Variable temperature waste heat recovery system

A waste gas recovery system for use with a process heater installation in which exhaust gases discharged from said installation are variable during each operating cycle, said system including a closed-loop heat transfer circuit through which a heat transfer liquid is circulated and having a first heat exchanger for extracting heat from said exhaust gases, a second heat exchanger adapted to pass a recipient fluid in heat transfer relation with said heat transfer liquid, and a reservoir for storing the heat transfer liquid circulated through said circuit, the improvement comprising said reservoir being operatively disposed in said heat transfer circuit intermediate the downstream end of said first heat exchanger and the upstream end of said second heat exchanger whereby heat transfer liquid heated in said first heat exchanger is passed to said reservoir prior to being passed to said second heat exchanger and said reservoir containing an amount of heat transfer liquid in excess of that contained in the remainder of said heat transfer circuit whereby variations in the temperature of said heat transfer liquid exiting said first heat exchanger are damped prior to entry of said heat transfer liquid into said second heat exchanger.