How Green is Blue Hydrogen?”: my comment on the reply to comment

Some days ago our paper Comment on “How green is blue hydrogen?” returned online, together with a Reply to comment on “How Green is Blue Hydrogen?” by Howarth-Jacobson (HJ).

Here, I am going to give my comment on the reply to comment on “How Green is Blue Hydrogen?” touching the following points:

• Expected emissions from future blue hydrogen plants
• Methane leakage
• Some final remarks and personal views

Expected emissions from future blue hydrogen plants

In our commentary, we highlighted the weak methodology adopted by HJ to estimate the energy and CO2 balance of future blue hydrogen plants. In few words, HJ picked numbers here and there from “real-world plants” and inappropriately derived energy consumptions and CO2 emissions from such data to estimate energy and CO2 balances of future blue hydrogen plants (please, refer to our discussion in section 2 of our paper, including the footnotes: https://onlinelibrary.wiley.com/doi/full/10.1002/ese3.1126).

For anyone with some experience in process engineering, it is evident that energy consumptions and emissions of future blue hydrogen plants can only be obtained from rigorous process simulations, taking into account thermal integration and heat recovery. In the current situation where “the regulatory and market conditions have not been sufficiently demanding to favor the deployment of commercial hydrogen plants with high CO2 capture rate at scale yet”, process simulations provide much more reliable balances than improper extrapolation of poorly interpreted “real-world data”. Ok, but how can one claim that the technology assumed for future blue hydrogen plants will really perform as it was simulated? Because the same technologies (ATR, MDEA-based CO2 capture with >99% and post-combustion CO2 capture) are currently already used commercially, for example in ammonia and urea plants.

For those who are not experienced in process engineering, let me try to make an (inevitably simplified) example referring to car manufacturing. With the same HJ logic, one could claim that Volkswagen (VW) cannot manufacture cars with maximum speed >300 km/h, because there are no “real-world” VW cars (i.e. hydrogen plants) passing 300 km/h (passing 60% CO2 capture efficiency). Obviously, VW does not manufacture 300 km/h cars because there is no market demand for VW supercars. However, if a regulation forced manufacturers to produce cars with maximum speed of 300 km/h (i.e. hydrogen plants with carbon capture efficiency > 90%), there are little doubts that VW will start producing engines with design similar to what Ferrari (biased comparison…) is doing since decades (i.e. ammonia and urea plants, that implement more advanced technologies).

So, in spite of the discrediting HJ wording, referring to “hypothetical calculations for energy use and emissions” and “theoretical constructs, not physical realities” for future blue hydrogen plants designed for high CO2 capture rates, process simulations are much more reliable than inconsistent calculations based on misused “real-world data”.

Methane leakage

Methane leakage is a big problem. Monitoring of emissions by independent entities and reduction of methane emissions must be a priority.

I have no elements to disagree with the sources cited by HJ to determine their default 3.5% leakage rate assumption, except from the fact that it included 0.8% of methane leakage derived from storage, transport and distribution derived from data on urban centers along the US east coast, which is not relevant for a large industrial plant not connected with leaking urban distribution networks. Nevertheless, I am with HJ when they claim that “We firmly believe our baseline estimate of 3.5% better represents global average emissions”.

But, is it correct to draw sharp conclusions on natural gas, based on the today world average leakage rate, when the variance is so high? Would it be appropriate to claim that tap water should not be drunk because the world average tap water is not potable?

This is why, to deal with the high variance in space and time of the leakage rate and to show the effect of the methane GWP, we showed the results through 6 charts (not just one to support a desired narrative).

At the lower bound of our sensitivity, we considered a leakage rate of 0.2%. HJ strongly criticized our lower bound assumption, taken “from a cartoon on a web site from an oil and gas industry trade group” (this one), and they “find it amazing that Romano et al. rely so heavily on this value in their criticism”. Actually, it is unfair to claim that we so heavily relied on that 0.2%. That value should be treated as we originally wrote, i.e. “a low leakage rate, representative of current low‐emission value chains and the OGCI target”. So, a honest reader understands that citing this “cartoon on a web site” does not mean that we consider this source as reliable as a peer-review scientific paper to depict the current emission levels. Nevertheless, we consider it as a significant source, as it is the declared target of major oil & gas producers. Also, even though such low emission levels represent an exception today, significant examples exist. For instance, according to this recent paper, the measured loss from 10 fields accounting for 48% of Norwegian gas production have a production-weighted average loss rate of 0.012%.

In summary, while stressing again that much more efforts should be dedicated to monitoring and quickly reducing methane leakage (independently of the deployment of any blue hydrogen project!), I still support our original statement: “the large variability of emissions from different NG value chains and the large potential in their reduction means that the climate impact of blue hydrogen plants should be evaluated on a case‐by‐case basis, considering the specific NG value chain associated with the plant.”

Some final remarks, with my personal vision

The positions on keeping a balanced view on blue hydrogen are not in contrast with the idea (that I fully support!) that decarbonization of our economy should primarily proceed through quick deployment of renewables and on electrification. The substitution of the existing fossil-based power generation with renewables and the electrification of heat production and mobility should be THE priorities in the energy transition.

In mature economies, CO2 capture and storage will have a minor role in the power sector, but will be needed to decarbonize some industrial sectors (e.g. cement and lime production, waste to energy), it should be very welcome in other sectors (e.g. iron and steel, refining) and in exploiting opportunities for negative emissions, especially when coupled with biofuels production.

Uncertainties and challenges of CCS should not be ignored, especially on the storage side (see for instance this paper). There are both success stories (e.g. Sleipner) and failures (e.g. Gorgon) of non-EOR CO2 storage projects, but the examples are still too few and it is too early to declare the technical success or the failure of CCS. This decade will be decisive to demonstrate the technical and economic viability of the full CCS chain, starting from the Longship Norwegian project and the four EU large scale Innovation Fund projects. True environmentalists should not oppose to CCS a priori, as its stoppage would preclude or delay the decarbonization of some important industrial sectors. True environmentalists should watch that CCS is deployed where it provides true advantages.

I think that hydrogen will also play a role (how large is still a big question mark to me) in the storage of intermittent or remotely produced renewable electricity (also via e-fuels) and in the decarbonization of high temperature industrial heating and heavy vehicles. It will also be a good candidate if used as a reducing agent (e.g. in iron production) and to increase the yield of biofuels. Green hydrogen from electrolysis of renewable electricity is of course environmentally superior to blue hydrogen and is preferable in the long run. However, producing large amounts of green hydrogen in the short-term involves subtracting the still scarce renewable electricity to its direct use to displace fossil-based power generation, to produce low temperature domestic and industrial heat and in the mobility sector, where the decarbonization potential is higher at lower cost. In this context, blue hydrogen will allow decarbonizing some sectors in the short period, while penetration of renewables and electrification (whose speed of deployment is the bottleneck for decarbonization) proceed.

So, sustaining that blue hydrogen can have a bridging role (if integrated in monitored, low emission value chain!) in the decarbonization path is absolutely compatible with the desirable parallel electrification of the economy and with a reduction of the consumption of natural gas and other fossil fuels.

It is time to break the renewables vs. CCS polarization.