Steam cracking variables

Liquid feedstocks for olefin production are light naphtha, full range naphtha, reformer raffinate, atmospheric gas oil, vacuum gas oil, residues, and crude oils. The ratio of olefins produced from steam cracking of these feeds depends mainly on the feed type and, to a lesser extent, on the operation variables. For example, steam cracking light naphtha produces about twice the amount of ethylene obtained from steam cracking vacuum gas oil under nearly similar conditions. Liquid feeds are usually... 

Ethylene production by steam cracking of ethane Eonr cases with two or three objectives from (1) maximization of ethane conversion, (2) maximization of ethylene selectivity, and (3) maximization of ethylene flow rate. NSGA-n Reactor inlet temperatnre and length were observed to be the most important decision variables. Tarafder et al. (2005b)... 

Cracking temperature and vapor residence time were the most important parameters controlling the cracking reactions. Within the range of conditions tested, other variables such as type and area of cracking surface, the vapor concentration of the feedstock and presence of steam made little difference to the yields of BTX and ethylene. Steam is used as a diluent and... 

The uniqueness of this process results from the fact that the steam provides the total heat necessary for the primary cracking stage. It is not therefore a simple vapo-cracking. This process intervenes simultaneously while suppressing to the maximum the formation of tars and coke by dilution of steam and partial reduction of the steam pressure resulting from the heavy hydrocarbons produced. Additionally, this process is very flexible and it is suitable for the treatment of highly variable feed rates of waste. 

Catalytic tar elimination over nickel-based catalysts mainly proceeds by steam and dry (CO2) reforming reactions, although there can be simultaneous thermal reactions of cracking and, perhaps, of hydrocracking. Therefore, the steam and COj contents in the flue gas have an important role in the overall tar elimination. Tar conversion (elimination) depends on the properties of the catalyst used, on the space-time (or space-velocity), bed temperature, H2O to carbon to be reformed ratio and on the operation variables of the upstream gasifier such as equivalence ratio and temperatures in the bed and in the freeboard. 

Gases and liquids permeate fluoropol5miers to different extents depending on variables such as temperature, pressure, and the composition of the processing fluid. An increase in temperature accelerates the rate of permeation into the polymers. Thermal cycling can cause a part to stress-crack or form blisters because of successive evaporation and condensation of permeated chemicals. Steam is a well-known permeant of polytetrafluoroethylene and can create blisters upon cycling. 

K is a function of feedstock, cracking severity, dilution steam ratio and other system variables it is an empirical factor. 

Union Carbide pioneered the development of products derived from ethylene and propylene in the 1920 s and 30 s. Our original cracking furnaces were designed and built with very limited knowledge of the chemistry of hydrocarbon pyrolysis. Information, especially quantitative information, on the effect of such variables as pressure, partial pressure of furnace gas, and the time/temperature relationship was almost nonexistent. Steam was added to the cracking mixture early - but only because it was found that steam eliminated formation of carbon particles which were rapidly eroding out furnace tube bends. 

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