NOVELTY - Process (I) for producing ethanol comprises: introducing acetic acid vapor feed stream (106) comprising acetic acid into first reactor (107); hydrogenating acetic acid in first reactor in presence of first catalyst to form first reactor product (108) stream comprising ethanol and residual acetic acid; cooling first reactor product stream in first heat exchange stage; hydrogenating residual acetic acid in second reactor (109) in presence of second catalyst to form second reactor product (110) stream comprising ethanol; and cooling second reactor product stream in second heat exchange stage.    USE - The processes are useful for producing ethanol (claimed), which is useful: in fuel applications (as a fuel blend with gasoline for motor vehicles e.g. automobiles, boats or small piston engine aircrafts); in non-fuel applications (as a solvent for toiletry, cosmetic preparations, detergents, disinfectants, coatings, inks or pharmaceuticals); as a processing solvent in manufacturing processes of medicinal products, food preparations, dyes, photochemicals or latex processing; as a chemical feedstock to make other chemicals e.g. butanol, vinegar, ethyl acrylate, ethyl acetate, ethylene, glycol ethers, ethylamines, aldehydes or higher alcohols; and in the production of ethyl acetate.    ADVANTAGE - The process utilizes the heat exchange stages that allow the efficient use of heat generated in one part of the hydrogenation reactor to be retained within another part of the process, hence improving the overall efficiency and reducing the costs.    DETAILED DESCRIPTION - Process (I) for producing ethanol comprises: introducing an acetic acid vapor feed stream (106) comprising acetic acid into a first reactor (107); hydrogenating the acetic acid in the first reactor in the presence of a first catalyst to form a first reactor product (108) stream comprising ethanol and residual acetic acid; cooling the first reactor product stream in a first heat exchange stage, where the first reactor product stream is cooled to a temperature that is equal to or greater than a feed temperature to the first reactor; hydrogenating the residual acetic acid in a second reactor (109) in the presence of a second catalyst to form a second reactor product (110) stream comprising ethanol; and cooling the second reactor product stream in a second heat exchange stage. An INDEPENDENT CLAIM is also included for a process (II) for producing ethanol, comprising: hydrogenating acetic acid from an acetic acid vapor feed stream in a reactor in the presence of a catalyst to form a crude reactor product; flashing the crude reactor product to form a vapor stream and a liquid stream comprising ethanol, ethyl acetate, water and acetic acid; separating at least a portion of the liquid stream in a first distillation column to produce a first distillate comprising ethanol, ethyl acetate and water, and a first residue comprising acetic acid; transferring heat of the first distillate in a first heat exchange stage; separating a condensed portion of the first distillate in a second distillation column to produce a second distillate comprising ethyl acetate and second residue comprising ethanol and water; separating a portion of the second residue in a third distillation column to produce a third distillate comprising ethanol and third residue comprising water; and cooling a portion of the third residue in a second heat exchange stage.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of a hydrogenation system.    Vapor feed stream (106)    first reactor (107)    First reactor product (108)    Second reactor (109)    second reactor product (110)