Stuart and I also discussed the possibility of disposing of the crop residue in abandoned coal mines. At the time you said you were concerned about oxidation there and if the environment were anoxic, conversion to methane. KABOOM! I proposed coal mines, since they would not involve ocean disposal (obvious) and might be closer to the fields.
The issue of oxidation time is, I believe, not trivial. While it would be desirable to have the carbon gone forever, as in the case of deep ocean disposal, a storage time of 100 years would be attractive as well. If one believes that major technological advances are going to be made in the areas of renewable energy and also in air capture of carbon dioxide within the next 100 years, then placing the residue in an environment where it would slowly decay might be acceptable also. The carbon credits could then be priced and prorated to reflect storage lifetimes. Example: a ton of unbaled wheat straw will completely oxidize to CO2 in a field in 3 months (my estimate). The same ton baled up next to the field will last for 5 years (another made up estimate just for the purpose of comparison). Storage in an arid environment might extend the lifetime to 25 years. As for the methane issue, why not cover some of the crop residue and collect the methane for use as fuel for transportation of the residue to deep ocean or other disposal locations? This would not require any complex technology as this is how methane is collected from municipal waste landfills. Methane from landfills is a proven use of stranded energy and could be applied to crop residue disposal as well. If the methane cannot be directly used to provide fuel for transportation of the crop residue, it could be sold and the funds generated used to purchase diesel fuel. The cost of diesel fuel appears to be the single greatest cost of the CROPS strategy and reducing that cost with stranded energy generated by the process seems like a win win plan. ----- Original Message ----- From: "Stuart Strand" <sstr...@u.washington.edu> To: "Andrew Lockley" <andrew.lock...@gmail.com> Cc: <xbenf...@aol.com>; "geoengineering" <geoengineering@googlegroups.com> Sent: Tuesday, February 03, 2009 7:22 PM Subject: [geo] Re: CROPS paper I thought I explained the methanogenesis issue pretty well previously and I don't understand your reasoning in the first paragraph below. The oceanographers I have talked to agree generally with my analysis, so I think I'll leave it at that. Temporary storage of crop residues in the river basin is a good idea. Probably at local depots, away from flood prone areas. = Stuart = It methanogenesis starts, it can fairly quickly undo a lot of your work. Even if it doesn't directly reach the atmos. any effect on partial pressure may affect exchange with the atmos and thus raise methane concentrations in the atmos. Even if the methane is oxidised, all that CO2 is eventually going to cause you problems. Open storage in the desert should be possible. Here in England we have massive warehouse-sized towers of straw bales. They take ages to rot, even in our rainy weather. Fire is the biggest problem. As regards carbon content, it's not readily available for various different kinds of straw, husk, cob etc that you might be dumping. I assume it varies between plants? The purpose of pyrolysing to char is to reduce bulk, enhance consistency and reduce bioavailability. I wasn't intending to use it as an energy recovery process. Surely a few hundred kgs of char powder is easier to handle and sequester than a ton of damp straw? A 2009/2/3 Stuart Strand <sstr...@u.washington.edu>: > 1. Significant methane production seems unlikely, but it may be possible > in deep deposition sites. Anaerobic metabolism in ocean sediments is > dominated by sulfate as the electron acceptor, not CO2, as in freshwaters. > We expect crop residue mineralization under anaerobic conditions inside > the bale to be slow, so sulfate in surrounding waters would have time to > diffuse into the bales. But if the bales are stacked too deep sulfate > will be exhausted and methanogenesis will start. If methane is produced > it will not be as bubbles (which could penetrate the thermocline), but as > dissolved methane, due to the pressure. Dissolved methane will be > oxidized as it diffuses up through the sediment and the water column where > aerobic and anaerobic methane oxidation occurs (the latter coupled with > sulfate reduction). So methane from the crop residues is unlikely to > reach the atmosphere. > > The above is our working hypothesis, but this is a question that must be > answered with experiments in situ, which would also provide data to > estimate parameters needed for modeling and design. > > 2 and 3. I am working on comparisons to pyrolysis now and I have > discussed first impressions previously on this group. > > 4. readily available info, Andrew > > 5. see above > > 6. C Lossy. Andrew, biomass is a poor energy source, whether you make > methane, ethanol or biochar from it. > > 7. Not as safe as the ocean I would judge. But it is something we could > do temporarily, while ocean research and the expected political wrangling > on CROPS is done. But transportation costs to and from deserts and the > landfilling operations to try to keep moisture would be costly and CO2 > productive. > > > > = Stuart = > > Stuart E. Strand > 167 Wilcox Hall, Box 352700, Univ. Washington, Seattle, WA 98195 > voice 206-543-5350, fax 206-685-3836 > skype: stuartestrand > http://faculty.washington.edu/sstrand/ > > Using only muscle power, who is the fastest person in the world? > Flying start, 200 m 82.3 mph! > http://en.wikipedia.org/wiki/Sam_Whittingham > Hour http://en.wikipedia.org/wiki/Hour_record > 55 miles, upside down, backwards, and head first! > > > -----Original Message----- > From: geoengineering@googlegroups.com > [mailto:geoengineer...@googlegroups.com] On Behalf Of Andrew Lockley > Sent: Tuesday, February 03, 2009 3:05 AM > To: xbenf...@aol.com; geoengineering > Subject: [geo] CROPS paper > > > I've read through your paper in detail and I note the following. (I > may have missed some things of course) > > 1) You don't discuss anaerobic decomposition to methane in the ocean. > Is it a risk? Outgassing may be immediate or by clathrate > destabilisation. > 2) You don't discuss pyrolysing the waste to char before sequestration. > 3) You consider burying the waste, but you do not consider creating > biochar and burying that to create terra preta > 4) You reject the idea of burning crop residues and using CCS, but do > not provide a quantitative analysis of the carbon content of biomass > by % compared to other fuels, so it cannot be determined whether > burning is relatively more efficient than for other fuels. > 5) You do not directly consider the production of char by pyrolysis > then onward transport of the fuel to be burned in sites suitable for > CCS. It may be that thermal and industrial inefficiencies preclude > this, but this cannot be assumed. Further, char is likely to be > compatible with existing coal plant, when raw crop waste is not. > 6) You do not consider anaerobic digestion of the crop waste to make > methane gas for power generation or large-vehicle transport fuel. > This technology is used extensively in the UK for food waste, albeit > on an emergent scale. > 7) You do not consider the alternative of storage of waste in the > desert. If transported by rail to the desert, crop waste could dry > naturally and then be sealed with plastic in bales. This is an > obvious alternative destination for the waste. > > A > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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