Oil is processed for use through a multi-stage refining process, primarily involving distillation to separate crude oil components based on their boiling points.
Here's a breakdown of the key steps involved in oil processing:
1. Distillation
This is the primary process for separating crude oil into different fractions.
- Heating: Crude oil is heated to very high temperatures (typically around 400°C or 750°F) in a furnace. This causes most of the crude oil to vaporize.
- Atmospheric Distillation Tower: The hot vapor and remaining liquid enter a distillation tower. This tower is designed with a temperature gradient, cooler at the top and hotter at the bottom.
- Separation by Boiling Point: As the vapor rises in the tower, different hydrocarbons condense at different levels, based on their boiling points. Heavier, higher-boiling-point hydrocarbons (like bitumen) condense lower in the tower, while lighter, lower-boiling-point hydrocarbons (like gasoline and butane) condense higher up.
- Collection of Fractions: Various fractions are collected at different levels of the tower. These fractions include:
- Gases (e.g., methane, ethane, propane, butane) - used for fuel and chemical feedstock.
- Naphtha - used as a feedstock for gasoline production and the petrochemical industry.
- Kerosene - used for jet fuel and lighting.
- Diesel - used for diesel engines and heating oil.
- Heavy fuel oil - used for power generation and ship fuel.
- Residue (bitumen) - used for asphalt and roofing.
2. Conversion Processes
Some fractions obtained from distillation are not directly usable or are in surplus compared to demand. Conversion processes are used to modify these fractions. Common processes include:
- Cracking: Breaks down large hydrocarbon molecules into smaller, more valuable ones (like gasoline and propylene). This can be achieved through thermal cracking (using heat) or catalytic cracking (using heat and a catalyst).
- Alkylation: Combines smaller hydrocarbon molecules into larger ones to produce high-octane gasoline components.
- Isomerization: Rearranges the structure of hydrocarbon molecules to improve their properties, such as octane number for gasoline.
3. Treatment Processes
These processes remove impurities and improve the quality of the refined products.
- Desulfurization: Removes sulfur compounds, which can cause air pollution when burned. This is typically done using a process called hydrodesulfurization (HDS).
- Hydrotreating: Uses hydrogen to remove impurities like nitrogen, oxygen, and metals, as well as to saturate olefins and aromatics.
- Sweetening: Removes mercaptans (sulfur-containing compounds) from gasoline and other products, improving their odor.
4. Blending
Different refined products are blended together to meet specific quality requirements and market demands. For example, gasoline is blended with additives to improve its octane rating and performance.
Summary
In essence, oil processing is a complex series of steps that takes crude oil and transforms it into a variety of usable products, primarily through distillation, conversion, and treatment processes. The specific processes used and the products obtained depend on the composition of the crude oil and the demands of the market.
