Multiphase Desander – Hydraulic Capacity, Turndown, & Performance (B-FSM089)
The graph below illustrates the hydraulic information from the previous two articles. Both the Plitt-based hydraulic throughput model and the Arterburn-based hydraulic performance model are combined on the same graph.
To restate, this graph is for hydraulic (liquid only) flow. Pneumatic (gas) and multiphase flow will be shown on subsequent posts.
The abscissa shows the pressure drop, with a focus on the range 5-50 psi (0.34-3.45 bar). The ordinate shows the resulting water (liquid only) flow rate in barrels per day (BPD). Multiple lines on the graph are given for a range of insert sizes. All desanders shown are insert style (single cyclone).
The bottom (red) line shows the range of operation for a WH4 (4” diameter) desander. At 5 psi pressure drop the unit has a throughput of ~1100 BPD, while at 50 psi pressure drop the throughput increases to slightly less than 4000 BPD. The corresponding separation performance at these two ends are 30 micron and 15 micron separation size (D98). The separation size is coarser at the lower pressure drop due to less centrifugal spin. The WH4 desander can operate fully across the 5-50 psi pressure drop range and will exhibit 15-30 micron separation size accordingly.
The same data is given for 6”, 8”, 10”, 16”, and 20” desanders. The WH10 desander operates with a throughput of ~5500-15000 BPD and corresponding separation size (D98) of 47-25 microns.
Again, this data is for water only flow. The basis is separating sand (2650 kg/m3 density) from fresh water (1000 kg/m3 and 1.0 cP).
The range of 5-50 psi is used for this specific illustration. The minimum pressure drop of 5 psi (in water) is required to maintain the cyclone vortex, while the maximum of 50 psi is given to balance wear life on the insert.
Cyclone inserts are physically quite small (10-50 liters internal volume). This results in an average residence time of 1.3-4.2 seconds. Desanders are very robust to changes in volumetric flow – which will be illustrated in detail in a future article.
Performance at pneumatic (gas) conditions will be presented in the next article.
References
- Rawlins, C.H. 2017. “Separating Solids First – Design and Operation of the Multiphase Desander”, paper 185658-MS presented at the SPE Western Regional Meeting, Bakersfield, CA, 23-27 April.
