[Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Greetings, all!

Okay, the official refinery rates are weird, producing (at SM+5) a half-tonne of rocket fuel per hour, which is way more than is required to run the refinery using same fuel.

But! While this used to be a fuzzy area, I'm planning to officially declare that my setting has a common practice of synthesising a fuel from ubiquitous components when there's abundant energy.

Perhaps the simplest way to make sure it doesn't run out of control is to see how much energy can be gained from the given amount of fuel, and declare that it takes twice as much energy to synthesise it. That means that if a fuel cell (1 Power Point) can work for 24 hours on a tank of fuel, then it takes 2 Power Points to produce one fuel tank of said fuel (over same duration; 1 PP if working over 48 hours etc.). But perhaps there is some reason these numbers don't make sense.

My intent is to make sure that fuels are an option, not a must-have, when pitted against batteries. (TL6+3^ batteries; can provide up to 2 Power Points over up to 6 hours, and can recharge from any power source, with no spontaneous discharge, no risk of explosion, and ability to be safely recharged thousands of times at the very least.)
At those numbers, IMO, fuel-powered (motorised) yachts still make more economic sense than battery-powered ones (because you need more endurance), but ornithopters and semi-reactionless* (0.5G per PP) aircraft can easily get by on batteries, since those are easy to recharge and rarely, if ever, need to stay in the air for more than 6 hours at a time.

So, cost of fuel seems like a prime balancing factor. Making fuel requires a refinery module, a power source, access to raw materials (cheap, you still need to have them right here now), and of course a place to store fuel and refuel the clients. Logistically, fuelwork seems pretty complicated compared to essentially reselling electricity.
So, what are reasonable price ranges for a fuel that is synthesised from ubiquitous components in a manner described above? How are they likely to compare to prices of raw power?

Another issue is the balance of jets against MPDs. But since a single fueltank is enough for 1 hour of jet flight, while a single battery can power two MPDs for 3 hours, things seem okay. (Jets are still better in terms of maximum acceleration per unit mass.)

Thanks in advance!

* == Mono-Polarised Displacer. Essentially, a more expensive variant of a unidirectional magnetic planetary drive, but with no side effects whatsoever. Also works in space, somewhat.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Why do you need to have the fuel use up more energy during synthesis than it produces? Even some energy-intensive processes, like thermal depolymerization (which turns biomatter into oil), are a net producer of energy (and are typically powered by the same stuff they create). The reason it doesn't violate any laws of thermodynamics is that using that fuel doesn't produce products that can then be re-ran through the system again.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

I'm assuming that a there's some waste of energy in the process.

O2 + 2×H2 -> 2×H2O + energy
energy + 2×H2O -> 2×H2 + O2

Isn't it?

(Note that I am postulating the use of inert, ubiquitous components, not something that already stores a significant amount of chemical energy. A typical space-operatic example would be mining ice asteroids and turning them into rocket fuel.)

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

The problem isn't in how much per hour is processed, but in how much is actually produced (the ratio of end product vs raw materials). The rate for processing is for the raw material and doesn't mean that you have that same amount of usable fuel after processing.

Consider the Titanic Gas Mining Platform in Spaceships 6. At TL 10, it processes 30,000 tons of atmosphere per hour to result with 5.5 tons of fuel per day. That's 6 refineries (+13 SM) processing enough fuel in one day to fill one +6 SM fuel tank (with a half a ton excess). A +13 SM MHD Turbine (TL 10) would provide 2 PP energy with an internal tank size of 5000 tons and run for 12 hours. The refinery would not be able to process enough fuel to sustain its own operations. It's a good thing the Titan uses fusion reactors to provide energy.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Hasn't it been said that the stats for chemical power plants are unrealistically good in order to make them useful?
Makes no sense when your refinery is, for instance, electrolyzing water. Not all 'refining' is extracting a trace component.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

I think this is the core question. Is the refinery taking complex, energy-rich hydrocarbons and processing them into a usable form? Or is it doing the more energy-intensive task of extracting Hydrogen from more complex molecules? The former requires specific chemical inputs that won't be available on all worlds, the latter consumes more energy than it produces. Spaceship's description of the Refinery implies the latter, but the stats it gives indicate the former.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

It's not a question, the answer is that the Refinery section covers both of those and a number of other material-processing roles besides.

Giving all those things the same stats may be not entirely appropriate, of course.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Generally speaking, a refinery that works on cheap, common input should produce a relatively fixed number of $/hr, not any particular volume, because the cost of fuel is basically (cost of raw materials) + (cost to refine the raw materials) + (cost to transport the raw materials or finished fuel). This doesn't work very well where your input material is high value or very unevenly distributed, since the first and third terms become substantial at that point, but it's good for things you can get by refining water.

In the end, a refinery is just a special case of a factory.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Raw Materials: Water costs, ah ... Spaceships says it costs G$20 per ton.

Refine Costs: (power plant module + refinery module) * 1.5 (upkeep, maintenance, staffing and operation assumption; feel free to adjust) / 50 (years) / 365 (days) / (24 hours) = cost to refine per hour.
Assuming a TL9 fusion reactor module from Spaceships 1.

Transport Costs: Um ...

Total:
10 + (330k * 1.5 / 50 / 365 / 24) + X = G$1.13 per 0.5 tons of fuel, plus transportation costs.

However, this assumes it is producing "rocket fuel (liquid hydrogen / oxygen)", which Spaceships prices at G$800 per ton. That is quite a bit of transportation cost! Heh. (G$398.87 per half-ton.)

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

This is called 'spaceships economics is broken'. Which isn't really news. Though I would divide by 10 years, not 50.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Yeah, I'm not worried so much about getting stats that provide an accurate economic model, as getting stats that don't blatantly break the laws of physics.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

This is why I'm asking about reasonable numbers. I think my 50% efficiency WMG is too crude.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

I was only using an example as given to illustrate that the discussion should be more on the efficiency of the refinery and the lack of information on the ratio of raw materials to processed goods for the various fuels. Even electrolyzing water will have some loss going from water to hydrogen and oxygen.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

Ah. In that case, I would suggest utterly discarding the spaceships information and use real-world stuff.

If you insist on using Spaceships,

Given that a refinery module in a SM+5 spaceship is rated at 0.5 tons of fuel produced per hour and that this costs the spaceship 0.5 tons of water and 1 power point allocation for that hour and that a mhd turbine SM+5 module runs for six hours on internal fuel or twenty-four hours from a fuel tank and that it provides two power points when running and that a fuel tank sm+5 ship module holds 1.5 tons of fuel ...

So it produces 48 pp-hours from 3 pp-hours, given 1.5 tons water as an input. Erm.

3 pp-hours of input should produce between 1.5 pp-hours of output at 50% efficiency. So the new time-per-tank should change from 24 hours to 40 minutes assuming you keep everything else the same.

... this doesn't look very competitive with the batteries.

Change the efficiency? Even at 100% efficiency, you shouldn't get more energy out of a given amount of gas than it costs to create that gas mix from water especially given that the gas mix converts back to water as it reacts.

I dunno. I suspect I'm misunderstanding something.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

2 H2O -> 2 H2 + O2
Water (liquid) to Hydrogen (gas) + Oxygen (gas)
2 (-285.8 kj/mol) -> 2 (0 kj/mol) + (0 kj/mol)

Costs no less than 285.8 kj per 18 grams of liquid water reacted, producing 2 grams of hydrogen gas and 16 grams of oxygen gas.

Reversing the reaction gives you no more than 285.8 kj, though the usual efficiency is about 50% and so you'd only get 142.9 kj.

0.5 tons is 454,000 grams, and so should cost no less than 7,208 mj to react. Burning the hydrogen and oxygen to produce should give around 3,604 kj.

Assuming I'm not messing up the physics or my math, of course.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

I think you're ignoring the contribution of entropy there and temperature and pressure should factor in...

Definitely the right line of reasoning to get the energies involved. Unfortunately Spaceships tries hard to make the actual energies it uses inaccessible so it's hard to relate that to power points.

Re: [Spaceships] Reasonable numbers for Refinery Systems / 'Artificial' Fuel?
 

It seems that indeed some sort of misunderstanding occurred.

When I say 50% efficiency, I mean that it would take a refinery X PP×hours of energy input in order to synthesise (or otherwise produce) as much fuel as will be required to get X×50% PP×hours when burned.