Cement Kilns 

Technical Support Document

for the NOx FIP

January 2001

EPA, OAR, OAQPS, AQSSD, OPSG
CONTENTS

PAGE

INTRODUCTION.....................................................................................1

UNCONTROLLED EMISSIONS ............................................................3

EMISSION CONTROL TECHNIQUES..................................................7

COSTS/COST EFFECTIVENESS .........................................................13
1

Introduction

In cement manufacturing, conditions favorable for formation of nitrogen oxides (NOx) 

are reached routinely because of high process temperatures. Essentially all NOx emissions 

associated

with cement manufacturing are generated in cement kilns. In cement kilns, NOx emissions are 

formed during fuel combustion by two primary mechanisms: Oxidation of molecular nitrogen 

present in the combustion air which is termed thermal NOx formation, and oxidation of nitrogen 

compounds present in the fuel which is termed fuel NOx formation. Often the raw material feed 

to the kiln may also contain a significant amount of nitrogen compounds which may lead to feed 

NOx formation similar to fuel NOx formation. Because of the high temperatures involved in the 

burning or clinker formation step, thermal NOx formation provides the dominant mechanism for 

NOx formation in cement manufacturing.

There are four different types of cement kilns used in the industry: long wet kilns, long 

dry kilns, kilns with a preheater, and kilns with a precalciner. The long wet and dry kilns and

most preheater kilns have only one fuel combustion zone, whereas the newer precalciner kilns 

and preheater kilns with a riser duct have two fuel combustion zones. Since the typical 

temperatures in the two types of combustion zones are different, the factors affecting NOx

formation are also somewhat different depending on the kiln type. In a primary combustion zone 

at the hot end of a kiln, the high temperatures lead to predominantly thermal NOx

formation; whereas in the secondary combustion zone lower gas-phase temperatures suppress 

thermal NOx formation. 

In addition, to the specific NOx formation mechanisms, the energy efficiency of the 

cement-making process is also important as it determines the amount of heat input needed to 

produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of 

heat and fuel and would produce less NOx emissions. Since the four types of cement kilns 

exhibit different combustion characteristics as well as energy efficiencies and heat requirements, 

the available NOx emissions data are grouped by these cement kiln types. The data indicate 

substantial spread in the reported NOx emissions with large overlap for different kiln types. The 

four different cement kiln types, however, do appear to have different levels of NOx emissions 

and different characteristics influencing NOx formation.

In the NOx SIP Call final rule, EPA determined that NOx emissions from large cement 

kilns (among other source categories) can be decreased by highly cost-effective controls by an 

average 30 percent.1 As defined in the NOx SIP call rule, “large” is defined as a cement kiln 

which emitted, on average, greater than 1.0 ton/day during the ozone season.1 “Highly cost 

effective controls” are defined in the NOx SIP call as controls which are less than $2,000/ton of 

NOx reduction in 1990 dollars during the ozone season.1 In the final FIP rulemaking associated 
2

with this TSD, EPA is promulgating a rule applicable to large cement kilns to achieve the 

average 30% reduction called for by the final NOx SIP call rule. In the October 27, 1998 final 

NOx SIP call rule, EPA identified about 90 large cement kilns. The EPA recently made 

corrections in its final NOx SIP call budget2.

A recent NESCAUM report estimates the control costs and NOx emission reductions for 

large cement kilns. For four types of controls that achieve at least a 30% reduction, the report 

estimates the cost effectiveness for the ozone season to be less than $1,000 per ton.3( For 

comparison to other recent EPA rule makings, the costs and cost effectiveness can be escalated 

to 1997$ using a factor of 1.21, resulting in $1,210/ton.) 
3

Uncontrolled Emissions

In cement manufacturing, conditions favorable for formation of nitrogen oxides 

(NOx) are reached routinely because of high process temperatures. Essentially all NOx emissions 

associated with cement manufacturing are generated in cement kilns. In cement kilns, NOx

emissions are formed during fuel combustion by two primary mechanisms: Oxidation of 

molecular nitrogen present in the combustion air which is termed thermal NOx formation, and

oxidation of nitrogen compounds present in the fuel which is termed fuel NOx formation. Often 

the raw material feed to the kiln may also contain a significant amount of nitrogen compounds 

which may lead to feed NOx formation similar to fuel NOx formation. Because of the high 

temperatures involved in the burning or clinker formation step, thermal NOx formation provides 

the dominant mechanism for NOx formation in cement manufacturing.

There are four different types of cement kilns used in the industry: long wet kilns, long 

dry kilns, kilns with a preheater, and kilns with a precalciner. The long wet and dry kilns and

most preheater kilns have only one fuel combustion zone. The newer precalciner kilns and 

those preheater kilns which have a riser duct have two fuel combustion zones. Since the typical 

temperatures in the two types of combustion zones are different, the factors affecting NOx

formation are also somewhat different depending on the kiln type. In a primary combustion zone 

at the hot end of a kiln, the high temperatures lead to predominantly thermal NOxformation; 

whereas in the secondary combustion zone lower gas-phase temperatures suppress thermal NOx

formation. 

 In addition, to the specific NOx formation mechanisms, the energy efficiency of the 

cement-making process is also important as it determines the amount of heat input needed to 

produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of 

heat and fuel and would produce less NOx emissions. Since the four types of cement kilns 

exhibit different combustion characteristics as well as energy efficiencies and heat requirements, 

the available NOx emissions data are grouped by these cement kiln types. The data indicate 

substantial spread in the reported NOx emissions with large overlap for different kiln types. The 

four different cement kiln types, however, do appear to have different levels of NOx emissions 

and different characteristics influencing NOx formation.

For thermal NOx, the primary source is fuel combustion in the kiln burning zone as the 

gas temperatures are well above 1,400OC (2,550 F). In contrast, the fuel combustion 

temperature in a precalciner or in a kiln riser duct is well below 1,200 C (2,200 F), which 

suppresses thermal NOx formation. Mainly fuel and feed NOx may be formed in the secondary 

firing zone of preheater and precalciner kiln systems. Along with the combustion temperature, 

the gas-phase residence time and the available oxygen concentration in the high temperature kiln 

burning zone are important parameters. Longer residence times at the high temperatures will 
4

allow the NO to be formed in the equilibrium quantities. Greater amounts of oxygen in the 

combustion zone will of course lead to greater amounts of NOx formation. Once formed, the 

decomposition of NOx at lower temperatures, although thermodynamically favorable, is 

kinetically limited. Thus, strategies to reduce NOx emissions need to be based upon reducing 

formation of thermal NOx which may be achieved by reducing combustion temperature, oxygen 

concentration in the high temperature combustion zone, and the gas residence time at high 

temperatures.

Fuel NOx is formed by the conversion of nitrogen present in the fuel used. A recent 

survey of the cement industry by Portland Cement Association indicates that almost 82 percent 

of the energy requirement of the cement industry is provided by coal. Natural gas contributed 

about 3 percent of the energy demand, oil about 1 percent, and other fuels such as waste solvents 

provided about 14 percent of the energy.

The amount of fuel NOx formed is difficult to identify separately from thermal NOx as 

measurements indicate the overall NOx formed. In general, however, thermal NOx is assumed 

to be the dominant mechanism in cement kilns. Typically, natural gas burners produce more 

intense and hot flames compared to the less intense “lazy” flames produced by coal burners. 

Thus, gas-fired kilns may be expected to produce greater thermal NOx as compared to coal-fired 

kilns. Coal, on the other hand, contains much greater amounts of fuel-bound nitrogen than 

natural gas which has almost no fuel-bound nitrogen. The coal- fired kilns may thus be 

expected to produce more fuel NOx than natural gas-fired kilns. A study of natural gas-and coal 

fired kilns, however, clearly indicated that natural gas-fired, dry-process kilns typically produce 

almost three times more NOx than the coal-fired, dry-process kilns. This fact indicated the 

dominance of thermal NOx in overall NOx formation.

The four types of cement kilns have different combustion characteristics as well as 

energy efficiencies and heat requirements. For the 1994 ACT document, NOx emissions data 

were collected from 51 cement kilns. Uncontrolled emission data were obtained from 22 wet 

kilns, 10 long dry kilns, 10 preheater kilns and 9 precalciner kilns. Wet kilns were found to 

produce the highest NOx emissions ranging from 3.6 to 19.5 lb NOx/ton of clinker with an 

average of 9.7 lb NOx/ton of clinker. The long dry kilns consume significantly less energy than 

wet kilns(about 4.5 MMBtu/ton on average) and produce less NOx emissions that ranged from 

6.1 - 10.5 lb NOx/ton of clinker with an average of 8.6 lb NOx/ton of clinker.4

For preheater kilns, NOx emissions ranged from 2.5 to 11.7 lb NOx/ton of clinker with a 

average of 5.9 lb NOx/ton of clinker. The highest values of 8.1 and 11.7 lb/ton were found in 

natural gas burning kilns. Energy consumption of preheater kilns was much lower, about 3.8 

MM Btu/hr. In addition, combustion of a part of the fuel at a lower preheating temperature is 

expected to reduce the NOx emissions as compared to burning all the fuel in the hot kiln burning 

zone. These two factors account for the lower NOx emissions in preheater kilns as compared to 

wet or long dry kilns.

The precalciner kilns produced the least NOx emissions ranging from 0.9 to 7.0 with an 
5

average of 3.8 lb NOx /ton of clinker. These kilns are the most energy efficient with an average 

energy consumption of 3.3 MM Btu/ton of clinker. Precalciner kilns have lower NOx emission 

rates because they burn more fuel at the calcining temperature.

Subsequent to the ACT document, EPA and members of the cement industry initiated an 

effort to update information on available techniques used to control NOx emissions from cement 

kilns. In September 2000, EC/R completed a report for EPA which updates information in the 

ACT document.5 New uncontrolled emissions data were obtained from eight state air pollution 

control agencies along with additional test data and industry literature. This data is summarized 

below.

UNCONTROLLED NOX EMISSIONS - STATE AIR AGENCIES

Cement kiln type Average rate(lb/ton 

of clinker)

Range(lb/ton of 

clinker)

Number of data 

points

Wet kiln 6.2 1.9-13.4 10

Long dry kiln 4.5 2.5-7.1 6

Preheater kiln 1.7 0.4-3.7 6

Precalciner kiln 2.9 1.1-5.6 12

A comparison of these rates with the 1994 ACT document and the AP-42 section revised 

in 1995 is shown on the next table.

 UNCONTROLLED NOX EMISSIONS(LB NOX/TON OF CLINKER)

Kiln Type 1994 ACT AP-42 New Data

Wet 9.7 7.4 6.2

Long Dry 8.6 6.0 4.5

Preheater 5.9 4.8 1.7

Precalciner 3.8 4.2 2.9

As shown in this table, the four different cement kiln types appear to have different levels 

of NOx emissions. The rates calculated from the State data are generally lower than the 1994 

ACT . The state data are not necessarily more representative than the 1994 ACT document. 

The lower rates in the “New Data” probably result from the assumptions made regarding kiln 

production level and level of NOx control. The lower emission rate in the new data for 

preheater kilns relative to precalciner kilns is contrary to expectations and could be due to the 

lack of data points for preheater kilns.

The AP-42 factors are also lower than the 1994 ACT document but are primarily based 
6

on short term tests, which do not reflect the inherent variability of kiln NOx emissions. Also, 

the data are all over 10 years old. Because the data used to calculate the 1994 ACT document 

are newer and include more CEMS data, the ACT rates are more representative of modern kilns. 

The uncontrolled emission rates in the ACT are used in calculating emission reductions from 

various NOx controls and the cost effectiveness of these controls.
7

Emission Control Techniques

In the NOx SIP call budget calculation, EPA divided cement kilns into 4 categories–long 

wet, long dry, preheater, and preheater/precalciner--and assigned a 30 percent emissions decrease 

on average to each category based on information in EPA’s ACT document for cement kilns. 

As stated in the preamble to the proposed rule, the controls to achieve this 30 percent emissions 

decrease are: low-NOx burners(LNB), mid-kiln firing, or equivalent controls. For all large 

cement kilns, EPA believes that 30% control is achievable on average and that NOx controls are 

highly cost-effective. Highly cost-effective means that the cost-effectiveness for the control is 

less than $2,000/ton in 1990 dollars for the ozone season. This is demonstrated in the ACT 

document for cement kilns.4 In addition, the following sources provide supporting information 

(see docket A-96-56):

* “Status Report on NOx Controls” - December 2000 - NESCAUM(Reference 3) 

* “NOx Control Technologies for the Cement Industry” - September 2000 - EC/R 

(Reference 5)

* “Assessment of Control Technologies for Reducing Nitrogen Oxide Emissions from 

Non-Utility Point Sources and Major Area Sources,” Final Ozone Transport Assessment 

Group (OTAG) Policy Paper, July 1996; Chapter 5, Appendix C, to the OTAG Final 

Report, http://www.epa.gov/ttn/rto/otag/index.html.

Based on information contained in the EC/R report and the NESCAUM, which were both 

completed after the FIP proposal, EPA believes that there are additional controls that achieve 

30% NOx reduction and that these controls are highly cost effective. These controls are 

CemStarR, low-NOx precalciner, tire-derived fuel at a preheater or precalciner kiln, and selective 

non-catalytic reduction including biosolids injection.

1. Kiln Types - NOx Controls

A. Long Wet and Long Dry Kilns

The following control techniques are highly cost effective technologies applicable to long 

wet and long dry kilns and are capable of achieving on average at least a 30% reduction in NOx 

emissions: mid-kiln firing, LNB, and CemStarR.

3-5

 Mid-kiln firing has been demonstrated to 

be effective at reducing NOx emissions while recycling scrap tires at potential profit generating 

rates.5

 Information on the required time for installation of NOx controls was obtained from 

the Portland Cement Association(PCA), CemStarR, Cadence and from the NESCAUM Status 

Report. PCA estimates the total time required for NOx controls to range from 15-31 months.6 

This includes the times for engineering study, equipment design, permit application, permit 

review, manufacturing of the control technology, on-site construction and equipment startup. 
8

For mid-kiln firing, Cadence estimates the engineering analysis to take 1 week; 1 month to 

prepare design; 4-6 months for completing the installation and a few days for startup. 7,8 

CemStarRestimates that it takes 6 weeks to 3 months from the time a decision is made to install 

the control to the time the system is ready for operation.9,10 In the NESCAUM 2000 Status 

Report, estimates are given for three plants.3 At one plant, the total project time needed to 

install low NOx burners and mid kiln firing on a long dry kiln was 1 year. The kiln was shut 

down four weeks for installation. At another cement plant, two days of shutdown were required 

to install CemStarRon a long wet kiln. At another cement plant that installed mid-kiln firing on 

a long dry kiln, shutdown was one week. From the award of contract to startup took 28 weeks.

B. Preheater Kiln

The following control techniques are highly cost effective technologies applicable to 

preheater kilns and are capable of achieving a 30% reduction: low-NOx burners, low-NOx

precalciners, CemStarR, tire-derived fuel and selective non-catalytic reduction including 

biosolids injection.3-5

C.Preheater/Precalciner Kiln

The following control techniques are highly cost effective technologies applicable to 

preheater/precalciner kilns and are capable of achieving a 30% reduction: low-NOx burners, 

CemStarR, low NOx precalciners, tire derived fuel and selective non-catalytic reduction including 

biosolids injection.3-5 Selective non-catalytic reduction has been demonstrated in the United 

States and is operating at 18 kilns in Europe.5

A summary of the various NOx controls and their applicability to the several types of 

kilns is shown on the next table.

TYPE OF CEMENT KILN

NOx Control Wet Long-Dry Preheater Precalciner

Low NOx 

Burners

Yes Yes Yes Yes

Mid-Kiln Firing Yes Yes No No

Tire-Derived 

Fuel

Yes Yes Yes Yes

CemStar Yes Yes Yes Yes

SNCR No No Yes Yes

Low NOx

Precalciner

No No Yes Yes
9

2. SUMMARY OF NOx CONTROLS

A.Low NOx Burners(LNB)

For LNB as noted in the preamble to the proposed rule, the ACT document has one 

emission test with a reduction of 28% and experimental tests show 20-30% reductions. In 

January 2000, the Portland Cement Association provided results of a survey of 81% of the 

cement facilities that indicated that 14% of the operating kilns(22 kilns) have installed a LNB. 

Updated information including more recent emission test reports on LNB is contained in the 

EC/R report. This information is summarized in the following table. For the 12 kilns tested, 

the NOx reduction ranged from 14-47% with an average of 29%.

LNB TEST RESULTS

Kiln Type Uncontrolled(lb/ton) Controlled (lb/ton) Reduction (%)

50% coal added to 

reduction zonePrecalciner kiln

2.8 1.9 31

100% coal -

reduction zonePrecalciner kiln

2.8 1.6 44

Unknown 970 ppm 650 ppm 33

 “ Not Given Not Given 30

 “ 650 ppm 460 ppm 29

 “ 900 ppm 730 ppm 19

 “ Not Given Not Given 15

Unknown 774 ppm 409 ppm 47

 “ 865 ppm 664 ppm 23

 “ 484 ppm 350 ppm 28

 “ 487 ppm 336 ppm 31 

Long wet kiln 277 ppm 239 ppm 14

B. Mid-Kiln Firing

Mid-kiln firing(MKF) is a type of staged combustion of fuels that injects solid fuel into 

the calcining zone of a rotating long kiln using a specially designed feed injection mechanism. 
10

MKF is applicable to conventional long wet and long dry kilns. The solid fuel which is often 

tires, burns at a temperature of 600 to 900 C(1,100 to 1,650F) which is much lower than the 

clinker burning temperature of 1,200 to 1,480C (2,200 to 2,700F). One facility uses baled 

industrial waste as a fuel and the use of energy waste materials from carpet scrap to 

pharmaceutical waste is being studied.

By adding fuel in the main flame at mid-kiln, MKF changes both the flame temperature 

and flame length. These changes may reduce thermal NOx formation by burning part of the fuel 

at a lower temperature and by creating reducing conditions at the solid waste injection point 

which may destroy some of the NOx formed upstream in the kiln burning zone. MKF may also 

produce additional fuel NOx depending upon the nitrogen content of the fuel. However as 

discussed in the section on uncontrolled emissions, fuel NOx is unimportant relative to thermal 

NOx emissions. 

Waste-derived fuels with high heating values represent an economical energy source for 

the cement industry and its consumption has been increasing during the past decade. MKF is a 

proven technology and at least 21 cement kilns in the U.S. have been modified with MKF.

 A summary of emission test data on the performance of MKF from the EC/R report 

follows.

MKF - EMISSION TEST RESULTS

 Emissions(lb NOx/ton of clinker) Reduction (%)

Dry Kilns 

A NA 14

B NA 11

C NA 45, 55

D 2.7 NA

E 10.2 14

F NA 47, 50, 28

Average(Dry kilns) 6.4 33

Wet kilns

G NA 59

H NA 35
11

I NA 28

Average(Wet kilns) NA 41

Average(Dry&Wet) 6.4 35

NA- not available

C. CemStarR

CemStarRis a feed modification that was developed by and is patented by TXI Industries. 

CemStarRis applicable to all types of kilns. This process adds a small amount of steel slag to 

the raw kiln feed. Steel slag has a low melting temperature and is chemically very similar to 

clinker. Since many of the chemical reactions required to convert steel slag to clinker have 

already taken place in a steel furnace, the fuel needed to convert steel slag into clinker is low. It 

is estimated that CemStarRcan increase production by 15 percent.

Kilns with lower initial baseline NOx emissions would have less NOx percent reductions 

with CemStarRthan those with higher baseline emissions. Wet and long dry kilns would have 

greater NOx reductions with CemStarR because more energy is used per ton of clinker produced 

than preheater/precalciner kilns.

Wet kilns may achieve the greatest NOx reductions with CemStarR because the addition 

of steel slag would reduce the amount of water needed to create the slurry and consequently 

decrease the amount of heat needed for drying. 

Eleven facilities are using or in the process of incorporating CemStarR. CemStarR 

requires little extra equipment and the addition of steel slag to the feed mix can result in a 

reduction or elimination of the need for some mineral sources, such as shale or clay. 

A summary of emission test results data for CemStarRfrom the EC/R report follows.

CEMSTARR - EMISSION TEST RESULTS

Type of kiln Uncontrolled(lb 

NOx/ton of clinker)

Controlled(lb NOx/ton 

of clinker)

Reduction(%)

Preheater/precalciner 5.6 3.9(normal feed rate) 30

 “ ” 5.6 3.2(maximum feed rate) 44

Wet kiln (long term) 5.2 4.0 24

Wet kiln (short term) 17.5-24.7 11.2 36-55
12

D. Selective non-catalytic reduction(SNCR)

SNCR is the reduction of NOx in the exhaust gases by ammonia or urea without the use 

of a catalyst. Ammonia or urea are injected into the kiln at a temperature between 870 to 1,090 

C(1,600 to 2,000 F). For long dry and wet kilns, the appropriate location for reagent addition 

is the middle of the kiln. Because of the rotating nature of a long dry or wet kiln, continuous 

injection of reagents is not possible. Therefore, SNCR is not applicable to long dry or wet 

kilns.

In preheater/precalciner kilns, the temperatures at the cooler end of the rotating kiln, in 

the riser duct, and in the lower section of the cyclone preheater are likely to be in the SNCR 

temperature window. Such kilns are therefore good candidates for application of SNCR. 

In the US, SNCR has been tested in two kilns. NOxOut(an SNCR process using aqueous 

urea) was tested under ten different operating conditions at a preheater/precalciner kiln. NOx

emissions were effectively reduced from 3.5 to 6.0 lb NOx/ton of clinker. Another test showed 

a NOx reduction of 10 to 20 percent from a low baseline of 350 pounds NOx/hour. 

SNCR is presently being used in 18 cement suspension preheater or precalciner kilns in 

Europe.5 The most common reagent is 25% ammonia water. NOx reduction rates vary from 

10 to 50 percent. Two preheater/precalciner kilns achieved 80 to 85% reduction.

E. Biosolids Injection(BSI)

The BSI process was developed by the Cement Industry Environmental Consortium and 

is presently being used at one plant, Mitsubishi Cement, Lucerne Valley, California. BSI can 

be considered to be a form of SNCR. The ammonia is contained in the dewatered biosolids 

obtained from wastewater treatment plants. The biosolids are injected into the mixing chamber 

where the flue gas stream leaving the kiln and calciner mix. Emission test results indicate a 

50 percent NOx reduction from BSI going from 2.4 to 1.2 lb/ton of clinker.

F.Low-NOx Precalciners

Low-NOx Precalciners typically consist of injecting a portion of the fuel into the feed end 

of the kiln. This fuel is burned in a sub-stoichiometric oxygen environment to create a strongly 

reducing atmosphere. This reducing atmosphere inhibits the formation of fuel NOx and destroys 

a portion of the NOx formed in the kiln burning zone. Most of the major cement kiln suppliers 

are offering these systems for new kilns. Also, several precalciner kilns in the US have recently 

been retrofitted with these controls. NOx reduction has been reported to be as much as 46 

percent.

G. Tire-Derived Fuel at a Preheater/Precalciner Kiln

Tire-derived fuel can be added to the feed end of a preheater or precalciner kiln. One 
13

California plant has been adding whole waste tires to its precalciner kiln since 1993. From the 

EC/R report, emission test results indicate NOx emissions were reduced by 30 to 40 percent.5
14

COSTS/COST EFFECTIVENESS

The average cost effectiveness for large cement kilns using the above mentioned 

technologies has recently been estimated for EPA in the EC/R report.5 The key variables in 

determining average cost effectiveness are the average uncontrolled emissions at the existing 

source, the projected level of controlled emissions, annualized costs of the controls, and number 

of hours of operation in the ozone season. The ACT document uses an average uncontrolled 

level which varies among the 4 types of kilns from 3.8-9.7 lb/ton of clinker and assumes nearly 

continuous operation in the ozone season. The EPA believes the ACT document provides a 

reasonable approach to calculating cost effectiveness for cement kilns. Further, EPA believes 

the cost-effectiveness analysis should use updated data as described in the EC/R report. The 

EPA acknowledges that specific values will vary from kiln to kiln. 

1. LOW NOX BURNERS(LNB)

For LNB, cost information was obtained from a supplier of LNB for the EC/R report. 

The cost of a burner depends on the size or heat duty as well as the number of different types of 

fuels that can be burned, e.g., only coal, or coal and gas or coal, waste-derived liquid fuel and 

gas. The principal equipment cost of LNB using coal as the fuel is typically about $100,000 

for a 200 MMBtu/hr heat duty. For a multi-channel burner the cost is higher. The capital 

cost of a multi-channel retrofit LNB is about 100 percent greater than that for a single channel 

burner for the same heat duty. From the limited available data a linear correlation (R2=0.98) 

was developed for the approximate purchase cost for a retrofit application as a function of heat 

duty. This equation is:

PEC = 172,000 + 152 H where

PEC = Multi-channel LNB purchase equipment cost

H = Burner heat duty in MM Btu/hr.

The cost of a single channel LNB is obtained by dividing the PEC of a multi-channel burner by 

2. 

For LNB, indirect firing is required. Conversion of a direct-fired kiln to an indirect-fired 

kiln reduces the amount of primary air and increases the proportion of secondary air input to the 

kiln. As shown in the EC/R report. the total cost to convert an existing dry process facility with 

two kilns, with a combined 100 tons/hr clinker capacity and a 225 Mm Btu/hr heat duty, was 

$5.6 million in 1998. The total installed cost is estimated to be $3.8 million (in 1997 dollars).

A summary of the capital and annual costs of LNB for various model kilns with existing 

indirect-fired kilns from the EC/R report is summarized below.

COSTS - LNB - INDIRECT-FIRED KILNS - 1997$
15

Kiln type Capacity(tons/hr) Capital Costs Annual Costs

Wet 30 511,000 136,000

Wet 50 618,000 152,000

Long dry 25 473,000 130,000

Long dry 40 546,000 141,000

Preheater 40 538,000 140,000

Preheater 70 678,000 161,000

Precalciner 100 761,000 173,000

Precalciner 150 966,000 204,000

The capital and annual costs for existing direct-fired kilns are summarized below.

COSTS - DIRECT-FIRED KILNS - 1997 $

Kiln type Capacity(tons/hr) Capital Costs Annual costs

Wet 30 1,600,000 298,000

Wet 50 2,200,000 389,000

Long dry 25 1,210,000 241,000

Long dry 40 1,630,000 304,000

Preheater 40 1,490,000 282,000

Preheater 70 2,130,000 378,000

Precalciner 100 1,930,000 348,000

Precalciner 150 2,540,000 439,000
16

In calculating cost effectiveness for LNB, an average cost effectiveness of 25 percent was 

used in the EC/R report. Cost effectiveness of LNB for an existing indirect-fired kiln range 

from $330-620/ton of NOX removed. The cost effectiveness of LNB installed in an existing 

direct-fired kiln range from $760-1,200/ton of NOX removed. The next two tables present 

cost effectiveness for LNB.

Cost effectiveness - retrofit LNB - Indirect fired kiln -1997$

Kiln type Capacity

(tons/hr)

NOx Removed 

(tons/yr)

Annual costs Cost 

effectiveness 

($/ton)

Wet 30 320 136,000 430

Wet 50 500 152,000 300

Long dry 25 210 130,000 620

Long dry 40 400 141,000 350

Preheater 40 240 140,000 580

Preheater 70 500 161,000 320

Precalciner 100 400 173,000 430

Precalciner 150 400 204,000 510

Cost effectiveness - Retrofit LNB - direct-fired kiln - 1997 $

Kiln Type Capacity 

(tons/hr)

NOx Removed 

(tons/year)

Annual Costs Cost 

effectiveness($/ton)

Wet 30 320 298,000 930

Wet 50 500 389,000 780

Long dry 25 210 241,000 1,100

Long dry 40 400 304,000 760

Preheater 40 240 282,000 1,200

Preheater 70 500 378,000 760

Precalciner 100 400 348,000 870

Precalciner 150 400 439,000 1,100
17

2. MID-KILN FIRING (MKF)

For mid-kiln firing of tires, the costs associated are those for kiln modifications necessary 

to facilitate secondary combustion of fuels as well as those for a conveying system required for 

the secondary fuel. For the EC/R report, costs were obtained from a vendor for four kilns - two 

wet kilns and two dry kilns. The purchased equipment cost for each of the four kilns is 

approximately $1.5 million. The annual costs include a fuel credit for the tire derived fuel(15% 

of the heat duty) as well as a tipping fee of $ 42 per ton of whole tires.

COSTS FOR MID-KILN FIRING - 1997 $

KILN TYPE CAPACITY

(TONS/HR)

CAPITAL COSTS ANNUAL COSTS

Wet 30 3,170,000 - 15,000

Wet 50 3,240,000 -370,000

Long Dry 25 3,150,000 190,000

Long dry 40 3,210,000 - 9,000

Cost effectiveness for mid-kiln firing of tires is shown below. The NOx reduction 

efficiency for wet kilns was 40% and for long dry kilns; 30%. The cost effectiveness 

includes a fuel credit for using waste-derived fuel and a tipping fee for tires.

COST EFFECTIVENESS FOR MID-KILN FIRING - 1997 $

KILN TYPE CAPACITY

(TONS/HR)

NOx REDUCTION

(TONS/YR)

COST 

EFFECTIVENESS 

($/TON)

Wet 30 500 -30

Wet 50 800 -460

Long dry 25 260 730

long dry 40 440 -20

3. CEMSTARR

The costs associated with installing this process are primarily material handling 
18

equipment for the steel slag. TXI, the developer and patent holder of this process, estimates the 

cost of this equipment to range from $200,000 to $500,000. The annual costs for a 42 

tons/hour, long, wet kiln are $220,000 which includes the cost of steel slag, royalties, and credit 

for the reduction in raw materials. A credit for the increased production of 

clinker(approximately 3 tons/hour) is not included. Costs for other installations are not 

available.

Costs for model plants could not be developed because the addition of steel slag is 

completely plant dependant. There is no set ratio of steel slag injection to kiln production rate. 

The amount of steel slag needed depends on the plant raw material and can vary from 5 to 10 

percent addition of steel slag, based on kiln production. The addition of steel slag results in a 

production increase. This is approximately an equal trade-off; that is, one ton of steel slag is 

equal to one ton of clinker. Steel slag cost $5-15 per ton whereas clinker cost $72 per ton. Thus 

the average cost savings is $62/ton times the increase in production. In most plants, production 

is increased by 5 to 10% with the addition of the CemStarRprocess. Also, the addition of steel 

slag typically reduces the need for iron used in raw material feed. This can result in a savings 

of $.50 to $1.00 per ton of clinker produced. The facility installing the technology has to pay 

TXI $16 per ton of steel slag used. 

In the EC/R report, cost effectiveness was determined for the 42 tons clinker/hour; long, 

wet kiln. As mentioned above the annual costs are $220,000. Using an average emission 

reduction of 30%, the NOx emission reduction is 480 tons/year. The cost effectiveness for this 

facility is $550/ton of NOx reduced.

4. BIOSOLIDS INJECTION

The costs associated with this technology include the sludge system and the sludge 

conveying system. For a 215 tons of clinker/hour preheater/precalciner, the purchased 

equipment cost is $240,000. Biosolids are added at a 20 tons/hour rate. The total capital 

investment is $1,200,000. Annual costs are a savings of $320,000 which is based on a tipping 

fee of $5/ton.

Cost effectiveness for this 215 TPH precalciner is based on the annual cost of $-320,000 

and a 50% NOx reduction. Cost effectiveness is a credit of $-310/ton.

5. SELECTIVE NON-CATALYTIC REDUCTION

Costs for this technology using NOxOut were obtained from Nalco for two 

preheater/precalciner kilns for the EC/R report and are summarized in the table below. 

COSTS - SNCR - NOxOUT - 1997 $

Kiln Production Rate(tons of 

clinker/hr)

92 133
19

Capital Costs $1,060,000 $1,200,000

Annual Costs $560,000 $2,000,000

Cost effectiveness was calculated based on 40% efficiency and is $1,000/ton for the 

smaller kiln and $2,500/ton for the larger kiln.

6. Tire-Derived Fuel - Preheater/Precalciner

From the EC/R report, costs for a tire-derived fuel system at a precalciner kiln with a 

capacity of 215 TPH were obtained from the facility. The annual costs for the system is 

$-1,600,000 which includes a fuel credit for using waste-derived fuel and a tipping fee for 

tires($42.50/ton). Using a NOx emission reduction of 30%, the cost effectiveness is $- 1,900/ 

ton.

Cost Factors

Monitoring costs

In the NOx FIP proposed rulemaking, EPA assumed periodic emissions testing. The 

EPA now believes that CEMS may be an important part of the cement kiln’s successful 

operation. That is, such monitoring equipment may be necessary to assure stable operation and 

optimization of the kiln.5 While EPA strongly encourages States and industry to consider CEMS 

as part of the overall operating system, it is one option in the FIP rule. Other monitoring options 

are annual emission testing or alternate monitoring approved by EPA.

Experience with NOx Controls at Cement Kilns

Since the 1994 NOx ACT was written, the industry has gained much experience in 

controlling NOx emissions. This is particularly true with mid-kiln firing, CemStar, selective 

catalytic reduction in Europe, and low-NOx burners. Data available to EPA demonstrate that 

application of various NOx control technologies can achieve an average of 30% reduction. 

Time to Implement Controls for Cement Kilns

Based on information primarily from manufacturers of control equipment, EPA believes 

the time between a request for cost proposal and field installation is less than 31 months.3,6-10

Fuel Savings

Implementation of mid-kiln firing or other fuel replacement techniques to reduce NOx 

emissions can yield substantial cost benefits and fuel savings. Up to 15% of the fuel may be 

replaced in mid-kiln firing by scrap tires. In addition, a fee may be collected by the cement kiln 

operator for collection and disposal of the tires, a revenue source. 
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21

REFERENCES

1. 63 FR 57356 - 10/27/98

2. 65 FR 11222 - 3/2/00

3. NESCAUM. Status Report on NOx Controls for Gas Turbines, Cement Kilns, Industrial 

Boilers, Internal Combustion Engines. Boston, MA. December 2000.

4. U.S. Environmental Protection Agency. Alternative Control Techniques Document - NOx

Emissions from Cement Manufacturing. EPA-453/R-94-004. Research Triangle Park, NC. 

March 1994.

5. EC/R Incorporated. NOx Control Technologies for the Cement Industry. Chapel Hill, NC. 

September 19, 2000.

6. Email from Garth Hawkins, Portland Cement Association to Bill Neuffer, US EPA. 

12/19/00.

7. Email from Kim Bramble, Cadence to Bill Neuffer, US EPA. 12/02/00

8. Email from Kim Bramble, Cadence to Bill Neuffer, US EPA. 11/30/00

9. Email from Greg Mayes, TXI to Bill Neuffer, US EPA. 12/01/00

10. Email from Greg Mayes, TXI to Bill Neuffer, US EPA. 12/01/00