Many desander installations will require a secondary accumulator – also called the external accumulator. This is a sand holding vessel located directly below the desander vessel. The primary desander has a holding section, termed integral accumulator, so why is a secondary accumulator used and how do you size it?

**A Secondary Accumulator is Used When…**

- The desander has an operating pressure >100 psig (6.9 barg)
- When you want highly-controlled discharge of solids
- To minimize gas/vapors flashing from the slurry
- To minimize liquid loss from process

**Accumulator (ACC) Sizing**

- Typically 2:1 or 3:1 aspect ratio (height:diameter)
- Total volume for reasonable collection time (8-12 hours at least)
- Recommended solids fill height ~75%
- Use level switch to automate discharge process
- The quantity of solids reporting to ACC equals inlet concentration to Desander multiplied by separation (capture) efficiency
- Volume of solids must be corrected for particle packing efficiency (0.62 average) – e.g. 100 liters of particulate solids packs at 161 liters effective volume

The next article will start the discussion on apex flux balancing.