The effort described herein is focused on reducing the atmospheric CO2 emissions from the 150GT of carbon (550GT CO2) emitted by microbes and decomposition annually and storing about 12GT of carbon (44GT of CO2 Equivalent) at the bottom of the ocean. The goal will be to decrease the level of atmospheric CO2 by more than 4GT per year while increasing the carbon concentration in the deep ocean by about 1% per century. This world wide effort herein will be called “Deep Ocean Carbon Sequestration” or “DOCS”.
All organic matter is carbon based and it is relatively easy to capture compared to atmospheric CO2. An 8% reduction in worldwide microbial respiration and degradation CO2 output will make the Earth carbon negative. This, in turn, is expected to reduce Global Warming and get our planet back to a more ideal temperature range without severely curtailing anthropogenic activity.
Some of the needed biosequestration of the carbon in organic matter can be accomplished through simple means, including waterlogging organic matter at sea and letting it sink down to the deep ocean. The size of the problem is about 38GT/a of anthropogenic CO2 and for that, a more active human involvement is likely to be needed to bring biosequestration of the carbon in organic matter up to the needed level.
Hydrous Pyrolysis
Hydrous Pyrolysis of organic matter can separate carbons and/or hydrocarbons from organic matter. It would take thousands of large, high energy consuming, super pressure cookers, as big as barns and operating at very high pressures to make a significant dent in the ≈1400GT of excess atmospheric CO2 that has accumulated over the last 200 years as a result of anthropogenic CO2 emissions. It is a huge job, but DOCS could be a significant component of a plan that could accomplish a carbon negative Earth and do it without a massive change on our daily lives or strangling the world’s GDP.
Pyrolysis is the decomposition of organic matter by heating it in the absence of oxygen. Unlike fire or other forms of combustion that exhaust CO2, pyrolysis releases little or no CO2 due to the lack of oxygen. Any organic matter can be a source of raw material for pyrolysis including vegetation, animals and their byproducts, garbage, sewerage, household plastics, even you and me. The byproducts of pyrolysis very depending on how the pyrolysis is accomplished but typically include:
- Char- a Fuel – Similar to powdered coal it is carbon separated from the organic matter
- Gas - a Fuel – Similar to natural gas containing propane, ethane, butane, etc.
- Oil – a Fuel – Something like sweet crude oil.
The char is a solid and can be stored away so that it is not cycled back into the atmosphere for a very long time. The char, gas and oil can be processed into the fuels we used in our daily lives but it will be “Net Zero” fuel and not “fossil” fuels, since they are not from a fossil source.
For reducing atmospheric CO2, pyrolysis of organic matter in this plan will be done on very large quantities of organic matter underwater to achieve the needed decomposition. This requires very high temperatures, very high pressures, and a massive source of carbon free energy to make a dent in the atmospheric CO2 buildup over the past 200 years. Also, there is a need to store the char that is where it will not be disturbed for millions of years.
HYDOTHERMAL VENTS
Hydrothermal vents in the deep ocean were first photographed off Equator’s Galapagos Islands in 1976s. Since then over 720 hydrothermal vent fields have been identified and are listed in the InterRidge Vents Database 3.48. Figure 3 is a map showing the spreading rates of known hydrothermal vent fields. There are about six times as many hydrothermal vent fields as there are stars in the figure. Most of the vent fields are located along the 60,000km long Mid-Ocean Ridge. Some of the areas where there are no stars are tectonic plate subduction zones.
Typically the magma chambers which can supply the energy for the needed coalification process is closest to the ocean floor near the fastest spreading tectonic plate boundaries. Speed is relative and in this case the Mid-Atlantic Ridge is slowly spreading at 0.2cm/yr. while in the South Pacific the tectonic plates are spreading at a very fast 1.4cm/yr.
The energy released naturally at hydrothermal vent fields falls well short of the energy required for a pyrolysis effort that can reduce the level of atmospheric CO2 to levels of a century ago but the vent fields are areas where excess energy is being released.
HYDROTHERMAL BOREHOLE VENTS (HBV) (Patent Pending)
The energy stored in the magma chambers below hydrothermal vent fields is more than enough to power the needed decarbonization. It is basically carbon free energy that can power the process and the ocean bottom below the mid-ocean ridge is a great place to leave the carbon loaded char that emanates from the process. The carbon char will piles up, and likely form coal seams that won’t reach a continental plate subduction zone for millions of years.
The energy emitting from the 1200°C magma chambers can be tapped using techniques commonly used for offshore oil exploration and shown in Figure 4. When the dill bit of Figure 4 is actively drilling as in Figure 5a, high pressure water is pumped through the drill bit shaft at rate that will force the ground up rock out of the borehole. This also cools the drill bit as the temperature increases as the drill bit gets closer to the1200°C lava chamber.
Once the borehole is drilled as shown in Figure 5a, a liner is added as shown in Figure 5b when needed to prevent the walls of the borehole from collapsing. The output from the bore hole at the ocean floor as shown in Figure 5d will be separated from the input plumbing. From that point, the hot water is likely to be stored for used on demand, piped into a hydrothermal borehole vent (HBV) oven as shown in Figure 6, or brought to the surface for use high pressure steam to drive turbines.
Figure 6 us a HBV oven with a municipal garbage barge feeding organic matter into the HBV oven through a Sea Silo capable of holding multiple day’s refuge while it is waiting to be processed into char.
Figure 7 is a graph of the approximate pressure at depths below the ocean’s surface as well as the approximate state of the water. The values are approximate because fresh water is lighter than salt water, brine is heavier to than salt water, and deep water is compressed due to the high pressure. Below the boiling point curve it will be hot water and to the right of the boiling point curve it will be steam. In the lower right corner of the chart the water will be supercritical where there is no difference between water and steam, the density is about 1/3 that of the surrounding water, and the supercritical water is a solvent capable of penetrating pores rocks.
Figure 8 depicts a typical HBV oven at the bottom of the ocean with the borehole drilled near the 1200°C magma chamber and the char being discharged down the side of mid-ocean ridge accumulating in the deep ocean reactive sediment of Figure 1.
Under the wide ranging set of processing conditions anticipated for the HBV hydrous pyrolysis, a wide range of organic and some inorganic matter can be broken down while optimizing the output of char being adding to the bottom of the ocean. The gas and oil produced during the hydrous pyrolysis process will be brought to the surface avoiding water pollution and processed into carbon neutral fuel. The char can also be brought to the surface and burned as fuel should that become advantageous but it would defeat the goal of lowering atmosphere CO2 concentrations.
The volume of organic matter needed to be run through pyrolysis to achieve the goal of negative carbon emissions for the planet is enormous. The municipal waste operation of Figure 6 is attractive because the organic matter is already being collected, the cost of obtaining land for a land fill operation is rising, the release of methane from landfills would no longer be a problem, and for some municipalities the operation will provide a cost savings. Unfortunately, municipal waste is expected to solve about 1% or 2% of the anthropogenic atmospheric CO2 accumulation problem. For the rest of effort, many industrial sized operation will be need