European Project CITADEL

• Funded by EU since January 2024, funding: 13.6 M€
• Coordinated by HZDR

Main Objectives:

• Advanced electrical heating technologies (resistive heating, microwave plasma heating and DC plasma heating) shall be integrated into five high-temperature processes from different industrial sectors (production of (i) refractory firebricks, (ii) glass, (iii) steel making, (iv) concrete recycling and production of (v) copper wires) to replace up to 100% natural gas combustion for each demonstration case.
• The integration of highly efficient electrical heating technologies requires the development of new engineering design concepts (design equations and rules, detailed mechanical drawings, new fabrication concepts). Demonstrators will be implemented on pilot-plant scale for each of the considered use cases by scaling up starting from TRL 5 to TRL 7.
• The full potential of renewable energy is to be unlocked by simulating interoperability with the grid, green energy systems (renewable power generation: wind, solar) and energy storage (electric batteries or high-temperature thermal storage) and demonstrating the techno-economic benefits at pilot scale.
• Scalability and cost efficiency shall be demonstrated for each of the proposed technologies.

Demo case 1 – Production of refractory firebricks

Refractory production is one energy intensive sectors of the ceramic industry and depends strongly on fossil fuels for raw materials calcination and sintering, as well as firing of ceramic bonded bricks within a temperature range of 1250 – 1750 °C.

• Replacement of gas burners by microwave plasma heating
• Design of a pilot section of firing zone operated with full plasma heating
• Comparison of CO2 emissions in firing zones with background measurements
• Scaleability & cost efficiency will be estimated after pilot and industrial tests

Demo case 2 – Glass production

Glass production is an energy intensive process where 75-85% of the total energy is spent for heating of raw materials or waste glass in the glass melting furnace to more than 1500°C running continuously through its entire lifetime (approx. 8-10 years). Europe’s glass industry primary operates end fired furnaces which use both gas and electricity (<10 electricity share).

• Installation of a First-of-a-kind HyBrid rEgenerative glAss fuRnace (BEAR)
• Up to 40% electric (boosting) melting share
• 50% natural gas consumption reduction, 35% GHG emissions avoidance
• Full hybrid operation in 2025, CITADEL goal -> super hybrid



Demo case 3 – Steel making

In 2022, the steel industry emitted around 2.6 to 2.7 billion tons of CO2 equivalent, which is about 7 to 8% of all global emissions. The most widely implemented method of preheating in steel plants is using heat from gas-air combustion burners. Apart from the high level of CO2 emissions consequence of this process, main drawback of convectional gas-fired burners is their low thermal efficiency ranging from 5 to 15%.

• CITADEL addresses the preheating of ladles and tundishes
• Natural gas burners for ladle preheating will be replaced with oxy-fuel or plasma burners
• The tundish will be equipped with resistive heaters



Demo case 4 – Concrete recycling

Cement production is responsible for 8% of the world’s CO2 emissions. Concrete recycling provides an important contribution to the circular economy, as it saves enormous amounts of energy and material resources. An electric technology for the recycling of concrete waste is being developed within the CITADEL project to provide the process heat for thermal cracking at temperatures of between 500 and 700°C which is used to separate sand and cement constituents from each other. Implementation of an electric heating system to achieve the following advantages:

• With the reduction of carbon dioxide emissions to zero, the environmental balance is decisively improved, provided that the electricity is green and validated by a life cycle assessment.
• The new design includes a fully closed gas circuit and enables therefore a high rate of heat recuperation, resulting in significant energy savings and reduced overall operating costs.
• The improved temperature control will allow thermal activation of the recycled cement particles so to improved their potential as supplementary cementitious materials (SCMs) in blended cements.



Demo case 5 – Copper wire production

The escalating demand for uninterrupted electricity supply and the development of distribution infrastructures and power transmissions are primarily augmenting the copper wire market around the world. Thermal treatment in the coper wire production is usually performed in gas powered bell surfaces, where wires are treated for 18 to 24 hours. Annealing represents the problematic step due to several reasons: (i) It is powered by natural gas and directly causes CO2 emissions, (ii) Annealing is a batch process, while initial and final rolling are continuous processes.

• Elimination of natural gas consumption and CO2 emission if green electric energy is used,
• Batch operation of gas annealing will be replaced by continuously operated plasma annealing  dead time in production process is reduced,
• Achieving 30% energy reduction by substituting the gas fired bell furnace (100 kWh of natural gas per ton of processed wire) with Plasma annealers (70 kWh of electricity)
• Plasma surface treatment results in better surface activation/passivation, which improves the performance of the coating processes in downstream production.