Citizens Against Burning of Tires have not been sitting still and waiting for the
CABOT Review of Science On Implications of Burning Tires as Industrial Fuel
Compiled and reviewed by Allan Sorflaten, M.Sc.
Released for publication: March 21, 2007
EXECUTIVE SUMMARY
Fifteen science based research projects have been intensively reviewed from the literature. Each of these projects is devoted to investigating some aspect of co-combusting tires with another fuel, in most cases coal. Nine of the reviews concern research that was directed at industries other than cement, most often electric power generation. Five pertain directly to the use of tires as fuel by the cement industry and the last one to occupational health issues of workers in the cement industry.
To set the introductory framework a basic distinction first is made between the use of whole tires as (industrial) fuel and shredded tires. Whole tires are as different from shredded tires in their combustion characteristics as they are from coal. The literature confirms that these differences in the fuel are critical to related environmental and health implications.
Energy economics also is of consequence. A significant feature to do with operating costs and related bottom line results for Lafarge concerns their plan to cut a whole in the side of the kiln and dump in whole tires. This is a cheap and primitive alternative to other options that exist. One of these would be to use a more technologically sophisticated approach whereby tires first are prepared by chipping and shredding into tire-derived fuel/ TDF and then, using the right equipment, the TDF is injected into the kiln for burning. This option obviously involves greater capital expenditure than the first alternative but from our review of the literature that follows, is far more preferable.
The European Community is using legislative authority to deal with cement plants that persist with unsafe practices in tire incineration. There, a recent EU Community directive specifies that older cement works will no longer be allowed to burn tires after 2008. This directive appears intended to bring an end to the unsound technology associated with burning whole tires as fuel by old cement plants in the manner that has been proposed by Lafarge Brookfield.
Whole tires are used by Lafarge at only 5 locations in
The absence of research on burning whole tires as industrial fuel simply indicates that it probably has not been done. It probably also indicates that the cement industry sees no benefit to undertake, sponsor or otherwise prompt comparative investigations into whole tire burning. Without industry participation, any such research is really a non-starter, likely because dumping 20 lb. passenger tires into the kiln (not to mention 40 lb. + truck tires) from the point of view of kiln dynamics would be akin to dumping in 20 lb.+ lumps of coal. It’s just not done! The process engineers from Dalhousie we expect will have more to say on this point.
Section 1.0 reviews the first 9 articles of the science based research as it concerns burning TDF as fuel by industries other than cement manufacturing (mostly power plants). These articles as such provide better understanding to the tire burning issue overall. Section 2.0 reviews the 5 additional science based journal articles that are based on industry sponsored research of TDF at cement plants.
1.0 Science Based Research of TDF Use By Other Industries (Non-Cement)
Research from
- that “the use of tire-derived fuel (TDF) leads to higher emissions of various metals (over coal only).” The articles points out that although some environmental pollutants are substantially reduced (e.g.NOx emissions), using tires as fuel may lead to considerable increases in the levels of other pollutants “most notably of Zn and Pb.” The results show emissions of Zn going from 55 gm/hr at the coal only baseline to 2,400 gm/hr with only 5% TDF, a 4,200% increase. Cadmium (Cd) emissions increased 500% from the level of pure coal. Mercury emissions remained the same for both fuel types. (CABOT Bibliography Nos. 28).
- elevated solid waste ash content levels of zinc/Zn, sulfur oxide/SOx and arsenic/As and reductions of nickel/Ni, copper/Cu and lead/Pb. The authors point out that “the finer particle sizes of fly ash from shredded tire co-combustion concurrently capture and thereby emit increased levels of volatile trace elements (i.e. heavy metals) into the atmosphere.”
- bulk concentrations of Zn in combustion products derived from TDF burning are 238, 3,850 and 61,500 p.p.m. in bottom ash, mechanical separator ash and electrostatic precipitator (ESP) ash, respectively. The authors suggest that these concentrations are high when compared to the pure coal values of 68, 106 and 3,450 p.p.m. They conclude that the increase may lead to higher Zn concentrations in both atmospheric emissions and leachates from ash disposal sites.
Our Comment: The authors make a rather alarming statement at the outset of this article, as follows: “The potentially harmful effects of burning tires (as fuel) are yet to be fully discovered.” (Source: R. Giere, S. LaFree et. al.
1.1 Technology Induced Reduction of TDF Pollutants
Various science based technologies have been studied for reducing harmful pollutants that result from burning TDF. One of these, based on a project at the University of Sao Paulo in Brazil (CABOT Bibliography Nos. 9 and 49) looked at the combustion of small/1 cm. waste tire chips in fixed beds (no coal as baseline) in a highly controlled laboratory situation with primary furnace temperatures ranging from 500º C to 1000º C, under pyrolitic conditions (in nitrogen) with effluents channeled to a secondary furnace for further treatment at 1000º C. Sampled species included CO², CO, poly-nuclear aromatic hydrocarbons (PAHs), particulates, nitrogen oxides (NOx) and sulfur oxides (SOx). The results showed:
- “the effectiveness of a nominally premixed flame for oxidizing the sampled species” ------ and also ----- “that a sequential pyrolysis-oxidation process has the potential for low emissions in waste tire-to-energy plants.” A significant point to note here is that the burning process studied in this case is sequential or staged, in concept not unlike that used in modern, state-of-the-art incineration facilities.
- the operating temperature of the primary furnace and the existence of the secondary furnace or afterburner together had marked influences on the emissions of pollutants. The use of combustion staging with an additional air mixing section had very beneficial effects. It drastically reduced the emissions of CO (by factors of 0-10), of particulates (by factors of 2-5) and of cumulative PAHs (by factors of 2-3). “Many health-hazardous PAH components were practically eliminated.” As well, the operating primary furnace temperature (pyrolysis temperature) also proved to be important, with temperatures at the low side of the 500-1000 degrees C. range producing fewer pollutants after treatment in the afterburner.
Our Comment: The requisite technology and techniques exist to mitigate toxic emissions that result from co-combusting coal with small (1 cm.) chips of TDF. As well, modern state-of-the art industrial incinerators are equipped with the kind of “afterburner” technology demonstrated by this project.
1.2 Technology Induced Reductions of Heavy Metals Emissions
“Heavy metals appear in the effluents of many combustion processes and their release into the environment is a cause for public concern and regulatory scrutiny. The metal species contained in the waste can be neither destroyed nor manufactured during high-temperature incineration and will subsequently condense to form metallic particles during the cooling of the flue gas. These toxic metals may exit the process in molten slag, in dry collected ash, in wet scrubber ash, or as an airborne aerosol exiting the stack.1,2 Extensive material in the literature shows that many toxic metals are concentrated in the sub-u particle size range. Particles of this size range are difficult to collect and remove from combustion flue gases by conventional air pollution control devices such as wet scrubbers.or baghouses.”3,4,5
“Previous studies of heavy metal control6,7,8 indicate that it is difficult to control the volatilization of metals during high-temperature processes. An alternative control technology for heavy metal emissions is the use of solid sorbents to capture metals by physical deposition and chemical adsorption. Among the available incineration systems, the fluidized bed-incinerator appears to be most suitable for this purpose, because it provides intensive mixing of sorbents and metal compounds.”4 ( Source: CABOT Bibliography No. 38 “The Effects of Chloride Additives on Adsorption of Heavy Metals During Incineration/pp. 1116-1120).
Researchers at the National Chung-Tsing University in Taiwan, China investigated the adsorption of selected heavy metals, Chromium/Cr, Copper/Cu, Lead/Pb, and Cadmium/ Cd on a sorbent (silica sand with limestone) under various chloride additive conditions (no chloride; an organic chloride; polyvinyl chloride/PVC; and an inorganic chloride (NaCl), and estimated the adsorption saturation point of the sorbent during fluidized bed incineration of municipal waste.
From the perspective of controlling heavy metal emissions, the results indicated that; (1) using the NaCl additive generally led to a higher adsorption capacity than did a PVC additive or no additive at all; and (2) cadmium was extremely difficult to remove in any situation. With the NaCl additives, the adsorption capacity of the sorbent for the four metals followed the sequence Cu>Cr>Pb>Cd.
Using sorbents to control heavy metals emissions from an incinerator requires understanding of the mechanisms of heavy metals adsorption on the sorbents. These results will allow the effects of various chloride additives on the efficiency of adsorption of heavy metals to be evaluated and thereby to determine when the sorbents should be renewed.
Our Comment: Chemically engineered process technologies exist with which to modify or control heavy metal emissions in managing emissions from waste (tire) incineration. As demonstrated by this study, however, even with these technologies there are limits or exceptions. “From the perspective of controlling heavy metal emissions, cadmium was extremely difficult to remove in any situation.” Cadmium we know is a persistent heavy metal toxic pollutant when using TDF.
1.3 Technology Induced Reductions of Mercury Emissions
Mercury is of concern whenever coal is burned because mercury emissions from coal and TDF burning industries pose significant hazards to public health (USEPA). Pilot scale studies were carried out at the Energy and Environmental Research Centre, University of North Dakota in an effort to evaluate the impacts of co-firing TDF and coal on mercury species in flue gas. The TDF was pre-shredded, screened to -40 mesh, and then fed with a separate feeder directly into the pneumatic coal feed line at rates corresponding to 5 and 10% of the feed coal (mass based) rate
Improvements in mercury emissions are indicated by changes in the levels of oxidized mercury with changes in the levels of TDF co-firing. With 100% coal firing there was only 16.8% oxidized mercury in the flue gas compared to 47.7% when 5% TDF (mass basis) was co-fired and 84.8% when 10% TDF was co-fired. Thus, co-firing of TDF with coal was concluded to have a significant effect on mercury speciation in the flue gas. The researchers also concluded that this significantly enhanced mercury oxidation “may be the result of additional homogenous gas reactions between Hgº (gaseous elemental mercury) and the reactive chlorine generated in the TDF/co-fired flue gas”.
The authors explain the significance of oxidized mercury in the context of this study. Hgº or gaseous mercury, they say, is most likely to escape air pollution control devices and be emitted into the atmosphere. It is generally agreed that all the mercury in coal is vaporized in combustion and is expected to be Hgº (gaseous) in the high-temperature zone. Hgº can be oxidized by gaseous oxidants in flue gas, most likely by chlorine species, to form gaseous mercuric compounds (Hg²+). Atomic chlorine (Cl) in the flue gas is probably the dominant reactant for mercury oxidation. Fly ash compounds also play important roles in mercury partitioning in flue gas. Experimental data from other research has “demonstrated that residual carbon in fly ash enhanced the sorption of mercury.”
1.4 Chlorine: The TDF ash sample in the
Our Comment: this high chlorine level exists at levels of 5%/10% TDF co-combustion. The question must be asked; “How much higher would the chlorine level be at 20% co-combustion of whole tires (dumped into the side of the kiln) as is being proposed by Lafarge for
chlorine + air/oxygen + high temperatures = dioxins
Test results from 4
Burning TDF in cement kilns thus has the potential to create incremental increases in dioxin emissions. The Lafarge Brookfield proposal thus holds important carcinogenic implications for human health. Most telling of all in this regard is the threshold debate on dioxins that tells us “no level is a safe level.”[3]
As such, the North Dakota research on mercury emissions when co-firing TDF suggests to CABOT that a trade-off is involved; namely, that the purported benefit of attaining higher levels of oxidized mercury/Hg²+ (which to the layman sounds a bit anomalous since there are other serious environmental implications associated with the disposal of mercury based compounds/particulate matter) over reduced levels of gaseous mercury (Hgº) atmospheric emissions when burning tires, will be offset by the higher levels of chlorine that are known to exist in the TDF feed. Unfortunately, the researchers make no mention of the resultant dioxin emissions that are liable to be released into the atmosphere or ESP/CKD cement kiln dust. During his recent visit to
2.0 Science Based Research of TDF Use By Cement Manufacturers
CABOT was able to reference only a few TDF items directly pertinent to the cement industry in its review of the published research. Though we can’t be absolutely certain that the review is exhaustive, it was approached as a broad based search intent on sourcing published journal articles about cement manufacture using tires as fuel. A further noteworthy point is that so far as we’ve been able to take it, the few scientific journal reports that we’ve been able to locate on the subject originate out of
TDF Use by Unicem Group
The Unicem plant at
Atmospheric emissions at this highly modern, state-of-the-art plant are treated with an electrostatic precipitator (ESP) and a fabric filter (FF) for highly efficient particulate removal. Emissions then are directed from the top cyclone discharge, through the stack and into the atmosphere.
Size characteristics of the fuel, feeding location, and injection modes of waste tire chips all were selected after a careful evaluation of the most important process requirements
Not unexpectedly, the study reports a clear reduction of NOx obtained with shredded tire chip utilization as well as SO2 reductions in the stack emissions, both of which are related to the lower nitrogen and sulfur contents of the TDF. In contrast however, stack concentrations of chromium increased from a petroleum coke baseline of 0.2 ug/m³ to .7 ug/m³, for an increase of 250% when burning chipped tires. As well, manganese emissions increased from the petroleum coke baseline of .1 ug/m³ to 1.5 ug/m³ with chipped tires, an increase of 1,400%.
The results for lead and zinc, two of the most volatile elements of concern that are present in TDF, were comparable. The authors conclude that these results “can be attributed to the high removal efficiencies developed by the Fabric Filters over the particle size range of interest.” However, as pointed out in the study, this result seems worthy of further investigation because of the “observations of other authors who report significant emission increases for these two elements during tire utilization.” (Source: Carrasco et. al. Journal of Environmental Science and Technology, 1998, No. 19, 461-474).
Emissions of Trace Organics – The Unicem Barletta results show low level emissions of trace organics (PAHs and PCDD/F) for both the baseline and TDF co-firing tests, thus implying that emissions are not influenced by the TDF. The authors mention, however, that other researchers have reported PAHs “to increase significantly when burning tires with respect to conventional fuels”. (See: Levendis et. al., Journal of Environmental Science and Technology 1998, No. 32 3767-3777 and Levendis et. al. Environ. Sci. and Technol. 1996, 30, 2742-2754). Divergent results like these suggest the need for further research.
On The Shredding of Whole Tires - The Unicem Barletta study starts with the premise that proper combustion is a function of fuel particle size. The authors point out that cement plants provide interesting opportunities to study this practice (i.e. the use of scrap tires as a substitute for conventional fuels in industrial production processes) in terms of process operating conditions. They are careful to point out, however, that “the feasibility of the industrial application should be carefully investigated with dedicated, full-scale trial burn tests for evaluating the potential influence of conventional fuel replacement on combustion and process conditions, clinker product quality, and emissions-related issues.”
The study results from Unicem Barletta (
- completely “state-of-the-art” (5 cyclone pre-heaters, pre-calciners, etc.)
- equipped with efficient pollution control devices including electrostatic precipitator (ESP) and a fabric filter/baghouse
The research is especially valuable for the new information that it brings to bear on the tire shredding operation (for instance, kinetic/combustion related impacts of variable particle size) and for optimum injection modes with respect to their effect on combustion conditions. On this point, the results showed that the pneumatic conveyor system installed for feeding the shredded tires to the furnace (at the pre-calciner entrance) provides for high precision in material proportioning and good flexibility for different operating conditions.
Unicem Barletta Implications for Lafarge Brookfield
- Significantly, the Lafarge Brookfield proposal to burn whole tires by dumping them through a hole in the kiln at mid-point is highly primitive and completely alien to the process that was studied at Unicem Barletta. Context and specificity requirements are entirely unmet. For these results to have potential application here, the 42 year old
- Required plant modifications would necessitate a 5 stage cyclone pre-heater, an appropriately modified pre-calciner, a modernized, properly functioning and reliable ESP, a state-of-the-art Baghouse to supplement the current pollution control system, sophisticated facilities to shred tires and an accompanying pneumatic injection system with which to properly introduce TDF to the combustion process. Only after these changes are implemented would it be in order for Lafarge Brookfield to be compared with Unicem Barletta and qualified as such to undertake a closely monitored TDF test burn.
TDF Use By Finnsementii (Parainen)
In earlier tire-burning tests using chipped tires at the Parainen plant in Finland, the authors mentioned mixed results and several related disturbances, including:
- ring formation in the kiln
- large amounts of unburned fuel
- problems with the electro-static precipitator and flue gas analysis.
When the Parainen study was done, shredded tires were being used at a rate of between 5% and 10% of the total amount of fuel burned in the kiln.
Some comments made by the authors during the course of their research are as follows:
- “Several tests were carried out to find the best possible location for feeding the tire chips into the riser duct. Feeding points were tested at the lowest possible position in the riser duct and it was found that it was not possible for the chips to be lifted by the gas stream and pyrolyse. Instead, they fell to the bottom of the riser duct, on the slope to the kiln inlet, and melted together forming big lumps of unburned fuel.”
- “Occasionally this led to the formation of CO gas in the kiln system. This gas formation led to malfunctioning in the electrostatic precipitator (ESP), whereupon dust emissions rose rapidly.”
- “In the cyclones the tire chips are mixed with large amounts of hot kiln feed. This causes a lack of oxygen content on the surface of the chips and the pyrolysis gases cannot combust although the temperature is high enough to melt the rubber and, again, the rubber chips can form bigger lumps that may cause blockages in the cyclone. This may lead to a full stop of the kiln system.”
CABOT Comments – This research is focused on operating processes within the Paraienen plant and the internal changes that took place when burning shredded tires (whole tire feed is not a consideration here; no mention whatsoever is made of whole tires). Conditions are identified in the co-combustion with shredded tires that lead to malfunctions in process stability and concurrent upset conditions. The study, however, gives no attention to the increased atmospheric emissions that result from the combustion process under upset conditions in the kiln.
As well, the researchers identify the deposits or so-called ‘rings’ that form, as a result of the metal/steel in tires, on the inside surface of the kiln, “resulting (again) in blockages”. But they make no mention of the increased heavy metals emissions that are documented in the literature to form as a result of these rings. It is not unfair to surmise that the terms of reference for this industry-sponsored study did not allow for any consideration of the environmental implications of burning (shredded) tires. In this regard, the study received funding support from Heidelberger Cement Nordic,
The Finnish study also holds up for critical examination the Lafarge Brookfield proposal to dump whole tires directly into a whole cut in the side of the kiln at about mid-point of its length. The research is based entirely on the use of shredded/chipped tires. It found that the results were much better when the smallest chips (≤ 20x20x10 mm) were injected at the highest location in the riser duct. However, even here, it was found that these smaller chips “followed the flue gases and went into the lower cyclones” (as described above, causing blockages in the cyclone, which may lead to a full stop of the kiln system). Related discussion in this paper (as well as other research documents that were uncovered in our literature search) serves to alert the reader about the grave uncertainties that are associated with the Lafarge proposal to burn whole tires at Brookfield/Pleasant Valley. Also emphasized is the need to be “familiar with the new fuel and able to predict its behavior during combustion.” To date, CABOT research has been unable to locate scientifically based, credible research that meets this need.
Conclusion
The research literature provides interesting support to the proposition that proper combustion when burning TDF is a function of fuel particle size. By virtue of its absence, the review seems to indicate that virtually no investigations have been done into the use of whole tires as industrial fuel. Substantive, rigorous and intensive research efforts have been made into the use of tire derived fuel, both in power generation and (though to a lesser extent) in the cement industry, but always as chipped or shredded TDF.
Furthermore, the cement industry apparently sees no benefit to undertake, sponsor or otherwise prompt comparative investigations into using whole tires as industrial fuel. Lafarge of course is no exception. Although burning TDF is less harmful than whole tires to human health and the environment, the process entails greater capital expense and therefore is not in the business interest of Lafarge (even with a fuel input subsidy of $2.65 per tire from consumers by way of the NS/RRFB).
Source Bibliography
Carleton Elaine, Jody K. Tishmack, et. al. “Investigation of Atmospheric Conditions of Tire and Coal.” Geological Society of
Gieré, R. “Environmental Impact of Energy Recovery from Waste Tires.” In Gieré and Stille, Energy, Waste and the Environment: A Geochemical Perspective. Geological Society, special publication, Vol. 236,
Lafree Sara, Loran Carleton, et. al. “Characterization of solid waste products from co-combustion of tire and coal.” Geological Society of America 2003 Annual meeting. Vol. 35. No. 6. pp. 403, Nov. 2003.
Zingg Anatol, Jody Tishmack, et. al. “Impact of tire-derived fuel on the chemical composition of coal-combustion products.” Geological Society of
Caponero, J., J. Tenorio, et. al. “Emissions of Batch Combustion of Waste Tire Chips: The Pyrolysis Effect.” Combustion Science and Technology. Vol. 177. No. 2. 2005, pp 347-381.
Lavendis Y., J. Carleson, et. al. “Emissions of Batch Combustion of Waste Tire Chips: The Afterburner Effect.” Energy and Fuels 17 (1): 225-239. Jan-Feb, 2003.
Lavendis Y., J. Carleson, et. al. “On the correlation of CO and PAH Emissions from the combustion of pulverized coal and waste tires.” Environmental Science and technology 32 (23): 3767-3777. Dec. 1998.
Jyh-Cherng, Chen, Mingh-Yen, Wey, et. al. “The effects of chloride additives on adsorption of heavy metals during incineration.” JAWMA. 49:1116-1120. Sept. 1999.
Zhuang Ye, and
Giugliano Michele, Stefano Cernuschi, et. al. “Experimental evaluation of waste tires utilization in cement kilns.” Journal of Air and Waste Management 49 (1999): 1405- 1414.
Pipilikaki P., M. Katsioti, D. Papgeorgiou, et. al. “Use of tire derived fuel in clinker burning.” Cement and Concrete Composites. Vol. 27 (2005): 843-847. (*D. Papgeorgiou is employed by the Titan Cement Company).
Stemmermann Peter, Klaus-Rainer Brautigam, et. al. “Impact of the use of waste on trace elements concentrations in cement and concrete.” Waste Management and Research 23: (2005) 328-337.
Kääntee Ursula, Ron Zevenhoven, Rainer Backman, et. al. “The impact of alternative fuels on the cement manufacturing process.” Paper presented at the 2000 conference,
Al-Neaimi Y.I., J. Gomes, and O.L Lloyd. “Respiratory illnesses and ventilatory function among workers at a cement factory in a rapidly developing country.” Occupational Medicine. Vol. 51, No. 6, pp. 367-373.
[1] Source: E-mail correspondence to CABOT spokesperson L. Sorflaten from James Kirkpatrick, Lafarge Brookfield Plant Manager, dated March 2, 2007.
[2]
[3] David Mackie,
[4]