Forced-Circulation (FC) Crystallizer
Engineering reliability first. An external loop circulates a crystal slurry at 2–3 m/s through the heater and back, relieving moderate flash-generated supersaturation on suspended crystals. Medium crystals, wide distribution — and continuous stable operation on the high-TDS, scaling, mixed-salt systems where anything else stops.
Four Numbers That Define FC
Reference ranges under typical operating conditions on inorganic salt systems.
Circulate, Flash, Grow, Repeat
The same circulating architecture as forced-circulation evaporation — with crystal slurry control added as the design objective.
Simplified FC Crystallizer Flow Diagram
Slurry → Circulation pump → Heater (ΔT ≤10 °C, no wall boiling) → Flash in vapor body → Supersaturation relieved on suspended crystals → Loop
Supersaturation never touches a hot wall — it is created by the flash in the vapor body and consumed by the suspended crystals in the loop.
Slurry Circulation
The external pump keeps a crystal slurry moving at 2–3 m/s — nothing settles, nothing scales undisturbed.
Sensible Heating
The heater warms the slurry without boiling it — the ≤10 °C rise keeps the tube wall out of the nucleation business.
Flash & Supersaturation
In the vapor body the slurry flashes; concentration crosses saturation and moderate supersaturation appears.
Growth & Discharge
Crystals in the loop consume the supersaturation; product slurry is drawn off continuously to separation.
FC vs. DTB vs. Oslo
Three vessel configurations, three priorities: FC puts engineering reliability first, DTB puts product quality first, Oslo puts crystal quality first.
d50 ranges reflect typical operating distributions on inorganic salt systems; actual PSD depends on residence time, fines management, seed control and the cooling/evaporation profile.
When to Pick FC — and When Not To
FC is the answer when fouling resistance and on-stream time outweigh crystal size; the wrong answer when product spec needs classification.
FC is a Dimension D crystal growth configuration — it pairs with any Dimension C supersaturation method, and it is the typical carrier for evaporative crystallization on difficult liquors. The selection logic is explicit: accept higher energy consumption in exchange for continuous stable operation on high-salinity, high-viscosity, scaling-prone systems. What you give up is crystal size control — no internal classification means wide PSD. All figures are indicative ranges for preliminary screening, not a process guarantee.
FC Crystallizer Questions We Answer Most
Recurring questions from engineers choosing a growth configuration.
No — that is the trade. FC has no internal classification; crystal size lands at 0.2–0.8 mm with a wide distribution. If the product spec (or downstream centrifuge yield) needs narrow PSD, the answer is DTB with classified-fines removal, not a tuned FC.
You feel it in three places: product spec — undersized d50 fails downstream handling; availability — putting Oslo on a fouling-prone feed drives cleaning cycles that kill on-stream time; yield — fines escaping the crystallizer carry dissolved product back and increase purge.
Because once evaporation is the supersaturation driver, supersaturation is high and scaling accompanies it. The FC body at 2–3 m/s tolerates what a classified bed would not — that is exactly the ZLD mixed-salt duty.
The architecture is identical — pump, heater, flash body, loop. This page covers crystal-side design: slurry control, residence and discharge. The evaporation-side logic (stable concentration of difficult liquors) lives on the FC evaporation page.
Screening an FC Configuration?
Send us feed composition, fouling tendency, target PSD and purity. We will return a preliminary FC vs. DTB vs. Oslo screening with indicative crystal size — not a brochure.