Reactors petroleum refining

Fig. 2 Petroleum refining reactors. (View this art in color at www.dekker.com.)...

The terms space time and space velocity are antiques of petroleum refining, but have some utility in this example. The space time is defined as F/2, , which is what t would be if the fluid remained at its inlet density. The space time in a tubular reactor with constant cross section is [L/m, ]. The space velocity is the inverse of the space time. The mean residence time, F, is VpjiQp) where p is the average density and pQ is a constant (because the mass flow is constant) that can be evaluated at any point in the reactor. The mean residence time ranges from the space time to two-thirds the space time in a gas-phase tubular reactor when the gas obeys the ideal gas law. 

Gas-phase process, of ethylene-propylene polymer manufacture, 10 711 Gas-phase reactions flow mixing for, 14 613 pressure and, 14 623 Gas-phase reactor (GPR), 20 533 Gas-phase sedimentation, 18 142 Gas-phase synthesis, in silicon carbide manufacture and processing, 22 533 Gas pipeline systems, 12 366 Gas pretreatment, 13 841 Gas processing, in petroleum refining, 18 663... 

In parallel with an analytical and mathematical description of chemical reactors, we will attempt to survey the petroleum and chemical industries and related industries in which chemical processing is important. We can divide the major processes into petroleum refining, commodity chemicals, fine chemicals, food processing, materials, and pharmaceuticals. Their plant capacities and retail prices are summarized in Table 1-1. 

Figure 2-12 Qualitative flow sheet of reactants, reactors, and products in petroleum refining.

Recall that the petroleum refining industry involves multiple reactions because crude oil contains an almost infinite number of molecules, and almost the same number of product molecules is produced by each of the reactors we described in Chapter 2. However, in a sense the petroleum refining industry is simply a sophisticated cooking of large molecules to crack them down to smaller molecules. 

Endothermic reactions can also be run with interstage heating. An example we have considered previously is the catalytic reforming of naphtha in petroleum refining, which is strongly endothermic. These reactors are adiabatic packed beds or moving beds (more on these in the next chapter) in which the reactant is preheated before each reactor stage. 

Finally, we return to the four major reactors in petroleum refining, which we introduced in Chapter 2. All of these reactors are sketched in Figure 12-23. 

Figure 12-23 Sketches of the four major chemical reactors in petroleum refining. These were considered first in Ch ter 2, but now they are seen to be multiphase catalytic reactors using catalysts and requiring careful design for heat transfer and mass transfer.

The evolution of chemical engineering from petroleum refining, through petrochemicals and polymers, to new applications is de.scribed so that students can see the relationships between past, present, and future technologies. Applications such as catalytic processes, environmental modeling, biological reactions, reactions involving solids, oxidation, combustion, safety, polymerization, and multiphase reactors are also described. 

Fixed- or packed-bed reactors refer to two-phase systems in which the reacting fluid flows through a tube filled with stationary catalyst particles or pellets (Smith, 1981). As in the case of ion-exchange and adsorption processes, fixed bed is the most frequently used operation for catalysis (Froment and Bischoff, 1990 Schmidt, 2005). Some examples in the chemical industry are steam reforming, the synthesis of sulfuric acid, ammonia, and methanol, and petroleum refining processes such as catalytic reforming, isomerization, and hydrocracking (Froment and Bischoff, 1990). 

Possibly the chemical industry does not have as much need for mathematical models in process simulation as does the petroleum refining industry. The operating conditions for most chemical plants do not seem subject to as broad a choice, nor do they seem to require frequent reappraisals. However, this is a matter which must be settled on the basis of individual circumstances. Sometimes the initial selection of operating conditions for a new plant is sufficiently complex to justify development of a mathematical model. Gee, Linton, Maire, and Raines describe a situation of this sort in which a mathematical model was developed for an industrial reactor (Gl). Beutler describes the subsequent programming of this model on the large-scale MIT Whirlwind computer (B6). These two papers seem to be the most complete technical account of model development available. However, the model should not necessarily be thought typical since it relies more on theory, and less on empiricisms, than do many other process models. 

The previous notes give our readers the minimal information that is necessary to appreciate the possibly very complex bifurcation, instability and chaos behavior of chemical and biological engineering systems. While the current industrial practice in petrochemical petroleum refining and in biological systems does not heed the importance of these phenomena and their implications on the design, optimization and control of catalytic and biocatalytic reactors, it is more than obvious that these phenomena are extremely important. Bifurcation, instability and chaos in these systems are generally due to nonlinearity... 

Well over 50 large-scale EO model-based RTO applications have been deployed for petroleum refining processes. These model applications have been deployed in petroleum refineries Liporace et al., 2009 Camolesi et al., 2008 Mudt et al., 1995, both on separation units (crude atmospheric and vacuum distillation units) and on reactor units (including fluidized catalytic crackers (FCC), gasoline reformers, and hydrocrackers). 

Evaluation techniques and equipment are as varied as the individual catalytic processes themselves. The long term goal of catalyst evaluation is to reduce the size of the testing equipment consistent with reliable and accurate data as it relates to the commercial process. Invariably, the farther removed in physical size the process simulation attains, the more likely that errors will be introduced which can affect data accuracy, accuracy being defined as commercial observations. In addition, smaller equipment size also places less demand on the physical integrity of a catalyst particle therefore, additional test methods have been developed to simulate these performance characteristics. Despite these very important limitations, laboratory reactors fully eight orders of magnitude (100 million times) smaller are routinely used in research laboratories by both catalyst manufacturers and petroleum refiners. 

Dualforming A process that enables a petroleum refiner to improve the catalytic reforming step at minimal capital cost. A new reactor with continuous catalyst recirculation is integrated into the existing reactor train. Developed and offered by Axens. 

What are typical operating conditions (temperature, pressure) of a catalytic cracking reactor used in petroleum refining ... 

In a trickle bed reactor the gas and liquid flow (trickle) concurrently downward over a packed bed of catalyst particles. Industrial trickle beds are typically 3 to 6 m deep and up to 3 m in diameter and are filled with catalyst particles ranging irom to in. in diameter. The pores of the catalyst are filled with liquid. In petroleum refining, pressures of 34 to 100 atm and temperatures of 350 to 425°C are not uncommon. A pilot-plant trickle bed reactor might be about 1 m deep and 4 cm in diameter. Trickle beds are used in such processes as the hydrodesulfurization of heavy oil stocks, the hydrotreating of lubricating oils, and reactions such as the production of butynediol from acetylene and aqueous formaldehyde over a copper acetylide catalyst. It is on this latter type of reaction,... 

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