Types of Visbreaking

There are two types of visbreaking technology that are commercially available  

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The two types of visbreaking are similar and only differ in their temperatures and residence times. Product quality and yields from the coil and soaker visbreaking processes are essentially the same at a specifled severity. 

The number, length, and diameter of furnace tubes as well as diameter and height of the soaker reactor vary, of course, depending on the design and type of visbreaking unit. For instance, Reza et al. (2011) reported the simulation of a commercial visbreaker unit with the following characteristics of coil and soaker reactors ... 

A combination unit is a special type of unit that was developed to reduce the investment for a small refinery. In effect, one main distillation unit serves as a crude fi-actionator as well as the cat unit primary fractionator. This same tower also serves the naphtha reformer and visbreaker. A schematic diagram of a combination unit is shown in Figure 2. Crude oil is topped (material boiling below 650°F is removed) in the atmospheric tower, and the topped crude is sent to the combination tower along with cat products and naphtha reformer products. These latter streams provide heat to distill the topped crude and also, being more volatile than topped crude, provide a lifting effect which assists in vaporizing more of the crude. 

The fuel vacuum pipe still is also used to recover cracked gas oil from the tar formed in residuum cracking (visbreaking) processes. In this service, it it frequently referred to as a vacuum, flash unit. Pipe stills designed for the production of asphalt are usually the fuel type of unit. 

While it is often reported that, generally, polypropylene produced with any industrial process presents broad MWD (Q = 8-12) with any type of catalytic system, and that in order to obtain a narrow MWD a polymer visbreaking process should be used, studies on the control of MWD by means of high yield catalytic systems are being more and more frequently announced. Such systems, developed by Montedison in cooperation with Mitsui Petrochemical are formed of MgCl -electron donor-TiCl and AIR3. 

Treatment for crude oil residues is intended to minimize the adverse effects of the presence of asphaltenes during thermal processing. Generally, two types of treatment possibilities are available. There are physical and chemical treatments. The physical treatment essentially involves deasphalting whereas the chemical treatment includes thermal processes such as visbreaking and coking. 

The values of kinetic parameters (reaction rate coefficients, activation energies, pre-exponential factors) reported by the authors were obtained from experiments at different temperature, pressure, residence time, type of operation (continuous or batch reactor, coil or soaker visbreaking), and type of feed (atmospheric residue, vacuum residue, asphaltenes separated from crude oils from different sources). 

Asphaltene-type deposition may, however, result from the mixing of fuels of different origin and treatment, each of which may be perfectly satisfactory when used alone. For example, straight-run fuel oils from the same crude oil are normally stable and mutually compatible whereas fuel oils produced from thermal cracking and visbreaking operations that may be stable can be unstable or incompatible if blended with straight-run fuels and vice versa (ASTM D-1661). 

Aqua-conversion. Catalytic process that uses catalyst-activated transfer of hydrogen from water added to the feedstock in slurry mode. The homogeneous catalyst is added in the presence of steam, which allows the hydrogen from the water to be transferred to the heavy oil when contacted in a coil-soaker system normally used for the visbreaking process. Reactions that lead to coke formation are suppressed and there is no separation of asphaltene-type material (Houde et al., 1998). 

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