h a l f b a k e r yMy hatstand runneth over
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Go to any oil or gas refinery in the world, and you will find somewhere the humble flare. They're probably the most noticeable part of the refinery, and the part most easily identifiable by the ordinary layperson. They typically run idle, just keeping a pilot flame lit, but their most important function
is as a safety device. For every gram of oil or gas entering the refinery, it must be possible (in case of emergency) to keep the whole lot from entering the processing plant. Initially it will be stored, but it's impossible to store these volumes for long, so the rest is burned by means of a flare.
Flares are quite incredible things - it's not uncommon for a flare to be able to burn upwards of 100 tonnes of gas per minute. That's a lot of gas. Because of this, the flare tips must be very carefully designed. The idea is to get the flame to burn as hot as possible to destroy any toxic pollutants, and to get as much fuel through the flare as possible. Since the tips tend to be made of steel, that's a lot of steel, that has to withstand high temperatures, and that has to be hoisted up to the top of the elevated flare stack by crane (say 100+m in the air). So much for steel - it's only served well enough for long enough. Lets see if it can be improved...
Carbon-fibre. The stuff of racing cars. And bikes. It's strong, light, and resists enormously high temperatures. That means you can burn the flame hotter (using a smaller tip), and you can keep the mass of the tip down allowing you to use a smaller (cheaper) crane to pop it up there. It's less likely to soot up (being hotter), and much less likely to melt, meaning your maintenance/replacement schedule can be much longer. Sounds like a wonderful idea. The only fly in the ointment is that carbon fibre is porous - that's why carbon fibre exhausts are lined with glass. Now clearly glass is going to melt, and the whole thing is going to be ruined; but I see this not as a problem, but an opportunity. What else is porous, and you burn gas through? A gas mantle!
Now, not only can you vent off all your input in an emergency purge, but you can light the whole refinery in a clean white glow at the same time. If you were to plan ahead, you could arrange some kind of solar apparatus to do something useful with the light produced. Perhaps it could generate elecricity, heat water, or maybe be reflected back to the flare tip like some kind of solar furnace.
Now, it's been a while since I've used a gas mantle, but how much light do you think you could get out of 100 tonnes of gas per minute?
Devil's Breath
The_20Devil_27s_20Breath
my humble alternative was to suggest cast iron [xenzag, Jan 31 2007]
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What sort of heat tolerance are you seeing for carbon fiber composites? I am having trouble finding anything higher than 320C. |
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And there I was thinking this was a method of avoiding getting frayed jeans. |
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Why not use this heat source to generate electricity for the refinery? Since the source is variable the electricity would have to be used to create a storable electric source of some kind or be fed into the general electric net. |
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My thought about the heat is that carbon fibre is used for F1 racing car brake discs. In this application it's regularly subjected to heats in the order of 1000 degrees celcius. Steel brake discs get very upset before this stage. |
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I'm not sure that it would need to be a composite - just plain woven carbon fibre could do the job. I don't expect it to be load bearing (beyond its own weight), and it shouldn't be necessary to absorb any impacts beyond those needed to mount the tip. |
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One possible thought I've had is to use the heat/light generated to drive an air compressor to feed the flare. It's important to get a lot of air into the system to burn the hydrocarbons effectively. If you use the energy emitted to drive a forced air induction system, it avoids the need to make a choice about running separate compressors from an alternative fuel source, or feeding the flame by convection. |
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Dunno - that's just off the top of my head just now... |
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OK, you are talking reinforced carbon-carbon. Not just carbon fiber. That is some EXPENSIVE stuff. And hard to work with. |
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Why not just use ceramics? Ceramics in bell foundries are typically able to withstand temperatures in the 3000 F range. |
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I'd much rather see HRSG (Heat Recovery Steam Generator) sets on all flares at refineries. Or some kind of high-capacity bulk storage system. I wonder what percentage of the total chemical energy potential of the product passing through the refinery is wasted on these flares? is it as much as 5-10%?? If so, you'd definitely be within the feasibility bounds of putting a steam circuit in place, let alone a compressor/tankage system. |
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Oh btw using the light from the flame to generate power is about as low yield/efficiency as you can get. Much better off using the heat as in steam plant, etc which can approach 50% efficiency under the right circumstances. |
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The stuff used in brake discs is a type of carbon ceramic composite, I think. Plain old carbon fiber is full of resin which burns off. |
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Yep - I accept that the HRSG method would be fantastically more efficient at recovering the energy. The point was more to build the most brilliantly (in any sense) overpowered gas mantle in the world, and have some ancillary benefits in terms of cost and efficiency. |
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If it comes down to reinforced carbon-carbon, yes that would put a big dent in the economics. Even with the smalle gauge flare you could conceivably use for the same throughput, and the associated savings in materials, lifting equipment hire (these cranes are certainly not cheap), and test equipment... It may just not come out economically viable. I reckoned it would be possible with plain (fairly cheap) carbon fibre, but I could well be wrong there. |
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Ceramics would give you better heat resilience than steel, yes, but they wouldn't give you a huge weight benefit for loading it onto the flare, and they wouldn't give you that cosy glow when they fire... |
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In terms of what's burned off in the plant, I don't believe it's as much as 5% typically. You tend not to see the toxic gases being burned off because they commonly go through "ground flares", which aren't dissimilar to big open-topped boxes full of gas nozzles at the bottom. You can't actually see them flaring, so unless you're sitting looking at a meter in a control room, you'll never know... The elevated flares tend only to fire in an emergency, or if a significant part of the plant is shut down for maintenance. |
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The elevated flares tend not to fire often enough to justify putting a huge amount of generating apparatus onto them, which is why I suggested only using that energy to drive an air compressor just to feed the flame. And I know that a solar farm to generate power from the flame of burning fossil fuels is about as inefficient as it gets - I just felt that it fits in with the theme of building the brightest stick in the world :) |
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The problem with plain carbon fiber is that it's floppy. You need to mix something in with the fiber to stiffen it up. Typically this is some form of plastic (tarted up with the name "resin"). Although it could be glass, steel, or more carbon (in vapor deposited form). |
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Tons of people currently use coal power-plants for energy...the amount of energy that could be derived from 100 tonnes of gas per minute would VERY easily replace that...we just need to close the loop. |
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Having spent some time around a kiln, I must argue that ceramics would indeed give you a cozy glow, and if it was poured as a sort of mesh, there might be some reduction in weight. At the sizes you are looking into, and from the distances you are likely to be from it, the difference in light output would likely be rather negligible. |
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Also, ceramics would be much cheaper than carbon fiber. Sadly, it would also be the most fragile of fragile mantles in the world. |
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Just at a guess, I would say that with the temperature ranges you would need, and the pressure of 100 tonnes of gas per minute, the possibility of shattering any kind of mantle would be very real. |
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