Visbreaking is a thermal cracking process that reduces the viscosity of a liquid by breaking its molecular bonds. It can be induced through coil or soaker methods, or a combination of both. The process aims to increase the amount of middle distillate, which is more valuable than other by-products. Residues from the process include tar and coke, which have industrial uses.
Visbreaking refers to the process of reducing the viscosity of a liquid through high temperatures. This is a type of thermal cracking that works by breaking the molecular bonds of the liquid. The large molecules that made up the liquid are “broken” into smaller molecules. This allows the molecules to flow more easily, reducing the viscosity of the liquid. There are two general technologies used to induce visbreaks: coil and soaker.
The term visbreaking comes from the words “viscosity” and “breakage”. It is a non-catalytic process, which means that a catalyst is not used to lower the temperature at which cracking occurs. Instead, preheated air is injected into the oven to rapidly raise the temperature.
A coil visbreaker uses a furnace tube called a coil to heat the feed stream. In the oil industry, feed or feed stream refers to crude oil. The kiln temperature and speed are mostly controlled through the feed flow and the airflow in the kiln.
In soaker visbreaking, the feed needs relatively low temperature but long processing time for cracking. The heated feed is absorbed by the visbreaking unit, called the drum. Then it moves to a fractionator, which separates the feed into different by-products. The lower temperature uses less energy and reduces the amount of residue in the process.
Some visbreaking units use the properties of both processes by combining them. The initial cracking occurs in the kiln tube where much of the feed is heated. The feed then passes through a quencher to reduce its temperature. After the feed has been quenched, it is immersed in a drum for further cracking.
Feed extinction slows down the production of coke, a low-value product. Slow coke production leads to less decoking, which usually saves time and costs. Coke that builds up in the drum is often recycled back into the feed.
The petroleum industry has developed visbreaking to produce petroleum products. When oils are first extracted, they are in an unrefined state. This is where the term “crude” came from. Oil refineries use the visbreaking process to convert this crude oil into different end products.
Crude oil products are commonly divided into three categories: gaseous distillates, middle distillates, and residuals. Middle distillates are more valuable than other by-products. Gas distillates and residues, while not as valuable, still have industrial uses.
A visbreaker unit typically aims to increase the amount of middle distillate. Gasoline and petroleum are two of the most valuable middle distillate byproducts obtained from crude oil. By increasing the amount of middle distillates in the feed stream, the oil refinery increases its profits.
Residues from the visbreaking process include tar and coke. They are used for different purposes like roofing and dry cell manufacturing. Gas distillates such as LPG are commonly sold as household fuel.
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