Energy Crisis theme 1: Hot bubbles
Posted Dec14-10 at 02:27 PM by Jon Richfield
Objections and Concerns
Adverse Effects of Salt Injection or Disposal
A very reasonable question concerns the ecological hazards of soluble inorganic materials such as salts. Most of them should not be very hazardous under the conditions contemplated. If the working fluids are gases such as air or argon, which are not solvents at temperatures around 700C-1700C, there should be very little discharge and we could ignore pollution problems stemming from their use.
Where more powerfully solvent fluids such as water and CO2 are extracted from or pumped through deep hot rock, they are likely to carry substances that one does not normally think of as being soluble, such as silica and various ore chemicals. Some are harmful and are best removed, preferably for commercial exploitation of their chemical content. Most are perfectly safe to discard at sea in diluted forms once any toxic components have been removed or immobilised. Insoluble sludges are harmless as long as they are not allowed to smother large areas. Soluble chemicals of low toxicity that occur routinely in sea water are harmless as long as they are diluted soon enough; in fact, most common substances to be expected in solutions leached from rocks, such as Ca, Mg and K compounds, would be desirable as nutrients in sea water. They would have the added attraction of precipitating or neutralising dissolved CO2.
If molten salts were used in or extracted from the shaft, most of them would be moderately benign and could be discharged into the sea without any ecological threat whatever. The most obvious candidates would be salts of sodium, magnesium, calcium and so on. Any breakdown products in the event of overheating or chemical reaction, say chlorine from chlorides, could easily and cleanly be scrubbed and neutralised.
One certainly would not want too much of most salts to escape into the soil, and certainly not noticeable amounts of sodium and chloride salts. Soil salination is a widespread problem and to pollute fresh ground water with more than a few parts per thousand of even nutrient salts is unacceptable. Firstly, this means that effluent must be disposed of with care, and secondly, if the shaft contains any substances undesirable in ground water, suitable precautions must be routine and reliable.
The necessary precautions vary with the site and conditions. For example, where ground water is already uselessly salt and has been stagnant in a limited area for a long time, one need not be too fussy about small spills. Such sites are common. Also, as a rule, serious drilling or shaft sinking of types relevant to this discussion tends to be many times deeper than any ground water of practical importance. In fact, ground water could be a serious nuisance, so power schemes of this type probably would shun sites where ground water is plentiful.
Adverse Effects of Salt Injection or Disposal
A very reasonable question concerns the ecological hazards of soluble inorganic materials such as salts. Most of them should not be very hazardous under the conditions contemplated. If the working fluids are gases such as air or argon, which are not solvents at temperatures around 700C-1700C, there should be very little discharge and we could ignore pollution problems stemming from their use.
Where more powerfully solvent fluids such as water and CO2 are extracted from or pumped through deep hot rock, they are likely to carry substances that one does not normally think of as being soluble, such as silica and various ore chemicals. Some are harmful and are best removed, preferably for commercial exploitation of their chemical content. Most are perfectly safe to discard at sea in diluted forms once any toxic components have been removed or immobilised. Insoluble sludges are harmless as long as they are not allowed to smother large areas. Soluble chemicals of low toxicity that occur routinely in sea water are harmless as long as they are diluted soon enough; in fact, most common substances to be expected in solutions leached from rocks, such as Ca, Mg and K compounds, would be desirable as nutrients in sea water. They would have the added attraction of precipitating or neutralising dissolved CO2.
If molten salts were used in or extracted from the shaft, most of them would be moderately benign and could be discharged into the sea without any ecological threat whatever. The most obvious candidates would be salts of sodium, magnesium, calcium and so on. Any breakdown products in the event of overheating or chemical reaction, say chlorine from chlorides, could easily and cleanly be scrubbed and neutralised.
One certainly would not want too much of most salts to escape into the soil, and certainly not noticeable amounts of sodium and chloride salts. Soil salination is a widespread problem and to pollute fresh ground water with more than a few parts per thousand of even nutrient salts is unacceptable. Firstly, this means that effluent must be disposed of with care, and secondly, if the shaft contains any substances undesirable in ground water, suitable precautions must be routine and reliable.
The necessary precautions vary with the site and conditions. For example, where ground water is already uselessly salt and has been stagnant in a limited area for a long time, one need not be too fussy about small spills. Such sites are common. Also, as a rule, serious drilling or shaft sinking of types relevant to this discussion tends to be many times deeper than any ground water of practical importance. In fact, ground water could be a serious nuisance, so power schemes of this type probably would shun sites where ground water is plentiful.
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