In this unit the you will learn how the chemical injection systems operate, how the main components of these systems function, and how the system’s operation is controlled.
CHEMICAL INJECTION SYSTEMS
Three chemical injection systems are used in the production system areas.
The chemical injection systems used are
- Demulsifier injection system.
- Scale inhibitor injection system.
- Corrosion inhibitor injection system.
Chemicals are injected into many different parts of the production process flow.
Figure 23‑1 shows three chemical injection systems in a production plant.
The chemical storage tank, the dosing pumps and the operating controls for each system are all fitted into a single unit. We call this a skid and the chemical injection equipment is said to be skid mounted.
During normal operation one or more pumps are running and the others are on standby.
Chemical Injection Systems
DEMULSIFIER INJECTION SYSTEM
Wet crude oil coming into the production plants contains different amounts of water and salts. Large droplets of water are heavy and quickly sink to the bottom of separators. However, small droplets of water mixed up with the crude oil make an emulsion. An oil film surrounds these water droplets, keeping them separate. The oil film can be removed chemically using a demulsifier.
Demulsifier is a chemical that breaks down the oil film around the water droplets in the crude. Demulsifier is injected into the production header upstream of the production separators and into the test header upstream of the test separators. After the demulsifier breaks down the oil film round the water, the water droplets join together to make bigger droplets, which sink to the bottom of the separators.
The chemical dosing rate depends on the water cut (content) and the type of demulsifier used. The dosing rate is normally decided by the production chemical engineering department.
Sometimes the normal demulsifier system is not enough. When the crude oil coming from the separators is ‘off specification’ other injection points may also be used. If this is necessary demulsifier can be injected at other places in the production plant process.
SCALE INHIBITOR INJECTION SYSTEM
Crude oil and formation water contain many impurities. Some of these are very small particles of different types of minerals. These minerals can build up inside a pipe or vessel and cause a condition known as ‘scaling’.
Scale is a name given to a coating, like a skin, which can build up inside pipes and vessels and cause them to become clogged. See Figure 23‑2.
Scale build‑up can block pipes and damage equipment.
Once scale builds up in the pipes and equipment it is very difficult to remove. Scale inhibitor is a chemical that is used to prevent this. It is injected into crude oil production headers, into wash water systems and back‑up wash water systems to prevent scale build up.
The scale inhibitor dosing rate is decided by the production chemical engineering department.
CORROSION INHIBITOR INJECTION SYSTEM
The pipes and vessels of a production plant are made of steel. These pipes and vessels can corrode when their steel walls are gradually eaten away by chemical action. The chemicals that react with the steel are oxygen (02) hydrogen sulphide (H2S) and carbon dioxide (C02) as well as the salt in the crude oil.
When steel pipes and vessels corrode, their walls become thinner and weaker. These weaker walls are unsafe and may leak or break.
Corrosion inhibitor is a chemical that prevents corrosion in steel pipes and vessels by building a protective coating on their inside surfaces.
Corrosion inhibitor is injected into the water outlets from the separators into the desalter wash water system.
The dosing rate of corrosion inhibitor is decided by the production. chemical engineering department.
Demulsifiers, scale inhibitors and corrosion inhibitors can injure you if they are allowed to touch your skin, eyes, or clothing. For this reason there are special safety rules for handling these chemicals.
When chemical storage tanks are being filled you must follow these safety rules and precautions.
- Wear chemical handling safety clothing as follows (see figure 23‑3):
- Elbow‑length rubber gloves.
- A rubber apron.
- A face shield.
- Rubber boots.
- Make sure that maintenance personnel working on chemical systems wear the same safety clothing as you do.
- Make sure that the safety shower and eyewash station near the chemical handling area is working properly.
- Clean up all chemical spills immediately.