In the oil and gas industry, the process of separating water and other impurities from crude oil and natural gas is crucial for efficient and safe production. One of the most common methods used to achieve this is through the use of free water knockouts.
In this article, we will explore what free water knockouts are, how they work, and the different types and design considerations to keep in mind when implementing them.
How Free Water Knockouts Work
Free water knockouts are vessels that use gravity separation to remove water and other impurities from crude emulsions containing 30% water or more. As the mixture enters the vessel, the water and heavier impurities sink to the bottom of the vessel, while the lighter oil and gas float to the top. The separated water is then drained from the vessel through a drain valve. The key components of a free water knockout system include an inlet section, a settling section, a water outlet, an oil outlet, and a gas outlet.
The performance of a free water knockout can be affected by factors such as the flow rate, temperature, pressure, and viscosity of the mixture, as well as the size and internal design of the vessel. It is important to select the appropriate size and design of the vessel based on the requirements of the operation as well as appropriate integration with existing equipment.
Benefits Of Free Water Knockouts
By separating free water (typically any percentage higher than 30%) and other impurities from crude emulsions, FWKO’s optimize crude cleanup with less energy by allowing the firetube in a treater to heat more emulsion than water ultimately making it easier to refine and transport, but saving valuable energy in the process.
Types of Free Water Knockouts
There are several types of free water knockouts to choose from, including horizontal or vertical designs, two-phase vs three-phase designs, and skid-mounted tturn-key to field-tied units.
Horizontal FWKO’s offer a greater interface surface to assist in separation of close specific gravities between the emulsion and water, and also accommodate more firetube duty, if desired. Vertical systems may be adequate and less costly for applications with already high inlet temperatures and a greater specific gravity spread.
Two-phase FWKO’s are used to separate oil and gas from water, allowing the upstream FWKO to hold pressure using the downstream treater’s back pressure control valve. Three-phase FWKO’s are used to separate oil, gas, and water but require 3-phase piping with separate gas measurement and back pressure instruments and controls.
Design Considerations for Free Water Knockouts
When designing a free water knockout system, there are several considerations to keep in mind, including temperature, pressure, retention time, shell materials and coatings, and location. The size and capacity of the vessel should be selected based on the expected flow rate and the amount of water and impurities that need to be separated.
Maintenance and Troubleshooting
Regular inspection and cleaning are crucial for maintaining the performance and efficiency of a free water knockout system. Common problems include solids blockages, leaks, and corrosion, which can be addressed through proper design, cathodic protection upkeep, maintenance and periodic repair.
Summary
Free water knockouts are an important component of oil and gas production operations, providing an effective way to separate water and other impurities from crude oil and natural gas. By selecting the appropriate size and design, materials and coatings, and location and accessibility, operators can ensure their free water knockout system performs efficiently and effectively, while complying with environmental regulations and reducing maintenance and repair costs.