[HN Gopher] Cement recycling method could help solve one of the ...
___________________________________________________________________
Cement recycling method could help solve one of the big climate
challenges
Author : timthorn
Score : 131 points
Date : 2024-05-23 18:03 UTC (4 hours ago)
(HTM) web link (www.cam.ac.uk)
(TXT) w3m dump (www.cam.ac.uk)
| gnabgib wrote:
| There was some discussion yesterday [0] (21 points, 4 comments)
|
| [0]: https://news.ycombinator.com/item?id=40446764
| dr_dshiv wrote:
| Incredible! They use a massive arc furnace (used for steel
| recycling) to recycle concrete. They suggest that solar power
| could power the arc furnaces, resulting in zero emission
| concrete. As concrete currently constitutes 7.5% of anthropogenic
| carbon emissions, this tech could make a big difference.
|
| Arc furnaces are crazy energy intensive. But if solar power keeps
| doubling every 2 years, we will very soon have way more power
| than we know what to do with (at certain times in the day). Arc
| furnaces are a good way to suck up the negative electricity spot
| prices!
| tempestn wrote:
| Often the problem with using excess solar capacity is that the
| capital cost of the thing that would use it (desalination
| plants are one example) is so great that it's not cost
| effective to leave them idle at other times of the day. Any
| idea whether that would be the case with these arc furnaces as
| well?
| ahi wrote:
| IANAMetallurgist. Arc furnaces for steel making already rely
| on cheaper off peak power, so utilization is already a
| factor.
| s1artibartfast wrote:
| I didn't think they varied their use pattern by time of
| day.
|
| They might rely on cheaper power to lower the average cost
| make financial sense, but that is a different than soley
| utilizing excess power.
|
| If they cant rationalize the opex running 8 hours a day,
| there is still a problem. My understanding is that many of
| these plants cant even shut down and be restarted.
| kragen wrote:
| the normal kind of arc furnaces are shut down many times
| a day; it's a batch process, not a continuous one
| s1artibartfast wrote:
| Do they operate 24/7?
|
| Even if it is batch process, going from 24 hours to 8
| hours is like tripling plant cost vs productivity.
| colechristensen wrote:
| You may be thinking of aluminum plants which can't be
| shut down and restarted without significant damage, but
| they are indeed still throttled up and down. In that case
| it's electrochemistry at high temperatures to strip the
| oxygen off of aluminum. If it gets cold the apparatus
| gets damaged, but it can be throttled down a significant
| percentage.
| avianlyric wrote:
| Arc furnaces tend to be first in line to voluntarily
| shutdown to deal with grid instability, or projected
| power shortages. Network operators will basically pay
| them equivalent amount of money as they would to buy
| electricity, if the furnace operator is happy to shutdown
| at a moment's notice.
|
| After, to a power grid, removing large loads are
| functionally equivalent to adding additional generation.
| So if you're operating an arc furnace, and can shutdown
| quickly (which arc furnaces can), then grid operators
| will pay you for _privilege_ of being able to shut you
| down at moments notice, and then pay even more for the
| electricity you're not consuming, if the grid is forced
| to call upon that additional "capacity" due other issues
| on grid.
|
| I'm not sure if arc furnaces today vary their usage in
| direct response to variable electricity prices through
| the day, rather than only acting as emergency ballast to
| be jettisoned in an emergency. But I would be very
| surprised if they didn't, they're a large enough load
| that they'll have coordinate the usage with their local
| grid, and large enough that shifting the usage pattern to
| avoid high cost peaks would save them a very material
| amount of money.
| Gibbon1 wrote:
| This is one of the reasons I believe 'base load' demand is
| more fungible than people assume.
|
| I think in California 6% of electricity demand is pumping
| water. I'm almost willing to go on record and say that's
| the California Aqueduct and the actual number is higher.
| Okay I'm going to look.
|
| https://www.ppic.org/publication/water-and-energy-in-
| califor...
|
| > The water system uses approximately 20% of the state's
| electricity and 30% of its natural gas for business and
| home use, according to data from 2001--accounting for more
| than 5% of California's greenhouse gas emissions.
| samatman wrote:
| Did you miss the stat directly underneath that?
|
| > _Heating and other energy-intensive water uses in homes
| and businesses make up almost 90% of water-related energy
| use, while treatment, pumping, and conveyance of water
| and wastewater account for the rest._
|
| That's 2% for everything which isn't heating water.
| Pumping is some smaller fraction of that.
| abakker wrote:
| you are right. The thing that is interesting is that
| pumping loads overall take a lot of the grid's energy,
| it's just that most pumps are refrigeration loads, not
| water transport.
| avianlyric wrote:
| Great thing about heating water, is that it stays hot
| after you've heated it.
|
| Water heating is basically the poster child for "demand-
| response" technologies. You can easily heat your water a
| few hours earlier than normal with basically no
| consequences to the user. But you need to get reasonable
| smart about modelling people water usage, as people don't
| tend forget or forgive a cold shower.
| kragen wrote:
| i didn't know what ahi said (that minimills already depend on
| cheap off-peak power) but intuitively i would expect an arc
| furnace to be pretty cheap compared to the power it uses;
| it's just a water-jacketed chamber lined with castable
| refractory with a lid with three big carbon electrodes
| lowered through it, and all of those are cheap materials and
| low-precision (tight tolerances won't withstand white-hot
| flaming steel for long). the machinery is large and heavy,
| but only in proportion to the volume of material it
| processes. the electrical energy consumption, on the other
| hand, is comparatively enormous
|
| (admittedly maybe the capex for running the power lines to
| the facility is significant, but in the same proportion to
| the cost of the energy used as running transmission lines
| anywhere else)
|
| there's a nice video illustrating the process at
| https://www.youtube.com/watch?v=T1CJ5NPW8MU. don't be
| alarmed, the part that looks like a major industrial accident
| is just what happens normally when they turn it on. a more
| detailed documentary with explanations, though unfortunately
| of an atypically large arc furnace, is in
| https://www.youtube.com/watch?v=eZRuVEfxIVI
|
| in that particular case they say it runs 24/7
| abdullahkhalids wrote:
| The important thing here is that it only recycles concrete.
| Most of the 7.5% emissions are from new concrete constructions
| - new roads and new buildings - as we increase the total
| concrete in use. Very little is from old buildings/roads being
| destroyed and then replaced by something else.
|
| This will make a small dent in the 7.5% at scale.
| marcosdumay wrote:
| Once you solve energy producing and handling, 100% of the
| remaining is composed of tiny little problems.
|
| This one is large enough for several companies to make a
| living. What means it's large enough to care about.
| s1artibartfast wrote:
| I dont understand your point. Are you saying there isnt
| enough recyclable concrete to meet the demand for new
| construction?
|
| If we create half as much concrete waste as demand, that 7.5%
| could drop by half.
| trimethylpurine wrote:
| Home Depot seems to suggest that old concrete is already in
| high demand. If we need it for roads and we can't get it
| because concrete is more valuable, now we have to go find
| road building materials. Is the manufacture of road
| building materials cleaner than concrete?
|
| https://www.homedepot.com/c/ah/how-to-dispose-of-
| concrete/9b...
| s1artibartfast wrote:
| I dont think that suggests there is a high demand for
| used concrete. It does however highlight the fact that
| there may be insurmountable transportation and handling
| costs for recycled concrete.
|
| It is hard to imagine it being cost effective to
| transport it to recycling centers.
| 3abiton wrote:
| What's the catch
| mechhacker wrote:
| Nuclear has a large heat source (or can make a large heat
| source instead of converting to electric first) to do a lot of
| things like this.
| Animats wrote:
| Nope. Nuclear isn't hot enough. Only about 315degC at the
| output end. Electricity, though, has no thermodynamic upper
| limit on what temperature can be generated.
| bruckie wrote:
| Is there a cost effective way to move that heat to where it
| could be used?
|
| Nuclear reactors can produce very high temperatures, but in
| most reactors the heat is moved to turbines using water. Are
| there ways to move the heat at the high temperatures required
| to melt steel? (AFAIK, even molten salt is too cold.)
| seventyone wrote:
| How does this address the emissions of concrete's curing
| process? There's no way you can have "zero emission concrete".
| I've seen proposed additives that will reduce the emissions
| during the curing process but that chemical reaction is going
| to have to happen regardless.
| bobfromhuddle wrote:
| Concrete absorbs co2 while curing. It's the calcination
| process, where we heat limestone up until the co2 burns off,
| that has unavoidable emissions. Since this concrete is
| recycled, that's already happened.
| logtempo wrote:
| It's math time, let's look what wikipedia say about electric
| arc furnace:
|
| - 1.44 gigajoules (0.4MWh) is required for 1 ton of steel. In
| theory.
|
| - 300T of steel needs 132 MWh, and a "power-on time" (the time
| that steel is being melted with an arc) of approximately 37
| minutes.
|
| ---- wikipedia end -----
|
| From https://ourworldindata.org/grapher/electricity-prod-
| source-s...: total world electricity from renewable was
| 10,700TWh in 2021. 11,600 TWh in 2023.
|
| 1.5 billions (metric) tons of crude steel were produced in
| 2023. 30% of it by electric power.
|
| ------------------------
|
| (A) Let's assume that 20% of those 30% already come from
| renewable (which is not the case, anyway). 30x20% is 6%. It
| means 24% of the 1.5 billions tons are looking for renewable.
|
| It means 360 millions of tons needs its green energy.
|
| It means we need to find 360 millions x 0.4MWh = 144 TWh.
|
| If we don't assume (A), we get 152 TWh.
|
| It means we need to dedicate ~1.5% of renewable worldwide
| energy to replace 24% of crude steel "e-production". In
| theory...
|
| We observed +5% of renewable energy production worldwide. If we
| wanted to make the steel *production* go green (1.5*3.33 = 5%),
| in theory it could be possible in one year...in theory.
|
| Tbh, I expected a more crazy conclusion. I'm quite sure the
| number is off by more than 10% though. But even if it was off
| by 100%, it would mean it's possible in 2 years.
|
| On a side note: it's useless anyway if those 5% are not coming
| with a decrease of 5% of coil&gas consumption. Which is not
| what's happening...
|
| Feel free to redo the math, I can make a mistake!
| Hooray_Darakian wrote:
| > But if solar power keeps doubling every 2 years, we will very
| soon have way more power than we know what to do with
|
| How soon is soon to you?
| https://www.eia.gov/todayinenergy/detail.php?id=50357
| ben_w wrote:
| Nice, this was one of the bigger things I have on my "I hope
| someone knows how to solve this" pile.
| mandibeet wrote:
| What else is in that pile?
| dylan604 wrote:
| Creating clean energy with fusion, desalinating salt water
| for near limitless clean water, reducing plastic use, curing
| cancer and on and on and on
| ant6n wrote:
| Black holes, portals, FTL, electoral reform...
| darknavi wrote:
| > desalinating salt water for near limitless clean water
|
| Don't forget the free salt!
| sandworm101 wrote:
| >>The Cambridge researchers found that used cement is an
| effective substitute for lime flux
|
| So they can only "recycle" this concrete as a substitute
| ingredient during steel making? That cannot scale. We would have
| to start making epically more amounts of steel in order to
| process even 1% of the concrete that we would want to recycle.
| j2bax wrote:
| Is there a reason they couldn't just reuse the same steel over
| and over just to process the cement at scale?
| sandworm101 wrote:
| Lime is used to remove impurities from the melt. So I imaging
| they would have to re-add those impurities each time. I doubt
| that would be energy-efficient.
| dylan604 wrote:
| The industries in the Steel Belt liked your post
| bell-cot wrote:
| Very likely no - so long as electrical power is free-ish.
| Because if they aren't actually producing X units of steel
| along with Y units of cement in each batch, then they'll have
| to pay for the whole thing out of just the cement sale
| revenues.
| zharknado wrote:
| No, they sub it for lime flux, which had the side effect of
| reactivating the cement (makes "clinker"), which can then be
| used again in new concrete.
|
| Pretty cool hack!
| adolph wrote:
| Seems like the "big if feasible" part is reducing concrete to
| hydrated cement paste.
|
| From actual paper:
| https://www.nature.com/articles/s41586-024-07338-8
|
| _Recovered cement paste (RCP) is not commercially available at
| scale at present. . . . The value of the improved recovered
| aggregates is not at present high enough to cover the extra cost
| of processing, so RCP is currently landfilled. However, the know-
| how and the technologies required to produce RCP at scale exist.
| [22]_
|
| 22. Thermomechanical beneficiation of recycled concrete
| aggregates (RCA):
| https://www.sciencedirect.com/science/article/pii/S095006182...
|
| The cited paper does not support the assertion that tech to
| recycle concrete into RCP exists. The paper discusses removing
| adhered mortar (AM) from recycled concrete aggregate (RCA).
| mandibeet wrote:
| Cement production is a significant contributor to global carbon
| dioxide emissions. Amazing that the development of effective
| cement recycling methods is in process.
| magicalhippo wrote:
| Another way is to build stuff that doesn't have to be torn down
| after 10 years. Quite a lot of large concrete buildings in town
| have been torn down less than 20 years, some just 10.
|
| Seems quite wasteful, surely there's a better way with some
| planning and foresight.
| hcarvalhoalves wrote:
| ... or already build planning for tear down. Steel and wood.
| magicalhippo wrote:
| Yea that's what I was thinking of. Either switch materials or
| build with future use in mind.
|
| We've recently gotten a fairly large wooden tower[1] here in
| Norway, will be interesting to see how it fares in this
| regard.
|
| [1]: https://www.architecturaldigest.com/story/worlds-
| tallest-tim...
| card_zero wrote:
| Nice. That's only 5 feet shorter than the (steel-framed)
| Flatiron Building.
| onlypassingthru wrote:
| It may not be a panacea, but using busted up chunks of concrete
| in gabions is a great way to re-use an otherwise worthless
| material. For those who don't like the aesthetic of _post-
| industrial wasteland_ , just use the concrete chunks in the
| interior of the gabion and put the pretty rocks on the exterior
| faces so that no-one will ever know your beautiful gabions are
| filled with demolition debris.
| ksenzee wrote:
| But the point of the article is that used concrete is no longer
| a worthless material, because it can now be recycled, which
| avoids the huge carbon impact of manufacturing new concrete.
___________________________________________________________________
(page generated 2024-05-23 23:00 UTC)