How Degasser Tower Designed?

 The design basis of a degasser tower in a water treatment plant will depend on several factors, including the specific application, the type of water being treated, and the level of degassing required. However, some general design considerations include:

  1. Sizing: The degasser tower must be sized appropriately to handle the flow rate of water being treated. The tower's size will depend on the required retention time, which is the time needed for the water to pass through the tower, and the height of the packing material or trays used in the tower.

  2. Packing Material: The packing material or trays used in the degasser tower should be carefully selected to provide maximum surface area for gas-liquid contact, allowing for efficient degassing. The material should also be chemically resistant to the water being treated and the gas used for degassing.

  3. Gas Distribution: The design of the gas distribution system is critical for efficient degassing. The gas should be distributed uniformly across the packing material or trays, to ensure that all areas of the tower are in contact with the gas stream.

  4. Flow Control: The flow rate of the gas and water must be carefully controlled to ensure that the water has sufficient contact time with the gas for effective degassing. The flow rate of the gas is typically controlled by a metering valve or flow controller, while the flow rate of the water is controlled by the inlet and outlet valves of the tower.

  5. Maintenance: The degasser tower should be designed with maintenance in mind, to ensure that it is easy to access and inspect, and that packing material or trays can be replaced as needed. The tower should also be designed to minimize fouling and scaling, which can reduce the efficiency of the degassing process over time.

The design of a degasser tower involves determining the appropriate water and air flow rates for efficient degassing. The flow rates are typically calculated based on the specific application, the type of water being treated, and the desired level of degassing. The following formulas can be used as a starting point for designing the water and air flow rates in a degasser tower:

  1. Water Flow Rate:

Qw = V / t

Where: Qw = water flow rate (m3/s) V = volume of water in the degasser tower (m3) t = retention time of water in the degasser tower (s)

The retention time can be calculated based on the desired level of degassing and the height of the packing material or trays in the degasser tower.

  1. Air Flow Rate:

Qa = K * Qw

Where: Qa = air flow rate (m3/s) Qw = water flow rate (m3/s) K = volumetric gas-liquid mass transfer coefficient (m/s)

The value of K depends on the specific application and the type of packing material or trays used in the degasser tower. It can be estimated based on empirical correlations or determined experimentally.

It's important to note that these formulas are a starting point for designing the flow rates in a degasser tower. Other factors, such as the type of gas being used, the size and geometry of the tower, and the packing material or trays used, can also affect the flow rates and should be considered in the design process.

The volumetric gas-liquid mass transfer coefficient (KLa) is a measure of the rate at which gas is transferred from the gas phase to the liquid phase in a degasser tower. The value of KLa depends on several factors, including the type of gas being used, the type and size of packing material or trays in the tower, and the properties of the liquid being degassed.

For DM (de-mineralized) water, the value of KLa can vary depending on the specific application and design of the degasser tower. Generally, KLa values for degassing DM water range from 0.01 to 0.5 s^-1.

However, it's important to note that the KLa value for DM water will be affected by the dissolved gases in the water, such as oxygen or carbon dioxide, as well as the temperature and pressure conditions in the tower. In practice, the KLa value for a specific application is often determined experimentally, using pilot-scale testing or other methods.

The retention time in a degasser tower is the amount of time that the water being treated spends inside the tower, and it is an important design parameter to ensure that the water has sufficient contact time with the gas for effective degassing. The retention time can be calculated using the following formula:

Retention Time (t) = Volume of Tower (V) / Flow Rate of Water (Qw)

where:

  • t is the retention time in seconds (s)
  • V is the volume of the degasser tower in cubic meters (m3)
  • Qw is the flow rate of water in cubic meters per second (m3/s)

The volume of the degasser tower is typically calculated based on the desired retention time and the flow rate of water. For example, if the desired retention time is 60 seconds and the flow rate of water is 10 cubic meters per hour (0.0028 cubic meters per second), then the volume of the tower can be calculated as:

V = Qw * t = 0.0028 m3/s * 60 s = 0.17 m3

In this example, the volume of the degasser tower would need to be at least 0.17 cubic meters to achieve the desired retention time of 60 seconds.

It's important to note that the retention time is just one factor in the design of a degasser tower, and other factors such as the type and size of packing material, gas flow rate, and gas-liquid mass transfer coefficient also need to be considered to ensure efficient and effective degassing.

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