Lime Kiln

About

• Lime Kiln Calculations - $2400 for a minimum 100kW heater element for 1 ton batch kiln, lasts 150-300 heats.
• Bulk lime is $150-200 per ton - 10 cents per lb.
• Around 1.4 kwhr/kg of lime production - or 1400Mwhr for a ton
• Basic cost of open source - with 1 Cent Solar - we have 1400 kWhr * 1 cent/kWhr = $14 in electricity
• Absolute base cost is $14 energy and $12 in Kanthal A1 wear - making a 100 lb sack of concrete mix come out to $1.50 + rock, which is near zero marginal cost. Far below the $7.5/ 100 lb sack of industrial concrete.
• It's worth doing. For 3000 psi concrete, need to use Metakaolin mixed during cement mix phase, Commercially, they fire with 20% clay-containing limestone at slightly higher temperature, 1200C. But can do pure limestone at 1100 and then add metakaolin.
• Otherwise, get lime concrete at 1500 PSI.

Free Pozzolan

Economic Analysis: Pozzolan Production

If you have $0.01/kWh electricity and $10/ton limestone, your energy and raw material costs are world-class. In this specific scenario, paying $60–$100/ton for Fly Ash does indeed double or triple your "binder" cost.

To keep your economics in line with your ultra-cheap power, you should calcine your own local clay to create your pozzolan.

The "Free" Pozzolan Strategy

Since your power is essentially negligible, you can run a second "calcining" cycle in your 100kW kiln for the clay.

• The Cost: At $0.01/kWh, firing 1 ton of clay to <math>750^{\circ}C</math> (roughly 600 kWh) costs only $6.00 in electricity.
• The Yield: This transforms "free" site clay into a high-performance pozzolan for roughly $6.00/ton, which is 10x cheaper than buying Fly Ash.

Step 1: Dry Processing (Skip the Water)

To make this practical for many houses, do not wash the dirt. Washing is for pottery-grade purity. For 3,000 psi concrete, "impurities" like fine silt and sand in the clay act as beneficial micro-aggregates.

• Excavate: Dig up the clay-rich subsoil on your site.
• Dry: Spread it out in the sun until it is bone-dry and brittle.
• Crush: Use a simple jaw crusher or hammer mill to break it into 1-inch chunks.

Step 2: The "Pozzolan Fire"

1. Load the crushed clay chunks into your 1-ton Kanthal kiln.
2. Heat to <math>750^{\circ}C</math> and hold for 2–3 hours.
3. Warning: Do not hit your <math>1,100^{\circ}C</math> lime temperature, or you will turn the clay into "grog" (hard ceramic), which is chemically dead and won't react with the lime.

Step 3: Final Pulverization

This is the only way to get 3,000 psi. You must grind the fired clay into a micro-fine flour.

• The Tool: Since you are building many houses, buy or build a Continuous Ball Mill.
• The Process: Tumble the fired clay with steel balls until it passes a 325-mesh screen. This increases the surface area so the lime can "grab" it instantly.

Conclusion

By using your cheap $0.01/kWh power to fire local clay at <math>750^{\circ}C</math>, you can produce a high-strength pozzolan for approximately $6–$10 per ton (electricity + labor). This matches your $10/ton lime cost and keeps your total binder cost around $20/ton, which is roughly 85% cheaper than buying Portland cement or Fly Ash.