Oil bitumen is solid and semi-solid, which is produced directly through the distillation of crude oil and the process of blowing air. This type of heavy residue is formed by the distillation of crude oil, and the amount of bitumen in crude oil varies from zero to half. Bitumen refineries must choose their crude oil with a certain sensitivity because it has a great impact on the quality produced. Distillation is an important process in the crude oil process.
In the first stage, the crude oil is heated in the distillation tower to a temperature between 650 and 800 degrees Fahrenheit and then transferred to the separation column. In this case, the light cuts remain at the top solution of the tower and its residue, which is bitumen-shaped and is referred to as atmospheric residue is at bottom of tower. Due to the fact that many crude oils contain high boiling point cuts, not all of them can be used in atmospheric distillation.
A secondary separation tower that operates in vacuum conditions is used to separate these cuts and provide the appropriate quality. The residue from this process is called direct extraction, which has little effect on the properties of it in the production of asphalt using vacuum distillation other than permeability. Other factors affecting the quality include the source of the crude oil used.
Although the bitumen obtained in the vacuum tower can be used, but in most cases, it does not have the appropriate and practical properties and corrections should be made on it and the most important of which are blowing air as follows:
This type was first discovered in 1890 by the reaction of hot bitumen with oxygen, and a lot of research is been done on the process and design of the devices required in the reaction. In the aeration process, is exposed to air. And due to the contact of air, it hardens and its thermal sensitivity decreases.
The amount of improvement in this process has a great impact on the type of feed, temperature, viscosity, time, aeration ratio and type of equipment. The use of this type has many applications in asphalt and road construction and insulation, asphalt bricks and many other applications. Aeration in this way includes de hydrogenation, polymerization and oxidation, in which some oils are converted to resin and some resins are converted to asphaltene.
This process results in the formation of a gel-like colloidal structure that is one of the technical indicators of blown bitumen. In this process, the amount of combined oxygen is only 5 to 25 percent and remains bonded in the bitumen, and the rest is released as water vapor and other gases. The amount of oxygen in the product increases with increasing aromatic content of the feed, increasing aeration and decreasing the temperature of the process.
This type has a lower degree of penetration and a higher soft spot than the original pure bitumen obtained from the distillation of crude oil, and its thermal sensitivity has also been reduced. Due to the fact that this process is hot, it is very important to control the temperature and adjust the amount of feed. This process is performed continuously and discontinuously as follows:
In this process, the initial feed is filled to the desired level in the tower after the initial heating, and aeration begins when the temperature reaches a temperature between 190 and 240 degrees Celsius. Due to the fact that this process is thermal, the temperature resulting from the reaction causes the temperature to reach 240 to 260 degrees Celsius, which is maintained in this range.
After sampling, the operation is stopped at different time intervals until the desired specifications are obtained. Depending on different technical specifications, this operation can vary between 3 to 24 hours. The bitumen aeration tower has a height of 12 meters and a diameter of 3.65 meters and the air is injected from the bottom of the tower through the distribution pipes.
The reaction variables cause the production of bitumen with different technical characteristics. Additional vapors released from the top of the tower include decomposed oil, air, light water vapor particles, and other gases and light hydrocarbons. One of the obvious points of production in this method is the ability to produce a product with different technical specifications.
The start of the continuous process is the same as discontinuous, and when the technical specifications reach the desired level, the finished product is taken out through the height controller and the feed is entered separately with flow control. In this process, temperature control is performed using methods such as initial feed heating in the furnace, heat exchanger or cooling using water injection.
The effective blowing temperature in this method is 260 °C and this method will be more useful if the goal is to produce the product with specific technical specifications and in bulk. Currently, in Iran, two types of 60/70 and 85/100 are produced by direct and semi-blown methods. Bitumen has different physical properties and is generally classified into the following four main types: