apologies, sent from the wroing e-mail address for googlegroups Peter ----- Original Message ----- From: "Peter Read" <[email protected]> To: "Ron Larson" <[email protected]>; "geoengineering" <[email protected]> Cc: "Ken Caldeira" <[email protected]> Sent: Friday, October 02, 2009 7:45 PM Subject: Re: [geo] Re: Grass root answer to Ken's question
> > Sorry Ron but can't respond in detail at present but many thanks for all > this work > But Re > "" *[RWL1a: Peter: I have nowhere found Ken's land numbers to be > error. Can you clarify, or point out where? I defend Ken's land value > by noting his last sentence on the 27th: "" > I noted in a delayed message yesterday that I had read Ken's 10^14 as > 10e14, which I think resolves some of the discrepancies > Peter > > ----- Original Message ----- > From: "Ron Larson" <[email protected]> > To: "geoengineering" <[email protected]> > Cc: "Peter Read" <[email protected]>; "Ken Caldeira" > <[email protected]> > Sent: Thursday, October 01, 2009 6:33 PM > Subject: Re: [geo] Re: Grass root answer to Ken's question > > >> List - but primarily Peter and Ken >> >> This is to extend Peter Read's last message on Biochar issues. The >> headings below are mine - not in Peter's original. >> >> Peter Read wrote (I believe primarily talking to Ken): >>> * <snip first four paragraphs - mainly on scientific notation for >>> (mostly large) numbers>* >>> >>> So grazing and pasture broadly interpreted as about one third of that is >>> 5e13 m^2 >>> Looks as though Ken is out by a factor of 10 and Lovell Ward quoted by >>> Stephen by 100 >> *[RWL1a: Peter: I have nowhere found Ken's land numbers to be >> error. Can you clarify, or point out where? I defend Ken's land value >> by noting his last sentence on the 27th: >> _ >> Ken1: _*/ "What fraction of total ecosystem net productivity will be >> converted to biochar after taking into account processing costs etc? >> Let's say 10%. So this is 0.1 W/m2. Therefore, we will need about 1.2 * >> 10^14 m2 or the same order of magnitude as all of the land in the >> world."/*] >> >> [RWL1b: ** To get into the same units that Peter and I have been >> using, Ken's area above translates to 12 Gha. If Ken used the same >> (50%) char conversion efficiency as Peter and I, he would get 2.4 Gha to >> achieve 9.5 Gt C/yr. **Using hydrothermal carbonization [HTC], the >> equivalent efficiency number is 95%; values between 50 and 65% are >> possible for other pyrolysis technologies. This 10, 50, 65 or 95% is the >> achievable percent of the carbon in the Biochar relative to the carbon >> in the biomass feedstock. The remaining 20% difference (2.4 Gha vs 2.0 >> Gha) will disappear if a global average increases Ken's 200 W/m2. This >> insolation figure is subsumed in my alternative assumption leading to 1 >> kg biomass C/m2-yr - a number Ken does not explicitly show. Ken's >> assumed conversion value of 10% is quite defensible when trying to >> maximize biofuel output; Peter and I are attempting to balance Biochar >> and biofuels. >> >> Key Number 1: Assumed ratio of carbon in Biochar to biomass carbon: >> 50% >> **** >> * >>> *[Peter2 - Re existing productivity efficiency: <snip a sentence>* >>> Re Ken's : "Normal ecosystem efficiencies are typically around 0.5 %. If >>> we >>> assume average sunlight at ground at 200 W/ m2, we get 1 W/m2 ecosystem >>> rates of producing reduced carbon." >>> >>> *[Peter continued: *Net global terrestrial fixation of ~60GtC/yr. = ~ >>> 120Gt dry biomass/yr = >>> ~1800 EJ/yr at 15GJ/t dry biomass = >>> 1.8e21(J/yr)/3e7(seconds/yr)=0.6e14W. >>> 0.6e14W/1.5e14m^2 = 0.4W/m^2 = 0.2 per cent of 200. As I said before, >>> nature doesn't do very well >> *[_RWL2 - Method #1_: Peter is showing an alternative approach to >> Ken's to obtain potential global biomass energies. No problem with >> Peter's numbers, but I think they show a large potential for growth, >> rather than showing a problem. Much of the existing (valuable) lockup of >> 500 or so Gt C in above-ground biomass is in a steady-state (no net >> annual additions; growth = death). It is generally not available for >> energy or Biochar applications. Peter's next computations below are >> much more meaningful in looking at the "9.5 wedge" potential for >> Biochar - the topic under discussion. Note that Peter's 0.2% value >> above is conservative compared to Ken's 0.5% (which were obtained via a >> different approach).] >> Any key number via Peter's Method #1? - No (I don't believe anything >> here is helpful in understanding the potential of Biochar. Peter did not >> later use any number from above) >> * >>> >>> *[_Peter3 - Method #2 Annual Energy Sequestration per unit area_: >>> *"Normal management of eucalypt forestry in well watered tropical >>> regions gets 25 dry biomass tons/Ha /yr or 400GJ/Ha yr (I believe 80 >>> dry tons/Ha-yr is >>> the record with a bit of TLC at research establishments in Brazil). >>> 400e9J/ha-yr)/(1e4m^2/Ha*3e7 seconds/yr) = ~1.3W/m^2 >>> (Not 0.4 -- as I said before, nature doesn't do very well). With a bit >>> of learning by doing we can likely get it up to 2W/m^2" >> * _[RWL3 - Method #2 - Energy (and carbon) per unit area_**: In >> my computations focusing on carbon (not energy), I have assumed slightly >> smaller numbers: 20 dry tons biomass/ha-yr (which goes to 10 tons >> C/ha-yr and 5 tons C /ha-yr in the form of charcoal). These same values >> per square meter are respectively: 2, 1 and 0.5 kg /m2-yr. **To repeat >> Peter's computation in energy and power terms (to work towards Ken's >> desired approach), we need to put the assumed carbon-in-Biomass (not >> Biochar) value of 1 kg C/m2-yr into energy terms by multiplying by 30E6 >> J/kg and dividing by 31.5E6 secs/yr (and using 1 J=1 W-sec), obtaining >> approximately 1*30/31.5 =1 W/m2 for the sun's captured energy in the >> form of Biomass (same value as obtained by Ken; Peter a little higher.). >> ** >> >> To put this in annual energy terms: 1W*8760 hours gives about 9 >> kWh per m2 per year (or 90 MWh/ha-yr). >> Trying to put this in crude economic terms: assuming 2 cents per >> kWh ($20/MWh) and moving up to the hectare scale, we have about >> ($20/MWh)*(90 MWh/ha-yr) = $1800/ha-yr; half (by assumption) is in >> charcoal value. This would equate for the assumed 5 t C/ha-yr (just in >> the charcoal) to ($1800/ha-yr)/(5 t C/ha-yr) = $360/t C. Thus is about >> 360/3.67 = $100/ t CO2. All this economics only by assumption. >> >> To put this in Joules, multiply again by 3600 secs in an hour to >> obtain about (9 kWh/m2-yr)*(3600 secs/hr) = 30 MJ/m2-yr = .03 MMBtu/m2-yr >> (or about 300 MMBtu/ha-yr) >> >> Key number 2a: Assumed biomass carbon productivity = 10 t C/ha-yr >> = 1 kg C/m2-yr (half to be converted to char) >> Key number 2b: Assumed char productivity = 5 T C/ha-yr = 0.5 >> kg/m2-yr >> ** Key number 3: Biomass average power density = 1 Watt/m2; >> sequestered average power density as Biochar = 0.5 W/m2 >> Key number 4: Annual energy gain in Biomass = 30 MJ/m2-yr = 9 >> kWh/m2-yr; half as Biochar >> * =300 GJ/ha-yr = 90 MWh/ha-yr >> * >> * >>> *[_Peter4 - Global Energies_:* "2Gha*400GJ/Ha-yr = 800EJ/yr cf global >>> commercial energy demand of about >>> 500EJ/yr >>> Which 2GHa?. Well Len Ornstein has given us 1.6GHa of irrigated desert >>> (maybe use the spare 300 EJ to pump the desalinated water up) >>> Maybe pump salt water up and let evaporation do the trick as suggested >>> recently, then recuperating some of the energy as the brine flows back >>> to sea level >>> And there's that 5Gha of grassland though I guess some of that is >>> near-desert and we mustn't double count " >> *_[RWL4 - Same Global Energies, but from a carbon perspective_: >> Unlike my last message, I do not change Peter's assumption of 2 G ha. >> Thu**s is about 13% of the available land area of 15 Gha - about half of >> the number proposed by Dr. Caldeira. >> If we ever got to this land area ** (and remembering that "exa" >> means 1E18)**, we would have available (using Key Number 4), 2E9 >> ha*300E9J/ha-yr = 600 EJ/yr, with about half (300 EJ/yr) going to char >> being unavailable for other energy purposes.** >> Aside: 1 Exajoule is very nearly a Quad - a very large energy, >> given (as Peter has said above) that we are consuming globally about 500 >> GJ/yr (the US over 100 Quads)]. I use my lower value of 600 EJ/yr >> rather than Peter's 800 since the resulting numbers are easier to work >> with, and because I used them last time. >> >> ** Key number 5: Assume world available land area of 2 Gha >> Key number 6: This land area can give 600 EJ per year. ** The >> total of Biomass energy production exceeds the worald total energy >> consumption in 2009. 2 Gha devoted to Biomass can generate a quite >> respectable amount of energy - albeit much less than can be accomplished >> with solar systems - which would be about 10 times larger. Wind and >> biomass can use the same land without much competition. >> ** Key number 7: I assume half or 300 EJ/yr each in pyrolysis >> gases and Biochar, given 2 Gha dedicated to Biomass production. >> >> _[RWL5 - "Maximum" Global Annual Carbon Sequestration_: Peter's >> above paragraph 3 is only about annual energy (EJ/yr) - and NOT annual >> Biochar (Gt C/yr). The remainder of this is to emphasize the carbon side >> of the discussion. >> >> ** If we assume 30 EJ/Gt C in charcoal, we get (300EJ/yr)/(30 EJ/Gt >> C) = 10 Gt C/yr **( a bit more than the 9.5 Gt C/yr Lehmann number that >> Peter and I are trying to justify). * >> * Key number 8: 2 Gha can sequester worldwide about 10 Gt C/yr in the >> form of Biochar, with equal production of consumable carbon in other >> energy forms (thermal, gas, liquid, chemical) >> >> ** >> To summarize what I have termed key numbers for Ken, Peter and myself: >> >> 1. Assumed carbon in charcoal relative to carbon in biomass: 0.1; 0.5; >> 0.5** >> 2. Assumed biomass carbon productivity in kg C/m2-yr : (not given, but >> about 1); 1.3; 1 >> Char productivity in same units: >> (0.1; .65; .5) >> 3. **Biomass average power density in Watt/m2: 1; 1.3; 1 >> 4. Annual energy gain in Biomass in MJ/ m2-yr: (not given); (not >> given, but would be 40); 30 >> * in kWh/m2-yr: >> (not given); ( not given but would be about 12); 9 >> * 5: Assumed world available land area in Gha: 3.75; 2; 2 >> 6. Maximum biomass energy in EJ/yr: (not given, but would exceed >> 1000); 800; 600** >> 7: Maximum energy in Biochar in EJ/yr: (not given, but would be about >> 100); 400; 300* >> *8: Maximum sequestered carbon in the form of Biochar in **Gt C/yr**: >> (striving for 9.5, could get much more); 13; 10 >> >> ** >> ** So, Peter and Ken, can you endorse these potential (not >> predicted) Biochar numbers (to support me in defense of Johannes >> Lehmann)?* >> >> <snip few paragraphs> >> >> *RWL Conclusion: * I think we have had only one major disagreement. I >> believe we can convince Ken to increase his Key Number 1 from 10% to 50%. >> With that single change then I believe he can agree that land of about >> one-half he proposed would allow the controversial 9.5 Gt C/yr to be >> considered possible. >> >> Apologies in advance if I have made an arithmetic error. I feel good >> that we are really all very close. >> >> Ron, 30 Sept. (ps I have been working on an extension beyond 2030 of >> the 1 Gt/yr scenario given at the IBI web-site - and will discuss what I >> learned shortly. Hint: about 500 Gt might be sequestered by 2100 - >> maybe we don't want as much as 10 Gt C-yr, even if plausible.) >> >> >> > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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