A progress report on the Energy-Efficient Quarry project · Mountsorrel quarry, UK, a typical large quarry producing some 3 million tonnes of crushed-rock aggregates per year. The

ECEEE 2012 SUMMER STUDY on EnERgY EffiCiEnCY in inDUSTRY 129

A progress report on the Energy-Efficient Quarry project

Dr Ian HillDepartment of Geology, University of LeicesterUniversity Road, Leicester LE1 7RH, [email protected]

Antonio BaronaSolintel

Laura Sanchez AlonsoSolintel

Carlos Martin PortuguesAcciona Infraestructuras

Rafael RodriguezAridos Carmona (CAMT)

Elena Lopez MartinezCentro Tecnologico del Marmol (CMT)

Daniela ReccardoD’Appolonia

Ricardo ChavezEPC-France

Stelios ZontosExergia S.A.

Jon AumonierMineral Industry Research Organisation (MIRO)

Vini FilippiS & B Industrial Minerals S.A.

Piotr SwiezewskiMostostal Warszawa

Keywordsenergy efficiency improvements, modelling, quarrying, indus-trial energy saving, industrial minerals

AbstractThe EE-QUARRY project aims to address the energy con-sumption of the quarrying industry, which is characterized by high energy demands and consequent CO2 emissions. The use of crushed stone, which is essential to the infrastructure of our society, could increase more quickly than any other major material. Given the market size, ample resources and stable growth potential of this industry, the understanding and dis-semination of Energy-Efficiency (EE) opportunities is para-mount for overall European EE goals. Further, since there are several thousands of quarries throughout Europe, there is a huge opportunity for replication of such EE measures. This paper will present a progress report of the project 2 years into its 4-year lifetime. The objective of the project is to develop a new modelling and monitoring Energy Management tech-nique. This project will first review the stone extraction and crushing production processes. This project is analysing in detail the energy use in each operational stage such as rock blasting, transportation, crushing, conveying screening and added-value-processing. Standard construction EE measures such as illumination retrofits and support system optimization are insignificant relative to overall plant energy use. The iden-tification of energy opportunities thus relies heavily on overall production systems optimization, which not only encourages EE, but typically benefits productivity as well. EE measures which also yield productivity improvements offer economic incentives that have the magnitude and quick payback to facilitate industry-wide adoption and replication. Once the

quarry and its processing plant reach the end of their life-cy-cle, further opportunities for CO2 neutralizing activities arise. The intended project outcome is to use the Energy Manage-ment model to generate EE opportunities and CO2 compensa-tion activities to minimise the environmental impact created throughout the quarry life-cycle.

IntroductionThe quarrying industry surely rates as one of the primary in-dustries mankind has invented. Minerals of all kinds, fuel (coal, peat), metaliferous (iron-ore, bauxite), precious (diamond, ruby), industrial minerals (fluorite, silica sand) and aggregates (sand and gravel, crushed rock) have been quarried throughout recorded history. Indeed we divide the stages of our culture in terms of sophistication of mineral use, Stone Age, Bronze Age, Iron Age etc. As our culture becomes more sophisticated the demands for raw materials evolves, and also grows. For this reason an effective and efficient quarrying industry is essential to our culture. By its very nature it is heavy industry, handling, processing and transporting heavy materials in large quantities. Thus its energy efficiency and its carbon emissions are a key component of any national environmental budget. For instance in UK annual energy consumption in the mineral industry is about 3 million Tonnes of oil equivalent (Toe), about 10 % of all industrial energy usage.

Within this project we have to place limits on the range of quarrying activities we can address. We have chosen to concentrate on the most common forms of quarrying, since this potentially can produce the most effect on a European scale. This rationale directs us to the bulk materials, Sand and Gravel, Crushed Rock and Industrial Minerals, where we are

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130 ECEEE 2012 SUMMER STUDY on EnERgY EffiCiEnCY in inDUSTRY

1. PROGRAMMES TO PROMOTE INDUSTRIAL ENERGY EFFICIENCY

usually dealing with large volumes of low-value materials used across almost the whole of Europe. The vast majority of Euro-pean citizens will know of a quarry of this type in their home region.

Aggregates, whether crushed rock or sand and gravel, are heavy items. It is trivial to compute that beyond a certain dis-tance range, the energy (and financial) cost of transport of ma-terial far outweighs the production energy. This is important for two reasons. The first is that it explains the abundance of aggregate-producing quarries spread across the whole of Eu-rope. The second is that the availability of appropriate rock material is determined by the geological structure, while the accessibility of the materials is often limited by planning con-straints. Thus even in this early stage of consideration, our en-ergy efficiency is dependent on natural geological processes, and political decision-making.

Within this project therefore we are concentrating on the en-ergy-efficiency of the quarrying process itself up to the product at the quarry gate, and not directly addressing the outbound logistics problems. Even this simplified remit leaves us with a huge variety of different operations, from large crushed-rock aggregate quarries producing several million tons of products per year, to SME operations for local sand and gravel supplies. Our project partners contribute a complementary diverse range of expertise which can address all the separate energy-consuming stages of the quarrying process. We are applying that expertise to develop improved tools for either carrying out each stage, or optimising the efficiency of existing methodolo-gies. In the later stages of the project we will demonstrate the effects of integrating the individual efficiency increases into the overall quarry operation. To facilitate the integrated as-sessment of the energy-efficiency of all the separate stages of a single quarry operation we need to have a system for analysing and modelling the operation in terms of energy consumption, a “Top-Level Model”.

The quarrying operation; component stages and challenges

QuArry DesIgnMany older quarries owe their existence to a long history of progressive development, which in the early stages may have had little formal design with little national regulatory frame-work. Often there has been little geological investigation, per-haps just continuous extension from a surface outcrop. In this case the reserves available are essentially unknown, and varia-tions in the geology are coped with as they are discovered.

The considerable capital investment in new quarry plant demands that the correct purchasing decisions are made, but the type of plant and its most efficient siting within the devel-opment can only be designed if the underlying geology of the deposit is known. This requires detailed site investigation.

Site investigation covers a large range of disciplines, but will generally start with a desk study, move forward to a drilling campaign, which may be accompanied by geophysical surveys to define both the extent of the mineral deposit, and at least as crucially the variations in rock properties within the deposit. Figure two illustrates how drilling and geophysics can be com-plementary. Drilling at 100 m intervals recovers samples of the material for laboratory analysis, but fails to show the lateral var-iation in the deposit. The resistivity image shows the variation in resistivity of the sand and gravel layer, but does not provide any absolute lithological information about specific physical properties of the rock material. Using the drilling to calibrate the variations shown by the geophysics provides a detailed and robust model of the deposit.

Given a reliable geological model, then the quarry design itself can be carried out, and minimising the energy consump-tion in extraction and particularly transport within the site, and processing, can be assessed as a critical criteria for the design.

Figure 1. Mountsorrel quarry, UK, a typical large quarry producing some 3 million tonnes of crushed-rock aggregates per year. The scale can be judged by the vehicles in the foreground. The quarry is approx. 1 km in diameter.



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BlAsTIng & DrIllIngThe purpose of blasting is not only to loosen the rock into a form where it can be handled, but to break the rock into the most appropriate particle sizes for future processing. Obvious inefficiency in blasting is shown by comparing the images in Figure 3.

Since explosives are a much cheaper way of fragmenting the rock than mechanical crushing, then optimising the design of the explosive blast for the required degree of fragmentation is required. This however becomes a complex issue in balancing the requirements for minimum wasted energy, and minimum vibration to the surrounding area, with optimum fragmenta-tion and correct shaping of the rock-pile, all the time allowing for lateral variability in the rock properties.

HAulAge & loADIngMoving the blasted rock from the face to the crushing plant is again energy intensive. For transport the usual options are trucks or conveyors. Conveyors are more energy efficient, but less flexible in use and require fine fragmentation of the rock since large boulders cannot be carried. Conveyors can only be used where there is high confidence that the working faces will be in fixed positions for considerable time, so the instal-lation costs of the conveyor can be justified. Loaders must be matched to the capacity of the trucks being used. Thus these

apparently simple issues are linked to both the quarry design, and the blasting design. For maximum efficiency, both in terms of energy and operational activity, the blast design must suc-cessfully produce the fragmentation which is appropriate for the loading plant and haulage trucks, or the conveyor system. Blast design needs to take account of naturally occurring vari-ations in the rock material, so a good geological model of the site is also required.

CrusHIng & sCreenIngTo produce products which meet standard particle size distri-butions requires both controlled fragmentation of the rock, and accurate monitoring of this. The optimum is that the blasting produces an ideal size range for input to the crushing plant. Measuring the particle size distribution in coarse materials is no easy task. Not only is the energy requirement for sieving large volumes of material a problem, but the issue of represent-ative sampling is equally difficult. Sorting the size distribution by passing through progressively finer screens is the industry standard method and will likely remain so for sorting poten-tial product materials after crushing. While this is essential for the bulk of the material, some more effective monitoring tool would be very useful for intermediate processing steps. In this project we are investigating the practicality of video image analysis as described below.

Figure 2. A resistivity imaging survey of a sand and gravel deposit. Drilling at intervals of about 100 m is shown by vertical lines. Pale shad-ing is sand and gravel, dark is surrounding clay.

Figure 3. Controlling energy and gas emissions during blasting; (a) Uncontrolled energy and gas emissions shown by ejected gas and dust from explosive shotholes; (b) Blast with controlled energy and gas emissions with no visible gas and dust emission, all the energy used in breaking the rock. (Images – EPC-France)

a) b)

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ouTBounD logIsTICsAs mentioned in the introduction this is an important issue, but is affected not only by technology, but by geological occur-rence of materials and the planning legislation of each region. The project will take note of this, but not be attacking this issue in detail. As a general guide, energy and financial costs become prohibitive if transport distances for aggregates by road haulage approach 50 km. There are exceptions to this. For construction of the Olympic site in London, aggregates were transported over 100 km to the site. There are no sources of hard-rock ag-gregates close to London, and in this case the supplying quarry and the receiving site both had rail-heads with a direct main-line link.

QuArry DIsposAl AnD AfTer-useInevitably quarries create large holes in the ground which can be used for a variety of purposes, from landfill storage to eco-parks. The issue here is to consider the life-cycle energy impact

of the restoration or after-use of the quarry. Examples of pos-sible after-use scenarios are shown in Figure 5.

The Integrated Quarry ModelConsidering each of the individual stages of the quarry proc-ess as listed above, it is a tractable problem, at least qualita-tively, to see the way in which energy efficiency for each stage could be assessed. As we have developed this project we have become increasingly aware of the complex web of interac-tions and feedback loops that link between each of the stages. Being aware of this, it becomes apparent that the optimum energy-efficient solution for a specific complete quarry is not simply the result of optimising separately each of the indi-vidual stages of quarry operation. Rather we have to explore the possibility of building a model expressing the complexity of the feedback loops between stages, and then optimise the whole model.

a)

b)

Figure 4. Different types of fragmentation caused by blasting; (a) Coarse fragmentation, with many large blocks which will need additional energy to break them, and will cause difficulties for transport for further processing; (b) Fine fragmentation, Very few large blocks, most of the rock mass is well broken and will be easy to transport and to process.



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Relationships between the blasting, haulage and crushing stages have already been referred to above as an example. At the extreme, there are clearly links between the stages at the extreme ends of the quarry cycle, from initial quarry design to the after-use. Both must depend on the geological model, and decisions made in the initial design can enhance or negate pos-sible options for the eventual after-use. In large quarries, these two stages may span a timescale of many decades, and technol-ogy, environmental pressures and legislative frameworks may change substantially within these long timeframes. Building considerations of such long-term and poorly constrained end-use options into initial quarry design has obvious difficulties.

Current Activities and results

revIew of CurrenT ACTIvITIes AnD prACTICes In THe QuArryIng InDusTryIn the early months of the project considerable effort has been put into scanning for established current and evolving new practices across the quarrying industry, both in terms of geo-graphic regions and types of deposits worked. In general the industry is very aware of its high energy consumption, and the associated costs. There are many examples of good practice and development of corporate policies to improve energy efficiency. An example is haulage by trucks. Encouraging efficient driving styles by operators can cut energy consumption by over 10 %, and is a relatively quick and simple one-time gain. Using the most recent design of energy efficient trucks would produce an even greater gain, but the capital investment in plant which may otherwise have a useful lifetime of greater than 10 years, makes this an option that will only incrementally be taken up.

In general existing studies approach individual topics within one of the stages of the quarry process. These are all individual-ly valuable, but the complexity of the interactions between dif-ferent stages of the quarrying activity, as argued earlier, means that the optimum design for the whole quarry does require an integrated model. Our project has a number of work programs

investigating specific new technologies, or novel applications of existing technologies, and will then seek to demonstrate the ways in which all of these can be optimally integrated into cur-rent quarrying operations to produce an increase in energy ef-ficiency for the overall quarrying process. We review some of the current activities below.

THe geologICAl MoDelOne work program led by Leicester is seeking to develop meth-odologies for producing an improved geological model of the mineral, which is then used for the quarry design and later for the blast design. Very few mineral deposits are uniform throughout a whole quarry, and the extent and location of min-eral quality variations is an important input into quarry design. If variability is high, the quarry will want to work multiple faces simultaneously so that low quality mineral on any one face does not stop the quarry’s production, and if possible materials of different qualities can be blended to optimise production vol-umes and avoid waste.

Geophysical surveys are being carried out in quarries with large-scale variability in such factors as overburden thick-ness and mineral quality, to assess the additional value they can provide to the geological model. Where such surveys are used, the accuracy of the resulting geological model is being tested by continuous monitoring of the quarry faces as they work through the volumes of rock previously surveyed. This monitoring of faces using photogrammetric techniques (Fig-ure 5) is in itself a useful and relatively simple technique which can contribute to the better understanding of deposits where there is substantial and complex geological variability in the mineral deposit.

BlAsTIng AnD frAgMenTATIonA work Program led by our colleagues in EPC-France is de-veloping software to improve blast design by allowing input of geological characteristics of the rock mass, the complex topography of the face to be blasted, the desired fragmenta-

Figure 5. A 3D computer image of the quarry face from an active limestone quarry. The image may be zoomed and rotated to view in details the geological features on the face. As extraction continues and images are compiled of successive faces, a composite model is produced showing the geological structure of the rock mass in 3D. This allows extrapolation to predict the rock mass yet to be extracted.

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tion, and the ground vibration, and will design an optimum configuration of shot boreholes, and the loading pattern for each hole. This software is nearing completion and available for testing. Ideally this detailed blasting design will be able to utilise the detailed geological model, particularly relating to local variability in the rock mass, provided by the geophysi-cal surveys.

MeAsurIng frAgMenTATIonWe have two teams working on measurement of fragmenta-tion and particle sizes by remote video monitoring. Workers at MIRO are using video image capture and analysis to meas-ure the fragmentation of material as it is delivered to the feed hopper of the primary crusher in quarries. This is a possible method for actually measuring the relative effectiveness of rock fragmentation at a stage after the blasting and transport, but before the primary crusher. This has potential to provide a quantitative measurement of the relative contributions of the blasting and crushing stages, and would be a useful monitor-ing tool for any consideration of the overall performance of the quarry.

An alternative use of video image capture would be to have a real-time system providing surveillance of the processing systems and conveyors of a plant and identifying out-of-speci-fication materials in the processing system. This is a consider-

able computing challenge, but is being investigated by another working group.

CrusHIng AnD sCreenIngPartners led by MIRO are working on the quantitative energy analysis of the multiple functions of a complete crushing and screening processing system. Here they are using software packages to predict the efficiency of different configurations of crushing and screening systems, and checking the results against real output from quarry operations. This requires a detailed database of the performance of individual commer-cial plant items, both in terms of their output products, and their energy consumption under different operating condi-tions.

AfTer-useEach quarry must eventually be worked out and the resulting excavation must be either remediated or exploited for further and different industrial or social activities. Partners led by Ac-ciona are collating experience from the literature as well as their own experience of exhausted quarries, to compile a compre-hensive catalogue of the available options for after-use, and the factors which may place constraints of the range of options for any particular site. Figure 6 gives a brief summary of the range of options currently under consideration.

Figure 6. Stages in the measurement of fragmentation by video image capture. (a) image of rock material; (b) image processed to identify individual blocks of material; (c) derived size distribution curve; (d) real video image of the feed hopper of a primary crusher.

a) b)

c) d)



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Dissemination of project progress and resultsThe results of the project will be of little value if not widely disseminated, so a dissemination plan is an integral part of the project. This includes both promulgation of information about the project during its lifetime, but also the delivery of project deliverable documents, and training materials and courses, af-ter the end of the project. Naturally at this stage of the project little of this content yet exists. However a sequence of reports of the investigation phase of the project are now accumulating, and are becoming available for electronic download.

The main mechanism for this is the project website now available at: http://www.ee-quarry.eu. In addition to the for-mal project reports this allows download of project newslet-ters, profiles and contact details for project partners, and other information.

DiscussionOur project is not yet at its midpoint, and the final shape of our conclusions is not yet clear. Despite this, there are some specific points which have been recognised as of primary importance:

• The importance of energy efficiency in the quarrying indus-try is widely accepted, from both environmental and finan-cial viewpoints.

• New technologies are emerging which will allow more pre-cise monitoring and control of extraction and processing operations.

• Within a single quarry operation, optimisation of the over-all energy efficiency is more important, and much more complex, than optimisation of each individual separate stage of the operation.

• Initial design (and consequent revision of the quarry design during the operational life of the quarry) is fundamentally important in placing bounding constraints on the optimum energy efficiency of the overall operation.

referencesAllington, R, and D Jarvis. A Quarry Design Handbook. URL:

http://www.sustainableaggregates.com/library/docs/samp/samp_3_E_002.pdf, Birmingham: MIRO, 2007.

BCG. Aggregates Sector Strategy Review: Consolidated Steering Committee Presentations. URL:, London: Carbon Trust, 2009.

BGS. European Mineral Statistics 2005-2009. Product of the world mineral statistics database, Keyworth, Nottingham: British Geological Survey / NERC, 2011.

Brierley, E, Z Shang, M Cook, S Dubuc, A Angus, and P Howsam. Vertical Integration: Low Carbon Energy Produc-tion for the Mineral Industry. URL: http://www.sustain-ableaggregates.com/library/docs/mist/ma_4_3_001.pdf, Birmingham: MIRO, 2005.

DETR. Energy Consumption Guide 70: Energy Use in the minerals industries of Great Britain. URL: http://www.carbontrust.co.uk/publications/pages/home.aspx, DETR Energy Efficiency Best Practice Programme, 1998.

Table 1. examples of possible future uses of quarries and constraints on their development.

USES CHARACTERISTICS REQUIREMENTS COMPATIBILITY

AGRICULTURE -Fruit trees. -Cereal. -Vineyards. -Forage.

-Soft slopes. -Drainage system. -Fertile and well balanced soil. -Cultivation adapted to soil conditions.

- Natural habitat - Leisure areas - Forest in certain cases

FOREST -Plantation of trees for wood purposes. Increases biodiversity and prevents erosion.

-Moderate slopes. -Fertile and well balanced soil. -Drainage system. -Proper species selection.

- Natural habitat - Leisure areas - Agricultural in certain

cases

NATURAL HABITAT & LEISURE AREAS

-Land recovery or development of a new habitat. -Natural reserve for flora and fauna.

-Fertile and well balanced soil. -Proper species selection. -Shape of water banks.

- Natural habitat - Leisure areas - Forest - Agricultural in certain

cases - Urban planning in

certain cases -

INDUSTRIAL -Industrial park. -Parking lots. -Water deposits. -Solar, wind farms

-Soft slopes and good geotechnical properties and sealing of the hole -Access/ Infrastructures & Proximity to urban centers. -Security measures for users.

- Urban planning in certain cases

- Landfills

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Goodquarry. Blasting. 2011. http://www.goodquarry.com/arti-cle.aspx?id=155&navid=19#cp (accessed August 8, 2011).

—. Crushing. 2011. http://www.goodquarry.com/article.aspx?id=155&navid=19#cp (accessed August 08, 2011).

—. Screening. 2011. http://www.goodquarry.com/article.aspx?id=158&navid=19#s (accessed August 08, 2011).

Jeffrey, K, Ian Hill, and P J Fitch. Waste minimisation by the application of integrated technology. Electronic: http://www.sustainableaggregates.com/library/docs/mist/ma_4_2_002.pdf, Birmingham: MIRO, 2005.

Jeffrey, Kip, Gavin McKee, and Eddie Bailey. Sand and Gravel Deposits: Improved Characterisation Technology. Electron-ic: http://www.sustainableaggregates.com/library/docs/mist/ma_3_2_002.pdf, Birmingham: MIRO, 2004.

Korre, Anna, and Sevket Durucan. “Aggregates Life Cycle Assessment (LCA) Resources.” Aggregain. August 2009. http://aggregain.wrap.org.uk/sustainability/sustainabil-ity_tools_and_approaches/aggregates_lca.html (accessed August 08, 2011).

Lindqvist, M. “Energy considerations in compressive and impact crushing of rock.” Minerals Engineering, 2008: 631-641.

Morrell, S. “Predicting the specific energy required for size re-duction of relatively coarse feeds in conventional crushers and high presssure grinding rolls.” Minerals Engineering, 2010: 151-153.

Sanchidrian, J, P Segarra, and L Lopez. “Energy components in rock blasting.” International Journal of Rock Mechanics & Mining Sciences 44 (2007): 130-147.

Tarmac Ltd. Towards meeting the challenges of sustainable aggregate production: Mine to Mill Process. Electronic: http://www.sustainableaggregates.com/library/docs/cur-rent_research/l0008_ma_7_g_5_004.pdf, Birmingham: MIRO, 2011.

Tromans, Desmond. “Mineral comminution: Energy efficice-ncy considerations.” Minerals Engineering, 2008: 613-620.

AcknowledgementsIn addition to the project partners, trials of techniques are underway at quarries with active participation of two major quarrying companies, Lafarge Aggregates and Holcim. The project would like to acknowledge their contribution to the project.

Documents

A progress report on the Energy-Efficient Quarry project · Mountsorrel quarry, UK, a typical large quarry producing some 3 million tonnes of crushed-rock aggregates per year. The