Operation Of Separators: Complete Technical Guide

The operation of separators is the discipline that decides what the cement mill delivers: the separator is the classifier inside the grinding circuit that separates the finished product from the oversize particles and sends the coarse back to the mill: the fineness of the cement, the capacity of the mill, the energy per ton and the particle size distribution of the product are all born in the whirling chamber of this one machine: the operator who masters the separator masters the most powerful trimming wheel of the grinding department: this guide covers the static machines, the dynamic rotors, the high efficiency cages and the daily operation: the complete selection of the skill.

The Complete Cement Technical Package (931 files including the courses, the books, the Excel tools and the operating guides: $249.99 one-time: instant download via the PayPal payment) includes the full Operation of Separators file with its cut-point tables, the Tromp curve analysis, the speed settings and the troubleshooting catalog: the mill operators find the daily recipes, the designers the classification mathematics: the honest framework of the package: the classification knowledge, measured.

This article follows the order of the file: the principle of separation first, the machine generations second, the operating parameters third, and the quality control and maintenance last: each section carries the lists, the tables and the plant numbers: the reader can work beside the separator control screen: the intention of the document.

1. Why the Grinding Circuit Needs a Separator

The grinding in the tube mill is a slow lottery: the mill feeds the material, the media break the particles, and the product emerges as a mixture of the fine finished cement and the coarse material that needs more grinding: to return only the coarse particles to the mill while removing the fine ones, the circuit needs the classifier: the separator receives the mill discharge, divides the flow into the two streams and sends the oversize back: without the classification, the mill energy would grind everything to an ever finer mass, with the energy wasted on the fines and the capacity of the mill falling: the closed circuit with the separator is the standard of the cement grinding.

• The closed circuit: the mill discharge goes to the separator: the fine stream is the finished cement, the coarse stream returns to the mill inlet: the loop repeats;
• The circulating load: the ratio of the coarse return to the new feed: the typical ball mill circuits run 150 to 350 percent: the heart beat of the loop;
• The control variables: the separator speed, the vane angle, the feed rate and the air flow: each of them moves the fineness and the capacity;
• The energy saving: the closed grinding with the efficient separator reduces the specific energy of the finish grinding by 20 to 30 percent against the open circuit: the classified removal of the fine mass;
• The product quality: the separator shapes the particle size distribution of the cement: the narrow distributions of the high-efficiency machines: the set, the water demand and the strength follow;
• The cooling the separator with the air volume carries the heat of the mill: the cement discharged at 90 to 120 °C cooler than the mill exit: the silo protection built into the machine.

The separator is often called the “brain of the mill”: the mill is the muscle and the classifier is the judgment: the operator who trims the separator speed trims the quality of the cement and the capacity of the mill in one action: the modern plant controls the fineness with the separator as the first actuator and adjusts the mill power after it: the article gives the separator its central place in the loop.

2. The Physics of the Separation: The Cut Size, the Sharpness and the Tromp Curve

Every classifier works on the same equilibrium: the particles entering the classifying zone feel the air drag that carries them outward or upward and the centrifugal force that whips them to the wall: the particles that cannot escape the drag leave with the fine stream, the rest falls to the coarse stream: the size at which half of the particles leave one way and half the other is called the cut size, d50: the ideal classifier would cut like scissors at the single size: the real classifier cuts over a band: the sharpness of the band is measured by the Tromp curve, the probability curve of the separation for each size:

• The d50 (cut size): the particle diameter with 50 percent probability to the coarse stream: the set point of the machine: the modern cage classifier runs 15 to 45 micrometers cut size;
• The bypass: the fraction of the feed that short-circuits directly to the fine stream without classification: the fine dust carried by the air, the poor seals: the modern machines push the bypass below 15 percent;
• The fish hook: the dip in the Tromp curve at the very fine sizes where the agglomerated fine particles re-enter the coarse stream: the agglomeration effect: the cause of the hidden capacity loss;
• The sharpness factor: the ratio d75/d25, or d25/d75 of the Tromp curve: the 1.0 means the perfect separation: the second generation 1.3 to 1.5, the third generation 1.1 to 1.25;
• The imperfect: the statistical measure of the class imperfection I = (d75-d25) / d25: the lower the better, the modern cage classifier 0.1 to 0.2: the old machines 0.3 to 0.5;
• The selectivity curves: the series of the classification functions for the feed: the toolkit of the separator analysis: the yield diagram of the mill circuit.

The Tromp curve is the identity card of the separator: the plant can measure it from the sieving of the coarse, the fine and the feed streams: the file includes the blank Tromp worksheet and the worked example with the actual mass balance data: the shape of the curve: the flat indicates the old machine, the steep the modern; the small bypass the sealed; the fish hook the agglomeration: the curve is the geometry of the influence, and the operator reads it monthly: the curve, not the guess, guides the tuning.

3. The Static Separators: The Simple Classification Without the Rotor

The classification does not need the moving parts: the static separator uses the centrifugal force of the rotating air itself: the pneumatic air separator of the old plants, the V-separator in the material circuits and the cyclone separators have no rotor: the principle: the air enters with the feed, the spiral movement throws the coarse particles to the wall, the fines continue with the air to the filter: the coarse falls back to the mill: the machine is robust, cheap and nearly maintenance-free, but its classification is soft, with the imperfection 0.3 to 0.6, and one setting only: the geometry.

• The pneumat pumps: the air sweeps the mill: the airspeeds convey the material to the static classifier: the compact plants of the old generation: the simple machine with the blades around the column;
• The air separation of the raw circuit: the drying and the classification in one machine on the air-swept raw mills: the static upstream combined with the cyclones;
• The V-separator: the exponent-slot static machine of the roller press circuits: the feed falls through the blades, the air crossflow classifies the fines: the oversized de-agglomerates in the machine itself;
• The use today: the static acceptance now serves the pre-classification, de-dusting and the mill internals: the sieving “de-lumping” the dried materials;
• The pros and cons: the robustness and 3 to 5 kW of the static versus the impossibility of the dynamic control: the fineness fixed by the slot geometry and the air volume.

The static machine belongs in the full picture: the plants that understand the classification know where the static saves the money: the V-separator in the roller press circuit and the static pre-classifiers in the ball mill circuits: the file plots the classification curves of the statics against the dynamics so the designer selects the appropriate for the task: the best machine: only the one whose curve fits the requirement of the circuit.

4. The Dynamic Separator of the First Generation: The Rotating Whirlwind of the 1930s

The rotating mechanical air separator appeared with the modern cement grinding circuits: the feed drops onto a rotating distributor plate, the air is sucked up through the cylindrical classification chamber, and the vanes of the second air system rotate inside to control the amount of air that carries the fine: the coarse tumbles out at the bottom of the cone, the fines leave the top and settle in the cyclones or the baghouse: the machine power is small and the geometry simple: the separation is controlled by the rotating speed of the classification vanes:

• The principle: the coarse falls back by the gravity against the upward air: the terminal velocity of each particle balances the airspeed: the cut size sets;
• The fineness control: the vanes speed: higher centrifugal whisk divides the coarser particles to the lines: the fineness range of 3000 to 4200 Blass reachable on the clinker:
• The efficiency: the impurity 0.4 to 0.6, the bypass 20 to 40 percent: the fine particles agglomerate in the influence, and the air short-circuit in the seals:
• The today: the converted into the second-generation with the added cyclones, or still runs in the modifications where the fineness demand is moderate:
• The mixed circles: the standard closed circuit of the 1960-1980 plants: the liners, the chain, the static: on the classic tube mill trains: the reliability of the machine won its decades.

The first generation explains the physics of the later: the rotating air propeller itself is the rotating classifier, and its speed is the primary trim of the product: the engineers of the old circuits trimmed the separator rev by the hours and the technicians adjusted the feed: the file includes the calibration curves of the first generation: the air volume per speed and the class progression: the historical chapters give the modern operator the instinct of the machine: the speed, the air and the fineness: the same trio in every generation.

5. The Second Generation: The Cyclone-Air Machines and the Better Sharpness

The second generation of the 1960s-70s kept the rotating classification chamber of the first generation but replaced the simple aspiration with the dedicated fans and the cyclone array: the air circuit became a closed loop: the fines carried out by the air, the cyclones settled them, and the cleaned air returned to the separator: the separation chamber operated at a stable air flow independent of the mill ventilation: the result: the sharper cut, the higher capacity and the fineness range up to 5000 Blass: the machine became the standard finish-mill equipment of the 1980s plants.

• The air circuit: the closed loop with the separate circulation fan at the inlet air and the cyclones: the pressure balance adjusts with the damper: the stable classification zone:
• The lubrication and the drive: the central shaft with the variable speed or the multi-speed drive: the speed variation as the tuning knob of the fineness:
• The feed distribution: the feed drops from above onto the distributor plate and the cascade down around the shaft: the balanced feed distribution across the full ring:
• The efficiency data: the imperfection 0.3 to 0.45: the bypass 15 to 30 percent: an improvement over the first generation yet the sharp high-efficiency of the third is still far:
• The legacy: thousands of the second-generation machines still operate: the retrofit with the third-generation classifier cages inside the old shells is a documented upgrade path of the file: the capacity gains 15 to 30 percent.

The second generation taught the industry the value of the air volume control: the constancy of the classification air through the cyclone loop: the modern machines inherit that closed-loop architecture: the file describes the retrofit math: the modern cage wheel fit inside the old body: the expected capacity and fineness achieved: the payback time of the retrofit measured in the plant’s own energy bill: the massive inventory of the installed machines made the retrofit one of the most profitable projects of the 90s.

6. The Third Generation: The High-Efficiency Dynamic Classifiers

The modern cement grinding circuit operates the high-efficiency separator: the cage-type classifier in which the classifying air passes through a rotating cage of vanes: the feed enters with the air, the coarse particles are thrown outward by the cage speed and dropped to the grit cone, the fine particles pass through the gaps of the cage and exit with the air: the machine combines the sharp cut (imperfection 0.1 to 0.2), the low bypass (5 to 15 percent) and the fineness control across a wide range by the rotor speed only: this one machine unlocked the high-performance cements and the vertical mills:

• The rotor cage: the cylindrical vane wheel: 40 to 120 rpm for the 100-200 t/h machines: the speed is the primary fineness actuator;
• The air distribution: the guide vanes and the inlet spiral distribute the air evenly through the whole circumference of the cage: the balanced air eliminates the dead zones;
• The feed and the dispersion: the feed enters the classifying space fully dispersed: the de-agglomeration with the high velocity and the air jets: the dispersion is the secret of the sharp cut:
• The discharge: the coarse falls through the inner and outer discharge flaps, the fine exits with the air to the baghouse: the coarse stream carries the residual 8 to 15 percent of the fine product:
• The performance data: the cut range 12 to 60 micrometers, the fineness range of 3,000 to 6,000 cm2/g easily, the specific power 1.5 to 4 kWh/t:
• The variants: the classifiers of the vertical mills (the LNV separator on the raw and cement VRMs), the sand classification of the minerals, the reject and the conveying versions: the family of the same principle.

The third generation delivers what the cement industry needs: the narrow particle size distribution with the low fines below 3-4 microns (which would otherwise raise the water demand) and the minimal coarse tail above 32: the modern cement specification requires the distribution that improves the packing and the strength: the classifier is the instrument of that discipline: the file teaches the mechanical tuning of the cage speed, the vane angle, the airflow and the differential pressure with the practical examples from the production plants.

7. The Operating Parameters: Rotor Speed, Air Volume, Vanes and the Pressures

The operator of the third-generation separator commands a set of variables, and the fineness is the sum of their balance: the master variable is the rotor speed: every 10 percent of the speed change moves the fineness by roughly 300 to 500 cm2/g on a typical clinker: the second variable is the air volume through the classifier, controlled by the fan speed of the separator fan and the damper: the third is the internal geometry: the vane angle of the inlet spiral, the clearance of the rotor to the housing, and the position of the feed chutes: the plant calibrates the machine curves at the start-up and re-calibrates after every major service:

• The rotor speed: the direct fineness knob: the set by the control loop against the on-line Blain-like instrument;
• The separator fan: the air flow through the machine: the air-to-solid ratio on the typical clinker 0.8 to 1.5 m3/kg: the higher air, the coarser product at the same speed: the careful balance;
• The guide vanes: the tangential direction of the entering air: the angle scrolls the pre-rotation that helps or hinders the cage: the factory setting as the reference;
• The feed rate: the capacity of the classifier in kg/m3 of air: the overfeed builds the coarse leakage: the feed within the rating holds the curve:
• The differential pressure: the delta across the separator, 1500 to 3000 Pa typical: the blockage indicator of the air recipe and the material:
• The temperature: the mill gas at 70 to 110 °C on the cement circuit: the high temperatures loosen the air density and the age: the cold ambient air enters with the mill ventilation.

The operating parameter table of the modern high-efficiency separator (indicative):

Parameter	Raw mill duty	Cement finish duty	Effect of increase
Rotor speed, rpm	900 to 1400	450 to 800	finer product, lower capacity
Fan air flow, m3/h per t/h feed	1800 to 2500	1500 to 2200	coarser product at same speed
Guide vane opening	30 to 60%	40 to 70%	more air to the cage, finer
Differential pressure, Pa	2000 to 3500	1500 to 3000	blockage warning if rising alone
Feed material ratio, kg feed/(m3 air)	0.5 to 0.8	0.8 to 1.2	coarser product, lower efficiency

The parameter table is the starting picture of the tuning: each plant builds its own curves at the commissioning with the fineness test series at the speeds: the file includes the blank test matrix of the speed sweep and the reporting form: the curves become the operator’s reference, and the deviations from the curve become the alarm of the drift: the parameters of the machine, disciplined by the experiment, are the true voice of the separator.

8. The Fineness Control: From the Sieve Residue to the Laser Distribution

The purpose of the separator operation is the fineness target of the product: the control requires the measurement: the plant combines the rapid methods and the laboratory methods:

• The 45 micrometer sieve: the queen of the cement quality: the residue 1 to 15 percent depending on the cement type: the hourly sieve measurement on the product and the reject:
• The Blaine fineness: the 3500 to 4200 cm2/g classics, the specific surface: the measure of the cement quality and the water demand: the separator speed calibrates against the Blaine:
• The laser particle size: the full distribution: the percentage below 3, below 32 micrometers: the modern optimization: the plant moves from the residues to the distribution targets:
• The on-line analyzers: the pneumatic sampling and the on-line fineness (Blaine-like) or the laser: the closed loop: the separator speed trimmed every 2 to 5 minutes:
• The loop structure: the outer loops (the feed rate for the load control) and the inner loop (the separator speed for the fineness): the cascade: the synchronous control of the mill and the classifier.

Typical distribution targets of the cement products:

Cement	Fineness cm2/g	R45 residue %	R32 residue %	% below 3 micron
CEM I 42.5 R	3900 to 4200	2 to 6	8 to 14	10 to 14
CEM II/A-LL 42.5	4000 to 4300	2 to 5	7 to 12	11 to 15
CEM I 52.5	4900 to 5500	0.5 to 2	2 to 6	15 to 20
Slag blend CEM III/A	4200 to 4800	2 to 5	7 to 12	8 to 12

The fineness world moved from the single sieve to the distribution: the reason is the cement performance: the share between 3 and 32 micrometers contributes the strength, the <3 micron raises the water demand, the > 45 slow hydration: the separator shapes this distribution, and the modern plant defines its fineness target as the vector, not the scalar: the file includes the matrix of the target distributions and the method of the daily control from the single residue: the measurement discipline of the classification.

9. The Circuit Integration: The Mill Load, the Circulating Load and the Separator

The separator does not work alone: it is tuned together with the mill load: the law of the loop: the finer the separator cuts, the more the coarse returns to the mill, the higher the circulating load, the heavier the mill feed: the operating point of the circuit is the equilibrium of the two machines: the modern control coordinates the mill feed rate, the separator speed and the circulating load, and the plant benefits from the mathematical description of the loop:

• The circulating load: the mass flow of the return divided by the fresh feed: the range 150 to 350 percent: the optimization: the higher circulating load raises the classification sharpness effect but costs the pneumatic transport power;
• The mill mill factor: the load influence: the mill tonne per hour against the fineness: the families of the operating corners: the plant knows its curve interactive:
• The separators selection: the capacity margin: the separator must pass the peak of the feed from the mill: the bottleneck if undersized: the energy audit includes the machine:
• The dynamic control: the mill at constant load, the fineness by the separator: or the fineness fixed, the mill load by the feed: the two philosophies in the modern mills: the coordinated hybrid: both machines:
• The reject to the mill: the classifier reject content check: the 8 to 15 percent of the fine in the reject: too much fine in the reject: the wasted mill work:

Interaction trends of a finish grinding circuit:

Operating change	Mill load	Circulat. load	Fineness	Specific energy
Separator speed +10%	falls	rises	finer	rises
Separator fan +10%	stable	rises slightly	slightly finer	rises slightly
Mill feed +10%	rises	falls	coarser	falls
Vane angle closed	stable	rises	finer	rises

The interaction table is the practical course of the operator: every trim of the mill side shows on the separator side within minutes: the synchronized operation keeps the loop at the optimum: the file’s chapter 9 explains the calculation of the circulating load from the sieve data of the three streams and the interpretation of the graphs over the shifts: the loop is the organism, and the organism is the two machines.

10. The Daily Operating Routines: Start, Steady State and the Shift Checks

The daily operation of the separator is a sequence of the actions, and the file codifies the hourly routine:

• The start sequence: the auxiliary starts: the separator fan, then the rotor, then the feed onto the running machine: the sequence protects the bearings and the dispersion system: the interlock order per the manual;
• The steady-state check: the vibration, the temperature of the bearings (max 70 to 85 °C), the current of the rotor motor, the pressure drops, the oil level of the lubrication: the round walk every two hours;
• The fineness trim: the sieve results from the product feedback: the rotor speed adjustment per the plant’s curve: the changes in 2 to 5 percent steps with the settling time of the loop (20 to 40 minutes on the large circuits):
• The reject inspection: the visual check of the reject vs the fresh feed: the appearance of the coarse material: the early the sensor of the classification health;
• The end of shift: the log: the speeds, the loads, the fineness, the bearing temperatures, the abnormalities: the shift handover note;
• The filter monitoring: the baghouse of the separator air: the differential across the bags: the cleaning cycle: the pressure over 1500 Pa: the filter service.

The routine is the insurance: the separator failures announce themselves hours before the breakdown through the vibration and the drift: the plant organized the routine, the walk: the file includes the checklist sheet of the shift with the fields, the page to print: the discipline of the routine multiplies the machine life and the quality stability: the operator’s walk around the whirling machine is the cheapest condition monitoring of the plant.

11. The Maintenance and the Wear: The Rotor, the Vanes, the Seals and the Bearings

The separator wears where the velocity meets the material: the rotor vane tips, the guide vanes at the air entrance, the housing around the trap, and the discharge flaps: the wear pattern of the rotor: the abrasion by the fine quartz of the feed: the separator of the cement circuit wears through the finish mill’s lifetime and needs the periodic rebuilding: the wear refractor and the clearance control drive the classification stability:

• The rotor vanes: the wear on the tip edges: the profile change: the classification drifts: the inspection weekly in the hard campaigns, the rebuilding at the scheduled shutdowns;
• The rotor clearance: the gap between the rotor and the housing: the 2 to 8 mm typical: the worn clearance: the bypass: the air short-circuits: the check with the feeler gages at the overhauls;
• The guide vanes: the fixed vanes at the inlet: the wear and the angle drift: the rebuild with the hardened steel profiles: the air distribution returns to the design state:
• The bearing units: the top and bottom bearings of the vertical rotor: the temperature and the vibration monitored: the greasing regime of the file, 5-10 g per 100 hours, and the purges:
• The seals of the air ducts: the air loss distorts the classification: the flap and the seal hygiene at the joints: the air balance measured during the commissioning and the re-check at the annual stop:
• The wear protection: the modern machines line the high-abrasion zones with the wear-resistant tiles or the cast liners: the inspection instead of the worn walls.

The maintenance of the separator is on the critical path of the grinding plant: the file provides the wear inspection checklist, the spare parts list with the change frequency, and the job cards of the rotor change: the plant that monitors the rotor wear trend replaces the vanes before the classification drifts beyond the quality window: the planned maintenance of the classifier is a quality function, not only a mechanical one: the rotor of the machine, the vane of the quality.

12. The Troubleshooting Matrix: The Symptoms and the Remedies

The final operating chapter of the file is the troubleshooting matrix: the operator meets the symptom and looks up the cause and the remedy: the classification failure modes are finite, and the experienced plant recognizes them at a glance:

Symptom	Probable cause	Correction
Fineness coarser at the same speed	rotor vane wear, higher feed rate, coarse feed	speed up by steps, check the feed, inspect the rotor
Finer product at the same speed	fan air reduced, vane closure, clip moisture	restore the air flow, check the damper, dry the feed
Rotor current high	feed overload, cage damage, foreign material	reduce the feed, inspect the cage, clean the gap
High reject with the fine material	poor dispersion, high moisture, low air	increase the air, check the dispersion plates, warm the mill
Vibration high	rubble in the cage, bearing wear, loose bolts	remove the rubble, check the bearings, retighten
Pressure drop rising alone	blockage of the air duct or the filter	purge the duct, clean the filter bags, check the flaps

The matrix covers the 90 percent of the daily cases: the file extends the list to the 45 rows with the photos and the case studies: the operator posts the first ten rows at the control room: the discipline of the systematic troubleshooting replaces the trial and error: the machine is large and noisy, but its language is simple once the matrix is learned.

13. The Frequently Asked Questions

Which speed should I set for 4000 Blaine?

The speed is plant-specific: the fresh machines run the calibration curves from the factory test, but the wear, the feed and the air condition shift them: the plant’s the daily curve: set the speed for the target, confirm with the sieve or the Blaine measurement after 30-40 minutes of the steady operation, and correct within 5 percent steps: a reference for the typical 100 t/h cement separator: 50-65 percent of the maximum speed for the 4000 cm2/g with the air at the design volume.

Why does my product fineness jump at the same separator speed?

Check the feed rate, the feed fineness and the air flow first: the mill working state changes the feed to the separator: the moisture or the temperature also shifts the classification: the rotor wear changes the speed-fineness curve: the monthly Tromp check catches the drift: the variability of the classification is almost never the machine alone.

How do I measure the Tromp curve?

Take the representative samples of the feed to the separator, the coarse (reject), and the fine product simultaneously, sieve them over the family of the mesh (e.g. 4, 8, 16, 32, 45, 63, 90, 125 micrometers), and compute the separation probability per size: the file includes the worksheet: the measurement must be done at the steady state, and the mass balance must close within 5 percent for the valid the curve.

Is the separator the bottleneck of my grinding line?

Compare the separator capacity rating against the mill peak discharge: measure the feed rate and the return: if the circulating load rises while the feed stays and the fineness target swells, the separator is overloaded: the third generation machine upgrade: capacity gains of 20 to 40 percent: the energy audit of the file includes the separator capacity check at the step 3 of the audit.

How often should I clean the separator?

The internals need the inspection every 1000-2000 operating hours: the bags of the separator filter on the weekly purge cycle, the rotor vanes a dry-cleaned whenever the fineness drifts: the annual overhaul: the rotor rebuilt, the air seals renewed, the bearings measured: the cleaning schedule in the maintenance plan of the file.

14. Conclusion

The operation of the separator is the operation of the whole grinding circuit: the machine that judges every particle and keeps the mill’s work on the useful sizes: the static to the high efficiency: the speed to the Tromp: the operator who runs the separator with the discipline of the measurement runs the mill at the maximum capacity and the exact product: the classification is the art of the boundary, and the file gives the knife.

The Complete Cement Technical Package includes the Operation of Separators guide with the full parameter tables, the Tromp curve worksheets and the troubleshooting catalog: the one-time 249.99: the instant download: the library of the cement plant: the separator machinery: the operator and the production: the file that sorts the entire knowledge of the sorting: the career of the classifier, finished right.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.