WHAT IS BLOWN BITUMEN?
Bitumens used in a wide variety of ‘industrial’ applications including roofing, flooring, pipe-coating etc. They are produced by passing air through soft bitumen/flux mixtures under controlled temperature conditions. British Standard grades (BS 3690) are normally designated by two numbers representing the mid-points of their softening point and penetration ranges.
How to produce blown asphalt (Blown Bitumen)?
1. Bitumen heating to 265-270 °C
2. Transferring melted bitumen to blowing towers
3. Blowing air to bitumen
4. Cooling melted bitumen with water
The procedures of producing bitumen are as follows:
1.Continuous blowing procedure
2.Discontinuous blowing procedure
These two procedures are done by other two procedures named catalysis and anticatalysis .
Catalysis means adding some chemical material during the process In order to decrease blowing reaction time.
For the following reasons:
• Ease and simplicity in changing blowing condition and have production with different grades as a result.
• Ease in generating the unit.
• Ease in technology and also low expense in investment. The discontinuous producing procedure is chosen.
Technical point and operating conditions are as follows:
• The blowing should be done from the bottom of blowing tanker. The reaction between bitumen and air is calorific .If the heat produced during the mixture is high, the heat of reaction is controlled by water injection.
• Admixture of air and the volume of blowing air is two important variants in blowing process. In bitumen producing plant, bitumen 60/70 is usually got by blowing. In this case for making bitumen 90/15 or 85/25 distilled used oil or crude oil should be injected to the product according to the volume 20-25 % otherwise the fragility in bitumen lead to inferior production.
• Increasing the heating temperature, air injection amount, time and tower pressure increase the speed of production process reaction. The suitable temperature for production operation is 265-270°C which should be controlled not to be ascended since in high temperature and in 288°C intensity of reaction becomes more sever and incontrollable which lead to explosion in tower.
• The long time stay of bitumen in tower in any condition is not in favor of system and should be delivered to drum or empty tanker after being ready.
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