Innovations In Cement Manufacturing: Complete Guide & Downlo

With the change to predominantly dry process clinker manufacturing technology, the water usage of cement plants has been substantially reduced compared to wet process technology, and Chapter 6.4 of the Innovations in Cement Manufacturing series places that historical reduction at the center of its subject: water is still necessary, however, for non-contact cooling of drives, bearings, air compressors, air conditioners, and various probes in hot process stages as well as hot gas streams, both in the pyro-processing system and cement grinding mills. The efficiency of water circulation, retention, and recycling becomes paramount in areas of water scarcity, and a water retention, processing, and recycling pond at a cement plant in the United States is the chapter’s illustration of exactly that practice. This article expands the original chapter into a complete technical package covering the water uses of the modern dry-process plant, the cooling water systems that carry the plant’s largest water duty, the treatment and conditioning of the water through its cycles, the retention, processing, and recycling infrastructure that the scarcity of water has made fundamental, the water balance of the plant and its management, and the innovations of the zero-discharge era that have made the cement plant a model of industrial water stewardship.

The purpose of this article is to give the utilities engineer, the environmental manager, and the plant designer a complete command of the water discipline of the cement plant: where the water goes, how the cooling systems are designed and operated, how the water is treated to protect the equipment and the environment, how the retention and the processing of the plant water close the recycling loops, how the water balance is metered, computed, and minimized, and how the innovations of water management, from the closed-loop cooling to the zero-liquid-discharge designs, are applied in the dry-process plants of the modern era.

1. Water in the Wet Era and the Dry Turn

The water history of the cement industry is the history of the process change that dominates this series. The wet process, the technology that built the industry of the first half of the twentieth century, mixed the raw materials with 30 to 40 percent water into a slurry, pumped the slurry into the long rotary kilns, and evaporated that water with the kiln’s heat: the wet kilns consumed a half tonne of water or more per tonne of clinker for the slurry alone, their specific heat consumption was double that of the modern dry process because of the evaporation, and their plants drew their water from whatever source the region could supply. The water usage of the cement industry was, in that era, a first-order environmental issue, the competition with the municipalities and the agriculture for the scarce resources, and the driver of the slurry pump stations and the water treatment plants that the wet plants carried.

The turn to the dry process, the suspension preheaters, the precalciners, and the vertical raw mills of the succeeding chapters, removed the slurry’s water entirely: the dry raw meal is ground, blended, and fed to the kiln as a powder, and the only process water of the dry kiln is the dust suppression, the conditioning, and the cooling duties that the next sections detail. The reduction was historical in scale: the modern dry plant’s process water consumption, per tonne of clinker, is measured in tens of liters if the non-contact cooling is recycled, against the hundreds of liters of the wet plants, and the energy reduction followed the water reduction, because the evaporation heat is gone.

The remaining water duties of the dry process are the subject of this chapter, and they are the non-contact duties that the chapter names: the cooling of the drives, the bearings, and the lubrication circuits of the kiln, the mills, and the crushers; the cooling of the air compressors and the air conditioning of the electrical and the control rooms; the cooling of the probes and the sampling equipment in the hot process stages and the hot gas streams; the conditioning of the dust for the return and the disposal; the dust suppression of the material handling; and the sanitary and the potable water of the plant’s personnel. Each duty has its own water quality requirements, its own treatment, and its own place in the plant’s balance.

The chapter’s central theme follows from the list: because the modern plant’s remaining water uses are largely non-contact and largely recyclable, the efficiency of the circulation, the retention, and the recycling decides the plant’s water footprint, and in the regions of water scarcity, which include a growing share of the industry’s worldwide capacity, that efficiency is no longer an environmental nicety but an operating requirement, the difference between the plant that operates and the plant that cannot obtain its make-up water.

2. The Water Uses of the Modern Plant

The water uses of the modern dry-process plant divide into the process, the utility, and the sanitary families. The process family, though small in volume, is the most water-chemistry-sensitive: the dust conditioning and the pelletization of the collected dusts, the dust suppression of the crushers, the stockpiles, and the roads, the slurry and the wetting duties of the special processes, and the water injection into the mills where the finish mill cooling or the moisture control requires it. Each of these contacts the process materials, and each therefore returns to the plant’s circuits carrying the chemistry it picked up: the contact water of the dust conditioning is alkaline, loaded with the fine solids and the dissolved salts, and its management is the discipline of the retention and the processing sections.

The utility family is the volume leader: the cooling water of the non-contact services that the chapter enumerates. The kiln’s main drive and its auxiliary drives, the mill gear reducers and the lubrication systems, the air compressors, the bearings of the crushers and the fans, the air-conditioning and the electrical equipment cooling, and the sampling probes of the hot process gas streams, all reject their waste heat to water in the closed and the open circuits that the next section describes. The utility water is non-contact by design, which is why it can circulate, be cooled, and be reused indefinitely, and its quality is maintained by the treatment and the blowdown that the maintenance of the circuits requires.

The sanitary family serves the personnel and the facilities: the potable water of the buildings and the amenities, the showers and the washrooms, the laboratories, and the fire water of the hydrant systems. The potable water is typically purchased or drawn from the dedicated source and kept entirely separate from the process circuits, for the obvious reasons of the public health and the contamination risk, while the fire water, a large instantaneous demand, is often stored in dedicated tanks or drawn from the retention ponds that the later sections describe, and its quality requirements are the modest ones of the fire suppression duty.

The modern plants complete the water picture with the rainfall and the drainage: the storm water of the yards and the roofs, and the process drainage of the equipment areas, are collected, directed, and managed as part of the plant’s water inventory, with the oil separators and the settling facilities protecting the environment, and the clean storm water often joining the retention ponds that supply the utility circuits, so that the plant’s water supply is blended from the sources, the purchased make-up, the recycled circuits, and the captured rainfall.

3. The Cooling Water Systems

The cooling water systems of the cement plant are its largest water infrastructure, and their design families are the once-through and the recirculating systems. The once-through system draws the water from the source, passes it through the heat exchanges, and discharges it: its simplicity and its low capital cost suit the water-rich plants of the past, but its water demand is enormous, its discharge is thermally and chemically regulated, and its era has passed with the era of the abundant water. The recirculating system, the modern standard, circulates the same water through the plant’s heat exchangers and through a cooling tower, where the heat is rejected to the air, so that the plant’s net withdrawal is only the make-up that replaces the tower losses and the blowdown.

The cooling tower is the heart of the recirculating system, and its engineering is the engineering of the evaporation: the warm water from the circuits is distributed over the fill, where it falls in thin films through the air drawn by the fans, and a fraction of the water evaporates, absorbing the heat of the vaporization that cools the remainder. The tower types of the industry are the induced-draft and the forced-draft towers, the counterflow and the crossflow arrangements, and the natural-draft hyperboloid towers of the very large stations, and the tower’s performance parameters, the approach to the wet-bulb temperature, the range of the cooling, and the drift of the water droplets, are the report cards of its operation. The evaporation of the tower is the plant’s largest water loss, and the recirculation ratio, the circulation divided by the make-up, is the measure of the system’s water economy, with the well-run modern plants reaching ratios above 20.

The non-cooling-tower alternatives serve the special places of the plant: the closed-loop cooling systems, in which a treated water or a glycol-water circuit cools the critical equipment through the plate heat exchangers against the tower water, protect the kiln bearings and the mill lubrication systems from the fouling and the pressure excursions of the open circuit; and the dry and the evaporative coolers, the air-cooled radiators, serve the small duties and the remote stations where the water cannot be justified, at the cost of the higher electrical consumption of the air fans. The chapter’s modern perspective values exactly these choices: the closed loops for the sensitive equipment, the dry coolers where the water is scarcer than the electricity, and the towers where the water economy is best.

The control and the instrumentation of the cooling circuits complete their discipline: the tower fans are controlled by the return-water temperature, the make-up and the blowdown by the conductivity and the level, the pumps by the pressure of the system’s head, and the heat exchangers by the approach temperatures of their services. The automation of the cooling systems, like the automation of the process, holds the circuits at their design points, and the energy of the cooling, the fans and the pumps, is itself a managed item of the plant’s electrical balance, so that the water economy and the energy economy of the plant are optimized together.

4. Water Treatment: Protecting the Circuits and the Environment

The water of the recirculating circuits needs its chemistry managed, because the natural water, heated and concentrated by the evaporation, deposits, corrodes, and grows: the hardness salts of the raw water, concentrated in the tower sump, scale the heat exchangers and the tower fill; the dissolved oxygen and the chlorides attack the metals; and the suspended solids and the biological growths foul the surfaces and the orifices. The water treatment of the recirculating systems is the engineering of these three enemies, and its instruments are the chemical dosing and the blowdown: the scale inhibitors, the phosphonates and the polymers, hold the hardness salts in solution; the corrosion inhibitors, the azoles and the stabilized phosphates, passivate the metal surfaces; and the biocides, the oxidizing and the non-oxidizing agents, control the biological populations, while the blowdown, the deliberate discharge of the concentrated water, holds the dissolved solids below their limits.

The cycles of concentration govern the treatment program: the cycles, the ratio of the dissolved solids in the circulating water to their concentration in the make-up, are limited by the scaling and the corrosion chemistry, with the typical towers running at three to six cycles, and the blowdown rate that holds the cycles in their window is the treatment’s main water cost. The savings of the higher cycles, less make-up, less blowdown, and less chemical, are balanced against the treatment’s ability to hold the water stable, and the modern programs, with the automated dosing controlled by the conductivity and the pH analyzers, hold the cycles safely at the higher ends of their ranges.

The water quality of the process-contact circuits is a separate discipline: the dust-conditioning water, the mill-injection water, and the wash water must be clean enough for their duties and compatible with the materials they contact, and their treatment, the filtration, the settling, and the pH control, belongs to the processing of the plant’s waters described in the next section. The quality of the make-up water itself decides the whole treatment burden: the plants on the hard groundwater treat their make-up through the softeners and the reverse-osmosis where the feed quality demands, while the plants on the good surface water run simpler programs, and the treatment train of a modern plant reflects its water source as directly as its process reflects its raw materials.

The environmental side of the water treatment is the discharge discipline: the blowdown and the discharges of the plant must meet the receiving-water standards, the suspended solids, the pH, the temperature, and the chemical residues, and the plants’ discharge permits define the limits that the treatment and the processing must meet. The trajectory of the industry is toward the discharge elimination, the recycling of the blowdown into the process, and the zero-discharge designs of the subsequent sections, and the treatment facilities of the modern plants are increasingly designed as part of that zero-discharge architecture rather than as the independent waste-treatment units of the past.

5. Retention, Processing, and the Recycling Ponds

The centerpiece of the chapter’s practice is the water retention, processing, and recycling infrastructure, and its heart is the pond system that the chapter’s illustration shows: the plant collects its waters, the cooling blowdown, the process drainages, the equipment-area runoff, and the storm water, into the retention ponds, where they settle, cool, and equalize, and the recovered water is then processed and returned to the circuits that can use it. The pond is the plant’s water reservoir and its first treatment step at once: the residence time in the pond settles the suspended solids, neutralizes the pH swings by the blending, and buffers the plant against the supply variations, and the modern plants design their pond capacities from the plant’s water balance and its storm statistics rather than from the site convenience.

The processing of the pond water follows its condition: the settled water is drawn, filtered, and, where the chemistry requires, conditioned to the quality of its next service, and the clean water returns to the utility circuits, the dust conditioning, and the non-contact duties, while the sludge of the ponds, the settled fine solids, is dredged and handled with the plant’s other solid streams. The recycling pond at the chapter’s plant is the model: the same water, cycled through the plant’s services and the pond’s settling, serves the plant’s cooling and its processing continuously, with only the evaporation and the blown-down losses replaced by the make-up and the captured rainfall.

The water balance of the recycling system is the engineer’s instrument: the inputs, the make-up, the rainfall on the ponds and the yards, and the process water sources; the outputs, the evaporation of the tower and the ponds, the drift, the blowdown, the water carried in the products and the sludges, and the discharges; and the internal flows, the recirculations of the circuits and the transfers between the ponds and the services, are metered and computed, so that the plant knows, month by month, the fate of every cubic meter. The water balance is the frame of the conservation programs of the plant, because every deviation, an unexplained draw, a rising blowdown, or a falling pond level, speaks in the balance’s language.

The pond system’s design details are the practical craft of the discipline: the ponds are lined and diked against the seepage, sized with the freeboard for the storms, fitted with the inlet baffles and the outlet weirs that manage the settling and the draw, and equipped with the pumps, the screens, and the level and the quality instrumentation that the operation needs. The safety of the ponds, the restricted access and the depth awareness, is part of the plant’s safety practice, because the retention ponds, like all water bodies on industrial sites, carry their own hazards, and the environmental management of the ponds, the spill prevention of the chemical storage around them, and the groundwater monitoring of the lined sites, belongs to the same regulatory discipline as the rest of the plant’s environmental systems.

6. The Water Balance of the Cement Plant

The following table presents a typical water balance frame of a modern dry-process plant, expressed in liters per tonne of clinker, with the ranges that the engineer uses for planning and the comparison with the wet-process era that defines the chapter’s perspective:

Water item	Modern dry plant, liters/t clinker	Wet-process comparison	Typical management
Slurry water (wet process only)	0	400–600	eliminated by dry grinding
Cooling make-up (tower + losses)	80–150	150–300	recycled at 20+ cycles
Dust conditioning and suppression	10–30	10–30	from recycled water
Process contact water	5–20	5–20	processed and recycled
Sanitary and potable	5–15	5–15	separate supply system
Total net withdrawal	100–200	600–1,000 and up	minimized by recycling

The balance’s message is the chapter’s message: the dry process cut the industry’s process water by an order of magnitude at the source, and the recycling practice cuts the remaining withdrawal by another order of magnitude at the circuits. The typical modern dry plant’s net water withdrawal, 100 to 200 liters per tonne of clinker, against the wet plants’ 600 to 1,000 and more, is the water steward’s comparison across the era, and the trajectory of the balancing practice, the metered circuits, the pond systems, and the zero-discharge designs, is the direction in which the remaining withdrawal is heading.

7. Zero-Liquid-Discharge and the Water-Scarce Plant

The frontier of the plant’s water practice is the zero-liquid-discharge design, the architecture in which nothing leaves the plant’s boundary as water except the evaporation and the moisture of the products: every stream, the blowdown, the drainages, and the discharges, is recovered, processed, and reused, and the plant’s withdrawal is only the make-up that the evaporation and the retention demand. The zero-liquid-discharge is the design goal of the plants in the water-scarce regions, and its engineering is the completion of the chapter’s recycling logic: the blowdown of the towers is routed to the process duties that tolerate its salts, the process waters are processed through the filtration and the treatment to the service qualities, the evaporation ponds and the crystallizers handle the ultimate concentrates where the chemistry demands, and the whole water network is instrumented and managed as a single integrated system.

The water-scarce plant adds its own disciplines on top of the conservation design. The selection of the dry cooling over the evaporative cooling wherever the water price justifies it; the capture of every rainfall through the treated catchments; the reuse of the domestic and the process waters at the cascading qualities, the cleanest to the cleanest services and the increasingly degraded to the tolerant ones; and the water efficiency of the processes themselves, the dust suppression that uses the driest possible methods and the conditioning that consumes the minimum water, are the practice set of the scarce sites, and the plants of the arid regions of the industry, the Middle East, the North African, the Australian, and the western American sites, operate as the demonstration of the practice.

The economics of the water practice complete the picture: the water price, the withdrawal and the discharge fees, the treatment costs, and the penalties of the scarcity, are the numbers that justify the retention, the recycling, and the zero-discharge equipment, and the modern plants compute their water economy exactly as they compute their energy economy, with the liters per tonne as a reported performance indicator on the same footing as the gigajoules per tonne. The water cost of the plants in the scarce regions, a line of the operating budget that grows with the region’s scarcity, has made the water discipline of this chapter one of the board-level issues of the industry’s site selection and its modernization planning.

8. The Regulatory and Environmental Frame of Plant Water

The plant’s water practice is conducted inside a dense regulatory frame, and the environmental manager’s discipline is the coordination of the frame’s instruments. The water withdrawals are governed by the source permits, the groundwater and the surface water rights, whose terms, the quantities, the seasons, and the reporting, the plant’s metering must satisfy; the discharges, of the blowdown and the treated waters, are governed by the discharge permits, whose limits, the suspended solids, the pH, the temperature, the oxygen demand, and the priority chemicals, the treatment must meet; and the storm water and the runoff, where the regulations treat the industrial storm water as a regulated discharge, are managed through the plant’s storm-water plans, the spill prevention, the containment, and the monitoring that the permits prescribe.

The drinking water of the personnel carries the public health frame: the potable supply is tested and certified to the drinking water standards, the backflow prevention protects it from the process circuits, and the sanitary facilities are maintained to the requirements of the health authorities. The groundwater protection around the plant’s facilities, the ponds, the tanks, and the storage, is the environmental discipline of the lining, the monitoring wells, and the spill response, and the closure obligations of the ponds and the facilities, when the plant’s life ends, are engineered into the designs from the start.

The frame’s management in the plant is the water program: the permit calendar, the reporting schedules, the sampling and the analysis plans, and the audit trail of the water operations are maintained with the discipline of the quality system, and the water program of the modern plant is, like its energy program, an ISO-managed system, documented, audited, and continuously improved. The chapter’s environmental message is the integrated one: the water practice of the plant, the conservation, the treatment, and the discharge, is not a set of separate compliance items but a single managed system, and the plants that run it as a system are the plants whose permits renew without incident and whose communities trust their stewardship.

9. Innovations in Industrial Water Management

The innovations of the plant water field have followed the two axes of the era, the conservation and the digitalization. On the conservation axis, the industry’s frontier is the further reduction of the evaporative tower losses: the adiabatic and the hybrid cooling towers, which pre-cool the air with the fine sprays and operate the dry sections when the ambient conditions allow, cut the evaporation by a third and more; the dry-cooled stations of the water-scarce sites eliminate the tower water entirely; and the advanced fill and drift eliminators push the tower’s performance, and its water economy, to the edge of their physics. The water recovery of the process streams, the condensate recovery of the air compressors and the process air systems, and the capture of the rainfall, complete the conservation set.

On the processing axis, the membrane technologies have arrived in the plant water field: the ultrafiltration and the reverse osmosis systems, used for the make-up treatment and increasingly for the recycling of the process waters, produce the qualities that the closed loops and the high-pressure services demand, and the brine management of the concentrate streams is the new engineering discipline that the arid plants carry. The biological treatment of the organic and the sanitary streams, where the plants must treat their own effluents, has followed the municipal practice into the compact package plants, and the treatment trains of the modern plants are designed from the water balance of the whole site rather than from the individual streams.

On the digital axis, the water network has joined the plant’s instrumentation: the flow meters and the conductivity, pH, and temperature instruments of the circuits stream into the control systems and the historians, the water balances are computed continuously rather than monthly, the leak detection and the equipment-condition monitoring of the pumps and the towers are maintained from the data, and the models of the plant’s water network, running alongside the energy models, optimize the routing of the water between the services and the ponds. The plants of the industry’s advanced group manage their water with the same real-time discipline as their kilns, and the trend of the field is the convergence of that discipline with the carbon and the energy management of the plant, in the integrated environmental operation that the future era will assume.

Frequently Asked Questions

Why did the dry process reduce the cement industry’s water use so dramatically?

Because the wet process mixed the raw materials into a slurry with 30 to 40 percent water, and the kilns evaporated that water at a cost of half a tonne or more of water per tonne of clinker. The dry process grinds and feeds the meal as a powder, eliminating the slurry water and its evaporation heat entirely, leaving only the non-contact cooling and the auxiliary duties that today’s plants recycle.

What are the main water uses left in a dry-process plant?

The non-contact cooling of the drives, bearings, gear reducers, air compressors, air conditioning, and probes in the hot process stages and the hot gas streams of the pyro system and the mills; the dust conditioning and suppression; the process contact water; and the sanitary and potable water of the personnel. The volume is dominated by the cooling circuits, which recycle at 20 or more cycles.

How does a cooling tower recycle the plant’s water?

The warm water from the circuits is distributed over the tower fill and cooled by evaporation into the induced or forced air draft; the cooled water returns to the circuits, and only the evaporated, drifted, and blown-down losses are replaced by make-up. The circulation-to-make-up ratio, typically above 20, is the measure of the system’s water economy.

What are cycles of concentration, and why are they managed?

They are the ratio of the dissolved solids in the circulating water to their concentration in the make-up, and they rise as the tower evaporates without them. They are limited by scaling and corrosion, so the treatment program, the inhibitors and the biocides, together with the controlled blowdown, holds the cycles in their window, balancing the water savings of the higher cycles against the treatment’s capability.

What is the role of the retention and recycling ponds?

The ponds collect the plant’s waters, the blowdown, the drainages, and the storm water, settle the suspended solids, equalize the flows, and buffer the supply, and the recovered water is processed and returned to the circuits. They are the plant’s water reservoir and its first treatment step, and their design capacity comes from the plant’s water balance and its storm statistics.

What does zero-liquid-discharge mean for a cement plant?

Nothing leaves the plant boundary as water except the evaporation and the product moisture: every blowdown, drainage, and discharge is recovered, processed, and reused, and the withdrawal is only the make-up for the losses. It is the design goal of the water-scarce sites, and its engineering is the completion of the recirculation and the pond logic at the whole-plant scale.

Final Summary

Chapter 6.4 of Innovations in Cement Manufacturing covers the water use, retention, and recycling of the cement plant, and this article has expanded the chapter into a complete technical package. The article established the historical frame, the wet process’s prodigious water consumption and its elimination by the dry process, and the remaining virtues of the modern plant, the non-contact cooling of the drives, bearings, compressors, and probes, the dust conditioning and suppression, and the sanitary duties. The engineering core covered the cooling systems and their towers, the water treatment that protects the circuits and the environment, and the retention, processing, and recycling ponds that form the chapter’s centerpiece.

The management dimension treated the water balance of the plant, consolidated in the per-tonne table that the planner uses directly, the zero-liquid-discharge and the water-scarce practice, the regulatory and environmental frame of the withdrawals, the discharges, and the groundwater protection, and the innovations of the conservation, the processing, and the digitalization axes that are driving the field forward. The result is a complete working picture of the water discipline that the chapter describes: the circulation, the retention, and the recycling whose efficiency, paramount in the areas of water scarcity, now defines the operating reality of the industry’s dry-process plants.

The conclusion of the chapter is that water, the ancient companion of the wet era, has been reduced by the dry process to a managed utility, and the modern plant’s water stewardship, the metered circuits, the treated loops, the retention ponds, and the zero-discharge architectures, has made the cement industry one of the models of industrial water conservation. The plants of the arid regions demonstrate the practice at its limit, and the innovations of the field, the dry and the hybrid cooling, the membrane processing, and the digital water network, will continue to reduce the industry’s water footprint, so that the liters per tonne, like the gigajoules per tonne, becomes a number that the industry continuously improves.

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.