\section{Some important facts about Sequestration}
%% see suck.tex and lastthing.mgp
What's the energy cost of sequestration?
Let's start by discussing sequestration from thin air.
If we change the concentration of \COO\ from 0.03\%
to 100\%, the ideal concentration machine does work
$kT \ln \rho_1/\rho_0 = kT \ln 3000 = 8kT$
per molecule.
That's the cost of separating \COO\ out in gas form.
If additionally we wish to compress the \COO\ into liquid form,
we need to compress it by a factor of about 1000.
% check density of COO liq and gas
This increases the energy cost by another
$kT \ln 1000 \simeq 7kT$
$kT$ per molecule is the same as 2.5\,kJ per mol,
so $15 kT$ per molecule is 37\,kJ/mol
% 37.5
which is about 850\,kJ/kg of \COO,
% 3125kJ/kg of C
or 0.24\,kWh per kg.
%% Keith et al say
%constant (8.3 J mol-1 K-1 ) and T is the working temperature. At typical ambient
%temperatures, k T is about 2.5 kJ/mol. The minimum energy required to capture
%CO2 from the air at a partial pressure of 4×10-4 atm and deliver it at one atmosphere
%is therefore about 20 kJ/mol or 1.6 GJ/tC (gigajoules per ton carbon).
%%%% which is 1.6 MJ/kg C, or 0.436 MJ/kg CO2 or 0.12 kWh/kg (to 1 atm)
% If we add
%the energy required for compressing the CO2 to the 100 atm pressure required
%for geological storage (assuming a 50% efficiency for converting primary energy
%to compressor work) the overall energy requirement for air capture with geologic
%sequestration is about 4 GJ/tC.
Compare this with the energy created when that kg of \COO\ is {\em{created}}:
one kg of oil yields about
%% energy density of gasoline
%% http://hypertextbook.com/facts/2003/ArthurGolnik.shtml
%% 12.7 kWh/kg or 8.76kWh/l
%%%%% was %% 30MJ/kg, which is about 8 units, (TOO LOW)
%% gross cal value of gasoline is 45.85 MJ/kg; net cal val=42.95
12\,kWh\ of energy and generates about 3\,kg
%% pr 44.0/ 14.0
%% 3.14285714285714
of \COO\@.
So we get about {\bf 4 units per kg of \COO}.
%% 2.65
If perfectly efficient.
%% That is an interesting conversion factor worth preserving!
\begin{tabular}{lc@{\ $\leftrightarrow$\ }c}\toprule
\multicolumn{3}{c}{\sc{Conversion factors}}\\ \midrule
Burning fossil fuels:
& {4\,kWh}
& {1\,kg of \COO} \\
Burning fossil fuels:
& {1\,kWh}
& {0.25\,kg of \COO} \\
Gas power station:
& {1\,\kWhe}
& {0.5\,kg of \COO} \\
Coal power station:
& {1\,\kWhe}
& {1\,kg of \COO} \\
\bottomrule
\end{tabular}
\label{sec.co2Seq}
%[Is this conversion factor correct?
% In lecture today Feb 2006, a Carbon Trust dude's slides
% asserted that The Carbon impact of Gas was 0.5kg per unit (0.445 kg \COO);
% and of coal, 1kg per unit (0.955 kg \COO).]
Now be realistic. If an oil-driven engine drives a real compressor,
the engine is perhaps 25\% efficient, and the compressor the same:
so get $1$ unit per kg, and
require $4\times 0.24 \simeq 1$ unit to do sequestration --
pretty much all the energy!
So much better to leave the fossil fuels where they are.
Check with manufacturers of {\COO}, what is the actual cost per kg.
Redo calculation with 33\% efficiency.
\begin{tabular}{lclcl}
{\bf{{Production:}}}\\
{1 kg of \COO} &
$\leftrightarrow$ & {4\,kWh} heat
& {$\begin{array}[t]{c}\leftrightarrow\\{/3}\end{array}$}&
{1.3\,kWh} useful energy
\\
{\bf{Sequestration:}}\\
{1 kg of \COO} &
$\leftrightarrow$ &
{0.24\,kWh} ideal cost
& {$\begin{array}[t]{c}\leftrightarrow\\{\times 3}\end{array}$}&
{0.7\,kWh} actual cost
\end{tabular}
Taking 0.7\,kWh per kg of \COO, that's an estimated energy
cost of 700\,kWh per \ton.
If one kWh has a wholesale price of 5p (9\cents), that's
a cost of \pounds 35 (\$65) per ton captured.
If the wholesale price of one kWh rises to 8p (15\cents),
then 700\,kWh per \ton\ means \$100 per ton.
%% see thinair.tex