Some math on sour gas boiler

[Padishar]

I've been experimentin from a few days to build a sour gas boiler in survival mode without space materials. Therefore during all these testing and calculation I discovered some interesting facts I would like to share with everyone interested in building such a device. In partcular, I was not sure if the whole process would be heat positive or negative (the different phase that the crude oil pass through have different heat capacities) and I don't know either if someone else already pointed that out (I've seen many sour gas boiler builds using a tiepidizer toinject heat into the system leading to the expactation of the process being heat negative).

My goal was to process 8kg/s of crude oil. The main idea has already being used in many other builds: use a counterflow system with a hot area at the top or the bottom to turn the crude into sour gas and a cold area at the bottom or top respectevely to condensate the sour gas in methane. Since I did not want to use space materials the hot area use one or more volcanos while the cold area is kept cold by thermoregulators filled with hydrogen.
The hot area does not present any major problematic, because the heat capacity of sour gas is bigger than the heat capacty of crude oil, thus with a very good heat exchanger you need to inject very little heat into the system.
However, the cold area is way more problematic, the reason is:

Heat capacity per kg (of crude oil) is:

for Sour Gas 1.898 (DTU/(g °C)=1.898 (kDTU/(kg°C))

for Methane/natural gas you have to consider that only 67% of the crude oil/sour gas mass is turned into methane/natural gas, thus

heat capacity is per kg of crude oil  2.191(DTU/(g °C)*67%= 1.468 (kDTU/(kg°C))

Therefore we can see that, assuming you can have perfect exchange between the two you end up with excess heat that needs to be deleted since you need to extract more heat from the sour gas than the natural gas can extract from the heat exchange counterflow system. For axmple using the numbers above:

To cool down by 150°C Sour gas you need to extract 284 KDTU/kg (2.191*150)
To heat up by 150°C Natural gas you need to inject 220 KDTU/kg (1.898*150)

this means that in a heat exchange with 150°C degree difference from the top to the bottom you need to extract about 60KDTU/kg if you want to maintain the same temperature at the top and the bottom of the system. Using thermoregulators that amount of heat occupy about 2 of them. So for 8kg/s needed to be processed I would need about 16 Thermoregulators (which is far from ideal).
Things get a little bit better if you counterflow the sulfur alongside the methane/natural gas, but that is still not very good because even then the combined heat capacity of sulfur and natural gas is lower than the one of sour gas. For my 150°C difference example, I end up with about 30 KDTU excess heat that needs to be deleted, which cuts the amount of thermoregulators needed by a factor of 2. However, I think that such amount is still too much for 8kg/s of crude oil, considering that the temperature difference in the cold heat exchanger is gonna be higher than 150°C.

At the end of the day I found out that, at least with this build, the sour gas boiling and condensation process is heat positive.
For this reasons I suggest to not build sour gas boiler without space materials, unless you want to process very small amount of crude oil (1-4kg/s max). Sidenote: you can use a thermoacquatuner filled with ethanol to precool the sour gas at about -100 and thus reduce the amount of thermoregulators needed.

 

[Hokaeru]

Hello, nice idea ! Is it just theory at the moment or did you craft a prototype ? 
As far as I am concerned, when I come to making a sour gas boiler, I do not care about saving some power though, I just want it to be failsafe.
But it is still nice to grab free energy ! 

[Padishar]

Others players already did it but their build process 1-2kg/s of crude oil (see here for example 

 )

I built something really similar to that (with 6 thermoregulators) but the colling system failed to keep up. So I redid the math and figure our that there is actually quite a lot of heat that need to be extracted from the system and that was the reason why the themoregulators could not move out enough heat to mantain the desired temperature to condensate the sour gas.
In fact to calculate the amount of heat that has to be extracted (including sulfur counterflow), you need to use the formula

Q[KDTU/s]=(1.898-1.468-0.231)*f*T 

where f is the amount of crude oil in kg/s and T is the temparature difference between the initial temperature of the sour gas entering the cold heat exchanger and the condensation temparature of the sour gas. The amount of heat is given in KDTU per second.
If you exclude the sulfur counterflow you need to delete the -0.231 term in the formula.

If you want to calculate the amount of theremoregulators needed to extract that amount you divide that number by 33.6 (which is the heat you can move per second with a thermoregulator full of hydrogen). Plus you have to consider that the heat exchanger is not perfect thus you need to add some margin, otherwise your system could fail because of this. As you can see if you reduce T you reduce the amount of thermoregulator needed (same for the amount of crude oil flow obviously). Reducing T can be done with a precooling system, for example a acquatuner filled with ethanol.

At the end of the day, my thought was that building precooling system and still having to build a lot of thermoregulator was not worthed, so I gave up my attempt to build a sour gas boiler with no space materials. However, if you really like challenges and you don't mind having a rather inefficient sour gas boiler you can certainly try and succeed to build one with no space materials.

[Fyrel]

Can't you counterflow the crude oil against the sour gas to remove the excess heat from the system?

[wachunga]

If your philosophy regarding the small packet mechanic allows it, you can use 1 kg/s of water in an aquatuner instead of hydrogen regulators. Less power efficient but about 74% more cooling per building. Which seems a fair trade and besides power is pretty meaningless with that much NG production.

The trick is to create a cooling loop where the small packets can never combine to break the pipes. Use a valve as your aquatuner bypass instead of a bridge and you can make a bypass path of the same length as the aquatuner path. The small packets will lineup and march around the loop like good little soldiers. Here is a screenshot from OCT 2018 using the principle to make liquid hydrogen. The rightmost loop with the small packets.

I don't recall why I had a shutoff bypassing the AT instead of automating the AT. Perhaps ATs didn't have automation back then or perhaps to avoid packets getting stuck in the AT when it is disabled. In any event, there are three paths of the same length. The shutoff path for when packets are cold enough, the first packet AT path because ATs take one second to start, and the regular AT path. Obviously this is rather old, but it still works just fine when I loaded the save.

[Padishar]

55 minutes ago, Fyrel said:

Can't you counterflow the crude oil against the sour gas to remove the excess heat from the system?

yes that is necessary. However, the sour gas will still have at least 100°C if your crude is incoming at 95°C and you have therefore a 262°C difference from the methane condensation temperature, which leads to rather big amounts of heat (due to diff in heat capacity between sour gas and natural gas +sufur ) that need to be extracted from the system.

[yoakenashi]

17 minutes ago, Padishar said:

rather big amounts of heat

This is true. I have two sour gas boilers that I made and after running them for hundreds of cycles, they both have a high average operating temperature. Thanks for sharing your build.

[TheMule]

8 hours ago, wachunga said:

you can use 1 kg/s of water in an aquatuner instead of hydrogen regulators.

I just wonder, any reason not to use 10kg/s of methane instead? It seems the obvious choice before supercoolant to me, in this application. It should be way more power efficient than 1kg/s of water...

[ghkbrew]

6 hours ago, TheMule said:

I just wonder, any reason not to use 10kg/s of methane instead?

Methane is only liquid in a ~20C window. Keeping that from breaking pipes is tricky. Plus you have the complications of producing that much methane in the first place.

[wachunga]

10 hours ago, TheMule said:

I just wonder, any reason not to use 10kg/s of methane instead?

Mostly the small liquid window as @ghkbrewsaid. Stuff like chilling in the cold plate and dealing with startup. All of the piping that the methane runs through will have to be brought down to temperature. Either by babysitting the methane and slowly allowing it through more and more of the pipes or by bolting on a hydrogen regulator system. Then at startup you have a lot of heat to move before the counterflow really gets going. Which means lots of excess methane cooling capacity to keep it within that small window or again having a secondary hydrogen regulator system. Or have a huge cold sink buffer and ramp the boiler's flow rate up very slowly to keep it within whatever excess cooling capacity you do have.

All of that is doable of course, I just find it tedious and not interesting/fun. And while lots of people think the small packet mechanic is the work of the devil, I think it's cheekily fun in select applications like this.

[TheMule]

11 hours ago, ghkbrew said:

Methane is only liquid in a ~20C window. Keeping that from breaking pipes is tricky. Plus you have the complications of producing that much methane in the first place.

AETNs are perfect to kickstart the process. You don't need much, you want full packets (10kg) but you don't technically need full pipes.
 

If you rule AETNs out, then of course you have to kickstart the process with Thermo Regulators and hydrogen. You are inevitably going to produce liquid metane somehow, but then yes bringing everything to temperature might be a problem. I think I've never tried methane w/o insulation, but based on LOX and LH2 handing in ceramic pipes it seems doable.

[ghkbrew]

@TheMuleI don't think anyone disagrees that it's possible, just that the complications involved aren't worth the increased efficiency.

Admittedly, it's largely theoretical since I've never actually seen a build that uses methane. Comparing real builds might be more enlightening.