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Mercury Emission Scenario World and Indian Cement Industry
TIWARY, N. K.; SELVARAJAN, M.; BOHRA, A; NATH, K R P; and MISHRA, A. K.
NATIONAL COUNCIL FOR CEMENT AND BUILDING MATERIALS
ABSTRACT
Mercury hazards are being studied for few sectors in India. The awareness to hazards caused by mercury pollution is increasing among Indian public. Industries such as Chloralkali,Thermal power plants, steel and cement plants are some of the major source of mercuryrelease to atmosphere and in some cases to surface water. Out of around 600 million tonnesevery year of coal consumption in India, Cement industry consumes around 5% of coal. Coalcontains mercury, hence, during its combustion mercury emission may take place due to its
semi-volatile characteristics. The Indian cement industry is the second largest producer in theworld. The possible sources of mercury from Cement Industry includes raw materials likelimestone, clay, bauxite, iron ore; blending materials like fly ash, slag, fuels like coal,
petcoke, alternate fuels etc. Raw Materials used for Cement production are one of the major sources for mercury emissions from Cement industry. Cement plants have a wide range of fuel inputs mainly coal resulting in mercury emissions because of the high temperature in
pyro-processing. Heavy metals such as mercury contained in conventional or alternate rawmaterials and fuels are mainly incorporated in clinker. Mercury, being the only metal whichcan be emitted with the clean gas in gaseous form, the input of mercury with raw materialsand fuels has to be carefully controlled. The present paper discusses the status of Mercuryemissions from cement plants worldwide, techniques and technologies adopted to controlmercury emissions, emission norms available, if any for mercury emissions in other countries
and future approach for Indian cement industry regarding mercury emissions.
Keywords: Cement Industry, Mercury, Coal, Mercury Emissions, Biosphere
1.0 INTRODUCTION
The average level of mercury in the atmosphere is around 1.1 1.7 nanograms/m 3
(UNEP 2008), which is largely due to Anthropogenic activities. There is a growinglevel of concern about mercury emissions from various industrial sources. Exposureto Mercury at higher concentrations may result in nervous system disorders,reproductive and developmental problems, kidney and liver damage, and other healtheffects. The global anthropogenic mercury emissions to atmosphere from different
regions of world is given in table 1.1. Asia is the largest emitter of mercury emissionscontributing 1281 tonnes (i.e. upto 66.5% of the total emissions) to the atmosphere.
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Table 1.1 : Global anthopogzonic mercury emission to atmosphere in world
S.NO. Continent Emissions, Tonnes %, Emissions1. Asia 1281 66.52. Europe 150 7.8
3. North America 153 7.94. South America 133 6.9
5. Russia 74 3.96. Oceania 39 2.07. Africa 9.5 5
(Source: The global atmospheric mercury emission; sources, Emissions and transport UNEP,2008)
The leading countries among emitters of mercury to atmosphere are China and India(Fig 1.1). The mercury hazards are being studied for few sectors, including cementworld over. Due to global awareness to hazards caused by mercury pollution concernis increasing among Indian public towards mercury emission from industry. In India,major source of mercury to atmosphere are fossil fuel combustion in thermal power emissions plants, chloralkali, cement plants, metal production (ferrous and non-ferrous), gold production, waste incineration etc as shown in figure 1.1. The
proportion of Global Anthropogenic Mercury Emissions from different sectors isgiven in figure 1.2 and table 1.2.
Figure 1.1 The global atmospheric mercury emission
(Source: Emissions and transport UNEP, 2008)
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India consumes around 600 million tonnes of coal every year in various industries likethermal power plants, steel, cement and others, where coal is used either to generate
power or as thermal energy input. Coal contains mercury hence during its combustionmercury emission takes place due to its semi-volatile characteristics. It is evident thatthermal power plants using fossil fuels are the major source of the mercury pollutionto Atmosphere.
Cement plants have a wide range of material as well as fuel inputs mainly coal,resulting in mercury emissions because of the high temperature in pyro-processing.Cement industry contributes around 10% of the total global anthropogenic mercuryemissions as shown in table 1.2 and figure 1.2. However, the current level of mercuryemissions from Indian Cement Industry due to various types of fuel, technology,geographical location, Pyroprocessing, raw material etc is not studied in detail.
(Source: The global atmospheric mercury emission; sources, Emissions and transport UNEP,2008)
2.0 MERCURY CYCLE
Mercury is bio-accumulative. Once released into the environment, mercury depositson soil, air, groundwater and surface water where it accumulates and moves up thefood chain. In water bodies, mercury is taken up from the sediment by smallorganisms, which are eaten by increasingly larger organisms until it ends up in fishthat is eaten by humans. At each step of the process, mercury levels increase inconcentration, which makes large food fish that exist at the top of the food chain,especially dangerous to eat. Mercury emissions are regulated based on concern for mercury entering the food chain and bio-accumulating to significant levels that can
Sectors Emission,Tonnes
Emissions%
ThermalPower Plants
878 45.6
MetalProduction
200 10.4
Large ScaleGoldProduction
111 5.8
Small scalegold prod. 350 18.2
CementIndustry 189 9.8
Chlor-Alkali 47 2.4WasteIncineration
125 6.5
DentalAmalgam
26 1.3
Table 1.2 Global anthropogenic mercuryemissions from different sectors
Figure 1.2 Global anthropogenic mercuryemissions from different sectors
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impact people eating fish. Cement kilns mercury emissions fall back to earth in a process known as deposition. As it is an element, mercury does not decompose but persists indefinitely in the environment once it has been released
Figure 2.1 Mercury cycle in food chain
3.0 STATUS OF INDIAN CEMENT INDUSTRY
The Indian cement industry is the second largest producer of cement in the worldcomprising 185 large cement plants and 365 mini cement plants. The installedcapacity and cement production during the year 2012-13 are 349 Mn.t and 240 Mn.trespectively. By the year 2020, it is expected that the installed capacity of Indian
Cement Industry will be increased to 600 Mn Tonnes per annum. Today, it is by andlarge comparable to the best in the world in respect of quality standards, fuel & power consumption, environmental norms, use of latest technology and capacity etc. Cement
being one of the six core sector industries, plays a vital role in infrastructuredevelopment especially in a developing country like India. The per capita cementconsumption in India is approx 200 Kg, against the world average of approx 500 Kg.It is lower than several developing countries like Thailand (366). Sustainable growthof the industry for enabling sustainable growth of infrastructure calls for leveraging
pollution control measures with rapid growth of the industry. The main clusters of cement industry in India are shown in Figure 3.1.
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Figure 3.1 : Clusters of Indian Cement Industry
3.1 Pyro-Processing Technology used in Indian Cement Industry
Wet Process
Semi-DryDry
Pre-Heater (PH)/ Pre - Calciner (PC)- Single/Double/Triple string- 4 stage PH- 5 stage PH- 6 stage PH
Inline Calciner (ILC)Separate Line Calciner (SLC)
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3.2 Process Profile of Indian Cement Industry
The technological spectrum in the cement industry is very wide. At one end of thespectrum are the old wet process plants, while at the other end, are the new state-of-the-art technology plants presently being built by the Industry. The Cement Industrytoday comprises mostly of Dry Suspension Preheater and Dry Precalciner plants and a
few old wet process and semi-dry process plants. Today, there are 178 kilns inoperation comprising 165 dry process kilns, 5 wet process kilns and 4 semi-dry
process kilns. In addition to these, there are more than 300 mini cement plants. Figure3.2, shows the percentage variation in process profile (i.e. Dry, Wet or Semi-Dry) of Indian cement industry in terms of no. of kilns and kiln capacity in TPD respectively.
Semi-Dry
0.4%Wet1.0%
Dry98.6%
Wet Semi-Dry Dry
Dry92.7%
Wet5.1%
Semi-Dry2.2%
Wet Semi-Dry Dry
Fig 3.2 : Process profile on Indian Cement Industry
4.0 SOURCES OF MERCURY EMISSIONS IN CEMENT INDUSTRY
The possible sources of mercury from Cement Industry includes raw materials likelimestone, clay, bauxite, iron ore; Blending materials like fly ash, slag, fuels like coal,
petcoke, alternate fuels etc.
Raw MaterialsLimestoneClayBauxiteIron Ore
Blending MaterialsGypsumFly AshSlag
FuelsCoalPetcokeImported CoalAlternate Fuels like Hazardous wasteLignite
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Table 4.2 Growth of Indian Cement Industry during last five years ( In Million Tonnes )
Year InstalledCapacity* Production*Coal
Consumption
in Process*
CoalConsumption
CPP*
Total CoalConsumption*
CaptivePower
Generation
Capacity $(MW)
2007-08
190.11 174.29 18.92 6.14 27.33 2545.99
2008-09
217.56 187.61 19.52 7.64 29.57 2791.11
2009-10 250.92 207.56 16.04 6.90 25.80 2676.74
2010-11 310.96 228.30 17.51 8.50 28.06 2697.34
2011-12 325.78 246.70 17.70 8.81 28.37 2688.14
*Source: Working group on cement industry for XII five years plan. Cement Statistics 2012. $DG set included
In 2020, the estimated cement production capacity of Indian Cement Industry mayreach around 600 Million Tonnes. As per Mercury Emission factor for global cement
production given in UNEP 2008 report, 0.1 gm mercury per tonne of cement production is emitted in the environment (Table 5.1). Hence, the mercury emissionfrom Indian Cement Industry is estimated to be:
At present, 33 Tonnes per year By 2020, it may be around 60 Tonnes per year
Future Growth in Indian Cement IndustryGrowth of Indian Ceme nt Industry
29 61133
318
600
21 49 98
220
414
0100200300400500600700
1981 1991 2001 2011 2020(E)
Year
M n
. T
Instal led Capacity (Mn.T) Cement Product ion (Mn.T)
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5.0 MERCURY HOTSPOTS FROM CEMENT INDUSTRY
Mercury present in raw materials and fuels used as inputs in cement industry comesout in the form of entrapment in clinker, emissions from stacks as shown in figure 5.1.
Sources of Mercury Emissions to atmosphere from Cement Industry
Entrapment in Clinker Emissions
Kiln and Raw Mill Stack Cooler Stack
Figure 5.1 Mercury sources and emission points from Cement industry
Heavy metals contained in conventional or alternate raw materials and fuels is mainlyincorporated in clinker. Mercury, being the only metal which can be emitted with theclean gas in gaseous form, the input of mercury with raw materials and fuels has to becarefully controlled.
Table 5.1: Mercury Emission Factors from different sectors
S.NO. Category Unit Emission factor
1. Coal Combustion in power plants g/Tonne coal 0.1 - 0.3
2. Oil Combustion g/Tonne oil 0.001
3. Cu Smelters g/Tonne Cu produced 5.04. Pb Smelters g/Tonne Pb produced 3.05. Zn Smelters g/Tonne Zn produced 7.06. Cement Production g/Tonne Cement 0.17. Steel Production g/Tonne Steel 0.048. Gold production g/ g gold mines 0.025 - 0.027
9. Municipal WasteIncineration g/Tonne waste 1.0
(Source : UNEP 2008 report)
Hot Gases(E)
Pyroprocessing
System
Raw meal(S)
Clinker En
Fuel (S)
(S) Source; (E) Emission, (En) - Entrapment
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6.0 MERCURY EMISSION LIMIT VALUES IN DIFFERENT COUNTRIES
Due to high awareness and concern to mercury hazards for flora and fauna countriesworld over have either evolved or in the process of evolving limit of mercuryconcentration in the environment. Standards and guidelines for some countries are
presented in Table 6.1.
Table 6.1 : Mercury Emission limit values in different countries
HgConcentration(mg/Nm3)
At reference O 2 %
for existingfacilities
0.012 mg/Nm/43 (21.5mg/tonne)
USA
for new ones 0.004 mg/Nm/14 (7 mg/tonne)Canada mg/Sm3 0.15 mg/Sm 3, 10% O 2 for
Hazardous Waste only.Morocco (1) 0.10 -Mexico 0.07 at 7% O 2El Salvador 0.05 at 10% O 2Costa Rica 0.24 Sum of Hg and Cd; at 10% O 2Colombia 0.05 at 11% O 2.Venezuela 0.05 at 10% O 2.Ecuador under review; reference value:
0.05 at 10% O 2.Brazil 0.05 (8) Sum of Cd, Hg, and Tl: 0.2 or
0.28 (at 7% O 2).
Argentina No limitChile 0.109 at 10% O 2Bangladesh 0.2Indonesia 5 0.2 @ 7% O 2Korea 0.1 @ 13% O 2Malaysia 10 @ 12% CO 2Philippines 5Thailand 0.10 @ 7% O 2Vietnam 0.5 (for waste incinerators)Australia 1.0 mg/Nm (permit limit)Europe 0.05 mg/Nm 3
(Source : UNEP 2008 report)7.0 MEASURES FOR MINIMISATION AND CONTROL OF MERCURY
EMISSIONS
7.1. Input control
Mercury enters the kiln system as a trace element through naturally present in rawmaterials and, to a lesser extent, in fuels. Best environmental practice is to carry out a
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careful selection and control of all substances entering the kiln in order to reducemercury input.
7.1.1. Raw materials
A. Raw Materials from Quarries
Mercury concentrations in raw materials (limestone, marl or clay) vary significantlyfrom quarry to quarry. There are even cases where mercury concentrations varysignificantly within a single deposit, thereby sometimes requiring selective mining.
In those cases, after exploration and analyses of the quarry, it is possible to definespecific parts of the quarry with higher mercury concentrations and to continueexploitation in zones where the concentration is lower (selective mining) . It has to behighlighted that such a procedure is complex to manage and cannot always be carriedout .
If mercury is present in all quarry layers, other options have to be considered.
B. Other Raw Materials and Waste Materials
Corrective materials such as bauxite, iron ore or sand may be required to adapt thechemical composition of the raw mix to the requirements of the process and productspecifications. To a limited extent, alternative raw materials are used to substitutenatural raw materials and correctives.
This consists of selecting materials with a low mercury content as well as in using aquality assurance system to guarantee the characteristics of the materials used.
In cases where alternative raw materials lead to a significant increase in the mercuryintake into the system they may have to be replaced by another alternative material.
7.1.2. Fuels
The cement production process usually uses fossil fuels such as coal, petroleum coke,oil and alternative fuels (tyres, wastes derived fuels, etc.). Fuels are not usually thedominant source of mercury in cement kiln input. Nevertheless, it can be necessary, inspecific cases, to also monitor the mercury content of the fuels (more particularlyalternative fuels). Literature review has shown that petroleum coke has lower Mercury(0.01 0.20 ppm), coal (0.01 0.43 ppm)
In principle, for alternative fuels, best environmental practice is to apply qualityassurance systems to guarantee the characteristics of the waste and to analyse andcontrol the mercury content if necessary.
7.1.3. Process integrated measures
In order to avoid an undesired increase of mercury in the kiln system, the periodic purging (bleeding) of cement kiln dust from the system is an efficient way to controlmercury emissions. Many preheater-precalciner kiln systems have raw mills in-line.
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Adsorption is favoured due to the very high dust loadings of up to several 100 g/m present in the raw mill gas streams from preheater-precalciner kilns. This purging process is more efficient in the mill-on mode than in the mill-off mode due to thehigher mercury concentrations in the dust.
During the mill-on operation mode, the finely ground raw material in the raw mill
retains mercury from the flue gases. This leads to lower mercury emissions in themill-on mode compared to the operating periods without raw mill (mill-off). About 80to 95% of the overall operating hours are carried out in the mill-on mode.
Furthermore, the temperature of the flue gas plays an important role. In general, theadsorption capacity for mercury increases with lower temperature.
For controlling mercury emissions, bleeding of the kiln dust system, whereby cementstandards allow for the incorporation of the collected dust into the cement, is suitable.This is a proven and safe procedure in many regions of the world, neither theenvironment nor the product quality is affected.
7.2 Other techniques tested in the cement industry
7.2.1. Adsorption on activated coke, Polvitec
The Polvitec system (CEMBUREAU, 1999) consists of several packed beds of activated coke. The dedusted kiln exhaust gas is passed across the activated cokewhereby compounds like heavy metals (and mercury), VOC, SO 2 and NH 3 areadsorbed. The cleaned gas is then released into the atmosphere. The spent activatedcoke is periodically extracted to a separate silo and replaced with fresh adsorbent.
Since volatile and semi-volatile heavy metals are effectively adsorbed on activatedcoke and since the clean gas dust content downstream of the activated coke device isdown to a few mg/Nm, the emission of heavy metals is virtually equal to zero.
Adsorption on activated coke is not economically viable. In the case of a Polvitecsystem installed in a Swiss cement plant, the project was only made economicallyfeasible through the financial contribution of the communities burning their sewagesludge in the kiln, the fees for burning other alternative fuels in the kiln and thecomplex problem related to different emission components.
7.2.2. Activated Carbon Injection
Activated carbon injection systems are well established as commercial air pollution
control processes for a variety of volatile organic compounds, dioxin-furan andmercury controls in waste incinerator applications (Richards 2005). Activated carboninjection processes are being considered in the US for widespread use in the coal-firedutility boiler industry.
For many reasons, the possible application of activated carbon injection systems incement kilns is considerably more challenging than in the case of coal-fired power stations. Cement kilns must recycle a major portion of the collected dust. Some kilnsuse the fabric filter system as an integral part of the raw material processing system.
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The temperature of this system would have to be carefully controlled to less than200C to ensure proper mercury adsorption and reduce the risk of activated carbonfires in the fabric filter or solids handling system.
If all other measures fail, installation of a powdered activated carbon injection systemand a further dedusting device (fabric filter) downstream of the main kiln filter may
be thought of. This last control option would be extremely expensive. The high costsare due to the need for a second fabric filter system, a new fan and an activated carboninjection system. The operating costs depend heavily on the cost of the adsorbent.Dust management is a subsequent issue. This is the reason why, so far, there are onlya few applications of such a technique in the cement industry.
7.0 ROLE OF NCB
National Council for Cement and Building Materials (NCB) has been engaged inR&D activities for cement and construction industries. It has given support services indifferent spheres of these industries. It has excellent environment managementfacilities and experienced team working in the area like air quality monitoring,EIA/EMP studies, LCA studies, carbon accounting and climate change studies,
pollution load studies, noise & ground vibration studies etc. The organization hasstate of the art instruments for air emission quality monitoring like ICPspectrophotometer, FT-IR, spectrophotometer, XRD/XRF, PSD analyser etc. Theenvironment management group has completed projects in the area of environmentmanagement for organizations like MoEF (India) UNFCCC, NATCOM etc. Withsuch expertise and experience, NCB can play important role in creating mercury data
base for Indian Cement Industry.
8.0 CONCLUSION
Mercury emission is an important global issue as the persistent pollutant remains inthe eco-system and enters the human food chain. Mercury consumption is hazardousto human health and especially prenatal development. The UN has led an internationalcoalition to measure and reduce global mercury emissions. The cement manufacturing
process directly accounts for approximately 10% of global mercury emissions.Developed countries like USA and Europe have taken steps to curb emission fromcement industry. In view of projected potential of mercury emission and lack of dataon mercury emissions from Indian cement industry, a detailed study is required for different elements of input, output, process, so that a suitable strategy can be designedfor curbing the catastrophic impact of mercury on flora & fauna. NCB can play a
pivotal role on estimation of mercury emission from Indian cement industry to make areliable data base.
ACKNOWLEDGMENT
This article is being published with the permission of Director General, NCB.
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10.0 BIBLIOGRAPHY
1. Annual Report 2011, Ambuja Cement Ltd.2. Annual Report 2011, ACC Ltd.3. Cement statistics 2011, Cement Manufacturers Association, India4. Report on Mercury in the Cement Industry April 2010, University of Liege,
Independently Commissioned by Cembureau CSI5. The Global Atmospheric Mercury Emissions: Sources, Emissions and Transport,
UNEP, 20086. Linda M. Hill (2006) PCA R&D, serial no. 2944, summary of PCA projects on
mercury topics.7. Rechards John, capabilities and limit hour of available control technology for
Mercury Emission from Cement Kiln, SN27 48 a, PCA, USA, 2005.8. NCB reports
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