Feedstock
A petroleum refining study starts with describing its feedstock, the crude oil and the range of products that are produced by the various processes. Crude oil comes from different parts of the world and has different physical and chemical characteristics. On the other hand, the products that are produced have to meet market requirements and as such, should comply with certain specifications.
Figure 1 shows the ratio of C/H in some of chemical compounds:
Crude oil is a non-uniform material. The composition depends on its location. The composition of crude oil, on an elemental basis, falls within certain ranges regardless of its origin.
Table 1 shows that carbon and hydrogen contents vary within narrow ranges. For this reason, crude oil is not classified on the basis of carbon content. Despite their low concentrations, impurities such as:
- Sulphur
- Nitrogen
- Oxygen
- Metals
The above item are undesirable because they cause concerns in the processability of crude feedstock and because they affect the quality of the produced products.
Elemental composition of crude oils
Products
Figure 2 shows typical refinery products with their carbon atom contents and boiling ranges. There are specifications for over 2000 individual refinery products. Intermediate feed stocks can be routed to various units to produce different blend products depending on market demand.
Fig 2 The typical refinery products with their carbon atom contents and boiling ranges
Liquefied Petroleum Gas (LPG)
Liquified petroleum gas is a group of hydrocarbon-based gases derived from crude oil refining or natural gas fractionation. They include ethane, ethylene, propane, propylene, normal butane, butylene, isobutane and isobutylene.
Gasoline
Gasoline is classified by octane ratings (conventional, oxygenated and reformulated) into three grades:
- Regular
- Midgrade
- Premium
Kerosene
Kerosene is a light petroleum distillate that is used in space heaters, cook stoves and water heaters and which is suitable for use as a light source.
Jet Fuel
This category comprises both gasoline and kerosene and meets specifications for use in aviation turbine power units.
Diesel Fuel
The quality of diesel fuels can be expressed as cetane number or cetane index. The cetane number (CN) is expressed in terms of the volume percent of cetane (C16H34) which has high ignition (CN = 100) in a mixture with alpha-methyl-naphthalene (C11H10) which has low ignition quality (CN = 0).
Fuel Oil
The fuel oils are mainly used in space heating and thus the market is quite high specially in cold climates.
- No. 1 fuel oil is similar to kerosene
- No. 2 fuel oil is very similar to No. 2 diesel fuel
- Heavier grades of No. 3 and 4 are also available
Residual Fuel Oil
It is mainly composed of vacuum residue. Critical specifications are viscosity and sulphur content. Low sulphur residues are in more demand in the market.
Lube Oil
Lubricants are based on the viscosity index. Paraffinic and naphthenic lubricants have a finished viscosity index of more than 75.
Asphalt
Asphalt is an important product in the construction industry and comprises upto 20% of products. It can be produced only from crude containing asphaltenic material.
Petroleum Coke
Carbon compounds formed from thermal conversion of petroleum containing resins and asphaltenes are called petroleum cokes. Fuel grade coke contains about 85% carbon and 4% hydrogen. The balance is made up of sulphur, nitrogen, oxygen, vanadium and nickel.
Storage feed and product
In most processes, there are many different types of equipment used for the storage of liquids and gases.
Importance of using the correct storage:
- Minimizing evaporation losses
- Reducing the cost of unnecessary capital investment in building additional tanks, lines, pumps, and loading or unloading facilities
- Improve safety (decrease flammability)
The following Considerations are necessary in choosing a suitable storage system:
- Type of storage unit
- Amount of storage
- Production of these units
The general types of storage units can be divided into two groups
- Low Pressure Storage
- High Pressure Storage
Low-pressure liquid storage tanks commonly contain fuels such as gasoline and diesel, but they often contain other hazardous materials such as other flammable solvents, oxidizers, corrosives, and toxic liquids. Typically working pressures on these containers range from 2.5-15 psi. The low pressure tanks are most common in refineries and the most common types of low pressure tanks are:
- Open Top Tanks
- Fixed Roof Tanks
- Floating Roof Tanks
Pressure vessels play an important role in various industries. These tanks are used as a tool to store gases, liquids and solids under pressure and are used in oil and gas, petrochemical, pharmaceutical and many other industries. In this article, we will introduce the types of pressure vessels and their applications. The most common types of high pressure tanks are
- Spherical Storage Vessels
- Cylindrical Storage Vessels
- Gas Cylinders