Direct Reduced Iron
Direct-reduced iron (DRI) is a metallic material formed by the reduction (removal of oxygen) of iron oxide (iron ore) at temperatures below the melting point of iron. DRI is produced by the use of a reducing gas (often a mixture of hydrogen and carbon monoxide). The temperatures for this process are significantly lower than those in a blast furnace, and capital requirements are also lower. DRI may have a sponge-like structure, leading to the alternative name "sponge iron". Suitable starting materials are very high-grade iron ores (70% iron content and up) or rusted scrap steel, which is mostly iron. These could not be used in an induction furnace, as the reduction is a chemical reaction while induction only melts the already-reduced iron. One of the global leaders in sponge iron production is India, which has numerous small or medium-sized facilities. DRI is commonly manufactured in a rotary kiln.
HDRI ("hot direct reduced iron"): moving the still-hot iron immediately for melting into an electric arc furnace or Induction_Furnace, to save energy.
Product ecology
Induction_Furnace -- could use HDRI
Gasifier -- to make the reducing gas: syngas is a mixture of H and CO
Biogas -- methane from biogas can be turned into the H/CO mix. Globally, fossil gas (a.k.a. "natural" gas) is the most commonly used fuel for DRI, so biogas is a possible replacement, although it would probably have to be upgraded first.
Waste heat -- This process produces waste heat that could be used for pyrolyzing biomass (pyrolysis = heating in the absence of oxygen). This process releases syngas, keeping the process going, all powered by solid biomass, generating biochar as a by-product (permanently fixed carbon) .
Biochar -- is a charcoal-like soil amendment. It is resistant to biodegradation, i.e. it is carbon that has been permanently removed from the atmosphere. Some of the syngas that is produced during pyrolysis could be used for making DRI. If these processes are combined, then biochar is a valuable by-product. The slurry from a biogas digester could be co-composted with biochar to make an excellent soil amendment.
Further information is needed !
- Is this actually feasible on the small scale ?
- Are we missing something here ?
- Does the process take place at atmospheric pressure ?
- Can a rotary kiln be designed at the village scale ?
- Are sufficient amounts of high-grade ores or rusted steel available ?
A: Scalability is feasible, but efficiency may not be as good. The processes of the largest plants can also be done on a table top. The question is - at what point does it still make sense to do so? If we have access to abundant energy, feasibility may occur at a village scale.
A: This appears as a good alternative for smaller scale, lower-cost process, worth adding to our general awareness.
External links
- Wikipedia: Direct Reduced Iron
- Wikipedia: Sponge Iron Reaction
- Wikipedia: Water Gas Shift => a way to increase the hydrogen content in syngas
- war-time 1942 TIME Magazine article on sponge iron