A continuous process for preparing acetylene and synthesis gas by partial oxidation of hydrocarbons with oxygen, in which a first input stream comprising one or more hydrocarbons and a second input stream comprising oxygen - are separately heated in preheaters (V1, V2), mixed in a mixing unit in a ratio of the mass flow of the second input stream to the first input stream corresponding to an oxygen ratio of less than or equal to 0.31, the oxygen ratio being understood to mean the ratio of the amount of oxygen actually present in the second input stream to the amount of oxygen which is needed stoichiometrically and is required for the full combustion of the one or more hydrocarbons present in the first input stream, - supplied via a burner block to a combustion chamber in which the partial oxidation of the hydrocarbons takes place, - to obtain a first cracking gas stream I g, wherein - the first cracking gas stream I g is cooled in a prequench by injection of an aqueous quench medium to a temperature in the range from 100 to 1000°C to obtain a second cracking gas stream II g, - in a solid-gas separation apparatus, 50 to 90% of the solids present in the second cracking gas stream II g are removed therefrom to obtain a solids stream I f and a third cracking gas stream III g, - the third cracking gas stream III g is cooled in a total quench by injection of water to 80 to 90°C to obtain a fourth cracking gas stream IV g and a first process water stream I liq, - the fourth cracking gas stream IV g is subjected in one or more scrubbing apparatuses (C, D) to a fine removal of solids to obtain one or more process water streams II liq, III liq and a product gas stream VI g, - the process water streams I liq, II liq, III liq are combined to give a combined process water stream IV liq, - the combined process water stream IV liq is recycled partly as stream V liq into the total quench and the rest is subjected as stream VI liq to cleaning by partial vaporization in a one-stage flash vessel, stream VI liq being vaporized in a proportion of 0.01 to 10% by weight, based on the total weight thereof, to obtain a cleaned process water stream VII liq which is cooled by means of a re-cooling device, partly recycled as stream VIII liq into one or more of the one or more scrubbing apparatuses (C, D), and the rest is discharged as stream IX liq, and supplied to the wastewater in need of treatment. - are separately heated in preheaters (V1, V2), mixed in a mixing unit in a ratio of the mass flow of the second input stream to the first input stream corresponding to an oxygen ratio of less than or equal to 0.31, the oxygen ratio being understood to mean the ratio of the amount of oxygen actually present in the second input stream to the amount of oxygen which is needed stoichiometrically and is required for the full combustion of the one or more hydrocarbons present in the first input stream, - supplied via a burner block to a combustion chamber in which the partial oxidation of the hydrocarbons takes place, - to obtain a first cracking gas stream I g, wherein - the first cracking gas stream I g is cooled in a prequench by injection of an aqueous quench medium to a temperature in the range from 100 to 1000°C to obtain a second cracking gas stream II g, - in a solid-gas separation apparatus, 50 to 90% of the solids present in the second cracking gas stream II g are removed therefrom to obtain a solids stream I f and a third cracking gas stream III g, - the third cracking gas stream III g is cooled in a total quench by injection of water to 80 to 90°C to obtain a fourth cracking gas stream IV g and a first process water stream I liq, - the fourth cracking gas stream IV g is subjected in one or more scrubbing apparatuses (C, D) to a fine removal of solids to obtain one or more process water streams II liq, III liq and a product gas stream VI g, - the process water streams I liq, II liq, III liq are combined to give a combined process water stream IV liq, - the combined process water stream IV liq is recycled partly as stream V liq into the total quench and the rest is subjected as stream VI liq to cleaning by partial vaporization in a one-stage flash vessel, stream VI liq being vaporized in a proportion of 0.01 to 10% by weight, based on the total weight thereof, to obtain a cleaned process water stream VII liq which is cooled by means of a re-cooling device, partly recycled as stream VIII liq into one or more of the one or more scrubbing apparatuses (C, D), and the rest is discharged as stream IX liq, and supplied to the wastewater in need of treatment.