Process for steam cracking of thermally unstable feedstock such as plastic pyrolysis oil, or olefin rich hydrocarbon cuts such as cracked gasoline, coker naphtha or diesel. The invention is also about a heat exchanger suitable for that process.

To enable long-term continuous operation by preventing blocking of a reaction pipe line disposed in a multi-pipe or double-walled-pipe heat exchanger, provided is a device for producing gas hydrate including a multi-pipe or double-walled-pipe device 1 for generating gas hydrate having a reaction pipe line 2 for flowing raw material water w and raw material gas g and a coolant circulation region 3 for circulating a coolant c and thereby cooling the reaction pipe line 2, wherein a coil spring 4 extending in the longitudinal direction of the reaction pipe line 2 is provided in the reaction pipe line 2.

To enable long-term continuous operation by preventing blocking of a reaction pipe line disposed in a multi-pipe or double-walled-pipe heat exchanger, provided is a device for producing gas hydrate including a multi-pipe or double-walled-pipe device 1 for generating gas hydrate having a reaction pipe line 2 for flowing raw material water w and raw material gas g and a coolant circulation region 3 for circulating a coolant c and thereby cooling the reaction pipe line 2, wherein a coil spring 4 extending in the longitudinal direction of the reaction pipe line 2 is provided in the reaction pipe line 2.