Settling Tanks

Settling Tanks

Settling tanks, also known as gravity settling tanks, are integral components in biodiesel production. Utilizing the simple principle of gravity, these tanks help separate heavier and lighter components from the mixture, ensuring that the end product meets the desired quality standards.

Why Settling Tanks are Important

  • Simplicity: A passive separation method that doesn’t require energy input.
  • Cost-effective: Once installed, they require minimal operational costs.
  • Efficiency: Provides a method for separating out impurities and undesired by-products from biodiesel.
  • Scalability: Suitable for small-scale producers and larger plants alike.
Working Principle

Settling tanks operate on the principle of gravity separation. In the context of biodiesel production:

  • Heavier components, like glycerol, settle at the bottom due to gravitational force.
  • Lighter components, such as biodiesel, remain on the top.

Given adequate time, a clear boundary or separation layer forms between these two phases.

Key Steps Involving Settling Tanks

1. After Transesterification
  • Once the transesterification reaction completes, the mixture is directed into settling tanks.
  • Here, glycerol, a by-product of the reaction, settles to the bottom due to its higher density.
  • The biodiesel, being lighter, floats to the top.
2. Water Washing (if employed)
  • If water washing is used to purify biodiesel, settling tanks allow the separation of wash water from biodiesel.
  • Water, being denser, settles at the bottom.
3. Design and Features
  • Material: Typically made from stainless steel or coated metals that resist corrosion and are compatible with biodiesel.
  • Size & Capacity: Varies from small tanks for batch processing to vast tanks for continuous industrial production.
  • Outlet Ports: Usually, there are two – one near the bottom to draw off the heavier phase (e.g., glycerol) and one on top to collect the lighter phase (e.g., biodiesel).
  • Inspection Windows: Some tanks come equipped with sight glasses or windows to monitor the separation process.
  • Sampling Ports: Allows for periodic extraction of samples to monitor the quality and progress of separation.
4. Considerations for Effective Settling
  • Dwell Time: Ensure the mixture remains in the tank long enough to achieve optimal separation.
  • Temperature: The separation can be affected by temperature. Some producers maintain a warm temperature to optimize the settling process.
  • Turbulence: Minimize agitation when transferring the mixture into settling tanks to expedite separation.
  • Regular Cleaning: Over time, impurities can accumulate at the bottom. Regular cleaning prevents cross-contamination and ensures efficient separation in subsequent batches.


Settling tanks are the unsung heroes in biodiesel production, silently ensuring that the biodiesel produced is of high quality. Through the simple, yet effective principle of gravity separation, they help biodiesel producers attain a purer product without complex machinery or high energy costs.