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Glossary · Energy industry & energy transition

High-temperature heat

High-temperature heat process heat Industry hydrogen exergy

High-temperature heat is heat at a temperature level far above that of space heating, hot water or low-temperature heating. It is needed mainly in industrial processes. There is no binding threshold. International analyses, such as those by the International Energy Agency (IEA), usually count heat above 400 °C as high-temperature heat. Below that comes a medium-temperature range. Depending on the source, its lower limit is 100 °C or 150 °C. German studies on process heat often use a different classification: below 100 °C, 100 to 500 °C, 500 to 1,000 °C and above 1,000 °C. Anyone comparing figures on high-temperature heat should therefore always check which temperature classes the source uses.

Typical applications are found in the basic materials industry. They include burning cement clinker and lime, melting glass, firing ceramics, producing and processing metals, and high-temperature steps in chemicals and refineries. Here, 800 °C to over 1,500 °C are often required. In Germany, according to an older analysis by ifeu and DLR, the largest share of industrial process heat demand falls on temperatures above 500 °C. Almost half is even above 1,000 °C, led by metal production. These figures describe the structure of demand. They are not suitable as a current statistic.

Amount of energy and temperature level

The quantity of heat is stated in kilowatt-hours or megawatt-hours. For high-temperature heat, this information alone is not sufficient. A kilowatt-hour of heat at 80 °C fulfils a completely different technical task than a kilowatt-hour at 1,000 °C. In thermodynamics, the term exergy describes the share of an energy that can at most be converted into work under given ambient conditions. For heat, this share depends on the ratio of the ambient temperature to the temperature of the heat, each calculated in kelvin. With an environment of 20 °C, this is only about 17 percent at 80 °C, but about 77 percent at 1,000 °C. High-temperature heat is therefore particularly valuable, but also harder to provide.

It follows that heat cannot be freely exchanged between temperature levels. The IEA gives a simple example: low-temperature heat from a heat pump cannot replace high-temperature heat from a gas boiler. Conversely, waste heat from high-temperature processes can be used further in stages, for example for preheating, for steam or for heat networks. This cascade use works only if site, heat exchangers, operating times and economic incentives fit together.

Distinction from process heat and space heating

High-temperature heat is a part of process heat, but not all process heat is high-temperature heat. Process heat comprises all heat for technical processes, for example for drying, heating, melting, distilling, sterilising or for chemical reactions. Many applications in the food, beverage, paper or textile industries lie in the range of low-temperature heat or at medium temperatures. There, heat pumps, electric boilers, waste heat use or solar thermal energy come into question. The IEA considers solar and geothermal heat economically usable mainly below 400 °C.

In high-temperature applications, temperature, precise heat control, material properties and process stability are closely linked. In a cement rotary kiln, a glass melting tank or a steelworks, heat transfer, residence time, the atmosphere in the furnace, chemical reactions, product quality and plant lifetime also matter. Many of these plants run continuously. If the heat fails, furnaces cool down, batches become unusable or downstream stages come to a standstill. Space heating in buildings, by contrast, is usually used in a decentralised, seasonal and comparatively flexible manner. Converting high-temperature processes therefore generally takes longer and costs more capital than replacing a heating boiler.

Pathways to decarbonisation

Industrial heat today comes predominantly from burning fossil fuels. It causes the largest share of industry's direct CO₂ emissions. According to the IEA, the best option depends on the individual process and its temperature. In principle there are several pathways, which can often be combined:

  • Efficiency and heat recovery: Better insulation, modern plants and recovery reduce heat demand before a decision is made on the energy carrier.

  • Direct electrification: resistance heating, electric arc, induction, infrared, plasma or microwaves. The IEA cites electricity-based steelmaking as an example of a high-temperature process that can be electrified. How much CO₂ is saved this way depends on how climate-friendly the electricity is.

  • Hydrogen, synthetic fuels and biomethane as fuel: They come into question mainly where flames or a specific furnace atmosphere are important.

  • Biomass: It can supply high-temperature heat, but according to the IEA it is available only to a limited extent and is economic and sustainable only under certain conditions.

  • CO₂ capture and storage or use (CCUS) as well as new processes and material cycles. CCUS is particularly important where CO₂ arises not only from the fuel but from the raw material itself. In cement clinker, for example, CO₂ is released from the limestone during lime burning. A change of fuel alone is not sufficient there.

Electrification and the power system

Electric processes often generate the heat directly in the material or immediately next to it. There are thus no flue gas losses as with a flame. For this reason, a kilowatt-hour of fuel cannot be equated across the board with a kilowatt-hour of electricity. Anyone who ignores process efficiencies, flue gas and wall losses and controllability arrives at wrong results. A resistance heater converts almost all electricity into heat. It does not follow, however, that every electric high-temperature application is economic. That depends, among other things, on electricity procurement costs, grid charges, investments, connection costs and flexibility options.

Electrified high-temperature processes create large new loads on the power grid. The consequences depend heavily on the load profile. A plant with 100 megawatts of connection capacity places different demands on the grid and on generation if it runs evenly around the clock than if it can increase its output in hours with plenty of wind and solar power. Such flexibility does not arise automatically. It must be technically provided for, for example through heat storage or hybrid plants with a burner and electric heating, and it must be secured contractually and operationally. No operator switches off a furnace just because the exchange price rises if a batch is lost as a result.

Hydrogen as fuel and raw material

Hydrogen can reach high temperatures in burners and enables processes that resemble today's firing systems. It is, however, not a mere substitute for natural gas. It burns differently, forms among other things different flames and nitrogen oxides, and places different demands on transport and storage. Climate-neutral hydrogen is generally obtained from electricity by electrolysis. If it is then burned, several lossy conversion steps lie between power generation and heat. This pathway therefore needs significantly more electricity than direct electric heating, provided both are technically equivalent. It makes sense mainly where direct electrification is not suitable.

One should also distinguish what hydrogen is used for. In the direct reduction of iron ore it serves mainly as a reducing agent, in ammonia and methanol synthesis as a raw material. In such cases it is not simply a fuel. For glass or ceramic furnaces, by contrast, one must check case by case whether electric processes, hybrid plants or hydrogen burners offer the best mix of product quality, costs, emissions and security of supply.

Common misunderstandings

A widespread mistake is to treat heat as interchangeable regardless of its temperature. Waste heat from a data centre can heat buildings, but cannot run a cement kiln. It is equally wrong to regard a fossil burner as advantageous just because the fuel has so far been cheap. A complete assessment also includes the CO₂ price, import dependencies, air pollutants and future infrastructure costs.

In political debates, high-temperature heat is sometimes used as evidence that industry can hardly function without fossil fuels. This statement is too coarse, because it lumps together very different processes. Equally imprecise is the opposite claim that all industrial heat can be electrified in the short term. What is realistic in which timeframe depends on technical maturity, age of the plants, investment cycles, permits, grid capacity, product standards and international competition.

Institutional and economic context

High-temperature heat lies at the interface of industrial policy, the electricity market, grid planning and climate policy. Companies do not decide on efficiency alone. They also assess price risks for energy and CO₂, connection costs, support rules, supply contracts, site ties and the risk of production outages. If an electric furnace needs a larger grid connection, the process decision becomes a question for distribution or transmission system operators. If hydrogen is to be used, pipelines, storage, guarantees of origin and long-term secured supply volumes matter. According to the IEA, a suitable legal framework is crucial for investments in low-emission industrial heat to actually materialise.

The term high-temperature heat is precise when temperature, process, energy carrier, mode of operation and infrastructure are considered together. It becomes imprecise when it serves only as a collective term for processes that are hard to decarbonise. For the power system, it is not only how much heat is replaced that counts. It is also important at what temperature level it is needed, at what times and via which conversion chain it can be reliably provided.

Sources

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Edited by eCMS on 12.11.2026 05:06

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