Processes Involved in Crude Oil Refining
Have you ever wondered how crude oil is converted into end-use goods like gasoline, heating oil, cooking gas etc.? It involves a process whereby crude oil is obtained as part of upstream activities, it is refined during midstream activities and finally, it is sold as petroleum products as part of downstream activities. The refining is done in petroleum refineries (with machinery such as pressure vessels) which are large-scale industrial complexes that produce saleable petroleum products from crude oil. This blog will explore further details around the refining process and will look at the various metrics involved in this regard.
Distillation
Distillation involves the separation of materials based on differences in their volatility. This is the first and most basic step in the refining process, and is the precursor to the subsequent steps of cracking and reforming. In this process, crude oil is heated until it boils and is fed into a distillation column. As the temperature of the crude oil in the distillation column rises, the crude oil separates itself into different components, called “fractions.” which are then captured separately. Each fraction corresponds to a different type of petroleum product (e.g., petrol, paraffin, diesel fuel etc.), depending on the temperature at which that fraction boils off the crude oil mixture.
Cracking and Reforming
The heaviest fractions obtained as part of distillation, including the gas oils and residual oils, are lower in value than some of the lighter fractions, so refiners go through a process called “cracking” to break apart the molecules in these fractions. This process can produce some higher-value products from heavier fractions. Cracking is most often utilized to produce gasoline and jet fuel from heavy gas oils. Reforming is typically utilized on lower-value light fractions, again to produce more gasoline. The reforming process involves inducing chemical reactions under pressure to change the composition of the hydrocarbon chain.
Chemical Processes
Apart from the above-mentioned processes, some of the major chemical processes involved in the oil refining process are stated as follows: –
- Desalter unit – This washes out salt from the crude oil before it enters the atmospheric distillation unit.
- Distillate hydrotreater – This desulfurizes distillates (such as diesel) after atmospheric distillation. Uses hydrogen to desulfurize the naphtha fraction from the crude oil distillation or other units within the refinery.
- Coking units – These process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product.
- Isomerization – This converts linear molecules such as normal pentane to higher-octane branched molecules for blending into gasoline or feed to pipe fabrication. It is also used to convert linear normal butane into isobutane for use in the alkylation unit.
- Cooling Towers – These circulate cooling water, boiler plants generate steam for steam generators, and instrument air systems include pneumatically operated control valves and an electrical substation.
Since modern petroleum refineries are highly automated and technically advanced, nearly all processes are contained within engineering controls and represent a decreased risk of exposure compared to earlier times. However, certain situations or work tasks may subvert these safety mechanisms, and expose workers to a number of chemical (see table above) or physical (described below) hazards. Examples of these scenarios include: System failures (leaks, explosions, etc.), Standard inspection, product sampling, process turnaround, or equipment maintenance/cleaning activities.
Closing Thoughts
The complexity of oil refinery processes corresponds to the staggering array of petroleum products in demand throughout the world. Refining is a very precise set of steps and, if not done correctly, will lead to the end products being compromised with regard to functionality and quality. It also requires significant investment in fixed assets and manpower; thus, a lot of effort is required to ensure that the refining is successful. Hence, the process from “crude” to “refined” is a long one and is very relevant considering the oil demands in the current VUCA world!