Installation for steam cracking hydrocarbons, with solid erosive particles being recycled

A hydrocarbon steam cracking installation comprising a plurality of furnaces disposed in parallel for cracking hydrocarbons introduced therein, an indirect quench heat exchanger connected to each respective furnace for cooling gaseous effluent leaving the furnace, direct quench means, respective effluent ducts connecting each of said indirect quench heat exchangers to said direct quench means, a particle injection duct cooperating with each said furnace for injecting solid particles into the respective furnaces, and common means for separating the solid particles from the effluents and for recycling the particles into said furnaces, said common means for separating and recycling comprising at least one cyclone separator, said separator including a solids outlet for discharge of solid particles collected by the separator, a tank for storing solid particles, said tank having an inlet connected to said solids outlet of said cyclone separator and having an outlet connected to said particle injection duct whereby solid particles may be introduced into said duct, a source of gas under pressure connected to said particle injection duct, and a conduit also connecting said source of gas under pressure to said tank for increasing the inside pressure of said tank to a value that is not less than the pressure in said particle injection duct, each furnace having a solid particles injection valve associated with said particle injection duct for individually controlling the flow of solid particles into the furnace, each furnace also having an isolating valve provided in the respective effluent duct connecting the indirect quench heat exchanger to said direct quench means, and each furnace also having a second duct connected to said effluent duct upstream from said isolating valve and connected to the common separation and recycle means, the isolating valve of a furnace being closed when the corresponding injection valve for that furnace is opened in order to direct the mixture of gaseous effluents and solid particles to said common separation and recycle means.