Prehomogenization And Storage: Complete Technical Guide

The prehomogenization and the storage is the discipline that makes the cement plant possible: the quarry delivers a material whose chemistry swings, and the plant must feed the kiln a constant tide: between the quarry and the mix there stand the reclaimers: the blending beds laid in the interleaved layers, the homogenizing silos aerating the powder, and the storage that absorbs the stops of the crusher and the mills: the art of the prehomogenization is the art of converting the variable into the constant.

The numbers tell the whole story: a quarry bench may present the CaO between 46 and 54% on a bad week; a well-designed preblending circuit delivers the kiln feed with the LSF variation of plus or minus 1.0-1.5 points: the ratio between the input variability and the output variability is the “homogenizing effect” of the installation: 5:1 for the good bed, 8:1 or better for the aerated silo: this article explains how those ratios are built, measured and managed, with the design tables that the file of the Complete Cement Technical Package provides in its storage section.

The complete package (931 files: the design handbooks of the bulk handling, the Excel models of the beds and the silos, the plant documents: $249.99 one time: instant download via PayPal) includes this whole chapter; the article below follows the logic of the file: the principles of the layering, the geometry of the beds, the reclaimers, the silo aerodynamics, the moisture and the housekeeping, and the practical operating notes of the yards.

1. The Statistical Principle: How the Layering Smoothes the Wave

The prehomogenization of the granular materials rests on one statistical fact: the average of many independent samples has a smaller variance than the samples themselves; the engineering consequence: if the incoming material is cut into N layers of thickness 1/N each, and the outlet takes them simultaneously in the cross-section, the resulting blend is the mean of the N layers.

• The formula: for the random uncorrelated variations, the standard deviation at the outlet of the perfect bed is approximately the input deviation divided by the square root of the number of layers: the bed with 100 layers reduces the sigma by a factor 10: the math of the averages;
• The realistic factor: the mixing is not perfect, the layers smear, so the practical homogenizing effect of the bed is 5:1 to 8:1, not the theoretical 10:1 of the 100 layers;
• The correlated variation: when the chemistry drifts slowly (the long-term geological trend of the quarry), the layering alone cannot cancel the trend: the bed must be laid against the trend, or the plant needs the correction material;
• The consequence for design: the more layers, the better the blend: 50-200 layers are the classics of the bed: the design compromise with the reclaimer path speed and the tonnage;

The file’s statistical chapter derives the formulas and provides the small Excel that the reader can feed with the measured sigma of his own quarry: the plant which installed a bed and trusted the “blending effect 8” without measuring is the plant that later discovered the effect was 3.

2. The Geometry of the Beds: The Chevron, the Windrow and the Cone-Parking

The bed is filled in layers of the bulk: the classic fillings are the chevron, the windrow and the cone-shell / parking lot:

Method	Layering	Reclaim direction	Typical effect	Notes
Chevron	Triangular layers along the ridge line	Across the face (side)	5:1 – 8:1	Simple, the classic; the segregation of the coarse at the toe
Windrow	Longitudinal rows side by side	Into the side of the rows	4:1 – 6:1	Less segregation, better for the sticky clays
Circle (transverse filling)	Concentric layers, the entire face	Full face cut	7:1 – 10:1	Best effect, circular hall used
Cone-shell out of the silo	Shear layers around the cone	Center discharge	3:1 – 5:1	The conical silo of the small plants

The chevron is the workhorse of the cement industry: the stacker runs along the ridge and drops the material in the alternated layers; the reclaim takes the full cross-section: the design parameters of the bed: the width/height (1:2 to 1:1.6), the length decides the tonnage of the pile (5000-40000 t typical), the layer count is set by the stacker speed and the reclaim cycle: the file gives the geometry calculator: the volume of the bed from the height and the angle of repose (37-40 degrees for the crushed limestone).

3. The Stackers: The Machines that Build the Layers

The stacker is the layer builder, and its type follows the bed type:

• The rail-mounted boom stacker: the parallelogram or the luffing boom travels the full length of the bed and lays the layers from one end to the other: the highest production (up to 2000-4000 t/h); the chevron and the windrow both served;
• The traveling tripper on the belt: the simplest and the cheapest: the belt discharges over the pile along the run: the material falls from the small height and the dust is low: fine for the moderate beds;
• The radial and the circular stacker: the fixed pivot with the boom sweeping the arc: serves the circular blending bed, which is the densest per footprint of the land;
• The portable/mobile stacker: moved between the several stockpiles of the secondary materials: the operators move it in hours;
• The layering considerations: the stacker travels with the constant advance speed so the layer thickness is even: the segregation is minimized by the drop height control (the dust suppression) and the half-swing motion of the shuttle.

The dispatch to the crusher never stops for the bed changeover: the two bays of the full-out/full-in (“the two piles”) the classic of the layout: the stacker fills the Bay 1 while the reclaimer empties Bay 2, and the changeover doesn’t disturb the flow: the same logic applies to the storage stacks of the finished products (the silos and the domes of the cement itself, as described in the package’s plant layout chapters).

4. The Reclaimers: The Cross-Cutting of the Layers

The reclaimer is the heart of the smoothing: the side-cutting machines that break the layers simultaneously:

• The bridge scraper: the bridge spans the bed, the scraper chains travel across the face, the material falls in the central run: the perfect face cut: the effect of the bed is fully exploited: the most common on the large beds;
• The portal (overhead) scraper: the gantry above the pile with the scraping, the portal reclaims the windrows and the chevrons of the medium capacities:
• The bucket wheel reclaimer: the wheel chews the face edge: the robust machine of the clay and the sticky materials: the effect slightly less than the bridge scraper;
• The drum-type reclaimer: the center drum with the scrapers on the conic face: for the circular stockpiles, the continuous reclaim of the 360 degrees;
• The reclaim rate control: the variable speed of the scraper regulates the tonnage to the plant: the flow and the moisture variation vs the face: the starved rate starves the crusher; the overspeed rakes the fresh material unreclaimed;

The reclaimers decide the dust and the maintenance of the yard: the service room of the machines is the “house” of the quarry: the file includes the reclaimer specs, the comparison matrix (cost, effect, capacity, sticky behavior) and the maintenance schedule: the plants of the industry spend the running hours of the yard where the reclaimer is the king.

5. The Homogenizing Silos: The Pneumatic Blend of the Fine Material

After the bed, one more stage of the discharge smoothing stands in the modern plant: the aerated (blending) silo of the raw meal:

• The continuous aeration silo: the silo floor divided into the sectors of the porous tiles; the air is pressurized alternately in the sectors: the powder fluidizes, the outflow mixes the axial: a surge of the fresh powder from the inlet mixes with the age of the silo: the “preblending” of the all-silo;
• The effect: the ratios out of the aeration silo are the 5:1 to 12:1, on top of the bed’s 5:1: the two in series (the bed + the silo) are the standard answer to the variable quarry: the total effect of the chain often reaches the 30:1 on the LSF sigma;
• The connected fans and the controls: the roots blowers (the 0.04-0.1 mbar per meter of the pad) and the sequencing valves cycle the sectors (10-40 min per the rotation); the aeration air also carries the fines to the bag filter;
• The operation: the fill level 30-70% ideally, the short-circuiting avoided by the “one third empty” rule, the silo emptied and refilled per batch in the fully mixed mode, or run continuously with the batch controller of the files;
• The multi-compartment: the large plants use the box chambers (the old X-silo) with the gravity mixing: the SILO X-concept of … the package supplies the design concept, the number of the compartments and the airflow table.

The storage of the raw meal also faces the “caking” enemy: the hygroscopic fine powder of the meal forms the crust and the bridges, and the aeration is the anti-cake of first line: the file’s silo operation chapter includes the bridging prevention and the relief measures: the sumps, the emptying cones, the aerated walk; the plugged raw meal silo is one of the classic “the kiln goes no,” problems that the plant learns once.

6. The Storage of the Raw Materials: The Volume, the Time and the Capacity

The storage is the buffer between the mining and the process: its size is an economic calculation:

• The design rule: the raw stone of the crusher + the process: the storage the plant: 2-5 days of the run-of-mine in the quarry silo under the crusher; 3-7 days of the limestone in the stockpile; 7-14 days of the clay in the covered piled yards (the clay moisture the exposure);
• The covered vs open: the open stockpile (the enormous, cheap, the windblown dust, the winter moisture) vs the covered hall (the capex 10-25% higher, the moisture protected, the winter value); the decision table of the file; the arid zones of the world store open with the bail out of the rain;
• The clay handling at the stock: the sticky clay compacts under its own weight in the pile: the excavator digging the compacted wall is slow; the “dome stable” piles of the clay are built with the live-bottom; the humidity story again;
• The limestone splitting: the plant stores the high-CaO and the low-CaO stone in the separate piles: the blending from the two piles in the ratio runs the LSF: the double-dip of the current system;
• The finished product analogy: the same stock logic serves the products: the cement silos for the days of the dispatch, the clinker storage (the quench pit), bag warehouses (the humidity guarded); the complete storage chapter of the package:

The covered storage today also serves the environmental rules: the dust extraction and the water runoff of the piles: the file’s environmental annexe lists the required hoppers, the filtration of the stacker, and the recycling of the yard water; the design that ignores them pauses the permission of the plant.

7. The Ratio: The Homogenization Effect in the Design and the Operation

The homogenizing effect (the ratio of the input sigma to the output sigma) is both the design target and the operational KPI:

• The measure: the standard deviation of the LSF (or the CaCO3) measured at the bed inlet (the belt sampler) and at the silo outlet (the raw meal sampler) for 30-60 days: the quotient is the effective ratio;
• The target: above 5 for the bed, above 8 for the silo, the combined 20-30: the LSF of the kiln feed should stay within +- 1.0 to 1.5 points of the set value (99% of the time);
• The failure modes: the low effect: the layer too few (the slow stacker vs the fast reclaimer), the segregation of the toes, the moisture channeling, the aeration plugged: the troubleshooting matrix of the file;
• The marketing KPI: the LSF spread is the number the quality dept quotes in the audits: a plant quoted with the 40% of the feed outside the spec has a homogenizing problem, not a quality problem:
• The optimization: the layer number vs the effect chart: the file’s model shows the 30 layers gives 4.5:1, the 60 gives 6:1, the 120 gives 8:1: the diminishing returns flag the investment wisely;

The effect also depends on the material’s particle size distribution: the coarse and the fine segregate in the pile (the fines at the inside of the cone, the coarse at the roundels) and the reclaim must take the whole section: the bridging scraper does; the flushing of the center (the “drainage” effect) can deliver the coarse-rich batch – the classic “the rock comes then the dust” phenomenon the old hands know.

8. The Worked Numbers: The Design of the Limestone Bed

The practical example that the file repeats, so the reader can repeat on his own deposit:

Given: the plant 3000 t/d of clinker; the raw consumption 1.55 t/t clinker = 4650 t/d of the crushed feed; the incoming limestone LSF-relevant sigma ±3.5 points of the CaCO3 76% (measured by the 20 days of the bank samples); the target LSF sigma at the kiln ±1.2 points, total required: the reduction the 2.9 times.

• Step 1: the bed with 120 layers and the chevron can give the factor 8 (per the model of the file); the silo aerated 8:1; the combined 8*8=64 (safely over the needed 2.9) – the chain capacity is more than enough, so the design can run the bed on the cheap mode: 40-60 layers;
• Step 2: the bed volume for the 4650 t/d + the 30% safety = 6000 t of the active: at the density 1.55 t/m3 loose = 3900 m3: with the height 10 m and the angle of repose 37 degrees: the length of the bed: equation L = V/A-sec: the file’s formula (the cross-section of the chevron ≈ 0.31 x H^2 / tan(alpha)…), the length ~110 m: the geometry;
• Step 3: the equipment: a boom stacker 1500 t/h + one bridge reclaimer 1000 t/h: the reclaim cycle in the field: 6:1 live vs the volumes; the operator: the two bays 60 m each, the walls of the concrete.
• Step 4: the cost estimate: the stacker 1.4-2.2 million, the reclaimer 2.5-3.5 million, the civil 40-60% of the machine: the file’s standard table 2025 prices.

The result: the bed delivers the feed with LSF sigma-the 1.2 points, the kiln feed stable, the fuel 2-4% saved (the kiln burns the constant better than the waves), and the alternative of the two/quarry-blend slack small: the worked sheet that the reader can load with his numbers is in the package’s prehomogenization Excel.

The detail numbers of the equipment: the stacker boom reach of 25-35 m with the belt speed 2-3 m/s, the stacking capacity 800-3000 t/h, the luffing 0-20 degrees; the bridge reclaimer with the 6-10 m face, the scraping speed 0.1-0.3 m/s and the cutting of the 150-400 t/h per pass: the electrical demand of the pair around 60-120 kW installed: the belt from the reclaimer to the raw silo transfers at the same nominal rate as the crusher discharge, so the plant never strangles the bed with the misaligned capacities: the file’s equipment table lists the makes and the models of the industry with the ides of the installed power, the weights and the availability figures (92-96% of the annual time).

The thermodynamic note of the storage: the raw materials hold the heat of their history: the winter stone at 10-25 mm carries the frozen water, the summer stone the radiation: the drying load of the raw mill changes with the season of the stock: the plants with the covered store run the constant; the open stockpile in the wet region pays the dryer fuel from the october to the april: the file’s energy chapters translate the moisture into the kcal that the dryer burns: the storage housekeeping is also the energy economy: every 1% of the moisture removed at the yard saves the 8-14 kcal/kg of the clinker at the drying of the raw mill: the number of the file.

The stockout accounting: the exact inventory of the pile at the month’s end reconciles the tonnes of the bed to the crusher output: the volume of the chevron is computed with the surveyed profiles (the drone or the laser) and the bulk density determined by the boxed samples: the discrepancy target below 1% of the movement: the file includes the inventory workbook with the profile-driven volume calculator: the yard people who know the true stock never fake the running count.

9. The Housekeeping: The Dust, the Spillage, the Safety of the Yard

The yards and the silos are made of the real hygiene of the plant: the five disciplines that run them:

• The dust control: the pickup point covers, the water spray at the stacker, the filters on the transfer towers: the enclosure of the reclaim: the monitoring at the fence (the TSP and PM10): the file’s emission table prescribes by the country:
• The spillage battle: the belt foreign material at the transfer, the scraper and the wiper presses, the return belts: the weekly spill audit of the yard: the spillage is the fuel of the fires and the dollars;
• The CO2 and the fires: the coal and the petcoke storage is a separate physics (the spontaneous ignition, the nitrogen inertion): the raw yard avoids the coal co-location: the safety rules: the no-smoking buffers, the water points, the CO2 detectors:
• The confined spaces: the silo clearing is the classic confined space entry: the lockout-tagout, the gas tests, the rescue plan: the fatal accidents of the industry come from the silo washouts:
• The stockpile audits: the volume measurement by the drone scanning vs the belt scales reconciled quarterly: the 1% of the unaccounted material at 3000 t/d is 30 t/d x 365 = 10,000 t/y of the money:

The housekeeping is also the operating history: the file’s section 11 is the walkthrough and the checklists of the yard (the shift round of 25 points) which the auditors of the safety stress: the reader leaves with the checklist that the walk around tomorrow morning.

10. The Operating Notes: The Regime of the Yards in the Daily Run

From the control room, the prehomogenization is a daily routine with the delicate points:

• The bay discipline: the “never reclaim a half bed” rule: cutting the face of the half-filled bed pulls the layers of the one end, the blending effect drops: the operators complete the fill before the reclaim;
• The moisture vs the winter: the raw material moisture warns with the bed’s lag: the wet of the january appears in the feed 3-4 days later: the control room compensates the feed with the dryer/damper preview:
• The corrective screw: the small corrective doses (sand and iron) are fed near the bed or the pile input: the corrections also ride the same homogenizing: the corrections are a layer of the bed, not the jetting into the silo;
• The quality board: the chemists publish the CaCO3 roller chart of the bed core: the “bed profile” stored: the operator knows exactly which part of the current pile is low and which part high: the pairing of the strategy comes from the profile:
• The surpluses and the catches: the sporadic off-spec loads (the wet quarried cornerstones) are routed to the side yard, never into the bed; the “poison pile” receives them behind the specs: the QC gives the “no go” list:

The best operators of the industry run the yard like the bank note of the currency: the bed profile on the wall of the control, the reclaim plan for tomorrow: the plants without the profile fly blind and the kiln pays: the file’s operating manual is the very list that the experienced supervisors keep in the drawer.

The alternatives of the small and the mid plants: not every plant follows the giant bed: the small plants (below 1500 t/d of clinker) use the lighter systems: the belt tripper and the discharge cart over the simple pile with the two storage cells (the standard for 100-600 t/h); the circular stockpile (the radius 30-50 m) with the central reclaim, the compact round footprint and the total enclosure, the effect 6:1 to 8:1; the multi-user dome shared between the limestone and the clay with the internal walls: the savings of the civil works at the cost of the flexibility: the open circuit with the front loader transfer (the old small plants) that works only with the very constant deposits and the recipe-free limestone: the file’s decision table weighs the capex, the effect, the land and the automation levels, with a recommendation per plant size.

The reclaim without the segregation: the uniformity of the face is the enemy of the segregation: the bridge scraper reclaims with the vertical face; the loaders cutting the pile from the outside pull the coarse of the toe first: the plant that uses the loader blending must level the pile and cut the full height in the thin slices: the operators learn this in the first season: the discipline of the full-face cutting is repeated in the file’s operator lessons: the profile of the pile is the truth, and the scoop of the loader is the liar.

11. The Operating: The Silo The Q Issues and the Case of the Bed

The following mini-cases are the recurring faces of the engineer on the forum, all of them included in the file’s “troubleshooting 25”:

• The LSF drop at the change of the quarry bench: the pattern: the feed LSF wavers and falls by 3-4 points for the hours, until the detection is full: the remedy: the bed split of the benches: the layer plan forces the mixed extractive: the quarry plan + the bed model;
• The “patient” of the aeration silo: the silo channels (the air the route of the path): the ratio falls from 9 to 3: the remedies: the rebalance of the aeration matrix, the silo cleaning, the reviewed padding: the file: the diagnosis tree;
• The coarse ridge of the chevron: the toe of the chevron collects the coarse and the dust: the reclaim face cuts it in the chunks: the feed spikes to the raw mills: the remedy: the bed capping (the fine layer at the top) or the reclaimer speed program:
• The winter mud: the wet and the striated the clays build the walls of the yard: the freezes matter: the remedy: the windrow filling with the drain layer, the spring cleanup of the sump:
• The drum killer: the caked powder in the silo after the long stop: the “wedding” of the disaster: the handheld vibration + the slow fill: the days don’t push: the file’s recovery plan:

Each case in the file is written with the symptoms, the cause, the remedy and the prevention: the style of the old handbooks of the process: the prehomogenization is the quiet discipline, but its problems knock loud: the file and this guide prepare the engineer for the five classics and the hundred variants.

12. The Conclusion

The prehomogenization and the storage is the first line of the quality defense of the plant: the quarry gives the paroxysms, the bed and the silo return the fine wave: the design of the layers, the reclaim of the face, the aeration of the powder and the discipline of the bays deliver the kiln a constant feed: the operators who master the yard hold the LSF band, the stable short free lime, the lower fuel bill and the reliable product: the numbers of this article translate directly to the currency of the plant.

The Complete Cement Technical Package (931 files: the storage and the preblending handbooks, the estimation Excel of the beds, the silo models and the troubleshooting, the training lessons: US$249.99 one-time: the instant download by PayPal) includes the complete prehomogenization chapter with the tables that the design office and the plant control room use; the button below opens the payment: the library of the cement professional is delivered: the file of the package is the desk copy of this article, and this article is the shortest class of the file.

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.