Cleaning of process equipment

A method of cleaning process equipment which includes a process vessel fouled by an organic foulant from a chemical process that involves oligomerisation and polymerization in the presence of a catalyst, the method including

• spraying a liquid hydrocarbon stream, which is not a catalyst poison for said catalyst of said process, at a pressure of at least 69 bar(g) at fouled surfaces inside the process vessel to forcefully dislodge the organic foulant from said fouled surfaces by means of shear provided by the high pressure hydrocarbon stream, the hydrocarbon stream being sprayed from at least one nozzle located inside the process vessel and the hydrocarbon stream being at a temperature below the melting point of the organic foulant or below the melting point of an organic component of the organic foulant when the organic foulant is a multi-component organic foulant to minimize dissolution of the organic foulant in the hydrocarbon stream;
• and
• removing the dislodged foulant from the process vessel.