Reference ID: MET-5848 | Process Engineering Reference Sheets Calculation Guide
Introduction & Context
The Extractor Type Selection Matrix is a rapid screening tool used in Process Engineering to decide whether an auger extractor is mechanically and hydraulically suited to a given solid–liquid extraction duty. It is normally executed before detailed sizing or costing, and is embedded in front-end studies such as Pre-FEED and FEED packages, as well as in vendor pre-selection algorithms embedded in CAPE-OPEN or in-house Excel/Python tools.
The matrix compares the process demand (volumetric throughput, required residence time, pressure, particle attributes, moisture) against vendor-supplied mechanical limits. If all constraints are satisfied, the auger extractor is carried forward to the next level of analysis; otherwise, an alternative extractor class (e.g., percolation, carousel, paddle, or centrifugal) must be evaluated.
Methodology & Formulas
Convert mass flow to volumetric flow
The wet feed rate is supplied on a mass basis; the extractor, however, is volumetrically constrained.
\[ Q = \frac{\dot{m}_{wet}}{\rho_{bulk}} \]
where
\( Q \) = volumetric flow rate (m3 h-1)
\( \dot{m}_{wet} \) = wet feed mass flow (kg h-1)
\( \rho_{bulk} \) = loose bulk density (kg m-3)
Validate against vendor envelopes
Each mechanical limit is treated as a hard constraint. The following table summarises the regimes for an auger extractor.
Parameter
Symbol
Lower Bound
Upper Bound
Unit
Volumetric flow
\( Q \)
\( Q_{min} \)
\( Q_{max} \)
m3 h-1
Residence time
\( \tau \)
\( \tau_{min} \)
\( \tau_{max} \)
min
Operating pressure
\( P \)
atm
\( P_{max} \)
bar (abs)
Particle size
\( d_p \)
—
\( d_{p,max} \)
mm
Moisture content
\( w \)
\( w_{min} \)
\( w_{max} \)
% w/w
A warning flag is raised if any of the following inequalities are violated:
\( Q_{min} \le Q \le Q_{max} \)
\( \tau_{min} \le \tau \le \tau_{max} \)
\( P \le P_{max} \)
\( d_p \le d_{p,max} \)
\( w_{min} \le w \le w_{max} \)
Decision logic
If all constraints are satisfied, the auger extractor is marked as feasible and the algorithm returns the volumetric flow rate for downstream sizing. If any constraint fails, the matrix recommends selecting an alternative extractor type.
The matrix is a decision table that maps common process conditions—such as feed concentration, viscosity, desired separation sharpness, and throughput—to the most cost-effective extractor type (e.g., centrifugal, mixer-settler, membrane, or column). Using it early in design prevents pilot-plant rework and shortens equipment procurement by 2–4 weeks.
At minimum you must enter:
Feed phase ratio (A/O) and total flow rate
Density difference between phases
Interfacial tension at operating temperature
Target stage efficiency or theoretical stage count
Presence of solids or emulsion-forming components
Missing any of these can shift the selection from a compact centrifugal unit to a large mixer-settler battery.
Apply the tie-breaker hierarchy:
CAPEX sensitivity—use the option with lowest installed cost per theoretical stage
Operability risk—favor the technology with the smallest number of moving parts
Future scale-up—select the configuration that can be modularly expanded without downtime
If still tied, run a 5 L batch test for each technology and compare separation time and clarity.
Yes, but you must switch to the reactive sheet in the workbook. This sheet adds criteria such as heat of reaction per theoretical stage, allowable residence time, and materials-of-construction limits. Centrifugal extractors are usually down-scored because of short residence time, while column extractors with external recirculation loops score higher for heat removal.
The latest Excel matrix (v3.2) is stored in the Process Engineering SharePoint under Tools & Templates > Extraction. After filling it out, attach the file to your PID review package; the principal process engineer and technology steward must e-sign before the project moves to 30 % design review.
Worked Example – Auger Extractor Pre-selection
A specialty-chemical plant needs to remove surface moisture from a filter cake before packaging. The process engineer must confirm whether a standard auger extractor is technically feasible for the duty.
Knowns
Feed type: solid, continuous
Wet feed rate: 30 000 kg h-1
Bulk density: 550 kg m-3
Moisture content: 70 % (wet basis)
Mean particle size: 5 mm
Required mean residence time: 30 min
Operating temperature: 65 °C
Operating pressure: 1.013 bar
Step-by-step check against auger limits
Convert mass flow to volumetric flow
\[ Q = \frac{30\,000}{550} = 54.545 \; \text{m}^3 \, \text{h}^{-1} \]
Compare \( Q \) with auger range
10 m3 h-1 ≤ 54.545 m3 h-1 ≤ 60 m3 h-1 → within range
Compare required residence time with auger range
20 min ≤ 30 min ≤ 40 min → within range
Check maximum allowable pressure
Operating 1.013 bar < 2 bar → acceptable
Check particle size
5 mm ≤ 8 mm → acceptable
Check moisture window
50 % ≤ 70 % ≤ 90 % → within range
Final Answer
All feed and process parameters fall within the validated operating envelope for a standard auger extractor. The unit is therefore pre-selected for further detailed design.
"Un projet n'est jamais trop grand s'il est bien conçu."— André Citroën
"La difficulté attire l'homme de caractère, car c'est en l'étreignant qu'il se réalise."— Charles de Gaulle
