ZESTY green iron and steel proves its credentials

With Calix’s Zero Emissions Steel TechnologY (ZESTY) proven at pilot scale, following a successful FEED study and ore testing, identification of a preferred site for the ZESTY Demonstration Plant is coming soon. But why does ZESTY matter, how does it work, and what are the costs?

Our newsletter feature takes a deep dive on ZESTY’s credentials.

Why it matters…

Iron and steel are essential materials for our economic prosperity and continued development, and yet, they are also one of the most carbon-intensive and hard-to-abate industries. Mitigating emissions from steelmaking is critical to ensuring industry and society can simultaneously meet social, economic and environmental sustainability goals.

Our results show that ZESTY has the potential to produce iron with near zero emissions at costs close to conventional fossil fuel based approaches.

A game changing opportunity

Today, ~90% of iron is produced by coal fuelled blast furnaces. While alternative methods exist, such as using a ‘syngas’ of hydrogen and carbon monoxide, and new methods are emerging, such as using green hydrogen to directly reduce iron ore for use in an electric arc furnace, they risk the simultaneous achievement of social, economic and environmental goals.

Syngas methods are not only more expensive, but still emit ~0.6 tonnes of CO2 for each tonne of iron produced. Emerging hydrogen direct reduced iron (H-DRI) technologies are particular in their input material, generally requiring high grade and pelletised ores, and consume large amounts of expensive green hydrogen. For H-DRI to become economic, hydrogen and heat must be delivered as efficiently as possible. Solutions should also be compatible with a range of ore types, maintain existing supply chains and leverage existing infrastructure.

Australia perhaps encapsulates the risks and opportunity of decarbonising iron and steel production better than anywhere. Over half the world’s iron ore comes from Australia, and iron ore dominates Australia’s export earnings. Almost all Australian ore, however, is of the hematite / goethite variety, and not suited to use in an electric arc furnace. For Australia, the compatibility of its iron ore with future low-carbon steelmaking is a significant sovereign risk.

Yet, Australia is the lucky country, abundant in both mineral and renewable energy resources. As Professors Rod Sims and Ross Garnaut point out, by combining these natural advantages with the right technology solutions, Australia could decarbonise around 8% of the world’s emissions, not just the 1% of global emissions Australia produces domestically. The supply of green iron to trading partners around the world would account for much of these emissions savings, and green iron exports can be expected to attract a green premium in a decarbonising global economy.   

Calix’s solution: Zero Emissions Steel TechnologY

Calix’s Zero Emissions Steel TechnologY (ZESTY) is a renewably powered H-DRI technology for the production of green iron and ultimately, green steel.

How it works…

ZESTY is yet another application of Calix’s platform technology’s indirect heating approach, which enables inefficient combustion to be replaced by precise and renewably powered electric heating. Like other H-DRI technologies, ZESTY uses hydrogen to remove oxygen from the iron ore to produce metallic iron and water. Unlike other approaches, however, ZESTY separates the heat source from the reaction to ensure hydrogen is not combusted or used as a fuel, and is easily recycled.

No fossil fuels. No carbon emissions.

Through efficient electric heating, the most efficient use possible of hydrogen, and the elimination of additional processing steps, ZESTY aims to deliver the lowest cost decarbonisation solution for green iron and steel.

ZESTY reactor diagram
Figure 1. ZESTY process flow diagram.

ZESTY’s key features & benefits

  • Electrification & renewable power – The entire ZESTY process can be renewably powered, including the delivery of high temperature heat required to convert iron ore to metallic iron.
  • Minimum hydrogen consumption – Calix’s unique indirect heating approach ensures that hydrogen is used only as a reductant in the production of green iron and steel. Hydrogen is not combusted or used as a fuel, and unreacted hydrogen is simply recycled.
  • Process fines & lower grade ores – ZESTY is ideally suited to process small particle sizes, creating multiple beneficiation opportunities for lower grade ores and fine material that may otherwise be discarded as waste. ZESTY’s compatibility with lower grade ores provides a pathway to decarbonise much of the world’s current iron ore supply that is otherwise not suitable for use in electric arc furnaces.
  • No pelletisation – ZESTY removes the requirement for iron ore fines to be pelletised, eliminating process steps and avoiding significant capital and energy costs.
  • No fluidised beds – ZESTY delivers a highly simplified process for the processing of iron ore fines and ultra-fines without fluidised beds.
  • Flexible operation – Compatible with intermittent and renewable sources of electricity, ZESTY’s electric heating provides a high degree of temperature control with fast start-up and shut down, and highly flexible production rates. As such, it may provide a versatile load balancing service to the energy grid.
  • Easily scalable – Calix’s modular technology can be simply scaled through duplication, de-risking technology scale up and enabling flexible production volumes.
  • Targeting lowest cost – By enabling efficient electric heating, minimal hydrogen use, and eliminating additional processing steps, ZESTY aims to deliver the lowest cost decarbonisation solution for green iron and steel.

Flexible pathways to green steel

ZESTY can be integrated directly at the iron ore source for the export of green iron, or by a steelmaker to feed a blast furnace, basic oxygen furnace, or electric arc furnace. Multiple processing routes provide flexible near-, medium- and long-term decarbonisation pathways for the industry.

For a fast and efficient route to emissions reduction, ZESTY can produce zero emissions Direct Reduced Iron (DRI) or Hot Briquetted Iron (HBI) to replace some of the iron ore charge to a blast furnace. This pathway leverages existing steelmaking infrastructure, and as over 80% of the emissions from steelmaking come from the conversion of iron ore to metallic iron, it can provide significant emissions reduction in the near-term. However, it is anticipated around 30% of the overall charge to the blast furnace can be replaced by DRI.

ZESTY can also deliver zero emissions DRI/HBI to a renewably powered electric smelter, such as that proposed in the collaboration between BHP, Rio Tinto and Bluescope. The smelter provides an additional process step that removes impurities from DRI to deliver an iron product suitable for use in basic oxygen steelmaking. In this way, a DRI to electric smelter route can replace coal and blast furnaces altogether to make steel with ~80% reduction in emissions, while maintaining compatibility with a variety of input ores.

Alternatively, ZESTY may process higher grade ores, or provide sufficient beneficiation of lower grade ores, such that the DRI product can be used directly in an electric arc furnace for close to zero emissions steel.

Testing ZESTY’s economic and environmental credentials

To demonstrate the ZESTY technology at a commercially relevant scale, Calix is building a 30,000 tonne per annum ZESTY Demonstration Plant. The FEED study for the plant, completed in February 2024, was part funded by the Australian Renewable Energy Agency (ARENA) and supported by an expanded ore testing program at Calix’s pilot scale facility in collaboration with the Australian Heavy Industry Low-carbon Transition Cooperative Research Centre (HILT CRC) and its partners.

The extensive pilot-scale tests included over 130 test runs using nine different Australian ores from multiple providers, covering a range of grades and particle sizes. The results are extremely encouraging.

Even at pilot-scale in a multi-purpose R&D plant, ZESTY delivered excellent metallisation rates. Most test runs at the targeted temperature range achieved the level of metallisation suitable for downstream use in either a melter or blast furnace, while several tests reached sufficient metallisation levels for feed directly to an electric arc furnace. Notably, these results are for hematite / goethite ores, representative of around 96% of Australia’s iron ore exports.

Figure 2. Pilot-scale results showing metallisation as a function of processing temperature for a range of ores.

The ZESTY Demonstration Plant FEED study found that HBI from low grade iron ore could be produced for ~AUD$630-$800 / tonne[1]. This cost includes the capital cost of the plant and processing costs, and excludes the cost of land and transport of the input and output materials.

The study showed that, even at demonstration scale, ZESTY could produce zero emissions iron at a cost close to the range of existing conventional HBI processing costs, despite using hydrogen as a reductant. Furthermore, it does not take credit for any carbon price, carbon border adjustment mechanism, or other green premium that a near zero emissions iron product may attract.

The estimated production cost is made possible by a combination of ZESTY’s minimal use of hydrogen, the relative simplicity and efficiency of the electrically heated process, and the elimination of the agglomeration and induration process steps.

ZESTY’s energy requirement is projected to be 4.2–4.6MWh / tonne of iron, with most of this energy going towards the generation of green hydrogen. Excluding hydrogen production, ZESTY is projected to require 0.9–1.3MWh / tonne of iron.

The overall capital and operating costs are expected to reduce further as the core technology is scaled and refined.

Towards commercial demonstration

With the ZESTY technology proven at pilot scale, and a FEED study for a commercial demonstration plant completed, commercial and financing contracts are now being negotiated to enable the location of the Demonstration Plant to be selected and a Final Investment Decision to be made. Announcements will be made as key milestones are achieved.

“The economic production of green iron and steel will not only help solve an urgent climate challenge, but could also add value to local iron ore exports, future-proof local industries, and support sustainable global development.

“I am grateful to the dedicated ZESTY team and all our partners who have helped demonstrate the promise of the technology so far. We look forward to making further announcements as we scale and commercialise our industry leading solution for green iron and steel.”

Phil Hodgson

Calix CEO And Managing Director

Figure 3. Render of 30ktpa ZESTY demonstration plant

[1] ZESTY FEED Study assumptions:

  • Total cash cost of iron ore of $54 AUD/ tonne, based on average production prices.
  • Cost of electricity based on forecast spot market pricing, with an average cost of $36-48 AUD/MWh, plus transmission and connection capital costs (included in the Capex analysis).
  • Effective levelised cost of hydrogen of AUD$5.5-$6.2/kg H2 based on electrolyser CAPEX and electricity costs.
  • Conservative (high) operational costs and other overheads based on averaged numbers from existing similar scale plants.
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