LBNL-72E

ERNEST ORLANDO LAWRENCE

BERKELEY NATIONAL LABORATORY

Energy Efficiency Improvement 

Opportunities for the 

Cement Industry 

Ernst Worrell, Christina Galitsky and Lynn Price 

Environmental Energy 

Technologies Division 

 

January 2008

This work was supported by the Climate Protection Partnerships Division of the 

U.S. Environmental Protection Agency as part of its ENERGY STAR program 

through the U.S. Department of Energy under Contract No. DE-AC02-

05CH11231. Revision of this report for use in China was undertaken with 

funding provided by the U.S. EPA’s Office of International Affairs, the Energy 

Foundation’s China Sustainable Energy Program and Dow Chemical Company. 
Disclaimer 

This document was prepared as an account of work sponsored by the United States Government. 

While this document is believed to contain correct information, neither the United States 

Government nor any agency thereof, nor The Regents of the University of California, nor any of 

their employees, makes any warranty, express or implied, or assumes any legal responsibility for 

the accuracy, completeness, or usefulness of any information, apparatus, product, or process 

disclosed, or represents that its use would not infringe privately owned rights. Reference herein to 

any specific commercial product, process, or service by its trade name, trademark, manufacturer, 

or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or 

favoring by the United States Government or any agency thereof, or The Regents of the 

University of California. The views and opinions of authors expressed herein do not necessarily 

state or reflect those of the United States Government or any agency thereof, or The Regents of 

the University of California. 

Ernest Orlando Lawrence Berkeley National Laboratory is an equal opportunity employer. 
Energy Efficiency Improvement Opportunities for the 

Cement Industry

Ernst Worrell, Christina Galitsky and Lynn Price 

Environmental Energy Technologies Division 

Lawrence Berkeley National Laboratory 

ABSTRACT

This report provides information on the energy savings, costs, and carbon dioxide 

emissions reductions associated with implementation of a number of technologies and 

measures applicable to the cement industry. The technologies and measures include both 

state-of-the-art measures that are currently in use in cement enterprises worldwide as well 

as advanced measures that are either only in limited use or are near commercialization. 

This report focuses mainly on retrofit measures using commercially available 

technologies, but many of these technologies are applicable for new plants as well. 

Where possible, for each technology or measure, costs and energy savings per tonne of 

cement produced are estimated and then carbon dioxide emissions reductions are 

calculated based on the fuels used at the process step to which the technology or measure 

is applied. The analysis of cement kiln energy-efficiency opportunities is divided into 

technologies and measures that are applicable to the different stages of production and 

various kiln types used in China: raw materials (and fuel) preparation; clinker making 

(applicable to all kilns, rotary kilns only, vertical shaft kilns only); and finish grinding; as 

well as plant wide measures and product and feedstock changes that will reduce energy 

consumption for clinker making. Table 1 lists all measures in this report by process to 

which they apply, including plant wide measures and product or feedstock changes. 

Tables 2 through 8 provide the following information for each technology: fuel and 

electricity savings per tonne of cement; annual operating and capital costs per tonne of 

cement or estimated payback period; and, carbon dioxide emissions reductions for each 

measure applied to the production of cement. 

This information was originally collected for a report on the U.S. cement industry 

(Worrell and Galitsky, 2004) and a report on opportunities for China’s cement kilns 

(Price and Galitsky, in press). The information provided in this report is based on 

publicly-available reports, journal articles, and case studies from applications of 

technologies around the world. 

Table of Contents 

Introduction................................................................................................................1

Energy Efficiency Improvement Opportunities ........................................................1

Raw Materials Preparation.............................................................................................. 2 

Fuel Preparation.............................................................................................................. 4 

Clinker Making - All Kilns............................................................................................. 5 

Clinker Making – Rotary Kilns....................................................................................... 8 

Clinker Making – Vertical Shaft Kilns ......................................................................... 17 

Finish Grinding ............................................................................................................. 18 

Plant Wide Measures .................................................................................................... 21 

Plant Wide Lighting...................................................................................................... 25 

Product and Feedstock Change..................................................................................... 26 

Acknowledgements..................................................................................................31

References................................................................................................................32

Tables 

Table 1. Energy Efficiency Measures and Technologies for the Cement Industry. ....................... 1 

Table 2. Energy Efficiency Measures for Raw Materials Preparation in Cement Plants............... 2 

Table 3. Energy-Efficiency Opportunities Applicable to All Kiln Types. ..................................... 5 

Table 4. Energy-Efficiency Opportunities Applicable to Rotary Kilns........................................ 10 

Table 5. Energy-Efficiency Opportunities Applicable to Vertical Shaft Kilns. ........................... 17 

Table 6. Energy Efficiency Measures for Final Grinding of Products in Cement Plants............. 19 

Table 7. Energy Efficiency Measures for Plant Wide Measures in Cement Plants...................... 21 

Table 8. Product and Feedstock Changes to Improve the Energy Efficiency of Clinker 

Production...................................................................................................................... 27 

Table 9. Prices and Transportation Modes for Different Additives Used in China...................... 28 

Introduction 

This report provides information on the energy savings, costs, and carbon dioxide 

emissions reductions associated with implementation of a number of technologies and 

measures applicable to the cement industry. The technologies and measures include both 

state-of-the-art measures that are currently in use in cement enterprises worldwide as well 

as advanced measures that are either only in limited use or are near commercialization. 

Mainly the focus is on retrofit measures using commercially available technologies, but 

many of these technologies are applicable for new plants as well. Where possible, for 

each technology or measure, costs and energy savings per tonne of cement produced are 

estimated and then carbon dioxide emissions reductions are calculated based on the fuels 

used at the process step to which the technology or measure is applied. The analysis of 

cement kiln energy-efficiency opportunities is divided into technologies and measures 

that are applicable to the different stages of production and various kiln types used in 

China: raw materials (and fuel) preparation; clinker making (applicable to all kilns, rotary 

kilns only, vertical shaft kilns only); and finish grinding; as well as plant wide measures 

and product and feedstock changes that will reduce energy consumption for clinker 

making. 

Energy Efficiency Improvement Opportunities 

Table 1. Energy Efficiency Measures and Technologies for the Cement Industry. 

Raw Materials Preparation All Kilns

Efficient transport systems (dry process) Improved refractories 

Raw meal blending systems (dry process) Kiln shell heat loss reduction 

Process control vertical mill (dry process) 

High-efficiency roller mills (dry process) 

Energy management & process control 

Adjustable speed drive for kiln fan 

High-efficiency classifiers (dry process) 

Slurry blending and homogenization (wet process) Vertical Shaft Kilns 

Conversion to closed circuit wash mill (wet process) Convert to new suspension preheater/precalciner kiln 

Fuel Preparation Kiln combustion system improvements 

Roller mills for fuel preparation 

Roller press for coal grinding Rotary Kilns 

Finish Grinding Preheater kiln upgrade to precalciner kiln 

Energy management and process control Long dry kiln upgrade to preheater/precalciner kiln 

High-pressure roller press Older dry kiln upgrade to multi-stage preheater kiln 

High efficiency classifiers Convert to reciprocating grate cooler 

Improved grinding media (ball mills) Kiln combustion system improvements 

General Measures Indirect Firing 

Preventative maintenance (insulation, compressed air 

system, maintenance) 

Optimize heat recovery/upgrade clinker cooler 

Seal replacement 

High efficiency motors 

Efficient fans with variable speed drives 

Low temperature heat recovery for power (capital costs 

given in $/kW) 

Optimization of compressed air systems High temperature heat recovery for power

Efficient lighting Low pressure drop cyclones 

Efficient kiln drives 

Product & Feedstock Changes 

Blended cements

Use of waste derived fuels 

Limestone cement 

Low alkali cement 

Use of steel slag in kiln 

1
Table 1 shows the energy efficiency measures included in this report by process step as 

well as general measures. Efficiency measures are described below in more detail in the 

applicable section, by process step. 

Raw Materials Preparation 

Table 2 shows fuel and electricity savings, estimated payback period and carbon dioxide 

(CO2) savings for each measure related to raw materials preparation (including the 

preparation of fuels). A description for each measure is given below. 

Table 2. Energy Efficiency Measures for Raw Materials Preparation in Cement Plants. 

More information can be found in the description of the measures below. 

Energy Efficiency Measure 

(for raw materials production) 

Fuel 

Savings 

(GJ/t) 

Electricity 

Savings 

(kWh/t) 

Estimated 

Payback Period 

(years) (1)

CO2

Savings 

(kgC/t) 

Efficient Transport System - 3.4 > 10 (1) 0.78 

Raw Meal Blending - 1.7-4.3 NA (1) 0.4-1.0 

Process Control Vertical Mill - 1.4-1.7 1 0.3-0.4 

High-Efficiency Roller Mill - 10.2-11.9 > 10 (1) 2.3-2.7 

High-Efficiency Classifiers - 4.8-6.3 > 10 (1) 1.1-1.4 

Slurry Blending and Homogenizing 0.5-0.9 < 3 0.1-0.2 

Wash Mills with Closed Circuit Classifier - 8.5-11.9 > 10 (1) 2.0-2.7 

Roller Mills for Fuel Preparation - 0.7-1.1 NA (1) 0.2-0.3 

Notes: 

All data is given per tonne of cement 

(1) Payback periods are calculated on the basis of energy savings alone. In reality this investment may be driven by 

other considerations than energy efficiency (e.g. productivity, product quality), and will happen as part of the normal 

business cycle or expansion project. Under these conditions the measure will have a lower payback period depending 

on plant-specific conditions. 

NA = not available 

Efficient Transport Systems (Dry Process). Transport systems are required to convey 

powdered materials such as kiln feed, kiln dust, and finished cement throughout the plant. 

These materials are usually transported by means of either pneumatic or mechanical 

conveyors. Mechanical conveyors use less power than pneumatic systems. Based on 

Holderbank, (1993) the average energy savings are estimated to be 2.0 kWh/t raw 

material with a switch to mechanical conveyor systems. Installation costs for the system 

are estimated to be $3/t raw material production based on the Holderbank study (1993). 

Conversion to mechanical conveyors is cost-effective when replacement of conveyor 

systems is needed to increase reliability and reduce downtime. 

Raw Meal Blending (Homogenizing) Systems (Dry Process). To produce a good quality 

product and to maintain optimal and efficient combustion conditions in the kiln, it is 

crucial that the raw meal is completely homogenized. Quality control starts in the quarry 

and continues to the blending silo. On-line analyzers for raw mix control are an integral 

part of the quality control system (Fujimoto, 1993; Holderbank, 1993). 

Most plants use compressed air to agitate the powdered meal in so-called air-fluidized 

homogenizing silos (using 1.1-1.5 kWh/t raw meal). Older dry process plants use 

mechanical systems, which simultaneously withdraw material from 6-8 different silos at 

variable rates (Fujimoto, 1993), using 2.2-2.6 kWh/t raw meal. Modern plants use 

gravity-type homogenizing silos (or continuous blending and storage silos) reducing 

2
power consumption. In these silos, material funnels down one of many discharge points, 

where it is mixed in an inverted cone. Gravity-type silos may not give the same blending 

efficiency as air-fluidized systems. Although most older plants use mechanical or airfluidized bed systems, more and more new plants seem to have gravity-type silos, 

because of the significant reduction in power consumption (Holderbank, 1993). Silo 

retrofit options are cost-effective when the silo can be partitioned with air slides and 

divided into compartments which are sequentially agitated, as opposed to the construction 

of a whole new silo system (Gerbec, 1999). The energy savings are estimated to be 1.0-

2.5 kWh/t raw meal (Fujimoto, 1993; Holderbank, 1993; Alsop & Post, 1995, Cembureau, 

1997b; Gerbec, 1999). Costs for the silo retrofit are estimated to be $3.7/t raw material 

(assuming $550K per silo and an average capacity of 150,000 tonnes annual capacity). 

Raw Meal Process Control (Dry process - Vertical Mill). The main difficulty with 

existing vertical roller mills are vibration trips. Operation at high throughput makes 

manual vibration control difficult. When the raw mill trips, it cannot be started up for one 

hour, until the motor windings cool. A model predictive multivariable controller 

maximizes total feed while maintaining a target residue and enforcing a safe range for 

trip-level vibration. The first application eliminated avoidable vibration trips (which were 

12 per month prior to the control project). The cited increase in throughput was 6% with 

a corresponding reduction in specific energy consumption of 6% (Martin and McGarel, 

2001b), or 0.8 – 1.0 kWh/tonne of raw material (based on Cembureau, 1997b). 

Use of Roller Mills (Dry Process). Traditional ball mills used for grinding certain raw 

materials (mainly hard limestone) can be replaced by high-efficiency roller mills, by ball 

mills combined with high-pressure roller presses, or by horizontal roller mills. The use of 

these advanced mills saves energy without compromising product quality. Energy 

savings of 6-7 kWh/t raw materials (Cembureau, 1997b) are assumed through the 

installation of a vertical or horizontal roller mill. An additional advantage of the inline 

vertical roller mills is that they can combine raw material drying with the grinding 

process by using large quantities of low grade waste heat from the kilns or clinker coolers 

(Venkateswaran and Lowitt, 1988). Various roller mill process designs are marketed. 

In 1998, Arizona Portland cement (Rillito, Arizona, U.S.) installed a roller mill for raw 

material grinding increasing throughput, flexibility, raw meal fineness and reducing 

electricity consumption (De Hayes, 1999). Investments are estimated to be $5.5/t raw 

material (Holderbank, 1993). 

High-efficiency Classifiers/Separators. A recent development in efficient grinding 

technologies is the use of high-efficiency classifiers or separators. Classifiers separate the 

finely ground particles from the coarse particles. The large particles are then recycled 

back to the mill. High efficiency classifiers can be used in both the raw materials mill and 

in the finish grinding mill. 

Standard classifiers may have a low separation efficiency, which leads to the recycling of 

fine particles, and results in to extra power use in the grinding mill. Various concepts of 

high-efficiency classifiers have been developed (Holderbank, 1993; Süssegger, 1993). In 

3
high-efficiency classifiers, the material stays longer in the separator, leading to sharper 

separation, thus reducing overgrinding. Electricity savings through implementing highefficiency classifiers are estimated to be 8% of the specific electricity use (Holderbank, 

1993). 

In 1990, Tilbury Cement (Delta, British Columbia, Canada) modified a vertical roller 

mill with a high-efficiency classifier increasing throughput and decreasing electricity use 

(Salzborn and Chin-Fatt, 1993). Case studies have shown a reduction of 2.8-3.7 kWh/t 

raw material (Salzborn and Chin-Fatt, 1993; Süssegger, 1993). Replacing a conventional 

classifier by a high-efficiency classifier has led to 15% increases in the grinding mill 

capacity (Holderbank, 1993) and improved product quality due to a more uniform 

particle size (Salzborn and Chin-Fatt, 1993), both in raw meal and cement. The better 

size distribution of the raw meal may lead to fuel savings in the kiln and improved clinker 

quality. Investment costs are estimated to be $2.2/annual t raw material production, 

according to Holderbank (1993). 

Slurry Blending and Homogenizing (Wet Process). In the wet process, the slurry is 

blended and homogenized in a batch process. The mixing is done using compressed air and 

rotating stirrers. The use of compressed air may lead to relatively high energy losses 

because of its poor efficiency. An efficiently run mixing system may use 0.3 – 0.5 kWh/t 

raw material (Cembureau, 1997b). The main energy efficiency improvement measures for 

slurry blending systems are found in the compressed air system (see below under plantwide measures). 

Wash Mills with Closed Circuit Classifier (Wet Process). In most wet process kilns, 

tube mills are used in combination with closed or open circuit classifiers. An efficient tube 

mill system consumes about 13 kWh/t (Cembureau, 1997b). Replacing the tube mill by a 

wash mill would reduce electricity consumption to 5-7 kWh/t (Cembureau, 1997b) at 

comparable investment and operation costs as a tube mill system. When replacing a tube 

mill a wash mill should be considered as an alternative, reducing electricity consumption 

for raw grinding by 5-7 kWh/t, or 40-60%. 

Fuel Preparation 

Coal is the most widely used fuel in the cement industry. Fuels preparation is most often 

performed on-site. Fuels preparation may include crushing, grinding and drying of coal. 

Coal is shipped “wet” to prevent dust formation and fire during transport. Passing hot 

gasses through the mill combines the grinding and drying. An impact mill would 

consume around 45-60 kWh/t and a tube mill around 25 – 26 kWh/t (total system 

requirements) (Cembureau, 1997b). Waste heat of the kiln system (e.g. the clinker cooler) 

is used to dry the coal if needed. 

Other advantages of a roller mill are that it is able to handle larger sizes of coal (no precrushing needed) and coal types with a higher humidity, and can manage larger variations 

in throughput. However, tube mills are preferred for more abrasive coal types. Coal roller 

mills are available for throughputs of 5.5 to 220 t/hour. Lehigh Portland Cement installed 

a vertical roller mill for coal grinding in 1999 at the Union Bridge, Maryland, U.S. plant. 

4
Blue Circle cement has ordered a vertical roller mill for the new kiln line V at the 

Roberta plant in Calera, Alabama, U.S. It has a capacity of 41.3 t/hr and was 

commissioned in early 2001. Coal grinding roller mills can be found in many countries 

around the world, e.g. Brazil, Canada, China, Denmark, Germany, Japan and Thailand. 

All major suppliers of cement technology offer roller mills for coal grinding. 

Vertical roller mills have been developed for coal grinding, and are used by over 100 

plants around the world (Cembureau, 1997b). Electricity consumption for a vertical roller 

mill is estimated to be 16-18 kWh/t coal (Cembureau, 1997b). The investment costs for a 

roller mill are typically higher than that of a tube mill or an impact mill, but the operation 

costs are also lower; roughly 20% compared to a tube mill and over 50% compared to an 

impact mill (Cembureau, 1997b), estimating savings at 7-10 kWh/t coal. 

Roller Press for Coal Grinding. Roller presses, like those used for cement and raw 

material grinding, are generally more efficient than conventional grinding mills. Roller 

presses can be used to grind raw materials and coal interchangeably, although coalgrinding equipment needs special protection against explosions. 

Clinker Making - All Kilns 

All kilns can implement improved refractories, kiln shell heat loss reduction measures, 

energy management and process control systems, and adjustable speed drives for the kiln 

fan. Although all kilns can benefit from kiln combustion system improvements, we have 

split this measure into two distinct measures for rotary and shaft kilns, in those respective 

sections, below. Distinctions between energy management and process control for each 

kiln type are explained in the measure description in this section. Table 3 provides 

information on the initial capital costs, the operations and maintenance (O&M) costs, the 

simple payback period, the specific fuel savings, the specific electric savings, the specific 

CO2 emissions reductions, and the lifetime associated with each of these measures. 

Table 3. Energy-Efficiency Opportunities Applicable to All Kiln Types. 

Capital 

Costs 

($/t) 

O & M 

Costs 

($/t) 

Payback 

Period 

(years) 

Fuel 

Savings 

(GJ/t) 

Electric 

Savings 

(kWh/t) 

CO2 

Savings 

 (kgC/t) 

Lifetime 

(years) 

Improved refractories NA NA 0.4-0.61 - 10.3-15.5 NA 

Kiln shell heat loss reduction 0.25 1 0.1-0.632 - 2.8-10.3 20 

Energy management & process 

control 

0.3-1.7 < 2 0.1-0.2 1.5-3.2 2.9-5.9 10 

Adjustable speed drive for kiln fan 0.23 0 2-3 - 6.1 1.4 10 

Note: Energy savings and costs are based on case study data from the U.S., except where noted. Costs in China will 

vary depending on technology and availability. Where possible, we have included more data for China in the following 

text. All data are given per tonne of clinker. For U.S. data, the estimated savings and payback periods are based on the 

average performance of the U.S. cement industry (e.g. clinker to cement ratio). 1

 Data taken from Chinese case studies 

2

 Data from Chinese case studies indicate savings of 0.46 to 0.63 GJ/t clinker, while U.S. data show savings of 0.1 to 

0.4 GJ/t clinker. 

NA = not available

Improved Refractories. Refractories protect the steel kiln shell against heat, chemical 

and mechanical stress. The choice of refractory material depends on the combination of 

5
raw materials, fuels and operating conditions. Extended lifetime of the higher quality 

refractories will lead to longer operating periods and reduced lost production time 

between relining of the kiln, and, hence, offset their higher costs (Schmidt, 1998; van Oss, 

2002). It will also lead to additional energy savings due to the relative reduction in startup time. The energy savings are difficult to quantify, as they will strongly depend on the 

current lining choice and management. 

In one vertical shaft kiln in South China, a new energy-efficient lining was applied. Fuel 

consumption was reduced from 930 to 950 kcal/kg clinker (3.9 to 4.0 GJ/t clinker) to 800 

to 820 kcal/kg clinker (3.4 to 3.5 GJ/t clinker), a savings of approximately 14% 

(ITIBMIC, 2004). The output also increased by about 1 tonne per hour. Another cement 

plant in North China utilizing vertical shaft kilns employed energy efficient lining and 

found a reduction of fuel use from 900 to 920 kcal/kg clinker (3.8 GJ/t clinker) to about 

800 kcal/kg clinker (3.4 GJ/t clinker) (ITIBMIC, 2004). The output of the kiln also 

increased per unit of raw materials input. 

Refractories are made by foreign companies operating in China, particularly in the 

Liaoning Province, such as Refratechnik (German) and RHI (Austrian) (Cui, 2006). 

China also produces medium and smaller refractories but the energy efficiency is poorer 

than those made by the leading international companies (Cui, 2006). 

Kiln Shell Heat Loss Reduction. There can be considerable heat losses through the shell 

of a cement kiln, especially in the burning zone. The use of better insulating refractories 

(e.g. Lytherm) can reduce heat losses (Venkateswaran and Lowitt, 1988). Refractory 

choice is the function of insulating qualities of the brick and the ability to develop and 

maintain a coating. The coating helps to reduce heat losses and to protect the burning 

zone refractory bricks. Estimates suggest that the development of high-temperature 

insulating linings for the kiln refractories can reduce fuel use by 0.12 to 0.4 GJ/t of 

clinker (Lowes and Bezant, 1990; COWIconsult, 1993; Venkateswaran and Lowitt, 

1988). Costs for insulation systems are estimated to be $0.25/annual tonne clinker 

capacity (Lesnikoff, 1999). Structural considerations may limit the use of new insulation 

materials. The use of improved kiln-refractories may also lead to improved reliability of 

the kiln and reduced downtime, reducing production costs considerably, and reducing 

energy needs during start-ups. 

Changjiang Cement Factory in Zhejiang City, Jangsu Province applied energy saving kiln 

lining to its shaft kiln and found energy savings of 0.46 to 0.63 GJ/t clinker (ITIBMIC, 

2004). In addition to these energy savings, they were able to increase production. 

Generally this technology is imported (Cui, 2006). 

Energy Management and Process Control Systems. Heat from the kiln may be lost 

through non-optimal process conditions or process management. Automated computer 

control systems may help to optimize the combustion process and conditions. Improved 

process control will also help to improve the product quality and grindability, e.g. 

reactivity and hardness of the produced clinker, which may lead to more efficient clinker 

grinding. In cement plants across the world, different systems are used, marketed by 

6
different manufacturers. Most modern systems use so-called 'fuzzy logic' or expert 

control, or rule-based control strategies. Expert control systems do not use a modeled 

process to control process conditions, but try to simulate the best human operator, using 

information from various stages in the process. 

One such system, called ABB LINKman, was originally developed in the United 

Kingdom by Blue Circle Industries and SIRA (ETSU, 1988). The first system was 

installed at Blue Circle's Hope Works in 1985, which resulted in a fuel consumption 

reduction of nearly 8% (ETSU, 1988). The LINKman system has successfully been used 

in rotary kilns (both wet and dry). After their first application in 1985, modern control 

systems now find wider application and can be found in many European plants. Other 

developers also market ‘fuzzy logic’ control systems, e.g., F.L. Smidth (Denmark) Krupp 

Polysius (Germany) and Mitsui Mining (Japan). Several companies in China also provide 

optimized information technology for energy management and process control, such as the 

ABB or the Chinese software company Yun Tian (Wang, 2006b). 

All foreign produced control systems described above report typical energy savings of 3 

to 8%, while improving productivity of the kiln. For example, Krupp Polysius reports 

typical savings of 2.5 – 5%, with similar increased throughput and increased refractory 

life of 25 –100%. Ash Grove implemented a fuzzy control system at the Durkee Oregon 

plant in 1999. 

An alternative to expert systems or fuzzy logic is model-predictive control using dynamic 

models of the processes in the kiln. A model predictive control system was installed at a 

kiln in South Africa in 1999, reducing energy needs by 4%, while increasing productivity 

and clinker quality. The payback period of this project is estimated to be 8 months, even 

with typically very low coal prices in South Africa (Martin & McGarel, 2001a). 

Additional process control systems include the use of on-line analyzers that permit 

operators to instantaneously determine the chemical composition of raw materials being 

processed, thereby allowing for immediate changes in the blend of raw materials. A 

uniform feed allows for steadier kiln operation, thereby saving ultimately on fuel 

requirements. Blue Circle’s St. Marys plant (Canada) installed an on-line analyzer in 1999 

in its precalciner kiln, and achieved better process management as well as fuel savings. 

Energy savings from foreign produced process control systems may vary between 2.5% 

and 10% (ETSU, 1988; Haspel and Henderson, 1993; Ruby, 1997), and the typical 

savings are estimated to be 2.5 to 5%. The economics of advanced process control 

systems are very good and payback periods can be as short as 3 months (ETSU, 1988). 

The system at Blue Circle's Hope Works (U.K.) needed an investment of £203,000 

(1987), equivalent to $0.3/annual tonne clinker (ETSU, 1988), including measuring 

instruments, computer hardware and training. Holderbank (1993) notes an installation 

cost for on-line analyzers of $0.8 to 1.7/annual tonne clinker. A payback period of 2 years 

or less is typical for kiln control systems, while often much lower payback periods are 

achieved (ETSU, 1988; Martin and McGarel, 2001a). 

7
Process control of the clinker cooler can help to improve heat recovery, material 

throughput and improved control of free lime content in the clinker, and to reduce NOx 

emissions (Martin et al., 2000). Installing a Process Perfecter® (of Pavilion Technologies 

Inc.) has increased cooler throughput by 10%, reduced free lime by 30% and reduced 

energy by 5%, while reducing NOx emissions by 20% (Martin et al., 1999; Martin et al., 

2001). The installation costs equal $0.35/annual tonne of clinker, with an estimated 

payback period of 1 year (Martin et al., 2001). 

Combustion control in vertical kilns is more difficult than in rotary kilns where the flow 

of raw materials is controlled by a mechanically-rotating horizontally-oriented shaft at a 

slight angle instead of just gravity (Liu et al., 1995). In these kilns, operating skills and 

hence, proper training is more important for energy efficiency and product quality. If 

automatic controls are going to be successfully implemented, they must link all processes 

from mine management to raw materials input into the kiln to kiln fuel input in order to 

realize stable production; none should be done manually (ITIBMIC, 2004). Control 

technologies also exist for controlling the air intake. (For more information on kiln 

combustion system improvements and controls for VSKs, see “kiln combustion system 

improvements” in Energy Efficiency Opportunities for Clinker Production – Vertical 

Shaft Kilns, below). Raw materials and fuel mix can be improved by a careful analysis of 

the chemical and physical characteristics of each, and by automating the weighing 

process and the pellet production (water content and raw feed mixtures), the blending 

process, the kiln operation (optimizing air flow, temperature distribution, and the speed 

of feeding and discharging). Cui (2006) reports that most technologies for this measure 

are made by international companies such as Siemens and ABB; few if any are made by 

domestic companies. 

Adjustable Speed Drive for Kiln Fan. Adjustable or variable speed drives (ASDs) for 

the kiln fan result in reduced power use and reduced maintenance costs. The use of ASDs 

for a kiln fan at the Hidalgo plant of Cruz Azul Cement in Mexico resulted in improved 

operation, reliability and a reduction in electricity consumption of almost 40% (Dolores 

and Moran, 2001) for the 1,000 horsepower motors. The replacement of the damper by an 

ASD was driven by control and maintenance problems at the plant. The energy savings 

may not be typical for all plants, as the system arrangement of the fans was different from 

typical kiln arrangements. For example, Fujimoto, (1994) notes that Lafarge Canada’s 

Woodstock plant replaced their kiln fans with ASDs and reduced electricity use by 5.5 

kWh/t of cement (6.1 kWh/t clinker). The Zhonglida Group, operating ten cement 

enterprises (with both VSKs and new dry rotary kilns), installed variable speed drives in 

40 large motors (over 55 kW) and over 40 of its smaller motors (< 55 KW) and found 

energy savings of over 30% (ITIBMIC, 2004). ASDs are currently being made in China, 

although many of the parts and instrumentation are still being imported from Germany 

and/or Japan (Cui, 2006). 

Clinker Making – Rotary Kilns 

For rotary kilns, an existing preheater kiln may be converted to a multi-stage 

preheater/precalciner kiln by adding a precalciner and an extra preheater, an existing long 

dry kiln can be upgraded to use a multi-stage preheater/precalciner kiln, and older dry 

kilns can be upgraded to multi-stage preheater/precalciner kilns. Other energy-efficiency 

8
technologies and measures include kiln combustion system improvements, reciprocating 

grate coolers, optimize heat recovery and upgrade the clinker cooler, seal replacement, 

low temperature waste heat recovery for power generation, high temperature waste heat 

recovery for power generation, low pressure drop cyclones for suspension preheaters, and 

efficient kiln drives. Table 4 provides information on the initial capital costs, the 

operations and maintenance (O&M) costs, the simple payback period, the specific fuel 

savings, the specific electric savings, the specific carbon dioxide savings and the lifetime 

associated with each of these measures. 

Installation or Upgrading of a Preheater to a Preheater/Precalciner Kiln. An existing 

preheater kiln may be converted to a multi-stage preheater/precalciner kiln by adding a 

precalciner and, when possible an extra preheater. The addition of a precalciner will 

generally increase the capacity of the plant, while lowering the specific fuel consumption 

and reducing thermal NOx emissions (due to lower combustion temperatures in the 

precalciner). Using as many features of the existing plant and infrastructure as possible, 

special precalciners have been developed by various manufacturers to convert existing 

plants, e.g. Pyroclon®-RP by KHD in Germany. Generally, the kiln, foundation and 

towers are used in the new plant, while cooler and preheaters are replaced. Cooler 

replacement may be necessary in order to increase the cooling capacity for larger 

production volumes. The conversion of a plant in Italy, using the existing rotary kiln, led 

to a capacity increase of 80 to 100% (from 1100 tpd to 2000 to 2200 tpd), while reducing 

specific fuel consumption from 3.6 to 3.1-3.2 GJ/t clinker, resulting in savings of 11 to 

14% (Sauli, 1993). Fuel savings will depend strongly on the efficiency of the existing 

kiln and on the new process parameters (e.g. degree of precalcination, cooler efficiency). 

The European Commission (2000) estimates a multi-stage preheater/precalciner kiln uses 

approximately 3 GJ/t clinker. 

Older precalciners can also be retrofitted for energy efficiency improvement and NOx 

emission reduction. Retrofitting the precalciner at the Lengerich plant of Dyckerhoff 

Zement (Germany) in 1998 reduced NOx emissions by almost 45% (Mathée, 1999). 

Similar emission reductions have been found at kilns in Germany, Italy and Switzerland 

(Menzel, 1997). Ash Grove’s Durkee, Oregon original 1979 plant installed new 

preheaters and a precalciner in 1998, expanding production from 1500 tonnes/day to 

2500 tonnes/day (Hrizuk, 1999). The reconstruction reduced fuel consumption by 0.16 to 

0.7 GJ/t clinker (Hrizuk, 1999), while reducing NOx emissions. Capitol Cement (San 

Antonio, Texas) replaced an older in-line precalciner with a new downdraft precalciner to 

improve production capacity. This was part of a larger project replacing preheaters, 

installing SOx emission reduction equipment, as well as increasing capacity of a roller 

mill. The new plant was successfully commissioned in 1999. Fuel consumption at Capitol 

Cement was reduced to 3.4 GJ/t clinker (Frailey & Happ, 2001). 

9
Table 4. Energy-Efficiency Opportunities Applicable to Rotary Kilns. 

Capital 

Costs 

($/t) 

O & M 

Costs 

($/t)1

Payback 

Period 

(years) 

Fuel 

Savings 

(GJ/t) 

Electric 

Savings 

(kWh/t)2

CO2

savings 

(kgC/t) 

Lifetime 

(years) 

Preheater kiln upgrade to precalciner kiln 9.4-28 -1.1 5 0.16-0.7 4.1-18.1 40 

Long dry kiln upgrade to 

preheater/precalciner kiln 

8.6-29 > 10 1.4 - 36 40 

Older dry kiln upgrade to multi-stage 

preheater kiln 

28-41 > 10 0.9 - 23 40 

Convert to reciprocating grate cooler 0.4-5.5 0.11 1-2 0.27 -3.0 6.3 20 

Kiln combustion system improvements 1.0 0 2 – 3 0.1-0.5 - 2.6-12.9 20 

Indirect Firing 7.4 NA 0.015-0.022 - 0.39-0.57 NA 

Optimize heat recovery/upgrade clinker 

cooler 

0.1-0.3 1-2 0.05-0.16 -2 0.8-3.7 20 

Seal replacement NA ≤ 0.5 0.011 - 0.3 NA 

Low temperature heat recovery for 

power (capital costs given in $/kW) 

800-1250 

($/kW)3

0.007 < 3 - 20-35 4.6-8.1 NA 

High temperature heat recovery for 

power

2.2-4.4 0.22-0.33 3 - 22 5.1 35 

Low pressure drop cyclones 3 > 10 - 0.7-4.4 0.16-1.0 20 

Efficient kiln drives +0-6% 4 NA - 0.55-3.9 0.13-0.9 10 

Note: Energy savings and costs below are based on case study data. Costs in China will vary depending on technology 

and availability. Where possible, we have included more data for China in the following text. All data are given per tonne 

of clinker. For U.S. data, the estimated savings and payback periods are based on the average performance of the U.S. 

cement industry (e.g. clinker to cement ratio).

1

 Negative numbers represent operation and maintenance savings. 2

 Negative numbers represent an increase in electricity due to the measure.

3 Domestic technology cost is 6000 to 10,000 RMB per investment, which is about 10,000 RMB less than foreign 

technology (16,000 to 22,000 RMB per kW). We use estimates from Chinese case studies to determine the numbers 

in the tables above. 4

 Initial costs given as the additional % required relative to standard U.S. technology (0 to 6%). 

NA = data not available 

According to Sauli (1993), average savings of new precalciners can be 0.4 GJ/t clinker. 

Sauli (1993) does not outline the investments made for the conversion project. Vleuten 

(1994) estimates the cost of adding a precalciner and suspension preheaters to be $28 

U.S./annual tonne clinker annual capacity (it is not clear what is included in this 

estimate). Jaccard and Willis (1996) estimate a much lower cost of $9.4/t clinker 

capacity. The increased production capacity is likely to save considerably in operating 

costs, estimated to be $1.1/t clinker (Jaccard & Willis, 1996).The Hejiashan Cement 

Company, Ltd. in Jiangshan City, Zhejiang Province installed two new dry process kilns 

in 2001 and 2003 at a cost of 105 million RMB for a 1000 tonne per day kiln and 156 

million RMB for a 1500 tonne per day kiln, respectively (ITIBMIC, 2004). This equates 

to roughly 300 RMB/t clinker ($37 U.S./t). Power consumption is expected to be 85.87 

kWh/t clinker and fuel consumption 2.5GJ/t clinker for the 1000 tonne per day kiln. 

Cui (2006) reports that many precalciner kilns have been constructed from 2001 and 

about 10 to 20% are imported while 80 to 90% are domestic technology. Cui states that 

domestic technology, made by a few leading manufacturers in China, costs roughly 1/3 to 

1/5 the cost of imported technology but doesn’t last as long. Most companies are 

10
adopting domestic technologies (Cui, 2006). Domestic technology, however, is not 

available for kiln sizes over 5000 tonne per day (Wang, 2006b). 

Conversion of Long Dry Kilns to Preheater/Precalciner Kiln. A long dry kiln can be 

upgraded to the current state of the art multi-stage preheater/precalciner kiln. Energy 

savings are estimated to be 1.4 GJ/t clinker for the conversion. These savings reflect the 

difference between the average dry kiln specific fuel consumption and that of a modern 

preheater, pre-calciner kiln based on a study of the Canadian cement industry and the 

retrofit of an Italian plant (Holderbank, 1993; Sauli, 1993). The Holderbank study gives a 

range of $23 to 29/t clinker for a pre-heater, pre-calciner kiln. Jaccard and Willis (1996) 

give a much lower value of $8.6/t clinker capacity. 

Dry Process Upgrade to Multi-Stage Preheater Kiln. Older dry kilns may only preheat 

in the chain section of the long kiln, or may have single- or two-stage preheater vessels. 

Installing multi-stage suspension preheating (i.e. four- or five-stage) may reduce the heat 

losses and thus increase efficiency. Modern cyclone or suspension preheaters also have a 

reduced pressure drop, leading to increased heat recovery efficiency and reduced power 

use in fans (see low pressure drop cyclones above). By installing new preheaters, the 

productivity of the kiln will increase, due to a higher degree of pre-calcination (up to 30 

to 40%) as the feed enters the kiln. Also, the kiln length may be shortened by 20 to 30% 

thereby reducing radiation losses (van Oss, 1999). As the capacity increases, the clinker 

cooler may have to be adapted to be able to cool the large amounts of clinker. The 

conversion of older kilns is attractive when the old kiln needs replacement and a new kiln 

would be too expensive, assuming that limestone reserves are adequate. 

Energy savings depend strongly on the specific energy consumption of the dry process 

kiln to be converted as well as the number of preheaters to be installed. For example, 

cement kilns in the former German Democratic Republic were rebuilt by Lafarge to 

replace four dry process kilns originally constructed in 1973 and 1974. In 1993 and 1995, 

three kilns were equipped with four-stage suspension preheaters. The specific fuel 

consumption was reduced from 4.1 GJ/t clinker to 3.6 GJ/t clinker, while the capacity of 

the individual kilns was increased from 1650 to 2500 tpd (Duplouy and Trautwein, 

1997). In the same project, the power consumption was reduced by 25%, due to the 

replacement of fans and the finish grinding mill. Energy savings are estimated to be 0.9 

GJ/t clinker for the conversion which reflects the difference between the average dry kiln 

specific fuel consumption and that of a modern preheater kiln, based on a study of the 

Canadian cement industry (Holderbank, 1993). The study estimates the specific costs at 

$39 to 41/annual tonne clinker capacity for conversion to a multi-stage preheater kiln 

while Vleuten (1994) estimates a cost of $28/annual tonne clinker capacity for the 

installation of suspension pre-heaters. 

Conversion to Reciprocating Grate Cooler. Four main types of coolers are used in the 

cooling of clinker: (1) shaft; (2) rotary; (3) planetary; and, (4) reciprocating grate coolers. 

There are no longer any rotary or shaft coolers in operation in North America; in China, 

there are few if any rotary or shaft coolers (Cui, 2006). However, some reciprocating grate 

coolers may still be in operation. 

11
The grate cooler is the modern variant and is used in almost all modern kilns. The 

advantages of the grate cooler are its large capacity (allowing large kiln capacities) and 

efficient heat recovery (the temperature of the clinker leaving the cooler can be as low as 

83°C, instead of 120 to 200°C, which is expected from planetary coolers (Vleuten, 1994). 

Tertiary heat recovery (needed for precalciners) is impossible with planetary coolers 

(Cembureau, 1997b), limiting heat recovery efficiency. Grate coolers recover more heat 

than do the other types of coolers. For large capacity plants, grate coolers are the preferred 

equipment. For plants producing less than 500 tonnes per day the grate cooler may be too 

expensive (COWIconsult et al., 1993). Replacement of planetary coolers by grate coolers is 

not uncommon (Alsop and Post, 1995). 

Modern reciprocating coolers have a higher degree of heat recovery than older variants, 

increasing heat recovery efficiency to 65% or higher, while reducing fluctuations in 

recuperation efficiency (i.e. increasing productivity of the kiln). In China, the Liulihe 

Cement Factory implemented a TCIDRI third generation grate cooler and achieved a heat 

recovery rate of over 72% on a 2500 tonne/day precalciner kiln (ITIBMIC, 2004). This 

aerated beam grate cooler also saves water by replacing the water spray cooling with air 

cooling (ITIBMIC, 2004). When compared to a planetary cooler, additional heat recovery 

is possible with grate coolers at an extra power consumption of approximately 3.0 kWh/t 

clinker (COWIconsult et al., 1993; Vleuten, 1994). The savings are estimated to be up to 

8% of the fuel consumption in the kiln (Vleuten, 1994). Cooler conversion is generally 

economically attractive only when installing a precalciner, which is necessary to produce 

the tertiary air (see above), or when expanding production capacity. The cost of a cooler 

conversion is estimated to be between $.044 and $5.5/annual tonne clinker capacity, 

depending on the degree of reconstruction needed. Annual operation costs increase by 

$0.11/t clinker (Jaccard and Willis, 1996). 

Kiln Combustion System Improvements. Fuel combustion systems in kilns can be 

contributors to kiln inefficiencies with such problems as poorly adjusted firing, 

incomplete fuel burn-out with high CO formation, and combustion with excess air 

(Venkateswaran and Lowitt, 1988). Improved combustion systems aim to optimize the 

shape of the flame, the mixing of combustion air and fuel and reducing the use of excess 

air. Various approaches have been developed. One technique developed in the U.K. for 

flame control resulted in fuel savings of 2 to 10% depending on the kiln type 

(Venkateswaran and Lowitt, 1988). Lowes and Bezant, (1990) discuss advancements 

from combustion technology that improve combustion through the use of better kiln 

control. They also note that fuel savings of up to 10% have been demonstrated for the use 

of flame design techniques to eliminate reducing conditions in the clinkering zone of the 

kiln in a Blue Circle plant (Lowes and Bezant, 1990). 

For rotary kilns, the Gyro-Therm technology improves gas flame quality while reducing 

NOx emissions. Originally developed at the University of Adelaide (Australia), the GyroTherm technology can be applied to gas burners or gas/coal dual fuel. The Gyro-Therm 

burner uses a patented "precessing jet" technology. The nozzle design produces a gas jet 

leaving the burner in a gyroscopic-like precessing motion. This stirring action produces 

rapid large scale mixing in which pockets of air are engulfed within the fuel envelope 

without using high velocity gas or air jets. The combustion takes place in pockets within 

12
the fuel envelope under fuel rich conditions. This creates a highly luminous flame, 

ensuring good irradiative heat transfer. A demonstration project at an Adelaide Brighton 

plant in Australia found average fuel savings between 5 and 10% as well as an increase in 

output of 10% (CADDET, 1997a). A second demonstration project at the Ash Grove 

plant in the U.S. (Durkee, Oregon) found fuel savings between 2.7% and 5.7% with 

increases in output between 5 and 9% (CADDET, 1997a; Videgar, Rapson and Dhanjal, 

1997). Costs for the technology vary by installation. An average cost of $1/annual tonne 

clinker capacity is assumed based on reported costs in the demonstration projects. 

Indirect Firing. Historically the most common firing system is the direct-fired system. 

Coal is dried, pulverized and classified in a continuous system, and fed directly to the 

kiln. This can lead to high levels of primary air (up to 40% of stoichiometric). These high 

levels of primary air limit the amount of secondary air introduced to the kiln from the 

clinker cooler. Primary air percentages vary widely, and non-optimized matching can 

cause severe operational problems with regard to creating reducing conditions on the kiln 

wall and clinker, refractory wear and reduced efficiency due to having to run at high 

excess air levels to ensure effective burnout of the fuel within the kiln. 

In more modern cement plants, indirect fired systems are most commonly used. In these 

systems, neither primary air nor coal is fed directly to the kiln. All moisture from coal 

drying is vented to the atmosphere and the pulverized coal is transported to storage via 

cyclone or bag filters. Pulverized coal is then densely conveyed to the burner with a small 

amount of primary transport air (Smart and Jenkins, 2000). As the primary air supply is 

decoupled from the coal mill in multi-channel designs, lower primary air percentages are 

used, normally between 5 and 10%. The multi-channel arrangement also allows for a 

degree of flame optimization. This is an important feature if a range of fuels is fired. 

Input conditions to the multi-channel burner must be optimized to secondary air and kiln 

aerodynamics for optimum operation (Smart and Jenkins, 2000). The optimization of the 

combustion conditions will lead to reduced NOx emissions, better operation with varying 

fuel mixtures, and reduced energy losses. This technology is standard for modern plants. 

Excess air infiltration is estimated to result in heat losses equal to 75 MJ/t of clinker. 

Assuming a reduction of excess air between 20% and 30%, indirect firing may lead to 

fuel savings of 15 to 22 MJ/t of clinker. The advantages of improved combustion 

conditions will lead to a longer lifetime of the kiln refractories and reduced NOx 

emissions. These co-benefits may result in larger cost savings than the energy savings 

alone. 

The disadvantage of an indirect firing system is the additional capital cost. In 1997, 

California Portland’s plant in Colton, California implemented an indirect firing system 

for their plant, resulting in NOx emission reductions of 30 to 50%, using a mix of fuels 

including tires. The investment costs of the indirect firing system were $5 million for an 

annual production capacity of 680,000 tonnes clinker, or $7.4/t clinker. 

Optimize Heat Recovery/Upgrade Clinker Cooler. The clinker cooler drops the clinker 

temperature from 1200°C down to 100°C. The most common cooler designs are of the 

13
planetary (or satellite), traveling and reciprocating grate type. All coolers heat the 

secondary air for the kiln combustion process and sometimes also tertiary air for the 

precalciner (Alsop and Post, 1995). Reciprocating grate coolers are the modern variant 

and are suitable for large-scale kilns (up to 10,000 tpd). Grate coolers use electric fans 

and excess air. The highest temperature portion of the remaining air can be used as 

tertiary air for the precalciner. Rotary coolers (used for approximately 5% of the world 

clinker capacity for plants up to 2200 to 5000 tpd) and planetary coolers (used for 10% of 

the world capacity for plants up to 3300 to 4400 tpd) do not need combustion air fans and 

use little excess air, resulting in relatively lower heat losses (Buzzi and Sassone, 1993; 

Vleuten, 1994). 

Grate coolers may recover between 1.3 and 1.6 GJ/t clinker sensible heat (Buzzi and 

Sassone, 1993). Improving heat recovery efficiency in the cooler results in fuel savings, 

but may also influence product quality and emission levels. Heat recovery can be 

improved through reduction of excess air volume (Alsop and Post, 1995), control of 

clinker bed depth and new grates such as ring grates (Buzzi and Sassone, 1993; Lesnikoff, 

1999). Control of cooling air distribution over the grate may result in lower clinker 

temperatures and high air temperatures. Additional heat recovery results in reduced 

energy use in the kiln and precalciner, due to higher combustion air temperatures. Birch, 

(1990) notes a savings of 0.05 to 0.08 GJ/t clinker through the improved operation of the 

grate cooler, while Holderbank, (1993) notes savings of 0.16 GJ/t clinker for retrofitting a 

grate cooler. COWIconsult et al. (1993) note savings of 0.08 GJ/t clinker but an increase 

in electricity use of 2.0 kWh/t clinker. The costs of this measure are assumed to be half 

the costs of the replacement of the planetary with a grate cooler, or $0.22/annual tonne 

clinker capacity. 

A recent innovation in clinker coolers is the installation of a static grate section at the hot 

end of the clinker cooler. This has resulted in improved heat recovery and reduced 

maintenance of the cooler. Modification of the cooler would result in improved heat 

recovery rates of 2 to 5% over a conventional grate cooler. Investments are estimated to 

be $0.11 to $0.33/annual tonne clinker capacity (Young, 2002).

Seal Replacement. Seals are used at the kiln inlet and outlet to reduce false air penetration, 

as well as heat losses. Seals may start leaking, increasing the heat requirement of the kiln. 

Most often pneumatic and lamella-type seals are used, although other designs are available 

(e.g. spring-type). Although seals can last up to 10,000 to 20,000 hours, regular inspection 

may be needed to reduce leaks. Energy losses resulting from leaking seals may vary, but 

are generally relatively small. Philips Kiln Services (2001) reports that upgrading the inlet 

pneumatic seals at a relatively modern plant in India (Maihar Cement), reduced fuel 

consumption in the kiln by 0.4% (0.011 GJ/t clinker). The payback period for improved 

maintenance of kiln seals is estimated to be 6 months or less (Canadian Lime Institute, 

2001). This technology is produced and available domestically in China (Cui, 2006). 

Low Temperature Heat Recovery for Power Generation 1 . Despite government 

 

1 The adoption of low temperature waste heat recovery for electricity production in cement plants changes 

the temperature profile of the flue gas which may impact the low-temperature, catalytic dioxin formation 

14
policies to promote adoption of the technology (through the China Medium and Long 

Term Energy Conservation Plan, for example), using low temperature waste heat for 

power generation has not been widely adopted by Chinese cements plants (GEI, 2005) 

although 45 cement rotary kilns have already adopted this measure (Cui, 2006). Even 

many large-scale rotary kilns built after 2003 do not use this technology. One plant has 

utilized this technology, received through donation from Japan (GEI, 2005). The Anhui 

Ningguo cement plant installed a power generation system on a 4000 tonne per day kiln 

cement production line and found electricity generated reached 39 kWh per tonne of 

clinker since operation began in 1998 (Anhui Ninggou, 2002). Pan (2005) estimates a 

cost for imported (Japanese) technology of 18,000 to 22,000 RMB ($2,250 to $2,750) per 

kW with an installation capacity over 6 MW. Chinese domestic technology was 

developed in 1996 and is currently available from three Chinese companies: Tianjin 

Designing Institute of Cement Industry, Zhongxin Heavy Machine Company, and 

Huaxiao Resource Co. Ltd. All three companies have on-going demonstration programs 

in Chinese cement plants. Installation cost of domestic technology and equipment is 

currently about 10,000 RMB ($1,250) per kW. The installation cost would be a bit lower 

if kilns and generation system are constructed simultaneously. At China United Cement 

Company, two 6000 kW systems were installed for RMB 101.8 million ($12.7 million 

2006 U.S.), RMB 36 million ($4.5 million 2006 U.S.) of private capital and RMB 64 

million of bank loans ($8 million 2006 U.S.), equaling about RMB 8500 per kW (CNBM, 

2005). The electricity being generated is 79.8 kWh/t clinker. Beijing Cement Ltd. also 

installed waste heat recovery equipment on its 2400 tpd and 3200 tpd kilns (BEIC, 2006). 

Total capacity is now 7.5 MW and the total investment was RMB 47.43 million ($6 

million 2006 U.S.), equaling about 6,300 RMB per kW ($800 2006 U.S. per kW). Of this, 

70% was provided by the Beijing Energy Investment Company. 

In another demonstration project summarized by GEI (2005), the waste heat from two 

clinker kilns of Taishan Cement Ltd is to be used. The capacity of the two kilns is 5000 

tonnes per day and 2500 tonnes per day. Operation was to begin on 1st Oct 2005; 

equipment has already been installed but is still under adjustment. Maximum capacity is 

designed at 13.2 MW and annual output of 95 GWh. Of this, 90.8 GWh would be 

supplied to cement production, accounting for more than 30% of the energy needs of 

cement production (Guo, 2004). 

ITIBMIC (2004) estimates for a 2000 tonne per day (730,000 annual tonne) kiln capacity, 

about 20 kWh/t clinker of electricity could be generated for an investment of 20 to 30 

million RMB. 

 reactions. Heat recovery from waste-to-energy boilers increases the residence time for the flue gas at the 

dioxin formation temperature window (700 -200 C) increases dioxin formation. Flue gas cooling 

temperature profile is one the important factors determining dioxin formation potential of a combustion 

facility. Some hazardous waste incinerators use rapid flue gas quenching to reduce residence time of the 

flu gas passing through the formation window for controlling dioxin formation. On the other hand, it may 

be due to less boiler surface area in the optimum temperature window in quenched vs. non-quenched 

systems, rather than a gas residence time. The surface area tends to accumulate reactive carbon and trace 

metals. More area likely means higher D/F concentrations. Research is needed to find out whether there is 

significant effect of waste heat recovery on dioxin emissions from cement kilns (Lee, 2006; Gullett, 2006). 

15
In May 2002, the Tianjin Cement Industry Design and Research Institute in cooperation 

with the Shanghai Wanan Enterprise Corporation began renovations on a 1350 tonne 

four-stage cyclone preheater kiln to generate low-temperature waste heat electricity 

(ITIBMIC, 2004). They installed domestic low temperature waste heat recovery 

technology, and the facility now generates over 1.8 MW of electricity, operating 7000 

hours per year. Including the 10% electricity required to operate the system, the facility 

generates an additional 11.34 GWh annually. With an electricity price of 0.50 RMB/kWh, 

the Tianjin Cement plant found savings of 11 to 14 RMB per tonne of clinker. The 

operating cost is about 0.06 RMB/kWh and the payback period about 3 years. Lowtemperature waste heat recovery has been implemented at other plants, as well, including 

the 4000 tonne/day precalciner kiln at the Ningguo Cement Factory of the Conch Group 

and the Liuzhou Cement Factory (ITIBMIC, 2004). 

ITIBMIC (2004) reports generating capacity of domestic technology to be approximately 

24 to 32 kWh, while foreign technology will generate about 28 to 36 kWh. Cui (2006) 

most recently reported domestic technology could produce 35kWh/t of clinker while 

Japanese technology now produces 45 kWh/t of clinker; German technology better but no 

data is available. Investment, however, is much less – about 6000 RMB for domestic 

technology and 16,000 RMB for foreign equipment. Running time and required labor are 

approximately the same. 

High Temperature Heat Recovery for Power Generation. Waste gas discharged from 

the kiln exit gases, the clinker cooler system, and the kiln pre-heater system all contain 

useful energy that can be converted into power. In the U.S., only in long-dry kilns is the 

temperature of the exhaust gas sufficiently high to cost-effectively recover the heat 

through power generation.2

 Cogeneration systems can either be direct gas turbines that 

utilize the waste heat (top cycle), or the installation of a waste heat boiler system that 

runs a steam turbine system (bottom cycle). This measure focuses on the steam turbine 

system since these systems have been installed in many plants worldwide and have 

proven to be economic (Steinbliss, 1990; Jaccard and Willis, 1996; Neto, 1990). Heat 

recovery has limited application for plants with in-line raw mills, as the heat in the kiln 

exhaust is used for raw material drying. While electrical efficiencies are still relatively 

low (18%), based on several case studies power generation may vary between 11 and 25 

kWh/t clinker (Scheuer & Sprung, 1990; Steinbliss, 1990; Neto, 1990). Electricity 

savings of 22 kWh/t clinker are assumed. Jaccard and Willis (1996) estimate installation 

costs for such a system at $2.2 to 4.4/annual tonne clinker capacity with operating costs 

of $0.22 to 0.33/t clinker. In 1999, four U.S. cement plants cogenerated 486 million kWh 

(USGS, 2001). In China, most high temp waste heat is recycled to the preheated and 

precalciner. 

Low Pressure Drop Cyclones for Suspension Preheaters. Cyclones are a basic 

component of plants with pre-heating systems. The installation of newer cyclones in a 

 

2

 Technically, organic rankine cycles or Kalina cycles (using a mixture of water and ammonia) can be used to 

recover low-temperature waste heat for power production, but this is currently not economically attractive, 

except for locations with high power costs. In China, however, low temperature heat is being recovered; see 

previous measure for details. 

16
plant with lower pressure losses will reduce the power consumption of the kiln exhaust 

gas fan system. Depending on the efficiency of the fan, 0.66 to 0.77 kWh/t clinker can be 

saved for each 50 mm W.C. (water column) the pressure loss is reduced. For most older 

kilns this amounts to savings of 0.66 to 1.1 kWh/t clinker (Birch, 1990). Fujimoto (1994) 

discussed a Lehigh Cement plant retrofit in which low-pressure drop cyclones were 

installed in their Mason City, Iowa plant and saved 4.4 kWh/t clinker (Fujimoto, 1994). 

Installation of the cyclones can be expensive, however, since it may often entail the 

rebuilding or the modification of the preheater tower, and the costs are very site specific. 

Also, new cyclone systems may increase overall dust loading and increase dust carryover 

from the preheater tower. However, if an inline raw mill follows it, the dust carryover 

problem becomes less of an issue. A cost of $3/annual tonne clinker is assumed for a 

low-pressure drop cyclone system. The best technology available in China is imported 

from the Austrian PMT Company (Cui, 2006). 

Efficient Kiln Drives. A substantial amount of power is used to rotate the kiln. The 

highest efficiencies are achieved using a single pinion drive with an air clutch and a 

synchronous motor (Regitz, 1996). The system would reduce power use for kiln drives by 

a few percent, or roughly 0.55 kWh/t clinker at slightly higher capital costs (+6%). More 

recently, the use of alternate current (AC) motors is advocated to replace the traditionally 

used direct current (DC) drive. The AC motor system may result in slightly higher 

efficiencies (0.5 – 1% reduction in electricity use of the kiln drive) and has lower 

investment costs (Holland, 2001). Using high-efficiency motors to replace older motors 

or instead of re-winding old motors may reduce power costs by 2 to 8%. 

Clinker Making – Vertical Shaft Kilns 

For vertical shaft kilns, the main energy-efficiency opportunity is to replace the VSK 

with new suspension preheater/precalciner kilns. In addition, combustion system 

improvements can be made for the kiln. Table 5 provides information on the initial 

capital costs, the operations and maintenance (O&M) costs, the simple payback period, 

the specific fuel savings, the specific electric savings, the specific carbon dioxide savings 

and the lifetime associated with each of these measures. 

Replace vertical shaft kiln with new suspension preheater/precalciner kilns. The new 

suspension preheater (NSP) technique is being developed for 1000 t/day, 2000 t/day and 

4000 t/day (GEI, 2005). NSP should be used for medium- or large-scale cement plants 

that are being either enlarged or rebuilt. For the small cement plants, earthen vertical kiln 

(and hollow rotary kiln with dry method) should be gradually abandoned. Further 

description of these kilns is made above. 

According to Liu et al. (1995), some “key” Chinese plants3 use 5.4 GJ/t clinker, while 

advanced precalciner kilns use about 3 GJ/t clinker; a savings of 2.4 GJ/t clinker. The 

Liulihe Cement Factory installed a precalciner kiln with a 5-stage preheater and a 

preburning furnace and found fuel consumption to be 3.011 GJ/t (ITIBMIC, 2004). 

 

3

 “Key” Chinese plants generally refer to large, centrally administered state-owned enterprises (Sinton, 

1996). 

17
Table 5. Energy-Efficiency Opportunities Applicable to Vertical Shaft Kilns. 

Capital 

Costs ($/t)

O & M 

Costs 

 ($/t) 

Payback 

Period 

(years) 

Fuel 

Savings 

(GJ/t) 

Electric 

Savings 

(kWh/t) 

CO2

savings 

(kgC/t) 

Lifetime 

(years) 

Convert to new suspension 

preheater/precalciner kiln 

28-41 NA 5-71 2.4 - 62 40 

Kiln combustion system 

improvements 

NA NA NA NA NA NA NA 

Note: Energy savings and costs below are based on case study data. Costs in China will vary depending on technology 

and availability. Where possible, we have included more data for China in the following text. All data are given per tonne 

of clinker. 

1

 Payback period calculated using approximate costs of bituminous coal for industrial boilers (bitu2) in China for the 

year 2005 (approximately $55/t coal). 

NA = data not available; efficiency data unavailable because case studies generally measure fuel savings for a package 

of measures; individual measures are rarely applied and hence, savings for them are often not measured or calculated 

(Liu et al, 1995). For example, Liu et al. (1995) reports a package of measures for VSKs usually result in a 10-30% 

savings in fuel intensity and a payback period of 2 years. 

By the end of 2004, China put into service 140 new suspension preheater/precalciner 

(NSP) and suspension preheater (SP) kilns; of those, 50 were new in 2004 (Cui, 2004). 

For more information on this technology, also see measures in Energy Efficiency 

Opportunities for Clinker Production – Rotary Kilns Section, above. 

Kiln Combustion System Improvements. Fuel combustion systems in kilns can be 

contributors to kiln inefficiencies, often resulting in higher CO formation. Inefficiencies 

are caused by incomplete combustion of fuel, combustion with excess or inadequate air, 

uneven air distribution, and oversupply of coal (Venkateswaran and Lowitt, 1988; Liu et 

al., 1995). Inadequate blower capacity and leakage can result in insufficient air supply. 

Improvement of air distribution requires better quality raw material pellets and precise 

kiln operation. Sophisticated VSKs are mechanized with automatic feeding and 

discharging equipment, while older VSKs are still operated manually (Liu et al., 1995). 

Oversupply of coal often results from coal powder that has been overground, supplying 

high fuel density. At low temperatures and insufficient oxygen, overground coal reacts 

with CO2 and generates CO. More information on automation of the kiln, feed, and 

blending can be found in the measure “Energy Management and Process Control 

Systems”, above. 

In China, domestic technologies are being used for medium and small cement plants; for 

larger plants, many are using imported technologies (Cui, 2006). 

Finish Grinding 

Table 6 shows fuel and electricity savings, estimated payback period and carbon dioxide 

(CO2) savings for each measure related to final grinding. A description for each measure 

is given below. 

Process Control and Management – Grinding Mills. Control systems for grinding 

operations are developed using the same approaches as for kilns (see above). The systems 

control the flow in the mill and classifiers, attaining a stable and high quality product. 

Several systems are marketed by a number of manufacturers. Expert systems have been 

commercially available since the early 1990’s. The Karlstadt plant of Schwenk KG 

18
(Germany) implemented an expert system in a finishing mill in 1992, increasing mill 

throughput and saving energy. The payback is estimated between 1.5 and 2 years in 

Germany (Albert, 1993). Magotteaux (Belgium) has marketed a control system for mills 

since 1998 and has sold six units to plants in Germany (Rohrdorfer Zement), Greece 

(Heracles General Cement), South Africa (PPC Group) and the United Kingdom (UK) 

(Rugby Group). Experience with a cement mill at the South Ferriby plant of the Rugby 

Group in the UK showed increased production (+3.3%) and power savings equal to 3%, 

while the standard deviation in fineness went down as well (Van den Broeck, 1999). 

Krupp Polysius markets the PolExpert system and reports energy savings between 2.5 

and 10% (typically 8%), with increased product quality (lower deviation) and production 

increases of 2.5 –10%, after installing control systems in finishing mills (Goebel, 2001). 

Similar results have been achieved with model predictive control (using neural networks) 

for a cement ball mill at a South-African cement plant (Martin and McGarel, 2001a). 

Pavilion Technologies (US) has developed a new control system using neural networks. 

Pavilion Technologies reports a 4-6% throughput increase (and corresponding reduction 

in specific power consumption) for installing a model predictive control system in finish 

ball mill (Martin et al., 2001). Payback periods are typically between 6 and 8 months 

(Martin and McGarel, 2001a). 

Table 6. Energy Efficiency Measures for Final Grinding of Products in Cement Plants. 

More information can be found in the description of the measures below. 

Energy Efficiency Measure 

(for Finish Grinding) 

Fuel 

Savings 

(GJ/t) 

Electricity 

Savings 

(kWh/t) 

Estimated 

Payback Period 

(years) (1)

CO2

Savings 

(kgC/t) 

Energy Management & Process Control - 3.8-4.2 < 1 to 2 0.9-1.0 

High Pressure Roller Press - 8-28 > 10 (1) 1.8-6.3 

High-Efficiency Classifiers - 1.9-6.0 > 10 (1) 0.4-1.4 

Improved Grinding Media in Ball Mills - 3-5 8 (1) 0.7-1.2 

Notes: 

All data is given per tonne of cement 

(1) Payback periods are calculated on the basis of energy savings alone. In reality this investment may be driven by 

other considerations than energy efficiency (e.g. productivity, product quality), and will happen as part of the normal 

business cycle or expansion project. Under these conditions the measure will have a lower payback period depending 

on plant-specific conditions. 

Advanced Grinding Concepts. The energy efficiency of ball mills for use in finish 

grinding is relatively low, consuming up to 30-42 kWh/t clinker depending on the 

fineness of the cement (Marchal, 1997; Cembureau, 1997b). Several new mill concepts 

exist that can significantly reduce power consumption in the finish mill to 20-30 kWh/t 

clinker, including roller presses, roller mills, and roller presses used for pre-grinding in 

combination with ball mills (Alsop and Post, 1995; Cembureau, 1997b; Seebach et al., 

1996). Roller mills employ a mix of compression and shearing, using 2-4 grinding rollers 

carried on hinged arms riding on a horizontal grinding table (Cembureau, 1997b; Alsop 

and Post, 1995). In a high-pressure roller press, two rollers pressurize the material up to 

3,500 bar (Buzzi, 1997), improving the grinding efficiency dramatically (Seebach et al., 

1996). 

Air swept vertical roller mills with integral classifiers are used for finish grinding, 

whereas a recent off-shoot technology which is not air swept is now being used as a pregrinding system in combination with a ball mill. A variation of the roller mill is the air 

19
swept ring roller mill, which has been shown to achieve an electricity consumption of 25 

kWh/t with a Blaine of 3000 (Folsberg, 1997). A new mill concept is the Horomill, first 

demonstrated in Italy in 1993 (Buzzi, 1997). In the Horomill, a horizontal roller within a 

cylinder is driven. The centrifugal forces resulting from the movement of the cylinder 

cause a uniformly distributed layer to be carried on the inside of the cylinder. The layer 

passes the roller (with a pressure of 700-1000 bar) (Marchal, 1997). The finished product 

is collected in a dust filter. The Horomill is a compact mill that can produce a finished 

product in one step and hence has relatively low capital costs. Grinding Portland cement 

with a Blaine of 3200 cm2

/g consumes approximately 23 kWh/t (Buzzi,1997) and even 

for pozzolanic cement with a Blaine of 4000, power use may be as low as 30 kWh/t 

(Buzzi,1997). 

Today, high-pressure roller presses are most often used to expand the capacity of existing 

grinding mills, and are found especially in countries with high electricity costs or with 

poor power supply (Seebach et al, 1996). After the first demonstration of the Horomill in 

Italy, this concept is now also applied in plants in Mexico (Buzzi, 1997), Germany, 

Czech Republic and Turkey (Duplouy and Trautwein, 1997). New designs of the roller 

mills allow for longer operation times (> 20,000 hours). The electricity savings of a new 

finish grinding mill when replacing a ball mill is estimated to be 28 kWh/t cement. The 

addition of a pre-grinding system to a ball mill will result in savings of 7-24 kWh/t cement 

for (Cembureau, 1997b; Holland et al., 1997; Scheuer and Sprung, 1990) Capital cost 

estimates for installing a new roller press vary widely in the literature, ranging from low 

estimates like $2.5/annual tonne cement capacity (Holderbank, 1993) or $3.6/annual tonne 

cement capacity (Kreisberg, 1993) to high estimates of $8/annual tonne cement capacity 

(COWIconsult et al., 1993). The capital costs of roller press systems are lower than those 

for other systems (Kreisberg, 1993) or at least comparable (Patzelt, 1993). Some new mill 

concepts may lead to a reduction in operation costs of as much as 30-40% (Sutoh et al., 

1992). 

High Efficiency Classifiers. A recent development in efficient grinding technologies is 

the use of high-efficiency classifiers or separators. Classifiers separate the finely ground 

particles from the coarse particles. The large particles are then recycled back to the mill. 

Standard classifiers may have a low separation efficiency, which leads to the recycling of 

fine particles, resulting in extra power use in the grinding mill. In high-efficiency 

classifiers, the material is more cleanly separated, thus reducing over-grinding. High 

efficiency classifiers or separators have had the greatest impact on improved product 

quality and reducing electricity consumption. 

A study of the use of high efficiency classifiers in Great Britain found a reduction in 

electricity use of 7 kWh/t cement after the installation of the classifiers in their finishing 

mills and a 25% production increase (Parkes, 1990). Holderbank (1993) estimates a 

reduction of 8% of electricity use (6 kWh/t cement) while other studies estimate 1.9-2.5 

kWh/t cement (Salborn and Chin-Fatt, 1993; Süssegger, 1993). Newer designs of highefficiency separators aim to improve the separation efficiency further and reduce the 

required volume of air (hence reducing power use), while optimizing the design. All 

major suppliers market new classifier designs, e.g. Polysius (SEPOL), F. L. 

20
Smidth/Fuller and Magotteaux (Sturtevant SD). The actual savings will vary by plant and 

cement type and fineness required. For example, the electricity savings from installing a 

new high-efficiency classifier at a cement plant in Origny-Rochefort (France) varied 

between 0 and 6 kWh/t (Van den Broeck, 1998), and investment costs were $2/annual 

tonne finished material based on Holderbank (1993). 

Improved Grinding Media. Improved wear resistant materials can be installed for 

grinding media, especially in ball mills. Grinding media are usually selected according to 

the wear characteristics of the material. Increases in the ball charge distribution and surface 

hardness of grinding media and wear resistant mill linings have shown a potential for 

reducing wear as well as energy consumption (Venkateswaran and Lowitt, 1988). 

Improved balls and liners made of high chromium steel is one such material but other 

materials are also possible. Other improvements include the use of improved liner designs, 

such as grooved classifying liners. These have the potential to reduce grinding energy use 

by 5-10% in some mills, which is equivalent to estimated savings of 3-5 kWh/t cement 

(Venkateswaran and Lowitt, 1988). 

Plant Wide Measures 

Table 7 shows fuel and electricity savings, estimated payback period and carbon dioxide 

(CO2) savings for each plant wide measure. A description for each measure is given 

below. 

Table 7. Energy Efficiency Measures for Plant Wide Measures in Cement Plants. More 

information can be found in the description of the measures below. 

Energy Efficiency Measure 

(Plant Wide Measures) 

Fuel 

Savings 

(GJ/t) 

Electricity 

Savings 

(kWh/t) 

Estimated 

Payback Period 

(years) 

CO2

Savings 

(kgC/t) 

Preventative Maintenance 0.05 0-6 < 1 1.3-2.6 

High Efficiency Motors - 0-6 < 1 0-1.3 

Adjustable Speed Drives - 6-8 2- 3 1-2 

Optimization of Compressed Air Systems - 0-6 < 3 0-1 

Efficient Lighting - 0-0.6 <3 0-0.1 

Notes: 

All data is given per tonne of cement 

Preventative Maintenance. Preventative maintenance includes training personnel to be 

attentive to energy consumption and efficiency. Successful programs have been launched 

in a variety of industries (Caffal, 1995; Nelson, 1994). While many processes in cement 

production are primarily automated, there still are opportunities, requiring minimal 

training of employees, to increase energy savings. Also, preventative maintenance (e.g. 

for the kiln refractory) can also increase a plant’s utilization ratio, since it has less 

downtime over the long term. Birch (1990) mentions that the reduction of false air input 

into the kiln at the kiln hood has the potential to save 0.05 GJ/t. Lang (1994) notes a 

reduction of up to 5 kWh for various preventative maintenance and process control 

measures (typically around 3 kWh/t). Based on similar programs in other industries, 

annual and start up costs for implementing this training are estimated to be minimal and 

would be paid back in less than one year. For preventative maintenance of compressed air 

systems, see below. 

21
High-Efficiency Motors and Drives. Motors and drives are used throughout the cement 

plant to move fans (preheater, cooler, alkali bypass), to rotate the kiln, to transport 

materials and, most importantly, for grinding. In a typical cement plant, 500-700 electric 

motors may be used, varying from a few kW to MW-size (Vleuten, 1994). Power use in the 

kiln (excluding grinding) is roughly estimated to be 40-50 kWh/tonne clinker (Heijningen 

et al., 1992). Variable speed drives, improved control strategies and high-efficiency motors 

can help to reduce power use in cement kilns. If the replacement does not influence the 

process operation, motors may be replaced at any time. However, motors are often rewired 

rather than being replaced by new motors. Power savings may vary considerably on a 

plant-by-plant basis, ranging from 3 to 8% (Fujimoto, 1994). Vleuten (1994) estimates the 

potential power savings at 8% of the power use. Based on an analysis of motors in the U.S. 

Department of Energy’s MotorMaster+ software, and a breakdown of motors in a 5,000 tpd 

cement plant given in Bösche (1993), it is assumed that high-efficiency motors replace 

existing motors in all plant fan systems with an average cost of $0.22/annual tonne cement 

capacity. 

Adjustable or Variable Speed Drives. Drives are the largest power consumers in cement 

making. The energy efficiency of a drive system can be improved by reducing the energy 

losses or by increasing the efficiency of the motor (see above). Decreasing throttling can 

reduce energy losses in the system and coupling losses through the installation of 

adjustable speed drives (ASD). Most motors are fixed speed AC models. However, motor 

systems are often operated at partial or variable load (Nadel et al., 1992). Also, in cement 

plants large variations in load occur (Bösche, 1993). There are various technologies to 

control the motor (Worrell et al., 1997). The systems are offered by many suppliers and are 

available worldwide. Worrell et al. (1997) provide an overview of savings achieved with 

ASD in a wide array of applications. The savings depend on the flow pattern and loads. 

The savings may vary between 7 and 60%. ASD equipment is used more and more in 

cement plants (Bösche, 1993; Fujimoto, 1993), but the application may vary widely, 

depending on electricity costs. Within a plant, ASDs can mainly be applied for fans in the 

kiln, cooler, preheater, separator and mills, and for various drives. For example, Blue 

Circle’s Bowmanville plant (Canada) installed a variable air inlet fan, reducing electricity 

and fuel use in the kiln (because of reduced inlet air volume), saving C$75,000/year in 

energy costs (approximately $47,000 in U.S. dollars) (CIPEC, 2001). One case study for a 

modern cement plant estimated potential application for 44% of the installed motor power 

capacity in the plant (Bösche, 1993). ASDs for clinker cooler fans have a low payback, 

even when energy savings are the only reason for installing ASDs (Holderbank, 1993). 

Energy savings strongly depend on the application and flow pattern of the system on which 

the ASD is installed. Although savings are significant (Holderbank, 1993), not many 

quantitative studies are available for the cement industry. One hypothetical case study 

estimates the savings at 70%, compared to a system with a throttle valve (or 37% compared 

with a regulated system) for the raw mill fan (Bösche, 1993). In practice savings of 70% 

are unrealistic (Young, 2002). Fujimoto, (1994) notes that Lafarge Canada’s Woodstock 

plant replaced their kiln ID fans with ASDs and reduced electricity use by 6 kWh/t. It is 

estimated that the potential savings are 15% for 44% of the installed power, or roughly 

equivalent to 8 kWh/t cement. The specific costs depend strongly on the size of the system. 

For systems over 300 kW the costs are estimated to be 70 ECU/kW (75 US$/kW) or less 

22
and for the range of 30-300 kW at 115-130 ECU/kW (120-140 US$/kW) (Worrell et al., 

1997). Using these cost estimates, the specific costs for a modern cement plant, as studied 

by Bösche (1993), can be estimated to be roughly $0.9 to 1.0/annual tonne cement capacity. 

Other estimates vary between $0.4 and $3/annual tonne cement (Holland et al., 1997; 

Holderbank, 1993). 

Compressed Air Systems. Compressed air systems are used in different parts of the 

plants, i.e. mixing of slurry (in wet process plants) and in the baghouse Pulse-Jet or 

Plenum Pulse dust collector filters and other parts. Total energy consumption by 

compressed air systems is relatively small in cement plants, however, it can amount to a 

considerable expense if the systems run continuously and end-uses are offline. Still, 

energy efficiency improvement measures may be found in these systems. Compressed air 

is probably the most expensive form of energy available in a plant because of its poor 

efficiency. Typically overall efficiency is around 10% for compressed air (LBNL et al., 

1998). Because of this inefficiency, if compressed air is used, it should be of minimum 

quantity for the shortest possible time, constantly monitored and weighed against 

alternatives. 

Maintenance of Compressed Air Systems. Inadequate maintenance can lower 

compression efficiency and increase air leakage or pressure variability, as well as lead to 

increased operating temperatures, poor moisture control, and excessive contamination. 

Improved maintenance will reduce these problems and save energy. Proper maintenance 

includes the following (LBNL et al., 1998): 

• Keep the compressor and intercooling surfaces clean and foul-free. Blocked filters 

increase pressure drop. By inspecting and periodically cleaning filters, the pressure 

drop may be kept low. Seek filters with just a 1 psig pressure drop over 10 years. The 

payback for filter cleaning is usually under 2 years (Ingersoll-Rand, 2001). Fixing 

improperly operating filters will also prevent contaminants from entering into tools and 

causing them to wear out prematurely. Generally, when pressure drop exceeds 14 to 20 

kN/m2, replace the particulate and lubricant removal elements, and inspect all systems 

at least annually. Also, consider adding filters in parallel that decrease air velocity, and, 

therefore, decrease air pressure drop. A 2% reduction of annual energy consumption in 

compressed air systems is projected for more frequent filter changing (Radgen and 

Blaustein, 2001). 

• Keep motors properly lubricated and cleaned. Poor motor cooling can increase motor 

temperature and winding resistance, shortening motor life, in addition to increasing 

energy consumption. Compressor lubricant should be changed every 2 to 18 months 

and checked to make sure it is at the proper level. In addition to energy savings, this can 

help avoid corrosion and degradation of the system. 

• Inspect drain traps periodically to ensure they are not stuck in either the open or closed 

position and are clean. Some users leave automatic condensate traps partially open at 

all times to allow for constant draining. This practice wastes substantial energy and 

should never be undertaken. Instead, install simple pressure driven valves. 

Malfunctioning traps should be cleaned and repaired instead of left open. Some auto 

drains, such as float switch or electronic drains do not waste air. Inspecting and 

maintaining drains typically has a payback of less than 2 years (Ingersoll-Rand, 2001). 

23
• Maintain the coolers on the compressor to ensure that the dryer gets the lowest possible 

inlet temperature (Ingersoll-Rand, 2001). 

• Check belts for wear and adjust them. A good rule of thumb is to adjust them every 400 

hours of operation. 

• Replace air lubricant separators according to specifications or sooner. Rotary screw 

compressors generally start with their air lubricant separators having a 14 to 20 kN/m2 

pressure drop at full load. When this increases to 70 kN/m2, change the separator 

(LBNL at al., 1998). 

• Check water cooling systems for water quality (pH and total dissolved solids), flow, 

and temperature. Clean and replace filters and heat exchangers per manufacturer’s 

specifications. 

Reduce Leaks. Leaks can be a significant source of wasted energy. A typical plant that has 

not been well maintained will likely have a leak rate equal to 20 to 50% of total 

compressed air production capacity (Ingersoll Rand, 2001; Price and Ross, 1989). Leak 

maintenance can reduce this number to less than 10%. Overall, a 20% reduction of annual 

energy consumption in compressed air systems is projected for fixing leaks (Radgen and 

Blaustein, 2001). Estimations of leaks vary with the size of the hole in the pipes or 

equipment. In addition to increased energy consumption, leaks can make air tools less 

efficient and adversely affect production, shorten the life of equipment, lead to additional 

maintenance requirements and increase unscheduled downtime. In the worst case, leaks can 

add unnecessary compressor capacity. 

The most common areas for leaks are couplings, hoses, tubes, fittings, pressure regulators, 

open condensate traps and shut-off valves, pipe joints, disconnects, and thread sealants. A 

simple way to detect leaks is to apply soapy water to suspect areas. The best way to detect 

leaks is to use an ultrasonic acoustic detector, which can recognize the high frequency 

hissing sounds associated with air leaks. After identification, leaks should be tracked, 

repaired, and verified. Leak detection and correction programs should be ongoing efforts. 

Reducing the Inlet Air Temperature. Reducing the inlet air temperature reduces energy 

used by the compressor. In many plants, it is possible to reduce inlet air temperature to the 

compressor by taking suction from outside the building. Importing fresh air can have 

paybacks of 2 to 5 years (CADDET, 1997b). As a rule of thumb, each 3°C will save 1% 

compressor energy use (CADDET, 1997b; Parekh, 2000). 

Maximize Allowable Pressure Dew Point at Air Intake. Choose the dryer that has the 

maximum allowable pressure dew point, and best efficiency. A rule of thumb is that 

desiccant dryers consume 7 to 14% of the total energy of the compressor, whereas 

refrigerated dryers consume 1 to 2% as much energy as the compressor (Ingersoll Rand, 

2001). Consider using a dryer with a floating dew point. 

Compressor Controls. The objective of any control strategy is to shut off unneeded 

compressors or delay bringing on additional compressors until needed. All units that are on 

should be running at full-load, except for one. Positioning of the control loop is also 

important; reducing and controlling the system pressure downstream of the primary 

24
receiver can result in energy consumption of up to 10% or more (LBNL, et al., 1998). 

Energy savings for sophisticated controls are 12% annually (Radgen and Blaustein, 2001). 

Start/stop, load/unload, throttling, multi-step, variable speed and network controls are 

options for compressor controls and described below. 

Start/stop (on/off) is the simplest control available and can be applied to reciprocating or 

rotary screw compressors. For start/stop controls, the motor driving the compressor is 

turned on or off in response to the discharge pressure of the machine. They are used for 

applications with very low duty cycles. Applications with frequent cycling will cause the 

motor to overheat. Typical payback for start/stop controls is 1 to 2 years. 

 

Load/unload control, or constant speed control, allows the motor to run continuously but 

unloads the compressor when the discharge pressure is adequate. In most cases, unloaded 

rotary screw compressors still consume 15 to 35% of full-load power while delivering no 

useful work (LBNL et al., 1998). Hence, load/unload controls can be inefficient. 

Modulating or throttling controls allow the output of a compressor to be varied to meet 

flow requirements by closing down the inlet valve and restricting inlet air to the 

compressor. Throttling controls are applied to centrifugal and rotary screw compressors. 

Changing the compressor control from on/zero/off to a variable speed control can save up 

to 8% per year (CADDET, 1997b). 

Sizing Pipe Diameter Correctly. Inadequate pipe sizing can cause pressure losses, 

increase leaks and increase generating costs. Pipes must be sized correctly for optimal 

performance or resized to fit the current compressor system. Increasing pipe diameter 

typically reduces annual energy consumption by 3% (Radgen and Blaustein, 2001). 

Heat Recovery for Water Preheating. As much as 80 to 93% of the electrical energy 

used by an industrial air compressor is converted into heat. In many cases, a heat 

recovery unit can recover 50 to 90% of this available thermal energy for space heating, 

industrial process heating, water heating, makeup air heating, boiler makeup water 

preheating, industrial drying, industrial cleaning processes, heat pumps, laundries or 

preheating aspirated air for oil burners (Parekh, 2000). It’s been estimated that 

approximately 50 MJ/hour of energy is available for each 0.05 m3

/second of capacity (at 

full load) (LBNL et al., 1998). Paybacks are typically less than one year. Heat recovery 

for space heating is not as common with water-cooled compressors because an extra 

stage of heat exchange is required and the temperature of the available heat is lower. 

However, with large water cooled compressors, recovery efficiencies of 50 to 60% are 

typical (LBNL et al., 1998). Implementing this measure saves up to 20% of the energy 

used in compressed air systems annually for space heating (Radgen and Blaustein, 2001). 

Plant Wide Lighting 

Energy use for lighting in the cement industry is very small. Still, energy efficiency 

opportunities may be found that can reduce energy use cost-effectively. Lighting is used 

either to provide overall ambient lighting throughout the manufacturing, storage and office 

spaces or to provide low-bay and task lighting to specific areas. High-intensity discharge 

25
(HID) sources are used for the former, including metal halide, high-pressure sodium and 

mercury vapor lamps. Fluorescent, compact fluorescent (CFL) and incandescent lights are 

typically used for task lighting in offices. 

Lighting Controls. Lights can be shut off during non-working hours by automatic 

controls, such as occupancy sensors which turn off lights when a space becomes 

unoccupied. Manual controls can also be used in addition to automatic controls to save 

additional energy in smaller areas. Payback of lighting control systems is generally less 

than 2 years. 

Replace T-12 Tubes by T-8 Tubes. In industry, typically T-12 tubes have been used. T-12 

refers to the diameter in 1/8 inch increments (T-12 means 12/8 inch or 3.8 cm diameter 

tubes). The initial output for these lights is high, but energy consumption is also high. They 

also have extremely poor efficacy, lamp life, lumen depreciation, and color rendering 

index. Because of this, maintenance and energy costs are high. Replacing T-12 lamps with 

T-8 lamps (smaller diameter) approximately doubles the efficacy of the former. 

Replace Mercury Lights by Metal Halide or High Pressure Sodium Lights. Where 

color rendition is critical, metal halide lamps can replace mercury or fluorescent lamps with 

an energy savings of 50%. Where color rendition is not critical, high pressure sodium 

lamps offer energy savings of 50 to 60% compared to mercury lamps (Price and Ross, 

1989). 

Replace Metal Halide HID with High-Intensity Fluorescent Lights. Traditional HID 

lighting can be replaced with high-intensity fluorescent lighting. These new systems 

incorporate high-efficiency fluorescent lamps, electronic ballasts and high-efficacy fixtures 

that maximize output to the work plane. Advantages to the new system are many; they have 

lower energy consumption, lower lumen depreciation over the lifetime of the lamp, better 

dimming options, faster start-up and restrike capability, better color rendition, higher pupil 

lumens ratings and less glare (Martin, et al., 2000). High-intensity fluorescent systems yield 

50% electricity savings over standard metal halide HID. Dimming controls that are 

impractical in the metal halide HIDs can also save significant energy. Retrofitted systems 

cost about $185 per fixture, including installation costs (Martin, et al., 2000). In addition to 

energy savings and better lighting qualities, high-intensity fluorescents can help improve 

productivity and have reduced maintenance costs. 

Replace Magnetic Ballasts with Electronic Ballasts. A ballast is a mechanism that 

regulates the amount of electricity required to start a lighting fixture and maintain a 

steady output of light. Electronic ballasts save 12-25 percent more power than their 

magnetic predecessors do (U.S. EPA, 2001). 

Product and Feedstock Change 

Product and feedstock changes include the production of blended cements, use of wastederived fuels, production of limestone cement and low alkali cement, and the use of steel 

slag in the kiln. Table 8 provides information on the initial capital costs, the operations 

and maintenance (O&M) costs, the simple payback period, the specific fuel savings, the 

26
specific electric savings, the specific carbon dioxide savings and the lifetime associated 

with each of these measures. 

Blended Cements. The production of blended cements involves the intergrinding of 

clinker with one or more additives (fly ash, pozzolans, granulated blast furnace slag, 

silica fume, volcanic ash) in various proportions. The use of blended cements is a 

particularly attractive efficiency option since the intergrinding of clinker with other 

additives not only allows for a reduction in the energy used (and carbon emissions) in 

clinker production, but also corresponds to a reduction in carbon dioxide emissions in 

calcination as well. Blended cement has been used for many decades around the world. 

Table 8. Product and Feedstock Changes to Improve the Energy Efficiency of Clinker 

Production. 

Capital 

Costs ($/t)

O & M 

Costs 

 ($/t) 

Payback 

Period 

(years) 

Fuel 

Savings 

(GJ/t) 

Electric 

Savings 

(kWh/t) 1

CO2

savings 

(kgC/t) 

Lifetime 

(years) 

Blended cements 0.7 -0.06 < 1 0.9-3.4 2 -11 21-85 20 

Use of waste-derived fuels 0.1-3.7 < 0 3 1 > 0.6 - 12 4 20 

Limestone cement 5 minimal -5% < 1 0.3 2.8 8.4 NA 

Low alkali cement (rotary 

only) 

0 0 Immediate 0.19-0.5 6 4.6-12.1 NA 

Use of steel slag in kiln * < 2 0.19 - 4.9 NA 

Note: Energy savings and costs below are based on case study data, except where noted. Costs in China will vary 

depending on technology and availability. Where possible, we have included more data for China in the following text. All 

data are given per tonne of clinker. 1

 Negative numbers represent an increase in electricity due to the measure. 

2

 Data from Chinese case studies indicate savings of 2.6 to 3.4 GJ/t clinker, while U.S. data shows savings of 0.9 GJ/t 

clinker (or 1.4 GJ/t cement at a clinker to cement ratio of 0.65). 3

 Reduces operating costs but amount is not known 

4 In calculating specific CO2 savings for this measure, we used an emission factor for solvents of 0.02 tC/GJ. 5

 Savings for this measure are calculated based on data given on a per tonne of cement basis and a clinker to cement 

ratio of 0.85. O&M savings are given based on percent savings in the kiln operating costs. 6 Some electricity is saved but exact amounts are unknown. 

* Total investment costs are $400,000 to $1,000,000 per installation. 

NA = data not available 

Blended cements are very common in Europe; blast furnace and pozzolanic cements 

account for about 12% of total cement production with Portland composite cement 

accounting for an additional 44% (Cembureau, 1997b). Blended cements were introduced 

in the U.S. to reduce production costs for cement (especially energy costs), to expand 

capacity without extensive capital costs, to reduce emissions from the kiln. In Europe, a 

common standard has been developed for 25 types of cement (using different 

compositions for different applications). It allows wider applications of additives. Many 

other countries around the world use blended cement. In China, a range of materials are 

used in blended cements (see below), but cement plants mainly produce Portland cement 

(about 95% of total output) (Cui, 2004). Blended cements demonstrate a higher long-term 

strength, as well as improved resistance to acids and sulfates, while using waste materials 

for high-value applications. Short-term strength (measured after less than 7 days) may be 

lower, although cement containing less than 30% additives will generally have setting 

times comparable to concrete based on Portland cement. 

27
In the U.S., the consumption and production of blended cement is still limited. However, 

Portland ordinary cement and Portland slag cement are used widely in cement produced 

in China (ITIBMIC, 2005). In addition, due to technical advancement and market 

development allowing the production of different kinds and grades of cement, some 

industrial byproducts like blast furnace slag, fly ash, coal gangue, limestone, zeolite, 

pozzolana as well as natural minerals are widely used in cement production. The average 

percentage of admixtures in Chinese cement products stands at 24% to 26% (ITIBMIC, 

2005). Table 9 gives the prices and different methods of transportation for the various 

additives used in China. Prices for different additives vary greatly. Prices change with 

location, output, market need, produce type and ways of handling. ITBIMIC (2005) 

estimates fuel savings of at least 10%, and a similar increase in production. 

Table 9. Prices and Transportation Modes for Different Additives Used in China 

Additive 

Blast 

Furnace 

Slag 

Fly ash Cinder Coal 

gangue 

Limestone Gypsum Pebble Kiln 

dust 

Price (Yuan/t) 13 - 80 12 - 35 14 - 26 10 - 38 11 - 40 52 19 0 

Method of 

transportation 

Train and 

truck 

Truck and 

pipe 

Train and 

truck Truck Truck and belt Truck Truck Pipe 

Adapted from ITIBMIC, 2005, Table 26. Prices of additives vary according to location, market need, product type and 

method of transportation. 

For blended cement with, on average, a clinker/cement ratio of 65%, the reduction in 

clinker production corresponds to a specific fuel savings of 1.42 GJ/t cement. There is an 

increase in fuel use of 0.09 GJ/t cement for drying of the blast furnace slags but a 

corresponding energy savings of 0.2 GJ/t cement for reducing the need to use energy to 

bypass kiln exit gases to remove alkali-rich dust. Energy savings are estimated to be 9 to 

23 MJ/t cement per percent bypass (Alsop and Post, 1995). The bypass savings are due to 

the fact that blended cements offer an additional advantage in that the inter-ground 

materials also lower alkali-silica reactivity (ASR), thereby allowing a reduction in energy 

consumption needed to remove the high alkali content kiln dusts. In practice, bypass 

savings may be minimal to avoid plugging of the preheaters, requiring a minimum 

amount of bypass volume. This measure therefore results in total fuel savings of 1.4 GJ/t 

blended cement (0.9 GJ/t clinker for 0.65 clinker to cement ratio). However, energy 

consumption is expected to increase, due to the added electricity consumption associated 

with grinding blast furnace slag (as other materials are more or less fine enough). 

The costs of applying additives in cement production may vary. Capital costs are limited 

to extra storage capacity for the additives. However, blast furnace slag may need to be 

dried before use in cement production. This can be done in the grinding mill, using 

exhaust from the kiln, or supplemental firing, either from a gas turbine used to generate 

power or a supplemental air heater. The operational cost savings will depend on the 

purchase (including transport) costs of the additives4, the increased electricity costs for 

(finer) grinding, the reduced fuel costs for clinker production and electricity costs for raw 

 

4

 To avoid disclosing proprietary data, the USGS does not report separate value of shipments data for 

“cement-quality” fly ash or granulated blast furnace slag, making it impossible to estimate an average cost 

of the additives. 

28
material grinding and kiln drives, as well as the reduced handling and mining costs. 

These costs will vary by location, and would need to be assessed on the basis of 

individual plants. An increase in electricity consumption of 16.5 kWh/t cement (11 kWh/t 

clinker) (Buzzi, 1997) is estimated while an investment cost of $0.72/t cement capacity 

($0.5/t clinker), which reflects the cost of new delivery and storage capacity (bin and 

weigh-feeder) is assumed. 

The Lianzhuo cement Factory in Guangdong Province, China, replaced some of its high 

grade limestone with 33 to 34% calcium oxide (CaO), along with copper tailing high 

content iron sulfide from a nearby county (ITIBMIC, 2004). They found fuel savings of 

2.6 to 3.4 GJ/t clinker, a coal savings of over 50%. The clinker production has increased 

from 2 tonne/day to 14 tonne/day, its strength has improved and its quality is stable 

(ITIBMIC, 2004). 

China produces 25 Mt of blast furnace slag per year and has a long history of using this 

type of waste (Cui, 2006). Where utilized, about 20 to 25% of clinker is replaced; the 

country’s highest slag ratio is 50% (Cui, 2006). In addition, blast furnace slag is added 

into concrete as well as clinker. Fly ash is also increasingly being used in China. China 

has 100 Mt of blast furnace slag and 300 tonnes of fly ash (Cui, 2006). 

Use of Waste-Derived Fuels. Waste fuels can be substituted for traditional commercial 

fuels in the kiln. For example, the U.S. cement industry is increasingly using waste fuels. 

In 1999 tires accounted for almost 5% of total fuel inputs in the industry in the U.S., 

while all wastes total about 17% of all fuel inputs. The trend towards increased waste use 

will likely increase after successful tests with different wastes in Europe and North 

America are performed. New waste streams include carpet and plastic wastes, filter cake, 

paint residue and (dewatered) sewage sludge (Hendriks et al., 1999). Cement kilns also 

use hazardous wastes. Since the early 1990’s cement kilns burn annually almost 1 Mt of 

hazardous waste (CKRC, 2002). The revenues from waste intake have helped to reduce 

the production costs of all waste-burning cement kilns, and especially of wet process 

kilns. Waste-derived fuels may replace the use of commercial fuels, and may result in net 

energy savings and reduced CO2 emissions, depending on the alternative use of the 

wastes (e.g. incineration with or without energy recovery). Currently, in China only three 

cement plants are burning waste fuels. Beijing Cement Plant has the capacity to dispose 

of 10 kt per year of 25 types of waste; the plant is burning solid waste from the chemical 

industry, some paints, solvents and waste sludge from water treatment (Cui, 2004; Wang, 

2006a). Shanghai Jinshan Cement Plant disposes of sludge dredged from the Huangpu 

River which runs through Shanghai (Cui, 2004). Hong Kong Cement Plant purchases 

waste from other provinces to utilize in its kilns (Wang, 2006a). Other plants are utilizing 

wastes but the amounts are very small (Wang, 2006a). 

A cement kiln is an efficient way to recover energy from waste. The carbon dioxide 

emission reduction depends on the carbon content of the waste-derived fuel, as well as 

the alternative use of the waste and efficiency of use (e.g. incineration with or without 

heat recovery). In Table 8, we used the carbon content of solvents to determine the CO2

savings. The high temperatures and long residence times in the kiln destroy virtually all 

29
organic compounds, while efficient dust filters may reduce some other potential 

emissions to safe levels (Hendriks et al., 1999; Cembureau, 1997b). 

In North America, many of the alternative fuels are focused on the use of tires or tirederived fuel. Since 1990 more than 30 cement plants have gained approval to use tirederived fuels, burning around 35 million tires per year (CKRC, 2002). The St. Lawrence 

Cement Factory in Joliette, Quebec completed a project in 1994 where they installed an 

automated tire feed system to feed whole tires into the mid-section of the kiln, which 

replaced about 20% of the energy (CADDET, 1996). This translates to energy savings of 

0.6 GJ/t clinker. Costs for the installation of the Joliette system ran about $3.70/annual 

tonne clinker capacity. Costs for less complex systems where the tires are fed as input 

fuel are $0.11 to $1.1/annual tonne clinker. Other plants have experience injecting solid 

and fluid wastes, as well as ground plastic wastes. A net reduction in operating costs 

(CADDET, 1996; Gomes, 1990, Venkateswaran and Lowitt, 1988) is assumed. 

Investment costs are estimated to be $1.1/annual tonne clinker for a storage facility for 

the waste-derived fuels and retrofit of the burner (if needed). 

Limestone Portland Cement. Similar to blended cement, ground limestone is 

interground with clinker to produce cement, reducing the needs for clinker-making and 

calcination. This reduces energy use in the kiln and clinker grinding as well as CO2

emissions from calcination and energy use. The addition of up to 5% limestone has 

shown to have no negative impacts on the performance of Portland cement, while 

optimized limestone cement would improve the workability slightly (Detwiler and 

Tennis, 1996). Adding 5% limestone would reduce fuel consumption by 5% (or on 

average 0.35 GJ/t clinker), power consumption for grinding by 3.3 kWh/t cement, and 

CO2 emissions by almost 5%. Additional costs would be minimal, limited to material 

storage and distribution, while reducing kiln operation costs by 5%. 

Low-Alkali Cement. In North America, part of the production of the cement industry are 

cements with a low alkali content (probably around 20 to 50% of the market), a much 

higher share than found in many other countries (Holderbank, 1993). In some areas in the 

U.S. as well as China, aggregate quality may be such that low-alkali cements are required 

by the cement company’s customers or by the climate in a particular region (e.g., alkali 

cements are more suitable the south of China in areas of higher rainfall than in drought 

areas in the North). Reducing the alkali content is achieved by venting (called the bypass) hot gases and particulates from the plant, loaded with alkali metals. The by-pass 

also avoids plugging in the preheaters. This becomes cement kiln dust (CKD). Disposal 

of CKD is regulated under the Resource Conservation and Recovery Act (RCRA). Many 

customers demand a lower alkali content, as it allows greater freedom in the choice of 

aggregates. The use of fly-ash or blast-furnace slags as aggregates (or in the production 

of blended cement, see below) may reduce the need for low-alkali cement. Low alkali 

cement production leads to higher energy consumption. Savings of 8 to 21 MJ/t (2 to 5 

Kcal/kg) per percent bypass are assumed (Alsop and Post, 1995). The lower figure is for 

precalciner kilns, while the higher figure is for preheater kilns. Typically, the bypass 

takes 10 to 70% of the kiln exhaust gases (Alsop and Post, 1995). Additionally, 

electricity is saved due to the increased cement production, as the CKD would otherwise 

30
end up as clinker and not cement, requiring further processing. For illustrative purposes, 

assume a 20% point reduction in bypass volume, resulting in energy savings of 0.19 to 

0.5 GJ/t clinker. There are no investments involved in this product change, although 

cement users (e.g. ready-mix producers) may need to change the type of aggregates used 

(which may result in costs). Hence, this measure is most successfully implemented in 

coordination with ready-mix producers and other large cement users. Low alkali cement 

is produced using domestic technology in China (Cui, 2006). 

Use of Steel Slag in Kiln. Texas Industries (Midlothian, Texas) in 1994 developed a 

system to use electric arc furnace (EAF) slags of the steel industry as input in the kiln, 

reducing the use of limestone. The slag that contains tricalcium silicate (C3S) can more 

easily be converted to free lime than limestone. The slags replace limestone 

(approximately 1.6 times the weight in limestone). EAFs produce between 0.055 and 0.21 

tonnes of slag per tonne of steel (on average 0.12 tonnes/tonne) (U.S. DOE OIT, 1996). 

The CemStar® process allows replacing 10 to 15% of the clinker by EAF-slags, reducing 

energy needs for calcination. The advantage of the CemStar® process is the lack of 

grinding the slags, but adding them to the kiln in 5 cm lumps. Depending on the location 

of injection it may also save heating energy. Calcination energy is estimated to be 1.9 

GJ/t clinker (Worrell et al., 2001). Because the lime in the slag is already calcined, it also 

reduces CO2 emissions from calcination, while the reduced combustion energy and lower 

flame temperatures lead to reduced NOx emissions (Battye et al., 2000). For illustrative 

purposes alone, using a 10% injection of slags would reduce energy consumption by 0.19 

GJ/t clinker, while reducing CO2 emissions by roughly 11%. Energy savings can be 

higher in wet kilns due to the reduced evaporation needs. Reductions in NOx emissions 

vary by kiln type and may be between 9 and 60%, based on measurements at two kilns 

(Battye et al., 2000). Equipment costs are mainly for material handling and vary between 

$200,000 and $500,000 per installation. Total investments are approximately double the 

equipment costs. CemStar® charges a royalty fee (Battye et al., 2000). Costs savings 

consist of increased income from additional clinker produced without increased operation 

and energy costs, as well as reduced iron ore purchases (as the slag provides part of the 

iron needs in the clinker). The iron content needs to be balanced with other iron sources 

such as tires and iron ore. In the U.S., the U.S. Environmental Protection Agency 

awarded the CemStar® process special recognition in 1999 as part of the ClimateWise 

program. 

China does not produce this technology domestically, and to date the measure has not 

been implemented in cement kilns in China (Cui, 2006). 

Acknowledgements 

This work was supported by the Climate Protection Partnerships Division of the U.S. 

Environmental Protection Agency as part of its ENERGY STAR program through the 

U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Revision of this 

report for use in China was undertaken with funding provided by the U.S. EPA’s Office 

of International Affairs, the Energy Foundation’s China Sustainable Energy Program and 

31
Dow Chemical Company. We would like to thank the U.S. EPA, the Energy Foundation 

and the Dow Chemical Corporation for their support in making this version of this report. 

Many people have been very helpful in the data collection and review of earlier versions 

of this report. We especially would like to thank Alexander Goebel (Krupp Polysius, 

Germany), Steve McGarel, Tom Evans, Amy George and Greg Martin (Pavilion 

Technologies Inc., Texas) for providing data for the earlier study. We thank the following 

people for reviewing the draft of earlier reports: John Chadbourne (Essroc), Greg Galvin 

(RMC Pacific), Gerald Young (Penta Engineering), Robert Miller (Metso Minerals), Joel 

Fleming (Lafarge North America), Greg Miller (CTL, IL), Hendrik van Oss (USGS), 

Robin Riester (FLS Automation), Dan Willis (Trinity Consultants, TX), and Ray 

Worthington (BMH Americas Inc.). We thank Tom Carter (PCA) for helping to collect 

the helpful suggestions. We thank Ann Dougherty and Gregg Miller (Portland Cement 

Association, Skokie, IL), George Lesnikoff (Hanson Cement, Cupertino, CA), and 

Michael Nisbet (JAN Consultants, Montreal, Canada) for reviewing earlier reports on 

which this report is based and providing technical information. We also thank Suzanne 

Giannini-Spohn (U.S. EPA) for her helpful guidance during the research and writing of 

the sections on kiln energy use and efficiency. We thank Prof. Wang Yanjia of Tsinghua 

University for the helpful review and information that she has provided to us. We thank 

Professor Cui Yuansheng, Vice President of the Institute of Technical Information for the 

Building Materials Industry of China, for meeting with us and providing documents and 

data regarding China’s cement industry. 

Any remaining errors in this report are the responsibility of the authors. The views 

expressed in this report do not necessarily reflect those of the U.S. Environmental 

Protection Agency, the U.S. Department of Energy or the U.S. Government. 

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