Trickle flow hydrocracking

Table IV. Effect of Bed Dilution with Fine Particles on Residence Time Distribution of Oil in a Bench-scale Reactor under Conditions of Trickle-flow Hydrocracking...

The HPC is a mild trickle flow hydrocracking process using a Shell proprietary catalyst and operating at typically 30-50 bar total pressure and at a temperature of about 300-350°C. The plant lay-out is very similar to that of a conventional gas oil hydrotreater. The HPC stage performs actually four functions ... 

Table IV presents some data on liquid residence time distributions measured under conditions of hydrocracking in trickle flow. It can be seen that bed dilution with fine inert particles results in a considerable improvement in the plug-flow character of the reactor, which supports the idea that the dispersion is largely determined by the packing of fine particles. Since in the range of Re numbers of interest the Bodenstein number is approximately a constant (see Figure 4), the Peclet numbers for beds of equal length should be inversely proportional to the particle diameter. Dilution of the 1.5 mm particles with 0.2 mm particles should raise Pe by a factor of about 7, which is approximately in line with the data in Table IV.

Trickle-bed reactors usually consist of a fixed bed of catalyst particles, contacted by a gas liquid two-phase flow, with co-current downflow as the most common mode of operation. Such reactors are particularly important in the petroleum industry, where they are used primarily for hydrocracking, hydrodesulfurization, and hydrodenitrogenation other commercial applications are found in the petrochemical industry, involving mainly hydrogenation and oxidation of organic compounds. Two important quantities used to characterize a trickle-bed reactor are... 

The trickle-bed reactor can be operated as a partially or completely vapor-phase reactor. It minimizes the energy costs associated with reactant vaporization. Mixed flow conditions at the catalyst surface exist in hydrocracking reactions, hydrogenation of crotonaldehyde and isomerization of cyclopropane. When the temperature rise in a trickle-bed reactor is significant (e.g., hydrodesulfurization and hydrocracking reactions), it can be conveniently controlled by the addition... 

A hydrocracker is a three-phase operation. The gas phase supplies hydrogen, the liquid phase supplies the heavy hydrocarbons, and the catalyst is the solid phase. This unit can be operated as a trickle bed reactor, with gas and liquid phases fed in at the top. Products, removed from the bottom, are in both the gas and the liquid phases. The key steps and analysis are similar to the packed bed reactor above. Pressure drop and holdup can be determined from the Ergun equation and gas and liquid phase Reynolds numbers. Relationships for transitions to pulsating and other flows can also be developed. ... 

The name trickle-bed reactor is usually applied in reference to a fixed bed in which a liquid phase and a gas phase flow concurrently throughout a bed of catalyst. By far the most important application, and hence much of the work, on these reactors has been in the hydrotreating of heavy feedstocks in the petroleum industry (hydrocracking, hydrodesulfurization, hydrodenitrogenation). However, this seems a very versatile processing method, and has not been exploited nearly to its potential in other areas such as waste water treatment—at least as the scientific literature would indicate. 

Trickle bed reactors have grown rapidly in importance in recent years because of their application in hydrodesulfurization of naphtha, kerosene, gasoil, and heavier petroleum fractions hydrocracking of heavy gasoil and atmospheric residues hydrotreating of lube oils and hydrogenation processes. In trickle bed operation the flow rates are much lower than those in absorbers. To avoid too low effectiveness factors in the reaction, the catalyst size is much smaller than that of the packing used in absorbers, which also means that the overall void fraction is much smaller. 

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