Manufacturing Process
Refinery Processes
In an oil refinery, the crude oil being processed is separated into different ‘cuts’ on the basis of their boiling range. In atmospheric distillation, which is the first stage of this continuous process, the crude oil is heated to 300°C-350°C and the more volatile components, e.g. petrol and kerosene, are distilled off. This leaves a residue called atmospheric residue, which is then further distilled under vacuum. The actual processing temperature of the residue is 350°C- 390°C, but because of the applied vacuum, the further effective distillation cut point is 500°C-560°C. This vacuum distillation process yields further volatile products known as vacuum distillates and leaves a non-volatile residue of high viscosity, which is called vacuum residue.Depending on the crude origin, the vacuum residue may be used directly as bitumen without further processing. For some crude oils though, or to meet particular specifications, additional processing may be required, such as air blowing of the residue. The air blowing process demands careful selection and control of process temperature, air rate and residence time to ensure consistent product. Sometimes bitumens are produced by blending vacuum residue with asphaltenes derived from the manufacture of lubricating oils. For example, propane-precipitated asphalt (PPA) is commonly used in the manufacture of bitumens when lubricating oils are produced at the same refinery.
The selection of crude is an important aspect of bitumen
manufacture, requiring expertise and experience to yield
a satisfactory product – not all crude can be used to make
bitumen. Few of the nearly 1500 available crude petroleum
oils are suitable for the manufacture of good quality bitumen.
Within the Australian context, a very small number of crude
oils are able to be used to manufacture bitumen compliant
with the current Australian Standard.
Cutback bitumens are produced by diluting the paving grade bitumen with a cutter or flux. Bitumen emulsions are made in a colloid mill by dispersing paving grade bitumen in water with the aid of an emulsifying agent.
For industrial bitumens, in order to produce a material that will soften at a higher temperature than paving grade bitumen of equivalent penetration, severe air blowing is required. The product is therefore also known as ‘air-blown’ or ‘oxidised’ bitumen. Typically the blower feedstock has a lower initial boiling point than for paving grade bitumens. It is this, combined with severe blowing, that gives industrial bitumens their special physical properties.
The production of high quality bitumen relies on a combination of skills, experience and modern refinery technology. These are used extensively to ensure the suitability of feedstocks and to monitor and control all stages of the process.
Cutback bitumens are produced by diluting the paving grade bitumen with a cutter or flux. Bitumen emulsions are made in a colloid mill by dispersing paving grade bitumen in water with the aid of an emulsifying agent.
For industrial bitumens, in order to produce a material that will soften at a higher temperature than paving grade bitumen of equivalent penetration, severe air blowing is required. The product is therefore also known as ‘air-blown’ or ‘oxidised’ bitumen. Typically the blower feedstock has a lower initial boiling point than for paving grade bitumens. It is this, combined with severe blowing, that gives industrial bitumens their special physical properties.
The production of high quality bitumen relies on a combination of skills, experience and modern refinery technology. These are used extensively to ensure the suitability of feedstocks and to monitor and control all stages of the process.
Storage
Bitumen is stored at refineries and large depots in large permanent tanks made of mild-steel plate, with capacities of between 100 and 10,000 tonnes. Steam or hot oil is pumped through heating coils in the heavily insulated tanks so that the bitumen remains fluid. Smaller depots and big users store bitumen in small permanent or semi-mobile tanks of up to 60 tonnes capacity, typically heated by electricity or flame heater tubes.
Distribution
As bitumen cools, it gradually becomes unworkable. Therefore the delivery of paving grade bitumen not only calls for the supply of bitumen to be provided at the right quality and quantity at the right time, but the product must also be kept between 150°C-190°C throughout the supply chain. When it is loaded into a road tanker, the temperature can drop by about 7°C-10°C and continue to fall by a further one or two degrees per hour while in transit.Road tankers with capacities of between 10 and 40 tonnes are normally used to take most of the bitumen from the refineries. They have insulated single-compartment tanks, usually with some kind of heating such as heating tubes. To transport bitumen to intermediary depots with reheating facilities, insulated rail cars are sometimes used. Their capacity ranges from 10 tonnes to 50 tonnes and they are also fitted with electric heaters or direct oil-fired flame tube heaters. When bitumen is moved by sea, it can be shipped in a variety of vessels from 300 tonne barges to ocean-going tankers of up to 30,000 tonnes capacity. The temperature of the hot-loaded bitumen is maintained by high pressure steam or hot oil passing through coils in the bitumen tanks.
