Innovative electric heater for high-temperature heating of process gases (e.g. hydrogen, syngas)

The SMS group has developed a proprietary technology for high temperature electric heating (up to 1050°C) suitable for different gases, including hydrogen and syngas. This patented technology consists in the combination of heating wires with checkers refractory, the latter being a technology used in blast furnace hot blast stoves plants (developed by SMS group).
Since 2021, the project led to the prototype validation at TRL 6 with air, H2 and other gases in a pilot plant in Italy.

TECHNICAL DESCRIPTION

The electric heater is easily scalable and generated from the combination of two technologies which are:
• Checkers bricks (holed refractories) typically used in blast furnace hot blast stoves;
• Electrified wires used as heating elements inserted within the checker holes.

Schematics and pictures of these technologies are available in the supplementary information attached.

This technology is applicable to the iron and steel industry as well as to other sectors, whenever gas or syngas heating at temperatures up to 1050°C is required. In particular, it is applicable to:
• Heating of hydrogen-based process gas in direct reduction plants for DRI /HBI production;
• Hydrogen, syngas and or natural gas heating for injection into blast furnaces to reduce BF CO2 emissions;
• Hydrogen and CO2 heating in sustainable aviation fuel (SAF) production plants using a reverse water gas shift process.

This electric heater solution is based on direct heating, meaning that the gas is in direct contact with the heating resistance. Exploiting the Joule effect, the electric power (P= I2R) is converted by the resistive elements in heat. The gas flows in the annular gap formed between heating element and checker hole (namely a “channel”), boosting the heat transfer capacity and allowing gas temperature over 1000 °C in a single pass-through. The module has a horizontal arrangement and compact layout.
Process control is realised with an automatic voltage regulator (AVR) system. Thanks to the refractory thermal inertia, the AVR regulation results in smooth gas temperature control also in the case of flow variations, which also improves the wires lifetime. A picture of the AVR can be found in the documentation attached.

The extensive use of refractories brings several advantages compared to state-of-art technology. In detail:
• Shell temperature is kept at approximately 100 °C, thus reducing thermal losses to the environment with thermal efficiency higher than 97% (scaling factor applies for industrial size allowing further increase of efficiency in multi-MW scale);
• The checker bricks provide self-electrical insulation between adjacent wires. With high electrical resistance and reduced electric permeability, capacitive/inductive effects are avoided. The result is a practically purely resistive equipment (Power Factor = 1), meaning the totality of supplied power is converted to heat by Joule effect;
• The refractories are meant for high temperature and are long lasting;
• Refractories thermal inertia against flow variations and sudden cooling extends the life of heating wires;
• The checkers geometry provides high specific surface (m2/m3) allowing a high-power density and a compact design;
• The system is conceived for continuous operation in harsh industrial environment.

Compared to indirect electrical heating (i.e. where the heating element is placed inside an electrically insulated cover, the latter in contact with the gas), direct heating brings extended lifespan because the wires temperature gets lower at same duty.
The design based on the blast furnace hot blast stoves refractories makes this technology suitable for continuous operation and large-scale installation (with an expected threshold of 40 MW module size). The optimal maximum size of the electrical heater will be a function of trade-off assessment, taking into account transport requirements, operational flexibility and costs. For DRI application, an installed heating power of 150- 250 MW is normally required, therefore the possibility to have large modules constitute an advantage compared in installation layout.
At present, basic engineering of an 8 MW module has been developed in the frame of the Norsk E-fuel feed study for a Sustainable Aviation Fuel (SAF) production plant in Norway. Concept engineer (i.e. process calculation, general assembly, layout arrangement) of 13.7 MW module has been carried out for integration into a hydrogen based direct reduction plant, which could be financed in the frame of the European RFCS 2025 programme (big ticket) if the application is successful.

DEGREE OF MATURITY
A proprietary mathematical model was developed in-house and, after analytical validation via FEM and CFD analysis, the main components were tested in laboratory. All information gained allowed the design and development of the first electric heater prototype featuring 0.5 MW size. This size was chosen for the equipment to have three-phases electric power supply, a must to have for properly evaluating the electric behaviour of the equipment. In the prototype, the geometry of checker holes and wires is the same in terms of geometry and size required for an industrial scale electric heater. In other words, the channels are the same and it is only a matter of increasing their number to achieve the industrial scale. This aspect reduces the risks related to scale-up.
The prototype was leak-tested with helium according to DIN EN 1779 and certified PED (2014/68/EU) and ATEX (2014/34/EU) by the Notified Body (DNV) as for applicable product directives.
The 0.5 MW prototype was installed in Italy where the technology has been validated at TRL 6 after stable and smooth response to operational changes at 1000 °C in different testing campaigns with air, H2, CO2 and H2-N2 gas mixtures. Each testing campaign featured continuous 24 h/d operation, with little more than 600 h of total working time at high temperature (also including few hours operation with CO2 heated at 1200 °C). The efficiency of the equipment has been validated at design conditions. There are now plans to scale up this technology in a large scale DRI plant to reach TRL 8.

OPERATIONAL PERFORMANCE
This electric heater brings a thermal efficiency higher than 97% in nominal conditions, much higher than other state-of-the art fired/regenerative heaters (See supplementary documentation attached). The heater also exhibits a power factor >0.999. This electric heater brings a particularly low vessel surface temperature of approximately 100°C due to its refractory lining technology. By comparison, any electric gas heater featuring higher vessel surface temperature will bring lower thermal efficiency due to higher heat losses.

Participant Companies