Actual min-max heat recovery from electrolysis

[avc15]

In a different thread I mentioned how sending cold water to an electrolyzer passes up some serious cooling potential, especially if that water originally started as 110C steam (ie piped in after cooling water out of a cool steam vent). This is a well known thing around here, but as I have just built a LH condenser I thought I might actually illustrate just how much heat you can sink into your water supply for electrolysis.

This build absolutely is min-maxing, though there are a few adjustments you could make to improve it for more specific purposes.

Step 1: procure a source of lukewarm / moderately hot water.

I mean, not boiling. I'm using a combined tank for toilet water (comes out ~~ 60C, since my clean water pipe to the bathroom comes in at 95C), my natural gas generators (constant 40C output), and my petroleum generators (~45C because I'm not clamping the generators themselves to 40C). This tank has gotten out of hand, so I really need to do something with it.

The water is a warm 45C.

 

Step 2: electrolyze water, but first pump as much heat from the output (gases) into the input (clean water) as possible.

Pretty basic looking here! You see a hot tank filled with p-water as secondary coolant, where the A/T sits. And a cold tank filled with ethanol as the secondary coolant, where we pipe gases through a radiator on their way out.

 

That A/T is set up to run as long as hot tank temp is below 98C and cold tank temp is above -115C. I thought I could get the hot tank up to around 102C but because of the heat generated by the machinery, I kept getting steam in with my oxygen and hydrogen. No bueno. 98C seems to be the hottest I can set that temp control.

Primary coolant is supercoolant.

 

Use steel radiant pipes for the output radiator, those measly 4 segments long are more than enough.

 

OK - I've been running this non-stop for 30 cycles or so and temps haven't stabilized yet. Right now we're pumping O2 and H2 out at -91C. By my estimation, cold tank temp should keep going down until gases come out between -100C and -105C. (That's what makes ethanol a very attractive secondary coolant here)

Step 3: profit (use the pre-cooled gases for whatever you want)

I'm doing a few things.

1) I have just too much O2, so I'm sending one of those 4 O2 outlets through the hot tank in my base cooler. This is a bit wasteful, because we pump heat, transfer that work to another secondary coolant, and then pump heat into it again - but for now it's a way to boost hydrogen production. Gotta send that O2 somewhere.

 

2) I still have too much O2, so I'm using about 500 g/s to cool space machinery.

 

3) The H2 and remaining O2 (about half) get sent pre-cooled to my LOX/LH condensers. It's amazing how low the duty cycle is on these two A/Ts, they barely have to work at all to liquefy this pre-cooled H2 and O2.

 

Haven't started sending LOX/LH to rockets yet.Getting ready for that next!

Again, temps haven't stabilized, so we're still losing about 10C in transit. That'll correct itself in time. (Pipe in using plain obsidian gas vent pipes, that's the lowest possible heat capacity - route them through space in vacuum)

Conclusion. Most builds won't directly cool the output by pumping heat directly from the input. But when you electrolyze hot water, you're deleting a huge amount of heat. Conversely, if you electrolyze moderately warm water, you're printing large amounts of heat into your base. Tsk.

This build is good for pre-cooling gases that'll go to a condenser. It's not a SPOM. All H2 goes to rocket fuel.

[Chthonicone]

Just a heads up, you got the spoiler tags wrong after step 2.

 

Cool setup though.

[avc15]

Here it is with a hot tank dedicated to heating H2 to 320C before burning it for electricity. So now we preheat water to 98C before electrolysis, and H2 to 320C before burning.

 

The engineering space evolved a fair bit over time. Also I let a little heat out of the steam chamber while building the new hot tank, and temps haven't recovered. Oops.

Pipes. My regrets if you open this spoiler. Everything really has a purpose even that dangling dead end on the left. What it boils down to is this:

(1) Each hot tank has a heat exchanger running through it to dump heat into some piped material that's getting heated. On the right, it's water to the electrolyzers. On the left, it's Hydrogen to the generator.

(2) Each cold tank has a primary side and a secondary side. Primary coolant is coming in from the A/T cooling the tank down. Secondary coolant is coming back from radiators in the base, circulating through & dumping heat into the tank.

(3) Each primary A/T loop buffers through a reservoir for stability.

(4) Returning secondary coolant goes through a pair of two reservoirs with a full pipe sensor in between. The full pipe sensor drives a fill signal when it's "not full". 

 

(5) The outlet for cold secondary coolant is on a load balancer - the inlet on the left (heating hydrogen to 320C) gets selected if that cold tank's temp is below -4C. If left cold tank temp is above -4C and right cold tank temp is below -4C, we use secondary coolant from the right (heating water to 98C). If neither condition is fulfilled, it reverts to a timer that switches sources every 200 seconds.

But.... my automation needs work. It's not really load balancing the way I described above. (I'm not the best at automation, but I keep trying)