Visbreaker fractionator

One successful application of a silicone antifoam chemical reported was in a visbreaker fractionator. At high conversions the tower bottoms tended to carry over into the normally clear distillate product. This situation was brought under control by injecting 10 ppm of an ARCO silicone defoamer into the vapor space above the fractionator bottoms. 

Btu. For example, 1 might use 0.025 for extract from tar sands. A really nasty service. Or visbreaker fractionator bottoms. Or resid from a deep-cut vacuum tower. 

Refinery sour water originates largely from delayed coker, hydrode-sulferizer reactor effluents, and catalytic cracker and visbreaker fractionators. The main contaminants are NHj and H S. Sour water stripper bottoms are reused in two places ... 

About 5 percent of the trayed towers have old style bubble-cap trays. Dirt and coke tends to accumulate under the cap. This cannot be seen unless the cap is removed. Coke underneath the bubble will restrict the vapor flow, increase vapor AP and promote downcomer backup and flooding, it only takes a moment to unscrew a bubble-cap using a crescent wrench. The maintenance folks will usually clean the deck, but not remove the caps. Liz injured herself crawling through a manway helping me discover this problem at the Motiva Refinery visbreaker fractionator in Convent, Louisiana. This tower flooded on... 

Fractions treated by this process are light products from the primary distillation LPG to Kerosene, or light products from thermal and catalytic cracking (visbreaking, coking, FCC). 

Product separation for main fractionators is also often called black oil separation. Main fractionators are typically used for such operations as preflash separation, atmospheric crude, gas oil crude, vacuum preflash crude, vacuum crude, visbreaking, coking, and fluid catalytic cracking. In all these services the object is to recover clean, boiling range components from a black multicomponent mixture. But main fractionators are also used in hydrocracker downstream processing. This operation has a clean feed. Nevertheless, whenever you hear the term black oil, understand that what is really meant is main fractionator processing. 

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. 

Visbreaking is a mild thermal pyrolysis of heavy petroleum fractions whose object is to reduce fuel production in a refinery and to make some gasoline. 

Coking processes are different from the other thermal processes found in a rehnery insofar as the reaction times may be longer and the reactions are usually allowed to proceed to completion (in contrast to, say, visbreaking where the reactions are terminated by quenching with a gas oil fraction). The coke obtained from the coking processes is usually used as a fuel for the process although marketing for specialty uses, such as electrode manufacture, increases the value of the coke. But, because of the tendency of the process to concentrate the feedstock sulfur in the coke the coker feedstock may have to be chosen carefully to produce a coke of sufficiently low sulfur content for a specialty use. 

Gebauer et al. [38] suggest visbreaking of waste plastics with vacuum residue. This is a thermal process, applied in refineries in order to convert partially atmospheric vacuum residue and decrease viscosity and melting temperature. According to the authors, addition of 5% of waste plastics in laboratory tests does not influence noticeably the process parameters and final products properties. As in the case of LCO and VGO fractions the application of vacuum residue and mixture of waste plastics is applicable in refineries. 

Visbreaking is a thermal cracking process in which the thermal reactions are not allowed to proceed to completion. It is used for partial conversion of the higher boiling fractions, usually the residua, fisbreaking, unlike the coking processes (Table 13.3), is a relatively mild thermal cracking operation mainly used to reduce the viscosity and pour point... 

A visbreaking unit consists of a reaction furnace, followed by quenching with a recycled oil, and fractionation of the product mixture. All of the reaction in this process occurs as the oil flows through the tubes of the reaction furnace. The severity is controlled by the flow rate through the furnace and the temperature typical conditions are 475-500°C (885-930" F) at the furnace exit with a residence time of 1-3 minutes operation for 3-6 months on stream (continuous use) is possible before the furnace tubes must be... 

Straight-run fuel oil fractions from the same crude oil normally are stable and mutually compatible. However, fuel oil produced from the thermal cracking and visbreaking operations may be stable by themselves but can be unstable or incompatible if blended with straight-run fuels and vice versa. Furthermore, asphaltic deposition may result from the mixing of (distillate and residual) fuel oils of different origin and treatment, each of which... 

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. 

---