Research Triangle Energy Consortium

The UNC Cleantech Summit last week had a panel on this topic, on which I served. Here is one take on this rapidly accelerating trend in the decarbonization of industrial processes. But first some fundamentals.

Processes use fossil fuel in four different ways. The most common use is to produce heat to enable a process. An example in the hard to abate cement/concrete industry is the calcination of limestone in a rotary kiln together with other oxides such as silica to produce clinker. The clinker is blended with crushed rock, known as aggregate, and acts a binder for the aggregate particles. The clinker blend usually comprises about 15% of the concrete. The clinker is often combined with other cementitious materials such as fly ash from coal fired power plants and blast furnace slag, the primary purpose being to reduce the amount of clinker used. This purpose in turn is driven in part by the desire to reduce the carbon footprint, and in part because these other materials ought to be cheaper and but for utilization in means such as this, would be treated as wastes. States such as North Carolina have had to deal with environmental crises such as storm induced overflow of fly ash “lagoons”.

The rotary kiln calcination process causes about 0.9 tonne CO₂ per tonne clinker produced. About half of this is from the fossil fuel combusted to produce the 1500 C temperatures required. The rest is from the chemical reduction of CaCO₃ to CaO and CO₂. One remedy is to produce the heat with electric heating. But this addresses only half the problem. Another electricity-based approach, one that was presented at the cited conference, is by Sublime Systems. They electrochemically decompose silicate minerals to produce Ca(OH)₂, which may be used in place of Portland Cement.

Fossil fuel is also used as reactant in the process. An example is the use of coke in an iron blast furnace. The carbon is oxidized to CO, which then reacts with the iron oxide in the ore to produce metallic iron and CO₂. The molten iron, containing about 4% C, is sent to a Basic Oxygen Furnace, where it is lanced with oxygen. The combustion of the contained C produces heat and serves to reduce the C to the desired amount in steel, which is usually less than 0.3 % for mild steel. This too produces CO₂. Overall, steel has a CO₂ footprint of about 2 tonne CO₂ per tonne steel. One approach to electrification of the process is that of Boston Metals, where they electrochemically dissociate iron oxide to molten iron.

Fossil fuel may also be used as raw material for a process. Hydrogen is produced today dominantly by the process of steam methane reforming. Methane is the raw material and is reacted with steam to produce hydrogen and CO₂. Roughly 9 Kg CO₂ is emitted per Kg of hydrogen produced. This is classified as gray hydrogen. If the CO₂ is captured and stored, the color turns blue. Hydrogen produced by electrolysis of water is termed green if the electricity is carbon-free. Yet another electrolytic process in late-stage development uses microwave pyrolysis of methane to produce hydrogen and carbon.

Finally, we have the use of fossil fuel to drive an engine. This covers the gamut from internal combustion engines for road vehicles to aviation. Electric vehicles are the best example of fossil fuel replacement. A variant is the use of hydrogen in fuel cells to produce electricity on board electric vehicles. A further possible use is in aviation as engine fuel, although biofuel derived jet fuel is the more likely workhorse. Electric drive planes will be limited in size and scope.

Availability of Green Electricity

The electricity substitutions discussed above are carbon mitigating only if the electricity is carbon-free or substantially so. Carbon-free grids are still at least a decade away, more likely two. This is largely due to the fact that solar and wind are the new sheriffs in energy town. They are the low-cost source of energy in many jurisdictions, clean or otherwise. But they have monthly average capacity factors well below 25% and 40%, respectively. Grids want them for the low cost and renewable feature but must fill the gaps with other sources. The principal longer duration gap filler today, and for the next decade at least, is natural gas. Also, the last 40% is expensive to get carbon-free. Remedies are available, in the form of geothermal, small modular reactors and innovative storage means, but they will be a while getting to scale.

To make matters worse, according to a recent story in the NY Times, all electricity demand is expected to increase steeply over the next decade after being essentially flat over the last one. This is presumably due to the explosion in data centers, most recently compounded by generative AI, which is extremely compute intensive (read power hog). Adding to the demand is the up and down phenomenon of bit coin, also compute intensive. And, of course, electric mobility.

This is not to say that electricity substitution of fossil fuels is impractical*. It is to say that individual operations will find it difficult to get 24/7/365 clean electricity, and it is also to say that carbon-free grids need policy support to accelerate the gap fillers. At least this ought to come in the form of drastic reductions in the times of permitting.

Technology is necessary, but not sufficient.

*Do you believe in magic? From Do You Believe in Magic, by the Lovin’ Spoonful, written by John Sebastian.

Vikram Rao