0 . 6 5   kg ▁Ca O ▁is ▁required / ▁kg ▁c ement ▁produced . ▁▁ ▁U . S . ▁electric ▁generation ▁capacity ▁( only ▁foss il ▁fu els ): ▁Natural ▁gas ▁= ▁ 4 1 5 ▁G W , ▁Co al = ▁ 3 1 8 ▁G W ▁& ▁Pet role um ▁= ▁ 5 1 ▁G W ▁▁▁ ▁C ement ▁consumption ▁in ▁U . S . ▁= ▁ 1 1 0 , 4 7 0   ×   1 0 3 ▁metric ▁tons ▁= ▁ 1 . 1 0 4 7 0   ×   1 0 8 ▁metric ▁tons ▁= ▁ 1 . 1 0 4 7 0   ×   1 0 1 1   kg . ▁ ▁Calcul ations ▁ ▁For ▁a ▁single ▁Ca - loop ing ▁cycle ▁installed ▁on ▁a ▁ 5 0 0 MW ▁power ▁plant : ▁▁ ▁Am ount ▁of ▁Ca O ▁from ▁pur ge ▁ann ually ▁= ▁ 1 2 . 6   kg ▁Ca O / s   ×   3 6 5 ▁days / year   ×   2 4 ▁hr / day   ×   3 6 0 0 s ▁/ ▁hour ▁= ▁ 3 . 9 7   ×   1 0 8   kg ▁Ca O / ▁year ▁ ▁C ement ▁that ▁can ▁be ▁obtained ▁from ▁pur ge ▁ann ually = ▁ 3 . 9 7   ×   1 0 8   kg ▁Ca O / ▁year   ×   1   kg ▁c ement / ▁