Conveying System: Complete Technical Guide

The conveying system of the cement plant is the circulatory system of the operation: the belts, the bucket elevators, the screw conveyors and the air slides that move limestone, clinker, gypsum, additives and finished cement from the quarry gate to the packing station: the engineering of these lines decides the daily throughput, the energy consumption, the dust emission and the maintenance budget of the whole site: the conveyor is not a glamorous machine, but the fact of the industry is simple: when a conveyor stops, the plant stops with it: the guide in hand is the difference between a plant that flows and a plant that chokes.

The Complete Cement Technical Package (931 files including the books, the courses, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes this conveying system guide with its selection tables, its calculation examples and its maintenance schedules: the file serves both the young engineer who draws his first conveyor line and the veteran who is rebuilding the belt that fails every winter: this article follows the document section by section: the reader learns the full family of conveyors, the belt conveyor calculation method, the elevators, the screws, the air slides, the transfer chutes and the maintenance logic that keeps the tonnage moving.

The promise of this page: after reading, you can select the correct conveyor for every duty in the flowsheet, size a belt conveyor with your own numbers, understand the transfer points and the dust control, and read the failure analysis of the lines that keep breaking down: the page follows the same order as the file: the same tables, the same worked examples, the same language of the mill floor: the reader can follow the article with the document open beside it: the page is the map, the file is the territory.

1. The Role of the Conveying System in the Cement Flowsheet

The design of the flowsheet begins with the map of the movements: a modern cement plant moves between 20,000 and 100,000 tonnes of material per day across dozens of discrete transport links: the annual tonnage transported by the conveyors of a single large plant easily exceeds 20 million tonnes: even at one percent of material spillage and transfer losses, the numbers give every plant a strong commercial reason to study and to optimize its transport system.

• The quarry links: the apron feeder under the dump hopper, the belt from the primary crusher to the stockpile: coarse, abrasive and dusty material: the biggest wear of all the transport lines;
• The raw material links: the belts from the reclaimers to the raw mill feed bins, the elevators into the mill circuit: wet, sticky and seasonal material that changes with the weather;
• The process links: the raw meal screw conveyors and the pneumatic pumps, the kiln feed, the drag chains under the grate cooler: material above 500 degrees Celsius requires special machines and special designs;
• The finish grinding links: the clinker and gypsum feeders into the cement mill, the finished cement transport to the silos by elevator, screw conveyor and air slide;
• The dispatch links: the cement from the silos to the packers and to the bulk loading terminals: the metered feeding and the packing logistics;

The design logic behind every flowsheet: each material state has its preferred conveyor family, and each family has its own envelope of tonnage, distance, angle and lump size: the file of the package maps the material state to the conveyor machine with a selection table that is the first practical tool of the document.

Conveyor type	Material state	Distance	Incline	Typical cement role
Belt conveyor	Dry bulk, 0 to 300 mm	10 m to 5 km	0 to 20 deg	Main backbone hauls
Bucket elevator	Powder, granulate	15 to 60 m lift	vertical	Mill bins, silo tops
Screw conveyor	Powder, wet fines	2 to 40 m	0 to 20 deg	Short dosing lines
Air slide	Aerated powder	10 to 100 m	2 to 8 deg	Raw meal, cement
Drag chain	Coarse, hot clinker	10 to 80 m	0 to 45 deg	Clinker transport
Pneumatic pump	Clean powder	100 to 600 m	any	Silo feeding, long runs

The selection procedure of the file: define the material, its size distribution, the moisture, the temperature, the tonnage, the trajectory and the available space: the table eliminates the impossible candidates: the remaining machines compete on energy consumption, dust containment, maintenance cost and first cost: the professional chooses the family first and the size second, and never the reverse.

2. The Anatomy of the Belt Conveyor: The Workhorse of the Plant

The belt conveyor carries about 80 percent of the material movements in the typical cement plant: the belt is the workhorse because it is simple, continuous, cheap per metre of installed length, and easy to dust-proof: its anatomy is the belt, the drive unit, the idler stations, the pulleys, the loading point and the take-up: understanding each element explains 90 percent of the maintenance surprises of the plant.

• The belt itself: the carcass of fabric or steel cord with rubber covers, the width from 600 mm up to 2,400 mm in the quarry lines: the splice is the weakest point of the system and the discipline of the first-class splice service decides the life of the belt;
• The drive unit: the motor, the gearbox, the coupling and the drive pulley: the design must be sized for the running resistance, the gradient, the acceleration and the starting torque that can reach 140 percent of the nominal torque;
• The idler stations: the carrying idlers, typically the 35 degree troughing set, support the load while the return idlers guide the belt back: the spacing ranges from 0.8 m for fine material to 1.5 m for coarse material: idler quality decides the belt life;
• The loading point: the transfer chute feeds the belt with a centered, low-speed and soft discharge: the skirt boards seal the edges of the belt at the feed zone: about 80 percent of belt wear occurs at the loading point and the transfer;
• The take-up: the screw or gravity take-up keeps the belt stretched over the pulleys: the correct tension avoids slip on the drive pulley and excessive elongation of the belt;

An interesting fact of the file: the belt life in the cement plants of the industry is typically 5 to 10 years, and the main killers are the chutes, the scrapers, the mistracking and the splices: each of the failures carries a measurable cost: one misaligned transfer adds two to five percent to the energy demand of the line and brings dust and spillage with it.

3. The Belt Conveyor Sizing Calculation: The Numbers of the file

The guide takes the reader through the standard conveyor calculation following the philosophy of the international standard ISO 5048 (and the German DIN 22101 method): the steps are fixed and the guide fills them with cement-specific examples that the engineer in the plant recognizes:

• The material properties: the bulk density: the raw mix around 1.25 t/m3, the clinker 1.4 to 1.5 t/m3, the finished cement 1.1 to 1.2 t/m3: the lump size depends on the size of the material: the angle of repose, the moisture content and the abrasiveness grade;
• The belt speed: 2 to 3.5 m/s for raw and clinker material, up to 4.5 m/s on special long lines: the speed together with the width defines the cross-section of the load;
• The cross-section of the load: with the 35 troughing set the theoretical cross-section is about 0.10 to 0.12 m2 per metre of load width at the 2 m/s reference: the guide tabulates the filling factors for the belt widths;
• The capacity equation: Q (t/h) = 3600 x A (m2) x v (m/s) x rho (t/m3) x k, where k is the filling factor of the order of 0.8 to 0.85 for standard material on a troughed belt;
• The power demand: the sum of the empty-friction power, the loaded-friction power, the lifting power and the material acceleration power: the total is multiplied by the 1.2 to 1.4 service factor for the motor;

Worked example of the file: a clinker line carries 250 t/h on a 1,200 mm belt at 2.5 m/s, over 400 m horizontally and an 8 deg slope: the file computes: the empty power 8 kW, the load friction power 18 kW, the lift power for 8 m and 250 t/h about 5.4 kW, the acceleration small, the effective total near 32 kW and the drive motor 45 to 55 kW with the service factor: the example is the weekly design reality of the plant engineer: the tables of the file cover the 650, 800, 1,000, 1,200 and 1,400 mm belts.

Belt width (mm)	Speed (m/s)	Capacity (t/h at rho=1.25)	Typical drive (kW per 100 m)
650	2.0	140	up to 22
800	2.0	210	up to 30
1,000	2.5	380	up to 55
1,200	2.5	560	up to 75
1,400	3.0	850	up to 110

The tables allow a first sizing in the office in five minutes and the full check within the hour: the modern designer also checks the belt tension chain: the take-up stroke, the maximum tension at belt start, the sag between the idlers below 1 to 2 percent of the span: the file warns the beginner against the two classic mistakes: confusing the bulk density with the loose density of the loaded section, and overloading the belt width without checking the lump size: these two checks catch about 80 percent of the drawing errors.

4. The Bucket Elevator: The Vertical Transport of the Plant

The vertical transport in the cement plant belongs to the bucket elevator: it lifts the raw material, the clinker and the finished cement up to 90 metres into the tower silos and into the mill circuits: the machine lives in two families: the twin-chain elevators for coarse and heavy duty, and the belt bucket elevators for powders and fine material: the choice between the two is one of the first decisions in the vertical layout of any department.

• The twin-chain elevator: for clinker, hot material and coarse feed: the buckets are carried on two chains, the lift reaches 40 to 60 m, and the material enters through the feed throat: the wear of this machine concentrates in the chain pins and the bucket bolts;
• The belt bucket elevator: the continuous belt carries the buckets of the centrifugal discharge: the lift reaches 60 to 80 m for cement: the machine is the cleanest and the quietest of the vertical options;
• The drag chain conveyor: the choice for hot clinker above 250 deg C: the bucket chain drags the material in a closed casing: the robust option of the clinker transport lines;
• The feeding discipline: the elevator eats exactly what the chute gives it: the feed must be continuous, centered, slow and without impact: oversized lumps and surges choke the buckets and damage the chain;
• The discharge design: the centrifugal or continuous discharge: the head pulley speed is calculated so the buckets discharge clean over the head: the classic rule of the file keeps the ratio of the bucket throw correct for the pulley diameter;

The damage report of the industry: the bucket elevators are among the first causes of unscheduled stops in the raw and finish departments: the chain elongation of 2 to 4 percent, the bucket bolt fatigue, the head pulley slip and the chokings: the file shows the alignment procedure of the two shafts in both planes, the correction of the take-up and the weekly inspection of the buckets and the pockets: the elevator is a tall, expensive and dangerous machine and the file treats it with the respect it deserves.

5. The Screw Conveyor and the Dosing Lines

The screw conveyor is the compact machine of the plant: a spiral flight rotating inside a trough, pushing the material by the arch effect of the helix: in the cement plant the screw lives in the dosing work, the additive feeding, the dust return and the short mixing lines: the guide covers the sizes, the accuracies and the design pitfalls of the machine.

• The layout: horizontal, inclined to 20 to 25 degrees, or vertical for lifts up to a few metres: the screw length above 40 m is exceptional and demands intermediate hanger bearings;
• The capacity data: the screw diameters of the plants range from 150 to 800 mm and the capacities from 5 to 1,000 t/h: the rotational speed is 20 to 90 r/min for fine material and 15 to 50 r/min for granular;
• The volumetric character: the screw is a volumetric machine: its accuracy depends on the fill ratio: about 30 to 45 percent for powder and 25 to 30 percent for granular material: the gravimetric weigh feeder is the friend of the dosing accuracy;
• The seals: the stuffing boxes and the glands at the discharge end: cement is fine dust and the screw leaks pressure and dust at the shaft: the seal quality is the weak point of every screw;
• The covers and the safety: the trough covers against dust and contact: the wind-down of the long tubes and the inspection doors for cleaning;

The rule of thumb of the guide: use the screw for the additive dosing and for the short lines, use the elevator for the vertical and long routes: the screw is rarely the right machine for a 500 m haul: the friction power grows with the length, the intermediate bearings wear, and the fines break down and dust everywhere: the correct flowsheet piece has the screw at the end of a belt, not as a substitute for one.

6. The Air Slide and the Aerated Powder Transport

The air slide is the elegant machine of the cement technology: a closed chute with a porous fabric bed through which low-pressure air fluidizes the powder so that it flows like a liquid down a slope of only 2 to 8 degrees, with no moving parts except the fan: the air slide is the standard of the cement mills and the raw meal systems of the modern plant.

• The principle: the fluidization of the powder makes it behave as a liquid: the material slides downhill, smoothed by the aeration: no moving parts in the material path, no wear of the flights;
• The geometry: the slope of 4 to 10 degrees for cement and 3 to 8 degrees for raw meal: the capacity reaches 200 to 400 t/h per metre of bed width in the fully fluidized state;
• The media: the air distribution cloth of synthetic fabric or ceramic plates: the porous bed with the correct aperture: the air demand of 0.5 to 1.5 m3/min per square metre of bed area;
• The air supply: the low-pressure blower of 5 to 15 mbar: the volume of 5 to 10 m3/min for a 10 m line: the fan is the only mover in the system;
• The sections: the slide is built in 6 to 10 metre sections with inspection ports, aeration chambers and cleanout doors: the discharge end couples directly to the next machine;

The air slide in the plant moves the finished cement from mill to packer and the raw meal to the kiln, at an energy cost of about one third of the belt drive, with the dust fully contained: the limitations: the powder must be dry and fluidizable: moisture and lumps kill the flow and choke the bed: the file details the start-up sequence: the aeration air first for 1 to 2 minutes, then the material valve: and the shutdown in the reverse order: the details that look small and decide the reliability.

7. The Transfer Chutes: The Quiet Determinant of the Belt Life

Every transfer point in the plant is a chute: the whole conveying discipline of the world runs on the chutes, and the chute design is where the conveying system earns or loses the money: the file gives the chute a full chapter, and the reason is the statistics of the failures: more than half of the belt damage, the chokings and the process delays of the plant happen at the transfers.

• The flow lines: the material must flow on the smooth chute surfaces: for cement the sliding angle against the steel should be 60 to 70 degrees: the most common error is the flat steel plate that catches the sticky material;
• The impact control: at the loading the material falls and damages the belt: the belt accepts the material at the same speed and the same direction as the belt: the transfer with the reduced fall height slows the impact: the severe drop chute;
• The rock box design: the material falls onto material: the stone in-flow passes through the choke of the product-on-product: the zero of the iron-on-steel impact: the transfer design results in the long service of the belt covers;
• The skirt boards: the rubber sealing around the edges of the belt at the feed zone prevent the penetration of the material under the belt: the skirting length, the rubber quality and the belt contact are the design parameters;
• The maintenance access: the cleanout doors, the air venting to the dedusting filter and the visible inspection ports: about 80 percent of the chute dust is displaced air that must be vented;

The acid test of the guide: the chute is well designed if the material runs through it without choking for one full shift of the plant: the rock boxes and the material-lined chutes extend the belt life by two to five times against the bare steel: the steel chute with the plunge drops chokes and tears: the chapter of the file is the one the plants half-read and the package insists on fully.

8. The Transfer Points and the Dust Control

The transfer point of the cement plant is the biggest dust source of the process: the fine material falls, the air is displaced and the dust rises: the regulations of the modern industry expect the visible fugitive dust close to zero: the modern plant is therefore designed dust-tight and the file treats the dust as a first-class engineering problem:

• The air displacement: the material entering the chute pushes the air out: the dusty air routes to the vents and the filters: the hood design and the venting volume of 0.5 to 1.5 m3 of air per m3 of material;
• The skirting seals: the two-piece skirt, the cloth and the bottom wipers: the skirt is buried in the material and sealed against the belt: the correct repair of the wear keeps the dust where it belongs;
• The belt cleaners: the primary scraper at the head pulley with the tungsten tip, the secondary cleaner at the discharge, the third and the full hygiene stations in the dusty lines: the cleaner reduces the spillage and the housekeeping work;
• The dust collectors: the bag filter at the major transfers: the air-to-cloth ratio of 2 to 6 m3 of air per m2 of cloth per minute: the dedicated guides of the package for the bag house are the standard reference of the industry;
• The enclosures: the canopy over the transfer and the full covers with the clamps over the troughed lines: the simple galvanized versions and the insulated versions for the hot service;

The number that impresses the beginners: a well-run belt system of the modern plant is 99.5 to 99.9 percent dust-tight: the rest is housekeeping: the guide sets the emission limits of the modern plants at 10 to 20 mg/Nm3 at the check points: the transfer environment runs 8,000 hours a year and every gram of dust that escapes is the cost of the process: the chapter of the file gives the complete box of solutions.

9. The Maintenance of the Conveyor Lines: The Calendar of the Plant

The maintenance of the conveying system is a calendar that the plant follows with the same discipline as the process log: the guide offers the complete maintenance program with the intervals, the content and the register templates:

Interval	The belt lines	The elevators	The screws
Daily	visual walk: spillage, tracking, scrapers, dust, hot spots	noise, chain, drive temperature	seals, fill, dust
Weekly	grease points, plows, scrapers, take-up stroke	chain stretch, bucket bolts	coupling, bearings
Monthly	pulley lagging, idlers, belt thickness	alignment, pins, sprockets	flight-to-liner clearance
Quarterly	audit of the transfer points, structure, rails	safety guards, brakes	trough wear, shafts
Annual	belt splice, tension, X-ray of the splices	overhaul, chains, buckets	shaft seals, screw segments

The main killers found in the files of the plants: the top five causes of the conveyor downtime are: the transfer point chokes, the belt mistracking, the idler bearing failures, the splice failures and the drive group failures: each one of them is recognized in its early stage only by the inspection that is actually performed: the file teaches the reading of the belt wear profile, the log of the bearing temperatures and the oil analysis of the gearboxes: the discipline of the logging is the eyes and the ears of the silent machinery.

10. The Energy Economy of the Conveying

The conveying energy is only 2 to 5 percent of the plant electricity, but the number of the motor hours is enormous: each belt runs 6,000 to 8,500 hours a year and the aggregated motor power of the conveying of a 5,000 t/d plant is typically 3,000 to 6,000 kW: the small savings per line multiply:

• The speed control: the variable speed drives on the lines that run partially loaded save 20 to 40 percent of the motor energy: the load-regulated lines of the raw and the clinker feed: the huge lever;
• The planning of the loading: the conveyor selected with the capacity matching the true hourly average instead of the peak: the fixed-speed motors run the expensive idle hours of the low-load shifts;
• The good idlers: the low-resistance idlers with the quality bearings save 30 to 50 percent of the rolling resistance against the worn impellers: the steel of the quality stations pays back in power and in life;
• The moderate speeds: at the same tonnage a lower speed with a wider belt saves the energy: the guide shows the trade-off table of the width versus the speed for the same capacity;
• The load tracking: the belt scale data on the shared lines: the empty and the loaded distribution over the week: the optimizer shifts the operations to the full lines: the energy and the wear together: the spreadsheets of the package follow the same logic;

The concrete case of the guide: a pair of quarry lines of 2 km each, 1.5 m wide, run half loaded: with the variable speed drives and the better idlers the plant saves about 380 MWh per year, more than 40,000 USD at typical tariffs, for an investment that returns within the year: the conveying energy is thin per line but the multiplication over the plant is the budget of a department.

11. The Safety Around the Conveyors: The Non-Negotiable Chapter

The conveyors hurt and the conveyors kill: the trapped limbs in the nip points, the belts that start while the worker clears a jam, the chokes that somebody enters to clean under a running line: the safety chapter of the file is the shortest and the hardest of the whole guide: the rules of the plants of the world:

• The lock-out and the isolation: every entry to a transfer, an elevator pit, a head or a chute begins with the isolation: the switch locked, the key with the worker: the photo evidence of the procedure;
• The guards: the nip points at the skirt, the pulleys and the take-up: the flange guards and the drive guards: the geometry of the guards follows the safety standards of the conveyor machinery;
• The emergency stops: the pull-cords on both sides along the whole length, the stop buttons at every transfer station and the interlocks of the sequence: the alarm on the control room when a cord is pulled;
• The personal protection: the harnesses on the high walks, the safety of the walkways, the absolute ban of riding the belt and the ban of crossing over a running belt: the work inside the head with two persons and an observer;
• The fire awareness: the conveyor bearings and the rubber belt fire are real hazards of the plant: the temperature monitoring of the pulleys, the suppression near the long lines and the weekly check of the extinguishers:

The statistics of the industry place the conveyors and the elevators among the top five sources of the serious injuries in the cement plants: the file follows the safety, as it should: every procedure of the package: the cleared jam, the spliced belt, the aligned pulley: begins with the same sentence: the stop, the isolate, the verify: the discipline of the safe entry is not a rule of paperwork, it is the difference between the report and the memory.

12. The Instrumentation and the Control of the Conveying System

The conveying system of the modern plant is a part of the plant control network: the file covers the instrumentation of the lines: the belt scales, the speed sensors, the metal detectors, the alignment switches, the plugged-chute detectors, the protection relays and the interlocks of the sequence.

• The belt scale: the weigh frames of four to eight idler rollers with the accuracy of 0.5 to 1 percent after calibration: the belt scale counts the quarry tonnage, the mill feed and the dispatch: the exact tonnages of the production and the reconciliation:
• The metal detection: the tramp metal on the belts before the crushers and the mills: the metal detectors and the magnetic separators in series: the protection of the crusher and the mill from the scrap: the catcher and the diverting gate;
• The sequence interlocking: the downstream stop of the whole line when the belt stops: the speed switch at 20 percent of the slip, the tilt switch in the chutes and the plugged-chute detectors of the transfer: the interlock of the system and its breaking: the automation logic;
• The condition monitoring: the vibrations of the gearboxes and the bearings, the temperature sensors of the hot pulleys and the belt alignment cameras: the expert systems that read the trends and warn the planner:
• The CMMS integration: the computerized maintenance system with the intervals, the part lists and the stock: the alarms of the failures that close the loop: the file carries the templates of the modern plants;

The control chapter closes the loop: the conveying transport is now observed, counted and alarmed: the historian collects the months: the trend of the throughput, the load of every motor and the signature of the next failure: the operator screen shows the skeleton of the plant in mimic and the planner works from the data instead of the memory: the file hands the architecture, the parts and the protocols, and the newcomer builds the mimic of his own plant from them.

13. The Frequently Asked Questions About the Conveying Systems

What is the difference between a belt conveyor and a screw conveyor?

The belt conveyor moves large tonnages over long distances at a low energy per tonne with a sparse maintenance: the screw conveyor is the short solution for the dosing and for the short transfers: the rule of the guide: over 50 metres with bulk material, prefer the belt: under that, the screw wins on the compactness and the sealing.

Why does the raw mill use an air slide and not a belt?

The air slide needs no moving parts in the material path, no wear of the flights and no drives along the route, and it seals the powder completely: the price is the slope and the aeration: the cement and the raw meal are perfectly suited: for the coarse and the abrasive material, the belt remains the answer.

How do I stop a belt from mistracking?

The mistracking has only a few causes: the misaligned pulleys, the wrong splicing, the uneven loading, the worn idlers and the belt makes an issue: the correction order is always the same: verify the alignment of the structure, then the pulleys, then the splice geometry, then the loading: most cases are solved by the structure inspection and nothing else: the file gives the step-by-step crowning of the operators.

What is the best angle of the skirt board against the belt?

The skirt sealing edges should run parallel to the belt direction with a gap of 2 to 10 mm and the bottom edge in contact: the seal must never be pinned into the belt: the skirt length must cover the complete loading zone of the chute: the design, the tight, the pleasure of the file.

Does the package include the excel calculators of the belt?

Yes: the Complete Cement Technical Package includes the spreadsheet tools of the belt conveyor selection and the screw conveyor sizing: the engineers input the tonnage, the density and the length and receive the width, the speed and the power in seconds: the 931 files include the tools of this guide.

Can I use one belt for the wet and the dry material?

One belt can handle both if the loading, the speed and the cleanliness are managed: the wet sticky material demands the smooth idlers and the correct cleaners, and the change of the material changes the energy: the guide recommends the dedicated sources in the design and the answer.

13. The New Technologies of the Conveying: Where the File Points

The file is not nostalgic and the last technical chapter opens the future: the conveying systems of the plants are becoming measured, automated and physically lighter:

• The long-distance corridors: the single belt lines of 10 km with the intermediate drives bring the material from the far quarry to the plant without the fleet of trucks: the energy of the belt is per tonne below the truck by a factor of three to four;
• The tubular belt conveyors: the belt closes into a tube for the steep and curved routes and for the zero spillage: the radius of the curves makes the conveyor follow the terrain: the modern quarrying:
• The pipe feeding and the digital twins: the sensor networks on the lines feed the digital models: the predicted wear, the predicted splice life and the spare parts just in time: the disruptive maintenance of the new plants;
• The electrification: the regenerative drives on the descending lines return the energy to the grid: the quarry declines become the power producers of the plant network: the reverse of every old habit;

The conveying system is the living backbone of the cement plant: the chapter of the future tells the reader that the discipline of the basics: the correct selection, the correct sizing, the dust control and the maintenance: remains the foundation of every digital upgrade: the file of the package: the foundation with the vision: the perfect document for the engineer who wants both.

14. Conclusion of the Guide

The conveying system is the circulatory system of the cement plant and this guide is its anatomy textbook: the family of the machines, the sizing of the belts, the elevators, the screws, the air slides, the chutes, the dust control, the maintenance, the energy, the safety and the control: the professional who walks the line with the tables of this file sees the plant with different eyes: every noise, every leak and every belt tension speak the same language.

The Complete Cement Technical Package includes the conveying system guide with the tables, the worked calculations, the maintenance registers and the Excel tools: the one-time purchase of 249.99: the instant download: the library of the cement: the conveying file is one of the 931: the knowledge of the moving plant: the belts, the elevators and the slides: the cement engineering, complete.

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.