Memorandum

TO: Rulemaking Docket FROM: Keith Barnett, US EPA , Environmental Engineer
SUBJECT: Combust ion in a Cement Kiln and Cement Kilns’ Use o f Tire s as Fuel DATE: April 25 , 2011 A cement kiln that combusts any non - hazardous solid waste is subject to regulation as a Commercial or Industrial Solid Waste Incineration (CI SWI ) unit pursuant to section 129 (g) (1) of the Clean Air Act. In order for a cement kiln to be classified as a CI SWI unit, it must have an input that is a non

- hazardous solid waste, and the cement kiln must “combust” the solid waste. EPA has recently

promulgated a definition of non

- hazardous secondary materials which are solid wastes

. See 76 FR 15456 (March 2 1, 2011).
Th is memorandum describes the Portland cement production process and discusses whether certain secondary materials used in that process are combusted in the kiln. This memorandum also addresses the question of whether tire s burned by certain cement kilns in their performance testing would have been defined as solid wastes under the recently

- promulgated definition of non

- hazardous secondary materials that are solid wastes had that definition applied at the time of the burning

. Since combustion is not defined in the CAA, we use a common definition of combust which is “an act o r instance of burning” or “a chemical process (as an oxidation) accompanie d by the evolution of light and heat”. 1

Basic Kiln Process In a cement kiln, there are two ty pes of inputs, fuels and ingredients. Fu els provide th e energy necessary

to produce the heat required to raise the temperature of the ingredient s to the level required for clinker formation

. Ingredients provide the materials that make up the actual clinker mass. The ingredients are also called kiln feed or raw meal. Figure 1 presents a schematic of a typical long wet or dry cement kiln. Ingredients are introduced into the back or cold end of the kiln at 300 to 500  ̊F (cold here being a relative term)

. 2 The materials gradually move down the kiln over a period of 60

- 90 minutes and increase in temperature until they reach the temperature required for clinker formation (about 2600 to 2700  ̊F). The i ngredients undergo several different reactions as the temperature increases. Itis important that the mix move slowly enough to allow each reaction to be completed at the

1 Webster’s Ninth New Colleg1ate Dictionary . Merriam

- Webster Inc. 1990 2 Environmental Progress (vol. 11, No. 1) February,1992, Petroleum and Petrochemical Waste Reuse in Cement Kilns, David Gossmanappropriate temperature. Because the initial reactions are endothermic (energy absorbing), it is diff icult to heat the mix up to a higher temperature until a given re a ction is complete. 3

Figure 1. Schematic of a long c ement kiln

In contra s t to ingredients, fuels are introduced into the hot sections of the kiln (either the front end or mid kiln) where gas temperatures are 1800 to 4000  ̊F . At these high temperatures the fuels immediately

burn when introduced into the kiln. Fuels are never i ntroduced into the cold end of the kiln. If they were, they

would slowly

heat resulting in creation of significant amounts of carbon monoxide emissions and a loss of fuel heating value.
The process in a preheater o r preheat precalciner kiln is similar to a long kiln. In gredients (feed) enter the top of the preheater tower , which is the equivalent of the cold end of a long kiln (see further discussion below)

. 3 The raw meal passes down the tower while hot gases rise up, gradually

heating the raw meal. By the time the time the materials have reached the bottom of the preheater tower the ingredients have partiall y calcined

. 3 A preheater tower is likely to have 4

- 6 stages

.

3 Northwestern Universit y. The Science of Concrete. http://iti.northwestern.edu/cement/Fuels enter a preheater kiln at the front end of the kiln and also may be introd uced at the bottom of the preheater tower. In the case of the precalciner kiln, fuel is introduced into a separate vessel t ypicall y located between the last two stages of the preheater tower. However, as is the case with a long kiln, the fuels are intro duced into high temperature zones where combustion of the fuels occurs.

Figure 2. Preheater or Preheater/Precalciner kiln

Combustion does not occur in the cold end of the cement kiln. As explained above, materials 4 placed in the cold end of the kiln are heated graduall y until they reach the temperature where clinker formation takes place (as opposed to the hot zone of a cement kiln where higher temperatures are applied as quickly as possible, not gradually)

. This is not a chemical process marked by

the evolution of light and heat. Rather, it is analogous to cooking as opposed to burning.
In a le tter dated April 8, 2011, the Portland Cement Association (PCA) questioned whether the cold end of a preheater/precalciner kiln engages in combustion when ingredients are added at that point. The top of the preheater tower in a preheater/precalciner kiln functions identically

to the cold end of a long kiln. In gredients are gradually heated

– cooked rather than burned. Again, this is not a chemical process marked by the evolution of light and heat. As such, the top of the preheater tower equates to the cold end of a long kiln and the ingredients are not combusted in those areas of the kiln.

4 We note again that fuels are never placed in the cold end of cement kilns (including preheaters).PCA’s April 8 letter also raised a re lated question concerning ingredients added at

different levels of the preheater tower, rather than the top of the tower. (See April 8 letter p. 3 asking whether ingredients placed in “preheater towers that use the heat produced by the kiln to preheat th e ingredients as they move through the various stages of the tower” would be combusted.) We believe that until the material reaches a high temperature zone of the kiln , which is the zone where fuel is being added, combustion does not occur for the reason s just given: ingredients are being heated graduall y through a controlled process For example, some long kilns feed tire fuel at a mid

- kiln location, so combustion occurs at mid

- kiln. However, the colder parts of the kiln represent areas where materials are still being gradually heated. In preheater/precalciner kilns, this would also apply to the various level of the preheater tower until the materials reached a point where fuel is being introduced, either into a precalciner or the feed shelf of the rot ary

part of the preheater kiln. Ingredients processed in high temperature areas of the kiln Cement kilns process many secondary

materials as ingredients, and almost alway s do so by introducing these materials into the cold end of the cement kiln (where combustion of ingredients does not occur , as explained above ). In its April 8 letter, PCA notes that ingredients are sometimes introduced into the hot (fuel) end of the kiln, and asks whether those materials are combusted within the meaning of CAA section 129 (g). The high temperature regions of cement kilns can engage in combustion , as when fuels are burned

. However, the secondary material ingredients used by cement kilns would not be combusted, as explained below. Two ty pes of materials are removed from the kiln exhaust gases, typicall y by the air pollution control devices for particulates , and returned to the process as ingredients. The first is incompletely

calcined m aterial that is recycled back into the kiln as a normal part of the clinker manufacturing process. The second is other fine

- grained, solid material removed from the s ys tem to allow the clinker to meet specific quality standards or to maintain process stabi lization. See PCA L etter of April 8, 2011, p. 3. These materials are often referred to as cement kiln dust.
The PCA letter noted that b oth of these materials may be reintroduced to the kilns in various places, depending on the kiln design and process. H owever, in this letter the PCA noted that in the case of preheater, preheater/precalciner, and long dry kilns that CKD is mixed with the raw meal feed and enter the cold section of the kiln. Therefore, these materials would not be considered to be combuste d for the reason stated previously

. However, as noted in the April 8 PCA letter, in the case of wet kilns, cement kiln dust may be added to higher temperature zone regions (mid

- kiln and the hot end). C ement kiln dust in this case mainly

consists of a material that has previously been heated and even partiall y calcined. There fore, this material would be expected to be inert from the standpoint of combustion, i.e. , it would not oxidize producing heat and light. In fact, cement kiln dust injected in hot end of the kiln within or in close proximity to the flame has the effect of cooling theflame. 5 This demonstrates the fact that these materials do not create heat and thus do not

combust. In its April 8 l etter, PCA states that the only ingredients presently

placed in kilns’ combustion zones (occasionally) are the cement kiln dusts. However, PCA raises the possibility of other h ypothetical ingredients being added to a cement kiln’s combustion zone. Itis not necessary to address hy

pothetical possibilities here. In addition, we believe the potential for placing non

- inert ingredients into kiln combustion zones is unlikely for two reasons. First, the raw materials must be chemically homogeneous

. 6 S ince ingredients must be combined and ground together in the raw mill and thoroughl y mixed , f eeding separate ingredients into other areas of the kiln would mean less through mixing of the ingredients

. In addition, for the reason discussed on page 3 (neces sity to heat ingredients graduall y), introducing raw materials into a hot section of the kiln would be expected to reduce kiln thermal efficiency

. It is also worth noting that non

- hazardous secondary materials used as an ingredient in a combustion unit ar e not solid wastes, 40 CFR section 241.3 (b), assuming the legitimacy criteria in section 241.3 (d) are satisfied.

. Tire s Used as Fuel As part of the development of the CI SWIrule, we requested additional information on the ti re - derived fuels used by all cement kilns in the proposed CI SWIrule data base based on their historic practices . This included over 30 cement kilns that previously reported using some ty pe of tire derived fuels and included all the larger cement companies. 7 Specifi call y, the ICR asked these questions regarding tires combusted during the emissions tests for the kilns : a) what is the source of the whole tires the kiln combust ed; b) did they come from tire piles or landfills, or from an established tire program , defi ned in the I CR as “one which harvests tires from vehicles and businesses, and then manages the tires carefully so they are not thrown away between collection and eventual use as fuel, for example by use of a tracking s ys tem”, and c) if the kiln received t ires from sources other than an established program, did they undergo processing to produce a tire derived fuel? 8 In general, virtually

all of the respondents indicated that they had obtained all of the tires they burned from established tire programs (as defined in the I CR). However, the kilns acknowledged that they

could not account for the source of every tire pro vided by

these programs . PCA, in its April 8 letter likewise indicated that “[s]ome companies obtain tires from brokers and do not know the source of all tires” (April 8 Letter, n. 5 ) . Some of the ICR

5 PCA R&D Serial No. 2728a, A Qualitative Examination of the Control of Major Gaseous Pollutants Generated in Portland Cement Kilns
. Walter L. Greer and Garth J. Hawkins, Portland Cement Association , 2004 6 See http://en.wikipedia.org/wiki/Portland_cement 7 See CI SWII CR Follo w Up Request for Information

– ( IC R No. 2286.01; OMB Control No. 2060

- 0616; EPA Form No. 5900

- 122) . January 28, 2011. 8 The I CR also asked if the kiln had been burning on

- specification or off

- specification used oil, and whether tires that had been ph ys icall y landfilled were too damaged or otherwi se contaminated to be suitable for burning b y a cement kiln.respondents further indicated that they knew that the se established programs occasionall y (for example, once a ye ar , or several days a year) would obtain tires from sources other than commercial sources, tire dealerships and other standard collection points. Examples mentioned in the responses are the annual tire ‘amnest y day’ or other cleanup programs whereb y established programs (or in one instance, the kiln itself) accept s tires from individuals

. It is EPA’s position that ultimate users are not responsible for knowing the source of all tires obtained from an established tire collection program. The certification required b y 40 CFR section 60. 2175 (w) requires a non - waste tire user to certify that tires were obtained from an established tire collection program, that the tires are not discarded and are h andled as valuable commodities from the point of removal through arrival at the burning facility. EPA does not interpret this language as requiring knowledge of each individual tire as this is a practical impossibility

. In certifying, users also should n ot assume that tires from established programs which participate in occasional cleanup day are discarded

– both because there is no information that the tires from the cleanup efforts were discarded (and these programs are designed to prevent discarding) and whether the kiln received tires from the sporadic cleanup day s in an y case. Rather, EPA interprets the certification requirement to be satisfied if the user deals with an established tire collection program (as defined in Part 241) which program can provide the user with reasonable assurance that it manages tires carefully from point of collection to point of burning and which does not receive tires which have been abandoned in landfills or otherwise abandoned . Virtually

all of the respondents to the IC R stated that they dealt with such established tire collection programs , and provided information reasonably supporting that conclusion (or otherwise provided sufficient information from which EPA determined that the tires came from established tire management programs)

. In those instances where the kilns indicated that some of the tires they received from an established tire program had been discarde d or suspected that that was the case, EPA counted the kil n as a CISWI(had the solid waste definition applied at the time of the performance test) in this anal ys is. The responses are summarized (b y quotation or near literal paraphrase) in the following table:
C ompany Plant

Location Ty

pe of Tire Fuel Tire Sources and Processing
Ash Grove Cement Inkom Whole Tires  Receives tires from ‘ four county

landfills ’ serving as sta g ing areas (areas where tires are collected for recycling rather than disposal) which landfills are ‘ designated to receive and store tires ’ by

State of Idaho as part of the used tire management sy stem (which s ys tem is ‘ distinct from the municipal solid waste management sy stem ’ ) 9

9 Staging of ti res at landfills

– using the landfill as a collection point without disposing of the tires in the landfill (or otherwise)

– is an acceptable means of avoiding their discard. The definition Sufficient information to determine that tires come from an established program and that kiln w ould not have been a CI SWI Ash Grove Cement Durkee ,

Oregon Whole

Tires  Receives whole tires from seven

sources, two are landfills which have areas designated as tire staging area s
 Oregon r egulations for used tires similar to I daho

 Sufficient information to determine that tires come from an established program and that kiln w ould not have been a CISWI Ash Grove Cement Midlothian Whole Tires  Receives tires from one privately

owned and operated waste management facility

.  Kiln has anecdotal information that supplier occasiona lly

picks up tires from illegal dumpsites, though most (but not all) of these tires are unsuitable for Ash Grove and are shredded and sent elsewhere.

 W ould probably

have been a CI SWI Ash Grove Cement Leamington ,

Utah Whole

Tires  Burns onl y Tire chips. No information

on ultimate source of tires.

 Per other responses (i.e. Holcim Devil’s Slide), UT has a state licensed program which oversees safe collection and management of tires

 Based on features of state law, tires come from an established tire collection program and kiln w ould not have been a CISWI
of “established tire management programs” in section 241.2 allows l andfills to be used as staging areas as part of collection programs. Programs with landfill staging of tires can be “ a comprehensive collection system that ensures scrap tires are not discarded and are handled as valuable commodities ... from the point of r emoval from the vehicle through arrival at the combustion facility.” .” A system which utilizes staging areas to collect tires for re

- distribution, even if that staging area happens to be located at a landfill, meets this definition if the tires are pla ced in the staging area on arrival and properly handled prior to delivery at the combustion facility

. For example, in this instance, Ash Grove noted its understanding that “all counties (sic) landfills purchased van trailers for the sole purpose of accum ulating tires as part of the state’s used tire management system” and that Idaho state law provides that landfills can be used as storage collection points for used tires under the state ’ s used tire management system.Ash Grove

Cement Seattle Whole Tires  Receives tires f rom one privately owned and operated tire source. State of Washington regulates transport and storage of tires

 Based on features of state law, tires come from an established tire collection program and kiln and kiln
w ould not have been a CISWI Buzzi Oglesb y Whole Tires  Vast majority of whole tire fuel supplied from brokers that obtained tires directl y from the generators (tire stores, etc.) and meets definition of established tire program

 Program regulated b y State of Illinois

 Would not have been a CISWI Buzzi Pryor ,

Oklahoma Whole

Tires  Unable to determine , but does not

presentl y burn TDF at all

 Not a CI SWIbased on existence of OK rules for tire collection programs noted by other cement kilns (which assure safe management after collection and predominantly remove tires from vehicles) Buzzi Mary

neal Whole

Tires  Vast m ajority of whole tire fuel supplied from brokers that obtained tires directl y from the generators (tire stores, etc.) ‘ To the best of our knowledge, this TDF was from an established management program administered under Texas Administrative Code Title 30, Part 1, Chapter 328, Subchapter F.’

 Would not have been a CISWI Cal Portland Colton Whole Tires  Established tire management program

run by count y. The county’s main tire source was not specified in the response but is likely

tire shops, etc.

 This county

also collects tires from the public and from i llegal tire piles a few times a year. These tires are sorted and some eventuall y are sent to the cement kiln.

 Would probably

have been a CI SWI due to known use of discarded tires Cemex Demopolis Whole  Tires are sourced through tire brokersTires through an established tire management program

 The ultimate source of the tires is not specified, but the tire must meet certain CEMEX specifications. The compan y cannot rule out the possibility

that landfilled or disposed tires may be included

 CEXEX does partne r with local municipalities to provide an outlet for amnesty tire collections which are designed “to avoid illegal tire dumps” and consist of individuals bringing tires to a kiln and not being charged a disposal fee.

 All CEMEX kilns use only whole tires

 Would not have been CISWI s Cemex Brooksville

- North Whole

Tires Cemex Miami Whole Tires and TDF Cemex Brooksville

-

South TDF
Cemex Clinchfield TDF Cemex Knoxville Whole Tires Cemex Blacones TDF

Essroc Bessemer Whole Tires  Has alway s used an established tire

management program, ‘one which harvests tires from vehicles and businesses, and then manages the tires carefully so they

are not thrown away between collection and eventual use as a fuel ’

 Would not have been a CISWI Essroc Frederick Whole Tires

Florida Rock Newberry Whole Tires  Receives tires from a private compan y.

Tires are collected directly from the source that removes the tire from the vehicle.

 Would not have been a CISWI Holcim Midlothian TDF  Tire Chips obtained from the Ada OK facility with no other processing

 OK has a tire cleanup program, and facility also accepts tires from businesses and tire stores; never from landfills

 Would not have been a CISWI due to use of tire fuel (but is CISWIbased on other secondary

fuels )

. Holcim Morgan TDF  Receives tires from a private compan y under a State program. The tires are processed into tire chips at Ada facility

 Holcim Ada does not accept landfill tires (see previous write

- up for Midlothian) Sufficient information provided to determine that obtains tire from an established program

 Would not have been a CISWI due to use of tire fuel (but is CISWIbased on other secondary

fuels). Holcim (This facility was not on the CI SWIL ist) Ada Whole Tires  Tires from businesses and tire stores

and from Oklahoma clean

- up program.
 Chips tires on site for other facilities.

 Holcim in general does not accept landfill tires

 Would not have been a CISWI Holcim (This facility was not on the CI SWIL ist) Hagerstown Whole Tires  Tires from businesses and tire stores.

 Holcim in general does not accept landfill tires

 Sufficient information provided to determine that obtains tire from an established program and w ould not have been a CISWI Lafarge Roberta TDF  Sources from tire manufacturer or a local retailer under and established tire management program

 Would not have been a CISWI Lafarge Joppa Whole Tires  Tires from a variet y of sources

including tire manufacturers, tire retail outlets, tire collection forms, auto and racing organizations, and tire processers.
 Well established tire management program approved b y the State of South Carolina

 On rare occasions the plant participates in community

cleanup and/or state funded cleanup efforts.

 Would not have been a CISWI Lafarge Tulsa Whole Tires  Tire brokers who process tires under

established tire management programs.

 A State program allows reimbursement if 5 percent of the tires come from tire piles, landfills, or community clean

- up efforts. (No mention if Lafarge or their tire brokers partic ipate)

 Would not have been a CISWI , since it obtains tires from an established tire collection program and there is noindication discarded tires are burned by the kiln Lafarge Whitehall Whole Tires  Sources from tire dealers or

automotive shops under an established tire management program

 Would not have been a CISWI Lafarge Harley

ville Whole Tires  Tires from a variet y of sources

including tire manufacturers, tire retail outlets, tire collection firms, auto and racing organizations, and tire processers.
 Well established tire management program approved b y the State of South Carolina

 Would not have been a CISWI Lafarge Seattle Whole Tires  Tires obtained from retailers in an

established tire management program under State regulation

 Would not have been a CI SWI Lehigh Cement Leeds Whole Tires  Use an established tire management

program
 All L ehigh plants use whole tires

 Would not have been a CISWI Lehigh Cement Redding Whole Tires Lehigh Cement Evansville Whole Tires Lehigh Cement York TDF

Mitsubishi Cement Lucerne

Valley Whole

Tires  Established tire management program

but no absolute assurance that some tires could have been discarded

 Would not have been a CISWI Monarch Cement Monarch Whole Tires  Established tire management program

 Would not have been a CISWI

National Cement of CA Encino TDF  Tire chips and tire fluff. Fluff is from a facilit y that produces crumb rubber products.

 Ultimate tire source not specified.

 Status not certain, but reasonable to assume not a CI SWI because of California rules establishing tire management programs and due to producing TDF to specification
ConclusionBased on this information presented above, we conclude that no cement kiln would have

been classified as a CISWIunit based on the use of secondary materials as an ingredient had the solid waste definition in P art 241 been promulgated at the time of the testing or the time of promulgation of the final NESHAP

. Inaddition, all cement kilns surveyed obtained tire fuels from an establis hed tire collection program. W ith the exception of the facilities that either acknowledged accepting tires that had been discarded or provided information from which some acceptance can reliabl y be inferred , the use of tire derived fuel by itself w ould not have resulted in a cement kiln being defined as a CISWI unit.