Hydrochar Briquettes for EAF Slag Foaming: A New Path

Anthracite is not the only way to build a working foam in an electric arc furnace. The latest evidence says hydrochar briquettes for EAF slag foaming can do the job—and the difference between untreated and pyrolyzed hydrochar could determine whether the idea works economically at plant scale.

That is the part procurement teams should pay attention to. This is not a vague promise about turning waste into fuel. Researchers made hydrochar–mill-scale briquettes, dropped them into molten EAF slag and produced foam in every one of seven tested formulations.

We still need plant trials before calling hydrochar a universal replacement. But the research has moved the conversation from whether green-waste hydrochar can foam slag to a more useful question: which formulation gives a furnace the right gas-release profile at the right replacement mass?

The headline: all seven recipes generated foam

The study tested seven briquette formulations and reported successful slag foaming across the full set. The experiments used roughly 20 grams of briquette in 600 grams of molten EAF slag at 1,923 K. On a process basis, that corresponds to a tested addition rate of 30 grams per kilogram of slag.

For an industrial buyer, that broad result is more useful than a single best-case recipe. It suggests that suppliers and steel plants may have room to tune the composite around available hydrochar and mill-scale streams instead of chasing one fixed product formula.

The researchers also varied the fixed-carbon-to-iron-oxide molar ratio widely, from 0.07 to 0.90. That is a substantial formulation range. It tells us that the reaction system can support successful foaming under multiple carbon and oxide balances, although the exact operating target still has to be established for each plant.

In other words, hydrochar should be bought as an engineered briquette system, not as a generic bulk carbon. The recipe matters.

PGWH gives buyers a better replacement ratio

Here is the number that changes the commercial discussion: 1 kilogram of anthracite was replaced by 2.4 kilograms of untreated green-waste hydrochar, but by 1.9 kilograms of pyrolyzed green-waste hydrochar.

Substitution option	Mass needed per 1 kg anthracite replaced	What it means
Untreated GWH	2.4 kg	Higher replacement mass in the tests
Pyrolyzed PGWH	1.9 kg	More material-efficient tested option

PGWH was made by pyrolyzing GWH at 873 K. That extra treatment appears to have improved the way the material generated gas and reduced the amount required for the same anthracite replacement basis reported in the research.

This is where a simple price-per-tonne comparison can lead buyers in the wrong direction. PGWH may involve more processing, but it also requires less replacement mass in the reported tests. The right calculation is delivered cost per unit of anthracite displaced, including transport, handling, briquette density and dosage.

We would also ask every supplier for a defined replacement basis. Is the comparison based on fixed carbon, total mass, foaming performance or another plant-specific metric? Without that definition, two hydrochar offers may look comparable while behaving very differently in the furnace.

More foam is useful—but timing matters just as much

The briquettes produced maximum foaming heights of 1.6 to 2.5 times the initial slag height. That is a strong signal that the composites were not merely reacting at the slag surface; they were generating enough gas to expand the molten slag substantially.

But the duration data may be even more valuable for operators. Foaming lasted between 1.5 and 3.4 minutes, depending on the formulation and hydrochar type.

Operating behavior	Reported observation
GWH response	Rapid foaming from abrupt volatile release
PGWH response	More gradual, longer-lasting foaming
PGWH gas-generation mechanism	CO and CO₂ formation during carbothermic reduction
Maximum measured height	1.6–2.5 times initial slag height
Foaming duration range	1.5–3.4 minutes

Untreated GWH released volatiles abruptly, creating rapid foaming. PGWH took a more controlled route, generating CO and CO₂ during carbothermic reduction and sustaining the response for longer. That difference gives process engineers something to work with.

A furnace that needs a quick burst may favor a different profile from one where stable slag coverage over a longer interval is the priority. The strongest product is therefore not necessarily the one with the most dramatic initial reaction. It may be the one whose timing fits the furnace’s power input, oxygen injection and slag practice.

No appreciable sulfur or phosphorus transfer at tested dosage

Performance is only half the qualification exercise. In steelmaking, the material also has to avoid introducing unwanted impurities. In the reported experiments, hydrochar caused no appreciable sulfur or phosphorus transfer into the slag at the tested dosages.

That finding directly addresses one of the concerns buyers may have about waste-derived carbon. Green waste is not automatically a clean metallurgical input simply because it is renewable or biogenic. Ash chemistry, contamination and processing history all need to be checked.

The result is encouraging, but it belongs inside a disciplined supplier qualification process. We would request:

• A full ash and elemental analysis
• Sulfur and phosphorus values for each production lot
• Feedstock traceability for the green-waste input
• Pyrolysis conditions for PGWH
• Briquette dimensions, strength and moisture data
• Demonstrated foaming curves rather than a single performance claim
• Results from testing at a dosage relevant to the intended EAF

The reported dosage was 30 grams of briquette per kilogram of slag. A commercial plant may use different slag weights, addition practices and thermal conditions, so the research should guide the trial design rather than replace it.

Steelmakers looking for qualified materials can use a [link:biochar-marketplace] to compare hydrochar producers and identify suppliers able to provide consistent technical documentation.

The procurement opportunity is bigger than fuel substitution

Hydrochar composite briquettes connect three industrial needs: anthracite substitution, green-waste utilization and mill-scale integration. That does not prove a particular project will lower cost or emissions. It does create a credible basis for testing a lower-carbon alternative in a defined EAF application.

The most promising route appears to be PGWH where controlled gas generation and lower replacement mass are priorities. GWH may still have a role where rapid volatile release fits the operating window or where processing economics favor untreated material.

The business case should be built around furnace results: foam height, duration, slag chemistry, electrode and energy behavior, handling performance and total delivered cost. Avoid making the decision on feedstock story alone.

Conclusion: test the formulation, not just the material name

The research gives the industry a practical starting point. Hydrochar–mill-scale briquettes foamed EAF slag in all seven tested formulations, expanded slag to 1.6–2.5 times its initial height, and maintained foaming for 1.5–3.4 minutes. PGWH required 1.9 kilograms per kilogram of anthracite replaced, compared with 2.4 kilograms for GWH.

Our takeaway is simple: hydrochar has earned a serious industrial trial, but the briquette recipe and gas-release profile must be part of the buying decision. Start with verified specifications, run a controlled comparison against anthracite and measure what the furnace actually needs.

Explore verified biochar, hydrochar and biocarbon suppliers through the BiocharLink marketplace.