Burning Chemical Wastes as Fuels in Cement Kilns

Jack D. Lauber New York State Department of Environmental Conservation

Albany, New York

wastes in the environment represent one of our most se- Ever increasing quantities of toxic wastes have

air, and water. Lack of adequate hazardous is a critical problem. Landfiiling toxic wastes

red safe. The tragedy of the Love Canal has need far proper baa" wade disposal facilities. cbmkal waste disposal method is process incin- Hnr have been used for burning toxlc chemical in- ctmada, Illichlgan, New York, Sweden, etc. Existing

when properly operated, can destroy most organic v.n the moat complex chlorinated hydrocarbons, be completely destroyed during normal cement

kdmal emlsslons to the environment. Burning in cen?8nl kilns, and other mineral Industries, o both industry, who generates such wastes,

nd Wvemment, who want to dispose properly of such , mrfromnentally acceptable manner. The added umservatbn b important, since large quantities of

Can be saved in the manufacture of cement when such

asks in the environment represent one of problems facing society today. Ever in-

uantities of these toxic residues have overburdened g environment (air, water, and land), which cannot

e increased rate of industrial waste generation and

inert form? New USEPA sponsored tests in Puerto Rico have revealed that even highly chlorinated, very toxic wastes can be completely destroyed in cement kilns without any mea- surable toxic air emissions.5!6

Many chemical wastes have significant heating values of 10,OOO Btuhb or more. Cement plants can save large quantities of energy from burning such liquid chemical wastes as alter- nate or synthetic fuels.

Incineration of Toxic Chemical Wastes

Incineration is a combination of pyrolysis and oxidation.7 Pyrolysis is a chemical change resulting from heat alone. Oxidation is the gross reaction of an organic species with oxygen and requires relatively low activation energies. Py- rolysis involves the breaking of stable chemical bonds, often resulting in molecular rearrangement, and higher molecular weight products. Pyrolysis occurs in a time scale of seconds, while oxidation occurs in milliseconds.

For efficient incineration, oxidation should be the dominant process, with pyrolysis occurring either incidentally to the oxidation or to put a material into a better physical form for oxidation.8

To incinerate toxic wastes such as PCB effectively, pyrolysis must be efficient and complete before oxidation of the mo- lecular chemical by-products can occur. This is why cement kilns are ideal. High kiln temperatures of greater than 140OOC (2500°F) and long residence times of up to 10 seconds, or more, insure complete pyrolysis or breakdown of such toxic halogenated organic wastes. Complete oxidation can then easily follow.

In order properly to burn complex chemical wastes in ce- ment kilns, it is important to know the technical information shown in Table I.

Incineration temperature and residence time for mixed chemical wastes cannot be readily calculated and are often determined empirically. Some common nontoxic solvents such as alcohols and toluene can easily be incinerated a t about 1000°C and one second residence time, while other more complex organic halogens require more stringent conditions such as the USEPA TSCA PCR incineration criteria of 1200°C and 2 sec residence time. ___ Copyright 19x2 Air I’iillution Control A ~ w ( i i i 1 i ~ m

2 Volume 32, No. 7 771

CONTROL TECHNOLOGY NEWS

Cement Kiln Technology

The wet process cement kiln shown in Figure 1 is the major type of portland cement kiln used in New York State. The newer dry type suspension pre-heater cement kilns may play a future role in chemical waste incineration. However, since dry cement kilns have not been significantly used for burning toxic chemical wastes, other than lubricating oils, and may experience system pluggage when burning halogenated wastes, such processes will not be reviewed in this paper.

A cement kiln is a large steel horizontal tube, with refractory linings and may be up to 25 f t in diameter and over 500 ft long. The kiln rotates slowly and has a gentle slope to allow material to pass through by gravity. Cement kilns are countercurrent. That is, solid materials travel in one direction and gases plus dust emissions travel in the opposite direction. A slurry of 30-40% water and crushed rock is fed into the kiln a t the left. A t the opposite end of the kiln is a powerful oil or coal fire. As the raw material passes slowly through the kiln (1-4 h), it first dries, then approaches the hot burning zone of the kiln. In the burning zone, 2700°F (1500°C) temperatures calcine and fuse the raw materials creating a complex calcium silicate alum- ino-ferrite mineral substance called “clinker” which is dis- charged from the lower end of the kiln a t the right and cooled in the clinker co01er.~

In a typical wet cement process, formation of the key cal- cium silicate components of the clinker does not begin until temperatures of approximately 2300°F (1260°C) are reached; consequently, in order to get a good quality cement clinker, the rotary kiln must reach (and maintain) temperatures of between 2500” and 2650°F (137Oo-145O0C) in the kiln burning zone.lO Control of cement quality requires that the clinker be heated to a minimum temperature of 2600°F. It is impossible for a cement plant to allow temperatures to fall to the point where the efficiency of waste destruction is com- promised.2

If waste liquid organic chemicals are fed into the firing end of the cement kiln, it can be readily seen that they will be subject to the high temperatures and long residence times of the cement clinker production process. Consequently, they will be completely destroyed by a combination of pyrolysis and oxidation.

Burning Chemical Wastes at St. Lawrence Cement Company

From 1974-76 the St. Lawrence Cement Company burned waste chemicals in two separate cement kilns a t their Miss- issauga, Ontario plant.

Waste chlorinated hydrocarbons, consisting of approxi- mately 45% PCB, 12% aliphatics, and 33% chlorinated aro- matics, were burned in a wet process cement kiln, shown in Figure 1. Stack tests performed during trial burns indicated a destruction efficiency of a t least 99.986% for the chlorinated hydrocarbons. About 50 ppb of volatile low molecular weight compounds (e.g. CC4) were found in the emission samples. It appears that these low molecular weight compounds found in the kiln emissions are not materials that have escaped de- struction, rather they may originate in the feedwater used to blend the clinker constituents.2 There were no detectable quantities of high molecular weight chlorinated compounds in the stack gases as determined by gas chromatography/mass spectroscopy tests. PCB were not found in the cement clinker.

A mass balance was carried out for chlorine and essentially all the chlorine was reacted with the process solids. This demonstrated that acid gases such as hydrochloric acid, which are generated by the pyrolysis and oxidation of chlorinated hydrocarbons, are effectively neutralized by process lime in

Table I. Technical information for incineration of chemical waste materials.

Critical waste incineration parameters Physical and chemical properties

C, H, 0, N, HzO, S, and ash Ca, Na, K, Cu, V, Ni, Fe, Pb, Hg,

Ultimate analysis Metals

Halogens Chlorides, bromides, fluorides Heating Value Btuhb or cal/gram Solids Size, form, and quantity to be

Liquids Viscosity, specific gravity and

Gases Density and impurities Organic portion Percent Special characteristics Corrosiveness, reactivity,

Disposal rates Peak, average, minimum Toxicity OSHA TLV, carcinogenicity,

etc.

received

impurities

flammability

aquatic toxicity, etc.

the cement kiln. This provides an additional benefit. Some cement plants have a need for a low alkali cement. In such cases, the burning of chlorinated hydrocarbons directly results in the lowering of the alkalinity of the cement products.

The test burns of chlorinated hydrocarbon wastes and PCB at St. Lawrence Cement indicated increased potential emis- sion rates of particulates. “Increased emission rates were not unexpected, since combustion of the chloride wastes produces HCl (hydrochloric acid) and Cla (chlorine), which react with the alkali components in the raw feed to form volatile alkali chlorides. At the precipitator, the particulate loading is therefore increased and, since the condensed alkali chlorides are very fine and have a different resistivity, the amount of material passing through the collector increases.”3

Even though potential particulate emissions can increase when burning halogenated chemical wastes, the actual par- ticulate emissions should not significantly increase, if the cement kiln air cleaning system is operating properly. The St. Lawrence experience involved the burning of some very con- centrated halogenated waste streams, which in some cases caused alkali halogen rings in the kilns, which also can increas particulate emissions. However, even in such cases, L. P. McDonald et al. concluded that “the higher emission rate did not significantly add to the suspended particulate in th ambient air in the vicinity of the plant.”3

Based on the St. Lawrence Canadian Cement plant tests, most cement plants now planning to burn halogenated chemical wastes, plan to limit the burning of such wastes less than 10% of the waste fuel stream. This will minimize k ring formation and particulate emissions. It is thus advis to limit the burning of waste chemicals to cement plants have highly efficient, reliable, and well maintained cement particulate air cleaning systems.

Burning the chlorinated waste during tests, the average replacement value was about 12%, while the heating value these wastes averaged about 10,000 BtuAb of waste. Fuel re- quirements for the kiln were reduced by about 65% of the ac- tual energy content of the wastes burned.2 It was estimat from these tests that chlorine can be added to a process kiln at rates of about 0.4-0.7% without dis operations.2

The burning of halogenated PCB wastes a t St. Lawr Cement Company, Mississauga was a technical success about two years, PCB containing wastes of up to 10,000 of PCB were burned su adverse environmental general public was, ho practices and when they PCB wastes in their co outraged, despite the fa

Journal of the Air Pollution Control Associat 772

mental reports were also clouded by emotional reactions.

Buming Chemical Wastea at the Stora Vlka Cement Plant

ated in the process. Any raw feed slurry.2

DUST SCREW

Flgwo 1. Burning toxic. liquid Ofgenic chemical wastes in cement kilns.

82 Volume 32, No. 7 773

CONTROL TECHNOLOGY NEWS

Waste destruction efficiencies of chlorinated aliphatics was 99.995-99.9998%. The destruction of PCB was greater than 99.9999%.’:’

Analyses were also conducted for dioxins and furans. This investigation did not find any detectable quantities of dioxins or furans containing four or six chlorines, the most toxic forms of these contaminants.’:’

Dust emissions from this plant increased during the ex- periments, as in the Canadian tests, due primarily to an in- crease in potassium chloride concentrations in the kiln dust. I t appears that alkali chlorides generated when chlorine is added to the kiln may have a higher resistivity than typical kiln dust; this may require “tuning” the precipitator stages to reduce emissions to normal.2

Burning Chemical Wastes at Alpha Cement Co.

During the summer of 1981 the Alpha Cement Company began burning waste solvents as fuels in their wet process cement kilns a t Cementon, New York.14315

Generally, up to 15 gal/min of up to 2% organic chlorine content, waste solvents were burned in a demonstration project which may continue. These waste fuels average about 90,000 Btu/gal and are fired at up to 25% kiln fuel replace- ment.

Alpha Cement operates a wet process cement kiln which is 17 f t in diameter and 525 ft long. They normally burn 16 ton/h of coal and produce 60 ton/h of clinker. Emission control is provided by a 3-stage electrostatic precipitator which has been upgraded to meet fully New York State emission require- ments, and which can achieve particulate emission concen- trations of approximately 0.05 gr/DSCF or less.

Preliminary tests performed during this demonstration project have indicated about 58% lower SO2 emissions than by burning coal alone, and approximately a 94% retention of heavy metals in the particulate.

Alpha now has both audible and visual process control alarms which will be automated in the near future to shut off waste fuel feed to the kiln automatically when the following process variables indicate process upsets or abnormal oper- ating conditions: 1. 2200°F minimum front end kiln temperature. 2. Minimum 7 T/h coal feed rate. 3. 0.5% 0 2 in kiln exhaust. 4. Kiln speed of 60 RPH. 5. Negative draft in firing hood.

A continuous carbon monoxide gas monitor will be installed in the near future to insure that 99% or greater combustion efficiency will be maintained at all times, when chemical waste fuels are being burned, in accordance with New York State Department of Environmental Conservation control poli- cies.

The firm plans to conduct additional worst case trial burns involving various higher halogenated principal organic haz- ardous compounds in the near future, in order to demonstrate 99.99% or greater waste destruction and negligible emissions of toxic air contaminants.

Burning Highly Chlorinated Wastes at San Juan Cement Co.

During Fall and Winter of 1981 and 1982, USEPA con- ducted several worst case trial burns burning highly chlori- nated chemical wastes a t the San Juan Cement Co. in Puerto R i ~ o . ~

The San Juan tests were conducted in a wet process cement kiln 450 f t long by 10 f t in diameter, fired with #6 oil a t 25 gal/min. This kiln produces 25 T/h clinker and generally has

process temperatures of 2400°F and 4 sec residence time; it is equipped with a baghouse with an exhaust rate of ap- proximately 130,000 ACFM.

USEPA conducted eight test burns, burning up to 38% total chlorine waste fuels. The worst case waste fuel was composed of: 1.4% methylene chloride, 4% chloroform, 8% carbon tet- rachloride. Carbon tetrachloride is one of the most difficult principal organic hazardous compounds to destroy thermally. In all eight test runs, no dioxins or dibenzofurans were found in the emissions.

Virtually complete 99.99% or greater waste destruction and removal efficiency was achieved in most cases; however, it was difficult to demonstrate this in all cases, due to difficulties concerning analytical limits of detection for certain contam- inants.

These tests also demonstrated 99.7% removal of acid gases, as HCl, by reaction with alkaline materials within the cement kiln. Particulate emissions, SO2, NO,, and total hydrocarbon emission values were not significantly different from normal or baseline operations using fossil fuels only.6

Recommended Environmental Controls for Storage, Handling, and Process Disposal

The following recommended engineering controls and safeguards are designed to insure that toxic waste chemicals will be properly handled and destroyed in cement kilns, without any appreciable environmental discharges that could affect Dublic health or safety. 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Chemical wastes shouid be stored in an isolated area, preferably well fenced and locked, to provide good se- curity from intruders and vandals.ll All ground area within diked, storage areas to be sealed so that spills will not penetrate the ground. Sealed con- crete surfaces are recommended.” Well controlled drainage. All leaks, spills, rainwater, etc., should be easily collected and saved for destruction. Receiving area spills are particularly important.’ All liquid storage should be in closed tanks, not open lagoons.11 Methods to contain and recover piping leaks without environmental contamination should be pr0vided.l’ Adequate alarms for abnormal conditions should be provided. Leak free design should be specified whenever pos- sible.’ The waste liquid storage sump area should be enclosed and all vent gases from such area and storage tank should be vented to an emission control system.4 No runoff water from the waste chemical storage area should be discharged to city sewers. Any such runoff should be redirected into storage tanks for subsequent high temperature destruction in the kiln.4 Emergency equipment, such as fire extinguishers, self contained breathing masks, sorbent materials, and shower stations should be sited in the immediate vicinity of the waste chemical storage area. Employees should be trained in their proper use.2 No double-bottom tank trucks should be permitted for delivery of waste liquids to the plant? The company should be required to have specially trained and authorized personnel at the chemical waste storage and pumping site for unl chemical wastehynthetic fuels.4 When authorized operating personnel are not on site, the storage and pumping area should be made sufficiently secure to prevent site access and operation of the storage and unloading ~ y s t e m . ~ All volatile organic emissions from waste chemical storage and handling facilities should be exhausted and piped to the cement kiln for incineration and complete destruction. Explosion proof safety valves should be

Journal of the Air Pollution Control Association 774

ion with condition 15 to control organic. a back up carbon adsorption vapor control

be provided to control volatile organic age tank breathing emissions.' control and record keeping system shall dentifying the source, chemical compo-

ruction: These management and record keeping should be submitted to the environmental

ction by the environmental

a t all times in an oxidizing

ure and record combustible content of

Id take place unless the mal temperatures in the

ill be measured

es fall below 12OOOC.

low 60 RPH. hood.

e content in excess of zero

particulate emission tests to determine ny, of increase in emissions due to waste tion. The proposed facility should not

ning chemical wastes as synthetic fuels in should demonstrate compliance with the

r greater waste conversion and removal

combustion efficiency. tectable residual total organic halogens in the

82 Volume 32, No. 7

24.

25.

26.

27.

28.

air emissions (using gas chromatography/electron capture analytical methods).16

If the outside skin temperature of the kiln exceeds 480°C, the feed of waste liquid chemicals should be shut off from introduction into the kiln, and shutdown should be ini- tiated for repair of the refractory. Reintroduction of chemical waste liquids should not take place utitil such lining repairs are ~ o m p l e t e d . ~ Chemical waste liquid introduction into the kiln should cease in the event of mid-kiln ring formation. Reintro- duction of chemical waste liquids into the kiln should not take place until such ring is eliminated.4 Automated monitors should be employed to alert oper- ators in the event of a waste-fuel handling problem. A pressure transducer located in the waste piping at the entrance of the kiln should be provided to turn off the waste fuel pump automatically in the event of a sudden pressure drop due to pipe rupture or pump failure.2 Interlocks should be provided to stop the flow of waste fuels automatically if either normal fuel supply or com- bustion air flow are interrupted,2 or if carbon monoxide levels indicate less than 99.9% combustion effi- ciency.16 Monitoring systems capable of detecting volatile organic vapors should be placed at key process locations to signal accidental waste fuel leaks. Periodic monitoring for volatile organic compound emissions should be pro- vided.2

The Economics of Burning Chemical Wastes as Synthetic Fuels in Cement Kilns

Previous studies have shown that cement kilns can save large quantities of energy by burning chemical wastes as synthetic fuels. Some large cement plants could save up to 5 T/h of coal, by burning over 20,000 gallday of such synthetic fuels.'

Fuel costs, which can represent up to 65% of the cost of producing cement clinker could be substantially reduced through the use of waste fuel.2 Older wet process cement kilns use about 4wo or more fuel than newer dry process suspension preheater kilns. The use of chemical waste synthetic fuels may extend the useful economic life of wet process kilns by up to 10 years or more.'

Recent economic studies have been developed for a model cement kiln, assuming the following conditions.2

Kiln production-240,000 T/yr. Fossil fuel cost-$2.46/million Btu. Synthetic fuel chlorine limit-O.6% of kiln production. Synthetic fuel heating ualue-10,000 Btuhb. Investment + 15% return-Assume a synthetic fuel con-

taining 10% by weight chlorine is used, and 90% of the waste fuel's heating value can be recovered. At 17.8% kiln fuel re- placement, there would be a net savings of $1.37/T of cement if the firm paid $l/million Btu of synthetic waste fuel. Con- sequently, a cement plant could save $328,80O/kiln in fuel costs per year by burning a 10,000 Btu/lb synthetic fuel a t about 18% fossil fuel replacement; even paying $l/million Btu for a custom blended synthetic waste fuel. The kiln fuel sav- ings would be much greater of course if the waste fuels were delivered at less o r no cost.

Conclusions

The foregoing technical examples of burning liquid chem- ical wastes as synthetic fuels in cement process kilns in Can- ada, Michigan, Sweden, New York, and Puerto Rico, have demonstrated the ability to destroy completely such wastes, without significant environmental losses of these materials. Such operations are preferable to landfilling toxic wastes which could escape into the environment if the integrity of the landfill is ever disturbed due to unforeseen future conditions.

775

CONTROL TECHNOLOGY NEWS

The process incineration of hazardous liquid organic wastes, or the use of such wastes as synthetic process fuel, is the only way to insure that such materials are properly destroyed and don’t ever come back to haunt us in the future.

The current energy crisis has placed a premium on fossil fuels. The ability to burn waste chemicals as supplemental fuels in the mineral products industries can save large quan- tities of virgin fuels that can be used elsewhere to ease fuel shortages.

The burning of waste chemicals in cement kilns is not only economically beneficial to cement companies, but to the public as well. Cement companies can save large quantities of fossil fuels and will be able to operate older cement kilns more economically and be able to compete better with newer plants elsewhere. The burning of waste chemicals may extend the economic life of older wet process cement kilns by as much as 10 years or more. This could mean more jobs for the public, not only in the cement industry but in numerous other firms in the private sector which are economically related to these industries.

The burning of hazardous organic chemical wastes as syn- thetic fuels in cement plants has been proved to be safe. USEPA has concluded that the risks incurred in burning toxic wastes in cement kilns appear to be very low. Given proper controls, emissions of organic compounds are likely to be a t or below analytical limits of detection.2

Chemical wastes cannot be safely put into the ground for disposal, lest they become future toxic time bombs. Many “hazardous wastes” defined as such by USEPA-RCRA reg-

Ambient Air Providing in-depth infor- Monitoring mation on the design and

operation of ambient air quality monitoring networks and their associated quality

Training Series assurance programs.

For preferred registration, call or write

Carolyn Jenkins, Registrar

Northrop Services, Inc. P.O. Box 12313

Research Triangle Park North Carolina 27709

(9191 549-0652

course 63 Ambient Air Ouallty monnorkto~stems Aug 17-19,1982 . .Denver, CO

Course 70 Owlity Assurance for Ambient Air Monitoring sept 14-17,1982. .

DaVtona Beach, FL

Air quality and meteoro- logical measurement methods Siting of air quality and meteorological monitors Atmospheric dispersion modeling Requirements for SLAMS and PSD monitoring networks Quality assurance for ambient air monitoring

Northrop Environmental Training

CIRCLE 22 ON READER SERVICE CARD

776

ulations are no more hazardous than ordinary gasoline, or common industrial chemical products. The public should know that the transport, storage and use of these materials as fuels in cement plants has been proved to be safe.16

The public must ultimately pay the cost of environmental cleanup of toxic chemicals; whether directly by public funding or indirectly by increased costs of goods and services. The use of toxic organic chemical wastes as synthetic fuels in cement kilns and other mineral products industries will greatly lower the cost of disposing of these toxic wastes by realizing their potential as supplemental fuels. If these practices are imple- mented, both the public, industry, and government will reap significant environmental and economic benefits.

Acknowledgments

I wish to thank my friend and Canadian colleague, Mr. Earl Gagan formerly of Environment Canada who initially in- formed me of the Canadian PCB cement kiln trial burns about nine years ago. Mr. Gagan’s technical expertise and knowledge about cement plants and his contacts with the Ontario Min- istry of the Environment and St. Lawrence Cement Company proved extremely valuable in writing this paper.

I also want to thank Messrs. T. Cross and C. Duncan of the Ontario Ministry of the Environment for arranging the useful technical dialogs on the St. Lawrence Cement Plant waste chemical incineration project. Also my thanks to Mr. L. MacDonald of the St. Lawrence Cement Company for sharing his technical expertise of this project. My thanks also to Mr. Robert Mournighan of USEPA IERL

for giving me the latest information on the USEPA cement kiln-waste fuel demonstration project in Puerto Rico.

I also wish to thank Mr. Scott Horton of Alpha Cement for his cooperation and sharing of information on his project.

Last my thanks to Mrs. Grace McDermott and Ms. Dorothy O’Hare who labored over my manuscript and did a fine pro- fessional job of typing this paper.

References

1. J. D. Lauber, “Burning Toxic Chemical Wastes in Cement Kilns and Other Mineral Products Industries,” 5th World Congress of Engineers and Architects in Israel, Dec. 1979.

2. D. I,. Hazelwood, F. J. Smith, E. M. Gartner, L. Weitzman, “As- sessment of Waste Fuel Use in Cement Kilns,” Draft report for USEPA, Office of Research and Development, Aug. 1980.

3. L. P. MacDonald, D. J. Skinner, F. J. Hopton, G. H. Thomas, “Burning Waste Chlorinated Hydrocarbons in a Cement Kiln,” Canadian Environmental Protection Service Report No. EPS- WP-77-2, March, 1977.

4. “PCB Waste Disposal at Peerless Cement,” International Michigan-Ontario Air Pollution Board semi-annual report, April 3, 1978.

5. Personal communications with Robert Mournighan, USEPA Ind. Environ. Research Laboratory, Cincinnati, OH, March 1 and 15, 1982.

6. Personal communication, with James Peters, Monsanto Research Corporation, March 16,1982.

7. T. Shen, M. Chen, J. D. Lauber, “Incineration of Toxic Chemical Wastes,” Middle Atlantic States Section Air Pollution Control Association Technical Conference “Toxic Air Contaminants,” Newark, NJ, Oct. 21,1977.

8. W. H. Elliott, Jr., W. B. McCormack, “Incineration of Hazardous Substances,” Paper No. 77-19.1, 70th Annual Air Pollution Control Association Meeting, June 1977.

9. J. D. Lauber, “Controlling Air Pollution from Cement Plants” presented at 3rd World Congress of Engineers and Architects in Israel, Dec. 1973.

10. K. E. Peray, J. J. Waddell, The Rotary Cement Kiln, Chemical Publishing Company, New York, 1972.

11. Myron W. Black, Asher David, “Safe Disposal of PCB’s,” 1977 National Conference on Treatment and Disposal of Industrial Waste Waters and Residues, Houston, TX, April 1977.

12. Personal communication with Mvron W. Black. Peerless Cement Company, June 11,1979.

13. B. Ahling, “Destruction of chlorinated hydrocarbons in a cement kiln,” Swedish Water and Air Pollution Research Institute. En- oiron. Sci. Technol. 1 3 1377 (1979).

14. H. Faber, “Upstate cement project burns hazardous wastes,” The

Journal of the Air Pollution Control Association t