Influence of Residence Time

The residence time of the hydrocarbon feedstock in the cracking furnace is a crucial parameter for the product distribution. For short residence times, the formation of the primary cracking dominates and this leads to the desired short-chain alkenes. At higher residence times, however, more secondary reactions occur and this 

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Fig. 14.11 Influence of residence time on methane conversion and product yield [63]. Reaction conditions Temperature 703 K, pressure 34 bar, CH4/02 ratio 16/1.

Influence of Residence Time. An approximate calculation of the residence time of the particles in the jet, assuming that they reach the gas velocity instantaneously (which is probably true for the small particles), shows that this time is about 1 msec. Estimating the rate of heating of particles of various sizes shows that particles less than 50m in diameter will reach a temperature of 1000°C. in approximately 1 msec., assuming a gas temperature of 4700°C. —an average heating rate of 10 °C. per sec. These estimates indicate that... 

Awad, Y. M. and Abuzaid, N. S. (2000) Influence of residence time on the anodic oxidation of phenol. Sep. Purif. Technol. 18, 227-236. 

Residence Time. The influence of residence time on yields is similar to that of hydrocarbon partial pressure, but smaller. In principle, unsaturated components increase slightly with shorter residence time, depending on the cracking severity. At the same time, saturated components and pyrolysis fuel oil (PFO) decrease. The quality of pyrolysis fuel oil also is influenced by residence time. For constant P E, the ratio of carbon to hydrogen in PFO becomes smaller with decreasing residence time, which has a positive effect on coking tendency besides other parameters. 

The influence of residence time on the gasification efficiency was tested in the miniature plant for both glucose and pyrocatechol at 30, 60 and 120 sec. (feed 0.2 M 600°C, 250 bar, KOH). At these conditions the residual TOC content of the effluent solution of pyrocatechol gasification decreases from 2% to less than 0.1 % and the methane yield increases with reaction time (Figure 4). No tar or coke are formed and the effluent is colourless and odourless clear aqueous solution. 

Three sets of experiments have been conducted. The first set is examining the influence of methane/oxygen ratios on the performance of the catalyst the second set is studying the effect of temperature on the synthesis gas formation and the third set is investigating the influence of residence time on synthesis gas selectivity and yield. The experimental data are shown in tables 1 and 2. Selectivity, yield and conversion are defined according to the following ... 

Figure 6.25. Micro structure characteristics of CVD pyrocarbon [47] (a) influence of precursor partial pressure and temperature and (b) influence of residence time and temperature...

Moreover, the study of the influence of residence time showed that methylethylamine was the primary product of the reaction, whereas dimethylethylamine (methylation of EMA) was a secondary compound. The other products, issued from condensation and methylation reactions, were DMEA ((C2H5)2NCH3), DEFA (H-CO-N(C2H5)2), tea ((C2H5)3N) Moreover, we observed the formation of monomethylamine MMA (CH3NH2), dimethylamine DMA ((CH3)2NH) and trimethylamine TMA ((CH3)3N).. The overall reaction scheme of the transformation of MEA is ... 

Time-dependent effects influence of residence time in the viscometer for thixotropic and rheopectic fluids. 

Research on cadmium pollution has received increasing international attention inasmuch as cadmium is toxic and can cause severe human health problems such as kidney disorder and itai-itai disease (Webb, 1979 Alloways, 1995). The influence of residence time and organic acids on Cd desorption from pure goethite has been studied (Glover et al., 2002). However, pure iron oxides rarefy... 

Figuie 4. Influence of Residence Time on NO Reduction in Urea-Based SNCR Process. 

The influence of residence time on TOC removal in a PMR utilizing MR (Adapted from Chin et al., 2007b.)... 

The influence of residence time distribution (RTD) on performance, selectivity and yield is the same in microreactors as in conventional reactors. Therefore, the eflfects are well understood. Nonetheless, the demonstration of this at the microscale has hardly been reported so far. However, some experimental techniques have been developed to measure RTDs in microchannel flows which allow comparison between different types of flows or flows run at different parameters so that at least optimal flow conditions with regard to RTD can be found. 

Figure 6.6.3 Influence of residence time in the crack furnace on the yield of ethene for a typical naphtha cracker (here cracker 2 at BASF, Ludwigshafen). Adapted from HaertI etal., (1996).

Figure 6.7.4 Influence of residence time and temperature on the conversion of atmospheric and vacuum residue (calculated with the reaction rate constants as given in Figure 6.7.3).

Figure 6.7.4 shows the influence of residence time on conversion at different temperatures. For a residence time in the coke drum of 3 h both residues are almost completely cracked, if we use an average drum temperature of 450 °C. For preheating in the furnace with a maximum temperature at the outlet of the coil of about 500 °C, a 3 min residence time (at this temperature) would lead to a conversion of vacuum and atmospheric residue of 75% and 15%, respectively. Thus, we have to inspect the actual case of the non-isothermal heating process in the furnace in more detail. 

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