Section, Pub. L. 95–620, title III, § 302, Nov. 9, 1978, 92 Stat. 3306, authorized Secretary to prohibit use of petroleum or natural gas as primary energy source in existing major fuel-burning installations having coal or alternate fuel capability and, in installations in which mixtures of petroleum or natural gas and coal or other alternate fuels are found feasible, to prohibit excessive use of petroleum or natural gas in such mixtures.