-
1
- #1
moltenmetal
Chemical
- Jun 5, 2003
- 5,504
I suggest a thread where the technical and environmental aspects of various options for carbon capture and storage will be discussed.
Participants in this thread assume, for the purposes of the discussion, that fossil CO2 emissions to the atmosphere are undesirable and that it is a desirable outcome to not only stop the increase of CO2 in the atmosphere but also, possibly in future, wind it back somewhat from its present 410 ppm sustained level. Debate about the reality of climate change etc. can occur elsewhere, but it will be red-flagged in this thread as being distractingly off topic.
Here's a starter for discussion. Debate in relation to anything I've mentioned below is absolutely on topic and permissible- including telling me I'm full of CO2 if I've said anything stupid!
So far, most projects have involved CO2 capture from existing flues or CO2-rich process streams, and almost all of them have for economic and practical reasons focused on providing CO2 for enhanced oil recovery. The irony of this use should not be lost on readers, though I would also add that even if we were to eliminate the burning of fossils directly for energy, we will still need to recover petroleum efficiently for use as chemical feedstocks so CO2 injection into oil formations for recovery purposes and partial sequestration may be beneficial.
A simple mass and energy balance though quickly demonstrates that the option of continuing to provide a huge fraction of worldwide energy production needs by burning fossils and then stuffing the resulting CO2 into holes deep and large enough to keep it there forever is a fool's errand. CCS of this sort is only ever going to be a partial solution. There is some geological storage capacity and some geological sequestration capacity (volcanic rocks, converting silicates to carbonates etc.), but it is limited and the more you want to access, the greater an economic/energy efficiency penalty you'll end up paying to access it.
Other options often discussed are as follows:
1) Disproportionation of methane into carbon and hydrogen by thermal, catalytic or plasma etc., with hydrogen to be used to offset hydrogen by SMR/ATR with associated fossil CO2 emissions, or to be burned or converted to electricity etc. and the carbon being used to offset fossil sources for materials such as carbon black, graphite etc. or, perhaps someday, just buried.
2) Pyrolysis or gasification of biomass with the resulting char being used, with or without further treatment, as a soil amendment or just buried.
3) So-called "carbon recycling", where CO2 pulled directly from the atmosphere (or more intelligently recovered from CO2 rich sources such as cement kilns) and water are reduced back to useful products, with liquid hydrocarbon fuels being one option. The process uses renewable electricity, either via direct electrochemical reduction or reaction with hydrogen produced by the reduction of water.
I see 1 and 2 above as partial solutions- potentially good ideas, but of nowhere nearly enough practical sensible capacity to replace existing fossil fuels uses.
Similarly with 3, there are a few molecules where CO2 is a potentially sensible feedstock. In oxidation state terms though, these end at methanol- in fact they likely end well before methanol at things like formaldehyde and formic acid. Reducing CO2 and water back to hydrocarbons such as diesel or jet fuels? It's so thermodynamically unfavoured to glue combustion products back together in this way that it seems unlikely to make sense relative to just finding other ways to accomplish the same goal, i.e. replacing gasoline and diesel with battery storage where feasible and with biofuels where not.
There are other things such as using CO2 to force cure cement in concrete etc. that are at most options to reduce how much net CO2 is emitted by a process rather than being any kind of means to reduce atmospheric CO2 concentration.
In the end I see CCS as both a) a necessary partial solution and b) a dangerous distraction from the real work of getting us to transition to a combination of energy efficiency, renewables plus storage and nuclear.
Interested to hear other perspectives, but won't tolerate the thread becoming another AGW debate. No objection to that debate happening in other threads intended specifically for that purpose.
Participants in this thread assume, for the purposes of the discussion, that fossil CO2 emissions to the atmosphere are undesirable and that it is a desirable outcome to not only stop the increase of CO2 in the atmosphere but also, possibly in future, wind it back somewhat from its present 410 ppm sustained level. Debate about the reality of climate change etc. can occur elsewhere, but it will be red-flagged in this thread as being distractingly off topic.
Here's a starter for discussion. Debate in relation to anything I've mentioned below is absolutely on topic and permissible- including telling me I'm full of CO2 if I've said anything stupid!
So far, most projects have involved CO2 capture from existing flues or CO2-rich process streams, and almost all of them have for economic and practical reasons focused on providing CO2 for enhanced oil recovery. The irony of this use should not be lost on readers, though I would also add that even if we were to eliminate the burning of fossils directly for energy, we will still need to recover petroleum efficiently for use as chemical feedstocks so CO2 injection into oil formations for recovery purposes and partial sequestration may be beneficial.
A simple mass and energy balance though quickly demonstrates that the option of continuing to provide a huge fraction of worldwide energy production needs by burning fossils and then stuffing the resulting CO2 into holes deep and large enough to keep it there forever is a fool's errand. CCS of this sort is only ever going to be a partial solution. There is some geological storage capacity and some geological sequestration capacity (volcanic rocks, converting silicates to carbonates etc.), but it is limited and the more you want to access, the greater an economic/energy efficiency penalty you'll end up paying to access it.
Other options often discussed are as follows:
1) Disproportionation of methane into carbon and hydrogen by thermal, catalytic or plasma etc., with hydrogen to be used to offset hydrogen by SMR/ATR with associated fossil CO2 emissions, or to be burned or converted to electricity etc. and the carbon being used to offset fossil sources for materials such as carbon black, graphite etc. or, perhaps someday, just buried.
2) Pyrolysis or gasification of biomass with the resulting char being used, with or without further treatment, as a soil amendment or just buried.
3) So-called "carbon recycling", where CO2 pulled directly from the atmosphere (or more intelligently recovered from CO2 rich sources such as cement kilns) and water are reduced back to useful products, with liquid hydrocarbon fuels being one option. The process uses renewable electricity, either via direct electrochemical reduction or reaction with hydrogen produced by the reduction of water.
I see 1 and 2 above as partial solutions- potentially good ideas, but of nowhere nearly enough practical sensible capacity to replace existing fossil fuels uses.
Similarly with 3, there are a few molecules where CO2 is a potentially sensible feedstock. In oxidation state terms though, these end at methanol- in fact they likely end well before methanol at things like formaldehyde and formic acid. Reducing CO2 and water back to hydrocarbons such as diesel or jet fuels? It's so thermodynamically unfavoured to glue combustion products back together in this way that it seems unlikely to make sense relative to just finding other ways to accomplish the same goal, i.e. replacing gasoline and diesel with battery storage where feasible and with biofuels where not.
There are other things such as using CO2 to force cure cement in concrete etc. that are at most options to reduce how much net CO2 is emitted by a process rather than being any kind of means to reduce atmospheric CO2 concentration.
In the end I see CCS as both a) a necessary partial solution and b) a dangerous distraction from the real work of getting us to transition to a combination of energy efficiency, renewables plus storage and nuclear.
Interested to hear other perspectives, but won't tolerate the thread becoming another AGW debate. No objection to that debate happening in other threads intended specifically for that purpose.
