View Single Post
  #12  
Old 03-03-2018, 05:28 AM
Gelrir Gelrir is offline
Registered User
 
Join Date: Nov 2010
Posts: 226
Default

cement kiln: Portland cement needs clay, shale, limestone and gypsum ... and a lot of heat.

Proportions used are: 73% limestone, 24% clay or shale, 2% gypsum, and some other minor bits. 2678 kg of pure calcium carbonate (the best limestone) can be burned in an efficient kiln, using 300 kg of anthracite coal, to provide 1500 kg of quicklime (calcium oxide). Cements made with volcanic ash will include the addition of about 25% ash.

Required amounts of other fuels: poor coal, 430 kg; 340 kg of charcoal; or 660 kg of wood (15% moisture). Even garbage can be burned, but results in poor quality output (and sells for about 2/3 of the "good stuff").

A lime kiln built of brick is 1.8 meters on a side, and 3.7 meters tall (the brick part -- the metal chimney is 2.5 meters tall). It wouldtake about a month to build (if you have bricks and a blacksmith). It will hold about 1.75 tons of coal and limestone; the daily output would be about 1.5 tons of quicklime (and would require 300 kg of coal per day).

Producing the portland cement is another energy-intensive process: quicklime and the other components (not including the gypsum) are blended together, and then fed through a rotary kiln (more complex than the bulk kiln for producing quicklime); this product "clinker" is pulverized, mixed with gypsum, and then ground extremely fine to make cement.

In a fuel oil-fired rotary kiln, 0.106 kg of heavy fuel oil is burned per 1 kg of clinker passing out. Rotary kilns have the advantage that the fuel does not come into contact with the limestone, which allows more flexibility in the type of fuel used.

In an inefficient coal-fired rotary kiln circa 1906, 0.58 kg of coal is burned to produce 1 kg of cement. An efficient kiln of that period might use as little as 0.18 kg of coal for the same output. Variation is based on size (larger kilns are more efficient), the material being processed, and good technical methods.

1.5 tons of quicklime (plus the other components) results in (about) 2 tons of portland cement. To make a cubic meter of concrete, mix:
  • 307 kg of cement
  • 926 kg of sand
  • 950 kg of aggregate (typically gravel)
  • 163 liters of fresh water

Thus a cubic meter of concrete requires at least 46 kg of coal to be burned ... probably twice that much, since the rotary kiln needs to be pretty hot, also. That brick kiln is one of of a process that creates 6.5 cubic meters of concrete each day.

Our (classic-setting) campaign has some more info on the process: http://asmrb.pbworks.com/w/page/1131...neering#cement

--
Michael B.
Reply With Quote