Visbreaker process

The visbreaking process thermally cracks atmospheric or vacuum residues. Conversion is limited by specifications for marine or Industrial fuel-oil stability and by the formation of coke deposits in equipment such as heaters and exchangers. 

Table 10.11 provides some general performance data on a visbreaking process applied on a typical VR. 

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. 

HSC [High-conversion Soaker Cracking] A visbreaking process, developed and offered by Toyo Engineering Corporation, Japan. Demonstrated from 1988 to 1989 in the Schwedt... 

MHDV [Mobil Hydrogen Donor Visbreaking] A modified visbreaking process in which a hydrogen donor stream from the oil refinery is added to the heavy hydrocarbon stream before thermal cracking. Developed by Mobil Corporation... 

TERVAHL A visbreaking process, developed by the Institut Frangais du Petrole for ASVAHL and commercialized in a joint venture between Societe Nationale Elf Aquitane, Institut Frangais du Petrole, and Total Oil Company. One plant was operating in France in 1988. See also HYVAHL. 

TERVAHL A visbreaking process, developed by ASVAHL. One plant was operating in France in 1988. See also HYVAHL. 

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. 

Important variables in the visbreaking process include temperature, pressure, and residence time. Any one variable can be changed (within predetermined... 

The visbreaking process is used primarily a means of reducing the viscosity of heavy feedstocks by controlled thermal decomposition insofar as the hot products are quenched before complete conversion can occur (Speight,... 

In contrast to the visbreaking process, in which the general principle is the production of products for use as fuel oil, hydroprocessing is used to produce a slate of products for use as liquid fuels. 

Hydrogen sulfide (H2S) and mercaptans (R-SH) may be produced during thermal processes such as the visbreaking process and can occur in... 

This situation can be clearly seen when observing the time evolution of the tube metal temperature of the pyrolysis coils there is a fast initial increase and then a reduced asymptotic slope. Note that although the initial slope is initially related to the catalytic rate, it is also due to the relatively low thermal conductivity of the initial fibrous material as a result of the large void fraction. The thickness of this layer is in the order of 20-40 pm. The evolution of the fluid temperature over time either at the TLE outlet or in visbreaking processes and in delayed coking furnaces shows a very similar behaviour. 

As previously discussed, fouling is an important aspect in the visbreaking process too. The adiabatic reactor volume of the soaker allows the run length of... 

Visbreaking processes (degraded asphaltenes are smaller in size, more aromatic and less soluble in maltene than original asphaltene. This leads to coke formation). 

The blown bitumens do not exhibit peaks in the evaporation range when the system pressure is inereased to 10 bar, except for the dispersion medium of the bitumens 85/40 and 85/25, which demonstrate only an evaporation loss. The Arrhenius coefficients of the blown bitumen showed greater differences than those of the distillation bitumens. In the plot of half life time, versus the inverse Kelvin temperature, the distillation bitumens and their colloid components follow almost parallel lines, whereas the graphs for the blown bitumens and their colloid components diverge. The plot of versus 1 000/T shows the residence time required to achieve a conversion of fifty percent, at a preset reaction temperature, or which temperature is required to achieve a preset conversion at a preset residence time. This information is valuable in thermal processing, for example in selection of the crack severity of the visbreaking process. 

In crude oil refining, the visbreaker process, the delayed coking process (see Chapter 13.1.2) and thermal cracking are used in the middle-temperature range to convert heavy petroleum residues into lighter gasoline fractions and middle distillates. The aromaticity of the fractions recovered, however, is relatively low. 

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). 

Since its introduction in 1939, visbreaking process has been extensively used for upgrading refinery residues (atmospheric or vacuum residues) and other heavy streams to produce gas, naphtha, distillates, and visbroken residue. The term visbreaking comes from the words viscosity and breaking. ... 

Visbreaking is a thermal process (non-catalytic) that reduces the viscosity of the residual oil. The mild cracking conditions used in visbreaking favor a high yield of naphtha with less gas and coke production. Visbreaking process achieves about 30% of residue conversion to lighter products. Low residence times are required to avoid coke formation. 

The main limitation of visbreaking process is that the products can be unstable due to the presence of unsaturated compounds, e.g., olefins and diolefins in the naphtha, which undergo secondary reactions to form gum and nonvolatile tar. 

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