Method for recovering high grade process energy from a contact sulfuric acid process

In a process for the manufacture of sulfuric acid, comprising combustion of a source of sulfur with an oxygen-containing gas in a burner to produce a combustion gas stream comprising sulfur dioxide and oxygen, passage of the gas stream through a plurality of catalyst stages for progressive conversion of sulfur dioxide to sulfur trioxide, recovery of heat in useful form by cooling the gas stream exiting each of said catalyst stages, passage of the cooled gas stream from one of said stages through an absorption zone where the gas stream is contacted with sulfuric acid for removal of sulfur trioxide from the gas phase, and return of the gas stream from said zone to a further stage of said plurality of stages, the improvement which comprises:

• introducing water vapor into the gas stream at a point between said burner and the said absorption zone, at least a portion of the water vapor reacting with sulfur trioxide in the gas phase to produce sulfuric acid and thereby generate the heat of formation of sulfuric acid in the gas phase and
• recovering heat energy from the vapor phase heat of formation of sulfuric acid by transfer of heat in an indirect heat exchanger from said gas stream to steam having a pressure at least about 8 bar higher than the pressure of said water vapor as introduced into the gas stream or to feed water from which said steam is generated wherein said indirect heat exchanger is located upstream of said absorption zone.