Plastics and Rubbish

In the current “atmosphere” of climate change, politicians are taking more notice of the environment, to which as a sceptic I notice they are not prepared to do a lot about it. Part of the problem is following the “swing to the right” in the 1980s, politicians have taken notice of Reagan’s assertion that the government is the problem, so they have all settled down to not doing very much, and they have shown some skill at doing very little. “Leave it to the market” has a complication: the market is there to facilitate trade in which all the participants wish to offer something that customers want and they make a profit while doing it. The environment is not a customer in the usual sense and it does not pay, so “the market” has no direct interest in it.

There is no one answer to any of these problems. There is no silver bullet. What we have to do is chip away at these problems, and one that indicates the nature of the problem is plastics. In New Zealand the government has decided that plastic bags are bad for the environment, so the single use bags are no longer used in supermarkets. One can argue whether that is good for the environment, but it is clear that the wilful throwing away of plastics and their subsequent degradation is bad for it. And while the disposable bag has been banned here, rubbish still has a lot of plastics in it, and that will continue to degrade. If it were buried deep in some mine it probably would not matter, but it is not. So why don’t we recycle them?

Then first reason is there are so many variations of them and they do not dissolve in each other. You can emulsify a mix, but the material has poor strength because there is very little binding at the interface of the tiny droplets. That is because they have smooth surfaces, like the interface between oil and water. If the object is big enough this does not matter so much, thus you can make reasonable fence posts out of recycled plastics, but there really is a limit to the market for fence posts.

The reason they do not dissolve in each other comes from thermodynamics. For something to happen, such as polymer A dissolving in polymer B, the change (indicated by the symbol Δ) in what is called the free energy ΔG has to be negative. (The reason it is negative is convention; the reason it is called “free” has nothing to do with price – it is not free in that sense.) To account for the process, we use an equation

            ΔG = ΔH -T ΔS

ΔH reflects the change of energy between each molecule in its own material and in solution of the other material. As a general rule, molecules favour having their own kind nearby, especially if they are longer because the longer they are the interactions per atom are constant for other molecules of the same material, but other molecules do not pack as well. Thinking of oil and water, the big problem for solution is that water, the solvent, has hydrogen bonds that make water molecules stick together. The longer the polymer, per molecule that enhances the effect. Think of one polymer molecule has to dislodge a very large number of solvent molecules. ΔS is the entropy and it increases as the degree of randomness increases. Solution is more random per molecule, so whether something dissolves is a battle between whether the randomness per molecule can overcome the attractions between the same kind. The longer the polymer, the less randomness is introduced and the greater any difference in energy between same and dissolved. So the longer the polymers, the less likely they are to dissolve in each other which, as an aside, is why you get so much variety in minerals. Long chain silicates that can alter their associate ions like to phase separate.

So we cannot recycle, and they are useless? Well, no. At the very least we can use them for energy. My preference is to turn them, and all the organic material in municipal refuse, into hydrocarbons. During the 1970s oil crises the engineering was completed to build a demonstration plant for the city of Worcester in Massachusetts. It never went ahead because as the cartel broke ranks and oil prices dropped, converting wastes to hydrocarbon fuels made no economic sense. However, if we want to reduce the use of fossil fuels, it makes a lot of sense to the environment, IF we are prepared to pay the extra price. Every litre of fuel from waste we make is a litre of refined crude we do not have to use, and we will have to keep our vehicle fleet going for quite some time. The basic problem is we have to develop the technology because the engineering data for that previous attempt is presumably lost, and in any case, that was for a demonstration plant, which is always built on the basis that more engineering questions remain. As an aside, water at about 360 degrees Centigrade has lost its hydrogen bonding preference and the temperature increase means oil dissolves in water.

The alternative is to burn it and make electricity. I am less keen on this, even though we can purchase plants to do that right now. The reason is simple. The combustion will release more gases into the atmosphere. The CO2 is irrelevant as both do that, but the liquefaction approach sends nitrogen containing material out as water soluble material which could, if the liquids were treated appropriately, be used as a fertilizer, whereas in combustion they go out the chimney as nitric oxide or even worse, as cyanides. But it is still better to do something with it than simply fill up local valleys.

One final point. I saw an item where some environmentalist was condemning a UK thermal plant that used biomass arguing it put out MORE CO2 per MW of power than coal. That may be the case because you can make coal burn hotter and the second law of thermodynamics means you can extract more energy in the form of work. (Mind you, I have my doubts since the electricity is generated from steam.) However, the criticism shows the inability to understand calculus. What is important is not the emissions right now, but those integrated over time. The biomass got its carbon from the atmosphere say forty years ago, and if you wish to sustain this exercise you plant trees that recover that CO2 over the next forty years. Burn coal and you are burning carbon that has been locked away from the last few million years.

Thorium as a Nuclear Fuel

Apparently, China is constructing a molten salt nuclear reactor to be powered by thorium, and it should be undergoing trials about now. Being the first of its kind, it is, naturally, a small reactor that will produce 2 megawatt of thermal energy. This is not much, but it is important when scaling up technology not to make too great of leaps because if something in the engineering has to be corrected it is a lot easier if the unit is smaller. Further, while smaller is cheaper, it is also more likely to create fluctuations, especially with temperature, and when smaller they are far easier to control. The problem with a very large reactor is if something is going wrong it takes a long time to find out, but then it also becomes increasingly difficult to do anything about it.

Thorium is a weakly radioactive metal that has little current use. It occurs naturally as thorium-232 and that cannot undergo fission. However, in a reactor it absorbs neutrons and forms thorium-233, which has a half-life of 22 minutes and β-decays to protactinium-233. That has a half-life of 27 days, and then β-decays to uranium-233, which can undergo fission. Uranium-233 has a half-life of 160,000 years so weapons could be made and stored.  

Unfortunately, 1.6 tonne of thorium exposed to neutrons and if appropriate chemical processing were available, is sufficient to make 8 kg of uranium-233, and that is enough to produce a weapon. So thorium itself is not necessarily a form of fuel that is free of weapons production. However, to separate Uranium-233 in a form to make a bomb, major chemical plant is needed, and the separation needs to be done remotely because apparently contamination with Uranium-232 is possible, and its decay products include a powerful gamma emitter. However, to make bomb material, the process has to be aimed directly at that. The reason is, the first step is to separate the protactinium-233 from the thorium, and because of the short half-life, only a small amount of the thorium gets converted. Because a power station will be operating more or less continuously, it should not be practical to use it to make fissile material for bombs.

The idea of a molten salt reactor is that the fissile material is dissolved in a liquid salt in the reactor core. The liquid salt also takes away the heat which, when the salt is cycles through heat exchangers, converts water to steam, and electricity is obtained in the same way as any other thermal station. Indeed, China says it intends to continue using its coal-fired generators by taking away the furnaces and replacing them with a molten salt reactor. Much of the infrastructure would remain. Further, compared with the usual nuclear power stations, the molten salt reactors operate at a higher temperature, which means electricity can be generated more efficiently.

One advantage of a molten salt reactor is it operates at lower pressures, which greatly reduces the potential for explosions. Further, because the fuel is dissolved in the salt you cannot get a meltdown. That does not mean there cannot be problems, but they should be much easier to manage. The great advantage of the molten salt reactor is it burns its reaction products, and an advantage of a thorium reactor is that most of the fission products have shorter half-lives, and since each fission produces about 2.5 neutrons, a molten salt reactor further burns larger isotopes that might be a problem, such as those of neptunium or plutonium formed from further neutron capture. Accordingly, the waste products do not comprise such a potential problem.

The reason we don’t directly engage and make lots of such reactors is there is a lot of development work required. A typical molten salt mix might include lithium fluoride, beryllium fluoride, the thorium tetrafluoride and some uranium tetrafluoride to act as a starter. Now, suppose the thorium or uranium splits and produces, say, a strontium atom and a xenon atom. At this point there are two fluorine atoms as surplus, and fluorine is an extraordinarily corrosive gas. As it happens, xenon is not totally unreactive and it will react with fluorine, but so will the interior of the reactor. Whatever happens in there, it is critical that pumps, etc keep working. Such problems can be solved, but it does take operating time to be sure such problems are solved. Let’s hope they are successful.

The Fusion Energy Dream

One of the most attractive options for our energy future is nuclear fusion, where we can turn hydrogen into helium. Nuclear fusion works, even on Earth, as we can see when a hydrogen bomb goes off. The available energy is huge. Nuclear fusion will solve our energy crisis, we have been told, and it will be available in forty years. That is what we were told about 60 years ago, and you will usually hear the same forty year prediction now!

Nuclear fusion, you will be told, is what powers the sun, however we won’t be doing what the sun does any time soon. You may guess there is a problem in that the sun is not a spectacular hydrogen bomb. What the sun does is to squeeze hydrogen atoms together to make the lightest isotope of helium, i.e. 2He. This is extremely unstable, and the electric forces will push the protons apart in an extremely short time, like a billionth of a billionth of a second might be the longest it can last, and probably not that long. However, if it can acquire an electron, or eject a positron, before it decays it turns into deuterium, which is a proton and a neutron. (The sun also uses a carbon-oxygen cycle to convert hydrogen to helium.) The difficult thing that a star does, and what we will not do anytime soon, is to make neutrons (as opposed to freeing them).

The deuterium can then fuse to make helium, usually first with another proton to make 3He, and then maybe with another to make 4He. Each fusion makes a huge amount of energy, and the star works because the immense pressure at the centre allows the occasional making of deuterium in any small volume. You may be surprised by the use of the word “occasional”; the reason the sun gives off so much energy is simply that it is so big. Occasional is good. The huge amount of energy released relieves some of the pressure caused by the gravity, and this allows the star to live a very long time. At the end of a sufficiently large star’s life, the gravity allows the material to compress sufficiently that carbon and oxygen atoms fuse, and this gives of so much energy that the increase in pressure causes  the reaction  to go out of control and you have a supernova. A bang is not good.

The Lawrence Livermore National Laboratory has been working on fusion, and has claimed a breakthrough. Their process involves firing 192 laser beams onto a hollow target about 1 cm high and a diameter of a few millimeters, which is apparently called a hohlraum. This has an inner lining of gold, and contains helium gas, while at the centre is a tiny capsule filled with deuterium/tritium, the hydrogen atoms with one or two neutrons in addition to the required proton. The lasers heat the hohlraum so that the gold coating gives off a flux of Xrays. The Xrays heat the capsule causing material on the outside to fly off at speeds of hundreds of kilometers per second. Conservation of momentum leads to the implosion of the capsule, which gives, hopefully, high enough temperatures and pressures to fuse the hydrogen isotopes.

So what could go wrong? The problem is the symmetry of the pressure. Suppose you had a spherical-shaped bag of gel that was mainly water, and, say, the size of a football and you wanted to squeeze all the water out to get a sphere that only contained the gelling solid. The difficulty is that the pressure of a fluid inside a container is equal in all directions (leaving aside the effects of gravity). If you squeeze harder in one place than another, the pressure relays the extra force per unit area to one where the external pressure is weaker, and your ball expands in that direction. You are fighting jelly! Obviously, the physics of such fluids gets very complicated. Everyone knows what is required, but nobody knows how to fill the requirement. When something is unequal in different places, the effects are predictably undesirable, but stopping them from being unequal is not so easy.

The first progress was apparently to make the laser pulses more energetic at the beginning. The net result was to get up to 17 kJ of fusion energy per pulse, an improvement on their original 10 kJ. The latest success produced 1.3 MJ, which was equivalent to 10 quadrillion watts of fusion power for a 100 trillionth of a second. An energy generation of 1.3 MJ from such a small vessel may seem a genuine achievement, and it is, but there is further to go. The problem is that the energy input to the lasers was 1.9 MJ per pulse. It should be realised that that energy is not lost. It is still there so the actual output of a pulse would be 3.2 MJ of energy. The problem is that the output includes the kinetic energy of the neutrons etc produced, and it is always as heat whereas the input energy was from electricity, and we have not included the losses of power when converting electricity to laser output. Converting that heat to electricity will lose quite a bit, depending on how it is done. If you use the heat to boil water the losses are usually around 65%. In my novels I suggest using the magnetohydrodynamic effect that gets electricity out of the high velocity of the particles in the plasma. This has been made to work on plasmas made by burning fossil fuels, which doubles the efficiency of the usual approach, but controlling plasmas from nuclear fusion would be far more difficult. Again, very easy to do in theory; very much less so in practice. However, the challenge is there. If we can get sustained ignition, as opposed to such a short pulse, the amount of energy available is huge.

Sustained fusion means the energy emitted from the reaction is sufficient to keep it going with fresh material injected as opposed to having to set up containers in containers at the dead centre of a multiple laser pulse. Now, the plasma at over 100,000,000 degrees Centigrade should be sufficient to keep the fusion going. Of course that will involve even more problems: how to contain a plasma at that temperature; how to get the fuel into the reaction without melting then feed tubes or dissipating the hydrogen; how to get the energy out in a usable form; how to cool the plasma sufficiently? Many questions; few answers.

A New Way of Mining?

One of the bigger problems our economies face is obtaining metals. Apparently the price of metals used in lithium-ion batteries is soaring because supply cannot expand sufficiently, and there appears to be no way current methodology can keep up.

 Ores are obtained by physically removing them from the subsurface, and this tends to mean that huge volumes of overburden have to be removed. Global mining is estimated to produce 100 billion t of overburden per year, and that usually has to be carted somewhere else and dumped.  This often leads to major disasters, such as mine tailing causing dams, and then collapsing, thus Brazil has had at least two such collapses that led to something like 140 million cubic meters of rubble moving and at least 256 deaths. The better ores are now worked out and we are resorting to poorer ores, most of which contain less than 1% is what you actually want. The rest, gangue, is often environmentally toxic and is quite difficult to dispose of safely. The whole process is energy intensive. Mining contributes about 10% of the energy-related greenhouse gas emissions. Yet if we take copper alone, it is estimated that by 2050 demand will increase by up to 350%. The ores we know about are becoming progressively lower grade and they are found at greater depths.

We have heard of the limits to growth. Well, mining is becoming increasingly looking like becoming unsustainable, but there is always the possibility of new technology to get the benefit from increasingly more difficult sources. One such possible technique involves first inserting acid or lixiviant into the rock to dissolve the target metal in the form of an ion then use a targeted electric field to transport the metal-rich solution to the surface. This is a variant of a technique used to obtain metals from fly ash, sludge, etc.

The objective is to place an electrode either within or surrounding the ore, then the acid is introduced from an external reservoir. There is an alternative reservoir with a second electrode with opposite charge to that of the metal-bearing ion. The metal usually bears a positive charge in the textbooks, so you would have your reservoir electrode negatively charged, but it is important to keep track of your chemistry. For example, if iron were dissolved in hydrochloric acid, the main ion would be FeCl4-, i.e. an anion.

Because transport occurs through electromigration, there is no need for permeability enhancement techniques, such as fracking. About 75% of copper ore reserves are as copper sulphide that lie beneath the water table. The proposed technique was demonstrated on a laboratory scale with a mix of chalcopyrite (CuFeS2) and quartz, each powdered. A solution of ferric chloride was added, and a direct current of 7 V was applied to electrodes at opposite ends of a 0.57 m path, over which there was a potential drop of about 5V, giving a maximal voltage gradient of 1.75 V/cm. The ferric chloride liberated copper as the cupric cation. The laboratory test extracted 57 weight per cent of the available copper from a 4 cm-wide sample over 94 days, although 80% was recovered in the first 50 days. The electric current decreased over the first ten days from 110 mA to 10 mA, suggestive of pore blocking. Computer simulations suggest that in the field, about 70% of the metal in a sample accessed by the electrodes could be recovered over a three year period. The process would have the odd hazard, thus a 5 meter spacing between electrodes employed, in the simulation, a 500 V difference. If the ore is several hundred meters down, this could require quite a voltage. Is this practical? I do not know, but it seems to me that at the moment the amount of dissolved material, the large voltages, the small areas and the time taken will count against it. On the other hand, the price of metals are starting to rise dramatically. I doubt this will be a final solution, but it may be part of one.

Living Near Ceres

Some will have heard of Gerard O’Neill’s book, “The High Frontier”. If not, see The idea was to throw material up from the surface of the Moon to make giant cylinders that would get artificial gravity from rotation, and people could live their lives in the interior with energy being obtained in part by solar energy. The concept was partly employed in the TV series “Babylon 5”, but the original concept was to have open farmland as well. Looks like science fiction, you say, and in fairness I have included such a proposition in a science fiction novel I am currently writing, However, I have also read a scientific paper on this topic (arXiv:2011.07487v3) which appears to have been posted on the 14th January, 2021. The concept is to put such a space settlement using material obtained from the asteroid Ceres, and orbiting near Ceres.

The proposal is ambitious, if nothing else. The idea is to build a number of habitats, and to ensure such habitats are not too big but they stay together they are tethered to a megasatellite, which in turn will grow and new settlements are built. The habitats spin in such a way to attain a “gravity” of 1 g, and are attached to their tethers by magnetic bearings that have no physical contact between faces, and hence never wear. A system of travel between habitats proceeds along the tethers. Rockets would be unsustainable because the molecules they throw out to space would be lost forever.

The habitats would have a radius of 1 km, a length of 10 km, and have a population of 56,700, with 2,000 square meters per person, just under 45% of which would be urban. Slightly more scary would be the fact it has to rotate every 1.06 minutes. The total mass per person would be just under 10,000 t, requiring an energy to produce it of 1 MJ/kg, or about 10 GJ.

The design aims to produce an environment for the settlers that has Earth-like radiation shielding, gravity, and atmosphere. It will have day/night on a 24 hr cycle with 130 W/m^2 insolation, similar to southern Germany, and a population density of 500/km^2, similar to the Netherlands. There would be fields, parks, and forests, no adverse weather, no natural disasters and ultimately it could have a greater living area than Earth. It will be long-term sustainable. To achieve that, animals, birds and insects will be present, i.e.  a proper ecosystem. Ultimately it could provide more living area than Earth. As can be seen, that is ambitious. The radiation shielding involves 7600 kg/m^2, of which 20% is water and the rest silicate regolith. The rural spaces have a 1.5 m depth of soil, which is illuminated by the sunlight. The sunlight is collected and delivered from mirrors into light guides. Ceres is 2.77 times as far as Earth from the sun, which means the sunlight is only about 13% as strong as at Earth, so over eight times the mirror collecting are is required for every unit area to be illuminated to get equivalent energy. 

The reason cited for proposing this to be at Ceres is that Ceres has nitrogen. Actually, there are other carbonaceous asteroids, and one that is at least 100 km in size could be suitable. Because Ceres’ gravity is 0.029 times that of Earth, a space elevator could be feasible to bring material cheaply from the dwarf planet, while a settlement 100,000 km from the surface would be expected to have a stable orbit.

In principle, there could be any number of these habitats, all linked together. You could have more people living there than on Earth. Of course there are some issues with the calculation. The tethering of habitats, and of giving the habitats sufficient strength requires about 5% of the total mass in the form of steel. Where does the iron come from? The asteroids have plenty of iron, but the form is important. How will it be refined? If it is on the form of olivine or pyroxene, then with difficulty. Vesta apparently has an iron core, but Vesta is not close, and most of the time, because it has a different orbital period, it is very far away.But the real question is, would you want to live in such a place? How much would you pay for the privilege? The cost of all this was not estimated, but it would be enormous so most people could not afford it. In my opinion, cost alone is sufficient that this idea will not see the light of day.

Materials that Remember their Original Design

Recall in the movie Terminator 2 there was this robot that could turn into a liquid then return to its original shape and act as if it were solid metal. Well, according to Pu Zhang at Binghampton University in the US, something like that has been made, although not quite like the evil robot. What he has made is a solid that acts like a metal that, with sufficient force, can be crushed or variously deformed, then brought back to its original shape spontaneously by warming.

The metal part is a collection of small pieces of Field’s alloy, an alloy of bismuth, indium and tin. This has the rather unusual property of melting at 62 degrees Centigrade, which is the temperature reached by fairly warm water. The pieces have to be made with flat faces of the desired shape so that they effectively lock themselves together and it is this locking that at least partially gives the body its strength. The alloy pieces are then coated with a silicone shell using a process called conformal coating, a technique used to coat circuit boards to protect them from the environment and the whole is put together with 3D printing. How the system works (assuming it does) is that when force is applied that would crush or variously deform the fabricated object, as the metal pieces get deformed, the silicone coating gets stretched. The silicone is an elastomer, so as it gets stretched, just like a rubber band, it stores energy. Now, if the object is warmed the metal melts and can flow. At this point, like a rubber band let go, the silicone restores everything to the original shape, the when it cools the metal crystallizes and we are back where we started.

According to Physics World Zhang and his colleagues made several demonstration structures such as a honeycomb, a spider’s web-like structure and a hand, these were all crushed, and when warmed they sprang back to life in their original form. At first sight this might seem to be designed to put panel beaters out of business. You have a minor prang but do not worry: just get out the hair drier and all will be well. That, of course, is unlikely. As you may have noticed, one of the components is indium. There is not a lot of indium around and for its currently very restricted uses it costs about $US800/kg, which would make for a rather expensive bumper. Large-scale usage would make the cost astronomical. The cost of manufacturing would also always limit its use to rather specialist objects, irrespective of availabiity.One of the uses advocated by Zhang is in space missions. While weight has to be limited on space missions, volume is also a problem, especially for objects with awkward shapes, such as antennae or awkward shaped superstructures. The idea is they could be crushed down to a flat compact load for easy storage, then reassembled. The car bumper might be out of bounds because of cost and limited indium supply, but the cushioning effect arising from its ability to absorb a considerable amount of energy might be useful in space missions. Engineers usually use aluminium or steel for cushioning parts, but they are single use. A spacecraft with such landing cushions can be used once, but landing cushions made of this material could be restored simply by heating them. Zhang seems to favour the use in space engineering. He says he is contemplating building a liquid robot, but there is one thing, apart from behaviour, that such a robot could not do that the terminator robot did, and that is, if the robot has bits knocked off and the bits melt, they cannot reassemble into a whole. Leaving aside the fact there is no force to rejoin the bits, the individual bits will merely reassemble into whatever parts they were and cannot rejoin with the other bits. Think of it as held together by millions of rubber bands. Breaking into bits breaks a fraction of the rubber bands, which leaves no force to restore the original shape at the break.

Molten Salt Nuclear Reactors

In the previous post, I outlined two reasons why nuclear power is overlooked, if not shunned, despite the fact it will clearly reduce greenhouse gas emissions. I discussed wastes as a problem, and while they are a problem, as I tried to show they are in principle reasonably easily dealt with. There is a need for more work and there are difficulties, but there is no reason this problem cannot be overcome. The other reason is the danger of the Chernobyl/Fukushima type explosion. In the case of Chernobyl, it needed a frightening number of totally stupid decisions to be made, and you might expect that since it was a training exercise there would be people there who knew what they were doing to supervise. But no, and worse, the operating instructions were unintelligible, having been amended with strike-outs and hand-written “corrections” that nobody could understand. You might have thought the supervisor would check to see everything was available and correct before starting, but as I noted, there has never been a shortage of stupidity.

The nuclear reaction, which generates the heat, is initiated by a fissile nucleus absorbing a neutron and splitting, and then keeping going by providing more neutrons. These neutrons either split further fissile nuclei, such as 235U, or they get absorbed by something else, such as 238U, which converts that nucleus to something else, in this case eventually 239Pu. The splitting of nuclei produces the heat, and to run at constant temperature, it is necessary to have a means of removing that amount of heat continuously. The rate of neutron absorption is determined by the “concentration” of fissile material and the amount of neutrons absorbed by something else, such as water, graphite and a number of other materials. The disaster happens when the reaction goes too quickly, and there is too much heat generated for the cooling medium. The metal melts and drips to the bottom of the reactor, where it flows together to form a large blob that is out of the cooling circuit. As the amount builds up it gets hotter and hotter, and we have a disaster.

The idea of the molten salt reactor is there are no metal rods. The material can be put in as a salt in solution, so the concentration automatically determines the operating temperature. The reactor can be moderated with graphite, beryllium oxide, or a number of others, or it can be run unmoderated. Temperatures can get up to 1400 degrees C, which, from basic thermodynamics, gives exceptional power efficiency, and finally, reactors can be relatively small. The initial design was apparently for aircraft propulsion, and you guessed it: bombers. The salts are usually fluorides because low-valence fluorides boil at very high temperatures, they are poor neutron absorbers, and their chemical bonds are exceptionally strong, which limits corrosion, and they are exceptionally inert chemically. In one sense they are extremely safe, although since beryllium fluoride is often used, its extreme toxicity requires careful handling. But the big main advantage of this sort of reactor, besides avoiding the meltdown, is it burns actinides and so if it makes plutonium, that is added to the fuel. More energy! It also burns some of the fission wastes, and such burning of wastes also releases energy. It can be powered by thorium (with some uranium to get the starting neutrons) which does not make anything suitable for making bombs. Further, the fission products in the thorium cycle have far shorter half-lives. Research on this started in the 1960s and essentially stopped. Guess why! There are other fourth generation reactors being designed, and some nuclear engineers may well disagree with my preference, but it is imperative, in my opinion, that we adopt some. We badly need some means of generating large amounts of electricity without burning fossil fuels. Whatever we decide to do, while the physics is well understood, the engineering may not be, and this must be solved if we are to avoid a planet-wide overheating. The politicians have to ensure this job gets done.

Forests versus Fossil Fuels – a Debate on Effectiveness

The use of biomass for fuel has been advocated as a means of reducing carbon dioxide emissions, but some have argued it does nothing of the sort. There was a recent article in Physics World that discusses this issue, and here is a summary. First, the logic behind the case is simple. The carbon in trees all comes from the air. When the plant dies, it rots, releasing energy to the rotting agents, and much of the carbon is released back into the air. Burning it merely intercepts that cycle and gives the use of the energy to us as opposed to the microbes. A thermal power station in North Yorkshire is now burning enough biomass to generate 12% of the UK’s renewable energy. The power station claims it has changed from being one of the largest CO2 emitters in Europe to supporting the largest decarbonization project in Europe. So what could be wrong? 

My first response is that other than a short-term fix, burning it in a thermal power station is wrong because the biomass is more valuable for generating liquid fuels, for which there is no alternative. There are many alternative ways of generating electricity, and the electricity demand is so high that alternatives are going to be needed. There is no obvious replacement for liquid fuels in air transport, although the technology to make such fuels is yet to be developed properly. 

So, what can the critics carp on about? There were two criticisms about the calculated savings being based on the assumptions: (a) the CO2 released is immediately captured by growing plants, and (b) the biomass would have rotted and put its carbon back into the atmosphere anyway. The first is patently wrong, but so what? The critics claim it takes time for the CO2 to be reabsorbed, and that depends on fresh forest, or regrowth of the current forest. So replanting is obviously important, but equally there is quite some time used up in carbon reabsorption. According to the critics, this takes between 40 and a hundred years, then it is found that because biomass is a less energy-dense material during combustion, compared with coal you actually increase the CO2 emissions in the short-term. The reabsorption requires new forest to replace the old.

The next counter-argument was that the block should not be counted, but rather the landscape – if you only harvest 1% of the forest, the remaining 99% is busily absorbing carbon dioxide. The counter to that is that it would have been doing that anyway. The next objection is that older forests absorb carbon over a much longer period, and sequester more carbon than younger stands. Further, the wood that rots in the soil feeds microbes that otherwise will be eating their way through stored carbon in the soil. The problem is not so much that regrowth does not absorb carbon dioxide, but rather it does not reabsorb it fast enough to be meaningful for climate change.

Let us consider the options where we either do it or we do not. If we do, assume we replant the same area, and fresh vegetation is sufficient to maintain the soil carbon. In year 1 we release x t CO2. After year 40, say, it has been all absorbed, but we burn again and release x t CO2. By year 80, it is all reabsorbed, so we burn again. There is a net x t CO2 in the air. Had we not done this, in each of years 1, 40 and 80 we burn kx t CO2, giving us now 3kx t CO2, where k is some number <1 to counter the greater efficiency of burning coal. Within this scenario eventually the biofuel must save CO2. That we could burn coal and plant fresh forests is irrelevant because in the above scenario we only replace what was there. We can always plant fresh forest.

Planting more works in both options. This is a bit oversimplified, but it is aimed to show that you have to integrate what happens over sufficient time to eliminate the effect of non-smoothness in the functions, and count everything. In my example above it could be argued I do not know whether there will be a reduction in soil carbon, but if that is troublesome, at least we have focused attention on what we need to know. It is putting numbers on a closed system, even if idealized, that shows the key facts in their proper light. 

Transport System Fuel. Some passing Comments

In the previous series of posts, I have discussed the question of how we should power our transport systems that currently rely on fossil fuels, and since this will be a brief post, because I have been at a conference for most of this week, I thought it would be useful to have a summary. There are two basic objectives: ensure that there are economic transport options, and reduce the damage we have caused to the environment. The latter one is important in that we must not simply move the problem.

At this stage we can envisage two types of power: heat/combustion and electrical. The combustion source of power is what we have developed from oil, and many of the motors, especially the spark ignition motors, have been designed to optimise the amount of the oil that can be so used. The compression of most spark ignition engines is considerably lower than it could be if the octane rating was higher. These motors will be with us for some time; a car bought now will probably still be on the road in twenty years so what do we do? We shall probably continue with oil, but biofuels do offer an alternative. Some people say biofuels themselves have a net CO2 output in their manufacture. Maybe, but it is not necessary; the main reason would be that the emphasis is put onto producing the appropriate liquids because they are worth more than process heat. Process heating can be provided from a number of other sources. The advantages of biofuels are they power existing vehicles, they can be CO2 neutral, or fairly close to it, we can design the system so it produces aircraft fuel and there is really no alternative for air transport, and there are no recycling problems following usage. The major disadvantages are that the necessary technology has not really been scaled up so a lot of work is required, it will always be more expensive than oil until oil supplies run down so there is a poor economic reason to do this unless missions are taxed, and the use of the land for biofuels will put pressure on food production. The answers are straightforward: do the development work, use the tax system to change the economic bias, and use biomass from the oceans.

There are alternatives, mainly gases, but again, most of them involve carbon. These could be made by reducing CO2, presumably through using photolysis of water (thus a sort of synthetic photosynthesis) or through electricity and to get the scale we really need a very significant source of electricity. Nuclear power, or better still, fusion energy would work, but nuclear power has a relative disappointing reputation, and fusion power is still a dream. Hydrazine would make a truly interesting fuel, although its toxicity would not endear it to many. Hydrogen can work well for buses, etc, that have direct city routes.

Electricity can be delivered by direct lines (the preferred option for trains, trams, etc.), but otherwise it must be by batteries or fuel cells. The two are conceptually very similar. Both depend on a chemical reaction that can be very loosely described as “burning” something but generating electricity instead of heat. In the fuel cell, the material being “burnt” is added from somewhere else, and the oxidising agent, which may be air, must also be added. In the battery, nothing is added, and when what is there is used, it is regenerated by charging.

Something like lithium is almost certainly restricted to batteries because it is highly reactive. Lithium fires are very difficult to put out. The lithium ion battery is the only one that has been developed to a reasonable level, and part of the reason for that is that the original market was for mobile phones and laptops. There are potential shortages of materials for lithium ion batteries, but they would never cut in for those original uses. However, as shown in my previous post, recycling of lithium ion batteries will be very difficult to solve the problem for motor vehicle batteries. One alternative for batteries is sodium, obtainable from salt, and no chance of shortage.

The fuel cell offers some different options. A lot has been made of hydrogen as the fuel of the future, and some buses use it in California. It can be used in a combustion motor, but the efficiencies are much better for fuel cells. The technology is here, and hydrogen-powered fuel cell cars can be purchased, and these can manage 500 km on  single charge, and can totally refuel in about 5 minutes. The problem again is, hydrogen refuelling is harder to find. Methanol would be easier to distribute, but methanol fuel cells as of yet cannot sustain a high power take-off. Ammonia fuel cells are claimed to work almost as well as hydrogen and would be the cheapest to operate. Another possibility I advocated in one of my SF novels is the aluminium/chlorine cell, as aluminium is cheap, although chlorine is a little more dangerous.

My conclusions:

(a)  We need a lot more research because most options are not sufficiently well developed,

(b)  None will out-compete oil for price. For domestic transport, taxes on oil are already there, so the competitors need this tax to not apply

(c)  We need biofuels, if for no other reason that maintaining existing vehicles and air transport

(d)  Such biofuel must come at least partly from the ocean,

(e)  We need an alternative to the lithium ion battery,

(f)  We badly need more research on different fuel cells, especially something like the ammonia cell.

Yes, I gree that is a little superficial, but I have been at a conference, and gave two presentations. I need to come back down a little 🙂

The Apollo Program – More Memories from Fifty Years Ago.

As most will know, it is fifty years ago since the first Moon landing. I was doing a post-doc in Australia at the time, and instead of doing any work that morning, when the word got around on that fateful day we all downed tools and headed to anyone with a TV set. The Parkes radio telescope had allowed what they received to be live-streamed to Australian TV stations. This was genuine reality TV. Leaving aside the set picture resolution, we were seeing what Houston was seeing, at exactly the same time. There was the Moon, in brilliant grey, and we could watch the terrain get better defined as the lander approached, then at some point it seemed as if the on-board computer crashed. (As computers go, it was primitive. A few years later I purchased a handheld calculator that would leave that computer for dead in processing power.) Anyway, Armstrong took control, and there was real tension amongst the viewers in that room because we all knew if anything else went wrong, those guys would be dead. There was no possible rescue. The ground got closer, Armstrong could not fix on a landing site, the fuel supply was getting lower, then, with little choice because of the fuel, the ground got closer faster, the velocity dropped, and to everyone’s relief the Eagle landed and stayed upright. Armstrong was clearly an excellent pilot with excellent nerves. Fortunately, the lander’s legs did not drop into a hole, and as far as we could tell, Armstrong chose a good site. Light relief somewhat later in the day to watch them bounce around on the lunar surface. (I think they were ordered to take a 4-hour rest. Why they hadn’t rested before trying to land I don’t know. I don’t know about you, but if I had just successfully landed on the Moon, and would be there for not very long, a four-hour rest would not seem desirable.)

In some ways that was one of America’s finest moments. The average person probably has no idea how much difficult engineering went into that, and how everything had to go right. This was followed up by six further successful landings, and the ill-fated Apollo 13, which nevertheless was a triumph in a different way in that despite a near-catastrophic situation, the astronauts returned to Earth.

According to the NASA website, the objectives of the Apollo program were:

  • Establishing the technology to meet other national interests in space.
  • Achieving preeminence in space for the United States.
  • Carrying out a program of scientific exploration of the Moon.
  • Developing human capability to work in the lunar environment.

The first two appear to have been met, but obviously there is an element of opinion there. It is debatable that the last one achieved much because there has been no effort to return to the Moon or to use it in any way, although that may well change now. Charles Duke turns 84 this year and he still claims the title of “youngest person to walk on the Moon”.

So how successful was the scientific program? In some ways, remarkably, yet in others there is a surprising reluctance to notice the significance of what was found. The astronauts brought back a large amount of lunar rocks, but there were some difficulties here in that until Apollo 17, the samples were collected by astronauts with no particular geological training. Apollo 17 changed that, but it was still one site, albeit with a remarkably varied geological variety. Of course, they did their best and selected for variety, but we do not know what was overlooked.

Perhaps the most fundamental discovery was that the isotopes from lunar rocks are essentially equivalent to earth rocks, and that means they came from the same place. To put this in context, the ratio of isotopes of oxygen, 16O/17O/18O varies in bodies seemingly according to distance from the star, although this cannot easily be represented as a function. The usual interpretation is that the Moon was formed when a small planet, maybe up to the size of Mars, called Theia crashed into Earth and sent a deluge of matter into space at a temperature well over ten thousand degrees Centigrade, and some of this eventually aggregated into the Moon. Mathematical modelling has some success at showing how this happened, but I for one am far from convinced. One of the big advantages of this scenario is that it shows why the Moon has no significant water, no atmosphere, and never had any, apart from some water and other volatiles frozen in deep craters at the South Pole that almost certainly arrived from comets and condensed there thanks to the cold. As an aside, you will often read that the lunar gravity is too weak to hold air. That is not exactly true; it cannot hold it indefinitely, but if it started with carbon dioxide proportional in mass, or even better in cross-sectional area, to what Earth has, it would still have an atmosphere.

One of the biggest disadvantages of this scenario is where did Theia come from? The models show that if the collision, which happened about 60 million years after the Earth formed, occurred from Theia having a velocity much above the escape velocity from Earth, the Moon cannot form. It gets the escape velocity from falling down the Earth’s gravitational field, but if it started far enough further out that would have permitted Theia to have lasted 60 million years, then its velocity would be increased by falling down the solar gravitational field, and that would be enhanced by the eccentricity of its trajectory (needed to collide). Then there is the question of why are the isotopes the same as on Earth when the models show that most of the Moon came from Theia. There has been one neat alternative: Theia accreted at the Earth-Sun fourth or fifth Lagrange point, which gives it indefinite stability as long as it is small. That Theia might have grown just too big to stay there explains why it took so long and starting at the same radial distance as Earth explains why the isotope ratios are the same.

So why did the missions stop? In part, the cost, but that is not a primary reason because most of the costs were already paid: the rockets had already been manufactured, the infrastructure was there and the astronauts had been trained. In my opinion, it was two-fold. First, the public no longer cared, and second, as far as science was concerned, all the easy stuff had been done. They had brought back rocks, and they had done some other experiments. There was nothing further to do that was original. This program had been a politically inspired race, the race was run, let’s find something more exciting. That eventually led to the shuttle program, which was supposed to be cheap but ended up being hideously expensive. There were also the deep space probes, and they were remarkably successful.

So overall? In my opinion, the Apollo program was an incredible technological program, bearing in mind from where it started. It established the US as firmly the leading scientific and engineering centre on Earth, at least at the time. Also, it got where it did because of a huge budget dedicated to one task. As for the science, more on that later.