Clinker Coolers: Complete Technical Guide

Clinker coolers are the machines that receive the red-hot clinker from the rotary kiln and bring it down to the temperature of the storage: the coolers are much more than temperature devices: they are the heat recovery engines of the pyro system, the quality instruments of the clinker and the stability link of the whole line: this article is the complete technical guide to the coolers: the types, the physics, the parameters, the operation, the maintenance and the modern developments.

The Complete Cement Technical Package (931 files including the courses, the books, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes the Clinker Coolers module of the cement process technology course: the module covers the cooler technology in the depth of the industry practice: the cooler families, the mechanical construction, the heat recovery, the operation, the selection and the maintenance: this article walks the same content in the written form, section by section, with the numbers of the trade.

Why the coolers deserve their own chapter: the modern grate cooler recovers 60 to 75 percent of the clinker heat back to the process, feeding the secondary air of the kiln at 900 to 1,200 degrees and the tertiary air of the calciner: the cooler is also the equipment where the clinker quality is fixed by the quenching, and where the availability of the line is decided during the hot hours: the module, like this article, gives the complete understanding of the machines that close the pyro section.

1. The Cooler Families: The Historical and Modern Designs

The cooler chapter opens with the family tree of the clinker coolers, because each type is understood through its place in the history:

• The rotary cooler: the first mechanical cooler of the industry: a slowly rotating drum inclined with the counter-flow air: the clinker tumbled inside and the air entered the kiln directly: simple and robust, but with the poor heat recovery and the limited capacity: it served the medium kilns of the early era and remains on a few old lines;
• The planetary (satellite) cooler: the tubes mounted around the kiln shell itself: the clinker passes through the tubes and its heat radiates back into the kiln: the planetary cooler has no fan and no drive of its own, a handsome mechanical trick, but its diameter is limited by the kiln and the availability suffers: it is still seen on some lines around the world;
• The reciprocating grate cooler: the family that won the industry: the horizontal grate moves back and forth, pushing the clinker bed, while the air is blown through the bed from below: the first generation appeared after WWII and the generations evolved to the present day: the module presents the lineage: the first, the second and the third generation;
• The roller grate and the cross-bar coolers: the modern variants: the grate is replaced by the roller sieves or the overlapping cross bars, distributing the air more evenly through the bed: the cross-bar cooler (the moving-floor type) is a fresh generation of the industry, carrying the air beams and the lower maintenance: the module compares the modern systems fairly;

The module is honest about the strengths: the rotation and the satellite are history, the grate line is the present, and the modern grate technologies compete today on the recovery, the maintenance and the ownership cost: the reader learns the genealogy and the characteristics of each type with the numbers.

2. The Physics of the Grate Cooling: The Bed and the Air

The grate cooler works on the fluid-solid exchange of the packed bed, and the module teaches the physics before the mechanics:

• The clinker bed: the clinker forms the bed of 600 to 1,000 millimetres of depth on the grate: the bed is the packed body with the void fraction: the hot clinker at the top and the bottom of the bed all exchange with the air that rises through it: the bed is both the heat source and the resistor of the air flow;
• The air flow through the bed: the air is forced under the grate and passes through the holes of the grate plates into the bed: the air velocity in the bed voids is 1 to 3 m/s of the void-based: the pressure drop of the bed, 3,000-9,000 Pa, grows with the depth and the fines: the module: the flow-pressure relation and the fans of the zones;
• The heat exchange in the bed: the air entering cold at the bottom picks up the heat of the clinker and leaves hot at the top: the exchange is efficient in the shallow well-sorted beds and degraded by the segregation of the coarse and the fuel coal: the module gives the exchange efficiency curves of the grate cooler operating data;
• The air enthalpy balance: the energy of the clinker minus the energy of the cooled clinker equals the energy of the heated air plus the radiation and the losses: the module computes the balance for the 5,000 t/d line: the heat recovery, the demands and the losses are all accounted;

The physics of the bed is the intellectual core: the engineer who reads the cooler instruments but not the bed does not read the cooler: the module teaches the “the bed as the living element”: the correct depth, the correct air distribution and the correct temperature profile of the bed are the physics of the whole chapter.

3. The Construction of the Grate Cooler: The Mechanical Anatomy

The modern grate cooler is a sophisticated machine, and the module walks its construction part by part:

• The feed end: the clinker falls from the kiln into the feed chute and the distribution gate spreads it over the first section of the grate: the interface with the kiln hood and the kiln seal closes the process: the module: the refractory and the protection of the feed end, the first contact with the 1,400-degree clinker;
• The grate sections: the cooler is divided into the sections and the zones: each zone has its own air plenum below the grate and its own fans: the grate plates of the cast steel or the hard alloys, with the aeration holes: the plates move with the reciprocating frame: the module gives the drawing of the plate and the frame;
• The air distribution system: the fans below the cooler deliver the air per zone: the high-pressure fans at the inlet where the clinker is hottest, the larger volumes at the middle and the tail: the module teaches the fan duty and the pressure of the zones: the hydraulic of the modern coolers modulates the air of the 8-12 zones;
• The discharge end: the last section, the clinker breaker (the crusher of the large pieces), the chute to the transfer conveyor and the temperature measurement: the module: the clinker breaker and the hydraulic, the return of the spill, the loss control;

The anatomy chapter shows the cooler as the plant of its own: the module coverage: the mechanical, the air, the hydraulics and the instrumentation of the machine, with the design drawings and the data of the standard sizes: the reader can discuss the specification of a cooler with the vendord, knowing which section is critical and why.

4. The Operation of the Cooler: The Parameters of the Day

The cooling discipline is an operating discipline, and the module teaches the parameters of the daily control:

• The grate speed (the residence): the grate speed determines the residence of the clinker in the cooler: the regulation is coupled to the kiln production: the stable bed depth of 600-1,000 mm leads the automatic speed control: the module: the speed control loop and the design of the tie-in with the kiln feed;
• The zone air flows: each of the air zones follows its own setpoint: the high air at the inlet, the lower in the middle, the last: the module: the distribution of the air and the target temperatures: the air is the refrigerant of the bed, and its distribution is the art of the cooler;
• The secondary and the tertiary air: the two recovery air streams are the top priorities: the module: the hood temperature (the 900-1,200°C), the tertiary air temperature (the 850-1,000°C) and the way the operating does not let the recovery fall: the recovery is the economic operating of the day;
• The discharge temperature: the cooled clinker of the 70-130°C: the temperature is under the automatic and the manual watch: the rising temperature and the response: the air, the grate speed: the module: the cooling margin and the alarms of the hot clinker;

The operating chapter is the hand of the module: the engineer of the control room receives the normal windows of the cooler: the bed depth, the pressure per zone, the temperatures: the excursion cases: the blackouts, the kiln discharge of the big clinker: the module teaches the responses and the coordination with the kiln operator: the cooler operation discipline is a pre-requirement of the pyro operation.

5. The Heat Recovery: The Cooler as the Energy Machine

If the preheater recovers the heat of the gas, the cooler recovers the heat of the solid: the module devotes its quantitative part to the recovery:

• The recovered heat: the clinker leaves the kiln with 350-450 kcal/kg of the sensible heat: the modern grate cooler returns 60-75% into the secondary and the tertiary air: in the numbers: about 300-350 kcal/kg flow back to the flames of the kiln and the calciner: the module: the calculation of the recovery of the 5,000 t/d line in the terms of the fuel tonnes;
• The cool-linked volume: the total air flow of the cooler: 2.2-2.6 kg of air per kg of clinker: the excess beyond the combustion is vented at 250-350°C: the module teaches the balance between the cooling and the recovery: the excess vented = the loss of the unused heat:
• The design features for the recovery: the “recuperation” zones: the first section of the cooler is the box from which the secondary and the tertiary air are drawn: the deep bed and the press recover the heat: the module explains the recuperation design of the new coolers: the air recuperation fabric of the modern recovery;
• The waste heat of the cooler: the remaining exhaust: the cooling air that must leave: the modern plants add the waste heat recovery boilers to the cooler exhaust: the power generation of the 5-20 kWh per tonne of clinker from the cooler exhaust alone, the economics for the high-power regions: the module: the cooler: the last reservoir of the heat of the plant;

The recovery chapter gives the cooler its place in the energy map of the plant: the module equips the reader to compute the value of the cooler improvement in the fuel and the power of the year: the investment in the cooler modernization is evaluated in the language of the energy bill, not in the romance of the engineering.

6. The Quality Effects of the Cooling: The Quenching of the Clinker

The cooling rate is a quality control layer, and the module devotes the chapters to the effects:

• The rapid cooling and the glass: the fast cooling below 1,250°C freezes the melt into the glass: the glass activates the grinding and the hydration: the slow cooling lets the alite degrade into the belite and the free lime: the module: the mechanism and the laboratory evidence of the quenched vs the slow cooled clinker;
• The grindability: the cooled clinker: its hardness and the brittleness: the well-cooled clinker grinds with the better kWh/t: the module gives the grindability index of the cooled clinker and the mill economics of the cooling practice: the quality: the strength of the cement and the energy of the mill both improve: the cooling is the win-win of the pyro;
• The magnesia and the soundness: the large periclase crystals in the slowly cooled clinker bring the expansion problems in the hardened concrete: the rapid cooling keeps the MgO in the smaller crystals for the sound cement: the module: the soundness cases: the cooling as the safeguard of the produced cement;
• The hydration and the strength: the glassy phase hydrates faster and the early strength rises: the strength curves of the rapid vs the slow cooled clinker: the module: the “cooling is a strength technology” statement of the cement laboratory: and the measured difference in the 1day-28day:

The quality chapter connects the cooler to the cement: the module closes the loop between the pyro operation and the quality laboratory: the engineer of the coolers is also the beginner of the quality: the improvement of the cooling recovery and the quality of the clinker are the same action: the dual benefit of the module.

7. The Problems of the Coolers and the Troubleshooting

Every cooler has its problems, and the module carries the practical troubleshooting section:

• The grate plate failures: the grate plates crack, distort and burn: the module: the replacement of the plates, the choice of the material, the cooling of the plate with the air and the prevention: the number of the failed plates is the top-5 of the reported cooler problems;
• The bed dead zones and the “corns”: the clinker plugs in the corners of the cooler: the air bypasses: the “bubble” and the hot of the bed: the module: the air cannons, the quadrant orifices, the kill-bar: the establishment of the uniform bed: the craft of the “anti-corn” management;
• The clinker breakers and the jams: the breakers jam on the large coppice from the kiln: the discharge is blocked: the module: the breaker design, the stop and the removal of the oversized pieces, and the coordination with the kiln: the large balls of the kiln: the “coolerspread” and the prevention;
• The air leaks and the false air: the casing leaks let in the cold air: the recovery falls, the fan power up: the module: the leak hunting, the seal systems of the housing, the pressure test of the cool: the false air discipline of the cooler: as in the preheater: every kilogram of the false air is a slug on the recovery;

The troubleshooting chapter is the field guide: the symptom and the cause and the action for the daily problems of the cooler: the module gives the same structure as the preheater chapter: the reading of the cooler: the pressures, the temperatures, the vibration, the inspection: the engineer closes the chapter with the ability to keep the cooler out of trouble.

8. The Design of the Coolers: The Sizing and the Selection

The final technical chapter covers the design: how the cooler is sized for the line and how the plant selects the type:

• The sizing parameters: the clinker throughput (the t/d), the specific cooling: the cooling load (the clinker t/24h per m2 of the grate), the air demand, the grate area: the module gives the sizing of the grate surface for the type of the production: the 30-40 tonnes of clinker per m2 of the grate area per 24 h for the modern coolers: the chart of the sizing;
• The selection criteria: the capacity, the heat recovery demand, the clinker size, the fuel used (the alternative fuels affect the cooling), the maintenance philosophy, the capex and the opex: the module builds the decision matrix of the cooler selection: the plant engineer lays the parameters of his case and reads the candidate types:
• The integration: the cooler is chosen in balance with the kiln and the preheater: the tertiary air demand, the hood space, the heat of the plant: the module teaches the system view: the cooler is not a standalone: it is the last element of the same whole: the design skills that the vendor provides, the module gives the understanding to the buyer;
• The upgrades of the existing coolers: many plants modernize their existing coolers rather than replace them: the module covers the modern retrofit: the air distribution, the new zones, the recuperation, the control: the upgrading of the existing cooler is the cost-efficient program of the older plants: the module: the upgrade roadmap:

The design chapter completes the module: the reader passes from the machine knowledge to the project knowledge: the ability to evaluate, buy or upgrade the cooler of the line: the course therefore covers both the physical fundamentals and the industrial practice of the design, and the module closes with the full circle: from the physics to the numbers to the machine.

9. The Frequently Asked Questions

What is the difference between the clinker cooling and the clinker coolers?

The cooling is the process, the coolers are the machines: the clinkers are cooled in the coolers: the cooling chapter of the course describes the process (the purpose and the physics), and this coolers chapter describes the machinery family (the types, the construction, the operation): the two chapters of the course are complementary, and the package’s the course stages the pair of modules for the complete understanding.

How long does the clinker stay in the cooler?

Typically 20 to 40 minutes in the modern grate cooler: the residence time is set by the grate speed which follows the kiln output: the deep bed of 600-1,000 mm of clinker requires the extended time: the residence is the fundamental of the heat exchange and is the hidden timing of the whole cooling: the module: the residence values and the calculations.

Why is the air of the cooler hot and useful?

Because the air removes the heat from the clinker: the air heated to 900-1,200 degrees at the kiln–cooler interface is the secondary air of the kiln, and the 850-1,000 degree air to the calciner is the tertiary air: the preheated air improves the fuel efficiency of the two flames: this is the heat recovery of the cooler: the “recycling” of the heat of the process.

What is the “cooler bed” and why is it important?

The bed is the layer of the clinker spread on the grate: the targeted depth of 600-1,000 mm: the bed is the location of the heat exchange: its depth, the distribution, the temperature: the air channeled through the bed picks up the heat by the entire volume of the bed: the “bed” is the heart of the cooler: its condition is the prime indicator of the cooler state.

Why doesn’t the industry simply use the water-cooling of the clinker?

Because the water would quench the clinker with the steam explosion risk and destroy the material handling and the quality: the water in the clinker forms the steam in the storage and the mills, the cement quality and have the moisture issue: the industry cools the clinker with the air only, and recovers the heat of the air: the water is only a small add-on for the final clinker-typical sprays at the very end of a few plants, and the module covers the limits of that.

What is the difference between the second and the third generation grate coolers?

The second generation (around 1970-1990) uses the mechanical grate: the reciprocating, the air from the plenum through the bed with the under-grate pressure: the third generation (the 1990s): the grate plate with the integrated air, the separated air zones and the hydraulic drive: the third generation recovers more heat with a smaller air flow: the module’s the comparison of the generations: the specific air of the modern 2.0 kg/kg clinker or less against the 2.5-3.0 of the old.

10. Conclusion

The clinker coolers close the pyro process with the machines that recover the heat, fix the quality and protect the line availability: the family of the coolers (rotary, planetary, grate), the physics of the bed and the air, the construction, the operation, the recovery of 60-75%, the quenching quality, the troubleshooting and the design: the module of the course, and this article, have walked the total subject: the reader now sees the cooler as the full partner of the kiln: the machine that gives the heat back and the quality of the day.

The Clinker Coolers module belongs to the Complete Cement Technical Package (931 files: courses, books, Excel tools and presentations: $249.99 one-time, instant download, lifetime access): together with the Clinker Cooling chapter and the preheater and the kiln modules, the complete thermal sequence of the pyro section in the package: the engineer who works the three chapters reads the whole burning line with the master’s eye: the PayPal button below opens the download of the century: the knowledge of the cooling and beyond: the single click: the whole plant inside the disk.

13. The Cooler Retrofit: The Modernization of the Existing

The older plants rarely replace the clinker coolers as a whole: the modernization path and its stages are part of the engineers’ work, and the file’s chapter visits them:

• The increase of the grate area: the extension or the replacement of the grate plate zones to raise the cooling capacity and reduce the clinker layer thickness at the same design load: the capacity rescue of the older grate;
• The air distribution redo: the modern controlled flow plates replace the old boxes, the over/under-cooling of the zones balanced: the supply of the secondary air to the kiln improves, the kiln burners thank;
• The moving floor conversions: the grate plates modernization for the walking floor, the balanced distribution and the lower maintenance of the older designs:
• The auto controls: the cooler fans automatically trim the clinker bed temperature and the break of the grate drives: the thermal AO of the old cooler: the yielded: the stable cooling of the red clinker: the higher output, the same footprint:

The retrofit perspective is the reality of the plants: the modern cooler technology increasingly budgets the investment for the existing lines first, and the Operating discipline: the result reuses the trunnion, the casing and the silo of the quarry: the clinker cooling of the existing plant brought to the current level: the retrofit of the practical plant, the file’s last chapter of the coolers.

The performance of the cooler is reported in the two quotients the engineers use everywhere: the cooling intensity in tons of clinker per hour per square meter of grate (typically 20-40 t/h per m2), and the cooler efficiency expressed as the secondary air temperature and the heat loss per kilogram of clinker (80-130 kcal/kg in the modern grates against the older 150-180): the two numbers summarize the whole cooler and the file’s tables allow the engineer to find his own plant on the chart: the position on the chart decides the retrofit priority: the numbers, the map, the order.

13. The Cooler Master Table: The Family Portrait

The file summits the cooler family in two plates of the reference table: the mechanical side and the performance side:

• The mechanical colleagues: the grate area in the square meters, the number of the fans and their kW, the weight of the cooler and its floor area: the plant owners compare the layouts of the equipment;
• The performance colleagues: the cooling rate in the t/h per m2 (20-40 of the moderns), the venting% age (10-30), the clinker exit temperature, the specific heat recovery: the interquartile of the industry;
• The operating windows: the bed height in the mm (500-800 of the cross-flow), the grate speed in the m/min, the air velocities: the set points of the day;

The table plates let the engineer position his plant in the family: the contractors quote the tables of the file for the new kiln and the plant verifies the performance of the day against the same rows: the family portrait of the coolers: the one-page competence of the cooling.

The Dynamic Cooling Above the Velocity Threshold

The modern grate ’s detail: the cooling air crosses the clinker at a velocity that keeps the fine fines suspended — the velocity must stay above the threshold of the dust ’s and that cost is the invisible pressure drop of the grate:

• The fluidization: the fine clinker stays on the plate by the velocity limit: below the threshold the fines drop through the slots and the clinker at the bottom overheats: the fan curve and the grate ’s resistance decide the working zone of the design;
• The cleaning: every grate has the chamber clean — the clinker stone removed by the turn of the roller, the fine sand dropped through the slots into the conveying flight chamber below, and the chamber cleaned every shift: the cleaning cycle of the file ’s procedures list the leaks as the sign of the worn seats;
• The measuring: the differential pressure across the grate is the live index of the bed condition: the operator reads the dp trend and adjusts the grate strokes and the fan dampers to keep the bed at the engineered height: the automatic mode does this in the modern plants, the kV curves in the control room;

The velocity threshold is the reason the air is regulated per zone: the engineers use the velocity map of the file to verify the fan ’s zones after the modifications: the velocity and the cooling of the modern cross-flow grate are one engineering story.

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.