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High-efficiency liquid counter-flow heat exchanger (and petroleum boiler as example application)


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After quite a few failed experiments getting a good counter-flow heat exchanger for liquids going, I finally have a tower-design that works and can scale to different needs. The approach used works for liquid in general, it is not specific to petroleum boiling.

As an application, I present a 10kg/s petroleum-boiler that has an output temperature (petroleum) only about 3..4C (actually 23C, sorry) higher than the input temperature (crude oil), and hence has really low thermal losses. The overall boiling process can even cool the input down if desired. For example, I have 90C crude oil in and 70C petroleum out running nicely (not quite). This comes from using an aquatuner as heating element and petroleum having a slightly higher specific heat capacity than the same amount of crude oil. To achieve this, use the input crude oil flow to cool the super coolant going into the aquatuner.

Main characteristics:

  • Scales to any efficiency level desired (within the maximum vertical space of the map) by using modular components.
  • No special materials needed for the heat exchanger itself.  One heat-resistant pump needed for the upwards flow.  Either directly via building material or using the same tricks as are known to pump, for example, magma.
  • Input and output at the top.

Principle: Chain of separate heat-exchange chambers with gravity-assisted flow
Basic element: Here shown with input feeder and two stages below and liquid for petroleum boiling in there. The petroleum feed flows out to the right at the top. The automation wire is connected to a liquid level sensor at the bottom.

element01.png.6d86c0a2ea74c1e1c59901bc5a9218db.pngelement02.png.79af3f75598d58d2363aaebce80bcc15.pngelement03.png.54ee75fde90ff565cf544f31e2f094f9.png

Notes:

  • Needs to be vaccuumed out or have only one gas in there. Otherwise, the flow can get completely blocked.
  • For each element, if you stop the flow, expect about an additional 100kg of liquid per stage to flow until things settle
  • Only the 4 horizontal pipe segments per element need to be radiant pipes.

Example application: Petroleum boiler

  • Uses 24 basic elements for petroleum boiling
  • Temperature increase output - input observed (not really long-term): around 3...4C at 10kg/s 
    -> Long-term observation: +23C, output on input
  • Energy usage: Pump: 240W 
  • Energy usage: Heating (estimated): around 600W, disregarding heating up the super-coolant fed into the aquatuner. You can use the input oil at least partially for that. The nice thing is that as petroleum has a higher specific heat than crude oil, you can basically cool the output down a lot if you heat the super coolant with the input crude oil stream. You may need, e.g., a tepidizer, to prevent the temperature from going too low tough. Or you can get a bit of cooling out of it for other purposes.
    -> Long-term observation: Only around 240W for the aquatuner
  • Uses aluminum radiant pipes. Other metals work, but may need  more stages for the same efficiency. 
  • Heating element is a termium aquatuner fed with super coolant (around 1000kDTU/sec at 1200W consumption). This can be any other solution that can heat the liquid to around 410C.

Boiler element:

boiler01.png.651a10fe2484ad1032ce27c9c13ee9d0.pngboiler03.png.62e2298ff0e9070f72f6bbb35a14ceb9.pngboiler02.png.2cfcc1d99bf6735c1ae663d711a4bbb6.png

Built-details:

  • The aquatuner is fed with pre-heated super coolant at around 50C. Heat can be provided in part by the crude-oil input flow.
  • Target heating temperature (right thermo sensor) is 410C (optimized: 405C), pump activation (left thermo sensor) is at 405C (optimized: 403C).
  • The pump requires at least a level of 600kg (left liquid sensor) to start pumping petroleum upwards.
  • The right liquid sensor stops the crude oil feed (at the top) if the level goes above 50kg.
  • The signal line running left at the bottom is for uptime estimation of the aquatuner (not shown).

And here is a picture of the whole thing, with the measurement of uptime for aquatuner vs. elapsed time on the counters to the left:

tower_full.thumb.png.8ffe5eda8a5d39c8d0790e3dfe635162.png

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3 hours ago, TheMule said:

Nice! Did you compared it with a left leaning stair exchanger (of comparable size of course). I think it's both easy and effective, making for a perfect reference point.

Need to run it for some time to get solid numbers. Maybe then. 

Ok, first insight: That Petroleum has a higher specific heat is actually a problem. The waste-heat of the aquatuner and pump may be one too. The whole structure very slowly heats up. Which I should basically have expected. After about 150 cycles, the 3C difference between input and output has grown to 12C hotter coming out, which still is not bad. I am unsure whether that is the steady state or whether it will get worse. The temperature difference overall (including the input crude heating the super coolant) is now that the original crude is 4C colder than the petroleum coming out. That is still a very nice number. On the plus-side, it looks like the electricity consumption is far lower than I thought.

Still, I think I will stick with this design. The heat-exchanger itself is sound. 

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So you are saying that the design where you have it flow like 10 tiles one way, drip down, flow back the other way, drip down, etc gains nothing from being 10 tiles wide because all of the petrol on any given stair is the same temperature due to petrol's high conductivity?

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3 hours ago, psusi said:

So you are saying that the design where you have it flow like 10 tiles one way, drip down, flow back the other way, drip down, etc gains nothing from being 10 tiles wide because all of the petrol on any given stair is the same temperature due to petrol's high conductivity?

Ah, no?

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9 hours ago, psusi said:

So you are saying that the design where you have it flow like 10 tiles one way, drip down, flow back the other way, drip down, etc gains nothing from being 10 tiles wide because all of the petrol on any given stair is the same temperature due to petrol's high conductivity?

That's true only if you remove time from the equation. It takes time to transfer heat, expecially at lower deltas. The longer a 10kg packet spends in a pipe at a lower temperature, the more heat it looses but, of course, the initial 2 seconds are more impactful than the next 2 and so on. So a 4 tile long pipe segment isn't going to perform twice as well as a 2 tile long segment.

That said, an exchanger in which said 10kg packets spends 30 seconds in contact with colder pipes is probably better than one in which packets spend only 15 seconds.

In a stair design, if you have a 32 tile long pipe, only half of them are submerged, meaning a packet looses heat only for 16s. A serpentine design 7 tiles wide, 4 stores, has the same amount of tiles, but only 4 "elbows", counting the initial one, meaning packets loose heat for 28s.


So, if your metric to evaluate efficiency is total number of pipe tiles, the serpentine one is better. If you count only the submerged ones, the stair is better.

In my tests, the optimal was around 7-9 wide stores. In my playthrough I used both.

That said, the waterfall design, or if I understand correctly the bead one, beat both, w/o elbows (that is with the shorter pipe possible).

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2 hours ago, psusi said:

So why did you make the stairs so narrow and why two tiles of liquid high instead of only one?

What are you talking about? I made an original design, not an incremental one or a modification of one. In fact I completely ignored existing designs for this one. 

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22 minutes ago, Gurgel said:

What are you talking about? I made an original design, not an incremental one or a modification of one. In fact I completely ignored existing designs for this one. 

Now that I look again, I notice that you have the oil flowing down and the petrol is cooling off in the pipe flowing the other way.  Usually it's the petrol that flows down and the oil heats up in the pipe.  Still, why did you make the oil two tiles deep on each floor instead of only one, and why make each floor so narrow?

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1 hour ago, psusi said:

Now that I look again, I notice that you have the oil flowing down and the petrol is cooling off in the pipe flowing the other way.  Usually it's the petrol that flows down and the oil heats up in the pipe.  Still, why did you make the oil two tiles deep on each floor instead of only one, and why make each floor so narrow?

Maybe I can attempt an explanation... in heat transfer there's TC, temp delta, time and often (directly or indirectly) mass. By increasing the mass one of the media involved you increase its capacity for accepting heat. E.g. high mass means slower change in temp hence delta T remains larger for longer. Of course you can change the mass of one of the three media involved... you can't increase the mass of the radiant pipe (although aluminum has much higher SHC than most metals) nor you can increase the size of a 10kg packet inside the pipe.

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2 hours ago, TheMule said:

Maybe I can attempt an explanation... in heat transfer there's TC, temp delta, time and often (directly or indirectly) mass. By increasing the mass one of the media involved you increase its capacity for accepting heat. E.g. high mass means slower change in temp hence delta T remains larger for longer. Of course you can change the mass of one of the three media involved... you can't increase the mass of the radiant pipe (although aluminum has much higher SHC than most metals) nor you can increase the size of a 10kg packet inside the pipe.

A higher mass will slow down the temperature change, but only during startup.  The temperature will change less with more mass at first, but eventually it will reach equilibrium and then thermal mass doesn't matter.

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4 hours ago, psusi said:

A higher mass will slow down the temperature change, but only during startup.  The temperature will change less with more mass at first, but eventually it will reach equilibrium and then thermal mass doesn't matter.

Actually, it does matter in one aspect: This way you can heat the oil very close to changing to petroleum, but avoiding the change until at the bottom. If you have less mass in each stage, that will not work as any small heat spike will trigger the change. And this design gets blocked by petroleum changing in the stages. The closer you can get to the target temperature in the heat exchanger, the more efficient, obviously. Also, if you pump the crude, getting the same thermal buffering effect is more difficult. But it would be possible to do 1-tile stages for part of the design and only go to 2 tile ones near the bottom. Something I have to try out, I think.

As to why this thing is so narrow, that makes is more easily modular and for high mass (i.e. low relative flow) in each stage, you need to have more thermally insulated stages because relative time spent in each stage is larger. For low mass (i.e. high relative flow) that matters less and maybe not at all. May be a design drawback.

You may also have noticed that I am a bit of a heretic with respect to established designs. Actually, sort of a 2nd order heretic such that I ignore them completely (not just look at them and criticize them) until I have something that works by itself reasonably well. Then posting them here stirs things up a little and makes people question the established things and that tells me interesting things about both my design and the established ones.

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17 hours ago, Gurgel said:

Actually, it does matter in one aspect: This way you can heat the oil very close to changing to petroleum, but avoiding the change until at the bottom. If you have less mass in each stage, that will not work as any small heat spike will trigger the change. And this design gets blocked by petroleum changing in the stages. The closer you can get to the target temperature in the heat exchanger, the more efficient, obviously. Also, if you pump the crude, getting the same thermal buffering effect is more difficult. But it would be possible to do 1-tile stages for part of the design and only go to 2 tile ones near the bottom. Something I have to try out, I think.

Ahh, true.. I think it was @Saturnus that posted a nice design that had a half a dozen pipe temperature sensors and shutoffs on the last floor to divert the oil out of the petrol if it got too close to phase change.

17 hours ago, Gurgel said:

You may also have noticed that I am a bit of a heretic with respect to established designs. Actually, sort of a 2nd order heretic such that I ignore them completely (not just look at them and criticize them) until I have something that works by itself reasonably well. Then posting them here stirs things up a little and makes people question the established things and that tells me interesting things about both my design and the established ones.

Of course, which is why I'm comparing it to the older designs and trying to figure out if it is better and how.

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13 hours ago, psusi said:

Ahh, true.. I think it was @Saturnus that posted a nice design that had a half a dozen pipe temperature sensors and shutoffs on the last floor to divert the oil out of the petrol if it got too close to phase change.

My last stage has been stable at 397.6C...397.9C for a few 100 cycles now and I only need to heat the petroleum to 404C. (403C did not work.) With that I have a very low 150W average for the heating aquatuner at the full 10kg/s conversion.

Even if the rest turns out to be completely worse than the existing designs, I think this aspect is a plus. Of course combining stages from different designs is perfectly possible.

13 hours ago, psusi said:

Of course, which is why I'm comparing it to the older designs and trying to figure out if it is better and how.

Excellent! If you find out, let me know. I currently have no clue ;-)

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