Executive Summary: Fill a hole with a pressurized mix of hydrogen and oxygen, kept in place with a plug of ice. Blow it up.
The inserter is placed into a drilled hole in the work face. Oxygen is vented to cool the outer portion of the hole. Water is sprayed to freeze as the inserter is extracted, leaving behind small gas lines with one-way valves, and an igniter wire. Gaseous hydrogen and oxygen are pumped through into the space behind the ice plug.
When ignited, the mix turns to hot water vapor, as does the ice plug. No contaminants are left in the salt. The valves and the igniter are a mess, though.
Both hydrogen and oxygen can be useful in a mine, so supplying them for explosive use shouldn't be an added complication. Pure oxygen can accelerate fires, and even ignite grease, while hydrogen can burn and explode in air, so standard precautions will have to be followed. Safety should be comparable to or better than standard explosives.-- baconbrain, Jan 14 2008 Lion Salt Works http://www.lionsaltworkstrust.co.uk/The pub opposite is pretty good ... [8th of 7, Jan 14 2008] //Safety should be comparable to or better than standard explosives.//
Not really. ANFO is essentially inert until the F part is added. Most booster charges ie powergel can be used as a harmless flammable solid unless properly initiated. Hydrogen is extremely flammable, and will form explosive mixes in a wide range of concentrations. You've already mentioned the hazards with handling LO2. Lastly, hydrogen will leak from almost any system you build for handling it - probably where you least want it. Even more lastly, what orebody are you charging that will support (without major diffusion, although in a controlled manner, this might not be so bad) the pressurisation of the H2+O2 charge at any significant pressure?
Ugh - sorry, that was very negative, I'm just not satisfied you can get sufficient energy density here for the shattering effects you're probably after. Was this intended specifically for salt mines?
May I suggest you up the safety appeal by locally electrolysing the hydrogen and oxygen? Supply power (via trailing cable) to the rig, which would have onboard water storage and bulk electrolysing tanks. Maybe. It certainly gets rid of a large infrastructure of hydrogen and oxygen tanks/pipes in your (assumedly) underground mine.-- Custardguts, Jan 14 2008 not my bone by the way.-- Custardguts, Jan 14 2008 I saw a salt mine the other day on the television. It was an affair based upon pumping salt water and running it out over flat areas where evaporation left salt behind... no explosives used. Are there different types of salt mine?-- vincevincevince, Jan 14 2008 Yes. That was different. In some areas Salt (rock salt, even) occors as a formation. I'm almost clueless as to the complexities of mining salt, I work with bauxite and hard rock mining, but I imagine it's interesting, given it's corrosive, and solubility issues.-- Custardguts, Jan 14 2008 <rolls up sleeves>
<picks up whiteboard marker and uncaps it>
Most of the Cheshire plain in the North West of the UK is underlain by thick beds of rock salt. These resulted from the evaporation of ancient seas, which were then overlain by sediments. The beds are 30 - 50 metres below the current topsoil, and vary from 4 to 10 metres thick.
The atmosphere in the mines is very dry, since the salt is rasonably hygroscopic. Since there is no moisture, corrosion in the mines themselves is not a problem; nothing rusts. The major wear factor on equipment is the abrasive nature of the salt itself.
The mining process consists of leaving 10m x 10m pillars and removing the remaining salt on a grid pattern; a plan view of the mine resembles a gigantic Roman hypocaust. The salt is extarcted by drilling the working face with conventional pneumatic drills, then pumping in ANFO and shotfiring. The large lumps ops salt so produced are loaded into a crusher/conveyor by a bucket loader, and then dumped into a conventional tipper truck, brought down the shaft in sections and assembled underground. At the base of the shaft, the tipper truck empites into a hopper to fill skips for transport to the surface.
At the surface, where it rains a lot, there are huge corrosion problems. Much of the equipment is analagous to maritime designs, with brass etc. much in evidence.
Some salt is extracted from the thinner beds where minig would be less easy by pumping warm water down a borehole and pumping up the resultant saturated brine. This leaves a series of pear shaped cavities deep below ground, which are subsequently used as storage for ethylene as feedstock for local chemical plants (which take chlorine from the salt and ethylene to produce Vinyl Chloride and subsequently PVC).
Does that answer your question(s) ?
PS Sorry, [BB], but there is no way that an oxygen/hydrogen mixture can achieve the nexessary brisance to shatter rock. The energy density er unit mas is just too low. The nearest thing to what you've described is LOX explosives using a carbon matrix as the fuel. But no fishbone, because it's not that bad an idea, just impractical.-- 8th of 7, Jan 14 2008 There is also another boutique method which can work anywhere you have an acceptable brine. A long building resembling a hothouse is constructed, with large fans and heaters at one end and lots of dangly straps of polyethelene all the way along. The heaters and fans are turned on and filtered brine is forced through atomisers at the blowy hot end. As the droplets move down the house, the water evaporates off and is carried away in the airstream, while the particles of salt remaining tend to accrete on the polyethelene strips then fall to the floor in clumps.-- ConsulFlaminicus, Jan 14 2008 Yes [UB], for production of a particular, high-end table salt. The system is basicly set up in a long canvas mess-tent, run for several weeks in mid summer, then the salt collected and the apparatus dismantled. The salt is then bagged and sold on a cottage industry basis throughout the rest of the year. Saw a documentary on it once (Landline) - fascinating.-- ConsulFlaminicus, Jan 14 2008 In situations where ignition of dust or gas is a hazard, they use (or used to use - maybe this is out of date) explosives based on water. Basically, a stout glass envelope is sealed, with a heating wire and a small amount of water in it. When connected, the heating wire heats the water to huge temperatures, until the pressure is sufficient to rupture the glass tube. The supercritical steam then expands violently and without flame or spark.
Small versions of this make an alarmingly disproportionate amount of noise - never tried actually blowing something up with them.-- MaxwellBuchanan, Jan 14 2008 They're OK, but even for coalmining (where dust explosions are a constant hazard) it's more common to use "sheathed" blasting gelatin. The sticks are a cylinder of explosive surounded with a thick tube of powdered calcium carbonate or similar supressant. Effectively, when the explosive detonates, the sheating quenches any resultant dust explosion.-- 8th of 7, Jan 14 2008 But the water things are easier to make in the privacy of your own home. Actually, given that they can cause quite a devastating explosion without the use of any "sniffable" explosives, I'm surprised they're not more widely used for scullduggerous motives.-- MaxwellBuchanan, Jan 14 2008 That's because they require a substantial electrical power source, which is the same reason man-portable laser weapons aren't common. Besides, there are plenty of unsniffable explosives - try an aluminium/ammonium perchlorate blend. Zero vapour pressure.-- 8th of 7, Jan 14 2008 /the sheating quenches any resultant dust explosion./
I presume because the inert sheath is converted to dust, which displaces and dilutes any flammable dust. That is pretty neat.-- bungston, Jan 14 2008 //They require a substantial electrical power source// I wonder. Suppose you have 5ml of water (which makes a frightening explosion) and suppose you want to heat it to 300°C (that's a guess, to be frank) before the glass goes bang. That's roughly 1500J of energy. The conversion of electrical current to heat is almost 100% efficient, but there will be losses of heat from the tube. So, let's assume you need 3000J of energy.
A laptop battery normally delivers something like an Amp at 10V, has a capacity of about 4-5Ah, and can deliver much higher currents for short times. So, let's assume conservatively that a laptop battery is capable of delivering 2.5A at 10V for a good few minutes. That is 25W, or 25J/s. At that rate, it'll take just 2 minutes to blow the water tube. If the tube is fairly well insulated, it'll take less energy (since we're assuming heat dissipation of 50%).
In short, a laptop battery would provide adequate power to blow one of these things.-- MaxwellBuchanan, Jan 14 2008 Your mathematics are, as always, impeccable. But the point is that the battery probably weighs at least half a kilo, plus you need a very reliable switching mechanism. Can you predict accurately the delay between initiating the device and the explosion ? That's pretty important ....
For commercial (as opposed to IED) use, the important factors are cost and reliability. A 250-gram stick of blasting gelatin costs a couple of dollars, and a detonator maybe a dollar more; and they're very reliable. ANFO works out even cheaper in bulk - check out the price of a drum of Ammoblast. Another factor is that the containment vessel is going to fragment, flinging (presumably) nasty sharp bits outwards with some force ...... with conventional explosives, you get a lot of hot gas and not much else. The copper case of the detonator tends to be completely vaporised. Projectiles are a big concern when blasting ..... hence the extensive use of sandbags and blast mats.
For small scale, specialised or effects work, yes, but for anything large scale, probably not.-- 8th of 7, Jan 14 2008 Well, for commercial use, I agree. There's also the sad fact that the energy yield can be no higher than the energy input, which means lots of noise but only a modest amount of energy (=damage).
However, for scurrilous use, such a device is worryingly feasible, if built into a laptop. Precise timing is probably not important, and the fragmentation of the glass case (which tends to be reduced to powder, anyway) is irrelevant.-- MaxwellBuchanan, Jan 14 2008 random, halfbakery