 8-12% efficient. This was due to the fairly long cutoff period of the valve needed to ensure reliable torque, and the limited range of cutoff adjustment these valve mechanisms could provide. In addition, a great deal of heat was lost to the engine's porting- which was alternately heated then cooled by steam entering and leaving through the same passage. The characteristic bark of a steam locomotive's stack comes from the engine not expanding the steam fully in the cylinder, wasting energy in both steam pressure and latent heat. At least using said exhaust to induce boiler draft helps the engine to perform at its best by improving combustion in the boiler.

Corliss valve engines, which were common for stationary arrangements in factories, could reach 15% efficient before compounding. Because the steam did not leave through the same ports it entered, less heat was given up to the iron. Rather than being stuck with a fairly long cutoff and controlling the engine by changing its pressure, the Corliss valve would control its speed entirely by changing the cutoff. A short cutoff and high steam pressure would allow the engine to work on expansion, maximizing fuel economy. Even then a compound engine was required to expand the steam all the way, and there was still the latent heat being given up at the exhaust.


Factorio implements a somewhat realistic stoker boiler efficiency at 50%, but a fully unrealistic engine efficiency. Since the geometry of the engines does suggest a multi-cylinder arrangement, it is quite possible that the Factorio steam engine is intended to imitate a compound steam as used in stationary applications for its efficiency. Like so, if we assume that it is a double compound corliss valved engine perhaps we could have hit 20-30% efficient with it.

But to actually implement realistic efficiency in Factorio's engines would really mess with people's heads. Plenty possible sure- but from a gameplay point is it really necessary? We might as well re-scale the entire power generation scheme at that point to implement realistic efficiency while maintaining comparable output power densities. And you are going to need a LOT more coal.

Oh and rightly, if we wanted to make Factorio's steam engines really really efficient, we need a condenser. That way exhaust steam becomes still-hot water which can be reinjected into the boiler to become steam again, recovering some of the latent and sensible heat remaining in the exhaust.