A process for preparing acetylene and synthesis gas by partial oxidation of hydrocarbons with oxygen, is disclosed. The process consists of separately preheating and then mixing a first input stream containing a hydrocarbon and a second input stream containing oxygen, supplying the first input stream and the second input stream via a burner block to a firing space, quenching a cracking gas obtained to produce a process water stream and a product gas stream, cooling the product gas stream in a cooling column by direct heat exchange with cooling water, depleting soot in an electrostatic filter, combining all process water streams and passing through soot channels, subjecting the combined process water stream to a cleaning operation by partial vaporization in a one-stage flash vessel to obtain a cleaned process water stream, and recycling the cleaned process water stream into the process.