Cement Energy Calculations

Summary

A 10,000 square foot microfactory with a 200kW rooftop solar panel system can produce 1 ton of solar cement per day from limestone feedstock, neutralizing CO2 impact of cement production. Payback time for PV panel costs is 350 days if a sack of cement (100lb) is sold for $10. A solar electric kiln the size of chest freezer is required. PV is a choice here due to its flexible function and current low cost of PV at Sunelec.

Notes

Solar gain- 4MW/acre. 20% conversion - 800kW/acre.

• Cement - 20-55 kWhr/ton just electricity for motion. https://www.scribd.com/doc/19070918/Small-Scale-Production-of-Portland-Cement https://link.springer.com/chapter/10.1007/978-1-59745-173-4_14 electricity
• + 1040 kcal/kg heat (1.2kWhr/kg) of clinker. Or 1.2MWhr/ton - .
• Think of 200kW PV array - gets us the 1.2MWhr/day, or 1 ton per day - $200 worth of cement. $70k. 350 days payback if 1 Ton/day production!!! If use coal, 30MJ/kg - 8 kWhr - or 150 kg of charcoal per ton of cement. World’s first solar cement plant - eco-cement, carbon neutral.
• By electric, see below, 5x improved efficiency for 5 tons per day from 200kWhr PV array? That’s a sizeable array - perhaps 100kW is more reasonable. If .15 kW/sq m, need only 700 sq meters - only ⅙ of an acre. The next building should be ½ acre for the materials production facility. If we do small scale production - 100kW heat - 2.5 tons per day. That’s 25 tons of stabilized block. 3200lb per 4x8 wall section. That is 60 feet of wall - just a microhouse. That would be absolute minimum.
• 25 ton per day setup is open source in Small Scale Cement Plants. 20 bags per ton. 8 pallets per day - or 500 bags * $10/bag. $5000/day. Doable. That is a typical industrial value that needs to be produced per day.
• Electric - 800 kcal/kg for calcination - CaCO3 + Heat ->CaO + CO2. or 3 MJ/kg - or .8kWhr/kg. If we can transfer heat with 50% efficiency - then we have 10/2 = 5x increase over burning with charcoal. In general, electricity is cleaner and more efficient. So theoretical limit of 200kW PV array is 5 tons per day.

• Phase I realistic - 3 tons per day
• Phase II realistic - 5 tons per day.

• If 200kW gives us 1.2MWhr/day - that is 1200 kW hrs - or about $120 per day. If turned to cement, that would be 10x the value.