Environ Earth Sci (2017) 76:279 DOI 10.1007/s12665-017-6602-0
ORIGINAL ARTICLE
The investigation of Co2 emissions for different rock units in the production of aggregate Atac Bascetin1 • Deniz Adiguzel1 • Serkan Tuylu1
Received: 5 May 2016 / Accepted: 28 March 2017 / Published online: 3 April 2017 Springer-Verlag Berlin Heidelberg 2017
Abstract The negative effects of CO2-e, which are apparent on a global scale, should be monitored and controlled by responsible governmental authorities. This responsibility should be assumed because CO2 emissions (CO2-e) result from human activities, particularly the usage of fossil fuels which contribute to the phenomenon of global warming. This study will analyse the methods employed for CO2-e and energy calculation in the affected location of a quarry. One of the ways to optimise energy usage and minimise the effects of CO2-e is to ascertain the most detailed and comprehensive degree of planning and design for the mine location to be studied. In order to achieve this, essential, aggregate material properties should be defined then analysed by a related authority. Within the scope of this study, CO2-e unit value released during aggregate production in distinct formations was defined. The distribution of CO2-e values which are dependent on the energy consumption which occurs during aggregate production was also examined. In conclusion, it was found that the diesel fuel consumption had been the most significant CO2-e factor by a rate of 88%. Keywords Aggregate CO2 emission Aggregate production Efficient energy consumption
& Deniz Adiguzel
[email protected] 1
Mining Engineering Department, Engineering Faculty, Istanbul University, Avcilar, Istanbul, Turkey
Introduction The requirements of people increase depending upon the extent of a country’s growth rate in terms of industrialisation. The detectable level of CO2 emissions will also increase as a result. CO2 emissions, (abbreviated here as CO2-e), is the total amount of environmentally harmful gasses such as CO2, CO, NOx, CH4 which are introduced into the atmosphere. The emission of greenhouse gasses (CO2-e) which occur as a result of increasing energy consumption, a by-product of industrialisation must be controlled at every stage of production. Facilities and methods to optimise energy usage should be developed and adopted (Flower and Sanjayan 2007; Bascetin et al. 2011a). Concrete and asphalt are the most widely used materials which are produced by mixing the appropriate amount of aggregate and other mixtures. Therefore, the concrete and asphalt industries can be regarded as major sources of CO2e within the area of industrial production (O’Brien et al. 2009). The aggregate constitutes approximately 70% amount of concrete, which is generally used in the construction industry, and approximately 95% amount of asphalt. Aggregate production is one of the most significant reasons for CO2-e. Consequently, in terms of high aggregate consumption, even small reductions of CO2-e per ton of produced aggregate can cause negative effects which heighten the effects of global warning. Aggregate production in quarries generally begins with an explosion after which stone surfaces are broken and reduced to medium-sized particles. The rubble is removed by diesel-powered excavators and haulers. It is then deposited in an electric crushing and screening plant. Aggregate production is briefly composed of the following stages: blasting, excavation, hauling and crushing. The energy consumption in a quarry encompasses explosives
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(blasting), diesel (excavation and hauling) and electricity use (crushing and screening) (Bascetin et al. 2010). In the majority of the previous studies regarding CO2-e calculation which occurred in quarries, it can be seen that CO2-e calculation is taken into account only in relation to concrete production. For example, Flower and Sanjayan (2007) showed a systematic approach which includes estimations for CO2-e during typical concrete manufacturing processes with various components. A study conducted by Turner and Collins (2013) illustrated the results of a comprehensive analysis of CO2-e produced during the manufacturing of conventional and geopolymer concrete. Abbas et al. (2006) presented the objectives and main benefits of the production of green concrete including conventional concrete. O’Brien et al. (2009) composed a report that quantified the effect of fly ash substitution on CO2-e in the production of concrete. Jonsson et al. (1998) illustrated the environmental impact and life cycle of structural concrete and steel frames in buildings. Despite the fact that there are numerous studies regarding CO2-e estimations which relate to concrete manufacturing, the estimations which encompass aggregate production are still limited in number. In these studies, CO2-e calculation in aggregate production was not calculated in detail. Emissions from the diesel (excavation and hauling) groups were calculated using the CO2-e coefficients. However, in this study, diesel-powered excavators, trucks, loaders and drillers were monitored by a portable combustion gas analyser. Therefore, the reliability of emission calculation was heightened. The method mentioned in this study includes CO2-e estimations in aggregate production with various components as well as the calculation of the unit value of CO2-e per ton of aggregate produced in different formations. Thus, the effects of CO2-e can be evaluated based on material characteristics in aggregate production planning. On the other hand, CO2-e data collected from a typical quarry is also included in this study.
Method The levels of energy consumptions in the quarry are gathered into three groups by of CO2-e emissions type (Bascetin et al. 2011b): Table 1 CO2-e factors for explosives (EPA 1993)
Explosive type
1st Group; CO2-e from the explosive material disposal. 2nd Group; CO2-e from diesel fuel operating vehicles. 3rd group is the CO2-e from electricity consumption.
The CO2-e from blasting was calculated by emission factors depending on the explosive type (Table 1). The emission factors depending on the types of explosive materials and CO2-e value were found ascertained by Eq. 1 (EPA 1993). CO2 - e valueðkgÞ ¼ W EF
ð1Þ
W the amount of explosives (ton), EF emission factor (kg/ton). The calculation of CO2-e for a ton of ANFO usage is shown as an example as follows: CO2 - e valueðkgÞ ¼ ð1 34Þ þ ð18Þ ¼ 42 kg: In this study, diesel-powered excavators, trucks, loaders and drillers were monitored by the portable combustion gas analyser (MADUR GA-40 PLUS). The CO2-e was calculated by EN 1911. According to this measurement data, CO2-e from diesel fuel was calculated by using formulas presented in Eqs. 2, 3, and 4. kg CO2 - e value ¼ GasC FRc h
ð2Þ
FR ¼ A V
ð3Þ
FRc ¼ FR
273 273 þ aT
ð4Þ
Gasc, concentration of CO2 or NO2 (kg/m3), FRc, corrected flowrate (m3/h), FR, flowrate (m3/h), A, cross-sectional area of flue (m2), V, velocity of gas (m/h), aT, ambient temperature. The calculation of CO2-e for a vehicle is shown as an example as follows: Gasc 600 kg/m3 (Total Gas), A 0.0000785 m2, V 39,780 m/h, aT 224 C FR ¼ 0:0000785 39780 ¼ 3:12 m3 =h 273 FRc ¼ 3:12 ¼ 1:715 m3 =h 273 þ 224 kg CO2 - e value ¼ 600 1:715 ¼ 1029 kg=h: h
CO (kg/ton)
NOX (kg/ton)
CH4 (kg/ton)
Other gasses (kg/ton)
85
–
21
12 (H2S)
141
–
1.3
3 (H2S)
Gelatinide dynamite
52
26
0.3
2 (H2S)
ANFO
34
8
–
1 (SO2)
Black powder Dynamite
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• • •
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Table 2 The emission factors which result from the combustion of fuels (NGA 2009) Fuel type
Energy factor (Gj/m3) Emission factor (kg CO2-e/Gj) CO2
CH4
N2O
Natural gas
39.3 9 10-3
51.2
0.1
0.03
Coal
37.7 9 10-3
51.1
0.2
0.03
Biogas
37.7 9 10-3
0
4.8
0.03
The CO2-e value released from electrical energy was determined to use the natural gas amount that the power unit consumes to produce 1 kWh of electricity. This is because the electricity expended at the quarry site was generated through the consumption of natural gas. According to the information obtained from the relevant electricity company, 0.175 m3 of natural gas is consumed in order to produce 1 kWh of electricity (this is the standard value determined according to the type of power source which produces electricity) (TEAS 2004). The emission and energy factors which result from the combustion of fuels are illustrated in Table 2. CO2-e from the combustion of natural gasses was calculated by using Eq. 5 (NGA 2009). Eij ¼ ðQi ECi Ef i Þ=1000
3:14 0:175 ¼ 0:5495 m3 Natural Gas: The values of CO2, CH4, and N2O determined as a result of the combustion of 0.5495 m3 of natural gas can be calculated using the coefficients in Table 2 and the formula in Eq. 5. For CO2n: Eij ¼ 0:5495 39:3 103 51:2 ¼ 1:105 kg:
Eij ¼ 0:5495 39:3 103 0:1 ¼ 0:00215: For N2O:
Case study-description of the mine site which was studied The quarry, located in the Cendere region of Istanbul, produces aggregate material for concrete production. It was chosen as the subject for this study. The Cendere region and its immediate surroundings have remained as a whole within the Istanbul Palaeozoic area. This area comprises sedimentary rocks which were formed during the period between the Ordovician and carboniferous eras (Uz 2007). The quarry in question predominantly consists of sandstone. Different kinds of dyke and sandstone formations were observed in the mine site. The mine site was divided into 12 regions. The data which are used for CO2-e estimation in aggregate production are derived from 12 distinct regions in the quarry. These regions and formations are outlined in Fig. 1 and Table 3. The generally applied design parameters for blasting operations at the quarry are given in Table 4. In this study, it was determined that the productions were made with 12 different formations. In order to identify these distinct formations, density and uniaxial compression tests (UCS) were performed (ISRM 1983). As a Overburden
ð5Þ
Eij, the emission of gas type (CO2-e ton), Qi, quantity of the fuel type (m3), ECi, energy content factor of fuel type (Gj per m3), Efi, emission factor (kg CO2-e/Gj). If Qi is measured in gigajoules, then ECi is ‘‘1’’. The other calculations for the second formation are shown as an example as follows: It is necessary to calculate the amount of natural gas which was used in m3 of electricity produced at 3.14 kWh consumed per ton of aggregate produced.
For CH4:
Total CO2 - e ¼ 1:11 kg CO2 - e:
Eij ¼ 0:5495 39:3 103 0:03 ¼ 0:00064 kg
11
5th Bench 4th Bench
3rd
Bench
5 4
12
2nd Bench
6
9 7
10
8
3 2
1
1st Bench
Fig. 1 Segmentation of the open pit quarry Table 3 Regions and formations
Regions
Formations
1
Diabaz
2
Arkose
3
Arkose
4
Meta sandstone
5
Meta sandstone
6 7
Arkose Meta sandstone
8
Meta sandstone
9
Meta sandstone
10
Andezit
11
Meta sandstone
12
Meta sandstone
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Table 4 General applied design parameters for blasting Parameters
Value
Hole diameter (mm)
89
Slope ()
90
Hole length (m)
9–12
Bench height (m)
8–12
Burden (m)
3
Spacing (m)
3
Stemming (m)
3
Maximum charge per delay (kg)
30–50
Explosive
ANFO
Initiation system
Non-electric
Priming type
Emulsion
result of the experiments conducted in the laboratory, the amount of electricity consumed, and explosive material and diesel fuel consumption during the production of different formations identified by rock mechanics were observed. During the period of observation of the site, all of the energy consumption groups were examined in detail.
Results In this study, the data used for estimation of the CO2-e due to the production of aggregates were taken from 12 different regions in the quarry. The results of the density and UCS experiments were obtained from ten samples of each formation. The results are illustrated in Table 5. During the explosive excavation processes on site, formation differences were not taken into consideration. As the same range pattern is used for each of the 12 different formation types, the same amount of explosive was used during the production of each formation. The CO2-e values Table 5 The test results of UCS and densities for different formations Formation
Average density (g/cm3)
UCS (MPa)
1
3.07
138
2
2.81
83.6
3
2.75
85.9
4
2.87
58
5
2.98
6
2.78
7
2.56
25.3
8 9
2.92 2.87
63 37.8
10
3.2
160
11
2.6
46
12
2.85
66
123
34.3 108
which were accumulated through the consumption of explosives, calculated with emission factors, are given in both Table 1 and Eq. 1. The explosive consumption and the CO2-e values calculated by using this amount are given in Table 6. The total amount of material excavated by the explosion was *120.000 tons. The CO2-e values obtained as a result of explosive material consumption have been proportioned with the corresponding total material amount. Unit CO2-e (kg) values per ton were found to be 0.0089 kg/ton CO2-e (total CO2-e/total amount excavated). This calculation gives the value of kg CO2-e which occurred during the explosion and excavation of 1 ton of material. In ascertaining the CO2-e level generated by diesel-fuelled vehicles, it becomes apparent that the durations of operation and the fuel consumed by the excavators and drillers change by incremental amounts according to the type of formation. As a result, these changes were not taken into account and an average asset value was used in the calculations. In this study, diesel-powered excavators, trucks, loaders and drillers were monitored by the portable combustion gas analyser. According to this measurement data, CO2-e resulting from diesel fuel was calculated by using formulas presented in Eqs. 2, 3 and 4. The average of calculated CO2-e values is displayed in Table 7 (the amount of aggregate produced in the quarry was *600 tons per hour). According to Table 7 CO2-e per aggregate tonnage was found to be 6.86 kg/ton (total CO2-e/the amount of produced aggregates at an hour). The rate of electricity consumption examined during the observation period was calculated. Formation differences lead to changes in the crushing-screening plant. These levels of change were calculated by referring to the general counter, the counters on the crushers during the periods of measurement and by the determining the formation of the material fed into the crusher. Rock properties, especially UCS, affect the electricity consumption of the crushing-screening plants. In this study, electricity consumption of the crushing-screening plant was observed for 12 different formations. CO2-e values derived from electricity consumption of the crushing— screening plants are displayed in Table 2. Equation 5 for 12 different formations is illustrated in Table 8. According to Table 8, average CO2-e per aggregate tonnage was found to be 0.96 kg/ton. A simple regression analysis has been conducted in order to observe the relationship between the values of UCS and CO2-e in terms of the consumption of electricity. The constant values were obtained with reasonable correlation coefficients as illustrated below in Fig. 2. The variance analysis (Table 9) corresponds to CO2-e predictions for electricity consumption during aggregate production.
Environ Earth Sci (2017) 76:279 Table 6 The values of CO2-e for explosive consumption
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Explosive type Dynamite
Consumption (ton) 0.36
18.88
9.44
849.35
199.85
0
1049.20
Total
25.34
868.23
209.29
0.11
1077.62
The amount of CO2-e (kg/h) 884.12
0.11
28.42
Table 9 Analysis of variance Source
DF
Regression
Adj MS
P
1
0.335
0.000064 0.000064
1672.2
UCS
1
0.335
643.2
Error
10
0.008
916.62
Total
11
Trucks Loaders Total CO2-e
Total CO2-e values (kg)
24.98
Drillers Excavators
CH4 (kg)
ANFO
Table 7 The values of CO2-e for diesel-powered equipment Diesel-powered equipment
NOX (kg)
CO (kg)
R-Sq = 81.35%
4116.14
Table 8 The values of CO2-e for electricity consumption of crushing-screening plants
The adequacy and efficiency of the models has been tested by the ANOVA for the response shown in Table 9. The selected model as a response variable is the linear model as a p value (0.000064) \ 0.05 illustrated in Table 9. It is obvious that the most powerful relationships were found to occur between the CO2-e values and UCS. As a result, the constant results for UCS prediction can be explained by the reasonable correlation coefficient given in Eq. 6.
Region
Electricity consumption values a per ton material produced (kWh)
Natural gas consumption values a per ton material produced (m3)
Unit CO2-e value (kg/ton)
1
3.1
0.5425
1.09
2
3.14
0.5495
1.11
3
2.8
0.49
0.99
4
2.84
0.4970
1
5
2.15
0.3763
0.76
6
3.25
0.5688
1.15
ð6Þ
7
2.18
0.3815
0.77
8
2.5
0.4375
0.88
9
2.48
0.434
0.88
10 11
3.92 1.98
0.6860 0.3465
1.38 0.70
As a result of the statistical analyses performed as part of this study, the effects of UCS values with the CO2 values were determined. Empirical formulas were developed for use in estimating these values.
12
2.6
0.455
0.92
Average
CO2 - e ðkg=tonÞ ¼ 0:0042 UCS þ 0:6551 r ¼ 0:9
0.96
Electricity Consumption
Unit CO2-e Value (kg/tonne)
8.5
Blasting and Diesel eqipment 8.26
8
7.97 7.99 7.87 7.88
7.65
7.64
7.5
Average Line
8.03
7.85 kg/tonne
7.8
7.76 7.76 7.58
7 6.87 kg/tonne
6.5 6
1
2
3
4
5
6
7
8
9
10 11 12
Regions
Fig. 2 Graphs displaying UCS versus CO2-e values from electricity consumption
Fig. 3 Unit CO2-e values for regions
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Discussion In relation to the formation types observed, the total unit CO2-e values were calculated. This value gives the CO2-e value released as the result of energy consumed (blasting ? electricity ? diesel fuel) during one tonne of aggregate production (Fig. 3). The distribution of unit CO2-e values according to the energy sources for different regions is illustrated in Fig. 2. Thus, the average CO2-e generated from 1 ton of aggregate production was 7.85 kg CO2-e/tone. Unit CO2-e values from explosive and fuel (diesel) consumption were 6.87 kg CO2-e/tonne. The CO2-e values were ascertained during a study carried out in a basalt and granite quarry. In Flower and Sanjayan’s (2007) study, the value of CO2-e per ton of granite was found to be 45.9 kg (CO2-e/ton). The value of CO2-e of basalt per ton was found to be 35.7 kg (CO2e/ton). The electricity used in the basalt and granite quarry was generated through the use of coal and could be regarded as the most significant explanation for this result. In this study, CO2-e levels generated from the diesel (excavation and hauling) groups were calculated using the CO2-e coefficients. Unit CO2-e asset value from explosive and fuel (diesel) consumption was the same value for all regions. However, unit CO2-e asset value from electricity consumption was not same due to the formation of different UCS values. Accordingly, unit CO2-e values relating to the 1st, 2nd, 3rd, 4th, 6th and 10th regions were higher than the average unit of CO2-e value. On the other hand, unit CO2-e values of the 5th, 7th, 8th, 9th, 11th and 12th regions were lower than the average unit CO2-e value. The percentage distribution of these values according to the energy sources for average unit CO2-e values is displayed in Fig. 4. As only a single blasting pattern was performed for every formation in the quarry, all measurements in this study were made according to this pattern. It was suggested to the quarry management that blasting efficiency can be Electricity consumption 12%
Blasting 0%
Diesel equipments 88%
increased and CO2-e values can be decreased by performing alternative blasting patterns for the different formations examined in this study. As illustrated in Fig. 4, the most significant reason for CO2-e, asset value was the level of fuel (diesel) consumption. When the distribution of CO2 emission values (which were dependent on the energy consumption during aggregate production) was examined, it was apparent that *88% of CO2 emissions were derived from the use of diesel fuel. *12% was from electricity consumption, and *0.1% was from blasting. Therefore, the most important source of CO2 emissions was the use of diesel fuel. Formation difference and electricity production methods may alter these values. For example, the distribution of CO2 emission values were found during a study carried out in a quarry. The CO2 emission percentage was *32% for diesel fuel usage, *68% for electricity consumption and *0.1% for blasting (Flower and Sanjayan 2007). The electricity utilised in the quarry was generated through the consumption of coal. This factor could be considered to be a particularly significant reason for this finding.
Conclusion In this study, the different formations and the levels of energy consumption during aggregate production operations were observed in a quarry located in the Cendere region of Istanbul. The unit CO2-e emission asset value released during one ton of aggregate production for 12 regions with different UCS was calculated. In cases where the UCS values increased, unit CO2-e values also increase as predicted. As a result of the statistical analyses, an empirical formula was developed to be used in estimating unit CO2-e emissions. The percentage distribution of CO2 emissions during the aggregate production was observed. It was understood that the diesel fuel consumption had been the most important CO2 emission factor by a rate of 88%, with CO2 emissions of electricity consumption by the rate of 12%. The main reason why the CO2 emissions originated from electricity consumption remains comparatively low is due to the fact that the electricity being produced is derived from the consumption of natural gas. In the future, CO2 emissions from mining operations must be widely evaluated in order to minimise this tendency. Therefore, mines must be designed with careful consideration of energy consumption and CO2 emissions. Acknowledgements This study was supported by Istanbul University Scientific Research Projects (Project Numbers: 20481, 20710, 20818,
Fig. 4 The distribution of unit CO2-e values per ton aggregate
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Environ Earth Sci (2017) 76:279 20817, 42257). The authors would like to thanks to Istanbul University and Responsible and workers of the quarry.
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