FSM: Liquid Desander – Vessel Packing Design (B-FSM047)
Terminology for the flow streams and components for the hydrocyclone and desander were discussed in previous article. We will now look at vessel design and packaging. This discussion pertains only to the desander.
The following graphic shows cut-away schematics of the two main types of desander packaging – Single Cone (SC) versus Multi-Cone (MC).
Both the SC and MC designs are comprised of a pressure vessel housing with replaceable cyclonic internals.
Common Design Aspects
- Pressure vessel housing fabricated to appropriate design code, flange rating, and material of construction to match the rest of the process system. The housing is made to contain all fluids and operating pressure, but is not subjected to erosion. Access to the internals is made by un-bolting the pressure vessel housing.
- Cyclone internals are contained in the pressure vessel. These are replaceable (i.e. consumable) components. The internals are sized for the specific performance and flow rate of the application. The internals perform the separation duty and contain all erosion.
- The (integral) accumulator is a hold up section in the lower part of the pressure vessel housing. It is sized to contain solids for suitable batch discharge interval.
- The underflow valve is used to discharge the accumulated solids. It must match the flange rating, design, and materials of the pressure vessel housing. The valve may have manual or automated actuation.
- Both designs have continuous inlet and overflow streams with batch discharge of the underflow.
Single Cone Vessel
- As the name implies only one cyclone internal per vessel. In this design the internal is called an “insert”. The size (diameter) of the vessel dictates the maximum size of the insert. Increasing or decreasing design flow requires smaller or larger diameter insert and vessel as appropriate. Inserts are interchangeable, in that different sizes can be interchanged within the same vessel – though still only one insert per vessel.
- Inserts range from 4”-30” nominal diameter. The insert is most commonly fabricated from wear resistant metal due to size. Materials of construction may be duplex or 410 stainless steel with internal wear coating applied. Monolithic ceramics (i.e. silicon carbide) have been fabricated to these sizes on rare occasions, but are very costly.
- As the name implies the vessel may have multiple cyclone internals per vessel (sometimes several hundred). In this design the internal is called a “liner”. The size (diameter) of the vessel dictates the maximum of liners it can hold. Increasing or decreasing design flow requires smaller or larger diameter vessel with appropriate number of liners.
- Liners range from 0.5”-4” nominal diameter. The liner is most commonly fabricated from wear resistant ceramic or specialty metals. Materials of construction may be alumina, silicon carbide, or Stellite®.
The next article will discuss why there are two different vessel packing designs for desanders.
- Rawlins, C.H. and Wang, I.I. 2001. Design and Installation of a Sand-Separation and Handling System for a Gulf of Mexico Oil Production Facility. SPE Production & Facilities, August, pp. 134-140.