Carbon Footprint in Mining and Blasting Operation

Carbon Footprint Reduction in Mining and Blasting operation

Carbon Footprint reduction in Mining and Blasting operation Control of Greenhouse Gas emission is essential to promote Green Environment *** Partha Das Sharma (B.Tech-Hons. In Mining Engg.) E.mail - [email protected] and [email protected] . Website: http://miningandblasting.wordpress.com/ *** Introduction - The enormous threat posed by climate change is now widely recognized by mainstream science and is increasingly gaining public acceptance. Mining is a significant emitter of greenhouse gases and is the focus of increasing attention from green groups and regulators. Mining companies need to know their own carbon emissions and how they compare with the rest of the industry. Mining companies need to know where they fit in the emissions curve. Because of that, many countries are now thinking of introducing ‘Carbon Pollution Reduction Scheme’, in order to control Greenhouse Gases (GHGs) emissions. Increased atmospheric concentrations of GHGs are known to increase global temperatures by absorption of reflected infra-red radiation and are believed to be contributing to the recently measured global warming. The threat of global warming, and its increasingly prominent position in the public consciousness, demand that every major industry takes stock of its contribution to the rising atmospheric concentration of greenhouse gases (GHGs). Therefore, for every industry, there is now a greater urgency placed on identifying and delivering changes to reduce energy usage and GHGs emissions. Traditionally, mining and explosives industries are not slow in responding the challenges of reduction of ‘Carbon Footprint’ as many has been preparing itself for the change. The good news is, they have already started energy efficiency initiatives. However, as expected, these have targeted ‘Easier First’ mode, and initiated reduction by targeting unnecessary energy usage with items like motors and compressors, using recycled fuel in ANFO and explosives for blasting etc. Carbon Footprint – Carbon footprint is a ‘measure of the impact of human activities leave on the environment in terms of the amount of green house gases produced, measured in units of carbon dioxide’. It is meant to be useful for individuals and organizations to conceptualize their personal or organizational impact in contributing to global warming. In fact, reduction of carbon footprint is must, whether in coal, oil or gas, carbon is the essential ingredient of all fossil fuels. When these fuels are burned to provide energy, carbon dioxide (CO2), a "greenhouse gas", is released to the Earth’s atmosphere. As we’ve become more dependent on carbon-based fuels, we’ve seen a rapid increase in the atmospheric concentration of CO2; from around 280 parts per million (ppm) before the industrial revolution, to 370 ppm today. If current trends of fossil fuel use continue the concentration of CO2 is likely to exceed 700 ppm by the end of this century. According to experts, this could lead to global warming of between 1.4 and 5.8°C, which may results in more frequent severe weather conditions and damage to many natural ecosystems. Many believe that it is realistic to promote actions that ensure stabilization of atmospheric CO2 concentrations at around 500-550 ppm. This is a considerable challenge, given that global energy demand is expected to double between 2000 and 2050. In fact, GHGs comprise of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorcarbons (CFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs) and

Author: Partha Das Sharma (B.Tech – Hons. In Mining Engg.) (E.mail: [email protected])

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Carbon Footprint Reduction in Mining and Blasting operation sulphur hexafluoride (SF6). Each of these gases has a global warming potential (GWP) that has been normalized on a unit mass basis relative to CO2, which has been assigned a GWP of unity. The other GHGs have higher GWPs. For example, CH4 and N2O have GWPs of 21 and 310 respectively on a 100 year time horizon. N2O must be distinguished from the relatively shortlived NOx gases, which are not classified as GHGs and commonly arise in small quantities from explosive detonation. Emissions of all GHGs may thus be expressed in terms of tonnes of carbon dioxide equivalents (t CO2-e). Carbon dioxide is the major GHG, making up the largest proportion of emissions. To achieve carbon stabilization, we need to ask ourselves some tough questions: * What exactly is our current relationship with carbon? * How can we reduce our dependency on carbon emitting technologies and fuels - our carbon footprint? * What steps are others taking around the world? It is common amongst mining companies to track and report total energy usage, but most uses GHG intensity as a key performance metric. Several factors have combined to increase total energy use and emissions, including increased stripping ratios, greater mining depths (meaning longer hauls), lower ore grades and increased production. A key measure, therefore, has been energy efficiency and targets are to set for the reduction of emissions per unit of metal/coal mined. Unfortunately, in many cases these efficiencies and/or intensities have also increased, due to increased stripping ratios, lower-grades, etc. and it will be a considerable challenge for mining companies to keep within limit. Life Cycle Assessment (LCA) - As carbon footprint is the measure of carbon dioxide during the life of a particular industry, ‘life cycle’ concept of carbon footprint is familiar. The life cycle concept of the carbon footprint means that it is all-encompassing and includes all possible causes that give rise to carbon emissions. In other words, all direct (on-site, internal) and indirect emissions (off-site, external, embodied, upstream, downstream etc.) need to be taken into account. The carbon footprint can be efficiently and effectively reduced by applying the following steps: (a) Life Cycle Assessment (LCA) to accurately determine the current carbon footprint, (b) Identification of hot-spots in terms of energy consumption and associated CO2-emissions, (c) Optimisation of energy efficiency and, thus, reduction of CO2-emissions and reduction of other GHGs emissions contributed from production processes, (d) Identification of solutions to neutralise the CO2 emissions that cannot be eliminated by energy saving measures, (e) The last important step includes carbon offsetting; investment in projects that aim at the reducing CO2 emissions, for instance bio-fuels or tree planting activities. Carbon footprints are calculated using a method called life cycle assessment (LCA). This method is used to analyze the cumulative environmental impacts of a process or product through all the stages of its life. It takes into account energy inputs and emission outputs throughout the whole production chain from exploration and extraction of raw materials to processing, transport and final use. The LCA method is internationally accredited by ISO 14000 standards. Carbon footprint and explosives industry – It has stated above that, LCA has been the standard methodology for quantifying all environmental impacts associated with the entire life cycle of products and processes for over a decade. All emissions with the potential to cause environmental impacts are quantified along the entire life cycle from raw material extraction through to final


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Carbon Footprint Reduction in Mining and Blasting operation disposal. In addition, other sustainability metrics such as energy, non-renewable resource and water consumption, land use, ozone depletion potential, acidification and release of any toxic pollutants may be quantified. General outline of the ammonium nitrate based explosives product life cycle is shown (Fig.1).

Fig.1 Essentially, explosive manufacture begins with methane (CH4), usually in the form of natural gas, which is used both as feedstock and fuel in ammonia (NH3) production. About half the ammonia is converted to nitric acid which is then neutralized with the remaining ammonia to form ammonium nitrate. Fuel, generally diesel, is blended with the ammonium nitrate, either in emulsions for water resistant explosives or absorbed into porous prilled ammonium nitrate. Finally, the explosive is detonated at the mine-site for blasting purposes. The major emissions of GHGs along the AN production chain occur as per following sequence: * Fugitive CH4 and CO2 emissions from the extraction, storage and transport of natural gas, * CO2 emissions from ammonia production (conventionally the Haber-Bosch process), during the combustion of a proportion of the gas to provide process heat, * N2O emissions from nitric acid manufacture, * Emissions from electricity used to power the plants, * CO2 emissions from the extraction, refining and transport of diesel fuel, * Emissions arising from the supply of other inputs, such as materials and services required to run the entire manufacturing and delivery systems, * Emissions from detonation of the explosives. Some of these emissions arise directly on the site of the explosives manufacturer while some occur indirectly; either at an upstream supplier or a downstream consumer. The magnitude of each of these emissions is dependent on the specific process at each stage, with large variations possible. The final emission source, usually of most direct interest to blasting, is that arising from detonation. This constitutes only about 5% of the total life cycle emissions of the explosive. Essentially this comprises the combustion gases produced by the reactions of the fuel component with the ammonium nitrate oxidizer. Since this fundamental reaction drives the detonation process it cannot be avoided. However, the use of recycled fuels or bio-fuels instead of fossil fuels in explosives would result in lower overall CO2 emissions, as the bio-fuel growth phase removes an equivalent amount of CO2 from the atmosphere. GHG emissions and its intensity with Explosives and blasting in mines - Formulation and composition changes to commonly used modern bulk explosives result in very little variation of GHGs produced on detonation. As discussed, major changes in GHG intensity can be realised in the ammonium nitrate manufacturing process, but this does not impact mine site blasting emissions.


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Carbon Footprint Reduction in Mining and Blasting operation The exact final composition of detonation gases emitted to atmosphere is actually difficult to determine with certainty. Theoretical gas concentrations under idealized conditions may be calculated with ideal detonation codes such as IDeX (Braithwaite et al. 1996). However, these codes assume chemical equilibrium and a constrained product spectrum limited to common species. The likely GHGs from detonation that require consideration are CO2, CH4 and possibly N2O. However, CH4 could theoretically arise from oxygen-negative explosives. CH4 being 21 times more potent GHG than CO2, even modest quantities of CH4 could significantly increase the overall predicted GHG emissions and even exceed that of CO2. However, under actual detonation conditions the hot CH4 is likely to combust on contact with atmospheric oxygen provided it is above the lower flammability limit. Thus it would not be ultimately emitted to the atmosphere as CH4 but would instead combust to form CO2 and water. This phenomenon is commonly observed with highly oxygen-negative explosives as postdetonation flaring. Similarly, the fate of any CO would be expected to be ultimate oxidation to CO2. A similar fate could be proposed for any traces of solid elemental carbon in the detonation gases.

Fig.2


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Carbon Footprint Reduction in Mining and Blasting operation From the above figure (Fig.2) it’s clear that changes to the emissions profile of detonating explosives is impacting less than 1% of the problem. Even if the GHG emissions from detonating bulk explosives could somehow be reduced by half, the impact on mine GHG intensity would be in the order of 0.5% or less. Reduction of GHG emissions and management of carbon footprint through improved blasting - Efforts for energy and emissions reductions often be the same as those normally used in blast performance improvement programs. Increased OB throw, (or more accurately reduced handling of overall muckpile volumes by incorporating castblast) can lead to direct reductions in equipment energy consumption and thus GHG emissions. It has been observed that, reductions of 5% or more in GHG emissions through the use of electronic detonator delay sequences and improved blast design. These improvements were achieved without any additional explosives energy input to the blasts. For draglines with electricity consumption of the order of about 1.4 kWh/bcm, a decrease of 5% translates to an annual decrease of 2600 t CO2-e from electricity for a mine removing 35 Mbcm of overburden per year. The emissions from explosives are small in comparison to the downstream emissions associated with mining and mineral utilization. However, improved blasting can make a significant contribution to reducing the overall intensity of GHG emissions from mines. In this regard, improved coal or ore recoveries can make the largest impact. GHG intensity and management of carbon footprint in Open pit coal mining - In open pit coal mining, coal losses through the drill, blast and dig process results in losses from 5% to 25% of in-situ coal. While maintaining control of the top surface of coalseam when blasting is one of the main challenges, the most significant blast-related problem is coal edge losses. Another challenge in open pit coal blasting when a dragline is involved is minimising the amount of material that the dragline needs to move to uncover coal. Often this is pursued by maximising cast to achieve the final spoil profile. If less overburden material needs to be moved, then either less energy is used to uncover a given amount of coal, or conversely, a reduced energy (and therefore emissions intensity) profile can be achieved by uncovering more coal for the same energy and emissions profile. Similar cases prevail for truck/shovel fleets, particularly when dozer is used. GHG intensity and management of carbon footprint in metal mines - Greenhouse gas emissions are associated with the consumption of energy at every step in the metal or copper production chain, from exploration through mining to the production of refined metal, and also with the use of explosives in mining. Producers of primary metal or copper employ diverse technologies to mine, mill, smelt and refine several different types of ore, with every ore body having its own special character. Along the production chain, the various modes of transport of ores and intermediate products can also contribute to GHG emissions. Depending largely upon location, mines, smelters, refineries etc., plants consume energy in different proportions from the major primary sources – hydroelectricity, nuclear electricity, natural gas, petroleum products and coal – each with its own GHG impact. All of these factors mean that each unit of production (mine, smelter, hydro- or pyro-metallurgical plant etc.) has its unique GHG footprint, changing over time with movements in such factors as mine ore-to-waste ratios and pit depths, haulage distances, the energy efficiency of the mining fleet, process technical developments and changes in energy sourcing. To calculate the total GHG emissions associated with a unit of metal production from an individual mine, we include not only the emissions associated with the mining operation, but also trace through the transport and downstream processes that transform mine output into refined metal. The big driver of emissions generation in open pit metal mines is the comminution


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Carbon Footprint Reduction in Mining and Blasting operation process. Often, this accounts for 60% of total mine energy usage. Improved milling throughputs due to improved fragmentation from blasting have also been reported. Discussion on management of GHG in mining operations - Construction and mining activities that may cause environmental impacts include ground clearing, grading, excavation, blasting, trenching, vehicular and pedestrian traffic, and drilling. Typical activities during the construction and mining phase include ground clearing (removal of vegetative cover and topsoil), drilling, blasting, trenching, excavation, and vehicular and pedestrian traffic. Activities conducted in locations other than the facility site include construction for transport systems (including access roads, rail lines, and/or conveyor systems). Most importantly, the reduction of inpit coal or ore losses has the greatest potential to reduce the overall mine emissions intensity per unit of coal or ore. The only emissions increase arises from handling the additional coal or ore and all other mine emissions remain constant as production increases. Coal handling represents a small fraction of total mine emissions. In the case of metal ores, it is assumed that the extra ore is recovered through reduced dilution with gangue in the blast; hence total handling and milling duties remain similar. Thus, any increase in production achieved for essentially the same total mine emissions leads to a similar reduction in overall mine emission intensity. Apart, minimising mine sites waste stockpiles, significantly reduces carbon emissions from waste transportation and provides reusable fuel and oils at a reduced cost. Total hydrocarbon resource management improves coal mine profitability with significant environmental advantages. Waste

oil collected from mines are refined and blended with explosive agents providing further waste recycling initiatives. This enables to reduce mines diesel usage for explosives by up to 50% along with significant carbon credits. Present day, more and more mining company is contributing to climate change solutions. Mining

products are essential for building equipment to support alternative energy, and new mining technologies are contributing to carbon sequestration. They are concerned about climate change. They are working toward solutions, increasing efficiency and reducing greenhouse gas emissions. References: * International Standards Organization (ISO). 1998. ISO 14 040—Standard on Life Cycle Assessment. * Braithwaite, M., Byers Brown, W. & Minchinton, A. 1996. The use of ideal detonation computer codes in blast modeling. Proc. 5th Int. Symp. on Rock Fragmentationby Blasting—Fragblast 5, Montreal. Rotterdam: Balkema. * Dr. Ken Pollock, “What’s My Carbon Footprint?” (http://www.ebioant.com/archives/10296 ) * Partha Das Sharma, “Carbon Footprint” (http://knol.google.com/k/partha-das-sharma/carbonfootprint/oml631csgjs7/6 ) * Attalla, M., Day, S., Lange, T., Lilley, W. & Morgan, W. 2008. NOx emissions from blasting operations in open-cut coal mining. Atmospheric Environment 42: 7874–7883. * Barnett, T.P, Pierce, D.W & Schnur, R. 2001. Detection of anthropogenic climate change in the world oceans. Science 292: 270–274.


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Carbon Footprint Reduction in Mining and Blasting operation * Humphrey, J.D. 1990. The fundamentals of the dragline. Ohio: Marion-Dresser Ind. Inc. * Norgate, T. & Jahanshahi, S. 2007. Opportunities for reducing energy consumption and greenhouse gas emissions in mineral processing and metal production. Proc. Chemeca 2007, Melbourne, 23–26 September. * Partha Das Sharma, “Reduction of Carbon Footprint is necessary to save environment” (http://saferenvironment.wordpress.com/2008/09/04/reduction-of-carbon-footprint-is-necessary-to-saveenvironment/ ). * Stern, N. 2006. Stern Review: “The economics of climate change” (www.hmtreasury.gov.uk/independent_reviews/ stern_review_economics_climate_change/stern_review_ report. Cfm). * Brent, G.F., “Greenhouse gas implications of explosives and blasting”, Proc. Rock Fragmentation by Blasting, Fragblast – 9, Spain (PP: 673 – 681)(2009). * “Unearthing the Carbon Footprint” (http://www.oricaminingservices.com/Section.aspx?SectionID=290&CultureID=3 ) * Melanie Kuxdorf, “Mining a solution for climate change: industry”, (http://thetyee.ca/Blogs/TheHook/Labour-Industry/2009/08/21/MiningSolutionClimateChange/)

-------------------------------------------------------------------------------------------------------------------Author’s Bio-data: Partha Das Sharma is Graduate (B.Tech – Hons.) in Mining Engineering from IIT, Kharagpur, India (1979) and was associated with number of mining and explosives organizations, namely MOIL, BALCO, Century Cement, Anil Chemicals, VBC Industries, Mah. Explosives etc., before joining the present organization, Solar Group of Explosives Industries at Nagpur (India), few years ago. Author has presented number of technical papers in many of the seminars and journals on varied topics like Overburden side casting by blasting, Blast induced Ground Vibration and its control, Tunnel blasting, Drilling & blasting in metalliferous underground mines, Controlled blasting techniques, Development of Non-primary explosive detonators (NPED), Hot hole blasting, Signature hole blast analysis with Electronic detonator etc. Currently, author has following useful blogs on Web: • http://miningandblasting.wordpress.com/ • http://saferenvironment.wordpress.com • http://www.environmentengineering.blogspot.com • www.coalandfuel.blogspot.com Author can be contacted at E-mail: [email protected], [email protected], ------------------------------------------------------------------------------------------------------------------Disclaimer: Views expressed in the article are solely of the author’s own and do not necessarily belong to any of the Company. ***


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Carbon Footprint in Mining and Blasting Operation

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