Industrial Process Heat: Where the Hard Emissions Live
Decarbonising electricity is conceptually simple even where it is practically hard, because electrons are interchangeable regardless of source. Industrial heat is not like that. A process needing 80 degrees and one needing 1,450 degrees have almost nothing in common, and the second has no electrical answer currently deployed at scale.
Sorted by Temperature
Industrial heat divides into three bands, and almost everything about the decarbonisation problem follows from which band a process sits in.
Below about 100 degrees sits food processing, paper drying, textiles, washing and space heating within plants. This is roughly a third of industrial heat demand and it is the easy third: industrial heat pumps deliver it at a coefficient of performance of 3 or more, so electrifying it uses a third of the energy of burning gas. Commercial units now reach 150 degrees, which extends the easy band further than it used to go.
Between 100 and 400 degrees sits chemical processing, drying and much light manufacturing. Electric resistance heating works and is expensive to run. Concentrating solar collectors supply this range directly and are the fastest-growing application of that technology. Steam generated electrically or by biomass covers much of the rest.
Above 400 degrees the options thin, and above 1,000 they become scarce. Cement kilns run at 1,450, glass furnaces at 1,500, and steel blast furnaces at 2,000. Electric arc furnaces reach these temperatures and are standard for recycled steel, but for primary processes from ore the chemistry rather than the temperature is often the obstacle.
Why Cement Is the Hardest Case
Cement production emits roughly 8 percent of global carbon dioxide, and it is the case where changing the fuel achieves the least. The reason is that most of the emission is not combustion.
Making clinker requires heating limestone to about 1,450 degrees, where calcium carbonate decomposes into calcium oxide and carbon dioxide. That carbon dioxide was chemically bound in the rock and is released by the reaction itself. It accounts for roughly 60 percent of cement's emissions, and it would be released if the kiln were heated by sunlight, electricity or nuclear steam.
This is what the phrase process emissions means, and it is why carbon capture has a stronger case in cement than almost anywhere else. There is no alternative route that avoids the chemistry, so the choice is to capture the product or to change the material.
Changing the material is the other line of work. Clinker substitution replaces part of the cement with fly ash, slag or calcined clay, cutting emissions proportionally, and is already widespread where those materials are available. Novel binders using calcium silicates that absorb carbon dioxide while curing exist at pilot scale. Both reduce rather than eliminate, which is why most credible cement pathways end with capture attached to a kiln.
Steel and Chemicals
Steel accounts for around 7 percent of global carbon dioxide, and the problem is chemical too, though a different chemistry. Iron ore is iron oxide, and making iron means removing the oxygen. The conventional route uses coke, so the oxygen leaves as carbon dioxide - the carbon is a reagent rather than merely a fuel.
Hydrogen can perform the same reduction and produces water instead. Direct reduction plants running on hydrogen operate at demonstration scale in Sweden and are under construction in Germany, and the technology works. What it needs is enormous quantities of cheap clean hydrogen, which returns the problem to electrolysis capacity and electricity price.
Electric arc furnaces melting scrap already produce a large share of steel in some countries and emit far less, but they depend on scrap availability. A growing economy needs more steel than its scrap stream can supply, so primary production from ore remains necessary regardless.
Chemicals are more heterogeneous. Ammonia needs hydrogen as a feedstock and is therefore decarbonised by cleaning up hydrogen production. High-value chemicals from steam cracking need both extreme heat and hydrocarbon molecules, and electrified crackers are being demonstrated. The sector's difficulty is that carbon frequently ends up in the product rather than the atmosphere, which makes the accounting unlike anything in power generation.
The Overlooked Opportunity
Before any of this, there is waste heat. A substantial share of the heat generated in industry is rejected to the atmosphere at temperatures that remain useful - flue gases at 200 to 400 degrees, cooling water at 60 to 90.
Recovery technologies are mature and unglamorous. Economisers preheat feedwater with flue gas. Recuperators return exhaust heat to incoming combustion air. Organic Rankine cycle units generate electricity from heat too low-grade for a steam turbine. Heat pumps can lift waste heat to a useful temperature rather than discarding it. None of this is new; the barrier is that each installation is bespoke and nobody's job.
District heating is the underused outlet. A plant rejecting 50 megawatts of heat at 80 degrees next to a town that needs heating is an obvious match, and Denmark and Sweden have built networks on exactly that basis for decades. It requires infrastructure and long-term agreements between parties who do not otherwise transact, which is an institutional problem rather than a technical one.
The general point is that industrial heat is where efficiency has the largest untapped potential, precisely because it is diffuse, technical and invisible. A cement plant is a landmark; a heat exchanger retrofit is a line in a maintenance budget. The second saves more energy than the first is likely to, and attracts none of the attention.
Frequently asked questions
How much energy does industrial heat use?
Roughly two thirds of all industrial energy demand is heat rather than electricity or mechanical work, and producing it accounts for around a quarter of global energy-related carbon dioxide emissions. It receives a small fraction of the policy attention given to power generation.
Why does temperature matter so much?
Because it determines which solutions exist. Below 100 degrees, industrial heat pumps deliver heat at three times the efficiency of burning gas. To 400, electric and concentrating solar options work. Above 1,000 the choices narrow sharply, and for some processes the obstacle is chemistry rather than heat at all.
Why can't cement just switch to clean energy?
Because roughly 60 percent of its emissions come from the limestone itself. Heating calcium carbonate to 1,450 degrees decomposes it into calcium oxide and carbon dioxide, and that carbon dioxide is released by the reaction regardless of how the kiln is heated. Only capture or a different binder addresses it.
Can steel be made without coal?
Yes, by using hydrogen to strip oxygen from iron ore instead of coke, which produces water rather than carbon dioxide. Direct reduction plants running on hydrogen operate at demonstration scale in Sweden and are under construction in Germany. The constraint is the quantity of cheap clean hydrogen required.
What is the fastest thing that can be done?
Waste heat recovery. A large share of industrial heat is rejected at temperatures still useful for something else, and the recovery technologies - economisers, recuperators, organic Rankine cycles, heat pumps - are mature. The barrier is that each installation is bespoke and is nobody's specific responsibility.
