A process for producing acetylene and synthesis gas by partial oxidation of hydrocarbons with oxygen, wherein a first input stream comprising one or more hydrocarbons and a second oxygen-comprising input stream - are separately preheated, mixed in a ratio of the mass flows of the second input stream to the first input stream corresponding to an oxygen number λ of not more than 0.31, wherein the oxygen number λ is understood as meaning the ratio of the oxygen amount actually present in the second input stream to the stoichiometrically necessary oxygen amount as required for complete combustion of the one or more hydrocarbons present in the first input stream, - fed via a burner block to a combustion chamber in which the partial oxidation of the hydrocarbons is carried out - to obtain a cracking gas which is quenched to 80 to 90 degrees Celsius downstream of the combustion chamber by injection of an aqueous quench medium to obtain - a process water stream I liq and - a product gas stream I g which - is cooled in a cooling column by direct heat exchange with cooling water to obtain - a process water stream II liq as the bottom stream, - a product gas stream II g as the top stream and - a sidestream which - is depleted of soot in an electrofilter to generate in the electrofilter a process water stream III liq which is combined with the process water streams I liq and II liq to afford the process water stream IV liq, wherein the combined process water stream IV liq is subjected to a purification by partial evaporation in a decompression vessel, wherein the combined process water stream IV liq is evaporated in a proportion of 0.01% by weight to 10% by weight based on the total weight thereof to obtain a purified process water stream V liq which is withdrawn at the bottom of the decompression vessel and passed through soot channels having surface particle separators to obtain a process water stream VI liq freed of floating soot which is recycled into the process. - are separately preheated, mixed in a ratio of the mass flows of the second input stream to the first input stream corresponding to an oxygen number λ of not more than 0.31, wherein the oxygen number λ is understood as meaning the ratio of the oxygen amount actually present in the second input stream to the stoichiometrically necessary oxygen amount as required for complete combustion of the one or more hydrocarbons present in the first input stream, - fed via a burner block to a combustion chamber in which the partial oxidation of the hydrocarbons is carried out - to obtain a cracking gas which is quenched to 80 to 90 degrees Celsius downstream of the combustion chamber by injection of an aqueous quench medium to obtain - a process water stream I liq and - a product gas stream I g which - is cooled in a cooling column by direct heat exchange with cooling water to obtain - a process water stream II liq as the bottom stream, - a product gas stream II g as the top stream and - a sidestream which - is depleted of soot in an electrofilter to generate in the electrofilter a process water stream III liq which is combined with the process water streams I liq and II liq to afford the process water stream IV liq, wherein the combined process water stream IV liq is subjected to a purification by partial evaporation in a decompression vessel, wherein the combined process water stream IV liq is evaporated in a proportion of 0.01% by weight to 10% by weight based on the total weight thereof to obtain a purified process water stream V liq which is withdrawn at the bottom of the decompression vessel and passed through soot channels having surface particle separators to obtain a process water stream VI liq freed of floating soot which is recycled into the process.