Coke, combustion

The furnace (Fig. 2) maybe divided into four zones (from bottom to top). (/) Hearth and raceway as the coke descends through the furnace, it is heated by the ascending gases to about 1370°C. When it reaches the raceway in front of the tuyeres, it reacts immediately with the oxygen in the hot blast air. Equation 1, however, is actually the combination of coke combustion (eq. 6) and coke gasification (eq. 7, also referred to as solution loss). 

The impact that variations in coke content and burning conditions can have on the overall heat of coke combustion is shown in Table 2. Because the heat balance dictates the amount of heat that is required from burning coke, the heat of combustion then determines the amount of coke that must be burned. 

The catalysts used in this CCR commercial service must meet several stringent physical property requirements. A spherical particle is required so that the catalyst flows in a moving bed down through the process reactors and regenerator vessel. These spheres must be able to withstand the physical abuse of being educated and transferred by gas flow at high velocity. The catalyst particles must also have the proper physical properties, such as particle size, porosity, and poresize distribution, to achieve adequate coke combustion kinetics. 

Figure 9.10. Scheme of an FCC Unit. Cracking ofthe heavy hydrocarbon feed occurs in an entrained bed, in which the catalyst spends only a few seconds and becomes largely deactivated by coke deposition. Coke combustion in the regenerator is an exothermic process that generates heat for the regeneration and for the endothermic cracking process. 

Alternative layers of metal and coke are fed into the top of the furnace. The metal is melted by hot gasses from the coke combustion. Impurities react with the lime and are separated. 

Total unit heat dnty will typically be in the range of 500-1000 BTU per pound of feed to the unit. This set of process heat requirements establishes the amount of heat that must be supplied by combustion of coke. Because of the process control schemes that are normally employed in FCCUs, the unit operation will automatically adjust itself so that the energy produced via coke combustion equals the heat requirements of the process. If the balance is shifted by changes to the feed quality or operating conditions, shifts in catalyst circulation rate and regenerator temperature will occur until a new equilibrinm set of conditions is established. 

In order to establish an optimized FCC operation, it is often possible to influence factors impacting the heat balance. If coke combustion produces an amount of heat that causes regenerator temperature to rise above a preferred level, refiners may choose to reduce the feed temperature or lower the heat of combustion of the coke by reducing... 

Effect of the degree of coke combustion to CO2 on the bifurcation diagrams for the reactor temperature versus the catalyst circulation rate Figure 7.6... 

When the coke on catalyst I is burned off with an ozone-air mixture at temperatures between 300 and 523 K, a certain amount of ozone leaves the reactor. Figure 1 shows the ozone concentration at the reactor outlet. It can be seen that, undei these operating conditions, the ozone concentration at the outlet increases from 4 h onwards, though the coke combustion continues and it is not complete even at 10 h. 

Reaction-regeneration cycles have been carried out under the conditions Reaction temperature, in the 250-450 °C range contact time, 0.05 h time on stream, 12 h. After the reaction the catalyst bed was subjected to an inert gas stream (He) of 100 cm3/min for 15 min (time needed between cycles). Regeneration by coke combustion with air temperature, 550 °C time, 20 min. Under these conditions the catalyst fully recuperates activity, except in the first regeneration in which a fraction of strongly acidic sites are irreversibly lost. 

Meta-4 A process for converting ethylene and 2-butene into propylene by metathesis. The process operates in the liquid phase at low temperatures in the presence of heterogeneous catalyst based on rhenium oxide on alumina. The catalyst is constantly regenerated by coke combustion. Developed by IFP and the Chinese Petroleum Corporation of Taiwan. A demonstration plant was operated from 1988 to 1990 and the process was demonstrated at Kaohsiung, Taiwan, in 1999. Now offered by Axens. 

The process of coke combustion in bubbling or turbulent bed generally consists of the following steps ... 

Coke deposition was performed via cracking reactions of a real feedstock (gas-oil) operated in a fixed bed reactor which allows a wide range of experimental conditions [7] catalyst mass from 0.5 to 10 g reaction temperature from 723 K to 873 K pressure from 1 to 4 bar injected feed mass between 0.4 and 4 g feed injection time from 10 to 300 s. This reactor induces a coke formation very similar in quantity and nature to that observed on industrial plant catalysts [7]. Coke combustion was performed at 1773 K under oxygen flow in a Leco CR12 carbon analyzer. The global carbon content was extracted from the total volume of carbon dioxide produced during combustion... 

Results on the characterization of coke on catalysts used in MCP conversion can also be rationalized in terms of the metal-proton adduct model. Temperature-programmed oxidation of such catalysts displays two distinct peaks of CO2 formation, as is shown in Fig. 26. One peak is characteristic of coke combustion catalyzed by metal oxide, and the second peak, at... 

Kinetics of Coke Combustion during Temperature-Programmed Oxidation of Deactivated Cracking Catalysts... 

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