Multiphase Desander – Pneumatic Capacity, Turndown, & Performance (B-FSM090)
Similar to the previous article, the graph below illustrates information for pneumatic (gas) throughput and performance for insert-style desanders. Both the Stairmand-based pneumatic throughput model and the Leith-Licht-based pneumatic performance model are combined on the same graph.
To restate, this graph is for pneumatic (gas only) flow. Hydraulic flow was the subject of the previous article, and multiphase flow will be shown on a subsequent post.
The abscissa shows the pressure drop, with a focus on the range 0.5-5 psi (0.03-1.72 bar). The ordinate shows the resulting methane (gas only) flow rate in MMSCFD. 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 0.5 psi pressure drop the unit has a throughput of ~1 MMSCFD, while at 25 psi pressure drop the throughput increases to slightly less than 6 MMSCFD. The corresponding separation performance at these two ends are 8 micron and 3 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 0.5-25 psi pressure drop range and will exhibit 3-8 micron separation size accordingly. The gas flow rate conditions are based on 1450 psig and 40°C operating pressure and temperature.
The same data is given for 6”, 8”, 10”, 16”, and 20” desanders. The WH10 desander operates with a throughput of 5-30 MMSCFD and corresponding separation size (D98) of 13-4 microns.
The range of 0.5-25 psi is used for this specific illustration. The minimum pressure drop of 0.5 psi (in gas) is required to maintain the cyclone vortex, while the maximum of 25 psi is given to balance wear life on the insert. The pressure drop range in gas only flow is lower than that of liquid only flow.
Cyclone inserts are physically quite small (10-50 liters internal volume). This results in an average residence time of 0.3-2.1 seconds. Desanders are very robust to changes in volumetric flow – which will be illustrated in detail in a future article.
Performance at multiphase conditions will be presented in the next article.
- 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.