Project Visualization/Rendering

For as long as engineers have been designing plants, there has been a “disconnect” between what engineers visualize and others perceive. Engineers have the ability to read 2D drawings and visualize the project in 3D. However, it is very difficult to convey the vision of the final product to those who do not have this aptitude. Audiences are often composed of financial and management decision makers with little experience in plant design. In many cases, engineers find it difficult to communicate a design without some form of visual aid.

Figure 1- Project Visualization/Rendering

Visual aids are also necessary to improve communications with the public during the environmental permitting process. As soon as a company announces an expansion or new facility, public meetings are required to address the concerns of area residents. Unfortunately, the public attending these forums many times comes with a negative perception relating to the intent of the company and the detriments that the project may bring to the community.Fear of the unknown makes it difficult to sell the project to the public. The Owner has to be prepared to answer questions during public meetings and communicate the design of the new plant and its attributes in a form which is easily understood by the public. How is this facility going to look like from my house? Is it visible from the highway? They envision tall stacks and large structures. Visual aids are very useful in such cases where there is demand for clear communication.

Figure 2 – Visualization of a Terminal

Architects have known for years that providing 3D renderings to their clients before final design is essential to explaining their projects. When a client sees his house or building in 3D, he can communicate what he likes and dislikes in the design. Architects found 3D renderings and models a very valuable tool for feedback and improvement in the overall satisfaction of their clients.

Figure 3 – Visualization of a Clinker Cooler in a cement plant

PEC Consulting has the capability of providing this service to its clients. Renderings can be produced to show the project in 3D from many different views. Views can be created to show the visibility of the site from locations such as a neighbor’s home or the view from a vehicle passing the plant. The plant site can be super-imposed on a topographical map or Google Earth to show the plant in the area where it will be located. Views can be shown simulating either daytime or nighttime to show the plant at different times from different vantage points.

Figure 4 – Nighttime Rendering of the Plant

Now the Consultant has a means to better communicate the design of the plant; the placement on the site; and, how it fits in relation to the community around the plant. Decision makers and residents are able to make informed decisions about the future of the proposed design. In some cases, renderings can make the difference between a project going forward or not. It is another tool for new projects where the need to “visualize” the end product is very important.

The main contributor to this feature article is Ken Schweigert, PEC’s expert for the non-metallic minerals industries; he has many years of experience in mining and processing of lime, cement, calcium carbonates, aggregates, silica sand, diatomaceous earth, perlite and clays. His expertise includes plant design, selection of process equipment, project scope development, operations improvement, maintenance, plant personnel and equipment evaluations; due diligence analysis and construction services. Mr. Schweigert has a BS in Engineering Management from Missouri University of Science & Technology.

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Essential Study Phases to Determine Project Feasibility

A project life cycle has several phases: Conceptual, Pre-feasibility, Feasibility, Financing, Engineering, Construction, Commissioning and Start up. In this article, we will focus on the first three phases which are essential to determine the project’s viability and to the successful outcome of the project’s implementation.

Project development phases should be followed in a certain order of coverage and extent to make necessary determinations before proceeding to the next more advanced phase. No tasks within a phase should be skipped or missed, and a phase should not be shifted to the next level until it is completely defined. The intent is to advance the project following a systematic course of action, starting with Phase 1, and within the steps and activities of each one of the phases. All along, there has to be a high level of commitment on the part of the Owner/Investor to follow the process in order to ensure the project’s viability in a realistic and objective way.

The evaluation of a potential project starts with an analysis and research of the existing information on the project. This initial conceptual work will support the next phases. During each progressive phase, the study will focus on more extensive investigation of the raw materials resources, market, infrastructure, community, and general project economics. The final phase will be completed when a level of certainty of the project’s viability can be determined at an acceptable risk level. The activities of each phase are summarized below.

PHASE 1 — CONCEPTUAL STUDY (ALSO CALLED “SCOPING STUDY”)

During this phase, the project is conceptualized based on the needs of the Owner. The Owner must appoint a single source of contact for the project with appropriate authority. The Owner’s Management Team must choose a qualified and experienced Consulting Company with the qualifications necessary to provide credibility on the findings and conclusions of the study. The following activities take place during Phase 1 – Conceptual Study:

1. Analysis of the geology of each of the areas of interest and how they relate to potential mining operations.
   • Raw materials resources of ample supply and quality must be identified by the initial geological survey.
2. A market study to determine the processing capacities and help in the analysis of the economic viability of the projects.
   • The market analysis will determine the size of production plant which would be economical within the area of influence.
3. Permits must be considered along with any limitations that are likely based on local regulations.
   • This will form the basis of the preliminary Environmental Impact Assessment (EIA).
4. Development of mining and processing plant concepts with corresponding CapEx, OpEx, and an Economic Analysis.
5. The Conceptual design must be performed taking into consideration:
   • Plot Plan (plant layout at its physical location).
   • Logistics (access to and from the facility).
   • Infrastructure (utilities, natural gas, coal, process water, access).
   • Block Flow Diagram (graphical representation of the plant process).
   • CapEx (the plant’s cost – developed from references).
   • OpEx (the plant operating costs – developed based on the location).
   • Risk Analysis (outline of major risks and strategy).
   • Definition of Environmental Standards and all permitting requirements.
   • Preliminary Project Schedule.

The Conceptual Feasibility Study Report will provide a preliminary insight into the economic feasibility of the project.

PHASE 2 – PRELIMINARY (“PRE”) FEASIBILITY STUDY

The Pre-Feasibility Study is a more comprehensive study that determines the technical and economic viability of a mineral project. This phase refines the project as follows:

1. 1. 1. Geological Exploration Program
         • Extensive drilling and laboratory testing will be carried out as specified in the Conceptual Study Deliverables which will determine probable reserves of raw materials.

Figure 1 – Full geological evaluation means detailed geological mapping based on core samples, and ultimately developing an economical mining plan

1. 1. Plant Site
      • The site location and plant layouts are finalized.

Figure 2 – Selected Site

1. Market Analysis
   • Further definition is given to projected sales for the eventual production.
2. Technical Aspects
   • Raw material adequacy assessment and calculations.
   • Process evaluation of competing technologies.
   • Project Design Criteria.
3. Economic and Financial
   • CapEx (plants costs are developed from budgetary vendor information).
   • OpEx (operating costs are developed from refined location and plant design criteria).
   • Economic Analysis.
   • Market trends and future growth potential analysis.
4. Organizational
   • Assessment of support systems.
   • Recommendations for functionality and efficiency improvements.
5. Environmental and Social
   • Environmental and regulatory compliance system development.
   • Operating permit review (Federal, state and local agencies).
   • Permits applications for all permits are filed.
   • Public Relations consultant finalizes the assessment of social issues and a program to be implemented.
6. Engineering analysis
   • Plot Plan (defines the materials handling and process flow).
   • Logistics (access to and from the facility is further refined).
   • Equipment (an equipment list specific to quarry and plant is developed).
   • Block Flow Diagram (the graphical plant process is refined).
   • Risk Analysis (major risks are outlined).
   • Strategy (the overall plant strategy is developed with a view to moving the project forward).
   • Schedule (the Project Schedule is refined based on the changes and developments of the pre-feasibility study).

The Pre-Feasibility Study Report indicates if the project looks promising and has an attractive payback. The quarry and plant sites are now known, located in an area convenient in relation to the raw materials source and good logistics to the market. It will point out areas that need to be further refined.

Figure 1 shows a site where the ore geology is promising, as well as a good location for transportation and reasonable mining costs.

PHASE 3 – FEASIBILITY STUDY (ALSO CALLED “BANKABLE FEASIBILITY STUDY” AND “DEFINITIVE FEASIBILITY STUDY”)

A Feasibility Study will provide the information on the minerals reserves, infrastructure, and process designs which will serve as a basis for an investment decision and the support for project financing. During this phase, the development of the project reaches a high level of confidence.

The activities taking place during a Feasibility Study are as follows:

1. Raw materials
   • Mining plan to determine proven reserves.
2. Plant Site
   • The plant site location is refined.
3. Market Analysis
   • Final Market Study Report.
4. Technical Aspects
   • Process design to meet emissions standards.
   • Fuel sources.
   • Equipment List (Owner’s preferred equipment for upcoming firm equipment quotations)
5. Construction Strategy
   • Extent of the Owner’s participation is discussed. This raises further questions such as: will the savings of an EPCM project prevail, or will the project pay for passing the risk to a design-build contractor? Should the equipment supply be Owner purchased, and the construction design-build?
6. Economic and Financial
   • Integration of the technical and financial phases of the project The CapEx, OpEx and the logistics into the economic model for a realistic projection of the financials
7. Environmental and Social
   • Finalize filing of all necessary permit applications
   • Finalize assessment of social issues
8. Engineering Analysis
   • Plot Plan (materials handling is developed and the plot plan revised accordingly)
   • Logistics (all aspects of transportation and materials handling are valued)
   • Equipment list (the equipment list is refined)
   • Preliminary civil, structural, mechanical and electrical design is established
   • Detailed Geotechnical Study
   • Final Block Flow Diagram
   • Equipment Bid Package(s) are issued, comprising:
     • Design Criteria
     • Equipment Specs
     • Process Flow diagrams
     • Electrical and Automation specifications
     • Terms and Conditions
   • Short list of construction companies. A Bill of Quantities is issued to obtain budgetary offers
   • CapEx (update based on firm equipment pricing and budgetary contractor pricing)
   • OpEx (update based on equipment selection and fuel and electrical budgetary quotes)
   • Economic Analysis
   • Risk Analysis (risk strategy is implemented in conjunction with each item in the CapEx, OpEx, and Market)
   • Strategy (strategy to move the project to completion)
   • Schedule (the Project Schedule is established based on strategy).
9. Process Equipment Bidding
   • The Owner provides materials samples for the process equipment bidders. The equipment bidder does the laboratory testing and provides confident performance guarantees that will meet all the necessary emissions standards.
   • During the Feasibility stage, equipment bidders should have been able to respond to an RFQ in 12 weeks. The engineer’s technical bid evaluation period will depend on the number of bidders. Typically there is a period of clarification, checking and validation before the vendors are short-listed.

The Feasibility Study Report provides the Economic model required by the bank / external sources of finance. It provides professional financial projections and addresses the needs of investors and lenders.

The following Figure is a table with a summary of Feasibility Study activites.

The main contributor to this feature article was Rita Merz, Business Development Manager at PEC Consulting Group.

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Geological Exploration of Industrial Minerals

While precious and base metals deposits are usually evaluated according to the weight of the minable elements to be recuperated per ton of ore, industrial mineral deposits are evaluated according to the end user’s product specifications. For example, the characteristics of a calcium carbonate deposit are evaluated according to the end-user’s application, including but not limited to CaO, MgO, heavy metal contents, whiteness, brightness and other physical and chemical properties. Some clays are evaluated according to particle size distribution, iron content and capacity to de-flocculate and susceptibility to forming a ceramic paste.

Industrial minerals play an important role in construction and infrastructure as a source of raw materials for manufacturing many construction materials. Applications may vary from cement, lime, glass and ceramics to paint fillers and plastics. Some industrial minerals are used for manufacturing cosmetics and pharmaceuticals.

There are certain factors that should be considered in the evaluation of an industrial minerals deposit. A very important one is the cost of logistics. Most precious metals deposits justify the construction of expensive access roads to haul the mineral out of remote areas. The transportation of industrial minerals from remote locations is unaffordable. Industrial minerals are usually conveyed for relatively short distances to be processed; however, once the end product is developed, it can be transported longer distances where there is demand for it and it can be delivered at a competitive price. Another factor to be considered in the evaluation of an industrial minerals deposit is the policies of the region and country where the deposit is located. Politics and social conditions also play an important role.

In the long term, markets evolve and change depending on the state of development of the area or country. A developing country or region might need considerable amounts of cement, lime and aggregates while more developed regions may have greater need for furniture, public transportation, cars, computers, pharmaceutical products, paints, cosmetics and other products. Therefore, an analysis of the market where a specific industrial mineral intends to be sold is an important priority.

Regardless the type of industrial mineral, the characterization of the deposit is essential. Giving consideration to the end user, it is paramount to understand the mineral distribution in the deposit. Even when characterization of a deposit seems to be a simple process, mistakes are made due to lack of understanding of the process. The following paragraphs provide guidelines necessary to evaluate an industrial minerals deposit.

Figure 1 Core drilling in a remote area in Mexico. The equipment had to be kept as simple as possible due to the difficulties of moving it through the forest in an area without access roads. Construction of access roads was not justified at this evaluation stage. The deposit is a granitic rock being evaluated as a source of feldspar for the glass and ceramic industry.

Geological Mapping

Evaluation of mineral deposits should always start with a reliable geological map and a set of geological-structural sections. The set of geological-structural sections represents the first geological model, which can be created using any of the 3D modeling software available in the market. Geological models can be simple or sophisticated, depending on the structural setting and mineralization. The variables required by the end user will determine whether the model should integrate variations on the parameters of interest. The ideal industrial mineral deposit does not present many geological or structural changes; actually, the intent is to search for homogeneous materials which will produce an industrial mineral of high quality and consistency. Surface sampling should be conducted to identify the variation of different materialization parameters.

Characterization of the Mineral Deposit

The geological exploration should consider the variations associated to fractures, faults, bedding in the case of sedimentary deposits, and the variation of textures in the rock. Raw materials applicable for one industry may not necessarily comply with the requirements of other industries. For example, a white calcium carbonate may be used as filler for paints, but it will not necessarily comply with the specifications used in pharmaceuticals. The characterization of the deposit should be done according to the target industry. A deposit used for a specific application should be re-evaluated if the market specifications change or if the producer wishes to market to another end user with different requirements.

Eventually, the deposit will be drilled and the type of drilling required should be specified. There are two types of drilling: Core drilling and reverse circulation drilling. Core drilling provides more reliable information but it’s more expensive. Reverse Circulation (RC) is less expensive and faster, but some of the deposit characteristics may not be identifiable. For a true characterization of a deposit, a grid of boreholes using a core drilling rig may be necessary. RC drilling can be used later to obtain complementary information between core boreholes.

Data Organization and Data Management

There is a handful of software to organize borehole and complementary data. Borehole data may include borehole ID, XYZ location, total depth, orientation, inclination, lithologies, structural information, geochemical data, etc. Non-borehole data includes air photos, satellite images, contour lines, surface geochemistry, hydrology and geophysics.

The final objective of 3D modeling software is to visualize the deposit from any angle, which provides a better understanding of the deposit and facilitates the preparation of the mining plan. There are several ways to visualize the information. Geological cross-sections show the variations in the concentration of geochemical data in different directions. Horizontal sections at different elevations showing analytical results are commonly used for analysis. There is a wide range of visualization diagrams according to the type of data required to develop the mining plan.

Figure 2 RC drilling in an area with good access roads in the Democratic Republic of Congo. Limestone deposit being evaluated for the production of lime and cement. Note the size of the equipment.

Mining Plan

Industrial minerals are usually inexpensive compared to base or precious metals, which may be mined underground and under the water table level. Industrial minerals usually cannot afford to be mined underground and are rarely mined under the water table. Some exceptions are when mining some clays or sands using dredges. Industrial minerals are usually mined in open pits and the presence or lack of overburden usually plays an important role in the cost of the end product.

Transportation between the mine and processing plant is also important. The lower the yield, the higher the cost impact of transportation. It is important to get rid of overburden and rejects as close to the quarry as possible to avoid the transportation cost of non-saleable materials.

The movement of material and use of equipment in the quarry will influence the final mining cost. The equipment used in the quarry should be highly efficient to keep mining costs at a minimum, but the skills of the heavy equipment operators are also important. The decision between front-end loaders or excavators (tires vs. tracks), type of hauling trucks, size of loading buckets are all as important factors as well as the efficiency of different brands of heavy equipment which might work better in the country or region where the project is located considering service and replacement parts.

Location of the Processing Plant

The best location for the processing plant is adjacent the quarry, but this is not always possible. There are many parameters that have to be taken into consideration, for example availability of land, water, power source, labor, access, environmental issues, etc.

CONCLUSIONS

The exploration of industrial minerals should be based on the demand of the end product. Industrial minerals cannot afford to be hauled long distances. They are dependent on the specifications of the end user, so the location of industrial minerals deposits is tied to developed areas with appropriate infrastructure and access roads. Every deposit is different and therefore all factors should be considered. Cultural factors, construction methods, and the economy of the region are important considerations.

This article was contributed by Mario Mansilla, Senior Consultant/Geology at PEC Consulting Group. He has 30 years experience in the mining industry, mostly in industrial minerals. He has done evaluation of mineral deposits, and technical and geological studies for projects around the globe. He has a BS in Geology from the Universidad Autónoma de San Luis Potosi, México; an MS degree in Geology from Westfälishe-Wilhelms Universität Münster, Germany, and Postgraduate degree in Environmental Analysis, Instituto Tecnológico de Estudios Superiores de Monterrey.

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Best Practices in Frac Sand Plant Design

The sample project is a frac sand plant located in the beautiful hill country of Texas, U.S.A. It has been designed in two phases: the first one taking place now and the second phase to take place in the future. The latter will double the size of the plant to over 4 million tons per year, with logistics running 24 hours per day, 7 days per week.

An important starting point of all projects is permitting. Construction cannot start until permits are issued. A 3-D modeling presentation that demonstrates an environmentally friendly plant makes a better presentation for permitting meetings. Figure 1 is such a model. The border has earthen berms to hide the view from the passing public. The berms will be planted with native wild flowers and trees. Modeling will be used to prevent plant lights from distracting the passing public both in directionality and lamp shading.

Figure 1: Site plan viewed from entry road

There are two interconnected water collection ponds along the left diagonal of the site. The centermost pond has a pumping station to recycle water back into the process. All aspects of the site are designed for maximum water conservation. Processing efficiency was benchmarked at about 50% of water used in other similar operations in the area.

In Figure 1, on the right side of the property, a deceleration lane was designed for queuing the trucks off of the public highway. The maximum utilization of existing trees helps blending the site into the natural topography of the area. The access road around the perimeter of the plant weaves in and out of these trees.

By rotating the model to a view from a passing car’s perspective, the site looks like Figure 2. The berm height is 15’; it is shown here without vegetation. The load-out silos are the tallest point on the property and the dry screening plant is to the right of the silos. Using the model in this fashion, each neighbor will be able to see a rendering of the facility from their vantage point.

Figure 2: Motorist view from the highway

Figure 3: View from the back of the property. The primary crusher is on the right

Three quarters of a million dollars was saved by placing the Primary Crusher in the pit rather than building retaining walls around the primary crusher pit. This area is on the right side of the rendering (Figure 3). The trucks dump directly into the feed hopper. There is plenty of room for maintenance access around the equipment. Just to the left of the crusher is a creek bed. No traffic is allowed across the creek, so crusher access will be from the right. The secondary screening plant is on the left side of the page, with minus ¾” feed to the extreme left.

The primary crusher circuit includes a vibrating grizzly to remove the fines and a Jaw Crusher set at 2”. This closed side setting mates well with a vertical shaft impactor used as a secondary crusher.

The secondary screens are rated at 1,400 tph including the recirculation load. The traditional solution would be two 8’ x 24’ double deck vibrating screens. The screen shown in figure 4, a single 12’ x 24’ high horizontal impact screen for the same task was evaluated. This eliminated a complicated feed section (for two screens, three conveyor belts and a much larger building). Not counting electrical savings, the project saved over one million dollars and ended up with a highly reliable screen solution.

Figure 4: Ludowici double deck Banana screen

A common method to stockpile sand is by utilizing a radial stacking conveyor. One very easy way to increase the volume of stored material at little additional cost is by using a telescoping radial stacker. Figure 5 shows the original stacked volume (shown in lighter buff), which can be more than doubled by extending the stacker (shown in darker buff). A number of manufacturers offer telescoping radial stackers, which claim additional benefits of wind-rowing the storage to minimize segregation. Both stacking storage yards in this project utilize this technique.

Figure 5: Telescoping radial stacker can double the product storage volume for a modest cost increase.

Attrition scrubbers are used to break up the sandstone into individual particles. Hydraulic cyclone separators are used along with a hydrosizer to capture the particle size desired (ASTM 16 mesh to ASTM 70 mesh); the rest is sent to spoils. A second scrubber circuit is used to liberate any final sticky sand. This plant uses a bucket wheel to dewater the product. Spoils are pumped back to a vacant quarry rather than returned with an overland conveyor. This plant operates with about 25% product reclaim. With both phases in operation, 16 million tons will be mined annually and reclaim 4 million tons of products.

Figure 6: Wet plant tunnel section

The wet storage pile contains the product sizes desired. Figure 7 shows an important step in the preparation for the reclaim tunnel. A percolation field draws down the moisture content. Typically without the field, the 13% moisture in the wet plant discharge will reach about 6% moisture by utilizing inventory management (using the drained or older sand before the newly processed sand). By utilizing the percolation field, the 6% moisture can be reduced to 4% moisture.

Another feature of the design is to use an arched tunnel (see Figure 6) rather than a rectangular tunnel section. The obvious advantage is that the water from the storage migrates around the tunnel rather than lies on the flat roof and ultimately collects inside the collection system. Dewatering feeders collect water from the tunnel and pipe it to the outside. The grade of the tunnel is 1% for positive drainage. Hanging the conveyors from the concrete tunnel makes cleanup much easier.

One last feature of the tunnel system is that the pile orientation is such that the wind blows along the pile 95% of the time, rather than across the pile. The product sand is very susceptible to wind dune action. Pile orientation is a very important feature.

The wet pile area is under laid with an impervious membrane, which includes the low point of the pile to the collection pond (to the right in Figure 7). As much as possible, all process water is recycled.

Figure 7: Percolation field under wet storage

With today’s long range, low price outlook a natural gas generator may be used to generate both plant power and provide the energy from the turbine exhaust to dry sand in a rotary or fluid bed dryer. Payback depends on an agreement with the utility company and on the price of electricity. An analysis on this plant with moderate electrical costs the simple payback appears attractive (see Figure 8). Various models of Caterpillar generator sets were investigated (along the x-axis), since they are easily maintained by agreement with the local dealer, keeping ownership simple.

The graph includes various costs for natural gas ($3.00 to $5.00), and the resulting payback for the generator sets. The payback zone is a colored band over the several generator sets and given their costs (and switchgear plus installation) with the variation in gas costs.

Figure 8: Payback analysis based on cost of gas and moisture content of sand

To properly evaluate the gyratory screening equipment, the cost of the building must be included. Issues of changes in structural support between various OEM schemes including the finished product screen tower were evaluated.

Four products are distributed by the red colored bucket elevators on the left to 6 silos of the dispatch storage. The flat floor of the concrete allows the use of one discharge equipment set on rollers such that it may be placed in multiple locations. The flat slab keeps costs lower. The typical steel bins on structural legs were engineered earlier in the project. As the client’s loading capacity increased, this became less of an option. One problem with multiple steel bins is that with complex conveyor systems distributing product at the roof level, structural supports become very complex. With concrete silos, the flat roof provides needed support wherever it may occur.

The silo set has two analyzer rooms at the upper loading floor for quick quality control analysis of each truck as it is loaded. An average of 240 trucks is loaded each day, 7 days per week. For peak loading, 6 lanes were chosen with 140’ long scales so that easy access is provided under all loading positions.

Provisions were made for flushing silos should QC reject product. This structure is the tallest of all the buildings and, as noted in Figure 2, is the main focal point a passer-by will see of the facility.

Figure 9: Silo plan and elevation views

Prefabricated electrical rooms are very easy to fit into a project. As shown in Figure 10 the room is elevated to allow room for easy access with larger cables. The transformers can be easily located nearby and the rooms are provided with both cooling and pressurization to keep out the dust and sand. In this project, electrical rooms are divided and one part serves as the local control room for the operation of certain areas of the plant. For larger needs, multiple rooms can be joined. For other projects, electrical rooms have been elevated like the one pictured to the top of silos for easy modular controls.

Figure 10: Prefabricated electrical room

One feature of all projects that should be considered is the next phase. There is always a need to expand. Thinking about where the expansion goes, the access to the new phase should be considered right away. Electrical rooms need extra capacity and a location that is convenient to both phases. In this case, the permit application included the second phase emissions.

Another important feature of good design is to consider maintenance and access. For example, conveyors were hung from the tunnels for cleanup access. The transfer towers were constructed as slab-on grade with elevated slabs (because plants seem to buildup elevation over time) and k-bracing allowing bob-cat access for cleanup. Castigated s-section trolley beams (beams with punched holes in them for come-along anchoring) were specified. Each piece of equipment was checked for proper maintenance access. The use of roll-away chutes in front of multi-deck screens is recommended so that the crew that needs access for screen changes can roll away the chute work.

This article was contributed by T.W.Hedrick, PE Senior Consultant for PEC Consulting, he has been in manufacturing and engineering for 40 years, holds seven U.S. patents and has written several dozen technical papers for various magazines and conferences around the world.

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Quicklime and By-Products

Metallurgical

The largest use of lime is in steel manufacturing, where it serves as a flux to remove impurities (silica, phosphorus, and sulfur). Lime is used in basic oxygen furnaces and electric arc furnaces, as well as in secondary refining.

Iron & Steel

High calcium and dolomitic limes are used extensively as a flux in purifying steel in the traditional basic oxygen furnace (BOF) and the newer electric arc furnace (EAF). In the BOF, the lime factor per ton of steel averages 150lb/ton, while in the EAF the factor is 85lb/ton. Lime is very effective in removing phosphorus, sulfur, and silica and, to a lesser extent, manganese. The higher the silica and phosphorus content in the iron ore, the higher the quicklime consumption.

Nonferrous Metallurgy

Lime is also essential in the production of non-ferrous metals. For example, quicklime is used to remove silica from bauxite ore and for causticization in the manufacturing of alumina. Dolomitic quicklime is used to produce metallic magnesium by thermal reduction which reduces magnesium oxide. Lime is also used in the processing of ores and the subsequent smelting and refining of copper, zinc, lead, and other non-ferrous ores.

Environmental

The use of lime to address environmental problems is one of the fastest growing markets for lime products. Lime is used in almost every area of pollution prevention, including treatment of air emissions, treatment of drinking water and waste waters, and remediation of hazardous wastes.

Flue Gas Desulfurization

Flue Gas Treatment – Lime is used to remove sulfur dioxide (SO2) and hydrogen chloride (HCL) from flue gases. SO2 removal efficiencies using lime scrubbers range from 80 to 99% at electric generation plants. HCL removal efficiencies using lime range from 30 to 50% at municipal waste to energy plants¹.

Mercury Removal – There are many methods for controlling mercury emissions. One control technology currently being evaluated is using hydrated lime together with activated carbon to capture mercury in the off-gases from power plant and pyro-processing industries.

Water Treatment

Drinking water treatment – Lime is the main chemical used in the treatment of potable and industrial water.

– Water Softening – Hardness caused by bicarbonate and carbonate of calcium and magnesium is removed by using hydrated lime. Hardness caused by other calcium and magnesium salts is removed by using soda ash.

– PH Adjustment – Hydrated lime is used to adjust the pH of water to prepare it for further treatment. Lime is also used to fight “red water” by neutralizing acid water, therefore reducing corrosion in pipes.- Pathogen Growth

– Lime prevents the growth of bacteria and some viruses by controlling the water pH between 10.5 — 11.- Removal of Impurities – dolomitic lime is used to remove silica. Lime is also used to remove manganese, fluoride, and iron.

Wastewater Treatment – Lime is extensively used in industrial and municipal water treatment.

– Municipal Water Treatment – Lime precipitation is used in preventing eutrophication (algae build up) on water surface by precipitating phosphorous and other suspended and dissolved solids. In the process of coagulation, alum and ferric chloride are used to lower the pH. Lime is used to counteract the pH level and allow efficient nitrogen removal.

– Industrial Wastewater – Lime is used by neutralizing sulfuric acid in steel plants where the iron salts are precipitated. Lime also neutralizes and precipitates chrome, copper, and heavy metals in the treatment of water discharged from plating plants.

Sludge Treatment

Quicklime and calcium hydroxide is widely used and is a cost-effective option to treat biological wastes. Lime injection helps control the environment to prevent the growth of pathogens in waste water sludge like biosolids and convert sludge into a usable product.

– Calcium hydroxide creates a high alkaline compound with pH, as high as 12.4. At pH level above 12 the cell membranes of harmful pathogens are destroyed. The high pH also provides a barrier for flies and other insects to infect treated biological wastes.

– Quicklime injection creates an exothermic reaction increasing the temperature to 70°C which provides pasteurization that meets EPA’s Class A requirements.

– The high pH will precipitate most metals present in the waste and reduce the solubility. It also provides free calcium ions that react with odorous sulfur destroying the waste odor.- Adding lime also increases the solid content of the waste making it easier to handle.

Lime-treated biosolids are safe and promote recycling. As EPA notes “properly prepared biosolids provide a rich source of essential fertilizer elements needed by plants to produce food.”

Animal Wastes- Excessive buildup of animal waste creates an excess of phosphorus and nitrogen which cannot be absorbed by the soil. The addition of hydrated lime to animal manure converts manure to a usable form of fertilizer that contains the correct amount of nutrients which can be absorbed into the soil and used by plants.

Hydrated lime also aids in destroying odors, especially hydrogen sulfide odors, which result from the accumulation of large quantities of manure.

Currently, lime is not widely used to treat animal sludge, but it can offer a practical and economical option.

Acid Mine Drainage – Lime is used to neutralize highly acidic drainage from mines. Lime is also used in coal washing plants to reduce equipment corrosion.

Chemical and Industrial Uses

Agricultural Lime (Aglime) and fertilizer – Hydrated lime balances soil pH for proper plant growth and nutrient intake by neutralizing garden soils. Many plants cannot tolerate acidic soils and prefer soil conditions that are neutral to slightly alkaline, pH between 6 and 7.

Lime in the US has been substituted by ground calcium carbonate; however, in Europe hydrated lime is used in conjunction with nitrogen fertilizers reduces the use of fertilizer.

Glass – A glass batch is composed of approximately 70% sand, 18% soda ash, and 12% lime, usually in the form of dolomitic lime.

Paper and Pulp – Lime is an important additive in the papermaking industry; however, a shift from acidic to an alkaline process has changed levels of consumption as noted below:

Sulfate Process – The largest application of lime in pulp manufacturing is as a causticizing agent in sulfate (Kraft) plants. Wasted sodium carbonate is then reacted with high calcium lime to generate caustic soda for reuse in the process. Plants are able to recover about 90-98%² of the lime by dewatering the waste calcium carbonate mud, then re-calcining it in rotary kilns.

Sulfite Process – Plants using the sulfite process consumed large quantities of quicklime for the preparation of the calcium bisulfite liquor capable of dissolving the noncellulosic wood elements. This process is disappearing due to waste disposal problems.

Bleaching – lime is used as a bleaching agent for pulp.

Precipitated Calcium Carbonate (PCC) – PCC is use as a filler and coating pigment for premium quality paper enhancing the brightness, color, smoothness, and bulk of the paper, replacing more expensive paper pulp. Approximately 75%³ of worldwide PCC production is used in the paper industry.

PCC is also used as a plastic additive, white paint pigment, putty, sealer and adhesives ingredient. It is also an important ingredient in toothpaste.

Sugar Refining

Hydrated Lime is used in the production of sugar from both sugar cane and sugar beet. Approximately 200 kg of lime are required to produce one ton of beet sugar, and about 10 kg are required for one ton of cane sugar.

Crude sugar juice (sucrose) is treated with lime to raise the pH and to precipitate calcium salts of organic and inorganic acids. These insoluble compounds are filtered. Carbon dioxide is then passed through the suspension to precipitate excess lime as calcium carbonate. Precipitated carbonate sludge is filtered out. This process can be repeated several times in order to achieve greater purity of the sugar solution.

Construction

Asphalt – Hydrated lime acts as a mineral filler by stiffening the asphalt binder in hot mix asphalt (HMA), improving resistance to fracture, altering oxidation kinetics and interacting with products of oxidation to reduce their effects.

Building Uses – Hydrated Lime is added to cement and sand to create mortar with superior strength and low water permeability. Hydrated Lime is also used as an ingredient in stuccos and plasters, enhancing strength, durability and workability of these materials.

Soils Stabilization – Quicklime and hydrated lime can significantly improve subgrade engineering properties by increasing the stability, impermeability, and load bearing capacity of the subgrade. It is extensively used in soil stabilization beneath roads and similar construction projects. Quicklime is also used to dry wet soils at construction sites.

Other Construction – Lime is used with pozzolans and Portland cement in the manufacturing of lightweight cellular concrete products.

Refractories

Refractory dolomite is manufactured with dolomitic lime. Iron oxides are added to stabilize the resulting hard-burned quicklime against decomposition from moisture. This material is used to make refractory bricks

Silica Bricks, used for lining furnaces, are made by mixing ground silica with 1 to 3% milk of lime.

The U.S. Market

In 2012, an estimated 19.5⁴ million metric tons of quicklime and hydrated lime were produced in the U.S. The approximate breakdown of lime consumption by general end-use sectors was as follows: 38% for metallurgical uses, 31% for environmental uses, 22% for chemical and industrial uses, 8% for construction uses, and 1% for refractory dolomite (Table 1).

Commercial sales accounted for 91% of total lime consumption and 92% of domestic production. Captive lime accounted for the remainder of consumption and was used in the production of steel in basic oxygen furnaces (BOF), magnesia production, precipitated calcium carbonate production, sugar refining, and refractories (dead-burned dolomite). The data on captive lime consumption are withheld to avoid disclosing company proprietary information; so Table 1 only shows the application of lime for commercial uses.

¹National Lime Association – Environmental Uses, Flue Gas Treatment

²Lime Fact bulletin, National Lime Association, Pulp and Paper

³Lime Fact bulletin, National Lime Association, Precipitated Calcium Carbonate

⁴USGS Mineral Commodity Summaries, January 2013

Pompeyo D. Rios is a Consultant with PEC Consulting Group. He has been with PENTA Engineering for over thirteen years. Mr. Rios has a BS in Mechanical Engineering from the Universidad Metropolitana, Caracas, Venezuela, and a Masters in Business Administration from Regis University, Denver, CO. He has extensive knowledge of the cement and lime industries and is constantly keeping abreast of the latest technologies applicable to both these industries.

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Constructability – Heart of the Project Costs

Constructability review starts with the Original Equipment Manufacturer (OEM) contracts for equipment. Specifically, how many parts did the equipment price include? Where are these manufactured? What amount of site fabrication is required to assemble each machine? How complete was the equipment scope? This is the heart of the project cost, the sum of costs from the OEM, freight, site fabrication and scheduled time to completion.

For the constructability topic, two actual projects, Project 1 and Project 2, are used as examples in this article. Both projects start with the purchase of equipment (OEM contracts) and end with a working Brownfield cement production facility constructed next to a working cement plant. The sites have reserves of good quality raw materials and there is an increased market demand for production. Often, the Consultant is asked by the Client what will be the Capital Cost (CapEx) and Schedule for the Project. The Client also needs a cash flow analysis of capital expenditures and needs to know when he can expect the new facility to start producing a saleable product to obtain a payback.

Figure 1: Example of Project Cash Flow, by Quarter

Typically, some engineering costs take place in the early part of the project development before the OEM vendors are contracted to supply the equipment. Elements that bear on the constructability for the OEM contract include:

1. 1. The number of pieces included in the project
      a. For example: is the Kiln shell in 4 sections, or 40
   2. The amount of field welding expected by the contractor
      a. What length of welding is required, and what types and sizes
      b. Are the anchor bolts by the OEM or contractor
      c. Are the assembly bolts by the OEM or contractor
   3. The weight of the various sub-assemblies
      a. Necessary in comparing various OEM suppliers
      b. For logistics we need to know the shipping weight
      c. Contractor needs assembly lifting weights
   4. The Country of origin of the fabrication
      a. Important for logistics
      b. Important for taxes

Note that the two projects in this article are real.

Figure 2: Differences in Projects

Figure 3 illustrates Project 1 preheater cyclones being transported from barge to a staging area.

On both projects, the structural design was started simultaneously with the OEM contract award. For Project 1, one of the first fabrication contracts was the pre-heater tower steel fabrication. For Project 2, the first contract was the pre-heater slip formed concrete design. The duration of engineering was approximately the same for both projects.

Figure 3, Project 1 – Site Transport from Water transportation to site staging area

Figure 4 is of Project 2 during the slip-forming process. Both projects had slip-formed silos.

After the structural completion of the pre-heater, major vessels in Project 2 had to be elevated over the precast pre-heater and then erected into place. Figure 5 is of Project 1 during construction of the pre-heater. One advantage of a structural steel pre-heater tower is that the pyro-process vessels can be erected simultaneously with the structural steel. The same figure illustrates that the contractor had the kiln placed on the kiln piers and the bag-house at the time the pre-heater tower was finishing off.

Figure 4, Project 2 – Slip forming the homo silo and pre-heater structure

Site safety is affected by clutter and lack of proper sequencing of activities. Figure 6 is a photograph taken during the erection of the tertiary air duct on Project 1.

Figure 5, Project 1 – during the pre-heater construction

Figure 6, Project 1 – Construction of the tertiary air duct

Figure 7 was taken during the alignment over the first kiln pier looking toward the preheater tower on Project 2.

Figure 7, Project 2 – looking over kiln pier towards preheater tower

MSHA or OSHA safety officials would not allow the site clutter and violations as shown in Figure 8 of Project 2. Does safety pay? It certainly was evident with Project 1, which maintained the predicted schedule throughout its duration without time loss due to accidents.

Figure 8, Project 2 – Pre-heater foundation formwork

Throughout Project 2, there is heavy presence of fixed scaffolds. As noted in figure 9, the utilization of many man-lifts is customary in the U.S.

Figure 9, Project 1 – A very minimal amount of scaffold was used. Man lifts are very prevalent.

Figure 10 is uncluttered because the mason used an elevated scaffold. Primarily, this keeps the work height relative to each mason ideal for productivity.

Figure 10: Elevating Scaffold keep the Masons at ideal working elevation

Fixed scaffolding cannot keep masons at the ideal height but, as Figure 11 from Project 2 illustrates, ramps for the hod carriers do make for efficient delivery when a high-lift fork lift is not in use.

Figure 11, Project 2 – Masonry Scaffold with Ramps for efficient work height

We have looked briefly at two projects. Does scaffolding, project safety, or type of forming define a short or long schedule? Is there magic in a steel vs. a concrete pre-heater structure? Only to an incremental degree. When performing a constructability review, we consider how well the integration of OEM supply is to the engineering; the structural plans are thus available for bidding on time and the logistics, both to and through the site, are taken into consideration. Are the lay-down areas really just that, or are they pre-assembly areas that would have been better served at the OEM’s location than at the construction site?

We look for innovationlike in Figure 12, where the existing primary crusher operates throughout a retaining wall construction using gabions to maintain a wide and safe ramp for quarry feed stone. We look for realistic delivery schedules and integrated structures with the mechanical OEM equipment. We look for electric power to be installed and ready for use prior to commissioning.

Figure 12, Project 1 – Contractor used rock gabions for retaining walls

Experienced planning and a team that starts with the equipment purchase contract will result in a realistic and short construction schedule. Remember that the owner will not see a return on investment (ROI) until the plant is operating efficiently. The Constructability Review will definitely increase the ROI.

Which Owner will you be? As in Project 1, with a schedule completed in 19 months, or will you still be looking at construction costs 60 months later and wondering if you will ever produce? PEC Consulting’s staff has extensive experience on Constructability Reviews and stands by to assist you.

Thomas W. Hedrick, P.E. is a structural engineer with a specialty in materials handling. He has over 35 years’ experience in industrial projects and holds several US patents. Mr. Hedrick writes for many magazines, and maintains a passion for excellence in client relations and project execution. Please give us the opportunity to review your project for constructability.

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Selecting the Proper Lime Kiln Technology

Lime is a key industrial mineral used as a chemical additive by many industries. The industrial facilities that utilize Lime in various forms are metal ore processing, metallurgy, steel, paper, pharmaceuticals, sulfur removal, and water treatment. It is also used for generating many basic chemicals used to manufacture consumer goods.

Lime is produced through the calcination of carbonate minerals, calcium and magnesium in Rotary Kilns or Vertical Kilns.

The main types of Lime Kilns are:

Long Rotary Kilns

Main Advantages:

• • Large production volumes
  • Wide range of feed sizes
  • Medium to high reactivity Lime
  • Low sulfur Lime
  • Flexibility in fuels used
  • Production not affected by limestone decrepitation
  • Can use high sulfur coal and petcoke

Main Disadvantages:

• • High CAPEX
  • Highest OPEX (high energy usage)
  • Contact cooler may not be applicable if product is very fine

Preheater Rotary Kilns

Main Advantages:

• • Large production volumes
  • Wide range of Limestone feed sizes
  • Medium to high reactivity Lime
  • Fuel flexibility

Main Disadvantages:

• • Limestone decrepitation can cause “plugging” in the preheater
  • High CAPEX
  • OPEX higher then shaft kiln
  • Low fuel efficiency of rotary kilns
  • Cannot use high sulfur coal and petcoke for steel customers

Single Shaft Vertical Kilns

Main Advantages:

• • Low CAPEX
  • Short Schedule
  • Competitive fuel efficiency

Main Disadvantages:

• • Low production volumes
  • Will not work if Limestone decrepitates
  • Limited Limestone feed range
  • Low Lime reactivity

Annular Shaft Kilns

Main Advantages:

• • High concentration of CO2 in off-gas for use in further chemical processes
  • Good fuel efficiency
  • No need to wash limestone feed
  • Capable to adjust Lime reactivity production levels
  • Effective in producing dead-burned lime

Main Disadvantages:

• • Limited production volumes
  • Will not work if Limestone decrepitates
  • Limited Limestone feed range
  • Limited Lime reactivity

Parallel Flow Vertical Shaft Kilns

Main Advantages:

• • Best fuel efficiency of all Lime Kilns
  • Capable to produce medium to very high reactivity Lime

Main Disadvantages:

• • Will not work if Limestone decrepitates
  • Limited range of feed sizes

The decision on the technology to be used is based on many factors, including the desired product characteristics, limitations of the geographical area, fuel properties and cost, etc. Some of the most important aspects to be considered are:

1. Market (Lime use): Lime reactivity (low, medium or high) and sulfur contents are common specifications that depend directly on the technology used.
2. Availability of Limestone resources and industry capability to manage large amounts of fines:Rotary kilns allow kiln feed size variations. This allows utilizing the smaller stone particle [down to ¼” (6mm)] generated in mining, crushing and screening; hence, increasing the mine’s life.
3. Physical Properties of the Limestone and Lime: Although the fuel efficiency of vertical kilns is much higher than that of rotary kilns, limestone could break down into smaller pieces during calcination due to the “decrepitation” phenomenon which clogs vertical kilns, making the process not feasible. Likewise, the lime created during the calcination process should have sufficient physical strength to carry the weight of the limestone bed in the kiln.

LIME INDUSTRY– PEC Consulting Group’s Active Participation

PEC Consulting Group has provided technical assistance to industries and processing facilities that benefit from the use of lime. In doing so, we have actively helped industries meet the ever increasing demand for the production of quality lime. Sample Scopes of Work have included:

• Feasibility and Technical Studies for Greenfield lime production facilities
• Technical Studies for capacity increase of existing plants
•  Investigation of potential raw material deposits such as sea shells, travertine, and limestone through Geological exploration, core drilling programs, and testing for raw material physical and chemical properties
•  Mining Plans
•  Conceptual design of mine and plant
•  Flow sheets, layouts, equipment lists and basic designs.  Basic equipment specifications. Technology comparisons of major process equipment tenders
•  Capital cost and operating cost estimates
•  Logistics for supplying the mine facilities
•  Economic viability analysis of the projects

A study forms the foundation for future development and it is an absolute necessity for successfully carrying a project to completion. By delivering a well prepared and thorough study, PEC Consulting Group helps its clients achieve their desired goals and competitive edge.

Article contributed by Jorge L. Lerena

Jorge Lerena has extensive experience as a Consultant and Project Manager at PEC Consulting Group. His expertise also includes financial and economic valuation and design of industrial facilities. He has participated internationally in Brownfield and Greenfield lime plant projects, and in studies for the geological evaluation and process selection of Greenfield lime plants.

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Benefits of Plant Maintenance and Reliability Audits

Work processes and best practices that enhance equipment reliability expand realized capacity by avoiding unnecessary production interruptions. Production interruption due to lack of equipment reliability increases a unit’s production cost. In recent years, reliability engineering concepts have been adopted by process industries with the realization that significant improvements in financial performance can be achieved.

For each percentage of availability lost, facilities lose millions of dollars due to lower production capabilities. However, a small increase in equipment reliability converts to an increase in production and large increases in revenue, particularly for those products in strong demand (by the magic of incremental margins). Considering the high capital costs invested in the minerals industries, increasing reliability results in a high return on investment.

When investigated, the lost opportunities tend to fall into one of three categories:

1. Less than optimum work processes
2. Human error
3. Equipment faults

As a prudent defense, management must commit to training, improving work processes, evaluating equipment operations and documenting maintenance histories to determine improvement opportunities.

Typical results of an effective Enterprise Reliability Strategy include a 10% – 15% reduction in conversion cost accompanied by an 8% – 15% increase in real production capacity, with no significant capital investment in production equipment.

As capital-intensive industries around the world grapple with developing successful strategies for improved reliability, pacesetter companies have forged ahead of others by developing and implementing an Enterprise Reliability Strategy bringing with it these tangible benefits:

1. Accurate analysis of equipment maintenance, repair, and replacement records. Decisions become data driven rather than “reflex”. That’s not so say that a seasoned EAM (Enterprise Asset Management) team does not attain “unconscious competency” as the methods become second nature.
2. Increased availability of production systems and equipment yield more product at incremental cost rather than diluted cost.
3. Fewer failures of production systems and equipment, resulting in fewer unplanned outages. Repairs flow with improved efficiency and effectiveness. Crews deal with equipment on the company’s terms rather the equipment’s terms. Callouts and overtime are eliminated.
4. Improved product quality and an associated reduction in energy, material and labor costs related to losing or reprocessing product.  Fewer start-ups and cool downs reduce waste or off-spec product. Processes “flat line”.
5. Reliable equipment and histories, betters MACT, environmental, and MSHA compliance. Reliable equipment reduces insurance premiums.
6. Lower costs for system and equipment maintenance, spare parts inventory, and capital replacement. Rework is reduced.
7. Enhanced morale among management and the work team as they learn to enjoy a proactive environment instead of surviving in chaos. Employees are empowered to make a difference and see professional reward from their efforts.
8. Additional real capacity as operating units are able to operate at higher levels for sustained periods without excessive equipment failure, perhaps avoiding capital expansion.
9. Higher profits from the compounded effect of reduced conversion costs and increased output.

The competitive advantage will be to the player that can deliver its full capacity reliably, on time, with a quality product that meets the customer’s expectations.

Maintenance and Reliability – PEC Consulting’s Value Proposition

PEC Consulting has provided comprehensive Maintenance and Reliability Audits to mineral processing facilities identifying critical aspects which prevent plants from increasing their capacity and maximized competitiveness. We have provided recommendations and action plans to bring each plant to a World Class / Best in Class Maintenance facility.

We can analyze your Maintenance and Reliability management systems, preventive and predictive systems, organizational structure and staff, methods and procedures to benchmark and score your maintenance systems against industry best practice standards, making the appropriate recommendations for improvements, with follow-up audits to help with the implementation process.

Main feature contributor: Ken Rone, Senior Consultant

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The Importance of Lime

Lime is one of the oldest and most important chemical products. Today it is equally significant to the economy of industrial processes. It is extensively used in mining of raw metal ores. Other industries utilize lime in their processes to remove or neutralize hazardous emissions. Its use brings well-known efficiencies and solutions that benefit the mining of raw metal ores and protect the environment.

Lime is used in the production of steel in basic oxygen furnaces. In non-ferrous metallurgy, lime is used in copper, gold, and silver recovery. Lime is used to process alumina and magnesia, and to recover nickel by precipitation. Tailings that result from the recovery of precious metals, such as gold and silver, are treated with lime for environmental remediation purposes. It is used for softening municipal and plant process water and sewage treatment. In power plants and industrial plants, lime is injected into the flue gas to remove acidic gases. Hydrated lime may be used to control sulfur trioxide emissions at utility power plants. Lime is used by the pulp and paper industry and the chemical industry; it is used in sugar refining, in road paving, and in construction. Dead-burned dolomite, also called refractory lime, is the primary form of lime used in refractories.

LIME INDUSTRY– PEC Consulting Group’s Active Participation

PEC Consulting Group has provided technical assistance to industries and processing facilities that benefit the most from the use of lime. In doing so, we have actively helped industries meet the ever increasing demand for the production of quality lime. Sample Scopes of Work include:

• Feasibility and Technical Studies for Greenfield lime production facilities
• Feasibility and Technical Studies for capacity increase of existing plants
• Investigation of potential raw material deposits such as sea shells, travertine, or limestone to be used as a source for quick lime
• Geological exploration, core drilling programs, and testing for raw material physical and chemical properties
• Mining Plans
• Conceptual design of the mine and the plant
• Equipment Selection. Flow sheets, layouts, equipment lists and basic designs.  Basic equipment specifications. Technology comparisons of major process equipment tenders submitted by equipment OEMs
• Capital cost and operating cost estimates of the project
• Logistics for supplying the mine facilities
• Economic viability analysis of the project

A study forms the foundation for future development and it is an absolute necessity for successfully carrying a project to its completion. By delivering a well prepared and thorough study, PEC Consulting Group helps its clients achieve their desired goals and competitive edge. The efficient extraction of minerals and ores and how lime plays an important part in these processes is our specialty and expertise.

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Bulk Materials Storage Covers

The degree of sophistication of bulk materials storage product lines has increased considerably. Bulk storage is progressing from unfettered outside storage to covered structures; a more contained exposure to the environment. Fabric, steel, and concrete structures represent the environmental envelope over bulk materials.

Fabric Bulk Storage Structures

The structure is minimal, following the grain angle of repose. It is adaptable for various grain characteristics. For example, if the angle of repose were higher, the amount of skirt fabric overhang would be reduced. The retaining wall on the edge is fabricated with galvanized metal and functions as an integral part of the aeration system. As the grain is reclaimed, sections of the retaining wall are removed and the end loader has as much access as it is allowed by the removed sections.

Figure 1 – Fabric Covered Grain Storage

The center stacking column has a fan system that continuously sucks air through the bulk storage. The air is drawn through the peripheral retaining sections to the center column and exhausted. The negative pressure holds the fabric against the stored material, keeping the fabric from “flapping”.There is an elaborate anemometer system on the column that increases the negative pressure according to wind speed. Note that when the wind exceeds 40 mph (64 kph), a crew is required to monitor the stability of the fabric.

Figure 2 – Edge Retaining Structure

Another type of fabric structure consists of an arched structural frame over a conventional tripper conveyor (with a tunnel reclaim belt conveyor). Figure 3 shows a urea storage fabric structure draped over the steel frames. Since the building is held under negative pressure, the entry is an airlock structure.

This particular building was on a high water table. The center tunnel concrete structure enclosed the withdrawal belt tunnel and provided the structural support for the tripper conveyor support bents. The fabric support structure has an independent foundation. The owner used an asphalt floor between the tunnel and the building perimeter.

Figure 3 – Urea Tripper Building with Fabric Cover

Figure 4 shows a classic air supported structure. This structure was over a swimming pool; however, these types of structures are feasible for bulk materials storages.

Only the inflation fans provide rigidity to this structure. For industrial applications, large air-lock entries and backup power supply for the blowers are mandatory.

Figure 4 – Air Supporter Structure

Metal Rectangular Bunkers

Figure 5 shows one of the most common and traditional bulk storage arrangements. There is an outside tripper conveyor in the foreground. A metal structure with a tripper conveyor in the gallery is in the background. The product is elemental sulfur, which in most locations would not be a candidate for outside storage. This particular facility is in the Port of Dakar, Senegal, Africa.

Figure 5 – Foreground: outside tripper conveyor. Background: metal structure for inside storage

Figure 6 shows how a typical bunker building looks inside. A tripper conveyor distributes the bulk material. Under floor tunnel or tunnels are used to reclaim material.

Note that under-grade reclaim tunnels typically claim less than 1/3 of the storage volume. The majority of the stored material must be repositioned by dozer over the static reclaim positions. This work is done in an inhospitable environment for both the equipment and the operator.

The venting volume to keep the dust from escaping outside the building is uneconomical with the door open. Figure 6 – Inside a Metal Bunker Building

To increase the amount of reclaimable material, often the metal building is constructed with concrete retaining wall sides. Figure 7 shows a 3-meter high wall reinforced with a counterfort. This is an effective way to increase the depth of material. Typically, retaining walls taller than 3 meters are not economical.

Figure 7 – Retaining Wall with Counterfort

Steel Space Truss Domes

Figure 8 shows a typical reclaimer in a Space truss style dome. Circular stacker / reclaimers are very popular mechanical devices since they can be used for blending the material fed into the storage. The reclaimed volume is generally 100%. A “rake” reclaimer further develops the overall product mix. A popular cover is the steel space truss.

Figure 8 – Space Truss Storage Dome over a Circular Stacker/Reclaimer

Figure 9 actually shows the truss under construction, with the aforementioned “rake” over the reclaim bridge.

Figure 9 – Space Truss Dome Shell over a Blending Stacker/Reclaimer

Figure 10 shows an example of a portal stacker/reclaimer , which is a common type of linear blending system.

The typical cover for the linear storage is a frame type steel structure with metal cladding. It can be either a space frame or, in shorter spans, a conventional A-Frame.

Figure 10 – Linear Storage Blending System

Concrete Shell Storage Structures

Concrete shells offer one more degree of containment. Typically, they are very economical retaining structures. When used with a circular storage / reclaimer such as inFigure 11, the shell can support the bulk load to considerable heights.

The coal inside this 300 foot (91 m) diameter dome was stacked 55 foot (17 m) high against the shell.

Figure 11 – Circular Stacker Reclaimer inside a Concrete Dome

Figure 12 is an exterior photo of the same coal storage dome in Figure 11. The environmentally conscious Owner chose a white exterior for Powder River Basin Coal.

Earlier, it was noted that an open pile has less than 33% live storage (a pile with a central tunnel). Using the attractive structural cost of concrete dome construction, a couple of tunnels and a tall dome can increase the live storage well over 85%.

Figure 12 – White Exterior, Coal Storage Dome

In Figure 13, the concrete shell is designed to hold 200,000 t of cement clinker. The high percentage of gravity reclaim is possible because of the cylinder section under the hemispherical shell. During the feasibility studies, the project cost was optimized. The dome shell is more expensive, but there is no mechanical reclaim, just reliable gravity.

Figure 13 – Cement clinker stored inside this shell, with 4 tunnels, is over 85% gravity reclaim

PEC Consulting has significant expertise in bulk materials handling and storage. We can analyze your bulk storage requirements and advise you on the pros and cons of the various choices. We team each system with the most advantageous loading and reclaim system and evaluate the results. We offer the up-front studies that allow you to choose the best technical, environmental and economical solution for your application.

Main feature contributor: Thomas W. Hedrick, P.E.

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