Pre-emptive treatment of currently stored methane
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Any imminently unstable deposits of methane should be disrupted and captured or oxidised in preference to being allowed to decompose naturally and vent to the atmosphere. Making the decision as to which reservoirs are unstable is bound to be challenging.
Soil heating
Excursion of methane from soil is temperature dependent, and is especially driven by melting of permafrost.
1. It may be possible to temporarily increase local temperature with clear plastic sheets (similar to agricultural 'polytunnels' but on a larger scale) so that the methane would be released by localised heating. A further benefit is that release would be into a contained environment, allowing capture as later discussed. When extraction is locally complete, the 'polytunnel' system could then be moved. Clear plastic would allow vegetation under the sheets to survive. Thermal or biological processes (discussed later) may then be used to oxidise the methane. Removing soil covers in the winter may be desirable, to allow permafrost to re-form, sealing in unrecovered methane.
2. Heat pumps could be used to warm up the ground in one area by pumping heat in from the area where methane was last extracted. This process has a high energy cost, and will need to be thoroughly tested for net benefits.
3. It may be possible to thaw the permafrost deeper underground while the shallower layers still frozen serve as a cap, and get the underground gas out by drilling.
Soil aeration
Physical treatment of the soil to enhance aeration may be possible (e.g. ploughing). Hopefully, this would cause decomposition of organic matter to occur in an oxygen-rich environment. However, it may simply stimulate the excursion of methane, and further research is needed in this regard.
Mining of clathrates
In order to recover methane from a large volume of clathrates, it is necessary to use either heating or a reduction of pressure. The reduction of pressure can be achieved most simply by mining the clathrate deposits and raising them to the surface. This poses considerable practical difficulties, due to the depth at which such deposits lie. However, various mining techniques have already been explored.
Patents covering technology appropriate to clathrate mining exist.[2] Plans are currently in place for the commercial exploitation of methane clathrate as an energy source.[3] Due to its concentrated nature, any methane recovered from clathrate mining could easily and safely be destroyed by combustion, and may (subject to the necessary infrastructure being available) be available for commercial energy exploitation. The CO2 resulting can then be subject to carbon capture and storage.
Disruption of clathrates
If vulnerable to spontaneous decomposition, methane clathrates may be best treated by forcing this decomposition, to allow its capture or flaring (possible techniques discussed later). Whilst an energy company would be looking to capture the methane released from clathrate decomposition, the geoengineer may simply be wishing to flare off the methane. This requires a lower infrastructure overhead, and is thus suitable for more remote or less concentrated deposits. Methods of ignition and collection applicable to the resulting release are discussed later.
It may be viable to deliberately disrupt the clathrate deposit, in order to enable the methane to be released in a controlled fashion into the environment. If a large volume of methane is triggered in a controllable time and place, the opportunity for atmospheric flaring exists. The larger the release of methane from a sub-sea source, the more likely it is that the resulting gas will be sufficiently concentrated in the atmosphere to permit easy collection, or destruction by simple ignition. Therefore, disrupting large bodies of clathrates may be desirable. The greater the clathrate depth, the greater the concentration of discharge required to ensure the release to the surface will be sufficiently concentrated to ignite. More dispersed releases will not be capable of destruction by flaring.
Some possible techniques may therefore be of interest:
Heat could be used to decompose clathrates. This approach will allow the rapid disruption of deep deposits, and the energy injection can be carried out into a tightly controlled area. Provided the energy injection is carried out quickly, the excursion will result in appreciable surface releases that can be flared or captured. A slower release may promote diffusion of released methane into the ocean from bubbles or from the clathrate directly, but it is unlikely to be possible to achieve this on a large scale due to the capital cost of leaving equipment in situ. The injection of supercritical steam is attractive, and captured methane provides a readily available power source. However, there are serious practical difficulties involved in piping steam to such a depth. It is possible, therefore, to use steam generated electrically in situ to drive this process.
An alternative approach is the explosive disruption of clathrates. This may release a flammable plume, even from deep deposits. The use of chemical explosives will be relatively expensive due to their limited energy density. The use of nuclear bombs may be worth exploring, as this would allow the disruption of large volumes of clathrates in a short time. This technique will be troublesome. Radiation, tsunami, shockwave, steam release and other problems would of course occur, making this technique unattractive unless reasonable alternatives cannot be developed, or extreme urgency is needed to prevent a large methane release into the atmosphere.
Other methods such as ultrasound may be able to create transient pressure changes sufficient to decompose clathrate. Further research is needed.
In-situ burning of clathrates
By piping atmospheric or oxygen enhanced air down to the sea bed, clathrates could be burned underwater. This could be done using some kind of submarine ‘factory' which heated the clathrate under controlled conditions. However, the burning could possibly also be carried out in ‘open water'. This would be a kind of 'reverse flame thrower', as the fuel is already present in the environment, and the oxygen is being piped in.
Remediation of aquatic methane excursions
Methane from concentrated sources is emitted by bubbling, and if these bubbles are large and shallow enough when they form, they may reach the surface and deposit their methane load into the atmosphere. Various techniques are conceivable to remediate these bubbles.
Mixing of ocean layers
Geoengineering techniques for mixing ocean layers have already been proposed to create artificial upwelling and downwelling currents. These techniques have potential advantages for the reduction of methane excursions into the atmosphere. Methane bubbles may not reach the atmosphere if they travel through waters with little dissolved methane on their way up, as their contents may dissolve into the surrounding waters. If enhanced mixing of the ocean occurs, more of this methane will be dissolved into the ocean and will never reach the atmosphere. Therefore, the use of mixing processes may reduce atmospheric excursion from aquatic sources. Additionally, some of the equipment for mixing, such as impellers, may physically break up the bubbles, making them smaller and thus slower moving and with greater surface area - reducing further the likelihood of them reaching the surface. This can only be seen as a side effect, due to capital considerations.
Bubble capture
Funnelling bubbles into capture pipework may be practical. Large, 'Chinese hat' cones could be moored in the sea. These would be made of material with neutral buoyancy. They would have little effect on sideways currents, and upwelling/downwelling currents would be able to flow partially around them. However, bubbles would become trapped in the cone, and would be directed to a capture bag or pipe at its narrow, upper end. As an alternative to capture, the 'hat' could be perforated to release tiny bubbles slowly, making them more likely to dissolve completely on their ascent to the surface. These small bubbles could be directed to fine pipes laced with methantropic bacteria.
Lake aeration
Much methane is produced in permafrost regions by the oxidation of melting soils in lakes. The methane is produced by anaerobic decomposition of organic matter. By adding oxygen to the lake waters, this process can be disrupted, and instead the material will be broken down aerobically to CO2. Lake aeration technology is well developed, and can be as simple as an impeller to drive water down towards poorly-mixed layers. Various technologies exist, including bubbler ships, which are widely used to reduce anoxia in polluted rivers.
Biological oxidation by aquatic bacteria
Methane is broken down by methanogenic bacteria in water. This process could be enhanced by diffusing such bacteria into the water. The feedstock for this process could be created in bacterial farms, and distributed by surface spraying, deep water injection or by the use of 'soluble pellets' containing bacteria. These pellets would sink from the surface, spreading bacteria throughout the ocean strata, if this was necessary to speed the decomposition of dissolved methane. The process could potentially be enhanced by genetic engineering, in order to make bacteria as effective as possible for the intended task.
Remediation of concentrated atmospheric methane
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In some areas, concentrations of atmospheric methane are occasionally so high that it forms a flammable fuel-air mix at small scales. This opens up the possibility of a flame or spark-based ignition process in appropriate areas.
Capture and flaring
Plastic sheets could be laid over outgassing areas of soil, lakes or ocean, acting to concentrate the gases escaping into pipes where they could be flared off. The plastic sheets could be white (to increase albedo) or dark (to increase excursion of methane by soil heating, as discussed above). There would obviously be a significant environmental impact to such an approach, which would have to be set against the environmental impact of climate change.
Removing soil covers may be desirable in the winter, to prevent insulation of the ground causing further warming.
Electrical ignition of concentrated atmospheric methane
Flames are somewhat impractical, as they rely on a fuel source and are hard to run intermittently. In contrast, an electrical spark provides instant and highly controllable ignition. Sparking technology of this nature is extremely well established, used as it is in all petrol-engined cars. It should therefore be relatively simple to design small spark machines that could sit atop lakes, seas and soils. These would be placed in areas which were experiencing methane excursions, and would provide a regular spark to flare off the methane. Such devices would have to be rather robust to withstand the repeated heating and blast effects they would undergo.
Electrical power requirements would be fairly minimal, and could pre provided by a small wind turbine or solar panel array. The electronics would be relatively simple, consisting only of a battery, coil, spark plug and control/switching electronics. Such a device, floating on a small boat, anchored like a buoy or spiked to the ground, could prove to be quite robust in the field.
Distribution of these devices may be a challenge. They would be quite small, and could easily be deployed using trucks, hovercraft or pack animals. As an alternative, it may be possible to make robust variants which can be spread out of transport or ground attack aircraft. The technology for distributing small devices from aircraft is well established, and has been deployed in combat effectively on countless mine-laying and cluster bombing missions in combat.
Thermal ignition of concentrated atmospheric methane
Very large excursions of methane can potentially occur as a result of the breakdown of clathrate deposits. It may be possible to detect large releases using satellite or airborne monitoring equipment. Thermal ignition may then be possible. If at sea, ignition with large surface ships would not be possible, due to their negative buoyancy in bubble-rich waters. However, small inflatables or hovercraft could be used. Aircraft may also be affected by changes to the air's density. Any surface vessel or aircraft would also be likely to be destroyed by explosive flaring on a large scale, so ignition by artillery from a distance is likely to be safer and more controlled. This could be triggered by mechanisms such as shelling the affected area with white phosphorous munitions, illume rounds, or tracer. Artillery has a range of 20miles or more, so the coastlines of seas and lakes could be effectively flared with 50 guns per 1000 miles. Open water could be flared with 2500 guns per 1000mile x 1000mile square, given a suitable, highly buoyant vessel on which to mount each of them. Overlaps would exist with those arrangements. This overlap would allow detonation at high altitude, should this be necessary for safety or timing reasons.
Remediation of diffuse atmospheric methane
Thermal ignition by concentrated solar power
Concentrated solar power is able to drive the temperatures needed for simple thermal ignition of methane, even when rarified in the atmosphere. Such plants are also able to generate electricity on site, which will give the mechanical power needed to drive the necessary fans and steer the mirror arrays. Heat imparted into the air can be recovered by means of a boiler, like that in a power station. It may be more efficient to use the CSP plants to warm a heat-exchanger fluid to avoid the need to heat air directly, although losses will occur as a result of the transfer process. Further research on the efficiencies of this process need to be conducted.
Compression ignition
Diesel engines function by compression ignition. A typical diesel engine has a compression ratio of around 20, meaning that the air drawn in is compressed by a factor of 20. As a result, the temperature of the compressed air is raised to around 1000 degrees F, high enough for the diesel fuel to autoignite. Thus, there is no need for spark plugs for a diesel engine. Unfortunately, the ambient concentration for autoignition of methane is about 5% or around 50,000 ppm and at 1000 degrees F. So while a 5% methane in air fuel would probably burn in a diesel engine, lower levels would not.
However, by increasing compression by roughly a factor of two, spontaneous oxidation of atmospheric methane could be achieved. The engine would not need to be more robust than are existing designs, as far higher compression ratios are achieved in a conventional diesel engine during the firing phase of the cycle. The modification would therefore simply be a matter of fitting different turbochargers, conrods and/or cylinders to a conventional diesel engine. Power for this process could come from renewable energy. 'Idling' an engine uses little power, as energy expended in compression is partially recovered during expansion.
It may be prohibitively expensive to develop special engines for the process, but perhaps no more so than the 'fake plastic trees' envisaged by Lackner. Buy compressing building-sized volumes of air in a single stroke, the process could be greatly scaled up with power-station type infrastructure. Catalysts may reduce costs by reducing compression ratios and thus costs, but most catalysts require relatively high methane concentrations to work.
It is also possible that 'existing' transport engines could be used in a forced-idle. Their starter motors are sufficient to drive them, although these would need to be upgraded for life and power. A new generation of plug-in diesel electric hybrid vehicles could idle whilst plugged in, steadily processing the atmosphere. The stresses on an engine running in electrically-driven modes would be lower than those in normal operation, and therefore engine wear would be minimised, however, it would still of course be a factor, and maintenance costs would have to be considered. As discussed, boosting the compression ratio would be necessary. This could be easily achieved if future plug-in diesel hybrids had a special supercharger fitted,which would boost inlet pressure on demand, for use in this process. This process may be further enhanced by the use of catalysts, although fitting a catalytic layer inside the high-pressure environment of the cylinder (where it is needed) would be likely to disrupt the engine's normal operation, and could further be damaged by the normal combustion process.
Photochemical degradation by the enhancement of the ozone layer
Geoengineering approaches involving the distribution of sulfur aersol precursors into the stratosphere have already been proposed. In order to enhance the photochemical degradation of methane in the stratoshpere, ozone is required. By enhancing levels of ozone in the manner described for the distribution of sulfur compounds (aircraft, balloons, artillery), enhanced photochemical degradation could be achieved.
Balloons or airships could be used to lift ozone generating equipment to the stratosphere, to be used at height. This is limited by the need for a power source. Solar power is one opportunity, but is limited in its power. A 'nuclear airship' (similar to a nuclear submarine) could also be used. However, this would clearly have safety considerations. A potentially promising alternative is to send up energy using a microwave beam or laser. Similar technology has been proposed to power a space elevator.
. Photochemical degradation by H2
Hydrogen interacts with O2 in the presence of UV to produce OH and O2H radicals; both extremely strong oxidizers. They will convert C4H to CO2 very fast. The downside is that O3 may be lost as well; H2 is well known to be destructive of O3 in the presence of UV. SHould this method be found to be promising, H2 can easily be lofted by the emission of large plumes or balloons.
Chemical degradation by hydroxyl radical
Methane released from permafrost may well remain in the atmosphere longer than expected, due to hydroxyl depletion. Normally, most methane oxidizes over time in a reaction with hydroxyl radicals (OH). However, if much more methane gets released, hydroxyl levels could drop, increasing the time it takes for methane oxidation to occur, and thus amplifying methane's greenhouse effect over time.
Perhaps enough hydrogen could be produced and released into the atmosphere to - under the influence of UV light - produce extra hydroxyl radicals, in order to speed up methane oxidation. If so, then we should prepare (as a separate geoengineering project) for dramatic increases in the production of hydrogen, preferably by means of electrolysis powered by wind turbines, or by means of pyrolysis of biomass. This would cause a large and aggressive reduction of ozone in the stratosphere, and steps would need to be taken to produce and inject more ozone to replace such losses.