COKE DEPOSITION UNDER STEAM CRACKING CONDITIONS - STUDY OF THE INFLUENCE OF THE FEEDSTOCK CONVERSION BY MICROPILOTS EXPERIMENTS

Coke deposition phenomena are met in some refinery and petrochemical p rocesses such as steam cracking. In steam cracking furnaces the intern al surface of the reactor tubes are exposed to hydrocarbons at high te mperatures. This chemical system favours the deposition of carbon on t he surface of the tubes. Coking involves the massive accumulation of c arbon on the internal surface of the coils, reducing the efficiency of the reactor and entraining a number of detrimental consequences for t he operation of the cracking unit. The resultant problems include an i ncrease in the pressure drop through the furnace and a large increase in the heat transfer resistance across the tube wall. Consequently, at regular intervals the furnace must be decoked, i.e. the carbon layer deposited must be burned off using a mixture of air and steam. This de coking process is time consuming. Efforts are necessary to understand the coking phenomenon in order to reduce the rate and quantity of carb on deposited. For this purpose micropilots have been built to study th e influence of the profess conditions and the metallurgy of the coils. On some materials, the influence of conversion conditions of the feed stock will be presented.