Many RFQs say “I need a 500 L extraction tank,” but don’t define:
solids loading (kg/batch)
solvent ratio (L/kg)
mixing behavior (suspension vs slurry)
reflux/vapor behavior (headspace needs)
downstream rhythm (batches/day)
So suppliers guess. Then the tank is either:
too small (no headspace, foaming, solvent loss), or
too big (poor mixing, low efficiency, unnecessary cost).
This guide shows buyers how to size an extraction tank using batch capacity, working volume, and headspace—in a way suppliers can quote accurately.
If you’re still choosing what to call the equipment: Extraction Tank vs Vessel vs Reactor: What to Call It—and How to Choose
1) Key Terms (so your RFQ is unambiguous)
1.Batch capacity
How much raw material and solvent you process per batch (e.g., kg solids + L solvent).
2.Working volume
The liquid (or slurry) volume you actually operate at—not the tank nameplate volume.
3.Headspace
The empty volume above the working liquid level, needed for:
vapor expansion (especially with reflux heating)
foaming
agitation vortex control
safe level control and overflow margin
4.Nominal/total volume
The tank’s full geometric capacity. Suppliers often quote this number unless you specify working volume and headspace.
2) Start from Process Inputs (not from “L”)
Before sizing the tank, define these process inputs:
Solids per batch: ____ kg (dry basis if possible)
Solvent system: ethanol/water ratio or water only
Solvent-to-solid ratio: ____ L/kg (or kg/kg)
Extraction temperature: ____ °C (near boiling? reflux?)
Mixing goal: dissolve? suspend solids? prevent settling?
Foaming tendency: low/medium/high
Batch rhythm: ____ batches/day, ____ hours/batch
3) Calculate Working Volume (the simplest sizing math)
3.1 Liquid volume from solvent ratio
If your process uses a solvent-to-solid ratio of R (L/kg) and solids mass M (kg):
Solvent volume (L) = R × M
Example:
M = 100 kg solids, R = 6 L/kg → solvent ≈ 600 L
3.2 Add solids displacement (slurry effect)
Solids take up volume in the tank (and can swell). If you ignore displacement, you’ll overflow or lose headspace.
A practical approach for RFQs:
Add a displacement allowance (depends on bulk density and swelling)
If you don’t know it, tell supplier solids bulk density and swelling risk
3.3 Add circulation volume (if you use loops)
If you have external circulation lines, filters, or heat exchangers, the system holds additional liquid outside the tank. Include that in total working volume.
4) Headspace: How Much Do You Need?
Headspace is not “wasted volume.” It is safety and process stability volume.
4.1 Typical headspace targets (buyer-friendly rules)
Use these as starting points:
No reflux, low foam: headspace ~10–20% of total volume
Heated extraction, moderate foam: headspace ~20–30%
Reflux extraction / high foam / vigorous agitation: headspace ~30–40% (or more, case-dependent)
If you operate near solvent boiling and use a condenser, you are in reflux mode—see: Reflux Extraction Setup: When You Need It and How to Specify the Condenser Interface
4.2 Why reflux and ethanol need more headspace
vapor expansion and “boiling surges”
foam formation and entrainment
stable vapor space for safe venting and condenser routing
4.3 Overflow prevention is not the same as headspace
You still need:
level measurement margin
high-high level alarm/trip points
safe overflow route (if required by design)
5) Convert Working Volume + Headspace into Tank Nominal Volume
5.1 Basic sizing rule
Nominal tank volume ≈ Working volume ÷ (1 − headspace fraction)
Example:
Working volume = 700 L
Headspace target = 30%
Nominal volume ≈ 700 / 0.70 = 1000 L tank class
This is why “we process 700 L” often becomes “we need a 1000 L tank.”
6) The “Hidden” Sizing Drivers Buyers Forget
6.1 Agitation and solids suspension
If solids settle, you need:
correct impeller type
adequate motor power
proper baffles or geometry
adequate liquid height for impeller placement
Oversizing a tank can actually worsen suspension if agitation power density drops.
6.2 Viscosity changes during extraction
Some botanicals release gums/resins that increase viscosity. Higher viscosity requires:
stronger mixing design
higher torque motor/gearbox
sometimes larger nozzles and drains
If viscosity or fines are a known problem, also plan downstream:
filter clogging after UAE: causes & fixes (separation logic applies broadly)
6.3 Heating/cooling duty
Jacket/coil sizing must match:
heating time targets
temperature stability
solvent boiling behavior (if reflux)
If you say “heated tank” without heat duty or ramp time, you’ll get guesses.
6.4 Materials of construction and solvent compatibility
Specify 304 vs 316L and seal compatibility based on solvent system.
7) Sizing Examples (Buyer scenarios)
Example A: 100 kg botanicals, ethanol extraction, reflux heating
Solvent ratio: 6 L/kg → 600 L solvent
Solids displacement: assume +100 L (depends on bulk density/swelling)
Working volume ≈ 700 L
Reflux headspace target: 30–40%
Nominal tank ≈ 700/0.70 = 1000 L (at 30% headspace)
or ≈ 700/0.60 = 1167 L (choose 1200 L class) at 40%
Example B: low-temperature water extraction, low foam
Working volume 700 L
Headspace 15%
Nominal ≈ 700/0.85 = 824 L → choose 900 L class (or 1000 L for flexibility)
8) RFQ Checklist (What suppliers need for accurate tank sizing)
Copy/paste to suppliers:
Solids mass per batch (kg) and material description (swelling/foaming)
Solvent system and ratio (L/kg)
Target working volume (L) and headspace target (%)
Temperature range; reflux required yes/no
Mixing goal (dissolution vs solids suspension) + viscosity notes
Utilities (steam/thermal oil/chiller) and heat-up time target
Ports required (solids charging, CIP, condenser interface, sampling)
Safety scope (flammable solvent handling, interlocks, explosion-proof if required)
Downstream integration (filtration, concentration, recovery)
Helpful related reading to include in your RFQ:
FAQ (with answers)
1. What working volume should I use for extraction tanks?
Use the total slurry/liquid volume you operate at (solvent + solids displacement + any loop hold-up). Don’t use nameplate volume.
2. How much headspace is enough?
Depends on reflux and foaming. Low-foam, non-reflux: 10–20%. Reflux or foamy systems: commonly 30–40% as a starting point.
3. Why did my “500 L tank” overflow when I loaded solids?
Because solids displacement and swelling were ignored, and there wasn’t enough headspace for foam and agitation.
4. Is oversizing safer?
Not always. Oversizing increases cost and can reduce agitation power density, causing poor solids suspension and inconsistent extraction.
5. Do I need different sizing if I plan solvent recovery?
Yes. Recovery affects batch rhythm and may require reflux interface and downstream condenser sizing.
Request a turnkey extraction line proposal (PFD + equipment list)
We’ll size extraction tank, filtration, vacuum concentration, and solvent recovery to match your batches/day target.