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.)
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