In the first part of my assessment of Jacobson and Howarth’s lifecycle assessment of CO2e emissions from the manufacturing of CO2e, I covered the provenance of the paper, the scope variances of the two papers, and the likely CO2 capture rates used by the studies. In this second part, I step through differences in approach and the implications for the results, the “capacity factor” of CO2 capturing equipment (which Bauer et al appear to exclude entirely), and the big hitter — upstream methane emissions.
As before, I’ll be extracting relevant portions of the paper, providing additional context as necessary, and judging which paper appears more credible based on the choices made.
“The production of hydrogen from methane is an endothermic reaction and requires significant input of energy, between 2.0 and 2.5 kWh per m3 of hydrogen, to provide the necessary heat and pressure.”
This is basic physics. And to be clear, Howarth and Jacobson are once again conservative, choosing the mean 2.25 kWh figure, not the highest one, in effect giving industrial processes the benefit of the doubt.
This work up from the basics of processes using thermodynamic constants is actually very forgiving of real-world industrial components, which typically do not achieve the efficiencies stated in base chemical formulas and hypothetical maximums. A complaint one critic had of Jacobson and Howarth’s paper was that they did this — not one I find compelling. From my perspective, this is giving “blue” hydrogen the benefit of the doubt again.
By comparison, the Bauer et al paper summarizes pre-existing LCAs of various processes from multiple sources and attempts to consolidate them, something which has different challenges.
My preference in approach is Jacobson and Howarth’s in this regard, although I fully respect assessing the existing LCA literature and extrapolating as a methodology as well. In my extended case study of Carbon Engineering, I used both as appropriate and as information was available.
“Load is less than full load either when the carbon-capture equipment is down for repair or when the demand for carbon dioxide is lower than it is at full load. In this analysis, we use a value of 65% capture efficiency from flue gases for our baseline analysis.”
This is in the context of the equivalent of a capacity factor for flue-gas CO2 capture equipment.
As this table of outages from the failed Petra Nova facility makes clear, it was offline a lot, 20% of the year at best and 40% at worst. This is in line with the failed Boundary Dam project in Saskatchewan, where it was discovered it only operated 40% of one year.
The 92% that Bauer et al cite for Petra Nova was only the performance on days the entire system was operating, and there were a lot of days when the coal-generation unit was burning but the flue carbon capture components weren’t operational. The 65% efficiency of capture of total annual emissions from the generation unit flue emissions that Howarth and Jacobson use is very reasonable in this context.
But this still isn’t into the area of greater variance between the papers: upstream methane emissions.
“Our default value for methane emissions used above for gray hydrogen, blue hydrogen, and natural gas is 3.5% of consumption. […] For the sensitivity analysis, we also evaluate one higher rate and two lower rates of methane emission. The higher rate is from the high-end sensitivity analysis for shale gas emissions based on the global 13C data, or 4.3% of consumption. The lower rates we analyze are 2.54% and 1.45% of consumption.”
Jacobson and Howarth reviewed substantial data to arrive at these figures, and indeed Howarth has published multiple studies on the subject of upstream emissions of methane, several cited in the paper. Google Scholar returns 63 publications in journals and books by Howarth containing “methane.” Howarth is an acknowledged expert in this field, with the proviso that most of his publications concern shale oil and shale gas emissions in the USA. I don’t find this to be particularly concerning, as more and more natural gas globally is being extracted through fracking, and unconventional oil extraction techniques are also globalizing.
They reference many of the same analyses as Bauer et al, Alvarez et al’s bottom-up study among them.
Howarth and Jacobson select four rates of upstream emissions: 1.45%, 2.54%, 3.5% (primary), and 4.3%. By comparison, Bauer et al use 0.2% (unfathomably low), 1.5% (barely above the low end of the Howarth/Jacobson study), and 8% (well outside the range of literature) and ignored by all favoring the report. The implication is that the USA’s gas extraction is among the worst in the world, not an argument I find compelling. It certainly seems to be a place where Bauer et al are picking aggressively good numbers, not more reasonable world averages.
Unsurprisingly, the Howarth/Jacobson study, with its conservative choices that still skew in favor of “blue” hydrogen, finds significantly higher CO2e emissions than the Bauer et al paper.
As can be seen, at the reference case of 3.5% upstream emissions, the CO2e is more than half of all emissions pertaining to steam reformation of hydrogen.
By comparison, the numbers that people are touting from the Bauer et al case are from the 93% capture efficiency case with the unbelievably low 0.2% upstream methane emissions or the still low 1.5% upstream emissions. The latter is under a third of the Howarth/Jacobson numbers, while the former is a sixth, something which triggered more red flags.
Even at Bauer et al’s “median” number of 1.5% emissions, very close to Jacobson and Howarth’s 1.45%, Bauer et al have come up with completely different GWP20 and GWP100 results than Jacobson and Howarth. Their GWP20 numbers are roughly a third of Jacobson and Bauer’s at the same percentage upstream emissions.
There is clearly a significant difference in how Bauer et al are calculating total volume of methane consumed or some other challenge in their formulation. Given Howarth’s decades of peer-reviewed publication and testimony to governmental and legal climate change assessments globally, I have to give more weight to the calculations in this paper than to the ones in the Bauer et al paper.
“This best-case scenario for producing blue hydrogen, using renewable electricity instead of natural gas to power the processes, suggests to us that there really is no role for blue hydrogen in a carbon-free future. Greenhouse gas emissions remain high, and there would also be a substantial consumption of renewable electricity, which represents an opportunity cost.”
Jacobson and Howarth go further, and assess running the steam reformation process on natural gas using solely energy from renewably generated electricity. Their conclusion is correct, in my opinion.
So there we have it.
The Bauer paper uses much lower upstream methane emissions; beyond that, ends up with a third the upstream emissions as Jacobson and Howarth, implying that they are eliminating a large portion of the natural gas used from consideration; and are using much higher CO2 capture efficiencies than appear reasonable. They’ve apparently drawn their box of assessment, selected their sources, and interpreted them in such a way as to get very positive result for CO2e emissions from “blue” hydrogen.
Having read through both papers carefully now, and done and an apples-to-apples comparison of their results, I find Jacobson and Howarth’s results to be much more compelling. I suspect that the 1/3rd results of CO2e emissions at virtually identical upstream emissions of methane would trigger peer-review alarm bells at minimum, and it would be very reasonable for peer reviewers to challenge their choices of CO2 capture efficiency and their low upstream emissions choices as well.
As I said regarding the Bauer et al paper, even their results made it clear that there was no real place in the world for “blue” hydrogen, yet they concluded otherwise. But the Howarth and Jacobson paper, being substantially more compelling upon analysis, confirms this.
The future market for hydrogen is diminishing, not increasing, as both refining of petroleum diminish and ammonia-based fertilizer shrink as markets. There is no substantial growth market for hydrogen. There is no real place for “blue” hydrogen in our climate solutions discussion. Jacobson and Howarth are right.
Appreciate CleanTechnica’s originality? Consider becoming a CleanTechnica Member, Supporter, Technician, or Ambassador — or a patron on Patreon.
via CleanTechnica https://ift.tt/3AS5bsg