<prompt> Translate the following text to EnglishKwa kulinganisha, makadirio ya kihafidhina ya kiasi cha chuma kinachohitajika kwa mfumo kamili wa FGD ni chini ya au sawa na kile kinachohitajika kwa upgrading ya SCR.  <response>: By comparison, the conservative estimate of the amount of steel required for a full FGD system is less than or equal to that required for an SCR retrofit. 