Depending upon what process is used (wet, dry, preheater or precalciner) the energy range can be enormous. The order presented in the previous sentence represents the highest to lowest energy usage. Generally, pulverized coal is used as the heat source as the ash can be incorporated into the clinker.

Wet process kilns generally have fallen out of favor because of the energy required to evaporate the water but the blending and homogenization of the principle constituents is alot easier. If you have a wet source of calcium (as is generally the case in Florida), you would probably use this since your raw material is wet to begin with. Enrgy requirements are typically anywhere from 5-9 million BTU per ton of clinker produced. The kilns are gnerally quite long (from 400 feet up to largest I've ever evaluated at 525 feet) and range in diameter from 12.5 feet up to 19.5 feet.

Dry process kilns are similar but the materials are homogenized in a dry state and introduced dry into the kiln. generally their energy requirement is anywhere from 4-7 million BTU ton of clinker.

Preheater kilns require a shorter kiln and preheat (with some small amount of calcination in a tower composed of a series of large refractory lined cyclones. The kilns are usually quite short (~200 feet) and energy requirements are lower 3-6 MMBTU/ton clinker.

Finally the precalciners use a "flameless burning" of pulverized coal in a pre-calciner stage (in the same type of preheater tower, usually between the thrid and fourth stage. As the name implies, the calcium carbonate that makes up the largest proprtion of the raw material feed is calcined to calcium oxide in this stage and the rest of the preheat tower is used to get the raw materials up to the proper temperature for the high temperature zone of the kiln.

All cement production follows the same process: drying (whether wet or dry), calcining the carbonate to the oxide form (converting CaCO3 to CaO), and then bringing the the mixture of calcium, alumina, silica and iron up to the proper temperature for the exothermic reaction to occur that gives cement its various strength properties. The calcining temperature requires a minimum of 1500 °F to start, the exothermic "liquid phase" reaction takes place only above 2400 °F. Depending upon the cement qualities desired, the clinker temperature will reach temperatures approaching 3200 °F before being discharged from the kiln to be flash cooled in a clinker cooler whose sole purpose is to drop the temperature below 1850 °F in 10 minutes or less (ortherwise you get very hard to grind clinker AND cement properties that make it fairly worthless due to various strength and expansion properties).

In making concrete, cement and other aggregates are combined (either in a central mix unit or in what is known as truck mix) in a precise mixture of water, cement, aggregates and a few additives. Recently, flyash has been used as both a filler for certain aggreagtes and because it has certain properties that enhance the concrete's final set properties. It requires extremely residual carbon content in the flyash. Western coals that produce a highly alkaline (read calcium) ahs have been preferred in the past but other flyash has been tested and approved. Substitution of between 15-30 percent of flyash for the cement and fine aggragte is not uncommon.

Some of the metals in the flyash present some challenges in the mixing operation (e.g., arsenic) but one incorporated into the matrix, seem to be isolated and non-leaching.