The reactor is a vessel in which the cracked product vapors are: (a) separated from the spent catalyst by flowing through a set of two-stage cyclones within the reactor and (b) the spent catalyst flows downward through a steam stripping section to remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator. The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst line.
The reaction product vapors (at 535 C and a pressure of 1.72 bar) flow from the top of the reactor to the bottom section of the main column (commonly referred to as the main fractionator where feed splitting takes place) where they are distilled into the FCC end products of cracked petroleum naphtha, fuel oil, and offgas. After further processing for removal of sulfur compounds, the cracked naphtha becomes a high-octane component of the refinery's blended gasolines.
Although the schematic flow diagram above depicts the main fractionator as having only one sidecut stripper and one fuel oil product, many FCC main fractionators have two sidecut strippers and produce a light fuel oil and a heavy fuel oil. Likewise, many FCC main fractionators produce a light cracked naphtha and a heavy cracked naphtha. The terminology light and heavy in this context refers to the product boiling ranges, with light products having a lower boiling range than heavy products.
Chemical engineering professors Warren K. Lewis and Edwin R. Gilliland of the Massachusetts Institute of Technology (MIT) suggested to the CRA researchers that a low velocity gas flow through a powder might \"lift\" it enough to cause it to flow in a manner similar to a liquid. Focused on that idea of a fluidized catalyst, researchers Donald Campbell, Homer Martin, Eger Murphree and Charles Tyson of the Standard Oil of New Jersey (now Exxon-Mobil Company) developed the first fluidized catalytic cracking unit. Their U.S. Patent No. 2,451,804, A Method of and Apparatus for Contacting Solids and Gases, describes their milestone invention. Based on their work, M. W. Kellogg Company constructed a large pilot plant in the Baton Rouge, Louisiana refinery of the Standard Oil of New Jersey. The pilot plant began operation in May 1940.
Fluid catalytic cracking, or FCC, is the last step in the evolution of cat cracking processes-- also introduced in 1942, just like TCC or Thermafor Cat Cracking, during the Second World War in an effort to make high-octane number gasoline. Remember that high-octane number relates to high power as you can have higher compression ratios in the combustion engines.FCC really shows an excellent integration of the cracking reactor, an endothermic reactor, with the catalyst regenerator and exothermic reactor for very high thermal efficiency. FCC is now used universally in oil refineries throughout the world-- has replaced all the previous cat cracking processes.Now, in FCC, in the feed, that is gas oil preheated to about 300 degrees Fahrenheit-- is introduced into the reactor with steam. The riser part of the reactor where the hot catalyst particles-- as you see, the green line coming from the catalyst regenerator-- are full of dyes. The particles are full of dyes because they're smaller particles. They are full of dyes and flowing gases and vapors. So they have a huge surface area to meet the incoming feed at temperatures that are close to 1,000 degrees Fahrenheit.So cracking reactions on these very fine particles that are full of dyes and flowing with the reactants takes place in a very short space of time, something that could be measured with seconds. And the products are sent to a fractionator after going through a series of cyclones, obviously, to separate the small fluid dyes, the particles of the catalyst.In the fractionators, the products, as usual, are separated into gas, gasoline, light cycle oil, heavy cycle oil, and, finally, the heaviest fractions, decant oil.Remember that LCO is used in the US for making diesel fuel through hydrocracking and hydrogenation. And decant oil could be used as fuel oil or as feedstock for making carbon black or white coking to make needle coke for graphites, electrodes.Coming back to the reactors, the cat cracking reactor, the coked catalyst now, the end of the riser where this cracking reaction takes place, are sent through the regenerator. It's not fully coked on the surface, lost its activity. Through the red line, it's sent to the regenerator where air is introduced to burn off the coke.The temperatures in the regenerator could reach to 1,300 to 1,400 degrees Fahrenheit. You should remember that the catalysts now are much improved, as well. It may include zeolites that would take high temperatures and very controlled reactivities through pore size distribution and so forth.So the combustion products or flue gases from this catalyst regenerator could be sent to a CO boiler because the gas may contain significant amount of carbon monoxide, which could be burned to CO2 to provide additional heat or to generate additional heat.So the catalysts that are now regenerated are sent to the reactor to close the catalyst cycle through that green line, as you see, to meet the incoming feed. So our catalyst cycle is pretty much complete at this point.But note this excellent integration, thermal integration, of the catalyst regeneration, the exothermic process, with the cracking reactions where the catalysts that are heated in the regenerator are sent in a very effective manner to the reactor without much heat loss. So that is the ultimate, if you will, thermal efficiency of a process. And that's why FCC is now the universally accepted catalytic cracking process.
Short design cycles for integrated circuits and packages drive the need for efficient problem solving and rapid results. Improved mechanical modeling software and increased computing power have taken these computation-heavy tools and made them versatile enough to support main-stream, real-time production needs. The utility of these tools has been significantly improved by simplified work flows to create detailed geometries and complex assemblies, improved mesh generation algorithms, and solve time reduction. Mechanical modeling software has a wide range of application which traditionally has been focused on design of large structures. Despite their general applicability, these tools have not been optimized for microelectronics in terms of absolute dimensions, fine structure count, and range of scale from the smallest to the largest component. Finding solutions to these problems pays off in fewer design cycles and significant process yield improvements. This paper will show multiple examples of process-induced stress, driven by material properties and manufacturing. They have been created using a variety of FEM tools, including ANSYS and Abaqus.
Microelectronics and semiconductor design cycles are increasingly under pressure to improve time to market. Eliminating costly redesigns is a high priority. Toward that end, simulation and modeling are extremely useful in predicting performance and potential failure modes. And while electrical simulation has become nearly ubiquitous, mechanical stress simulation of integrated circuits has not always been required during product development. Slow adoption of mechanical modeling stems in part from the fact that the tools have their broadest application to much larger products. Consequently, mechanical modelers for integrated circuits face challenges unique to their applications. Most mainstream mechanical modeling tools have not been optimized for microelectronics in terms of absolute dimensions, fine structure count, and range of scale from the smallest to the largest component. Given these limitations, modeling engineers have found ways to work around these problems.
Fortunately, mechanical modeling tools are improving all the time. Some analysis techniques which were formerly too computationally intensive have been enabled by software and simulation hardware improvement. This paper highlights two such cases: rough surface modeling and crack prediction.
When dealing with small geometries or coarse manufacturing processes, one may encounter rough surfaces whose surface height variation is on the same order as the layer thicknesses (Figure 1). When these layers are subject to forces that may cause them to fail, mechanical stress simulation would be indicated. However, modeling the layer in question as ideally smooth may miss significant failure modes and geometry scaling relations, and stretch the credibility of the modeler. While there have been many examples of rough surface simulation using advanced techniques    , advances in simulation software and hardware now make this capability more accessible to the average working engineer. In particular, due to the increasing popularity of 3-D printing, many software tools have added the capability for working with stereolithography files (.STL) in which solids are described by their faceted bounding surfaces. Popular commercial modeling tools such as ANSYS can read and build geometries based on .STL files. Moreover, both commercial and many open source software tools can create, manipulate, and export .STL files. We examine one such application.
In a certain manufacturing process, a thin brittle layer is deposited over a relatively coarse ductile material. Due to differing coefficients of thermal expansion (CTE) between the two materials, large mechanical stresses in the brittle top layer may cause it to crack. We wished to discover potential failure modes and optimize the process and geometries to minimize the probability of failure over the product lifetime. We were not convinced that simulation of an idealized geometry would be sufficiently predictive.
Modeling stationary cracks with the conventional finite element method (FEM) involves having an initial discontinuity and considerable mesh refinement. The complexity increases for crack propagation simulation, making it more challenging and time consuming. Specifically, the mesh needs to be updated to match the geometry as the crack progresses. The extended finite element method (XFEM) makes modeling of cracks easier and accurate by allowing mesh independent crack initiation and propagation. 153554b96e